gsm call flow with defination
DESCRIPTION
rtreyerhrtTRANSCRIPT
GSM/DCS BSS
Signalling Examples
Training Document
Document Number/Issue Copyright © Nokia Telecommunications Oy 1 (159)NTC CTXX 0677/1.0 en Training Document
Copyright © Nokia Telecommunications Oy 2023. All rights reserved.
No part of this publication may be copied, distributed, transmitted, transcribed, stored in a retrieval system, or translated into any human or computer language without the prior written permission of Nokia Telecommunications Oy.
The manufacturer has made every effort to ensure that the instructions contained in the documents are adequate and free of errors and omissions. The manufacturer will, if necessary, explain issues which may not be covered by the documents. The manufacturer's liability for any errors in the documents is limited to the correction of errors and the aforementioned advisory services.
The documents have been prepared to be used by professional and properly trained personnel, and the customer assumes full responsibility when using them. The manufacturer welcomes customer comments as part of the process of continual development and improvement of the documentation in the best way possible from the user's viewpoint. Please submit your comments to the nearest Nokia sales representative.
NOKIA and the arrows logo are registered trademarks of Nokia Corporation.
No. of pages
159/TT
Edited by/Translator
14-May-97Miia Sjögren
Author
14-May-97Pasi Mehtonen
Approved by
14-May-97Philippe Esterman
Previous issue(x) approved
TABLE OF CONTENTS
1. MOBILE ORIGINATED CALL.................................................................
2. MOBILE TERMINATED CALL................................................................
3. LOCATION UPDATE.................................................................................
4. INTERNAL HANDOVER, INTRA CELL.................................................
5. INTERNAL HANDOVER, INTER CELL..................................................
6. EXTERNAL HANDOVER..........................................................................
Mobile Originated Call
1. MOBILE ORIGINATED CALL
Mobile Originated Call
MSC BSC BTS MSVLR
Channel Required
Channel Activation
Channel Activation Ack.
Immediate Assigment Command.
Channel Request ( RACH )
Immediate Assigment ( AGCH ).
CM Service Request ( SDCCH)
Establish IndicationCR (CM Service Request)Process Access Request
AuthenticateCC Authentication Request
Authentication Request ( SDCCH )
Authentication Response ( SDCCH )DT1 Authentication Response
Authentication Response
Set Ciphering ModeDT1 Ciphering Mode Command
Encryption Command Ciphering Mode Command ( SDCCH )
Ciphering Mode Complete ( SDCCH )DT1 Ciphering Mode Complete
Access Request Accepted
Forward New TMSITMSI Reallocation Command
TMSI Reallocation Command ( SDCCH )
TMSI Reallocation Complete ( SDCCH )TMSI Reallocation Complete
TMSI Ack.Setup ( SDCCH )
DT1 SetupSend Info for O.G. Call
Complete CallDT1 Call Proceeding
Call Proceeding ( SDCCH )
DT1 Assignment RequestPhysical Context Request
Physical Context Confirmed
Channel Activation
Channel Activation Ack.
Assignment Command ( SDCCH )
SABM ( FACCH )Establish Indication
UA ( FACCH )
Assignment Complete ( FACCH )DT1 Assignment Complete
Channel Release
Channel Release Ack.DT1 Alerting
Alerting ( FACCH )DT1 Connect
Connect ( FACCH )
Connect Ack.( FACCH )DT1 Connect Ack.
Measurement Report ( SACCH )Measurement Report/Result
Disconnect ( FACCH )DT1 ( Disconnect )
DT1 ( Release )
DT1 ( Release Complete)
DT1 ( Clear Command )
Release ( FACCH )
Release Complete ( FACCH )
Channel Release ( FACCH )
Deactivate SACCHDISC ( FACCH )
UA ( FACCH )Release Indication
RF Channel Release
RF Channel Release Ack.DT1 ( Clear Complete )
RLSD ( SCCP Released )
RLC ( SCCP Released Ack.)
