7. reset circuit, blocking & unequipped circuit 0299_02

ED 02 RELEASED RESET CIRCUIT, BLOCKING & UNEQUIPPED CIRCUIT

EVOLIUM0299_02

27/05/2002 3BK 11202 0299 DSZZA 1/81

SiteVELIZY

EVOLIUM™ SAS

OriginatorsR. MAUGER RESET CIRCUIT, BLOCKING & UNEQUIPPED CIRCUIT

B7.2

System : ALCATEL 900/BSSSub-system : SYS-TLADocument Category : PRODUCT DEFINITION

ABSTRACTThis document describes in the ALCATEL BSS:1 the method by which the BSS controls the availability of A interface, A Trunks and A Channels by

the use of the PCM Standard alarm signals and the GSM Unequipped Circuit, Blocking,Unblocking, Circuit Group Blocking and Circuit Group Unblocking procedures.

2 how the GSM Reset Circuit procedure is used by the BSS to initiate Clearing of a connection inthe MSC, and the interaction of the Reset Circuit, Blocking, Unblocking, Unequipped Circuit andother procedures in the BSS.

3 the method by which calls may be maintained by the BSS in the event of a 2 Mbit/s PCM failureand the mechanism by which the BSS shall clear the calls when 2 Mbit/s PCM failure persists.

ApprovalsNameApp.

J. ACHARDSYT CCM

S. BELLENSBSC DPM

R. MAUGERSYT DPM

NameApp.

REVIEW

HISTORYEd. 01 Proposal 01 1999/10/14 Based upon 3BK 11202 0177 DSZZA Ed 02

Changes for release B7.Incorporated CRQs which re-introduced Circuit GroupBlocking and UnblockingRemoved transcoder pool impacts.Remove references to HSCSD.Corrected handling of 2 Mbit/s alarms and some tidying up,but not enough!Improvement 2 from Error! Reference source not found.:Changes to handling of Unequipped Circuit from MSC.Improvement 5 from Error! Reference source not found.:Elimination of block/unblock procedures during BSC restart.

Ed. 01 Proposal 02 1999/12/10 Compared with 3BK 11202 0177 DSZZA Ed 01 to pick upall the other things which were implemented or not inrelease B6.2. Circulated within SYT

Ed. 01 Proposal 03 2000/01/10 A few more minor updates such as correcting somedocument references

Ed. 01 Released 2000/05/02 A few more minor updates to reflect the implemetationEd. 02 Released 2002/05/27 Takes into account CR20/106732 v4.


EVOLIUM0299_02

27/05/2002 3BK 11202 0299 DSZZA 2/81


EVOLIUM0299_02

27/05/2002 3BK 11202 0299 DSZZA 3/81

TABLE OF CONTENTS

1 SCOPE .............................................................................................................................................. 6

2 FUNCTIONAL DESCRIPTION.......................................................................................................... 62.1 GENERAL.................................................................................................................................. 62.2 HARDWARE PRESENTATION................................................................................................. 72.3 INTERFACE PRESENTATION ................................................................................................. 7

2.3.1 A Interface ....................................................................................................................... 72.3.2 A ter and A ter mux Interfaces......................................................................................... 7

2.4 PRESENTATION OF RESET CIRCUIT PROCEDURE ............................................................ 82.4.1 Reset Circuit triggered by BSS Telecom ......................................................................... 82.4.2 Reset Circuit triggered by MSC Telecom ........................................................................ 8

2.5 PRESENTATION OF UNEQUIPPED CIRCUIT PROCEDURE ................................................ 82.5.1 Unequipped Circuit triggered by BSS Telecom ............................................................... 82.5.2 Unequipped Circuit triggered by MSC Telecom .............................................................. 92.5.3 BSS reaction upon reception of UNEQUIPPED CIRCUIT sent by the MSC................... 9

2.6 PRESENTATION OF BLOCKING AND UNBLOCKING PROCEDURES................................ 92.6.1 Blocking triggered by Telecom ...................................................................................... 102.6.2 Blocking triggered by O&M ............................................................................................ 102.6.3 Unblocking triggered by Telecom .................................................................................. 102.6.4 Unblocking triggered by O&M........................................................................................ 10

2.7 O&M DISABLE and ENABLE................................................................................................. 10

3 DYNAMIC BEHAVIOUR.................................................................................................................. 113.1 GENERAL BEHAVIOUR ......................................................................................................... 11

3.1.1 O&M General behaviour ................................................................................................ 113.1.2 O&M and Telecom circuit states.................................................................................... 113.1.3 O&M and Telecom behaviour during intermittent faults on A ter, A ter mux or A Interface

113.1.4 BSS Telecom protocol restrictions ................................................................................ 12

3.2 BSS TELECOM TRIGGERED RESET CIRCUIT.................................................................... 123.2.1 CLEAR REQUEST sent "N_CLR_REQ" times.............................................................. 123.2.2 SCCP N DISC IND cause "SCCP Inactivity timer expiry".............................................. 133.2.3 Assignment procedure and T9110 expiry...................................................................... 13

3.3 BSS TELECOM TRIGGERED BLOCKING ............................................................................ 143.3.1 Reception of RESET from MSC .................................................................................... 143.3.2 Internally BSS detected Reset ....................................................................................... 153.3.3 Failure of Internal BSS detected Reset ......................................................................... 163.3.4 Reception of ASSIGNMENT REQUEST or HANDOVER REQUEST for an A Channel in

a Blocked state......................................................................................................................... 173.3.5 Reception of ASSIGNMENT REQUEST or HANDOVER REQUEST for an A Channel in

an Unblocked state .................................................................................................................. 173.3.6 Reception of RESET CIRCUIT for an A Channel in a Blocked state ............................ 183.3.7 Reception of RESET CIRCUIT for an A Channel in a Camped On Blocked state ........ 18

3.4 BSS A interface load control for multiple blocking and unblocking ................................ 193.5 GENERAL PROCEDURE INTERACTION.............................................................................. 20

3.5.1 Reset Circuit procedure collision ................................................................................... 203.5.2 BSS Reset Circuit and BSS O&M Disable..................................................................... 203.5.3 BSS Blocking procedure and BSS O&M Enable ........................................................... 213.5.4 BSS Unblocking procedure and BSS O&M Disable ...................................................... 223.5.5 Blocking, Unblocking, Reset Circuit procedures and SCCP Availability........................ 22

3.6 O&M EVENTS ......................................................................................................................... 223.6.1 Single DTC Reload when External 2 Mbit/s Alarm is present........................................ 233.6.2 DTC processor faulty..................................................................................................... 243.6.3 2 Mbit/s PCM Disable by O&M with Operator WAIT TRAFFIC CLEAR ........................ 253.6.4 External 2 Mbit/s PCM fault (TCH Calls are lost)........................................................... 263.6.5 O&M Operator Initialise action on an A Trunk and A Channel SBLs............................. 273.6.6 A Trunk O&M event handling in the presence of External 2 Mbit/s Alarms................... 27


EVOLIUM0299_02

27/05/2002 3BK 11202 0299 DSZZA 4/81

3.7 2 MBIT/S PCM FAULTS DURING CALLS with IGNORE_2MBIT_FAIL TRUE .................... 313.7.1 External 2 Mbit/s PCM transient fault (Calls are maintained) ........................................ 313.7.2 External 2 Mbit/s PCM persistent fault (Calls are eventually released) ......................... 323.7.3 Behaviour when MSC does not detect the PCM fault.................................................... 36

3.8 Detailed Behaviour ................................................................................................................ 373.8.1 BSS initiated Reset Circuit procedure ........................................................................... 373.8.2 MSC initiated Reset Circuit procedure........................................................................... 393.8.3 Single Circuit Blocking procedure.................................................................................. 393.8.4 Single Circuit Unblocking procedure.............................................................................. 413.8.5 Group Blocking procedure ............................................................................................. 433.8.6 Group Unblocking procedure......................................................................................... 453.8.7 BSS initiated Unequipped Circuit procedure.................................................................. 483.8.8 O&M and Telecom interface.......................................................................................... 493.8.9 O&M initiated Blocking and Unblocking due to O&M fault management....................... 503.8.10 Telecom Reset Circuit, Blocking and Unblocking detailed protocol behaviour.............. 50

4 INTERACTION BETWEEN PROCEDURES................................................................................... 754.1 INTERACTION WITH CALL RELEASE.................................................................................. 754.2 INTERACTION WITH ASSIGNMENT and EXTERNAL HANDOVER.................................... 754.3 INTERACTION WITH RESET ................................................................................................. 76

4.3.1 RESET from MSC.......................................................................................................... 764.3.2 Internally detected Reset (RESET sent to the MSC)..................................................... 764.3.3 Internally detected Reset (RESET is NOT Sent to the MSC) ........................................ 76

4.4 INTERACTION WITH SS7 ...................................................................................................... 764.4.1 O&M disable of a 2 Mbit/s PCM or SS7 slot .................................................................. 764.4.2 O&M enable of a 2 Mbit/s PCM or SS7 slot................................................................... 774.4.3 Loop-back of 2 Mbit/s PCM ........................................................................................... 774.4.4 Global connectionless message transfer....................................................................... 774.4.5 Connection orientated message transfer....................................................................... 78

5 TIMERS AND PARAMETERS ........................................................................................................ 785.1 TIMER LIST ............................................................................................................................. 785.2 PARAMETER LIST.................................................................................................................. 785.3 TIMER and PARAMETER RULES FOR T_BURST, B_NUM and T1.................................... 79

6 RELEASE CHANGES ..................................................................................................................... 796.1 Release 2................................................................................................................................. 796.2 Release 3................................................................................................................................. 796.3 Releases B4 and B5............................................................................................................... 796.4 Release B6 .............................................................................................................................. 796.5 Release B7.2 ........................................................................................................................... 80

7 FEATURES...................................................................................................................................... 80

8 GLOSSARY..................................................................................................................................... 80


EVOLIUM0299_02

27/05/2002 3BK 11202 0299 DSZZA 5/81

INTERNAL REFERENCED DOCUMENTSNot applicable

REFERENCED DOCUMENTS

[1] 3BK 11203 0057 DSZZA Transmission Functional Specification[2] 3BK 11202 0176 DSZZA BSS Global Reset[3] 3BK 11286 0286 DSZZA Normal Assignment[4] 3BK 11204 0167 DSZZA Network defense[5] 3BK 11202 0291 DSZZA Call Release[6] 3BK 11202 0290 DSZZA External Channel Changes[7] 3BK 11202 0300 DSZZA TC - BTS interface[8] 3BK 11202 0291 DSZZA Call Release, "O&M intervention" sections[9] 3BK 11202 0289 DSZZA Internal Channel Changes[10] 3BK 11204 0187 DSZZA Interface - coding rules[11] 3BK 11204 0254 DSZZA SBL concept

3GPP References

[12] TS 3GPP 08.60 Inband control of remote transcoders and rate adapters

RELATED DOCUMENTS

ALCATEL References

[13] 3BK 11202 0292 DSZZA Resource Allocation and management[14] 3BK 11202 0287 DSZZA Channel modification

3GPP References

[15] TS 3GPP 08.08 MSC - BSS interface Layer 3 specification[16] TS 3GPP 08.58 BSC - BTS interface Layer 3 specification[17] TS 3GPP 08.51 BSC - BTS interface. General aspects

Other References

[18] G.732 ITU-T Recommendations

PREFACE

OPEN POINTS / RESTRICTIONS


EVOLIUM0299_02

27/05/2002 3BK 11202 0299 DSZZA 6/81

1 SCOPEThis document specifies:

1 How the BSS shall use the GSM Blocking and Unblocking protocols together with the 2 Mbit/sStandard Alarm Signals [1], to control the availability of the A interface telecom resourcesbetween the BSS and the MSC.

2 When and how the BSS shall use the GSM Reset Circuit procedure to initiate clearing of aconnection in the MSC, and the interaction between the Reset Circuit, Unequipped Circuit,Blocking and Unblocking procedures.

3 How stable calls shall be maintained by the BSS during intermittent 2 Mbit/s failures, and howthe BSS shall clear these calls in the event that these failures continue.

2 FUNCTIONAL DESCRIPTION

2.1 GENERALTo cater for failures, inconsistency and maintenance actions in the system, GSM has defined Telecomprocedures which allow the BSS and MSC to control and maintain the status of circuits andconnections carried by circuits on the A interface. The following procedures have been defined for usein GSM on the A interface:• Reset procedure [2]• Reset Circuit procedure• Blocking procedure• Circuit Group Blocking procedure• Unblocking procedure• Circuit Group Unblocking procedure• Unequipped Circuit procedureIn the GSM system the MSC is responsible for choosing a circuit which is to be used to carry data orspeech. The MSC allocates the circuit when it is made aware (by higher layer signalling) that the call isabout to proceed and a TCH resource is required [3].The BSS is responsible for maintaining the transcoder equipment and transmission equipmentbetween the BTS, BSC and TC. If the availability of these equipments changes due to eithermaintenance actions or failures, the BSS shall inform the MSC of the availability status of the affectedA interface circuits by sending BLOCK (or CIRCUIT GROUP BLOCK) messages in order to stop theMSC from using resources and UNBLOCK (or CIRCUIT GROUP UNBLOCK) messages in order toallow the MSC to use resources.The Circuit group procedures are enabled by means of a parameter, EN_CIRCUIT_GROUP.To cover reset or software failures leading to the loss of calls or the corruption of databases, theaffected end (BSC or MSC) needs to inform the other end (MSC or BSC) that connections have beenlost and that resources and connections need to be released. The Reset and the Reset Circuitprocedures allow the BSC and MSC to synchronise each other either on a global basis by use of theReset procedure, or on a local basis, e.g. processor reset or crash by use of the Reset Circuitprocedure.To cover any possible database inconsistency for A interface circuits between the MSC and BSS, GSMPhase 2 provides the Unequipped Circuit procedure. This procedure informs a receiving entity that oneor more circuits1 previously referenced in messages sent by that receiving entity are unknown to thesending entity. This message shall be processed by the ALCATEL BSS whilst operating in either GSMPhase 1 or 2 mode of operation on the A interface. It shall only be sent whilst the ALCATEL BSS isoperating in GSM Phase 2 mode. On the A interface the sending of the UNEQUIPPED CIRCUIT maybe inhibited by an O&M Parameter: GSM PHASE.Upon reception of an UNEQUIPPED CIRCUIT message from the BSS, the MSC should henceforth notselect the indicated circuit(s). It is up to O&M procedures triggered by the operator to either reconfigurethe BSS or MSC so that the configuration of the A interface circuits are in step. 1 The UNEQUIPPED CIRCUIT message may be received by the ALCATEL BSS whilst operating ineither GSM Phase 1 or 2 mode on the A interface. However, it shall only be sent by the ALCATEL BSSwhen enabled by the parameter EN_UNEQUIPPED_CIRCUIT. If moreover the Circuit Groupprocedures are enabled (EN_CIRCUIT_GROUP = TRUE), the OIE CIRCUIT IDENTITY CODE LISTshall be included.


EVOLIUM0299_02

27/05/2002 3BK 11202 0299 DSZZA 7/81

The BSS shall never perform any circuit procedures for the circuits which it believes to be unequippedin the MSC (until they are requested to be reused by the MSC), and shall generate an alarm2 to informO&M if it detects an inconsistency.

2.2 HARDWARE PRESENTATIONFigure 1 shows the principle of the transmission O&M communications in the BSS. This is provided togive a better understanding of the effects of failures on the interfaces.See the Glossary in section 8 for details of the acronyms.

2.3 INTERFACE PRESENTATION

2.3.1 A InterfaceThe A interface between the MSC and the BSS is supported by a number of 2 Mbit/s PCM links, eachlink supports 31 x 64 kbit/s usable slots (timeslot 0 is used for the frame synchronisation).These slots are used for3:1 ITU-T Common Channel Signalling System No. 7 (SS7) signalling, across which Telecom

messages are passed to provide call handling;2 Semi Permanent Circuits (SPC), these are circuits reserved for other signalling requirements

either via the MSC (X.25) or internal to the BSS (Qmux, Alarms), in the latter case the equivalentA interface circuits are unusable.

3 Data and voice carrying circuits (A Channels), these circuits are for use for data and voicetransmission and are allocated and de-allocated during protocol exchanges across the SS7signalling link.

SS7 circuits shall never be blocked or unblocked by the ALCATEL BSS. If the MSC attempts to use acircuit configured in the BSS as in use for SS7 then the BSS shall initiate an Unequipped Circuitprocedure and shall send an UNEQUIPPED CIRCUIT message to the MSC.SPCs shall be blocked by the ALCATEL BSS to stop the MSC from selecting them.Data and Voice carrying circuits shall be blocked by the ALCATEL BSS, if so instructed by O&Mcommands, to stop the MSC from selecting them during fault conditions. They shall subsequently beunblocked when an O&M init command is requested so that the MSC may re-select them.The ALCATEL BSS uses the standard 2 Mbit/s alarm signals ([1] and [12]) to inform the MSC, duringinternal failures or the disablement of SBLs related to A Trunks, that the A Channels associated with a2 Mbit/s PCM trunk can not be used.It also generates the Remote Alarm Indication (RAI) signal when it detects a fault condition on theA interface received from the MSC. In this case Blocking and Unblocking procedures shall not beinitiated.

2.3.2 A ter and A ter mux InterfacesThese interfaces exist between the transcoder and the BSC.Submultiplexers are always used as shown in Figure 1. The submultiplexers are transparent to the RAIcondition and translate any other alarm condition into Alarm Indication Signal (AIS) on the remoteinterface. 2 The ALCATEL BSS will become aware of a mismatch between the BSC and MSC in two ways.The first way is upon reception of an UNEQUIPPED CIRCUIT from the MSC. The second is uponreception of a message from the MSC containing a circuit which is not believed to be equipped in theBSS. The BSC shall inform the O&M using two different O&M error reports in each of these two cases.3 There are some circuits in the BSS which have a circuit Identity Code (CIC) but are neitherequipped nor configured. This situation occurs in cases where not all slots of a 2 Mbit/s trunk are used.These circuits are defined in this release as being Unequipped (UE{xe "UE" \t "Unequipped"}). TheALCATEL BSS shall not generate any BLOCK, UNBLOCK nor RESET CIRCUIT messages for thesecircuits and shall initiate the Unequipped Circuit procedure if one of these circuits is selected by theMSC.

Error! Not a valid link.

Figure 1 BSS configuration


EVOLIUM0299_02

27/05/2002 3BK 11202 0299 DSZZA 8/81

Faults on the A bis interface and on the A ter interface can be detected by the BTS and can be notifiedto the BSC using the Connection failure indication procedure (cause "remote transcoder alarm").The TSC is responsible for the reporting of alarms from equipment connected to the BSC. It shallreport all errors which are reported to it by the Transcoder and the Sub-Multiplexer equipment. Formore details see [4].The SS7 signalling, SPC signalling and Traffic data pass across this interface transparently.

2.4 PRESENTATION OF RESET CIRCUIT PROCEDUREThe Reset Circuit procedure is performed across the A interface, this protocol uses messages whichare sent as global messages (i.e. in connectionless mode).

2.4.1 Reset Circuit triggered by BSS TelecomThe Reset Circuit initiated by the BSS informs the MSC that the BSS considers that a connectionassociated with a single Circuit Identity Code (CIC) is no longer active in the BSS and that the CIC maybe considered to be free for use for other connections. Note that the initiation of the Reset Circuitprocedure may be disabled by O&M parameter configuration (see the setting ofNBR_RESET_CIC_REP parameter).The Reset Circuit procedure shall be triggered by Telecom in response to the following events:1 the sending of CLEAR REQUEST "N CLR REQ" times without answer from the MSC [5].2 the reception of SCCP-N-DISC indication cause "SCCP Inactivity timer expiry" (corresponding to

the reception of an SCCP RELEASE message from the MSC (with cause "expiration of receiveinactivity timer") or the expiry of the BSC SCCP inactivity timer).

During the Assignment procedure [3] (TCH -> SDCCH, SDCCH -> TCH and Directed Retry) when theBSS believes the Mobile Subscriber (MS) to be lost to (i.e. Timer expiry), the circuit shall be madelocally idle in the BSC, and it may be reused by the MSC for another connection. See section 3.2.3.The Reset Circuit procedure shall never be triggered directly by O&M.If the BSS receives a RESET CIRCUIT message for a CIC belonging to a DTC which has a processoroutage problem, internal BSC hardware problem or is placed in a non operational mode due to O&Mintervention, no response is possible to the message.

2.4.2 Reset Circuit triggered by MSC TelecomThe Reset Circuit initiated by the MSC informs the BSS that the MSC considers that a connectionassociated with a single CIC is no longer active in the MSC.If the circuit is blocked at the BSS, a BLOCK message shall be returned to the MSC, and the MSC willthen return a BLOCKING ACKNOWLEDGE message.

2.5 PRESENTATION OF UNEQUIPPED CIRCUIT PROCEDUREThe Unequipped Circuit procedure occurs across the A interface. This protocol uses a message whichis sent as a global message (i.e. in connectionless mode).The Unequipped Circuit procedure is used by either the MSC or the BSS to inform the receiving entitythat the sending entity has detected that the circuit received in a previous message is unknown to thesending entity.It is possible to prevent the initiation of the Unequipped Circuit procedure for the ALCATEL BSSoperating in GSM Phase 2 mode on the A interface by an O&M Parameter(EN_UNEQUIPPED_CIRCUIT).The BSS shall handle the reception of an UNEQUIPPED CIRCUIT message if the BSS is operating ineither GSM Phase 1 or 2 mode on the A interface.

2.5.1 Unequipped Circuit triggered by BSS TelecomThe Unequipped Circuit procedure shall be initiated by the BSS when one of the following messagesare received containing a Circuit Identity Code which the BSS either: does not know; or knows butbelieves to be unequipped or in use for SS7 signalling:ASSIGNMENT REQUEST [3], HANDOVER REQUEST [6], RESET CIRCUIT,RESET CIRCUIT ACKNOWLEDGE, BLOCKING ACKNOWLEDGE, UNBLOCKING ACKNOWLEDGE,


EVOLIUM0299_02

27/05/2002 3BK 11202 0299 DSZZA 9/81

CIRCUIT GROUP BLOCKING ACKNOWLEDGE orCIRCUIT GROUP UNBLOCKING ACKNOWLEDGE.Note: If an UNEQUIPPED CIRCUIT message is received indicating a circuit which the MSC does not

know, the MSC should not return an UNEQUIPPED CIRCUIT message in response.For each inconsistency detected by the BSS, the BSS shall send to O&M an O&M error report. Thisshould cause the O&M operator to investigate the configuration between this BSS and the MSC towhich it is connected.

2.5.2 Unequipped Circuit triggered by MSC TelecomUnequipped Circuit procedures may be initiated by the MSC when one of the following messages arereceived containing a Circuit Identity Code which the MSC does not have configured for carrying trafficor which is not known by the MSC. The messages which may trigger the sending of the UNEQUIPPEDCIRCUIT message are :RESET CIRCUIT, RESET CIRCUIT ACKNOWLEDGE, BLOCK, UNBLOCK,CIRCUIT GROUP BLOCK or CIRCUIT GROUP UNBLOCKNote: If an UNEQUIPPED CIRCUIT message is received indicating a circuit which the BSS does not

know, the BSS discards the message.

2.5.3 BSS reaction upon reception of UNEQUIPPED CIRCUIT sent by the MSCWhen the BSC receives an UNEQUIPPED CIRCUIT message from the MSC which refers to a circuitthat the BSC believes to be equipped the BSC shall perform the following actions :• Stop any procedure related to that circuit.• Send an O&M error report “Unequipped circuit initiated by MSC”.• Put the circuit into O&M state IT.• Put the circuit into Telecom State TEL_UNEQUIPPED.• Put the circuit into resource state “Unequipped circuit”.The BSC Telecom shall not initiate any procedures related to a circuit which is in theTEL_UNEQUIPPED state.A circuit shall remain in the TEL_UNEQUIPPED state until an ASSIGNMENT REQUEST, aHANDOVER REQUEST or a RESET CIRCUIT message, referencing that circuit is received from theMSC. Upon receipt of such a message, the circuit shall enter the appropriate state

2.6 PRESENTATION OF BLOCKING AND UNBLOCKING PROCEDURESBlocking and Unblocking may be performed either one circuit at a time or a group of circuits may beblocked or unblocked using a single message. Not all MSCs will support the Circuit GroupBlocking/Unblocking procedures, so a flag, EN_CIRCUIT_GROUP shall be supported by the BSC toenable or disable the Circuit Group procedures. In general with one or two exceptions, when CircuitGroup procedures are enabled the single circuit procedures shall not be used.The Single and Circuit Group Blocking and Unblocking protocols use messages across the A interface,the messages are sent as global messages (i.e. in connectionless mode).The Single and Circuit Group Blocking procedures inform the MSC that the BSS considers that,respectively, a single CIC or a group of CICs are unable to carry traffic. The procedures shall berepeated only once for a given circuit or group of circuits and even if the procedures are unsuccessfulafter two attempts, the circuit or group of circuits shall be regarded as being blocked (i.e. the procedurecannot fail).The Single and Circuit Group Unblocking procedures inform the MSC that, respectively, a previouslyblocked CIC or group of CICs are now able to carry traffic. As for the Blocking procedures, theprocedures are repeated only once and never fail.The circuit groups shall be managed on a per trunk basis; i.e. when blocking is ordered for severalcircuits by O&M, the BSC shall send a single CIRCUIT GROUP BLOCK message for each A trunk towhich the circuits belong.Note:1. CICs belonging to DTCs which can not respond (either due to processor outage, an internal BSC

hardware problem or O&M intervention) cannot be Blocked by the BSC.2. No Single nor Circuit Group Blocking procedures shall be initiated as a result of a BSC restart


EVOLIUM0299_02

27/05/2002 3BK 11202 0299 DSZZA 10/81

2.6.1 Blocking triggered by TelecomThe Blocking procedure shall be initiated for all blocked CICs and SPCs:• when the BSC is carrying out an MSC initiated Reset procedure (i.e. upon reception of the RESET

message from the MSC).• when the BSC is carrying out the internally initiated Reset procedure (only in the case where the

BSC sends the RESET message to the MSC).• when RESET ACKNOWLEDGE message is received from the MSC or when the BSC has repeated

the Reset procedure the maximum number of times unsuccessfully.As noted above, if Circuit Group procedures are enabled then Single Blocking and Unblockingprocedures shall not be used with the following exceptions. In all cases, a single BLOCK messageshall be sent for a blocked CIC if the BSS receives an ASSIGNMENT REQUEST, a HANDOVERREQUEST or a RESET CIRCUIT message from the MSC for a Blocked CIC.