12
34
56
789
1011
12 1314
151617
18 1920 21
22232425 26
272829
303132
3334 35
363738
3940
4142
4344
454647
4849
5051
5253
5455
5657
5859
6061
6263
64 6566
6768
6970
717273
74
UA (SDCCH)
RADIOACCESSPART
ESTABLISHMENTPART
CIPHERING,AUTHENTICATIONAND CALL SETUPPART
TCH SEIZED
CONVERSATIONPART
RELEASE BY MS
CM Service Request
Ciphering Mode Command
Mobile Originated Call
1. CHANNEL_REQUEST
The MS requests a channel by sending a random access burst on a RACH channel via one BTS. Channel request -message contains the establishment cause. This can be 'Answer for paging', 'emergency call', 'other services (Mobile Originated Call, Short Message Service)' or 'Other', like location update. In addition to, this message contains Random Reference. This is 5 bits randomly selected by MS. The usage of random reference is: when two MSs are accessing to the network exactly the same time, the network can separate these Mobile Stations by using this random reference.
Mobile Originated Call
2. CHANNEL_REQUIRED
The BTS sends a channel required message to the BSC. By using this message, BTS delivers further on towards the BSC the channel request generated by MS. In practice Channel Required contains the same information as above but the BTS adds some information into it also. BTS numbers always the channels. In this case, the number of the Uplink CCCH (RACH -burst) is included. Request reference is directly coming from Channel request -message. Then, the first timing advance estimate called Access Delay is added into this message by the BTS.
Mobile Originated Call
3. CHANNEL_ACTIVATION
The BSC sends a Channel Activation message to the BTS. After receiving channel required from the BTS, the BSC starts to search and allocate SDCCH -channel for this call on certain terms, the most important is of course which BTS and then the channel configuration of this SDCCH. Parameters: DTX control, channel ID & description & mobile allocation, maximum power levels of the MS and BS and finally, the first timing advance concerning this access calculated by the BSC.
4. CHANNEL_ACTIVATION_ACK
Mobile Originated Call
A response to the channel activation message. When BTS has received this message it starts to send and receive SACCH -channel. The reference used in this case is the power levels received in Channel Activation message.
5. IMMEDIATE_ASSIGNMENT_COMMAND
The BSC tells the BTS about the SDCCH channel to be used.
Mobile Originated Call
6. IMMEDIATE_ASSIGNMENT
The BSS informs the MS on AGCH channel about the SDCCH channel to be used. In practice, this message is an order from the network to the MS to move to the SDCCH -channel defined before. Page mode, SDCCH channel description, associated SACCH and hopping frequency are included as parameters. In addition, request reference (same as establishment cause), initial timing advance and frequency allocation if frequency hopping applies are also included.
7. CM_SERVICE_REQUEST
Mobile Originated Call
The CM Service Request message is sent to the network by the MS to request a service for the connection management sublayer entities, like circuit switched connection establishment, supplementary services activation or short message transfer.
8. ESTABLISH_INDICATION
BTS acknowledges the Immediate Assignment Command by returning Establish Indication message. Establish indication -message has two uses. Firstly, when used in this phase it points out that from the BTS point of view, the MS is now on the SDCCH-channel. Thus, the BTS sends information back
Mobile Originated Call
to the BSC that the MS is now on this kind of SDCCH-channel which description is like this etc. Also the BTS identifies the link and adds received Layer 3 information into this message.
9. CM_SERVICE_REQUEST
The CM Service Request message is forwarded to the MSC.
10. UA
Mobile Originated Call
UA is normal Layer 2 level acknowledgement when setting up the Layer 2 level link in LAPDm -protocol.
11. PROCESS_ACCESS_REQUEST
MSC forwards MS's request for access management from VLR by Process Access Request message.
12. AUTHENTICATE
Mobile Originated Call
VLR initiates authentication request by sending an Authenticate message to MSC.
13. AUTHENTICATION_REQUEST
As a CC (Connection Confirmed) message, the MSC sends an Authentication Request message to the BSC. The message contains the RAND.
14. AUTHENTICATION_REQUEST
The BSC forwards the message via the BTS to the MS.
Mobile Originated Call
15. AUTHENTICATION_RESPONSE
The MS responds to the Authentication Request with the Signed Response SRES. The Authentication Response is sent to the BSC via the BTS.
In the MS Authentication procedure, two algorithms, A3 and A8 are used. In the SIM -card (In MS), both of these algorithms and 32 -digit key are stored) and the very same information can be found in Authentication Centre (AuC) also. When MS Authentication is requested by the network, AuC/VLR sends 32 -digit RANDom Number to the MS. MS calculates then Signed Response (SRES and returns that back to the VLR. VLR makes a comparison if received
Mobile Originated Call
SRES is same than it has received inside of the Authentication triplet from the AuC before. If these two SRESs are the same, authentication went OK and MS can continue the call setup.
Should you notice, the first 8 digits of the KI are used for Authentication and SRES calculation, the rest 24 are reserved for Ciphering Key calculation.
16. AUTHENTICATION_RESPONSE
Inside of this message, the SRES value from the MS is forwarded back to the VLR in order to finalize authentication procedure.
Mobile Originated Call
This and all other messages in the A-interface up to the releasing of the SCCP connection are transmitted by using SCCP DT1 (Data Form 1) messages.
17. AUTHENTICATION_RESPONSE
MSC sends a positive response to Authenticate message.
18. SET_CIPHERING_MODE
VLR sends MSC Set Ciphering Mode message which is used for changing MS-BTS connection ciphering status.
Mobile Originated Call
19. CIPHERING_MODE_COMMAND
The MSC asks the BSC start ciphering on the radio path. This message is sent in the A-interface in case the network wants to initiate ciphering over the radio interface. If the network uses ciphering then MS starts ciphering after receiving this message.
20. ENCRYPTION_COMMAND
The BSC stores the Encryption information to its memory and sends an Encryption command to the BTS to start ciphering mode operations.
Mobile Originated Call
21. CIPHERING_MODE_COMMAND
The BSS informs the MS about beginning of ciphering , and starts receiving in the ciphered mode.
22. CIPHERING_MODE_COMPLETE
The MS acknowledges ciphering command.
23. CIPHERING_MODE_COMPLETE
Mobile Originated Call
If ciphering is in use, this is the first ciphered message (by the MS) in the Air interface. The BSS acknowledges the Ciphering Command, informs the MSC that MS has started ciphering and starts sending information in ciphered mode.
24. ACCESS_REQUEST_ACCEPTED
VLR sends a positive acknowledge to Process Access Request message.
25. FORWARD_NEW_TMSI
Mobile Originated Call
VLR requests MSC to perform TMSI reallocation.
26. TMSI_REALLOCATION_COMMAND
The purpose of the TMSI reallocation procedure is to provide identity confidentiality. Usually the TMSI reallocation is performed at least at each change of location area. MSC initiates the TMSI reallocation procedure by sending TMSI Reallocation command message to the MS. TMSI Reallocation Command message contains a new combination of TMSI and LAI allocated by the network or a LAI and the IMSI if the used TMSI shall be deleted. Usually
Mobile Originated Call
the TMSI Reallocation Command message is sent to the MS by using a RR connection in ciphered mode.
27. TMSI_REALLOCATION_COMMAND
TMSI Reallocation Command is forwarded to the MS.
28. TMSI_REALLOCATION_COMPLETE
When the MS receives the TMSI Reallocation Command message, it stores the LAI in the SIM. If the received identity is the IMSI of the MS, it deletes any
Mobile Originated Call
previously stored TMSI. If the received identity is a TMSI, the MS stores it in the SIM. In both cases the MS send a TMSI Reallocation Complete message to the network.
29. TMSI_REALLOCATION_COMPLETE
TMSI Reallocation Complete message is forwarded to the MSC.