2.6.2 Blocking triggered by O&MO&M shall trigger Single or Circuit Group Blocking:• when an in service CIC is determined to be out of service (see sections on External 2 Mbit/s PCM

faults for exception cases).• in the case of a single DTC board reload (Note: a full BSC restart/reset/reload/reboot shall not

trigger Single Blocking and Unblocking procedures).• for A Channels which are unavailable for use (other than SS7) when either a DTC, an A Trunk or an

A Channel SBL is initialised by O&M Operator action

2.6.3 Unblocking triggered by TelecomTelecom shall never trigger a Single nor a Circuit Group Unblocking procedure.

2.6.4 Unblocking triggered by O&MO&M shall trigger a Single or Circuit Group Unblocking procedure:• when a previously out of service CIC or group of CICs are determined to be in service.• for usable A Channels when O&M issues an O&M Operator Initialise action on either a DTC, an

A Trunk or an A Channel SBL. (See sections on External 2 Mbit/s PCM faults for exception cases).• in the case of a single DTC board reload.When an Unblocking procedure is in progress for an A Channel or a group that contains an A Channelwhich is subsequently Requested by the MSC (i.e. in an ASSIGNMENT REQUEST or HANDOVERREQUEST) the BSS shall accept the request immediately and shall allow the CIC to be used even ifthe MSC has not yet confirmed the unblocking (i.e. by the reception of UNBLOCKINGACKNOWLEDGE or CIRCUIT GROUP UNBLOCKING ACKNOWLEDGE with the circuitacknowledged in the CIC list I.E.).The BSS shall not initiate a Blocking procedure for an A Channel if an Unblocking procedure ispresently active and the MSC requests the use of it for a connection.

2.7 O&M DISABLE and ENABLEThere are two types of O&M disabling: with Wait Traffic Clear (WTC); and without WTC.When a Disable is ordered by an Operator action, he may optionally Disable a specific SBL with aWTC period. This allows ongoing calls to be completed normally before the SBL carrying the traffic isdisabled and the call is cleared. During the WTC period the BSS shall not select the affected SBL forcarrying traffic.The operator will never order the Enabling of an A Channel whilst a WTC condition exists. O&M shallawait the disappearance of a WTC condition before allowing the Enable command to be given.When a Disable is ordered autonomously (due to BSS Reconfiguration or BSS Fault management) noWTC period is ever specified, any calls on the affected SBL shall be cleared.If there are multiple disabling events (e.g. Operator Disable followed by Autonomous Disable or viceversa) then the first O&M event shall be handled to the exclusion of the other (this means that duringan Operator Disable with WTC, no Autonomous Disabling shall be handled).O&M disabling and enabling actions due to autonomously detected events may occur as fast as theentities which have detected the events can process the events and issue the appropriate O&M action.


EVOLIUM0299_02

27/05/2002 3BK 11202 0299 DSZZA 11/81

3 DYNAMIC BEHAVIOUR

3.1 GENERAL BEHAVIOUR

3.1.1 O&M General behaviourThe O&M entities in the BSS are informed of Operator and Hardware events which require thedisabling/enabling of certain BSS hardware modules.Some of these hardware modules (when disabled) affect the ability of the BSS to accept traffic onspecific 2 Mbit/s PCM links or A Channels. When this occurs the O&M entity may disable the use ofthese A Trunks or A Channels.As and when a 2 Mbit/s PCM link or an A Channel becomes available the O&M entity may enable theuse of these A Trunks or A Channels.

3.1.2 O&M and Telecom circuit statesThe following table shows the possible A trunk state, A channel state and Resource available states.The A channel state is independent of the A trunk state.

O&M states Telecom statesA Trunk state A Channel state Resource available state A Channel state

IT NEQ Unavailable Unequipped (6)Blocked (7)

IT IT Available not confirmed(1)Available confirmed (2)

BusyBlocked (3)

Unequipped circuit (4)

IdleIdle

BusyBlocked

Tel_unequipped (4)IT OPR Locked/Blocked (2) Blocked

OPR/EF (5) SOS Blocked (2)Unequipped circuit(4)

BlockedTel_unequipped (4)

OPR/EF (5) orOPR/FLT

OPR Locked/Blocked (2)Unequipped circuit (4)

BlockedTel_unequipped (4)

Table 1 O&M and Telecom circuit states1 As far as the BSC is concerned the circuit can be used as there are no alarms detected

internally to the BSC, However the Unblocking procedure which was run when the circuit wasput into service was not confirmed by the MSC (i.e. non-receipt of UNBLOCKACKNOWLEDGE, RESET CIRCUIT, ASSIGNMENT COMMAND, HANDOVER REQUEST,RESET).

2 The MSC has acknowledged by use of messages the existence of the circuit.3 This state is entered due to the TC-TS state and is blocked in the BSC.4 The MSC has sent an UNEQUIPPED CIRCUIT message to the BSC.

Note: this state is exited by reception of a Telecom event (e.g. RESET CIRCUIT,ASSIGNMENT REQUEST etc.).

5 The EF state of the A trunk is not due to the reception of downlink 2 Mbit/s/s AIS from theMSC.

6 The circuit is unknown to the BSC, or known but not configured by O&M. Note that SS7Circuits when selected by the MSC are deemed to be unequipped.

7 Circuits used for X.25 and SPCs are Blocked.

3.1.3 O&M and Telecom behaviour during intermittent faults on A ter, A ter mux or A InterfaceTo enable the BSS to maintain calls during intermittent external failures of the 2 Mbit/s PCM an O&Mflag is implemented (IGNORE_2MBIT_FAIL) which when set (TRUE) shall ensure that any received2 Mbit/s standard alarm signals (on A ter, A ter mux or A interfaces), shall not cause the O&M entity toinitiate Call Release and Blocking on the affected interface.


EVOLIUM0299_02

27/05/2002 3BK 11202 0299 DSZZA 12/81

For persistent faults occurring on A bis, A ter or A ter mux interfaces, the BTS will generate the eventwhich causes the BSC to initiate the Call Release scenarios. The event that the BTS detects is eitherthe loss of transcoder synchronisation (detected by the BTS on the downlink path) or the transcoderurgent alarm (as a result of the transcoder detecting loss of synchronisation on the uplink path andsending the urgent alarm pattern on the downlink path to the BTS), the exact event will depend on thedirection of the alarm or fault and will be detected after the condition has persisted for a period definedby the timer T_SYNC [7]. This timer is implemented in both the BTS and Transcoder algorithms (itmust be noted that the T_SYNC timer in each entity might not have the same value). In this case theBTS will send to the BSC the CONNECTION FAILURE INDICATION message cause "Remotetranscoder failure" whereupon the BSC shall perform the appropriate Call Release scenario.The BTS repeats the CONNECTION FAILURE INDICATION message cause "Remote transcoderalarm" as long as the detected condition persists.For persistent errors detected on the A interface, the MSC will initiate the call release scenarios asspecified in [5].

3.1.4 BSS Telecom protocol restrictionsThe Telecom Reset, Circuit Group Blocking and Unblocking protocols differ slightly from the GSMprotocol as specified in [15].The number of times a Reset Circuit procedure may be repeated, when there is no response from theMSC, is controlled by an O&M parameter (NBR_RESET_CIC_REP). When NBR_RESET_CIC_REP isset to '0' no RESET CIRCUIT messages shall be sent to the MSC and the A Channel shall be releasedfor use immediately.

3.2 BSS TELECOM TRIGGERED RESET CIRCUITThe following scenarios show the Reset Circuit procedure triggered due to Telecom events (i.e. whenNBR_RESET_CIC_REP is not equal to '0'). When NBR_RESET_CIC_REP is equal to zero no ResetCircuit procedure shall be triggered for any of these scenarios. In these cases the A Channel shall bereleased locally in the BSC immediately.

3.2.1 CLEAR REQUEST sent "N_CLR_REQ" times

BSS TELECOM MSC

(1) CLEAR REQUEST --------------------------------->(1) start T9104(1) :(1) :(1) T9104 expiry(1) CLEAR REQUEST --------------------------------->(1) start T9104(1) :(1) :(1) T9104 expiry(2) RESET CIRCUIT ----------------------------------->

Figure 2 CLEAR REQUEST sent "N_CLR_REQ" times1 The BSS is attempting to clear a connection which has an associated A Channel but receives no

response from the MSC [5].2 T9104 expires for the "N_CLR_REQ" th time and the BSS initiates the Reset Circuit procedure by

sending a RESET CIRCUIT message (cause "Protocol error between MSC and BSC") andstarting T19.

Note: if the clearing has been initiated by O&M [8], T9104 will only expire once before the call isdeemed to be released. In this case no Reset Circuit procedure shall be initiated, the call iscleared in the MSC by the expiry of the SCCP inactivity timer.


EVOLIUM0299_02

27/05/2002 3BK 11202 0299 DSZZA 13/81

3.2.2 SCCP N DISC IND cause "SCCP Inactivity timer expiry"

MS BSS TELECOM MSC

(1) SCCP_N_DISC Indication(2) <------------------------------------------ CHAN REL(2) SCCP RELEASED ---------------------------------->(2) RESET CIRCUIT ----------------------------------->

Figure 3 SCCP N DISC IND cause "SCCP Inactivity timer expiry"1 The SCCP inactivity timer expires for an SCCP connection which has an associated A Channel

or an SCCP RELEASED message is received from the MSC with the release cause set to"expiration of receive inactivity timer".

2 The MS connection and SCCP connection is released with the scenario [5] N0500 and a ResetCircuit procedure is triggered for the A Channel by sending the RESET CIRCUIT message(cause "Protocol error between MSC and BSC"), if this is not idle yet for this SCCP connection.

Notes:If the associated A Channel is in a "Camped On Blocked" state no Reset Circuit procedure shall beinitiated. The Clearing in the MSC will be initiated by the expiry of the SCCP inactivity timer.The initiation of the release on Air and A bis interfaces is only performed if it has not already beenperformed.Upon reception of the SCCP RELEASED message, the MSC may initiate a Reset Circuit. A collisioncase may occur if the Reset Circuit message from the MSC is received before the BSC initiates its ownReset Circuit. In that case the BSC shall not send a Reset Circuit because the circuit has already beenput in idle state upon reception of the Reset Circuit from the MSC.

3.2.3 Assignment procedure and T9110 expiryThis scenario covers SDCCH -> TCH, TCH -> SDCCH, and directed retries.

MS BSS TELECOM MSC

(1) <---------------------- ASSIGNMENT COMMAND <----------------------- ASSIGNMENT REQUEST(1) start T3107(1) :(1) :(1) T3107 expiry(2) ASSIGNMENT FAILURE ------------------------->(2) start T9110(2) :(2) :(2) T9110 expiry(3) SCCP RELEASED --------------------------------->

Figure 4 Assignment procedure and T9110 expiry1 The Assignment procedure is initiated by the MSC. The BSS activates a TCH, reserves the

A Channel contained in the ASSIGNMENT REQUEST and sends the ASSIGNMENT COMMANDto the MS (T3107 is started to supervise the response from the MS) see [3] for more details.

2 No response is received from the MS and the timer guarding the procedures expires [3 and 9],the ASSIGNMENT FAILURE is sent to the MSC with cause "Radio interface message failure";both the SDCCH and the TCH RF channels are released immediately, and the A Channel islocally made available for reuse ([5] A0500). The SCCP connection is not released. T9110 isstarted to supervise the expected release by the MSC. The MSC does not respond with CLEARCOMMAND, or SCCP RELEASED.

3 T9110 expires and the BSS releases the SCCP connection ([5] A0600) without triggering theReset Circuit procedure because the circuit is either already idle or reused by the MSC foranother connection. If T_9110 expires it is technically still possible that a reset circuit is sent. Thisis if the call is in a started release phase and there is still a reference towards a certain entity ofthe BSC.

Note:


EVOLIUM0299_02

27/05/2002 3BK 11202 0299 DSZZA 14/81

If the A Channel is in a "Camped On Blocked" state no Reset Circuit procedure shall be initiated. TheClearing in the MSC may be initiated by either the reception of the SCCP RELEASED message or theexpiry in the MSC of the SCCP inactivity timer. This may happen if the Disable with WTC event occursjust after the ASSIGNMENT REQUEST was received from the MSC.

3.3 BSS TELECOM TRIGGERED BLOCKINGThe following scenarios show the Blocking procedures triggered due to Telecom events.

3.3.1 Reception of RESET from MSCThe following scenario shows Blocking triggered by the reception of the RESET message from theMSC (see [2] for more detailed information).

3.3.1.1 Single circuit blocking procedure

BSS TELECOM MSC

(1) start T13 <------------------------------------------------ RESET(2) start T1' BLOCK' ---------------------------------------------->(2) start T1'‘ BLOCK'' --------------------------------------------->(2) start T1'‘’ BLOCK''' -------------------------------------------->(2) start T1'‘’’ BLOCK'''' ------------------------------------------->(2) start T1'‘’’’ BLOCK''''' ------------------------------------------>(3) : :(3) : :(3) : :(4) T13 expiry(4) RESET ACKNOWLEDGE ------------------------>(5)

Figure 5 Reception of RESET from MSC - Single Circuit procedure1 BSS receives a RESET message from the MSC2 The flag EN_CIRCUIT_GROUP is FALSE; single blocking is triggered for all previously blocked

A Channels. The cause in the BLOCK messages shall be "O&M intervention".3 The BSS and MSC perform the Blocking protocol - see section 3.8.34 The timer T13 expires and the RESET ACKNOWLEDGE is sent to the MSC.5 The Blocking procedures previously started may not have finished at this point.

3.3.1.2 Circuit Group blocking procedure

BSS TELECOM MSC

(1) start T13 <------------------------------------------------ RESET(2) start T20’(2) T20’ expires CIRCUIT GROUP BLOCK' ----------------------->(2) start T20’’(2) T20’’ expires CIRCUIT GROUP BLOCK’'----------------------->(3) : :(3) : :(3) : :(4) T13 expiry(4) RESET ACKNOWLEDGE ------------------------>(5)

Figure 6 Reception of RESET from MSC - Circuit Group procedure1 BSS receives RESET message from the MSC2 The flag EN_CIRCUIT_GROUP is TRUE; Circuit Group Blocking is triggered for all previously

Blocked A Channels. Each message is related to a whole A trunk.3 The BSS and MSC perform the Group Blocking protocol - see section 3.8.3.


EVOLIUM0299_02

27/05/2002 3BK 11202 0299 DSZZA 15/81

4 The timer T13 expires and the RESET ACKNOWLEDGE is sent to the MSC.5 The Circuit Group Blocking procedures previously started may not have finished at this point.

3.3.2 Internally BSS detected ResetThe following scenario shows the initiation of Blocking upon internally generated Reset - see [2] formore detailed information.


BSS TELECOM MSC

(1) RESET ------------------------------------------------>(1) start T4(1) :(1) :(2) stop T4 <------------------------ RESET ACKNOWLEDGE(2) start T1‘ BLOCK' ---------------------------------------------->(2) start T1'‘ BLOCK'' --------------------------------------------->(2) start T1'‘’ BLOCK''' -------------------------------------------->(2) start T1'‘’’ BLOCK'''' ------------------------------------------->(2) :

Figure 7 Internally BSS detected Reset - Single Circuit procedure1 BSS detects a Reset event [2] and sends a RESET message to the MSC - see Note A.2 When the RESET ACKNOWLEDGE is received by the BSS if EN_CIRCUIT_GROUP is FALSE

the Blocking procedures are triggered for all previously blocked A Channels. The cause in theBLOCK messages shall be "O&M intervention" - see Note A.

Note A :As an option the BSS may not send the RESET message to the MSC (with the parameterNBR_RESET_REP). The Blocking procedures shall be initiated only when the RESET message is sentto the MSC.In the case when the RESET message is not sent, Blocking and Unblocking procedures which arepresently running shall be suspended and recommenced when the internal reset procedure ends.

3.3.2.2 Circuit Group Blocking procedure

BSS TELECOM MSC

(1) RESET ------------------------------------------------>(1) start T4(1) :(1) :(2) stop T4 <------------------------ RESET ACKNOWLEDGE(2) start T20' CIRCUIT GROUP BLOCK' ---------------------->(2) start T20'' CIRCUIT GROUP BLOCK'' --------------------->(2) : :

Figure 8 Internally BSS detected Reset - Circuit Group procedure1 BSS detects a Reset event [2] and sends a RESET message to the MSC - see Note A.2 When the RESET ACKNOWLEDGE is received by the BSS the Circuit Group Blocking

procedures are triggered (EN_CIRCUIT_GROUP is TRUE) for all previously Blocked A Channels- see Note A.

Note A:As an option the BSS may not send the RESET message to the MSC (with the parameterNBR_RESET_REP). The Group block procedures shall only be initiated when the RESET message issent to the MSC. However, in the case when the RESET message is not sent, if any Group Blocking &Unblocking procedures are presently running when the reset occurs, they shall be suspended and shallbe recommenced when the internal reset procedure ends [2].


EVOLIUM0299_02

27/05/2002 3BK 11202 0299 DSZZA 16/81

3.3.3 Failure of Internal BSS detected ResetThe following scenario shows the initiation of Blocking upon failure of the Internal BSS detected Reset- see [2] for more detailed information.


BSS TELECOM MSC

(1) RESET ------------------------------------------------>(1) start T4(1) :(1) :(1) T4 expiry(1) RESET ------------------------------------------------>(1) start T4(1) :(1) :(1) T4 expiry(2) BLOCK' ---------------------------------------------->(2) Start T1(2) T1 expiry BLOCK'' --------------------------------------------->(2) Start T1(2) T1 expiry BLOCK''' -------------------------------------------->(2) Start T1(2) T1 expiry BLOCK'''' ------------------------------------------->(2) :

Figure 9 Failure of Internal BSS detected Reset - Single Circuit procedure1 BSS detects a Reset event [2] and sends a RESET message to the MSC There is no response

from the MSC and the procedure repeats on T4 expiry.2 T4 expires for the Nth time and if EN_CIRCUIT_GROUP is FALSE the BSC triggers Single

Circuit Blocking procedures.


BSS TELECOM MSC

(1) RESET ------------------------------------------------>(1) start T4(1) :(1) :(1) T4 expiry(1) RESET ------------------------------------------------>(1) start T4(1) :(1) :(1) T4 expiry(2) start T20(2) T20 expiry CIRCUIT GROUP BLOCK' ---------------------->(2) start T20(2) T20 expiry CIRCUIT GROUP BLOCK'' --------------------->(2) :

Figure 10 Failure of Internal BSS detected Reset - Circuit Group procedure1 BSS detects a Reset event [2] and sends a RESET message to the MSC There is no response

from the MSC and the procedure repeats on T4 expiry2 T4 expires for the Nth time and if EN_CIRCUIT_GROUP is TRUE the BSC triggers the Circuit

Group Blocking procedures.


EVOLIUM0299_02

27/05/2002 3BK 11202 0299 DSZZA 17/81

3.3.4 Reception of ASSIGNMENT REQUEST or HANDOVER REQUEST for an A Channel in aBlocked state

If either an ASSIGNMENT REQUEST or a HANDOVER REQUEST is received for an A Channel whichis in the, TO BE BLOCKED, BLOCKING or BLOCKED, states the Request shall be refused with cause"Requested terrestrial resource unavailable" and a single BLOCK message with cause "Requestedterrestrial resource unavailable" shall be sent to the MSC.If either an ASSIGNMENT REQUEST or a HANDOVER REQUEST is received for an A Channel whichis in the TO BE CAMPED ON BLOCKED, CAMPED ON BLOCKING or CAMPED ON BLOCKEDstates the Request shall be refused with cause "Terrestrial circuit already allocated" and a singleBLOCK message with cause "Requested terrestrial resource unavailable" shall be sent to the MSC.Note : Even if Circuit Group Blocking procedures are enabled, a single BLOCK message shall be sentin this case. The message shall not be guarded by timer T1 and shall not be repeated.For definitions of the above states see section 3.8.10.3For more detail see [6 and 3].

BSS TELECOM MSC

(1) <-------------------------------------- ASSIGNMENTREQUEST or HANDOVER REQUEST

(1) ASSIGNMENT FAILURE or HANDOVERFAILURE ---------------------------------------------->

(2) BLOCK ---------------------------------------------->(3) <------------------ BLOCKING ACKNOWLEDGE

Figure 11 Reception of ASSIGNMENT REQUEST or HANDOVER REQUEST for an A Channel in aBlocked state

1 Either an ASSIGNMENT REQUEST or a HANDOVER REQUEST is received indicating anA Channel which is marked in the BSS as being in the "Blocked" state or "Camped On Blocked"state - see the list of states above. The Request is refused by the appropriate failure message [6and 3].

2 A single BLOCK message is sent to the MSC by the BSC for the associated A Channel.3 The MSC on reception of the BLOCK message will mark the A Channel as Blocked and return a

BLOCKING ACKNOWLEDGE message. For BSS behaviour on reception of the BLOCKINGACKNOWLEDGE see section 3.8.10.3

3.3.5 Reception of ASSIGNMENT REQUEST or HANDOVER REQUEST for an A Channel in anUnblocked state

If either an ASSIGNMENT REQUEST or a HANDOVER REQUEST is received for an A Channel whichis in the TO BE UNBLOCKED or the UNBLOCKING states the Request shall be accepted and thechannel state shall be set to Busy.For definitions of the above states see section 3.8.10.3For more detail see [6 and 3].

BSS TELECOM MSC(1) UNBLOCK -------------------------------------------->(1) <-------------------------------------- ASSIGNMENT

REQUEST or HANDOVER REQUEST(2) ASSIGNMENT COMPLETE or HANDOVER

COMPLETE ------------------------------------------>

Figure 12 Reception of ASSIGNMENT REQUEST or HANDOVER REQUEST for an A Channel inan Unblocked state

1 Either an ASSIGNMENT REQUEST or a HANDOVER REQUEST is received indicating anA Channel which is marked in the BSS as being Unblocked but the Acknowledge is not yetreceived from the MSC.

2 The Request is accepted, and the channel is reused (set to the state Busy).


EVOLIUM0299_02

27/05/2002 3BK 11202 0299 DSZZA 18/81

3.3.6 Reception of RESET CIRCUIT for an A Channel in a Blocked stateIf a RESET CIRCUIT is received for an A Channel which is in either the TO BE BLOCKED, theBLOCKING or the BLOCKED state (i.e. without an active call), a single BLOCK message shall be sentto the MSC with cause "O&M Intervention".For definitions of the above states see section 3.8.10.3.

BSS TELECOM MSC

(1) <----------------------------------- RESET CIRCUIT(2) BLOCK ---------------------------------------------->(3) <------------------ BLOCKING ACKNOWLEDGE

Figure 13 Reception of RESET CIRCUIT for an A Channel in a Blocked state1 The MSC has lost a Call reference (which had an associated A Channel) and initiates the Reset

Circuit procedure in an attempt to clear the connection in the BSS2 The A Channel indicated in the BSS has no active SCCP connection and is in the "Blocked" state

(see list of states above). The BSS sends a single BLOCK message to the MSC (cause "O&Mintervention").

3 On reception of the BLOCK message the MSC will stop the Reset Circuit procedure, send aBLOCKING ACKNOWLEDGE message and mark the CIC as Blocked. On reception of theBLOCKING ACKNOWLEDGE the BSC shall set the state of the A Channel to BLOCKED.

Note : Even if Group blocking procedures are enabled, a single BLOCK message shall be sent in thiscase. The message shall not be guarded by timer T1 and shall not be repeated.

3.3.7 Reception of RESET CIRCUIT for an A Channel in a Camped On Blocked stateIf a RESET CIRCUIT message is received for an A Channel which is in either the TO BE CAMPED ONBLOCKED, the CAMPED ON BLOCKING or the CAMPED ON BLOCKED state (i.e. with a call inprogress), a single BLOCK message shall be sent to the MSC with cause "O&M Intervention".Thereafter the BSS shall release the MS and SCCP connections.For definitions of the above states see section 3.8.10.3.

MS BSS TELECOM MSC

(1) <----------------------------------- RESET CIRCUIT(2) BLOCK ---------------------------------------------->(2) <------------------------------------------ CHAN REL(3) <------------------ BLOCKING ACKNOWLEDGE

Figure 14 Reception of RESET CIRCUIT for an A Channel in a Camped On Blocked state1 The MSC has lost a Call reference (which had an associated A Channel) and initiates the Reset

Circuit procedure in an attempt to clear the connection in the BSS2 The A Channel indicated has an active SCCP connection in the BSS, and is in one of the

"Camped On Blocked" states - see list above. The BSS therefore releases the MS connectionand the SCCP connection ([5] N1000) and sends a single BLOCK message (cause "O&Mintervention"). The state of the A Channel is then taken out of the "Camped On Blocked" state tothe "Blocked" state - see Note A.

3 On reception of the BLOCK message the MSC will stop the Reset Circuit procedure, send aBLOCKING ACKNOWLEDGE message and mark the CIC as Blocked. On reception of theBLOCKING ACKNOWLEDGE message the BSC changes the state of the A Channel to theBLOCKED state.

Note A: The transitions between the "Camped On Blocked" to the "Blocked" states are as follows:TO BE CAMPED ON BLOCKED -> TO BE BLOCKED,CAMPED ON BLOCKING -> BLOCKING,CAMPED ON BLOCKED -> BLOCKED.

Note : Even if Group blocking procedures are enabled, a single BLOCK message shall be sent in thiscase. The message shall not be guarded by timer T1 and shall not be repeated.


EVOLIUM0299_02

27/05/2002 3BK 11202 0299 DSZZA 19/81

3.4 BSS A interface load control for multiple blocking and unblockingThe Blocking and Unblocking procedure is used to control the state of a single A Channel between theBSC and MSC. As a result, when events occur in the System (e.g. Initialisation, hardware errors etc.),Blocking and Unblocking may occur for many CICs simultaneously.To ensure that the BSC or the MSC is not overloaded, the BSS provides two algorithms which controlthe number of Blocking and Unblocking procedures (respectively) which may be started at any onepoint in time.Each algorithm is based on two parameters: the Burst Number (B_NUM); and the Burst timer(T_burst).The Burst number controls the number of procedures which may be started at any one point in time byeach DTC processor. The Burst timer controls the period between which the procedures are started.The following message sequence chart shows the operation of the Blocking algorithm with BurstNumber equal to 5. The Unblocking algorithm has the same message sequence chart with the BLOCKmessage replaced by the UNBLOCK message.

BSC MSC

start T1 (CIC = 1) BLOCK (CIC = 1) --------------------------------->start T1 (CIC = 2) BLOCK (CIC = 2) --------------------------------->start T1 (CIC = 3) BLOCK (CIC = 3) --------------------------------->start T1 (CIC = 4) BLOCK (CIC = 4) --------------------------------->start T1 (CIC = 5) BLOCK (CIC = 5) --------------------------------->

start T_burst::

T_burst expirystart T1 (CIC = 6) BLOCK (CIC = 6) --------------------------------->start T1 (CIC = 7) BLOCK (CIC = 7) --------------------------------->start T1 (CIC = 8) BLOCK (CIC = 8) --------------------------------->start T1 (CIC = 9) BLOCK (CIC = 9) --------------------------------->

start T1 (CIC = 10) BLOCK (CIC = 10) -------------------------------->

etc.

Figure 15 BSS A interface load control for multiple Blocking and Unblocking

It must be noted that the behaviour shown above pertains to a single DTC with an SS7 link. As an SS7link always supports more than one trunk then the algorithm runs for each DTC. It will be observed thateach algorithm will run in parallel over the A interface and therefore the MSC will receive a group ofBlock (or Unblock) messages from each DTC processor in parallel.In the normal case, where there are multiple SS7 links the BSC shall ensure that the signalling load isevenly distributed across each link.Section 5 contains formulae for the correct setting of T_burst, B_NUM and T1. Use of these formulaewill allow all Blocking (or Unblocking) procedures associated with all CICs on a complete 2 Mbit/s linkto be initiated before the T1 timer for the first initiated procedure expires.In the case where Group Blocking (or Group Unblocking) procedures are enabled, the burst numberB_NUM and the timer T_burst are not required. There is only one CIRCUIT GROUP BLOCK message(and/or CIRCUIT GROUP UNBLOCK) for a whole DTC per T20 period, so the load is significantlyreduced. If there are multiple SS7 links, the BSC shall ensure that the signalling load is evenlydistributed across each link.


EVOLIUM0299_02

27/05/2002 3BK 11202 0299 DSZZA 20/81

3.5 GENERAL PROCEDURE INTERACTIONThis section describes some interactions which exist between entities in the BSS Telecom, BSS O&Mand MSC Telecom. The state machine definition in section 3.8 specifies the behaviour under allpossible combinations of internal and external events.

3.5.1 Reset Circuit procedure collisionIf the BSS and the MSC initiate the Reset Circuit procedure at the same point in time, the BSS willreceive a RESET CIRCUIT message whilst timer T19 is running. In this case the BSS shall respond tothe MSC with a RESET CIRCUIT ACKNOWLEDGE message. The Reset Circuit procedure in the BSCshall continue until the RESET CIRCUIT ACKNOWLEDGE is received from the MSC or until themaximum no of repetitions is reached.

MS BSS TELECOM MSC

(1) RESET CIRCUIT ----------------------------------->(1) start T19(2) : <----------------------------------- RESET CIRCUIT start T12(2) : :(2) : RESET CIRCUIT ACKNOWLEDGE -----------> stop T12(3) : <----------- RESET CIRCUIT ACKNOWLEDGE(3) stop T19

Figure 16 Reset Circuit procedure collision1 The Reset Circuit procedure is initiated by the BSC by sending the RESET CIRCUIT message

for the affected A Channel and the timer T19 is started2 The MSC also starts the Reset Circuit procedure (due to crossing of messages). The BSC

returns a RESET CIRCUIT ACKNOWLEDGE.3 The MSC has received the RESET CIRCUIT and responds with a RESET CIRCUIT

ACKNOWLEDGE. The BSC receives the RESET CIRCUIT ACKNOWLEDGE, T19 is stoppedand the Reset Circuit procedure completes.

3.5.2 BSS Reset Circuit and BSS O&M DisableIf the BSS is running a Reset Circuit procedure and the A Channel is disabled by O&M then the ResetCircuit procedure shall be stopped and a Blocking procedure shall be started.

BSC O&M BSC TELECOM MSC

(1) RESET CIRCUIT ----------------------------------->(1) start T19(1) :(2) A CHAN OOS ---------------------------->(2) stop T19(2) BLOCK ----------------------------------------------->(2) start T1

Figure 17 BSS Reset Circuit and BSS O&M Disable1 The Reset Circuit procedure is already running.2 O&M orders the Disabling of the A Channel. T19 is stopped and the Blocking procedure is

started.


EVOLIUM0299_02

27/05/2002 3BK 11202 0299 DSZZA 21/81

3.5.3 BSS Blocking procedure and BSS O&M EnableWhen the BSS is running a Blocking procedure as a result of an O&M command ("Disable ACH"),O&M shall not allow an INIT ACH until the SBL has left the WTC or MSD states [4]. If a WTC value of0 is given with the Disable command this shall occur after the BLOCK message is acknowledged bythe MSC with a BLOCKING ACKNOWLEDGE message; or, if the BLOCK message is notacknowledged, as illustrated in Figure 18. If a WTC value is given it shall occur on the expiry ofT_WTC.


(1) A CHAN OOS ---------------------------->(1) BLOCK ----------------------------------------------->(1) start T1(1) : (note A)(2) T1 expiry(2) BLOCK ----------------------------------------------->(2) start T1(2) : (note A)(3) T1 expiry(3) : (note B)(4) A CHAN IS ------------------------------->(4) UNBLOCK ------------------------------------------->(4) start T1

Figure 18 BSS Blocking procedure and BSS O&M Enable1 BSC O&M has ordered the Disabling of an A Channel and the BSC Telecom has been able to

start and send the first BLOCK message (see note C below). T1 is started.2 The BLOCK is not acknowledged and T1 expires. The BLOCK message is repeated and T1 is

started again.3 T1 expires for the second time, the circuit is put in the Blocked state and the procedure

terminates. The Channel_Block_Fail alarm is sent to the OMC. If T_WTC is not running, (or if it isrunning and a call on the ACH is cleared - i.e. the WTC condition is fulfilled), O&M is notified toallow for the enabling of the A Channel (see note B below).

4 A command is received to enable the A Channel, (see note B below). An UNBLOCK message issent and T1 is started.

Note A :If the BLOCK message is acknowledged here, the A Channel may be enabled at this point (seealso Note B).

Note B :If a WTC value is given with the O&M disable then the WTC time must elapse before O&M canenable the ACH. This applies whether the BLOCK message is acknowledged or not. (see also"3" above).


EVOLIUM0299_02

27/05/2002 3BK 11202 0299 DSZZA 22/81

3.5.4 BSS Unblocking procedure and BSS O&M DisableWhen the BSS is running an Unblocking procedure as a result of an O&M command ("INIT ACH"),O&M shall not allow an A Channel disable to occur until the SBL has left the MSD state [4]. This occursafter the UNBLOCK message is acknowledged by the MSC with an UNBLOCKING ACKNOWLEDGEmessage; or, if the UNBLOCK message is not acknowledged, as illustrated in Figure 19.


(1) A CHAN IS ------------------------------->(1) UNBLOCK ------------------------------------------->(1) start T1(1) : (note A)(2) T1 expiry(2) UNBLOCK ------------------------------------------->(2) start T1(2) : (note A)(3) T1 expiry(4) A CHAN OOS ---------------------------->(4) BLOCK ----------------------------------------------->(4) start T1

Figure 19 BSS Unblocking procedure and BSS O&M Disable1 The BSC O&M has ordered that a blocked A Channel be Enabled. The BSC Telecom initiates

the Unblocking procedure and sends the first UNBLOCK message to the MSC T1 is started.2 The UNBLOCK is not acknowledged, T1 expires and the UNBLOCK message is repeated. T1 is

started again.3 T1 expires for the second time, the circuit is put in the Unblocked state and the procedure

terminates. The Channel_Unblock_Fail alarm is sent to the OMC.4 A command is received to disable the A Channel. A BLOCK message is sent and T1 started.Note A :

If the UNBLOCK message is acknowledged here, the A Channel may be disabled at this point.

3.5.5 Blocking, Unblocking, Reset Circuit procedures and SCCP AvailabilityWhen the SCCP is unavailable, Blocking, Unblocking and Reset Circuit procedures cannot be initiated.If the SCCP entity becomes unavailable whilst any of the procedures are active, all procedures shall besuspended.When the SCCP becomes available the procedures shall recommence at the point within the protocolwhere they were suspended. The A interface load control mechanism will always ensure that theBlocking and Unblocking protocols are delayed irrespective of the SCCP availability. The SCCPavailability only relies upon the fact that the SCCP entities in the MSC and BSC can communicate witheach other. If the BSSAP in the MSC exists on another processor or is in the process of(re)initialisation and as a result is not able to process messages, it is possible that the SCCP entity inthe MSC will be available whilst the GSM application (BSSAP) is unavailable. In this case theseprocedures will run without the MSC BSSAP entity being aware of them. This could lead to resourcesbeing blocked in the BSC which could have been used - see section 3.8.4.2.

3.6 O&M EVENTSThere are three sources of events which provoke blocking and unblocking of entire A trunks.• Faults external to the BSC are detected as transmission faults. These are one of the following

standard alarm signals: Loss of Frame alignment (LFA), Loss of incoming signal (LIS or LOS);Excessive bit error ratio >10-3 (BER10-3); 2 Mbit/s Alarm Indication Signal (AIS), or Remote AlarmIndication (RAI). A persistency check is performed; the alarm must be present for a period of 70 msin a period of 100 ms

In some networks, transmission quality is marginal, and intermittent transmission errors are common.In such cases, sending blocking and unblocking messages for every external fault can seriouslyoverload the SS7 links. A flag, IGNORE_2MBIT_FAIL is provided to inhibit blocking and unblocking.

• Operator action can put an A Trunk out of service, or can cause a DTC to become unavailablebecause it is reset or is reloading.


EVOLIUM0299_02

27/05/2002 3BK 11202 0299 DSZZA 23/81

• Hardware or software faults in a DTC can deny service by making traffic channels unavailable, bydestroying an SCCP context or both or can simply cause a restart.

When a DTC Restart is either detected or ordered by an O&M operator, the DTC shall maintain callsthat are in a "Stable state"4, all Unblocking and Blocking procedures which were running prior to theRestart shall be restarted after the Restart has finished. Thus no Telecom scenarios are requiredrelated to DTC restart.External faults must be notified to the O&M software. This shall respond by sending a message to putthe A Trunk into the state Out Of Service due to External Fault. If enabled by the condition ofIGNORE_2MBIT_FAIL being FALSE, the BSC shall on reception of the OOS A TRUNK Ext initiate anMTP changeover (if configured); perform a call release for all connections which have an A Channelassociated with this A Trunk; initiate Blocking towards the MSC for each A Circuit associated with theA Trunk which is available for carrying traffic. Otherwise it shall do nothing. In particular, it shall notsend AIS since this would confuse external diagnostic operations.In any other case, DTC failure or Operator action, blocking shall be triggered (for all CICs marked asUNAVAILABLE on the PCM link) and Unblocking procedures (for all the other CICs on the PCM linkwith the exception of a CIC used for SS7 or those marked as Unequipped). This ensures that the MSCis in step with the BSS. The unavailability of the A Trunk shall be indicated by the DTC transmittingAIS 2 Mbit/s.The following sections contain scenarios which illustrate some of the possible interactions.

3.6.1 Single DTC Reload when External 2 Mbit/s Alarm is presentA DTC can be reloaded whether or not the A Trunk is receiving a 2 Mbit/s PCM alarm.It must be noted that Telecom does not perform this procedure for the full BSC System Reload orRestart.


BSC BSC PCM Alarm

MSC

O&M TELECOM Up Down

(1) AIS(1) AIS RAI(2) END DTC RELOAD -------------------------> RAI(3) start T1' BLOCK' ----------------------------------------->(3) start T1'' BLOCK'' ---------------------------------------->(3) start T1''' BLOCK''' ---------------------------------------->(3) start T1'''' UNBLOCK'''' ----------------------------------->(3) start T1''''' UNBLOCK''''' ---------------------------------->(3) start T1'''''' UNBLOCK'''''' ---------------------------------->

Figure 20 Single DTC Reload when External 2 Mbit/s Alarm is present - Single Circuit Blocking1 2 Mbit/s AIS is already applied towards the MSC as the DTC is Out Of Service.2 At the end of the DTC reload The BSS removes the 2 Mbit/s AIS (See Note A).3 Blocking and unblocking as described in section 3.6 is initiatedNote A: Because the AIS is removed before the triggering of the Blocking and Unblocking procedures,

none of the CICs will be usable by the MSC until the MSC has acknowledged the UNBLOCKmessages with an UNBLOCKING ACKNOWLEDGE.


4 The definition of a "Stable state" is that: an SCCP connection was established and/or an internal BSSSpeech/data path was set prior to the detection of the Restart.


EVOLIUM0299_02

27/05/2002 3BK 11202 0299 DSZZA 24/81

BSC BSC PCM Alarm

MSC

O&M TELECOM Up Down

(1) AIS(1) AIS RAI(2) END DTC RELOAD -------------------------> RAI(3) start T20' CIRCUIT GROUP BLOCK' ---------------->(3) start T20’' CIRCUIT GROUP UNBLOCK’' ----------->

Figure 21 Single DTC Reload when External 2 Mbit/s Alarm is present - Circuit Group Blocking1 2 Mbit/s AIS is already applied towards the MSC as the DTC is Out Of Service.2 At the end of the DTC reload, the BSS removes the 2 Mbit/s AIS.3 The Group Blocking is triggered for all CICs marked as UNAVAILABLE (BRU) on the PCM link

and Group Unblocking procedures for all the other CICs on the PCM link with the exception of aCIC used for SS7 or those marked as Unequipped. This ensures that the MSC is instep with theBSS.

3.6.2 DTC processor faultyA DTC can be significant to a call because it handles the A Channel, or because it is a BSSAPprocessor and it is handling the SCCP connection. Thus when a DTC fails, affected calls are one of thefollowing three types.

(i) Calls which have only their SCCP connection supported on the DTC that failed (anyassociated A Channel is supported on another (working) DTC);

(ii) Calls which have their SCCP connection supported on another (working) DTC but have anA Channel associated with it on the DTC that died.

(iii) Calls which have both their SCCP connection and an associated A Channel on the DTCthat failed.

The basic action in the DTC is shown in Figure 22. The clearing mechanism is explained in thefollowing subsections.

BSC BSC PCM Alarm

MSC

O&M TELECOM Up Down

(1) AIS(2) AIS RAI

Figure 22 DTC processor faulty1 The DTC detects a fault which means that the DTC is no longer operational and applies AIS.2 The Remote end of the transmission link replies with RAI.The method by which the Call clearing is performed in this case is dependent upon the following:

3.6.2.1 Only SCCP lostOn the MSC side : The MSC will detect that the SCCP connection no longer exists (SCCP

Inactivity timer expiry). The MSC will clear its resources and may initiate Reset Circuitprocedures, these procedures shall be responded to by the other (working) DTCs.

On the BSS side : When a BSSAP event is generated for the connection from the Air or A bisinterface side (this does not include DTAP message events) the BSC shall recognise that theDTC has died and shall clear the connection towards the MS. If a Speech or Data path existsacross the BSC this shall also be released which may trigger the other party to release theconnection [5].


EVOLIUM0299_02

27/05/2002 3BK 11202 0299 DSZZA 25/81

3.6.2.2 Only A Channel lostOn the MSC side : The MSC will detect the AIS and will clear the call by normal call release

scenarios. If the MSC does not detect the AIS, then the clearing will be initiated by the remotesubscriber.

On the BSS side : Since communication is impossible towards the DTC that has failed allrequests for A Channel resources on the faulty DTC shall be refused [6 and 3]. The BSS shallbe able to detect that A Channels are no longer usable and shall clear the calls.

3.6.2.3 Both SCCP and A Channel lostThe DTC will be unable to respond to any requests on the A interface as the traffic path andthe SCCP entity are both unusable, therefore any Reset Circuit procedures or normal clearingprocedures initiated by the MSC will not be responded to.Note: As a result of the non response by the BSC to the Clearing sequence the MSC may

initiate a Reset Circuit procedure (for those SCCP connections with an associatedA Channel). As a consequence these Reset Circuit procedures shall not be responded toas long as the DTC is faulty. If a Speech or Data path exists across the BSC this shallalso be released which may trigger the other party to release the connection [5].

3.6.3 2 Mbit/s PCM Disable by O&M with Operator WAIT TRAFFIC CLEARThe scenario described in this section shows the behaviour when there is no External 2 Mbit/s alarm -see section 3.6.6.

BSC BSC PCM Alarm

MSC

O&M TELECOM Up Down

(1) A TRUNK OOS (WTC period) ------------>(2) start T_WTC (WTC period)(3) start T1' BLOCK' ----------------------------------------->(3) start T1'' BLOCK'' ---------------------------------------->(3) start T1''' BLOCK''' ---------------------------------------->(3) start T1'''' BLOCK'''' --------------------------------------->(3) start T1''''' BLOCK''''' ---------------------------------------

>(3) start T1'''''' BLOCK'''''' -------------------------------------->(3) start T1''''''' BLOCK''''''' --------------------------------------

>(3) : :(3) : :(4) <----------------------- CLEAR COMMAND''''(4) CLEAR COMPLETE'''' ---------------------->(4) <-------------------------- SCCP RELEASE''''(4) SCCP RELEASE COMPLETE'''' --------->(4)(5) <-------------------------------- T_WTC expiry(6) CLEAR REQUEST''''' ------------------------

>(6) CLEAR REQUEST'''''' ----------------------->(6) CLEAR REQUEST''''''' ---------------------->(7) AIS(8) AIS RAI

Figure 23 2 Mbit/s PCM Disable by O&M with Operator WAIT TRAFFIC CLEAR1 The Operator asks for a DTC or A Trunk to be taken out of service giving a WTC period.2 The T_WTC timer is started in the BSC.3 A Blocking procedure is started immediately for all non blocked CICs with or without an ongoing

call. The complete scenario is not shown to simplify the message sequence chart.


EVOLIUM0299_02

27/05/2002 3BK 11202 0299 DSZZA 26/81

4 During the WTC period a Call is cleared by the MSC which has an associated A Channel, in thiscase the Normal clearing sequence ([5] N0600) is shown on the A interface.

5 The WTC timer expires in the BSC. Note there is an interaction between the WTC and anyongoing Call Release scenarios [5].

6 The BSC initiates a Call Release sequence ([5] N0300) for all calls which have an SCCPconnection supported by the DTC (the complete scenario and timers are not shown to simplifythe message sequence chart).

7 The DTC sends AIS to indicate that no circuits are available8 The remote end of the link responds with RAI

3.6.4 External 2 Mbit/s PCM fault (TCH Calls are lost)The following scenario shows the simplest case of BSS behaviour when a fault occurs on an A Trunkand there is no concurrent operator activity. When the flag IGNORE_2MBIT_FAIL is FALSE, the BSSreleases calls and blocks the affected A Channels. Note that because there is no fault in the BSC andthe operator has not put anything out of service, AIS is not sent from the DTC. Doing so would confusediagnostic activity.

BSC BSC PCM Alarm

MSC

O&M TELECOM Up Down

(1) Alarm(2) <---------------- O&M PCM ALARM BEGIN RAI Alarm(3) OOS A TRUNK Ext --------------------------> RAI Alarm(4) start T1' RAI Alarm BLOCK' ----------------------------------------->(4) start T1'' RAI Alarm BLOCK'' ---------------------------------------->(4) start T1''' RAI Alarm BLOCK''' ---------------------------------------->(4) start T1'''' RAI Alarm BLOCK'''' --------------------------------------->(4) start T1''''' RAI Alarm BLOCK''''' ---------------------------------------

>(4) start T1'''''' RAI Alarm BLOCK'''''' -------------------------------------->(5) RAI Alarm CLEAR REQUEST'''' ------------------------>(5) RAI Alarm CLEAR REQUEST''''' ------------------------

>(5) RAI Alarm CLEAR REQUEST'''''' ----------------------->(5) RAI Alarm :(6) RAI :(7) <------------------- O&M PCM ALARM END(8) A TRUNK IS ----------------------------------->(9) start T1' UNBLOCK' -------------------------------------

>(9) start T1'' UNBLOCK'' ------------------------------------>(9) start T1''' UNBLOCK''' ------------------------------------

>

Figure 24 External 2 Mbit/s PCM fault (TCH Calls are lost)Note: This scenario only shows the initiation of the procedures.1 The BSS Telecom receives a 2 Mbit/s alarm as specified in section 3.6.2 The BSS Telecom Layer 1 returns RAI (except when RAI is received5) and reports to O&M the

detection of the alarm,. The MSC receives the RAI and may remove the CICs associated withthis A Trunk from the A Channels available for carrying traffic. The O&M sends A Trunk ALARMBEGIN to the OMC.

3 O&M Disables the A Trunk by placing the states of the Blocked A Circuits and A Trunk intoExternal Faulty (EF) state.

5 The receipt of RAI does not indicate a fault on the downlink. It should be reported to O&M, but shouldnot be acknowledged at Layer 1. The scenario is identical, except that Uplink PCM Alarm remains inthe normal no alarm state throughout.


EVOLIUM0299_02

27/05/2002 3BK 11202 0299 DSZZA 27/81

4 On reception of the OOS A TRUNK Ext the BSS Telecom follows the procedure specified insection 3.6. The external PCM Alarm continues.

5 Normal Call Release scenarios are initiated for all Busy channels.6 At some point in time the PCM Alarm received by the BSS disappears.7 The RAI is removed and O&M is informed by a PCM ALARM END message.8 O&M orders A Trunk IS9 BSS Telecom Unblocks the CICs which are available for carrying traffic.

3.6.5 O&M Operator Initialise action on an A Trunk and A Channel SBLsIt is possible for the Telecom Unblocking and Blocking procedure to be initiated by O&M OperatorInitialise actions on either an A Trunk SBL or an A Channel SBL.The following message sequence chart shows the failure of a single Unblocking procedure and theO&M Operator Initialise action.


(1) T1 expiry(1) UNBLOCK -------------------------------------------->(1) start T1(1) :(2) T1 expiry(3) O&M operator init ------------------------->(4) UNBLOCK -------------------------------------------->(4) start T1

Figure 25 O&M Operator Initialise action on an A Trunk and A Channel SBLs1 The Unblocking procedure has been initiated for sometime and has sent the UNBLOCK

message "Nublk" times.2 On T1 expiry the A Channel is placed into the Blocked state.3 The Operator (upon finding a blocked resource) initiates the O&M Operator Initialise procedure

for the affected A Channel.4 The BSS Telecom initiates the Unblocking procedure again.

3.6.6 A Trunk O&M event handling in the presence of External 2 Mbit/s AlarmsThis section specifies the behaviour of the ALCATEL BSS when O&M events are received (for anA Trunk SBL) whilst an external 2 Mbit/s alarm is present

3.6.6.1 O&M DTC Disable and Enable and its relationship with external 2 Mbit/s alarmsThe Enabling of the DTC SBL shall always succeed (as long as the board itself is functional) and shallbe independent of the received alarm status of the 2 Mbit/s PCM connected to the DTC. Thus wheninitialised the DTC shall always transit to the In Traffic (IT) state.The status of the A Trunk and A Channels associated with the DTC is described in the following twosections.In the case where the A Trunk is available (i.e. IT) Blocking and Unblocking procedures may beinitiated (depending upon the Internal status of the circuits). When the External 2 Mbit/s alarm is stillpresent, the A Trunk state shall go to External Faulty (EF), and the A Trunk handler shall keepscanning until the external fault disappears. When the fault disappears, the A Trunk shall go to InTraffic (IT) and, messages if the state of the Flag IGNORE_2MBIT_FAIL is FALSE the handler shallsend Unblocking messages.


EVOLIUM0299_02

27/05/2002 3BK 11202 0299 DSZZA 28/81

3.6.6.2 O&M A Trunk and A Channel Disable and Enable events whilst IGNORE_2MBIT_FAILis FALSE

Figure 26 shows the behaviour of an A Trunk when an operator puts it out of service whilst there is areceived 2 Mbit/s alarm condition6. The received alarm disappears and then the operator puts theA Trunk back into serviceThe behaviour specified below allows an Operator to disable and enable an A Trunk independently offailures in the Transmission Equipment. In fact once the external 2 Mbit/s PCM alarm disappears theA Trunk and it's associated A Channels shall immediately go to In Traffic (IT).