Mobile Originated Call
30. TMSI_ACK
MSC sends VLR a positive response to reallocation of TMSI.
31. SETUP
After authentication, Identification and Ciphering, the MS is in the SDCCH channel and ready to start real call setup signaling. The MS sends a Setup message to the BSC to be forwarded to the MSC.
32. SETUP
Mobile Originated Call
The BSC sends the Setup message to the MSC in order to inform the MSC about the incoming call.
33. SEND_INFO_FOR_OG_CALL
VLR request for retrieval of call data.
34. COMPLETE_CALL
Call completion acknowledged by VLR for MOC.
Mobile Originated Call
35. CALL_PROCEEDING
The MSC responds to the Setup message.
36. CALL_PROCEEDING
When the call control entity of the MS receives a Call Proceeding message, it enters the "Mobile originated call proceeding" state.
37. ASSIGNMENT_REQUEST
Mobile Originated Call
This message starts the TCH allocation. In the A- interface, MSC is the master and it hunts the circuit used for this call through the A- interface. This message can contain some optional information according to GSM- recommendations. This optional information is: Priority of the call, Downlink Discontinuous Transmission (DTX), Radio channel identity and Interference band to use.
38. PHYSICAL_CONTEXT_REQUEST
By using this message, the BSC interrogates the actual timing advance from the BTS in order to start TCH allocation through the Abis -interface.
Mobile Originated Call
39. PHYSICAL_CONTEXT_CONFIRM
BSC receives the timing advance information from the BTS and starts TCH reservation and allocation. This reservation & allocation procedure is similar to the case of the SDCCH -channel.
40. CHANNEL_ACTIVATION
After the BSC's internal channel reservation and allocation, it activates the TCH by sending this message towards the BTS. Contents: channel number, activation type, channel mode (DTX/No DTX), channel type (Speech / data: if
Mobile Originated Call
speech, then GSM encoding algorithm included, if data, then information about transparency or non-transparency of the channel and data rate), channel identity, encryption information if received, BS & MS power levels as received in 'Physical context confirm' -message and timing advance.
41. CHANNEL_ACTIVATION_ACK.
The BTS returns current TDMA frame number and after that the TCH is activated through the Abis -interface.
Mobile Originated Call
42. ASSIGNMENT_COMMAND
The BTS delivers received information further on towards the MS. Contents: channel description, power levels, cell channel description, channel mode (Full / Half) and mobile allocation.
43. SABM (Set Asynchronous Balanced Mode)
This is Layer 2 message and contains some Layer 3 information. Content of this message: service request (look establishment cause!), ciphering key sequence, Mobile Station Classmark and Mobile Identity.
Mobile Originated Call
44. ESTABLISH_INDICATION
Establish indication -message has two uses. Firstly, when used this phase it points out that from the point of view of the BTS, the MS is now on the FACCH-channel. Thus, the BTS sends information back to the BSC that the MS is now on this kind of FACCH-channel which description is like this etc. Also the BTS identifies the link = main signaling channel and adds received Layer 3 information into this message. This layer 3 information is coming from the MS, of course.
45. UA
Mobile Originated Call
UA is normal Level 2 acknowledgement when setting up the Layer 2 level link in LAPDm-protocol.
46. ASSIGNMENT_COMPLETE
The MS informs it is now on the TCH and everything is OK.
47. ASSIGNMENT_COMPLETE
The BSS acknowledges the channel seizure to the MSC.
Mobile Originated Call
48. CHANNEL_RELEASE
When MS has informed the network it is in the TCH, there is no need to use the SDCCH -channel for this call setup any more. By Channel Release procedure it is released.
49. CHANNEL_RELEASE_ACK.
The BTS acknowledges the Channel Release message.
50. ALERTING
Mobile Originated Call
The MSC sends an Alerting message via BSS.
51. ALERTING
The MSC informs the MS that the called subscriber has been alerted. This message can contain also so-called progress indicator IE, which tells that there are in-band announcements or other similar information to be received. In brief, this means that the connection is not end-to-end ISDN connection. If the MS receives this element, it shall through-connect the speech path. In case it is not, the MS generates ringing tone in itself. This information can also be transferred in a Progress message.
Mobile Originated Call
52. CONNECT
The MSC sends a Connect message to the MS via the BSS. This message indicates the MS that a connection has been established through the network.
53. CONNECT
When the MS receives a Connect message, it attachs the user connection to the radio path, returns a Connect Acknowledge message, stops any locally generated alerting indication (if applied) and enters the "active" state.
Mobile Originated Call
54. CONNECT_ACK.
By using this message, the MS informs the MSC that the MS is now in the "active" state.
55. CONNECT_ACK.
The message is forwarded to the MSC.
56. MEASUREMENT_REPORT
Mobile Originated Call
When call is on, the MS sends measurement report concerning mainly the quality of the speech connection two times per second.
Mobile Originated Call
57. MEASUREMENT_REPORT/RESULT
If these measurement reports are preprocessed in the BTS then measurement results are sent towards the BSC. If the is no preprocessing in the BTS, then measurement reports are sent. In this phase, Nokia BTS does not make any preprocessing.
58. DISCONNECT
This request is sent by MS. Contents: clear end-to-end connection. This message stops the charging concerning this call connection.
Mobile Originated Call
59. DISCONNECT
The Disconnect message is forwarded to the MSC.
60. RELEASE
Actual release is coming from the MSC; real call is just about to end.
61. RELEASE
The Release message is forwarded to the MS.
Mobile Originated Call
62. RELEASE_COMPLETE
MS informs that it will release the transaction identifier, i.e. call release is proceeding.
63. RELEASE_COMPLETE
The Release Complete message is forwarded to the MSC.
64. CLEAR_COMMAND
Mobile Originated Call
This message is coming from the MSC and releases the associated dedicated resources, i.e. BSSAP connection concerning this call.
65. CHANNEL_RELEASE
Deactivation command of the used TCH. This is sent by the BSC towards the MS. Quite often this is also called '3rd layer disconnection'. In case of normal call setup case, the release cause is 'normal'.
66. DEACTIVATE_SACCH
Mobile Originated Call
By sending this message to downlink direction, the BSC inhibits system information message sending towards the MS. In fact, there is no use to send/receive any information in the SACCH channel any more, so it will be deactivated.
67. DISC
The MS send Layer 2 frame DISConnect to uplink direction in order to inform the BTS it is stopping the traffic in the TCH/FACCH.
68. UA
Mobile Originated Call
The BTS acknowledges DISC -frame. Consequences: the MS starts to listen BCCH -channel again and all the Air interface resources are released.
69. RELEASE_INDICATION
The BTS informs the BSC that the MS has no more any dedicated Air interface resources (i.e. TCH/FACCH) in use.
70. RF_CHANNEL_RELEASE
The BSC tells the BTS to release the rest of the radio resources.
Mobile Originated Call
71. RF_CHANNEL_RELEASE_ACK.
All the rest of the radio resources have been released; BTS send an acknowledgment to BSC. These radio resources are: TCH/FACCH and SACCH.
72. CLEAR_COMPLETE
This is acknowledgement to the message SCCP Data (Clear Command). Now the BSC informs the MSC that all radio resources related to this call are released.
Mobile Originated Call
73. SCCP_RELEASED
When all radio resources are released, BSSAP connection concerning this call is not needed any more. This message tells the BSC to release this SCCP connection. The message is sent as RLSD message.
74. SCCP_RELEASED_ACK.
BSC informs MSC that now the dedicated SCCP connection concerning this call is released. The message is sent as RLC message.
Mobile Originated Call
2. MOBILE TERMINATED CALL
Mobile Originated Call
MSC BSC BTS MSVLR
Channel Required
Channel ActivationChannel Activation Ack.
Immediate Assigment Command.