BSC BSC PCM Alarm

MSC

O&M TELECOM Up Down

MSC

(1) Alarm(1) <---------------- O&M PCM ALARM BEGIN RAI Alarm(2) OOS A TRUNK Ext --------------------------> RAI Alarm BLOCK' ----------------------------------------->(2) RAI Alarm BLOCK'' -----------------------------------------

>(2) RAI Alarm BLOCK''' ---------------------------------------->(2) RAI Alarm(3) OOS A TRUNK -------------------------------> AIS Alarm(3) AIS Alarm(4) IS A TRUNK -----------------------------------> RAI Alarm(5) RAI(6) <------------------- O&M PCM ALARM END(6)(7) IS A TRUNK Ext ------------------------------>(7) UNBLOCK'' ------------------------------------>(7) UNBLOCK'' ------------------------------------>(7) UNBLOCK''' ------------------------------------

>

Figure 26 O&M A Trunk and A Channel Disable and Enable events whilst IGNORE_2MBIT_FAILis FALSE PCM alarm disappears after IS A TRUNK

1 The BSS detects an External 2 Mbit/s PCM alarm and returns RAI. This is reported to O&M.2 BSS O&M automatically Disables the A Trunk (due to External 2 Mbit/s PCM fault) and the states

of the blocked A Circuits and A Trunk become External Faulty (EF).The BSS Telecom follows the procedure specified in section 3.6.

3 The Operator Disables the A Trunk by placing the A Channel and A Trunk into a state denotingOperator intervention (i.e. OPR). The DTC sends AIS to indicate that no circuits are available.

4 In this scenario the External 2 Mbit/s PCM alarm is still present when the A Trunk is placed backinto service by the Operator, so the BSS O&M holds off the initialisation of the A Trunk until theExternal 2 Mbit/s PCM alarm disappears. The DTC replaces AIS with RAI.

5 The External 2 Mbit/s PCM alarm is still present until some repair action is made elsewhere in theSystem.

6 When the External 2 Mbit/s PCM alarm disappears, this is echoed by the removal of RAI andO&M is informed.

7 BSS O&M: places into service the A Trunk, i.e. returns it to the In Traffic (IT) state immediately.BSS Telecom, reinitialises the SS7 link (if configured) and initiates Unblock procedures for thoseA Channels available on the associated A Trunk.Note : The O&M and Telecom status of the A Channels may change depending on the

outcome of the Unblocking procedures. 6 This isn’t a very good idea, because the AIS generated as a result of the operator putting the A Trunkout of service would confuse any diagnostic procedures. However, the scenario is possible.


EVOLIUM0299_02

27/05/2002 3BK 11202 0299 DSZZA 29/81

Figure 27 shows the case when the External 2 Mbit/s PCM alarm condition disappears during theperiod when the A Trunk is out of service.

BSC BSC PCM Alarm

MSC

O&M TELECOM Up Down

(1) Alarm(1) <---------------- O&M PCM ALARM BEGIN RAI Alarm(1) OOS A TRUNK Ext --------------------------> RAI Alarm BLOCK' ----------------------------------------->(1) RAI Alarm BLOCK'' ---------------------------------------->(1) RAI Alarm BLOCK'''-----------------------------------------

>(1) RAI Alarm(1) OOS A TRUNK -------------------------------> AIS Alarm(1) AIS Alarm(1) X X(1) AIS Alarm(2) <------------------- O&M PCM ALARM END AIS RAI(3) IS A TRUNK Ext ------------------------------> AIS RAI(4) IS A TRUNK -----------------------------------> RAI(4) UNBLOCK'' ------------------------------------>(4) UNBLOCK'' ------------------------------------>(4) UNBLOCK''' ------------------------------------

>

Figure 27 O&M A Trunk and A Channel Disable and Enable events whilst IGNORE_2MBIT_FAILis FALSE PCM alarm disappears whilst A Trunk OOS

1 This is identical to the scenario described in Figure 262 The fault on the A Trunk is cleared and since the DTC is still sending AIS, the remote end returns

RAI. O&M is informed by the message O&M PCM ALARM END.3 O&M responds with IS A TRUNK Ext but this has no effect since A Trunk is still OPR.4 The Operator places the A Trunk and A Channels back into service (IT): the SS7 is reinitialised;

AIS is removed towards the MSC; and the Unblock procedures are triggered.


EVOLIUM0299_02

27/05/2002 3BK 11202 0299 DSZZA 30/81

3.6.6.3 O&M A Trunk Disable/Enable events when IGNORE_2MBIT_FAIL is TRUEThe following message sequence charts show the behaviour on an A Trunk basis (Note: for anA Channel basis only single Blocking or Unblocking procedures shall be initiated).

BSC BSC PCM Alarm

MSC

O&M TELECOM Up Down

(1) Alarm(1) <---------------- O&M PCM ALARM BEGIN RAI Alarm(2) OOS A TRUNK Ext --------------------------> RAI Alarm(2) RAI Alarm(3) OOS A TRUNK -------------------------------> AIS Alarm(3) AIS Alarm BLOCK' ----------------------------------------->(3) AIS Alarm BLOCK'' ---------------------------------------->(3) AIS Alarm BLOCK''' ---------------------------------------->(3) AIS Alarm :(4) IS A TRUNK -----------------------------------> RAI Alarm(5) RAI(5) <------------------- O&M PCM ALARM END(6) IS A TRUNK Ext ------------------------------>(6) UNBLOCK' -------------------------------------

>(6) UNBLOCK'' ------------------------------------>(6) UNBLOCK''' ------------------------------------

>

Figure 28 O&M A Trunk Disable/Enable events when IGNORE_2MBIT_FAIL is TRUE PCM alarmdisappears after IS A TRUNK

1 The BSS detects an External 2 Mbit/s PCM alarm and returns RAI. This is reported to O&M.2 O&M orders the disabling of the A Trunk and places the A Trunk and A Channels into the state

External Faulty (EF). The BSS Telecom sees that IGNORE_2MBIT_FAIL is set to TRUE, so itdoes not send blocking messages, but if necessary it forces the SS7 to perform an MTPChangeover.

3 The Operator Disables the A Trunk. The BSS Telecom performs Call Release (if required) forconnections which have an association with an A Channel on the A Trunk, and Blocks theA Channels.

4 The Operator puts the A Trunk back into service whilst the External 2 Mbit/s PCM alarm is stillpresent, in this case the A Trunk and A Channels are placed into the state EF. Note the O&Mwaits for the PCM Alarm to disappear before initialising the A Trunk.

5 When the External 2 Mbit/s PCM alarm disappears, this is echoed by the removal of RAI andO&M is informed.

6 BSS O&M: places into service the A Trunk, i.e. returns it to the In Traffic (IT) state.BSS Telecom, reinitialises the SS7 link (if configured) and initiates Unblock procedures for thoseA Channels available on the associated A Trunk.


EVOLIUM0299_02

27/05/2002 3BK 11202 0299 DSZZA 31/81

Figure 29 shows the case when the External 2 Mbit/s PCM alarm condition disappears during theperiod when the A Trunk is out of service.

BSC BSC PCM Alarm

MSC

O&M TELECOM Up Down

(1) Alarm(1) <---------------- O&M PCM ALARM BEGIN RAI Alarm(1) OOS A TRUNK Ext --------------------------> RAI Alarm(1) RAI Alarm(1) OOS A TRUNK -------------------------------> AIS Alarm(1) AIS Alarm BLOCK' ----------------------------------------->(1) AIS Alarm BLOCK'' ---------------------------------------->(1) AIS Alarm BLOCK'''-----------------------------------------

>(1) AIS Alarm(2) <------------------- O&M PCM ALARM END AIS RAI(3) IS A TRUNK Ext ------------------------------> AIS RAI(4) IS A TRUNK -----------------------------------> RAI(4) UNBLOCK'' ------------------------------------>(4) UNBLOCK'' ------------------------------------>

Figure 29 O&M A Trunk Disable/Enable events when IGNORE_2MBIT_FAIL is TRUE PCM alarmdisappears whilst A Trunk is OOS

1 This is identical to the scenario described in Figure 282 The fault on the A Trunk is cleared and since the BSC is still sending AIS, the remote end returns

RAI. O&M is informed by the message O&M PCM ALARM END.3 O&M responds with IS A TRUNK Ext but this has no effect since A Trunk is still OPR.4 The Operator places the A Trunk and A Channels back into service (IT): the SS7 is reinitialised;

AIS is removed towards the MSC; and the Unblock procedures are triggered.

3.7 2 MBIT/S PCM FAULTS DURING CALLS with IGNORE_2MBIT_FAIL TRUE

3.7.1 External 2 Mbit/s PCM transient fault (Calls are maintained)The following scenario shows how the BSS shall maintain calls when there are transient A Trunk faults(lasting less than a T_SYNC period) when the BSS flag IGNORE_2MBIT_FAIL is set to TRUE. Notethat the interface shown is the A interface, however the behaviour shall be the same if the fault isdetected on either A ter or A ter mux interface - see Figure 1.

BSC BSC PCM Alarm

MSC

O&M TELECOM Up Down

(1) Alarm(2) RAI Alarm(3) <---------------- O&M PCM ALARM BEGIN RAI Alarm(3) RAI Alarm(4) RAI Alarm(4) RAI(5) <------------------- O&M PCM ALARM END

Figure 30 External 2 Mbit/s PCM transient fault (Calls are maintained)1 The BSS Telecom receives at Layer 1 one of the following standard alarm signals: Loss of

Frame alignment; Loss of incoming signal 2048 kbit/s; Excessive error ratio >10-3; 2 Mbit/s AISor Remote Alarm Indication (RAI).


EVOLIUM0299_02

27/05/2002 3BK 11202 0299 DSZZA 32/81

2 The transcoder Layer 1 returns RAI7 and reports to O&M the detection of the alarm after thealarm is persistent for a period of 70 ms in any 100 ms period. The MSC receives the RAI andmay remove the IDLE CICs associated with this A Trunk from the A Channels available forcarrying traffic.

3 The O&M sends A Trunk alarm event begin to OMC [10]. There is no command to Telecom todisable the A Trunk or to perform any Call Release scenarios as the flag IGNORE_2MBIT_FAILis set to TRUE.

4 The alarm condition disappears (before one second) and the RAI signal is removed.5 O&M is informed. O&M then informs the OMC that the alarm condition has been removed [10].

3.7.2 External 2 Mbit/s PCM persistent fault (Calls are eventually released)The following two scenarios show how the BSS shall clear calls when there is a persistent A Trunkfault (lasting more than a T_SYNC period) when the IGNORE_2MBIT_FAIL flag is set to TRUE. Itshould be noted that for a BSS which has a single SS7 link, the value of T_i must not be null [2].The scenario is further simplified when there is more than one SS7 configured. When there is only oneSS7 link the detection mechanism for SCCP unavailability shall start immediately.The behaviour is essentially the same for faults occurring on the downlink of the A interface, the A terinterface and the A ter mux interfaces. Uplink faults on the A interface are different from those on theA ter and A ter mux interfaces. A ter mux faults are much more likely to occur than A ter or A interfacefaults since the A ter interfaces are internal to the BSS equipment and the A interface is normally alocal connection at the MSC site.To show the BSC behaviour if the PCM alarm remains it is assumed that the MSC does not performCall Release scenarios when it detects the RAI. The expected MSC behaviour is consistent with theGSM option ([15] section 3.1.15) which allows the MSC to run a timer at this point in time, if this timerexpires then the MSC will initiate Call Release.Note that in the case of both uplink and downlink faults the recovery is triggered by the BTS. In thecase of simultaneous uplink and downlink failure the downlink scenario shall be followed. 7 Except when RAI is received in which case normal traffic shall continue to be transmitted


EVOLIUM0299_02

27/05/2002 3BK 11202 0299 DSZZA 33/81

3.7.2.1 Failure on the downlink.Figure 31 shows the result in terms of Telecom actions of a fault8 on the downlink A interface. O&Mreports are also made from all Network Entities. If the fault is on the A ter or A ter mux interfaces, thenthe MSC does not see any change at layer 1 on the A interface.

BTS BSC BSC A ter/mux TRAU

AInte

rface MSC

TELECOM O&M TELECOM Up Down

Up Down

(1) Fault(2) AIS RAI Fault(3) <------------------------

O&M PCM ALARMBEGIN

RAI AIS RAI Fault

(4) X RAI AIS RAI Fault X(5) X RAI AIS RAI Fault X(6) CONNECTION FAILURE

INDICATION RemoteTranscoder Failure ------>

RAI AIS RAI Fault

(6) CONNECTION FAILUREINDICATION' RemoteTranscoder Failure ------>

RAI AIS RAI Fault

(6) CONNECTION FAILUREINDICATION’' RemoteTranscoder Failure ------>

RAI AIS RAI Fault

(7) CLEAR REQUEST------> RAI AIS ------>

RAI Fault

(7) <--------------------------------

--------CLEAR REQUEST RAI AIS RAI Fault

(7) CLEAR REQUEST’------>

RAI AIS ------>

RAI Fault

(7) <--------------------------------

-------CLEAR REQUEST’ RAI AIS RAI Fault

(7) CLEAR REQUEST------> RAI AIS ------>

RAI Fault

(7) <--------------------------------

-------CLEARREQUEST’’

RAI AIS RAI Fault

X RAI AIS RAI Fault XX RAI AIS RAI Fault X

(8) RAI AIS RAI(9) RAI(10) <-------------------------------

- O&M PCM ALARMEND

Figure 31 External 2 Mbit/s PCM persistent downlink fault1 A fault occurs on the downlink A interface.2. The TRAU returns RAI to the MSC and sends AIS on the A ter interface. This is propagated via

the A ter mux alarm octet to the BSC A ter interface and thence to the DTC.3. The DTC responds with RAI and sends O&M PCM ALARM BEGIN to the BSC O&M software.4. No further action is taken in the BSC because the flag IGNORE_2MBIT_FAIL is set to TRUE.5. The BTS detects that the TRAU has lost the synchronisation [12] and starts a timer, T-SYNC,

awaiting re-synchronisation [7].6. The timer expires in the BTS, the CONNECTION FAILURE INDICATION (cause "Remote

transcoder failure") is sent (for all active calls for which the timer has expired). 8 Note that RAI is not a fault, it is a response to a fault in the received signal. The traffic channels in theframe can be valid even in the presence of RAI which is signalled by a bit in timeslot zero. Thecondition shall not be propagated by the TRAU and no action shall be taken by the BSS other than toreport the condition to O&M. Thus this scenario is not applicable when RAI is received,


EVOLIUM0299_02

27/05/2002 3BK 11202 0299 DSZZA 34/81

7. The BSC initiates Call Release towards the MS/BTS and towards the MSC ([5], event N0800).The signalling provided for SCCP connections supported on the affected A interface shall berouted to another available MTP entity in the BSS if the MTP entity can not function across thisA Trunk.

8. Eventually the A interface alarm disappears,9. The TRAU removes the resultant RAI and AIS conditions.10. The DTC removes RAI and sends a message O&M PCM ALARM END.

3.7.2.2 Failure on the A interface uplink.If the link between the TRAU and the MSC fails, the MSC will return RAI and eventually will clear thecalls. No action is required in the BSS.


EVOLIUM0299_02

27/05/2002 3BK 11202 0299 DSZZA 35/81

3.7.2.3 Failure on the A ter or A ter mux interface uplink.

BTS BSC BSC A ter/mux TRAU AInte

rface MSC

TELECOM O&M TELECOM Up Down

Up Down

(1) Fault(2) Fault RAI AIS(3) <-------- O&M PCM

ALARM BEGINFault RAI AIS RAI

(4) Fault RAI <---------------Urgent

Alarm viaQmux

AIS RAI

(5) <----------------------- -------------------------

Fault RAI --------Inband

RemoteTranscoder

Alarm

AIS RAI

(6) CONNECTIONFAILUREINDICATIONRemoteTranscoder Failure----------------------->

Fault RAI AIS RAI

(6) CONNECTIONFAILURE IND'RemoteTranscoder Failure----------------------->

Fault RAI AIS RAI

(6) CONNECTIONFAILURE IND'‘RemoteTranscoder Failure----------------------->

Fault RAI RAI Fault

(7) CLEARREQUEST--------->

Fault RAI----------------

>

AIS RAI

(7) <----------------------- ---------------CLEAR

REQUEST

Fault RAI AIS RAI

(7) CLEARREQUEST’-------->

Fault RAI----------------

>

AIS RAI

(7) <----------------------- ---------------CLEAR

REQUEST’

Fault RAI AIS RAI

(7) CLEARREQUEST’’------->

Fault RAI----------------

>

AIS RAI

(7) <----------------------- ---------------CLEAR

REQUEST’’

Fault RAI AIS RAI

X Fault RAI AIS RAI XX Fault RAI AIS RAI X

(8) RAI AIS RAI(9) RAI(10) <--------------- O&M

PCM ALARM END

Figure 32 External 2 Mbit/s PCM persistent uplink fault


EVOLIUM0299_02

27/05/2002 3BK 11202 0299 DSZZA 36/81

1 A fault occurs on the A ter or A ter mux interface uplink.2. The TRAU responds with RAI downlink and sends AIS Uplink to the MSC.3. The BSC detects the RAI and sends an O&M PCM ALARM BEGIN message to O&M. The MSC

detects AIS and returns RAI4. The TRAU detects loss of TRAU frames and sends “Urgent Alarm” via the Qmux and the TSC.

This is a relatively slow link.5. The transcoder also sends inband to the BTS “Remote Transcoder Alarm”.6. If the downlink transmission is still working, the BTS detects the “Remote Transcoder Alarm”

and sends the CONNECTION FAILURE INDICATION, cause "Remote transcoder failure", to theBSC for all active calls that are affected by the fault. If not then the downlink scenario takes overas shown in section 3.7.2.1

7. The BSC initiates Call Release towards the MS/BTS and towards the MSC ([5], event N0800).The signalling provided for SCCP connections supported on the affected A interface shall berouted to another available MTP entity in the BSS if the MTP entity can not function across thisA Trunk.

8. Eventually the A interface alarm disappears.9. The TRAU removes the resultant RAI and AIS conditions.10. The MSC responds by removing RAI and the BSC seeing its RAI disappear sends a message

O&M PCM ALARM END.Note: Some calls in the process of Channel change may not be released at this point as the

CONNECTION FAILURE INDICATION (cause Remote transcoder alarm) message may beignored [9], these calls shall be released after the Channel change procedure has terminated.

3.7.3 Behaviour when MSC does not detect the PCM faultWhen the flag IGNORE_2MBIT_FAIL is set to TRUE the BSS shall not initiate Blocking procedures orperform Call Release procedures on any externally detected 2 Mbit/s PCM failure as defined earlier.Instead the BTS transcoder detection mechanism shall be relied upon to perform the Call Releasewhen the fault is persistent [7]. It shall be assumed that the MSC will be able to see the PCM alarmand as a result will not select any A Channels on the affected A Trunk. However it is possible that theMSC might not see the 2 Mbit/s PCM alarm. In these cases the MSC will attempt to select A Channelson the affected A Trunk.See the algorithm in section 3.8.10.3 for more detailed behaviour.

3.7.3.1 Interaction with Telecom (Assignment and Handover)If the MSC attempts to select a free A Channel on an A Trunk which has a 2 Mbit/s PCM alarm activethe BSS shall refuse the request (i.e. ASSIGNMENT FAILURE or HANDOVER FAILURE cause"Terrestrial resource unavailable") and shall send a single BLOCK message to the MSC to Block theresource. These A Channels shall as a result enter the state IDLE WITH AIS BLOCKED. When the2 Mbit/s alarm disappears the BSS shall initiate an Unblocking procedure.If an Internal or External Reset procedure is initiated then a Blocking procedure shall be initiated for allA Channels in the state IDLE WITH AIS BLOCKED. As soon as the 2 Mbit/s alarm disappearsUnblocking procedures shall be initiated to free the resources.

3.7.3.2 Interaction with O&MWhilst a 2 Mbit/s alarm is active any requests from O&M to Disable A Channels or A Trunks shallcause Blocking procedures to be initiated unless the resource is already Blocked.If the operator enables an A Trunk or A Channel whilst a downlink alarm is present, the A Trunk orA Channel shall enter the External Faulty (EF) state. When the AIS disappears, the state shall becomeIn Traffic (IT), and the A Channels shall be Unblocked.


EVOLIUM0299_02

27/05/2002 3BK 11202 0299 DSZZA 37/81

3.8 Detailed Behaviour

3.8.1 BSS initiated Reset Circuit procedureThis section contains the general behaviour of the Reset Circuit procedure for successful andunsuccessful cases when the procedure has been initiated by the BSS.

3.8.1.1 Reset Circuit procedure successful cases

3.8.1.1.1 Reception of RESET CIRCUIT ACKNOWLEDGE or UNEQUIPPED CIRCUIT

BSC MSC

(1) RESET CIRCUIT ----------------------------------->(1) start T19(1) :(1) :(2) : <------- RESET CIRCUIT ACKNOWLEDGE or

UNEQUIPPED CIRCUIT(2) stop T19

Figure 33 Reset Circuit procedure successful - Reception of RESET CIRCUIT ACKNOWLEDGEor UNEQUIPPED CIRCUIT

1 The Reset Circuit procedure is started by sending the RESET CIRCUIT message and startingT19.

2 The MSC releases the A Channel and associated SCCP connection (if any) and returns theRESET CIRCUIT ACKNOWLEDGE. Upon reception of the RESET ACKNOWLEDGE message,the BSS stops the timer T19 and makes the A Channel available for use. If the MSC does notrecognise the circuit it may send an UNEQUIPPED CIRCUIT message. In this case the BSSsends an O&M error report Unequipped circuit initiated by MSC” to O&M and terminates theprocedure.

3.8.1.1.2 Reception of RESET from MSC

BSC MSC

(1) RESET CIRCUIT ----------------------------------->(1) start T19(1) :(1) :(2) : <------------------------------------------------ RESET(2) stop T19

Figure 34 Reset Circuit procedure successful - Reception of RESET from MSC1 The Reset Circuit procedure is running.2 The MSC has released all transactions associated with this BSS and sends the RESET

message. The BSC performs Call Release for all transactions [2 and 5]. For all on going ResetCircuit procedures the timer T19 is stopped and the A Channel is considered free for use.Blocking procedures are started immediately - see appropriate section.


EVOLIUM0299_02

27/05/2002 3BK 11202 0299 DSZZA 38/81

3.8.1.1.3 Detection of Internal Telecom Reset condition

BSC MSC

(1) RESET CIRCUIT ----------------------------------->(1) start T19(1) :(1) : (note A)(2) stop T19 RESET ------------------------------------------------>

Figure 35 Reset Circuit procedure successful - Detection of Internal Telecom Reset condition1 A Reset Circuit procedure has already been initiated by the BSC.2 The BSS detects an internal Reset condition (T_i expiry), and all calls are released in the BSS [2

and 5]. The RESET message may be sent to the MSC (See Note B) and the Reset Circuitprocedure is cancelled by, stopping T19 and placing the A Channel available for use.

Note: the Blocking procedures are started when the RESET ACKNOWLEDGE is received or when themaximum number of retransmissions is reached - see appropriate section.

Notes:A An internal Reset condition is detectedB The RESET message is sent if this action is required by a flag .

3.8.1.2 Reset Circuit procedure unsuccessful cases

3.8.1.2.1 T19 Expiry

BSC MSC

(1) RESET CIRCUIT ----------------------------------->(1) start T19(1) :(1) :(1) :(2) T19 expiry(2) RESET CIRCUIT ----------------------------------->(2) start T19

Figure 36 Reset Circuit procedure unsuccessful - T19 Expiry1 The Reset Circuit procedure is initiated. At this point an internal counter "Num_RES" is set to 1.2 On expiry of T19, "Num_RES" is compared with "NBR_RESET_CIC_REP". If it is found that

"Num_RES" is less than "NBR_RESET_CIC_REP" then the RESET CIRCUIT message isresent, "Num_RES" is incremented and T19 is restarted.

3.8.1.2.2 T19 Expires "NBR_RESET_CIC_REP" times

BSC MSC

(1) T19 expiry(1) RESET CIRCUIT ----------------------------------->(1) start T19(1) :(1) :(1) :(2) T19 expiry

Figure 37 Reset Circuit procedure unsuccessful - T19 Expires "NBR_RESET_CIC_REP" times1 The Reset Circuit procedure is already running.2 T19 expires and the Counter "RES REP" is incremented. It is found that the value of "Num_RES"

is equal to "NBR_RESET_CIC_REP": the Reset Circuit procedure is abandoned. The A Channelis made available for selection in the BSS.


EVOLIUM0299_02

27/05/2002 3BK 11202 0299 DSZZA 39/81

3.8.2 MSC initiated Reset Circuit procedureThis section contains the general BSS behaviour on reception of a RESET CIRCUIT message fromthe MSC. Not all cases are considered as they are described in other sections in this document.

3.8.2.1 RESET CIRCUIT for an allocatable A Channel which has an active transactionIn this case the Call is released using the scenario defined in [5] event N1000 and a RESET CIRCUITACKNOWLEDGE is returned.For Call Release scenarios during other procedures see [6, 3 and 9].Note during Channel change procedures the release on A and Air interfaces is deferred until thewhereabouts of the MS is known.

3.8.2.2 RESET CIRCUIT for an allocatable A Channel (IDLE state) which has no activetransaction

In this case a RESET CIRCUIT ACKNOWLEDGE is returned immediately there is no need to performa Call Release.

3.8.3 Single Circuit Blocking procedureThis section contains the general behaviour of the Blocking procedure for successful and unsuccessfulcases.

3.8.3.1 Blocking procedure successful cases

3.8.3.1.1 Reception of BLOCKING ACKNOWLEDGE during T1

BSC MSC

(1) BLOCK ----------------------------------------------->(1) start T1(1) :(2) : <------------------ BLOCKING ACKNOWLEDGE(2) stop T1

Figure 38 Blocking procedure successful - Reception of BLOCKING ACKNOWLEDGE during T11 The BSC initiates Blocking by sending the BLOCK message to the MSC containing the CIC to be

blocked; sets an internal counter "Num_BLK" to 1; puts the CIC state to BLOCKING and starts T1.2 The MSC marks the CIC as blocked, and sends in response, a BLOCKING ACKNOWLEDGE.

The BSC receives the BLOCKING ACKNOWLEDGE message: sets the CIC to Blocked andstops T1. .

3.8.3.1.2 Reception of RESET CIRCUIT during Blocking procedureIf during a Blocking procedure the BSC receives a RESET CIRCUIT message for the A Channel then itshall send a single BLOCK message.