Channel Request ( RACH )
Immediate Assigment ( AGCH ).
SABM Paging Response(SDCCH)
Establish IndicationCR (Paging Responset)Process Access Request
AuthenticateCC Authentication Request
Authentication Request ( SDCCH )
Authentication Response ( SDCCH )DT1 Authentication Response
Authentication Response
Set Ciphering ModeDT1 Ciphering Mode Command
Encryption CommandCiphering Mode Command(SDCCH)
Ciphering Mode Complete ( SDCCH )DT1Ciphering Mode Complete
Access Request Accepted
Forward New TMSITMSI Reallocation Command
TMSI Reallocation Command ( SDCCH )
TMSI Reallocation Complete ( SDCCH )
TMSI Reallocation CompleteTMSI Ack.
Setup ( SDCCH )DT1 Setup
Send Info for O.G. Call
Complete CallDT1 Call Proceeding
Call Proceeding ( SDCCH )DT1 Assignment Request
Physical Context Request
Physical Context Confirmed
Channel Activation
Channel Activation Ack.Assignment Command ( SDCCH )
SABM ( FACCH )Establish Indication
UA ( FACCH )Assignment Complete (FACCH)
DT1 Assignment CompleteChannel Release
Channel Release Ack.DT1 Alerting Alerting ( FACCH )
DT1 Connect Connect ( FACCH )
Connect Ack.( FACCH )DT1 Connect Ack.
Measurement Report ( SACCH )Measurement Report/Result
Disconnect ( FACCH )DT1 Disconnect
DT1 Release
DT1 Release Complete
DT1 Clear Command
Release ( FACCH )
Release Complete ( FACCH )
Channel Release (FACCH)
Deactivate SACCHDISC ( FACCH )
UA ( FACCH )Release Indication
RF Channel Release
RF Channel Release Ack.DT1 Clear Complete
RLSD ( SCCP Released )
RLC ( SCCP Released Ack.)
Paging RequestPaging Command
UDT Paging12
3
45
67
8 9
101112
13
1415
1617
1819 20
2122
2324
2526
2728
2930
31 3233
3435
363738
394041
4243
4445
4648
47
495051
5253
54 555657
585960
6162
6364
6566
6768
RADIOACCESSPART
PAGINGPART
UA (SDCCH)
ESTABLISHMENTPART
CIPHERING,AUTHENTICATIONAND CALL SETUPPART
TCH SEIZED
CONVERSATIONPART
RELEASE BY MS
PagingResponse(SDCCH)
Mobile Originated Call
Mobile Originated Call
1. PAGING
This message is sent by MSC when it has found out the called MS is somewhere under him (= MSC recognizes this is a GSM_END -call). This message contains mainly four kind of information: message type, IMSI of the called subscriber, TMSI of the called subscriber and Cell Identifier list. If TMSI -numbers are defined for use these have the priority one, for security reasons and if the network does not use TMSIs then IMSI -number is included only. The paging is sent as an UDT (Unit Data) message to the BSC.
2. PAGING_COMMAND
Mobile Originated Call
The BSC always calculates so called paging group. The idea of this calculation is to find out in which radio time slots the BTS can send the Paging Requests out towards the MS. Reason: in the network, there is a possibility to have at least three different kind of BCCH-TRX -radio time slot configuration and thus logical channel PCH can have at least three different kind of location. If the BSC receives both TMSI and IMSI from the MSC, then it uses always TMSI number when sending paging further on.
3. PAGING_REQUEST
The BTS sends paging on a PCH channel.
Mobile Originated Call
4. CHANNEL_REQUEST
The MS responds to the paging by sending a random access burst on a RACH channel via one BTS. Channel request -message contains the establishment cause. This can be 'Answer for paging', 'emergency call', 'other services (Mobile Originated Call, Short Message Service)' or 'Other', like location update. In addition to, this message contains Random Reference. This is 5 bits randomly selected by MS. The usage of random reference is: when two MSs are accessing to the network exactly the same time, the network can separate these Mobile Stations by using this random reference.