BSC MSC

(1) BLOCK --------------------------------------------->(1) start T1(1) :(2) : <----------------------------------- RESET CIRCUIT(3) : BLOCK --------------------------------------------->(3) : <------------------ BLOCKING ACKNOWLEDGE(3) stop T1

Figure 39 Blocking procedure successful - Reception of RESET CIRCUIT during T11 The Blocking procedure is running2 The RESET CIRCUIT message is sent from the MSC.3 A BLOCK message is sent to the MSC. The MSC returns a BLOCKING ACKNOWLEDGE, and

the procedure is stopped.


EVOLIUM0299_02

27/05/2002 3BK 11202 0299 DSZZA 40/81

3.8.3.2 Blocking unsuccessful cases

3.8.3.2.1 Blocking first T1 expiryWhen T1 expires for the first time the BSC sends the BLOCK message again.

BSC TELECOM MSC

(1) BLOCK ----------------------------------------------->(1) start T1(1) :(1) :(1) :(2) T1 expiry(3) BLOCK ----------------------------------------------->(4) start T1

Figure 40 Blocking unsuccessful - Blocking first T1 expiry1 The BSC initiates Blocking by sending the BLOCK message to the MSC containing the CIC to be

blocked, puts the CIC state into the BLOCKING state and starts T1.2 The MSC is unable to respond in time and the timer T1 expires (Note 5).3 The BSC sends the BLOCK message again.4 The timer T1 is started again.

3.8.3.2.2 Blocking second T1 expiryWhen T1 expires for the second time the BSC puts the circuit into the Blocked state and the Blockingprocedure is stopped for that circuit.


(1) BLOCK ----------------------------------------------->(1) start T1(1) :(1) T1 expiry(2) BLOCK ----------------------------------------------->(2) start T1(2) :(2) T1 expiry

Figure 41 Blocking unsuccessful - Blocking second T1 expiry1 The BSC initiates Blocking by sending the BLOCK message to the MSC containing the CIC to be

blocked, puts the CIC state into the BLOCKING state and starts T1. T1 expires for the first time2 The procedure repeats and T1 expires for the second time. . The BSS puts the circuit into the

Blocked state. The Channel_Block_Fail alarm is sent to the OMC.

3.8.3.2.3 Reception of UNEQUIPPED CIRCUIT during Blocking procedure

BSC MSC

(1) BLOCK ----------------------------------------------->(1) start T1(1) :(2) :(2) : <-------------------------- UNEQUIPPED CIRCUIT(2) stop T1(2) <----------------- O&M error report

Figure 42 Blocking unsuccessful - Reception of UNEQUIPPED CIRCUIT1 The BSC initiates Blocking by sending the BLOCK message to the MSC containing the CIC to be

Blocked, and starts T1.


EVOLIUM0299_02

27/05/2002 3BK 11202 0299 DSZZA 41/81

2 If the MSC does not know the Circuit, the MSC will return an UNEQUIPPED CIRCUIT message.The BSC receives the UNEQUIPPED CIRCUIT message, sets the CIC to Unequipped, stops T1,and sends an error report “Unequipped circuit initiated by MSC” to O&M.

Note : The circuit shall exit the Unequipped state automatically when any of the following messagesare received from the MSC :- ASSIGNMENT REQUEST,- HANDOVER REQUEST,- RESET CIRCUIT.

3.8.4 Single Circuit Unblocking procedure

3.8.4.1 Unblocking procedure successful cases

3.8.4.1.1 Reception of UNBLOCKING ACKNOWLEDGE during T1

BSC MSC

(1) UNBLOCK ------------------------------------------->(1) start T1(1) :(2) : <-------------- UNBLOCKING ACKNOWLEDGE(2) stop T1

Figure 43 Unblocking procedure successful - Reception of UNBLOCKING ACKNOWLEDGEduring T1

1 The BSC initiates Unblocking by sending the UNBLOCK message to the MSC containing the CICto be Unblocked, places the CIC state into the UNBLOCKING state and starts T1.

2 The MSC marks the CIC as UNBLOCKED, and sends in response, an UNBLOCKINGACKNOWLEDGE. The BSC receives the UNBLOCKING ACKNOWLEDGE message: sets theCIC to UNBLOCKED and stops T1.

3.8.4.1.2 Reception of RESET CIRCUIT during the Unblocking procedureIf during an Unblocking procedure the BSC receives a RESET CIRCUIT message for the A Channelthen the Unblocking procedure shall be stopped and the A Channel shall be freed for use.

BSC MSC

(1) UNBLOCK ------------------------------------------->(1) start T1(1) :(1) :(2) : <----------------------------------- RESET CIRCUIT

RESET CIRCUIT ACKNOWLEDGE ----------->(3) stop T1

Figure 44 Unblocking procedure successful - Reception RESET CIRCUIT during the Unblockingprocedure

1 The Unblocking procedure is running2 The RESET CIRCUIT message is sent from the MSC.3 The Unblocking procedure is stopped and the A Channel is made available for use.


EVOLIUM0299_02

27/05/2002 3BK 11202 0299 DSZZA 42/81

3.8.4.1.3 Internal or External Reset during the Unblocking procedureFor more detailed behaviour see section 3.8.10.3.If during an Unblocking procedure a RESET message is received from the MSC all Unblockingprocedures shall be stopped and the A Channels shall be made available for use.

BSC MSC

(1) UNBLOCK ------------------------------------------->(1) start T1(1) :(1) :(2) : <------------------------------------------------ RESET(3) stop T1

Figure 45 Unblocking procedure successful - Internal or External Reset during the Unblockingprocedure

1 The Unblocking procedure is running2 The RESET message is sent from the MSC.3 The Reset procedure is initiated [2]. The Unblocking procedure is stopped and the A Channel is

made available for use.If during the Unblocking procedure an Internal Reset is detected all Unblocking procedures shall besuspended. In the case where the RESET message is sent to the MSC (depending on the parameterNBR_RESET_REP) then all Unblocking procedures shall be stopped.In the case where the RESET message is not sent to the MSC the Unblocking procedures shall beresumed when the SCCP is available.

3.8.4.2 Unblocking procedure unsuccessful cases

3.8.4.2.1 Unblocking first T1 expiryWhen T1 expires the first time the BSC shall send the UNBLOCK message again.

BSC TELECOM MSC

(1) UNBLOCK ------------------------------------------->(1) start T1(1) :(1) :(2) T1 expiry(3) UNBLOCK ------------------------------------------->(3) start T1

Figure 46 Unblocking procedure unsuccessful - First T1 expiry1 The BSC initiates Unblocking by sending the UNBLOCK message to the MSC containing the CIC

to be Unblocked, puts the CIC into the UNBLOCKING state and starts T1.2 The MSC is unable to respond in time and the timer T1 expires.3 The BSC sends the UNBLOCK message again and the timer T1 is started.


EVOLIUM0299_02

27/05/2002 3BK 11202 0299 DSZZA 43/81

3.8.4.2.2 Unblocking second T1 expiryWhen T1 expires for the second time the BSC shall put the circuit into the Unblocked state and shallstop the Unblocking procedure for that circuit.


(1) UNBLOCK ------------------------------------------->(1) start T1(1) :(1) T1 expiry(2) UNBLOCK ------------------------------------------->(2) start T1(2) :(2) T1 expiry

Figure 47 Unblocking procedure unsuccessful - Unblocking second T1 expiry1 The BSC initiates Unblocking by sending the UNBLOCK message to the MSC containing the CIC

to be unblocked, puts the CIC into the UNBLOCKING state and starts T1. T1 expires for the firsttime.

2 The procedure repeats and T1 expires for the second time. The BSS puts the circuit in theUnblocked state. The Channel_Unblock_Fail alarm is sent to the OMC.

3.8.4.2.3 Reception of UNEQUIPPED CIRCUIT during Unblocking procedure

BSC MSC

(1) UNBLOCK ------------------------------------------->(1) start T1(1) :(2) :(2) : <-------------------------- UNEQUIPPED CIRCUIT(2) stop T1(2) <----------------- O&M ALARM

Figure 48 Unblocking procedure unsuccessful - Reception of UNEQUIPPED CIRCUIT1 The BSC initiates Unblocking by sending the UNBLOCK message to the MSC containing the CIC

to be Unblocked, and starts T1.2 If the MSC does not recognise the circuit the MSC will return an UNEQUIPPED CIRCUIT

message. The BSC upon receiving the UNEQUIPPED CIRCUIT message, shall set the CIC toUNEQUIPPED, shall stop T1, and shall send a Channel_Unblock_Fail alarm to O&M.

Note : The circuit will exit the Unequipped state automatically when any of the following messages arereceived from the MSC :- ASSIGNMENT REQUEST,- HANDOVER REQUEST,- RESET CIRCUIT.

3.8.5 Group Blocking procedureThis section contains the general behaviour of the Group Blocking procedure for successful andunsuccessful cases.

3.8.5.1 Group Blocking procedure successful casesThe BSC accepts any appropriate acknowledge to Group blocking from the MSC. That is to say GroupBlock procedures can be stopped for the concerned circuits when either BLOCKING ACKNOWLEDGEor CIRCUIT GROUP BLOCKING ACKNOWLEDGE is received.

3.8.5.1.1 Reception of CIRCUIT GROUP BLOCKING ACKNOWLEDGE during T20


EVOLIUM0299_02

27/05/2002 3BK 11202 0299 DSZZA 44/81

BSC MSC

(1) CIRCUIT GROUP BLOCK ----------------------->(1) start T20(1) :(2) : CIRCUIT GROUP BLOCKING

ACKNOWLEDGE or(2) : <------------------ BLOCKING ACKNOWLEDGE(2)

Figure 49 Group Blocking procedure successful - Reception of ACKNOWLEDGE during T201 The BSC initiates Group Blocking by sending the BLOCK message to the MSC containing the

CICs to be Blocked, puts the CICs state to BLOCKING and starts T20.2 The MSC marks the CICs as Blocked, and sends in response, a CIRCUIT GROUP BLOCKING

ACKNOWLEDGE or BLOCKING ACKNOWLEDGE message(s). The BSC receives themessage(s), and sets the CIC(s) to Blocked.

3.8.5.1.2 Reception of RESET CIRCUIT during Group Blocking procedureIf during a Group Blocking procedure the BSC receives a RESET CIRCUIT message for an A Channelto be blocked, then a single BLOCK message shall be sent.

BSC MSC

(1) CIRCUIT GROUP BLOCK ----------------------->(1) start T20(1) :(2) : <----------------------------------- RESET CIRCUIT(3) : BLOCK ------------------------------------------------>(3) : <------------------ BLOCKING ACKNOWLEDGE(3) :

Figure 50 Group Blocking procedure successful - Reception of RESET CIRCUIT during GroupBlocking procedure

1 The Group Blocking procedure is running2 The RESET CIRCUIT message is sent from the MSC for a channel to be blocked.3 A BLOCK message is sent to the MSC. The MSC returns a BLOCKING ACKNOWLEDGE, and

the channel is set Blocked.

3.8.5.2 Group Blocking unsuccessful cases

3.8.5.2.1 Group Blocking first T20 expiryWhen T20 expires for the first time the BSC sends the CIRCUIT GROUP BLOCK message again.

BSC TELECOM MSC

(1) CIRCUIT GROUP BLOCK ----------------------->(1) start T20(1) :(1) :(1) :(2) T20 expiry(3) CIRCUIT GROUP BLOCK ----------------------->(4) start T20

Figure 51 Group Blocking procedure unsuccessful - First T20 expiry1 The BSC initiates Blocking by sending the CIRCUIT GROUP BLOCK message to the MSC

containing the CICs to be Blocked, changes the CICs states to BLOCKING and starts T20.2 The MSC is unable to respond in time and the timer T20 expires.3 The BSC sends the CIRCUIT GROUP BLOCK message again.4 The timer T20 is started again.


EVOLIUM0299_02

27/05/2002 3BK 11202 0299 DSZZA 45/81

3.8.5.2.2 Group Blocking second T20 expiryWhen T20 expires for the second time the BSC puts the circuits into the Blocked state and the GroupBlocking procedure is stopped for those circuits.


(1) CIRCUIT GROUP BLOCK ----------------------->(1) start T20(1) :(1) T20 expiry(2) CIRCUIT GROUP BLOCK ----------------------->(2) start T20(2) :(2) T20 expiry

Figure 52 Group Blocking procedure unsuccessful - Second T20 expiry1 The BSC initiates Blocking by sending the CIRCUIT GROUP BLOCK message to the MSC

containing the CICs to be Blocked, puts the CICs into the BLOCKING state and starts T20. T20expires for the first time. See Note A.

2 The procedure repeats and T20 expires for the second time. The BSS puts the circuits into theBlocked state. The Channel_Block_Fail alarm is sent to the OMC.

Note A : Whilst the timer T20 is running, O&M may have ordered more CICs to be blocked; in whichcase the next CIRCUIT GROUP BLOCK message sent upon T20 expiry will be for the previouslyunacknowledged circuits (up to a limit of 2 times) plus the new circuits that require blocking (ifany). In the same manner, these new circuits will be repeated no more than once if notacknowledged.

3.8.5.2.3 Reception of UNEQUIPPED CIRCUIT during Group Blocking procedure

BSC MSC

(1) CIRCUIT GROUP BLOCK ----------------------->(1) start T20(1) :(2) :(2) : <-------------------------- UNEQUIPPED CIRCUIT(2) <----------------- O&M error report

Figure 53 Group Blocking procedure unsuccessful - Reception of UNEQUIPPED CIRCUIT1 The BSC initiates Blocking by sending the CIRCUIT GROUP BLOCK message to the MSC

containing the CICs to be Blocked, puts the CICs’ state to BLOCKING and starts T20.2 If the MSC does not know one or several circuits, the MSC will return UNEQUIPPED CIRCUIT

message(s). The BSC receives the UNEQUIPPED CIRCUIT message(s), sets the CIC(s) toTEL_UNEQUIPPED, and sends an error report “Unequipped circuit initiated by the MSC” toO&M.

Note : The circuit(s) shall exit the Unequipped state automatically when any of the following messagesare received from the MSC :- ASSIGNMENT REQUEST,- HANDOVER REQUEST,- RESET CIRCUIT.

3.8.6 Group Unblocking procedureThe BSC shall accept any appropriate acknowledge to Group unblocking from the MSC. That is to sayGroup Unblock procedures shall be stopped for the concerned circuits when either UNBLOCKINGACKNOWLEDGE or CIRCUIT GROUP UNBLOCKING ACKNOWLEDGE is received.


EVOLIUM0299_02

27/05/2002 3BK 11202 0299 DSZZA 46/81

3.8.6.1 Group Unblocking procedure successful cases

3.8.6.1.1 Reception of CIRCUIT GROUP UNBLOCKING ACKNOWLEDGE during T20

BSC MSC

(1) CIRCUIT GROUP UNBLOCK ------------------->(1) start T20(1) :(2) : CIRCUIT GROUP UNBLOCKING

ACKNOWLEDGE or(2) : <-------------- UNBLOCKING ACKNOWLEDGE

Figure 54 Group Unblocking procedure successful - Reception of an ACKNOWLEDGE duringT20

1 The BSC initiates Group Unblocking by sending the CIRCUIT GROUP UNBLOCK message tothe MSC containing the CICs to be Unblocked, places the CICs state into the UNBLOCKING stateand starting T20.

2 The MSC marks the CICs as UNBLOCKED, and sends in response, a CIRCUIT GROUPUNBLOCKING ACKNOWLEDGE or UNBLOCKING ACKNOWLEDGE message(s). The BSCreceives the message(s), and sets the CIC(s) to UNBLOCKED.

3.8.6.1.2 Reception of RESET CIRCUIT during the Group Unblocking procedureIf during a Group Unblocking procedure the BSC receives a RESET CIRCUIT message for an AChannel being to be unblocked then the Unblocking procedure will be stopped for this channel and itwill be freed for use.

BSC MSC

(1) CIRCUIT GROUP UNBLOCK ------------------->(1) start T20(1) :(1) :(2) : <----------------------------------- RESET CIRCUIT(3) : RESET CIRCUIT ACKNOWLEDGE ----------->

Figure 55 Group Unblocking procedure successful - Reception of RESET CIRCUIT1 The Group Unblocking procedure is running2 The RESET CIRCUIT message is sent from the MSC for a channel being to be unblocked.3 The Unblocking procedure is stopped for the A channel and the circuit is made available for use.

3.8.6.1.3 Internal or External Reset during the Unblocking procedureFor more detailed behaviour see section 3.8.10.3.If during a Group Unblocking procedure a RESET message is received from the MSC all GroupUnblocking procedures shall be stopped and the A Channels shall be made available for use.

BSC MSC

(1) CIRCUIT GROUP UNBLOCK ------------------->(1) start T20(1) :(1) :(2) : <------------------------------------------------ RESET(3) stop T20

Figure 56 Group Unblocking procedure successful - Reception of Internal or External Reset1 The Unblocking procedure is running2 The RESET message is sent from the MSC.3 The Reset procedure is initiated [2]. The Group Unblocking procedure is stopped and the

A Channels are made available for use.


EVOLIUM0299_02

27/05/2002 3BK 11202 0299 DSZZA 47/81

If during the Group Unblocking procedure an Internal Reset is detected all Group Unblockingprocedures shall be suspended. In the case where the RESET message is sent to the MSC(depending on the parameter NBR_RESET_REP) then all Group Unblocking procedures will bestopped.In the case where the RESET message is not sent to the MSC the suspended Group Unblockingprocedures (if any) will be resumed when the SCCP becomes available.

3.8.6.2 Group Unblocking procedure unsuccessful cases

3.8.6.2.1 Reception of UNEQUIPPED CIRCUIT during Group Unblock procedure

BSC MSC

(1) CIRCUIT GROUP UNBLOCK ------------------->(1) start T20(1) :(2) :(2) : <-------------------------- UNEQUIPPED CIRCUIT(2) <----------------- O&M ALARM

Figure 57 Group Unblocking procedure unsuccessful - Reception of UNEQUIPPED CIRCUIT1 The BSC initiates Group Unblocking by sending the CIRCUIT GROUP UNBLOCK message to

the MSC containing the CICs to be Unblocked, places the CICs state into the UNBLOCKING stateand starts T20.

2 If the MSC does not recognise one or several circuits, the MSC will return UNEQUIPPEDCIRCUIT message(s). The BSC receives the UNEQUIPPED CIRCUIT message(s), sets theCIC(s) to TEL_UNEQUIPPED, and sends a Channel_Unblock_Fail to O&M.

Note : The circuit will exit the Unequipped state automatically when any of the following messages arereceived from the MSC :- ASSIGNMENT REQUEST,- HANDOVER REQUEST,- RESET CIRCUIT.

3.8.6.2.2 Group Unblocking first T20 expiryWhen T20 expires for the first time the BSC sends the CIRCUIT GROUP UNBLOCK message again.

BSC TELECOM MSC

(1) CIRCUIT GROUP UNBLOCK ------------------->(1) start T20(1) :(1) :(2) T20 expiry(3) CIRCUIT GROUP UNBLOCK ------------------->(3) start T20

Figure 58 Group Unblocking procedure unsuccessful - First T20 expiry1 The BSC initiates Group Unblocking by sending the CIRCUIT GROUP UNBLOCK message to

the MSC containing the CICs to be Unblocked, puts the CICs state in to the UNBLOCKING stateand starts T20.

2 The MSC is unable to respond in time and the timer T20 expires.3 The BSC sends the CIRCUIT GROUP UNBLOCK message again and the timer T20 is started.


EVOLIUM0299_02

27/05/2002 3BK 11202 0299 DSZZA 48/81

3.8.6.2.3 Unblocking second T20 expiryWhen T20 expires for the second time the BSC puts the circuits into the Unblocked state and theGroup Unblocking procedure is stopped for those circuits.


(1) CIRCUIT GROUP UNBLOCK ------------------->(1) start T20(1) :(1) T20 expiry(2) CIRCUIT GROUP UNBLOCK ------------------->(2) start T20(2) :(2) T20 expiry

Figure 59 Group Unblocking procedure unsuccessful - Second T20 expiry1 The BSC initiates Group Unblocking by sending the CIRCUIT GROUP UNBLOCK message to

the MSC containing the CICs to be Blocked, puts the CICs state into the UNBLOCKING state andstarts T20. T20 expires for the first time. see Note A.

2 The procedure repeats and T20 expires for the second time. The BSS puts the circuits into theUnblocked state. The Channel_Unblock_Fail alarm is sent to the OMC.

Note A : Whilst the timer T20 is running, O&M may have ordered more CICs to be unblocked; in whichcase the next CIRCUIT GROUP UNBLOCK message sent upon T20 expiry will be for thepreviously unacknowledged circuits (up to a limit of 2 times) plus the new circuits that requireblocking (if any). In the same manner, these new circuits will be repeated once if notacknowledged.

3.8.7 BSS initiated Unequipped Circuit procedureThe BSS shall only initiate an Unequipped circuit procedure when the flagEN_UNEQUIPPED_CIRCUIT is TRUE.An UNEQUIPPED CIRCUIT message received from the MSC shall be handled even if the flag isFALSE.

3.8.7.1 Unequipped Circuit definitionAn Unequipped Circuit in the BSS is defined as follows:• A Circuit is unequipped in the BSS if it is not configured by O&M to exist in any DTC within the

BSS. This definition is independent of the state of the DTC, that is to say if a DTC is faulty or outof service due to O&M, then any circuits associated with that DTC are known to the BSS, theyare not unknown. Note - No response is possible from the affected DTC.

• A circuit is unequipped in the BSS if the circuit has a CIC but is either not configured or is markedas being unequipped. It should be noted that circuits used for X.25 and SPC are deemed to beequipped by the ALCATEL BSS.

• SS7 circuits when selected by the MSC are deemed also to be unequipped - this is a specialcase.

3.8.7.2 BSS reaction on detecting an Unknown CircuitIf the BSS receives a request for resources [6] and [3]) and the circuit contained in the request isUnequipped in the BSS, the BSS shall refuse the request for resources ([5] A0703 and EHT0605).Furthermore, if the BSS is operating in GSM Phase 2 mode on the A interface and the O&M parameterEN_UNEQUIPPED_CIRCUIT is true and, it receives an ASSIGNMENT REQUEST, HANDOVERREQUEST, BLOCKING ACKNOWLEDGE, UNBLOCKING ACKNOWLEDGE, CIRCUIT GROUPBLOCKING ACKNOWLEDGE, CIRCUIT GROUP UNBLOCKING ACKNOWLEDGE, RESET CIRCUITACKNOWLEDGE or RESET CIRCUIT message from the MSC containing the identity of a circuit whichthe BSS believes to be unequipped, the BSS shall send a single UNEQUIPPED CIRCUIT message tothe MSC.Notes:1 Telecom shall send an O&M error report to inform the O&M software that the BSS has detected a

Database inconsistency - Note that the O&M error report shall be sent whether or not theUNEQUIPPED CIRCUIT message is sent.


EVOLIUM0299_02

27/05/2002 3BK 11202 0299 DSZZA 49/81

2 A circuit which is either faulty, is not responding, or is out of service due to O&M command etc. isnot Unknown. UNEQUIPPED CIRCUIT should not be sent in these cases.

3.8.7.3 BSS reaction on MSC initiated Unequipped Circuit procedureAn UNEQUIPPED CIRCUIT message may be received by the BSS indicating only one circuit.If the circuit indicated in the UNEQUIPPED CIRCUIT message is Unequipped in the BSS then the BSSshall ignore the message.In all cases, where the BSS initiates a circuit related procedure for a circuit which it believes to beequipped, and the response from the MSC is an UNEQUIPPED CIRCUIT message, the BSS shallabandon the procedure for that circuit, shall place that circuit in the TEL_UNEQUIPPED state and shallgenerate an O&M error report “Unequipped circuit initiated by the MSC”.The circuit shall exit the TEL_UNEQUIPPED state automatically when the following messages arereceived from the MSC :

- ASSIGNMENT REQUEST (next state BUSY),- HANDOVER REQUEST (next state BUSY),- RESET CIRCUIT (next state IDLE).

If the BSC receives an UNEQUIPPED CIRCUIT message indicating a Circuit which is in one of thefollowing states:• in the process of being Blocked• about to be blocked as part of a Reset procedure, i.e. before triggering of the Blocking proceduresthen the Blocking procedure shall be stopped, the Circuit shall be placed into the Unequipped state andan O&M error report “Unequipped circuit initiated by MSC” shall be generated.If the BSC receives an UNEQUIPPED CIRCUIT message indicating a Circuit which is in the process ofbeing Unblocked then the Unblocking procedure shall be stopped, the Circuit shall be placed into theUnequipped state and an O&M alarm “Channel_Unblock_Fail” shall be generated.

If an UNEQUIPPED CIRCUIT message references a Circuit which has a call associated with it or aCircuit which is Idle then the BSS shall ignore the message and shall generate an O&M error report“Unequipped circuit initiated by MSC”.

3.8.8 O&M and Telecom interfaceThe interface between the O&M Fault management entity and the Telecom Blocking and Unblockingentity uses the following messages:

3.8.8.1 O&M -> Telecom1 A Trunk Out of Service (AT_OOS (WTC - see Note)): Command from O&M to place an A Trunk

Out of Service.2 A Trunk In Service (AT_IS): Command from O&M to place an A Trunk In Service.3 A Channel Out of Service (AC_OOS(WTC - see Note)): Command from O&M to place an

A Channel Out Of Service.4 A Channel In Service (AC_IS): Command from O&M to place an A Channel In Service.Note :The Operator sets the parameter WTC according to the length of time that he wishes to keep

calls for. WTC is set to 0 for O&M autonomous fault management actions which means that theyare immediately executed.

3.8.8.2 Telecom -> O&M1 Error report "Unequipped circuit initiated by the MSC" (NOTIFY). to inform O&M that the MSC

has initiated an Unequipped circuit procedure for a circuit known at the BSC.2 2 Error report "Unequipped circuit initiated by the BSC" (NOTIFY). to inform O&M that the

MSC has requested a circuit unequipped to the BSC.3 Alarm “Channel_Block_Fail” to inform OMC (through BSC O&M) that the BLOCK procedure or

the CIRCUIT GROUP BLOCK procedure has failed (no-answer from MSC).4 Alarm “Channel_Unblock_Fail” to inform OMC (through BSC O&M) that the UNBLOCK

procedure or the CIRCUIT UNGROUP BLOCK procedure has failed (reception ofUNEQUIPPED CIRCUIT from MSC).

Note : error reports are not sent to OMC.


EVOLIUM0299_02

27/05/2002 3BK 11202 0299 DSZZA 50/81

3.8.9 O&M initiated Blocking and Unblocking due to O&M fault managementFor definitions of the O&M states, and nomenclature [4].For more detail on the SBL hierarchy [11].The following diagram shows the SBL hierarchy applying to the ALCATEL BSS as seen from the OMC.

BSC

DTC

A Trunk

A Channels SS7

Figure 60 BSS SBL hierarchy - OMC viewThe following diagram shows the SBL hierarchy applying to the ALCATEL BSS as seen from the BSS.

DTC

A Trunk

A Channels SS7

Figure 61 BSS SBL hierarchy - BSS viewThe SBLs may be divided into two groups:• those that when they fail cause a 2 Mbit/s PCM to be disabled (e.g. DTC and A Trunk)• those that when they fail cause an A Channel to be disabled (e.g. A Channel).

3.8.9.1 SS7 SBLThe SS7 SBL is shown for completeness in both SBL hierarchy diagrams, however there are never anyBlocking, Unblocking or Reset Circuit procedures run for this SBL.If the MSC sends a HANDOVER REQUEST, ASSIGNMENT REQUEST, BLOCKINGACKNOWLEDGE, UNBLOCKING ACKNOWLEDGE, RESET CIRCUIT ACKNOWLEDGE or RESETCIRCUIT message with a CIC indicating a circuit used in the BSS for SS7 then a BSS operating inGSM Phase 2 mode on the A Interface may send (depending upon the O&M ParameterEN_UNEQUIPPED_CIRCUIT setting) an UNEQUIPPED CIRCUIT message in response.When the SS7 SBL is present in the hierarchy (i.e. it is present on an A Trunk) one of the circuits of theA Trunk has been reserved for use for SS7 signalling.Disabling of an A Trunk SBL which has a circuit for carrying SS7 shall cause the circuit to be no longeravailable for use in carrying SS7 signalling. In this case the MTP changeover procedure shall betriggered, ensuring that the SCCP connections can be supported across another SS7 SBL.When a DTC supporting an SS7 SBL is disabled the MTP changeover shall be triggered, howeverthere are no means for the SCCP entity supported or BSSMAP entities on the DTC to be transferred toanother DTC so that the connections may be maintained.

3.8.10 Telecom Reset Circuit, Blocking and Unblocking detailed protocol behaviourTo explain the required behaviour of the Telecom Reset Circuit, Blocking and Unblocking proceduresthe following logical entities are defined:1 Message checking and building;2 The Scheduler;3 The A Channel Reset Circuit, Blocking and Unblocking algorithmsNote: For the purpose of the Specification the description is very close to an implementation. However

Software designers do not have to comply with the description of the split implied in the Systemspecification, but the behaviour described is required.


EVOLIUM0299_02

27/05/2002 3BK 11202 0299 DSZZA 51/81

3.8.10.1 Message checking and building

3.8.10.1.1 Checking of ACKNOWLEDGE and RESET CIRCUIT messagesWhen checking BLOCKING ACKNOWLEDGE, UNBLOCKING ACKNOWLEDGE, RESET CIRCUIT orRESET CIRCUIT ACKNOWLEDGE messages• If the CIC indicates timeslot 0, the message is inapproporiate and shall be ignored.• If the BSS considers the CIC to be Unequipped the message is also inappropriate, an O&M

Error report shall be generated and, and if the O&M parameter EN_UNEQUIPPED_CIRCUIT =TRUE, an UNEQUIPPED CIRCUIT message shall be sent.

3.8.10.1.2 Checking of GROUP ACKNOWLEDGE messagesWhen checking CIRCUIT GROUP BLOCKING ACKNOWLEDGE orCIRCUIT GROUP UNBLOCKING ACKNOWLEDGE messages:Procedures common to CIRCUIT GROUP BLOCKING ACKNOWLEDGE and CIRCUIT GROUPUNBLOCKING ACKNOWLEDGE :

• If the first CIC and/or the range of CICs does not match with those of the initiated CIRCUITGROUP BLOCKING (resp. UNBLOCKING) message, the message is inappropriate and theCIRCUIT GROUP BLOCKING (resp. CIRCUIT GROUP UNBLOCKING) shall be repeated.

• Only CICs with status bit set in both the CIC code list of the initial GROUP (UN)BLOCK messageand the CIC code list of the GROUP (UN)BLOCKING ACKNOWLEDGE message shall beconsidered as acknowledged (their state shall be set to (Un)Blocked).

• If one or more CICs are acknowledged whereas they are not blocked (resp. unblocked) or aboutto be blocked (resp. unblocked) in the BSC, a CIRCUIT GROUP BLOCK (resp. UNBLOCK)message shall be sent for these circuits.

• If the BSS believes that one or more CICs are Unequipped, the message shall be discarded andan O&M error report “Unequipped circuit initated by the BSC” shall be generated. AnUNEQUIPPED CIRCUIT message shall be sent in response if enabled by the O&M parameterEN_UNEQUIPPED_CIRCUIT. The OIE CIRCUIT IDENTITY CODE LIST shall be added to themessage.

Procedures specific to CIRCUIT GROUP BLOCKING ACKNOWLEDGE :• if the message concerns CIC’s which are not blocked, send a CIRCUIT GROUP UNBLOCK for

these circuits.• if to the message concerns CIC’s which are unequipped, send a UNEQUIPPED_CIRCUIT

message.3.8.10.1.3 Checking of UNEQUIPPED CIRCUIT messageOnly the MIE CIRCUIT IDENTITY CODE shall be checked. The OIE CIRCUIT IDENTITY CODE LISTshall be checked if presentIf the CIC indicates timeslot 0, the message shall be discarded.If the message indicates a circuit (or several if there is an OIE CIC CODE LIST present) which is(are)unknown to the BSS, no UNEQUIPPED CIRCUIT message shall be returned for this(these) circuit(s).

3.8.10.1.4 Building a BLOCK messageThe CIC shall be set to the A Channel which is to be blocked.The cause shall be set to:• "O&M intervention" when O&M has triggered the Blocking procedure or when Blocking is

triggered during Reset procedure or when Blocking is triggered during Reset Circuit procedure.• "Terrestrial resource unavailable" when Telecom has triggered the Blocking procedure during the

Assignment or External handover procedures.

3.8.10.1.5 Building an UNBLOCK messageThe CIC shall be set to the A Channel which is to be Unblocked.

3.8.10.1.6 Building a CIRCUIT GROUP BLOCK messageThe CIC MIE shall be set to the first A channel of the group to be blocked.The status bits in CIC code list MIE shall be set to "blocked" for the following A Channels of the groupwhich are to be blocked. Other status bits of unaffected circuits shall be set to "no indication" [10].


EVOLIUM0299_02

27/05/2002 3BK 11202 0299 DSZZA 52/81

3.8.10.1.7 Building a CIRCUIT GROUP UNBLOCK messageThe CIC MIE shall be set to the first A channel of the group to be unblocked.The status bits in the CIC code list MIE shall be set to "unblocked" for the following A Channels of thegroup which are to be unblocked. Other status bits of unaffected circuits shall be set to "no indication"[10].

3.8.10.1.8 Building a RESET CIRCUIT messageThe CIC shall be set to the A Channel for which the release is required.The cause value shall be set to "Equipment failure".

3.8.10.1.9 Building a RESET CIRCUIT ACKNOWLEDGE messageThe CIC shall be set to the A Channel indicated in the received RESET CIRCUIT.

3.8.10.1.10 Building an UNEQUIPPED CIRCUIT messageThe CIC shall be set to the A Channel that is Unknown to the BSS.The CIRCUIT IDENTITY CODE LIST OIE shall be sent if the circuit group procedures are enabled bythe parameter EN_CIRCUIT_GROUP. The status bits in the CIC code list OIE shall be set to"unequipped" for all the unknown A Channels amongst those indicated in the MSC message.

3.8.10.2 The SchedulerThe Scheduler shall:1 Perform A Interface load reduction for single Blocking and Unblocking procedures. There is no A

interface load reduction foreseen for Reset Circuit procedures.2 Initiation and synchronisation of tasks depending on the availability of the SCCP entity in the BSS.3 Scheduling of A Channel Reset Circuit, single Blocking and Unblocking algorithms and Group

Blocking and Unblocking algorithms.4 Ordering the use of AIS.

AIS shall be applied when: the event is a BSS internally detected hardware failure; or when anOperator command to disable an SBL related to an A Trunk is successful.AIS shall be removed when: an internally detected BSS hardware failure has disappeared; orwhen an Operator command to enable an SBL related to an A Trunk is successful.

Note: An external 2 Mbit/s PCM Alarm detected by the BSC shall not cause AIS to be applied.The Scheduler shall take as its inputs the O&M Telecom interface (previously defined) and the SCCPstatus.The SCCP status shall provide the working status of the SCCP entity in the BSS (TRUE: available;FALSE not available).The following tables show the general actions to be taken by the scheduler on reception of O&MTelecom commands.

EVENT ACTION WITH SINGLE PROCEDUREAT_OOS(WTC) Send OOS(WTC) to all “single” algorithms on this A Trunk

Schedule all algorithmswhen all calls are released transmit AIS (See Note 1)

AT_IS Send IS to all “single” algorithms on this A TrunkSchedule all algorithmsstop transmitting AIS (See Note 1).

AC_OOS(WTC) Send OOS(WTC) to the affected “single” algorithmSchedule the appropriate algorithm

AC_IS Send IS to the affected “single” algorithmSchedule the appropriate algorithm

Table 2 Scheduler actions upon reception of O&M Telecom commands - Single procedures


EVOLIUM0299_02

27/05/2002 3BK 11202 0299 DSZZA 53/81

EVENT ACTION WITH GROUP PROCEDUREAT_OOS(WTC) Send T_OOS(WTC) to the “group” algorithm on this A Trunk

Schedule the relevant algorithmwhen all calls are released transmit AIS

AT_IS Send T_IS to the “group” algorithm on this A TrunkSchedule the relevant algorithmstop transmitting AIS

AC_OOS(WTC) Send OOS(WTC) to the “group” algorithm to which the channel belongsSchedule the appropriate algorithm

AC_IS Send IS to the “group” algorithm to which the channel belongsSchedule the appropriate algorithm

Table 3 Scheduler actions upon reception of O&M Telecom commands - Group proceduresNote 1 : The application and removal of AIS is dependent upon the type of failure see ordering of AIS

in this section.The Scheduling algorithm should ensure that when the SCCP is available, no more than B_NUMBlocking and Unblocking algorithms shall be initiated within any T_burst period per DTC processor.When a Reset Circuit protocol is active the Scheduler shall schedule the algorithm when the SCCP isavailable, A interface load control shall not be invoked for the Reset Circuit procedure.


EVOLIUM0299_02

27/05/2002 3BK 11202 0299 DSZZA 54/81

3.8.10.3 A Channel Reset Circuit, Blocking and Unblocking algorithmsThis section covers the Reset Circuit, Blocking and Unblocking algorithms for A Channels available forselection by the MSC for use in calls. It does not cover the detailed behaviour for SS7, SPC or NotEquipped A Channels, a state transition diagram is supplied for SPC Blocking procedures.

3.8.10.3.1 DefinitionsThe A Channel Blocking and Unblocking algorithm takes as its inputs the following list of events:

EXTERNALEVENT

DESCRIPTION

TEL_RES(RES_TYPE)

RES_TYPE (EXT_INT, INT_NO_RES)When RES_TYPE == EXT_INT

There has been a request from Telecom to perform a Reset procedure due tothe reception (from the MSC) of a RESET message or the reception of a RESETACKNOWLEDGE (during the internally detected Reset procedure when theRESET message is sent to the MSC)

When RES_TYPE == INT_NO_RESThe Telecom entity has performed an Internal reset but no RESET message hasbeen sent to the MSC.It is at this point the Algorithms decide if the A Channel which they control shouldhave a Blocking procedure run.

OOS(WTC period)

Request to place Out Of Service a specific CIC.Passed parameter: WTC (WAIT TRAFFIC CLEAR)The WTC period is specified in seconds and is used to set the period of the timerT_WTC. If this timer expires the algorithms cause a forced release of the call [5]N0300.

TOOS(WTC period)

Request to place Out Of Service a specific Trunk (only with Group procedures).Passed parameter: WTC (WAIT TRAFFIC CLEAR)The WTC period is specified in seconds and is used to set the period of the timerT_WTC. If this timer expires the algorithm cause a force release of all callsassociated to the Trunk - ref [5] N0300.

IS Request to place In Service a specific CICT_IS Request to place In Service a specific Trunk (only with Group procedures).

AIS_PRESNote A

The A Channel has a 2 Mbit/s PCM alarm active on its associated A Trunk

NO_AISNote A

The 2 Mbit/s PCM Alarm has been removed from the A Trunk associated with thisA Channel.

TS Request from Telecom to seize the Channel for use.This request comes from the Assignment [3] or the External handover [6]procedure.

TR(REL_TYPE) Request from Telecom to release the A Channel for re-use.This request comes from the Call Release [5], or Assignment [3] or Handover [6]procedures.REL_TYPE (NORM, ABNORM)

This is an indication from the BSSAP whether the release performed wasdeemed Normal or Abnormal.On Abnormal releases a Reset Circuit procedure shall be triggered if theA Channel is not disabled by O&M - for events see section "Presentation ofReset Circuit procedure"

SCHED This is a signal between the Scheduler and the Algorithm which indicates that theAlgorithm may start to perform either the Blocking or Unblocking procedure.For Reset Circuit protocolIt is sent when the Scheduler detects that the SCCP is available.For the Blocking or Unblocking protocolIt is sent when the Scheduler detects that the SCCP is available and the loadcontrol algorithm (controlled by T_burst and B_NUM) is such that another Blockingor Unblocking procedure may be scheduled.For the Group Blocking or Unblocking protocolIt is sent when the Scheduler detects that the SCCP is available.


EVOLIUM0299_02

27/05/2002 3BK 11202 0299 DSZZA 55/81

EXTERNALEVENT

DESCRIPTION

BLOCK ACK Reception of BLOCKING ACKNOWLEDGE message from the MSC - see sectionon message checking

GROUP BLOCKACK

Reception of GROUP BLOCKING ACKNOWLEDGE message from the MSC -see section on message checking

UNBLOCK ACK Reception of UNBLOCKING ACKNOWLEDGE from the MSC - see section onmessage checking

GROUPUNBLOCK ACK

Reception of GROUP UNBLOCKING ACKNOWLEDGE from the MSC - seesection on message checking

RESET CIR Reception of RESET CIRCUIT message from the MSC - see section on messagechecking

RESET CIR ACK Reception of RESET CIRCUIT ACKNOWLEDGE from the MSC - see section onmessage checking

UNEQUIPPEDCIR

Reception of UNEQUIPPED CIRCUIT from the MSC - see section on messagechecking

T1 Timer T1 expiryT19 Timer T19 expiryT20 Timer T20 expiry

Table 4 A Channel Blocking and Unblocking algorithm input eventsNote A: When the flag IGNORE_2MBIT_FAIL is TRUE the events AIS_PRES, NO_AIS, OOS and ISare used by the state machine. When the flag IGNORE_2MBIT_FAIL is FALSE the events OOS and ISare used by the state machine. In fact when only the events OOS and IS are used the eventsAIS_PRES and NO_AIS are included in the events OOS and IS respectively.The following internally generated timer events are used in the representation of the behaviour.

INTERNAL TIMERS DESCRIPTIONT1 The timer used to initiate the re-sending of the BLOCK or UNBLOCK

message.T_WTC The timer is set to obtain the Wait Traffic Clear period ordered by the

Operator O&M Blocking command.T19 The timer is used to initiate the re-sending of the RESET CIRCUIT message.T20 The timer is used to initiate the re-sending of the CIRCUIT GROUP BLOCK or

UNBLOCK message.

Table 5 Internally generated timer eventsThe following constants are used.

CONSTANTS DESCRIPTIONMAX_REP_T1 The Maximum number of times that T1 is allowed to expire.

MAX REP_T1 is hard coded with the value 2MAX_REP_T20 The Maximum number of times that T20 is allowed to expire for each channel

belonging to a group.MAX_REP_T20 is hard coded with the value 2

Table 6 Constants


EVOLIUM0299_02

27/05/2002 3BK 11202 0299 DSZZA 56/81

The following Internal variables are used to represent the behaviour.

INTERNALVARIABLE

DESCRIPTION

T1_count T1_count is a counter which counts the number of expiries of T1, it is used forboth the Blocking and the Unblocking protocols.

T20_count T20_count is a counter which counts the number of expiries of T20 for eachchannel belonging to a group, it is used for both the Group Blocking and theGroup Unblocking protocols.

Num_RES This is a counter which counts the number of times the RESET CIRCUITmessage has been transmitted to the MSC.It is set to 1 when the procedure is first startedIt is incremented on T19 expiry and the RESET CIRCUIT message is sent to theMSC.

Num_BLK This is a counter which counts the number of times the BLOCK message hasbeen transmitted to the MSC.It is set to 1 when the procedure is first startedIt is incremented when the BLOCK message is sent to the MSC.

Num_UNBLK This is a counter which counts the number of times the UNBLOCK message hasbeen transmitted to the MSC.It is set to 1 when the procedure is first started.It is incremented when the UNBLOCK message is sent to the MSC.

UnBlk_Reqd This is a flag which indicates that an Unblocking procedure must be carried outbefore entering the IDLE state.Its initial state is set to FALSE.It is set to TRUE when, during the UNBLOCKING state a command is receivedfrom O&M to place the A Channel out of service.It is set to FALSE when the A Channel is placed into the IDLE state.

Unequ_Reqd This is a flag which indicates that a channel must enter the TEL_UNEQUIPPEDstate during a Camped On Blocking procedure.It is set to TRUE when, during a Blocking with an associated call the MSC hasinitiated an Unequipped circuit.It is set to FALSE when the circuit exits the TEL_UNEQUIPPED state

Table 7 Internal variables


EVOLIUM0299_02

27/05/2002 3BK 11202 0299 DSZZA 57/81

The following states are defined for the Telecom protocol and are held in the Internal variableCHANNEL STATE :

CHANNEL STATE DESCRIPTIONIDLE State of an A Channel that is not in use on a connection.BUSY State of an A Channel that is in use on a connection

TO BE CAMPED ONBLOCKED

State of the Telecom Blocking protocol where the Call is on going and theprocedure is awaiting to be activated by the Scheduler

CAMPED ONBLOCKING

State of the Telecom Blocking protocol where the Call is on going and theBlocking procedure is running.

CAMPED ON BLOCKED State of the Telecom Blocking protocol where the Call is on going and theBlocking procedure has been successfully acknowledged by the MSC

TO BE UNBLOCKED State of the Telecom Unblocking protocol where the Unblockingprocedure is awaiting to be activated by the Scheduler

UNBLOCKING State of the Telecom Unblocking protocol where the Unblockingprocedure is running

TO BE BLOCKED State of the Telecom Blocking protocol where the Blocking procedure isawaiting to be activated by the Scheduler (there is no active call on theA Channel)

BLOCKING State of the Telecom Blocking protocol where the Blocking procedure isrunning (there is no active call on the A Channel)

BLOCKED State of the Telecom Blocking protocol where the A Channel has beensuccessfully Blocked (there is no active call on the A Channel).

TEL_UNEQUIPPED State of an A channel which is equipped in the BSS but the MSC hasinitiated an Unequipped circuit procedure

TO BE RESET State of the Telecom Reset Circuit protocol where the protocol is about torun awaiting the signal from the Scheduler informing it that the SCCP isavailable.

RESETTING State of the Telecom Reset Circuit protocol indicating that the protocol isrunning.

IDLE WITH AISNote A

State of a Free A Channel when an External 2 Mbit/s alarm is active onthe A Trunk.

BUSY WITH AISNote A

State of a Busy A Channel when an External 2 Mbit/s alarm is active onthe A Trunk.

IDLE WITH AISBLOCKED

Note A

State of a Free A Channel when an External 2 Mbit/s PCM alarm is activeon the A Trunk and the BSC has refused and Blocked (by sending 1BLOCK message) a request by the MSC to use the A Channel.

TO BE BLOCKED WITHAIS

Note A

A Reset procedure has been triggered requiring the A Channel to beblocked whilst the External 2 Mbit/s PCM alarm is active. The Blockingprocedure is awaiting scheduling.

BLOCKING WITH AISNote A

A Reset procedure has been triggered and the Blocking procedure hassent at least one BLOCK message to the MSC and the External 2 Mbit/sPCM alarm is still active.

BLOCKED WITH AISNote A

The MSC has responded with the BLOCKING ACKNOWLEDGE and theExternal 2 Mbit/s PCM alarm is still active.

TO BE UNBLOCKEDAFTER AIS

Note A

The External 2 Mbit/s PCM alarm has been removed and the A Channel isawaiting to be Unblocked.

UNBLOCKING AFTERAIS

Note A

The External 2 Mbit/s PCM alarm has been removed and at least oneUNBLOCK message has been sent to the MSC for the Unblockingprocedure.

Table 8 Telecom protocol statesNote A: All these states only exist when the IGNORE_2MBIT_FAIL is set to TRUE.The following predicates are used in the State table description of the behaviour for A Channel used forTCH.


EVOLIUM0299_02

27/05/2002 3BK 11202 0299 DSZZA 58/81

PREDICATE DESCRIPTIONP1 Num_RES == "NBR_RESET_CIC_REP"P2 NOT P1P3 T1_count == MAX_REP_T1P4 NOT P3P5 T20_count == MAX_REP_T20P6 NOT P5P7 REL_TYP == NORMP8 REL_TYP == ABNORMP9 RES_TYPE == EXT_INTP10 RES_TYPE == INT_NO_RESP11 Unblk_Reqd == TRUEP12 Unblk_Reqd == FALSEP13 Unequ_Reqd == TRUEP14 Unequ_Reqd == FALSE

Table 9 Predicate list

3.8.10.3.2 Single Block / Unblock algorithmsThe following State transition diagram shows the behaviour of the algorithm (for TCH configuredchannels) when subjected to the events given by the Scheduler and Telecom. To simplify the diagram,it is not exhaustive, the states TO BE CAMPED ON BLOCK, CAMPED ON BLOCKING and CAMPEDON BLOCKED are not shown. For more detail on the behaviour resulting from all possible events, seethe State transition tables.For the handling of the event AIS_PRES and NO_AIS see next state transition diagram.

Second T1 expiry

BLOCKING ACK/Stop T1

TEL_RES(EXT_INT)/Stop T1

IS/Stop T1

IS[Unblk Reqd = TRUE]

IS[Unblk Reqd =FALSE]

First T1 expiry/Restart T1

BLOCKING

Entry/send BLOCKTS

TO BE BLOCKED

UNBLOCK ACK/Send BLOCK

TS/Send BLOCK

UNBLOCKING

Entry/send UNBLOCK

TO BE UNBLOCKED

TS

IDLE

BUSY

RESETING

TO BE RESET

RESET CIC

UNBLOCK ACK

SCHED/Start T1

RESET CIC/Send BLOCK

TS

OOS (WTC)

RESET CIC/Send RESET CIC ACK

TR(NORM)

TR(ABNORM)

TEL_RES


BLOCKED

UNBLOCK ACK/Send BLOCK

TS/Send BLOCK

RESET CIC/Send BLOCK

TEL_RES(EXT_INT)

IS

SCHED/Start T1

First T1 expiry/Restart T1

Second T1 expiry

OOS (WTC)

RESET CIC/Send RESET CIC ACK;/Unblk Reqd = FALSE

TEL_RES(EXT_INT)/Unblk Reqd = FALSE

SCHED/Send RESET CIC;/Start T19

RESET CIC ACK/Stop T19

T19 expiry[< NumRES]/Send RESET CIC;/Restart T19

T19 expiry[= NumRES]



TEL_RES/Stop T19

TEL_RES(RES_TYP)/Stop T19

OOS (WTC)

OOS(WTC))/Stop T19

BLOCK ACK/Send UNBLOCK

BLOCK ACK/Send UNBLOCK

UNBLOCK ACK

TEL_RES

Note 3

Note 3

Note 3

TS/Stop T1

Note 1

Note 2

OOS(WTC)[Unblk Reqd =TRUE]

Figure 62 State transition diagram Scheduler and Telecom events1 Before the IDLE state is entered the flag Unblk_Reqd. shall be checked. If this flag is set TRUE

then the next state shall be TO BE UNBLOCKED. If this flag is set FALSE then the next stateshall be IDLE.

2 If the event “reception of IS” during the BLOCKING (or CAMPED ON BLOCKING state) occurs;and then “reception of OOS(WTC)” in the TO BE UNBLOCKED state. This means that the BSS isin the BLOCKED state whilst the MSC may not have responded or received the initial Blockmessage, that is to say the MSC believes the CIC is usable although Blocked in the BSS. This is


EVOLIUM0299_02

27/05/2002 3BK 11202 0299 DSZZA 59/81

not a grave problem as the A Channel will be Blocked if the MSC attempts to seize the AChannel.

3 These states also represent the states: TO BE CAMPED ON BLOCKED; CAMPED ONBLOCKING; & CAMPED ON BLOCKED. The only difference being the fact that A Channel is inuse on a Call.

This state transition diagram shows the required behaviour of Reset Circuit, Blocking and Unblockingwhen IGNORE_2MBIT_FAIL is set to TRUE for the events AIS_PRES and NO_AIS.

IDLENote 1

IDLE WITHAIS

BUSY WITHAIS

IDLE WITHAIS

BLOCKED

TO BEBLOCKEDWITH AIS

BLOCKINGWITH AIS

BLOCKEDWITH AIS

UNBLOCKINGAFTER AIS

TO BEUNBLOCKEDAFTER AIS

BUSYNote 1

AIS PRES

NO AIS

NO AIS

AIS PRES

TSNote 2

TEL RES(EI)

TRor TEL RESor RES CIR

BLOCK ACK

NO AIS

NO AIS

NO AIS

NO AIS

AIS PRESAIS PRES

UNBLOCK ACKor RES CIR

RES CIR

TEL RES

OOS(TO BE BLOCKED)

OOS(TO BECAMPED ONBLOCKED)

OOS(TO BEBLOCKED)

OOS(BLOCKED)

OOS(BLOCKED)

OOS(TO BEBLOCKED)

OOS(BLOCKING)

OOS(TO BEBLOCKED)

SCHED

SCHED

Figure 63 State transition diagram when IGNORE_2MBIT_FAIL is set to TRUE for the eventsAIS_PRES and NO_AIS

Notes :1 These states are included in this State transition diagram to show the relationship between this

State transition diagram and the previous one.2 A single BLOCK message is sent at this point.Note: The reception of an ASSIGNMENT REQUEST or HANDOVER REQUEST during this state

means that the MSC has not seen the AIS signal or it selected the A Channel before the AIS waspresent. The BSC sends a single BLOCK message to the MSC to stop the selection of the


EVOLIUM0299_02

27/05/2002 3BK 11202 0299 DSZZA 60/81

A Channels. In the case where there the MSC does not see the AIS signal, the MSC will graduallyrequest the use of the resources until all the resources have been requested and aresubsequently Blocked by the BSC.

The following State transition diagram shows the behaviour of the algorithm (for TCH configuredchannels) when subjected to the event TEL_RES (RES_TYPE), where RES TYPE is either EXT_INT(EI) or INT_NO_RES (INR) the "Camping" states are shown for completeness.

TO BEBLOCKED

RESETTINGTO BERESET

BUSY

TO BEUNBLOCKED

UNBLOCKING

IDLE

TEL RES(EI & INR)TEL RES

(EI & INR)TEL RES(EI & INR)

TEL RES(EI & INR)

TEL RES(EI

TEL RES(EI)

TEL RES(EI)

TEL RES(EI)

TEL RES(INR)

TEL RES(INR)


TEL RES(INR)

UNBLOCKINGAFTER AIS

TEL RES(INR)

IDLE WITHAIS

BUSY WITHAIS

TEL RES(EI & INR)

TEL RES(EI & INR)

BLOCKING

TEL RES(INR)Note 1

CAMPEDON BLOCKED

TEL RES(INR)Note 1

BLOCKINGWITH AIS

TEL RES(INR)Note 1

BLOCKED

TEL RES(INR)Note 1

CAMPEDON

BLOCKING

TEL RES(INR)Note 1

IDLE WITHAIS

BLOCKED

TEL RES(INR)Note 1

TO BECAMPED

ON BLOCKEDTEL RES(INR)Note 1

TO BEBLOCKEDWITH AIS TEL RES

(EI & INR)

BLOCKEDWITH AIS

TEL RES(INR)Note 1

TEL RES(EI) TEL RES

(EI)

TEL RES(EI)

TEL RES(EI

TEL RES(EI)TEL RES

(EI)

TEL RES(EI)

TEL RES(EI)

TEL RES(EI & INR)

Figure 64 State transition diagram when subjected to the event TEL_RES (RES_TYPE), whereRES TYPE is either EXT_INT (EI) or INT_NO_RES (INR)

Note 1: The procedures are suspended during the Internal Reset procedure and are then restartedonce the Internal Reset procedure has finished.

The following State transition diagram shows the behaviour of the algorithm (for TCH configuredchannels) when subjected to the event RES_CIR the "Camping" states are shown for completeness.


EVOLIUM0299_02

27/05/2002 3BK 11202 0299 DSZZA 61/81

BLOCKEDBLOCKINGTO BE

BLOCKED

CAMPEDON

BLOCKING

TO BECAMPED

ON BLOCKED

CAMPEDON BLOCKED

RES CIRSend BLOCK

RES CIRSend BLOCK

RES CIR

Send BLOCK

RES CIR

Send BLOCK

RES CIR

Send BLOCKRES CIR

Send BLOCK

RESETTING

RES CIRSend RES CIR ACK

TO BERESET


IDLE

BUSY

TO BEUNBLOCKED

UNBLOCKING





UNBLOCKINGAFTER AIS


IDLE WITHAIS

BUSY WITHAIS

RES CIR

Send RES CIR ACK


IDLE WITHAIS

BLOCKED

RES CIRSend BLOCK

TO BEBLOCKEDWITH AIS

RES CIRSend BLOCK

BLOCKINGWITH AIS

RES CIRSend BLOCK

BLOCKED

WITH AIS

RES CIRSend BLOCK


Figure 65 State transition diagram when subjected to the event RES_CIR


EVOLIUM0299_02

27/05/2002 3BK 11202 0299 DSZZA 62/81

The following State transition diagram shows the behaviour of the algorithm for A Channels configuredas Semi-permanent Circuits.Note: Initial state for this Algorithm is Blocked.

TO BEBLOCKED

TSSend 1 BLOCK msg

BLOCKEDTEL_RES

SCHED

BLOCKING

First T1 expiryNote 1

BLOCK ACKTEL_RES

TSSend 1 BLOCK msg

TSSend 1 BLOCK msg

Second T1 expiryNote 1

Figure 66 State transition diagram for A Channels configured as Semi-permanent CircuitsNote 1: The BLOCK message is sent again on T1 expiry. On second T1 expiry, the state is set to

BLOCKED.There are no State transition tables for this algorithm.The following State transition tables describe in detail the behaviour of the Single Blocking &Unblocking Algorithm for A Channels configured as TCH.

EVENT IDLE BUSY TEL_UNEQUIPPEDTS next state : (BUSY) Note 3 next state : (BUSY)

TR (REL_TYP) Not applicable P7 : next state :(IDLE)P8: next state :(TO BE RESET)

Don't care

OOS(WTC) next state :(TO BE BLOCKED)

start T_WTCnext state :(TO BE CAMPED ONBLOCKED)

Don't care

IS Don't care Not applicable Don't careTEL_RES

(RES_TYPE)Don't care next state : (IDLE)

Note 4next state : (IDLE)

RESET CIR send RESET CIR ACK send RESET CIRCUITACKNOWLEDGEnext state : (IDLE)Note 5

send RESET CIRCUITACKNOWLEDGEnext state : (IDLE)

UNEQUIPPEDCIR

Don't careSend O&M error report

Don't care - Note 12Send O&M error report

Don't careSend O&M error report

BLOCK ACK send UNBLOCK

State Table 1 IDLE, BUSY and TEL_UNEQUIPPED states


EVOLIUM0299_02

27/05/2002 3BK 11202 0299 DSZZA 63/81

EVENT TO BE CAMPED ONBLOCKED

CAMPED ON BLOCKING CAMPED ONBLOCKED

SCHED send BLOCKstart T1T1_count = 1next state : (CAMPED

ON BLOCKING)

Not applicable

TS Send 1 BLOCK message - Note 2TR (REL_TYP) P14: next state :

(TO BE BLOCKED)P13: next state :(TEL_UNEQUIPPED)

P14: next state :(BLOCKING)P13: next state :(TEL_UNEQUIPPED)

P14: next state :(BLOCKED)P13: next state :(TEL_UNEQUIPPED)

TEL_RES(RES_TYPE)

P9: next state :(TO BE BLOCKED)P10: Note 7

P9: stop T1next state :(TO BE BLOCKED)P10: Note 7

P9: stop T1next state :(TO BE BLOCKED)P10: next state :(BLOCKED)

T1 Not applicable P3: next state :(CAMPED ON BLOCKED)Send Channel_Block_FailalarmP4: send BLOCKstart T1increment T1_count

Not applicable

BLOCK ACK Don't care stop T1next state :(CAMPED ON BLOCKED)

Don't care

OOS (WTC) Not applicable - Note 9IS Not applicable - Note 8 & 9

RESET CIR Send 1 BLOCK msgNote 5next state :(TO BE BLOCKED)

Send 1 BLOCK msgNote 5next state :(BLOCKING)

Send 1 BLOCK msgNote 5next state :(BLOCKED)

T_WTC Note 10 - The state machine awaits the TR event before changing stateUNEQUIPPED

CIRUnequ_Reqd = TRUESend O&M error report

stop T1Unequ_Reqd = TRUESend O&M error reportnext state : (CAMPED ONBLOCKED) - see Note 12

Unequ_Reqd = TRUESend O&M error report

UNBLOCK ACK Send 1 BLOCK message

State Table 2 TO BE CAMPED ON BLOCKED, CAMPED ON BLOCKING and CAMPED ONBLOCKED states


EVOLIUM0299_02

27/05/2002 3BK 11202 0299 DSZZA 64/81

EVENT TO BE BLOCKED BLOCKING BLOCKEDSCHED send BLOCK

start T1T1_count = 1next state :(BLOCKING)

Not applicable

TS Send 1 BLOCK message - Note 1TR (REL_TYP) Not Applicable Don't care

TEL_RES(RES_TYPE)

P9: Don't careP10: Note 7

P9: stop T1next state :(TO BE BLOCKED)P10: Note 7

P9: next state :(TO BE BLOCKED)P10: Don't care

T1 Not applicable P3: next state :(BLOCKED), SendChannel_Block_Fail alarm

P4: send BLOCKstart T1increment T1_count

Not applicable

BLOCK ACK Don't care stop T1next state : (BLOCKED)

Don't care

OOS(WTC) Not applicableIS P11: next state :

(TO BE UNBLOCKED)P12: next state :(IDLE)

stop T1next state :(TO BE UNBLOCKED)

next state :(TO BE UNBLOCKED)

RESET CIR Send 1 BLOCK messageUNEQUIPPED

CIR Send O&M error reportnext state :(TEL_UNEQUIPPED)

stop T1Send O&M error reportnext state :(TEL_UNEQUIPPED)

Send O&M error reportnext state :(TEL_UNEQUIPPED)

UNBLOCK ACK Send 1 BLOCK message

State Table 3 TO BE BLOCKED, BLOCKING and BLOCKED states


EVOLIUM0299_02

27/05/2002 3BK 11202 0299 DSZZA 65/81

EVENT TO BE UNBLOCKED UNBLOCKINGSCHED send UNBLOCK

start T1T1_count = 1next state : (UNBLOCKING)

Not applicable

TS next state : (BUSY)Note 1

stop T1next state : (BUSY)Note 1

TR (REL_TYP) Not applicableTEL_RES

(RES_TYPE)P9: Unblk_Reqd = FALSEnext state : (IDLE)P10: Note 7

P9: Stop T1Unblk_Reqd = FALSEnext state : (IDLE)P10: Note 7

T1 Not applicable P3: Unblk_Reqd = FALSEnext state : (IDLE). SendChannel_Unblock_Fail alarm.P4: send UNBLOCKstart T1increment T1_count

UNBLOCK ACK Don't care stop T1Unblk_Reqd = FALSEnext state : (IDLE)

OOS(WTC) next state : (BLOCKED) Unblk_Reqd = TRUEnext state : (TO BE BLOCKED)

IS Don't careRESET CIR Send RESET CIRCUIT

ACKNOWLEDGEUnblk_Reqd = FALSEnext state : (IDLE)

RESET CIRCUITACKNOWLEDGE

stop T1Unblk_Reqd = FALSEnext state : (IDLE)

UNEQUIPPEDCIR

Send O&M alarmChannel_Unblock_Fail

next state :(TEL_UNEQUIPPED)

Stop T1Send O&M alarm

Channel_Unblock_Failnext state :

(TEL_UNEQUIPPED)BLOCK ACK Send 1 UNBLOCK message

State Table 4 TO BE UNBLOCKED and UNBLOCKING states


EVOLIUM0299_02

27/05/2002 3BK 11202 0299 DSZZA 66/81

EVENT TO BE RESET RESETTINGSCHED send RESET CIRCUIT

start T19Num_RES = 1next state : (RESETTING)

Not applicable

TS Note 11TR (REL_TYP) Not applicableRESET ACK Not applicable stop T19

next state : (IDLE)T19 Not applicable P1: next state : (IDLE)

P2: send RESET CIRCUITstart T19increment Num_RES

TEL_RES(RES_TYPE)

P9: next state : (IDLE)P10: next state : (IDLE)

P9: stop T19next state : (IDLE)P10: stop T19next state : (IDLE)

RESET CIR send RESET CIRCUIT ACKNOWLEDGEOOS(WTC) next state : (TO BE BLOCKED) stop T19

next state : (TO BE BLOCKED)UNEQUIPPED

CIRSend O&M error reportnext state :(TEL_UNEQUIPPED)

stop T19Send O&M error reportnext state :

(TEL_UNEQUIPPED)

State Table 5 TO BE RESET and RESETTING statesNotes :1 Telecom has attempted to seize a channel which is Blocked (or in the case of Unblocking is in the

process of Unblocking). This occurs for TCH Assignment and External handover procedures. Therequests shall be refused with message ASSIGNMENT FAILURE or HANDOVER FAILUREcause "Requested terrestrial resource unavailable". During Blocking a single BLOCK message issent. During Unblocking a single UNBLOCK message is sent. In either the Blocking or theUnblocking case no timer is started or stopped.

2 Telecom has attempted to seize a channel which is in use. This occurs for TCH Assignment andExternal handover procedures. The requests shall be refused with message ASSIGNMENTFAILURE or HANDOVER FAILURE cause "Requested terrestrial resource already allocated".

3 Telecom has attempted to seize a channel which is in use i.e. BUSY. This occurs for TCHAssignment and External handover procedures. The requests shall be refused with messageASSIGNMENT FAILURE or HANDOVER FAILURE cause "Requested terrestrial resource alreadyallocated".

4 The Call is released see ref [5] event N0900. For call release during Channel change proceduressee ref [6, 3, & 9].


6 The Call is released see ref [5] however due to the fact that there is a WTC condition a Blockingprocedure will be run, the connection in the MSC may remain "Camped on block" and will have towait for another event before the A Channel is released.

7 When the RESET message is not sent to the MSC by the BSC during the Internal Resetprocedure the BSS suspends all Blocking and Unblocking protocols and resumes the proceduresafter the Internal Reset procedure has been performed.


EVOLIUM0299_02

27/05/2002 3BK 11202 0299 DSZZA 67/81

8 O&M shall never issue another In Service event before the Telecom Release event (TR) hasbeen completed. As a result any In Service event (IS) which is detected by O&M shall be deferreduntil the Telecom Release has occurred, only then shall the In Service event (IS) be processed.

9 It is the responsibility of the O&M entity to keep track of the In Service (IS) and Out Of Service(OOS) events for each A Channel. From the point in time from the initial issuing of the first OOSevent till the Telecom Release (TR), O&M shall keep track of the availability of the A Channel,after Telecom has performed the release shall O&M initiate the next O&M action.

10 A call release is performed at this point, see ref [5] event N0300.11 The MSC has attempted to seize an A Channel which is in the process of Resetting. The

A Channel shall only be available when it is in the IDLE state. The request shall be refused (i.e.ASSIGNMENT FAILURE or HANDOVER FAILURE cause "Requested terrestrial resourceunavailable".

12 No call releases are performed for the concerned connections. The method by which the call willbe released will depend on either the WTC timer expiry or the SCCP inactivity timer expiry ornormal call release which ever occurs first.

The following state transition tables show the behaviour of the Reset Circuit, Blocking and Unblockingprocedures when IGNORE_2MBIT_FAIL is set to TRUE.

EVENT IDLENote 1

BUSYNote 1

IDLEWITH AIS

BUSYWITH AIS

TS Note 2 Send BLOCKnext state :(IDLE WITH AIS

BLOCKED)

Note 3

TR (REL_TYP) Note 2 NA P9: next state :(IDLE WITH AIS)P10: next state :(TO BE RESET)Note 4

OOS Note 2 next state :(TO BE BLOCKED)

next state :(TO BE CAMPED

ON BLOCK)IS Note 2 NA

AIS_PRES next state :(IDLE WITH AIS)

next state :(BUSY WITH AIS)

NA

NO_AIS NA next state :(IDLE)

next state :(BUSY)

TEL_RES(RES_TYPE)

Note 2 Don't care next state :(IDLE WITH AIS)

RESET CIR Note 2 Don't care next state :(IDLE WITH AIS)

UNEQUIPPEDCIR

Send O&M error reportNext state: TEL_UNEQUIPPED

BLOCKINGACKNOWLEDGE

Send 1 UNBLOCK message Send 1 UNBLOCKmessage - Note 5

State Table 6 IGNORE_2MBIT_FAIL is set to TRUE - IDLE, BUSY, IDLE WITH AIS and BUSYWITH AIS states

Notes :1 These states are included in this state table as well as in State Table 1.2 For behaviour see State Table 1.


EVOLIUM0299_02

27/05/2002 3BK 11202 0299 DSZZA 68/81

3 Send ASSIGNMENT FAILURE or HANDOVER FAILURE cause "Terrestrial resource alreadyallocated".

4 This document does not identify the states TO BE RESET WITH AIS or RESETTING WITH AISas after the Reset Circuit procedure is performed the next state will depend on whether AIS isactive for the Trunk associated with the AIS. i.e. next state is either IDLE or IDLE WITH AIS, ifduring the Reset Circuit procedure the A Channel is placed OOS then the states TO BEBLOCKED WITH AIS or TO BE BLOCKED shall be entered depending on the AIS state of theA Trunk.

5 Whilst in the BUSY WITH AIS state the reception of a BLOCKING ACKNOWLEDGE may meanthat the MSC believes that the circuit is Blocked in the MSC, in fact there is an ongoing call on theassociated circuit and the circuit shall be usable after the AIS disappears, in this case a singleUNBLOCK message is sent to the MSC.EVENT IDLE WITH AIS

BLOCKEDTO BE BLOCKED

WITH AISBLOCKING WITH

AISBLOCKED WITH

AISSCHED Not applicable Send BLOCK

Start T1Num_BLK = 1

Not applicable

TS Send BLOCKTR (REL_TYP) Not applicable

TEL_RES(RES_TYPE)

P11: next state TOBE BLOCKEDWITH AIS)P12: Don't care

P11: Don't careP12: Note 1

P11: stop T1next state (TO BEBLOCKED WITHAIS)P12: Note 1

P11: next state (TOBE BLOCKEDWITH AIS)P12: Don't care

T1 Not applicable P6: next state(BLOCKED WITHAIS)P5 and P4: Send

BLOCKStart T1increment T1_countinc Num_BLK

Not applicable

BLOCKINGACKNOWLEDGE

Don't care stop T1next state(BLOCKED WITHAIS)

Don't care

OOS (WTC) next state(BLOCKED)

next state(TO BEBLOCKED)

next state(BLOCKING)

next state(BLOCKED)

IS Not applicableAIS_PRES Not applicable

NO_AIS next state (TO BE UNBLOCKED AFTER AIS)RESET CIR Send BLOCK

UNEQUIPPEDCIR

Send O&M error reportNext state: TEL_UNEQUIPPED

UNBLOCKINGACKNOWLEDGE

Send BLOCK

State Table 7 IGNORE_2MBIT_FAIL is set to TRUE - IDLE WITH AIS BLOCKED, TO BEBLOCKED WITH AIS, BLOCKING WITH AIS and BLOCKED WITH AIS states


EVOLIUM0299_02

27/05/2002 3BK 11202 0299 DSZZA 69/81

Note 1: When the RESET message is not sent to the MSC by the BSC during the Internal Resetprocedure the BSS suspends all Blocking and Unblocking procedures and restarts theprocedures after the Internal Reset procedure has been performed.

EVENT TO BE UNBLOCKED AFTER AIS UNBLOCKING AFTER AISSCHED start T1

send UNBLOCKT1_count = 1Num_UNBLK = 1

Not applicable

TS Note 1TR (REL_TYP) Not applicable

TEL_RES (RES_TYP) P11: next state (IDLE)P12: Note 2

P11: Stop T1next state : (IDLE)P12: Note 2

T1 Not applicable P5 and P4: send UNBLOCKstart T1increment T1_countincrement Num_UNBLKP8: next state : (BLOCKED)


Don't care stop T1next state : (IDLE)

OOS(WTC) next state : (BLOCKED) next state : (TO BE BLOCKED)IS Don't care

RESET CIR Send RESET CIRCUITACKNOWLEDGE

next state : (IDLE)

Send RESET CIRCUITACKNOWLEDGE

stop T1next state : (IDLE)

UNEQUIPPED CIR Send O&M alarm Channel_Unblock_FailNext state: TEL_UNEQUIPPED

BLOCKINGACKNOWLEDGE

Send 1 UNBLOCK message

State Table 8 IGNORE_2MBIT_FAIL is set to TRUE - TO BE UNBLOCKED AFTER AIS andUNBLOCKING AFTER AIS states

Note 1: The request shall be refused with cause "Requested Terrestrial resource unavailable".Note 2: When the RESET message is not sent to the MSC the Unblocking procedure continues.

3.8.10.3.3 Group Block/Unblock algorithmsThe following State transition tables describe in detail the behaviour of the Group Blocking &Unblocking Algorithm for A Channels configured as TCH. The circuits are managed on a per trunkbasis.In the following tables, except when specified, the actions apply to all circuits in the samegiven state for a Trunk.

EVENT IDLE BUSY TEL_UNEQUIPPEDTS For the affected CIC:

next state : (BUSY)Note 3 For the affected CIC:

next state : (BUSY)TR (REL_TYP) Not applicable P7 : next state :

(IDLE)P8: next state :(TO BE RESET)

For the affected CIC:next state : (IDLE)


EVOLIUM0299_02

27/05/2002 3BK 11202 0299 DSZZA 70/81

OOS(WTC) For the affected CIC:next state :(TO BE BLOCKED)

For the affected CIC :start T_WTCnext state :(TO BE CAMPED ONBLOCKED)

Don't care

T_OOS(WTC) next state :(TO BE BLOCKED)

start T_WTCnext state :(TO BE CAMPED ONBLOCKED)

Don't care

IS Don't care Not applicable Don't careT_IS Don't care Not applicable Don't care

TEL_RES(RES_TYPE)

Don't care next state : (IDLE)Note 4

next state : (IDLE)

RESET CIR For the affected CIC:send RESET CIRCUITACKNOWLEDGE

For the affected CIC:send RESET CIRCUITACKNOWLEDGEnext state : (IDLE)Note 5

For the affected CIC:send RESET CIRCUITACKNOWLEDGEnext state : (IDLE)

UNEQUIPPED CIR Send O&M error report Don't care - Note 13Send O&M error report

Send O&M error report

BLOCK ACK For the affected CICs: send CIRCUIT GROUP UNBLOCK

State Table 9 Group Block/Unblock algorithms - IDLE, BUSY and TEL_UNEQUIPPED states

EVENT TO BE CAMPED ONBLOCKED

CAMPED ON BLOCKING CAMPED ON BLOCKED

SCHED T20_count = 1next state : (CAMPED ONBLOCKING)start T20 if stopped

Not applicable Not applicable

TS For the affected CIC:Send 1 BLOCK messageNotes 2 & 6.

For the affected CIC:Send 1 BLOCK messageNotes 2 & 6.

For the affected CIC:Send 1 BLOCK messageNotes 2 & 6.

TR (REL_TYP) For the affected CIC:P14: next state :(TO BE BLOCKED)P13: next state :(TEL_UNEQUIPPED)

For the affected CIC:P14: next state :(BLOCKING)P13: next state :(TEL_UNEQUIPPED)

For the affected CIC:P14: next state :(BLOCKED)P13: next state :(TEL_UNEQUIPPED)

TEL_RES(RES_TYPE)

P9:next state :(TO BE BLOCKED)P10: Note 8


P9:next state :(TO BE BLOCKED)P10: next state :(BLOCKED)

T20 T20_count = 1next state : (CAMPED ONBLOCKING)

See State Table 13 below Don't care

CIRCUIT GROUPBLOCK ACK

Don't care next state :(CAMPED ON BLOCKED)Note 7.

Don't care

BLOCK ACK Don't care For the affected CIC :next state :(CAMPED ON BLOCKED)

Don't care

OOS (WTC) Not applicableNote 10

Not applicableNote 10


T_OOS (WTC) Not applicableNote 10



IS Not applicableNote 9 & 10

Not applicableNote 9 & 10


T_IS Not applicableNote 9 & 10




EVOLIUM0299_02

27/05/2002 3BK 11202 0299 DSZZA 71/81

RESET CIR For the affected CIC:Send 1 BLOCK messagenext state :(TO BE BLOCKED)Notes 5 & 6.

For the affected CIC:Send 1 BLOCK messagenext state :(BLOCKING)Notes 5 & 6.

For the affected CIC:Send 1 BLOCK messagenext state :(BLOCKED)Notes 5 & 6.

T_WTC Note 11The state machine awaitsthe TR event beforechanging state

Note 11The state machine awaits theTR event before changingstate

Note 11The state machine awaitsthe TR event beforechanging state

UNEQUIPPEDCIR

For the affected CIC :Unequ_Reqd = TRUESend O&M error report

For the affected CIC :Unequ_Reqd = TRUESend O&M error reportnext state :(CAMPED ON BLOCKED)see Note 13

For the affected CIC :Unequ_Reqd = TRUESend O&M error report


For the affected CICs:send CIRCUIT GROUPBLOCK



State Table 10 Group Block/Unblock algorithms - TO BE CAMPED ON BLOCKED, CAMPED ONBLOCKING and CAMPED ON BLOCKED states


EVOLIUM0299_02

27/05/2002 3BK 11202 0299 DSZZA 72/81

EVENT TO BE BLOCKED BLOCKING BLOCKEDSCHED T20_count = 1

next state :(BLOCKING)start T20 if stopped

Not applicable Not applicable

TS For the affected CIC:Send 1 BLOCK msgNotes 1 & 6.

For the affected CIC:Send 1 BLOCK msgNotes 1 & 6.

For the affected CIC:Send 1 BLOCK msgNotes 1 & 6.

TR (REL_TYP) Not Applicable Not Applicable Don't careTEL_RES

(RES_TYPE)P9: Don't careP10: Note 8


P9:next state :(TO BE BLOCKED)P10: Don't care

T20 T20_count = 1next state :(BLOCKING)

See State Table 13below

Don't care

CIRCUIT GROUPBLOCK ACK

Don't care next state : (BLOCKED)Note 7.

Don't care

BLOCK ACK Don't care For the affected CIC:next state : (BLOCKED)

Don't care

OOS(WTC) Not applicable Not applicable Not applicableT_OOS(WTC) Not applicable Not applicable Not applicable

IS For the affected CIC:P11: next state :(TO BE UNBLOCKED)P12: next state : (IDLE)

For the affected CIC:next state :(TO BE UNBLOCKED)

For the affected CIC:next state :(TO BE UNBLOCKED)

T_IS P11: next state :(TO BE UNBLOCKED)P12: next state : (IDLE)



RESET CIR For the affected CIC:Send 1 BLOCK msgNote 6.

For the affected CIC:Send 1 BLOCK msgNote 6.

For the affected CIC:Send 1 BLOCK msgNote 6.

UNEQUIPPEDCIR

next state :(TEL_UNEQUIPPED)Send O&M error report

stop T1Send O&M error reportnext state :(TEL_UNEQUIPPED)

next state :(TEL_UNEQUIPPED)Send O&M error report

UNBLOCK ACK For the affected CICs:send CIRCUIT GROUPBLOCK



State Table 11 Group Block/Unblock algorithms - TO BE BLOCKED, BLOCKING and BLOCKEDstates

EVENT TO BE UNBLOCKED UNBLOCKING


EVOLIUM0299_02

27/05/2002 3BK 11202 0299 DSZZA 73/81

SCHED T20_count = 1next state : (UNBLOCKING)start T20 if stopped

Not applicable

TS For the affected CIC :next state : (BUSY)Note 1

For the affected CIC:next state : (BUSY)Note 1

TR (REL_TYP) Not applicable Not applicableTEL_RES

(RES_TYPE)P9:Unblk_Reqd = FALSEnext state : (IDLE)P10: Note 8

P9:Unblk_Reqd = FALSEnext state : (IDLE)P10: Note 8

T20 T20_count = 1next state : (UNBLOCKING)

See State Table 13 below

CIRCUIT GROUPUNBLOCK ACK

Don't care Unblk_Reqd = FALSEnext state : (IDLE)Note 7

UNBLOCK ACK Don't care For the affected CIC :Unblk_Reqd = FALSEnext state : (IDLE)

OOS(WTC) For the affected CIC :next state : (BLOCKED)

For the affected CIC :Unblk_Reqd = TRUEnext state : (TO BEBLOCKED)

T_OOS(WTC) next state : (BLOCKED) Unblk_Reqd = TRUEnext state : (TO BEBLOCKED)

IS Don't care Don't careT_IS Don't care Don't care

RESET CIR For the affected CIC :Send RESET CIRCUITACKNOWLEDGEUnblk_Reqd = FALSEnext state : (IDLE)

For the affected CIC :Send RESET CIRCUITACKNOWLEDGEUnblk_Reqd = FALSEnext state : (IDLE)

UNEQUIPPEDCIR

For the affected CIC :Send O&M alarmChannel_Unblock_Failnext state :(TEL_UNEQUIPPED)

For the affected CIC :Send O&M alarmChannel_Unblock_Failnext state :(TEL_UNEQUIPPED)

BLOCK ACK For the affected CICs:send CIRCUIT GROUPUNBLOCK

For the affected CICs:send CIRCUIT GROUPUNBLOCK

State Table 12 Group Block/Unblock algorithms - TO BE UNBLOCKED and UNBLOCKINGstates

EVENT CAMPED ON BLOCKING BLOCKING UNBLOCKINGT20 send CIRCUIT GROUP BLOCK

(all CICs CAMPED ON BLOCKING, BLOCKING)send CIRCUIT GROUP

UNBLOCK(all CICs UNBLOCKING)

P5: next state :(CAMPED ON BLOCKED),send Channel_Block_FailalarmP6: increment T20_count

P5: next state :(BLOCKED), sendChannel_Block_Fail alarmP6: increment T20_count

P5: Unblk_Reqd = FALSEnext state : (IDLE), sendChannel_Unblock_Failalarm.P6: increment T20_count

start T20 start T20

State Table 13 Group Block/Unblock algorithms - CAMPED ON BLOCKING, BLOCKING andUNBLOCKING states


EVOLIUM0299_02

27/05/2002 3BK 11202 0299 DSZZA 74/81

EVENT TO BE RESET RESETTINGSCHED send RESET CIRCUIT

start T19Num_RES = 1next state : (RESETTING)

Not applicable

TS Note 12TR (REL_TYP) Not applicableRESET ACK Not applicable For the affected CIC :

stop T19next state : (IDLE)

T19 Not applicable For the affected CIC :P1: next state : (IDLE)P2: send RESET CIRCUITstart T19increment Num_RES

TEL_RES(RES_TYPE)

P9: next state : (IDLE)P10: next state : (IDLE)

P9: stop T19next state : (IDLE)P10: stop T19next state : (IDLE)

RESET CIR For the affected CIC :send RESET CIRCUITACKNOWLEDGE

For the affected CIC :send RESET CIRCUITACKNOWLEDGE

OOS(WTC) For the affected CIC :next state : (TO BE BLOCKED)

For the affected CIC :stop T19next state : (TO BE BLOCKED)

T_OOS(WTC) next state : (TO BE BLOCKED) stop T19next state : (TO BE BLOCKED)

UNEQUIPPEDCIR

For the affected CIC :Send O&M error reportnext state :(TEL_UNEQUIPPED)

For the affected CIC :stop T19Send O&M error reportnext state :(TEL_UNEQUIPPED)

State Table 14 Group Block/Unblock algorithms - TO BE RESET and RESETTING statesNotes :1 Telecom has attempted to seize a channel which is Blocked (or in the case of Unblocking is in the

process of Unblocking). This occurs for TCH Assignment and External handover procedures.During Blocking, the request is refused with message ASSIGNMENT FAILURE or HANDOVERFAILURE cause "Requested terrestrial resource unavailable", and a single BLOCK message issent, without stopping or starting any timer.During Unblocking, the request is accepted, and no UNBLOCK message is sent.

2 Telecom has attempted to seize a channel which is in use. This occurs for TCH Assignment andExternal handover procedures. The requests will be refused with message ASSIGNMENTFAILURE or HANDOVER FAILURE cause "Requested terrestrial resource already allocated".

3 Telecom has attempted to seize a channel which is in use i.e. BUSY. This occurs for TCHAssignment and External handover procedures. The requests will be refused with messageASSIGNMENT FAILURE or HANDOVER FAILURE cause "Requested terrestrial resource alreadyallocated".



6 The message is not guarded by timer T1.7 See sections on checking of the CIRCUIT GROUP BLOCKING/UNBLOCKING ACKNOWLEDGE

messages.8 When the RESET message is not sent to the MSC by the BSC during the Internal Reset

procedure the BSS suspends all Blocking and Unblocking protocols and resumes the proceduresafter the Internal Reset procedure has been performed.


EVOLIUM0299_02

27/05/2002 3BK 11202 0299 DSZZA 75/81

9 O&M will never issue another In Service event before the Telecom Release event (TR) has beencompleted. As a result any In Service event (IS) which is detected by O&M will be deferred untilthe Telecom Release has occurred, only then will the In Service event (IS) be processed.

10 It is the responsibility of the O&M entity to keep track of the In Service (IS) and Out Of Service(OOS) events for each A Channel. From the point in time from the initial issuing of the first OOSevent till the Telecom Release (TR), O&M will keep track of the availability of the A Channel, afterTelecom has performed the release will O&M initiate the next O&M action.

11 A call release is performed at this point, see ref [5] event N0300.12 The MSC has attempted to seize an A Channel which is in the process of Resetting. The A

Channel will only be available when it is in the IDLE state. The request will be refused (i.e.ASSIGNMENT FAILURE or HANDOVER FAILURE cause "Requested terrestrial resourceunavailable".

13 No call releases are performed for the concerned connections. The method by which the call willbe released will depend on either the WTC timer expiry or the SCCP inactivity timer expiry ornormal call release which ever occurs first.

4 INTERACTION BETWEEN PROCEDURES

4.1 INTERACTION WITH CALL RELEASEThe following table describes the appropriate Telecom actions that are needed when the various SBLsare disabled.For Call Release scenarios see [5].

SBL TELECOM ACTIONDTC (with SS7) On the expiry of the WTC period all transactions which have an

association with this DTC shall be released - the Normal call releasingprocedure shall be used on Air/A bis and A interfaces.

DTC (withoutSS7)

On expiry of WTC period all connections supported by this DTC shall bereleased - the Normal call releasing procedure shall be used on Air/A bisand A interfaces.

A TRUNK On expiry of WTC period all SCCP connections associated with theA Channels associated with the A Trunk shall be released.If the A Trunk supports an SS7 link no call release shall be initiated for theSignalling only connections associated with the SS7 supported by the DTC- the Change over procedures of SS7 allow these SCCP connection tocontinue.

TC 16 On expiry of WTC period all SCCP connections associated with an AChannel supported by this TC16 will be released.

A CHANNEL On expiry of the WTC period any SCCP connection associated with thisA Channel shall be released.

SS7 The disabling of an A Channel supporting SS7 signalling shall cause theMTP change over procedure to be initiated (if it has not already beendone).

Table 10 Telecom actions upon SBL disablementWhen O&M has ordered a Disable no abnormal releasing sequences shall lead to the initiation of theReset Circuit procedure [5], this means that it is possible that the A Channel will remain CAMPED ONBLOCKED in the MSC until such time as the SCCP inactivity timer expires in the MSC.

4.2 INTERACTION WITH ASSIGNMENT and EXTERNAL HANDOVERThe behaviour described in this section is valid for both A Channels available for selection by the MSCand A Channels reserved for SPCs. Note - only the BLOCKED, TO BE BLOCKED and BLOCKINGstates shall be supported in the Blocking algorithm for an SPC.


EVOLIUM0299_02

27/05/2002 3BK 11202 0299 DSZZA 76/81

If the A Channel algorithms are in the following states (TO BE BLOCKED, BLOCKING, BLOCKED, TOBE UNBLOCKED, UNBLOCKING, TO BE RESET and RESETTING) then the request shall be refused(ASSIGNMENT FAILURE or HANDOVER FAILURE) with the cause "Requested terrestrial resourceunavailable".If the A Channel algorithms are in the following states (TO BE CAMPED ON BLOCKED, CAMPED ONBLOCKING and CAMPED ON BLOCKED) then the request shall be refused (ASSIGNMENT FAILUREor HANDOVER FAILURE) with the cause "Requested terrestrial resource already allocated".A single UNEQUIPPED CIRCUIT message shall be sent to the MSC if a request is received with a CICwhich the BSS believes to be Unequipped (see section 3.8.7.3) whilst the BSS is operating in GSMPhase 2 mode and when enabled by the O&M parameter EN_UNEQUIPPED_CIRCUIT. Note inaddition the BSC shall send an error report to O&M.A single UNBLOCK message shall be sent to the MSC if a request is received for the resource in thestates TO BE UNBLOCKED, UNBLOCKING.A single BLOCK message shall be sent to the MSC if a request is received for the resources in thestates TO BE BLOCKED, BLOCKING, BLOCKED, TO BE CAMPED ON BLOCKED, CAMPED ONBLOCKING and CAMPED ON BLOCK.If the A Channel algorithms are in the following states (BUSY) then the request shall be refused withthe cause "Requested terrestrial resource already allocated".If the DTC has failed due to Processor outage or has been placed into a state (by O&M) where theTelecom entities are disabled from running (e.g. OPR), then the request shall be refused with thecause "Requested terrestrial resource unavailable". No Block procedure shall be initiated on this event,no UNEQUIPPED CIRCUIT Message shall be sent.

4.3 INTERACTION WITH RESET

4.3.1 RESET from MSCWhen the BSS receives a RESET message from the MSC all A Channels in the BLOCKED,BLOCKING, TO BE BLOCKED, TO BE CAMPED ON BLOCKED, CAMPED ON BLOCKING andCAMPED ON BLOCKED states shall have a Blocking procedure initiated.For those A Channels in the BLOCKING and CAMPED ON BLOCKING states, the Blocking procedureshall be stopped and restarted.All Unblocking procedures shall be stopped and the A Channel shall be made available.All Reset Circuit procedures shall be stopped and the A Channel shall be made available.

4.3.2 Internally detected Reset (RESET sent to the MSC)When the BSS detects the need to perform a Reset procedure [2] Blocking procedures shall beinitiated after the reception of the RESET ACKNOWLEDGE from the MSC or when the maximumnumber of transmissions of the RESET message is reached.Unblocking procedures shall be stopped and the A Channel shall be made available immediately theRESET is sent to the MSC.All Reset Circuit procedures shall be stopped immediately when Ti expires, the RESET shall be sent tothe MSC and the A Channel shall be made available.

4.3.3 Internally detected Reset (RESET is NOT Sent to the MSC)No Blocking procedures shall be initiated towards the MSC.Unblocking and Blocking procedures shall be suspended and shall be restarted when the Internal resetprocedure is finished.All Reset Circuit procedures shall be stopped and the A Channels shall be released.

4.4 INTERACTION WITH SS7

4.4.1 O&M disable of a 2 Mbit/s PCM or SS7 slotA DTC may or may not have an SS7 function configured. If an SS7 function is configured for a DTCthe SS7 shall attempt to use a slot configured for use in carrying SS7 signalling on the 2 Mbit/s link


EVOLIUM0299_02

27/05/2002 3BK 11202 0299 DSZZA 77/81

supported by the DTC. If a 2 Mbit/s alarm occurs for the 2 Mbit/s link the O&M entity shall inform theSS7 function which shall in turn force an MTP Change over procedure to route messages to the MSCusing another available slot configured for SS7 signalling on another DTC. These actions shall beperformed independently of the flag IGNORE_2MBIT_FAIL.

4.4.2 O&M enable of a 2 Mbit/s PCM or SS7 slotWhen O&M orders the enabling of a 2 Mbit/s PCM link or SS7 slot the SS7 Link Test procedure shallbe initiated. Once this procedure has been acknowledged the link shall be placed In Traffic and theSS7 may start to use the slot for the transfer of messages.The Link Test procedure shall be run only during the enabling procedure as initiated by O&M. The LinkTest procedure shall not be run periodically.If the Link Test procedure fails (for example due to Loop-back) the slot will not be available until theLink Test procedure is successful.

4.4.3 Loop-back of 2 Mbit/s PCMThe 2 Mbit/s links between the BSC and the Transcoder may be transported by transmission linkswhich are the responsibility of the operators in the country in which the BSS is operating. As part oftheir maintenance procedures the operators perform Loop-back tests on this equipment. The effect ofthese tests on our System is outlined in the next two sections and is dependent upon the amount andtype of disturbance produced by the Loop-back action.

4.4.3.1 Application of Loop-back test PCM Alarm detectedIf the application of the Loop-back test causes a break in the PCM link long enough for the O&M entityin the BSC to detect the presence of a PCM alarm then the O&M entity shall initiate the disabling of theSS7 slot.Note: Disabling of the 2 Mbit/s PCM link and the associated A Channels are dependent on the settingof the IGNORE_2MBIT_FAIL.In this case the MTP change over procedure will be forced to redirect the SS7 messages onto anotherSS7 Slot which is In Traffic.If the progress of the Loop-back tests then removes the PCM alarm, O&M shall initiate the O&Menabling of the SS7 slot.Note: The enabling of the 2 Mbit/s PCM link and the associated A Channels are dependent on thesetting of the IGNORE_2MBIT_FAIL. In this case the SS7 Link Test procedure will be initiated and willfail. This situation will continue as long as the Loop-back is applied. Once the Loop-back is removedthe Link Test will be successful and the SS7 Slot will come back In Traffic and the MTP change backprocedure will occur.Whilst Loop-back is applied the BTS will be detecting the fact that the Transcoder is no longerconnected for TCH transactions and will be initiating the release of these transactions by sendingCONNECTION FAILURE INDICATION (cause "Remote transcoder alarms") to the BSC. The BSCmay, depending upon the procedure that is running at the time, release the connections.During this scenario the signalling for transactions are maintained.

4.4.3.2 Application of Loop-back test PCM Alarm not detectedIf a PCM alarm is not detected during the application or the removal of the Loop-back test the O&Mentity in the BSC shall not disable the SS7 slot. The behaviour of the SS7 entity is such that the MTPwill detect errors at Layer 2 due to the fact that the messages are not being acknowledged. Since theLink test procedure is not run periodically the Loop-back will never be detected.The releasing of TCH connections in the BSS will be triggered by the BTS detecting the absence of theTranscoder.The releasing of signalling connections in the BSC may be initiated by the SCCP (when the SCCPinactivity timers expire) or due to Reset Circuit procedures initiated by the MSC (due to SCCP inactivitytimer expiry).

4.4.4 Global connectionless message transferMessages such as the RESET, RESET ACKNOWLEDGE, RESET CIRCUIT, RESET CIRCUITACKNOWLEDGE, BLOCK, CIRCUIT GROUP BLOCK, UNBLOCK, CIRCUIT GROUP UNBLOCK andUNEQUIPPED CIRCUIT messages when sent shall be transferred as global connectionlessmessages.


EVOLIUM0299_02

27/05/2002 3BK 11202 0299 DSZZA 78/81

When SS7 slots are placed into and out of service each DTC shall ensure that these global messagesare shared across the available SS7 slots. It shall do this by keeping a list of the in service slots(updated by O&M) and by sharing the messages which it sends across the available slots.

4.4.5 Connection orientated message transferConnection orientated messages are routed across the SS7 slot associated with the DTC on which theSS7 function is supported. In the case where the 2 Mbit/s PCM link becomes unavailable the MTPchange over procedure is forced which means that the connection orientated messages are passedover another slot configured for SS7 signalling.

5 TIMERS AND PARAMETERS

5.1 TIMER LISTThe following timers are defined:T1 The time waited by the BSC before sending the second Block or Unblock message.T13 The reset guard period before the BSC sends a RESET ACK to the MSC.T19 The hold off time before attempting another Reset Circuit procedure.T20 The time waited by the BSC before sending the second Group Block or Group Unblock

message.T_BURST

The time waited before a single DTC may start to send a new burst of Blocking orUnblocking procedures.

T_SYNC Used in both the BTS and the Transcoder for the detection of loss of synchronisationbetween the BTS and Transcoder [7 and 12].

T_WTC The timer which holds off the releasing of the call for O&M operator actions. On O&Mautomatic actions T_WTC is zero.

5.2 PARAMETER LISTThe following parameters are defined :B_NUM The maximum number of single Blocking or Unblocking procedures

which may be initiated by a single DTC within anyT_BURST period.

Range 1 <= B_NUM <= 31 - Note this parameter is not changeableon-line but may be done by data population

NBR_RESET_CIC_REP The maximum number of times the Reset circuit procedure may beperformed before the procedure is abandoned. IfNBR_RESET_CIC_REP is set to zero, no Reset circuit procedure willbe initiated by the BSC.

EN_CIRCUIT_GROUP This O&M parameter is used to enable the BSS to manage theCircuit group procedures instead of the single procedures.

EN_UNEQUIPPED_CIRCUIT This O&M parameter is used to enable the BSS to send theUNEQUIPPED CIRCUIT message. It is valid if, and only if, theGSM_PHASE parameter is set to PHASE_2. When set to TRUE theBSS shall send the UNEQUIPPED CIRCUIT message. In addition, ifEN_CIRCUIT_GROUP is TRUE, the OIE CIC code list shall beadded to the message.

GSM_PHASE This parameter indicates which mode that the BSS is operating onthe A interface towards the MSC, it is either set to PHASE_1 orPHASE_2.

IGNORE_2MBIT_FAIL Parameter indicating if the reception of a 2 Mbit/s failure (on the DTCA ter interface) should cause Blocking and Call Release proceduresto be initiated by O&M.

NBR_RESET_CIC_REP The maximum number of times the Reset Circuit procedure shall beperformed before the procedure is abandoned. IfNBR_RESET_CIC_REP is set to zero, no Reset Circuit procedureshall be initiated by the BSC.


EVOLIUM0299_02

27/05/2002 3BK 11202 0299 DSZZA 79/81

Nblk The maximum number of Blocking procedures performed (withoutacknowledgement from the MSC) before the procedure terminates.When Nblk is set to '255' the Blocking procedure is repeated forever.

Nublk The maximum number of Unblocking procedures performed (withoutacknowledgement from the MSC) before the procedure terminates.When Nublk is set to '255' the Unblocking procedure is repeatedforever.

5.3 TIMER and PARAMETER RULES FOR T_BURST, B_NUM and T1The following formula shall be used when considering the setting of the parameters T_burst, B_NUMand T1.

(31 * T_burst)/B_NUM < T1

6 RELEASE CHANGES

6.1 Release 21 The BSS handles only GSM Phase 1 operation on A interface and handles only Phase 1 MSs on

the Air interface.

6.2 Release 31 The BSS handles two modes of operation GSM Phase 1 and GSM Phase 2 Modes.2 The UNEQUIPPED CIRCUIT message is handled by a BSS operating in either GSM Phase 1 or

2 mode. It is only ever sent by the BSS when enabled by O&M Parameter during operation of theBSS in GSM Phase 2 mode on the A interface. In addition the sending of this message by theBSS may be disabled by O&M parameter (EN_UNEQUIPPED_CIRCUIT).

3 The BSS timer T19 (guarding the Reset Circuit procedure) has changed its name to T12.4 The BSS sends to the MSC whilst in the IDLE state an UNBLOCK message on reception of a

BLOCKING ACKNOWLEDGE message5 The BSS sends to the MSC whilst in the BLOCKED state a BLOCK message on reception of an

UNBLOCKING ACKNOWLEDGE message.6 The BSS sends an O&M error report in the case where the Unblock procedure terminates

unsuccessfully. This changes the state on the circuit at the OMC to External Faulty (EF).7 The BSS generated O&M error reports on reception of the UNEQUIPPED CIRCUIT message

from the MSC.8 The BSS generates O&M error reports on the detection of a circuit used by the MSC but

Unequipped in the BSS. This Error report is made independent of whether the BSS sends theUNEQUIPPED CIRCUIT.

6.3 Releases B4 and B5No functional changes.

6.4 Release B61 BSC transcoder pools impacts.2 The BSS handles Circuit group messages if enabled by an O&M parameter.3 T1_long timer is removed, T1_short renamed T1. The Block / Unblock and Group block / Group

unblock procedures are repeated only once.4 Assignment or Handover request received during the unblocking stops the procedure and the

circuit is reused for the request without waiting for the Unblock acknowledge.5 Unequipped circuit procedure initiated by the MSC is such that the BSC will trigger no Telecom

procedures for this circuit.


EVOLIUM0299_02

27/05/2002 3BK 11202 0299 DSZZA 80/81

6 If the Assignment procedure fails when the MS is deemed lost to the BSS, the circuit is madeavailable for reuse upon sending the assignment failure message.

6.5 Release B7.21 BSC transcoder pools removed.2 Correct handling of 2 Mbit/s alarms.3 Handling of Unequipped Circuit from MSC corrected.4 Elimination of block/unblock procedures during BSC restart.

7 FEATURES6.17 Circuit group messages6.YYReset circuit & blocking improvements6.7b A interface handling

8 GLOSSARY3GPP 3rd Generation Partnership ProjectA (interface) The GSM standardised interface between the BSS (transcoder) and the

MSC as defined in 15.A bis (interface) Proprietary interface between the BSC and the BTSA ter (interface) Proprietary trunk interface, internal to the BSC, between the DTCs and the

submultiplexer, or internal to the transcoder, between the submultiplexer and theTRAUs. It is structured as 32 x 64 kbit/s timeslots according to ITU-T recommendationG.704. Each timeslot can carry; framing, O&M, signalling or a single TCH at 16 kbit/s.In the first generation BSS products, these interfaces could be used externally, so theywere implemented as standard G.703/G.704 interfaces with the usual layer 1 alarmconditions.

A ter mux (interface) Proprietary trunk interface combining three or four A ter interfaces. FourTCH occupy a single 64 kbit/s timeslot.

AIS Alarm Indication SignalBER10-3 Excessive bit error ratio > 10-3

BSC Base Station ControllerBSS Base Station SystemBSSAP BSS Application Part (of SS7)BTS Base Transceiver StationCIC Circuit Identity Code. Also used to refer to the circuit which has such an identity codeDTC Digital Trunk Controller. One of the BSC processor typesEF External Faulty (state)GSM Global System for Mobile communicationsHSCSD High Speed Circuit Switched DataIS In Service (state)IT In Traffic (state)ITU-T Telecommunications standardisation sector of the International Telecommunications

UnionLFA Loss of Frame AlignmentLIS Loss of Incoming SignalLOS Loss Of SignalMS Mobile SubscriberMSC Mobile services Switching CentreMSD Maintenance Seized (state)MTP Message Transfer Part (of SS7)OOS Out Of Service (state). Out Of Service (state)OPR Out of service as ordered by the Operator (state)PCM Pulse Code ModulationQmux Proprietary transmission service bus. It is conveyed over the A ter mux interface using

a reserved timeslot.


EVOLIUM0299_02

27/05/2002 3BK 11202 0299 DSZZA 81/81

RAI Remote Alarm IndicationRF Radio FrequencySBL Security BlockSDCCH Slow Dedicated Control ChannelSM SubmultiplexerSPC Semi-permanent CircuitSS7 ITU-T Common Channel Signalling System No. 7TC TranscoderTCH Traffic ChannelTRAU Transcoder Rate Adaption UnitUE UnequippedX.25 ITU-T standard for the interface to Public Packet Switched Data Networks

END OF DOCUMENT

7. reset circuit, blocking & unequipped circuit 0299_02

Documents