Mobile Originated Call
5. CHANNEL_REQUIRED
The BTS sends a channel required message to the BSC. By using this message, BTS delivers further on towards the BSC the channel request generated by MS. In practice Channel Required contains the same information as above but the BTS adds some information into it also. BTS numbers always the channels. In this case, the number of the Uplink CCCH (RACH -burst) is included. Request reference is directly coming from Channel request -message. Then, the first timing advance estimate called Access Delay is added into this message by the BTS.
Mobile Originated Call
6. CHANNEL_ACTIVATION
The BSC sends a Channel Activation message to the BTS. After receiving channel required from the BTS, the BSC starts to search and allocate SDCCH -channel for this call on certain terms, the most important is of course which BTS and then the channel configuration of this SDCCH. Parameters: DTX control, channel ID & description & mobile allocation, maximum power levels of the MS and BS and finally, the first timing advance concerning this access calculated by the BSC.
7. CHANNEL_ACTIVATION_ACK.
Mobile Originated Call
A response to the channel activation message. When BTS has received this message it starts to send and receive SACCH -channel. The reference used in this case is the power levels received in Channel Activation message.
8. IMMEDIATE_ASSIGNMENT_COMMAND
The BSC tells the BTS about the SDCCH channel to be used.
9. IMMEDIATE_ASSIGNMENT
Mobile Originated Call
The BSS informs the MS on AGCH channel about the SDCCH channel to be used. In practice, this message is an order from the network to the MS to move to the SDCCH -channel defined before. Page mode, SDCCH channel description, associated SACCH and hopping frequency are included as a parameters. In addition, request reference (same as establishment cause), initial timing advance and frequency allocation if frequency hopping applies are also included.
10. PAGING_RESPONSE
The MS responds to the paging on the signaling channel.
Mobile Originated Call
11. ESTABLISH_INDICATION
BTS acknowledges the Immediate Assignment Command by returning Establish Indication message. Establish indication -message has two uses. Firstly, when used in this phase it points out that from the BTS point of view, the MS is now on the SDCCH-channel. Thus, the BTS sends information back to the BSC that the MS is now on this kind of SDCCH-channel which description is like this etc. Also the BTS identifies the link = main signaling channel and adds received Layer 3 information into this message.
12. PAGING_RESPONSE
Mobile Originated Call
The BSC initiates the MSC about the connection by paging response, which is a CR (Connection Request) message.
Mobile Originated Call
13. UA
UA is normal Layer 2 level acknowledgement when setting up the Layer 2 level link in LAPDm -protocol.
14. AUTHENTICATION_REQUEST
As a CC (Connection Confirmed) message, the MSC sends an Authentication Request message to the BSC. The message contains the RAND.
15. AUTHENTICATION_REQUEST
Mobile Originated Call
The BSC forwards the message via the BTS to the MS.
16. AUTHENTICATION_RESPONSE
The MS responds to the Authentication Request with the Signed Response SRES. The Authentication Response is sent to the BSC via the BTS.
In the MS Authentication procedure, two algorithms, A3 and A8 are used. In the SIM -card (In MS), both of these algorithms and 32 -digit key are stored) and the very same information can be found in Authentication Centre (AuC) also. When MS Authentication is requested by the network, AuC/VLR sends
Mobile Originated Call
32 -digit RANDom Number to the MS. MS calculates then Signed Response (SRES and returns that back to the VLR. VLR makes a comparison if received SRES is same than it has received inside of the Authentication triplet from the AuC before. If these two SRESs are the same, authentication went OK and MS can continue the call setup.
Should you notice, the first 8 digits of the KI are used for Authentication and SRES calculation, the rest 24 are reserved for Ciphering Key calculation.
17. AUTHENTICATION_RESPONSE
Mobile Originated Call
Inside of this message, the SRES value from the MS is forwarded back to the VLR in order to finalize authentication procedure.
This and all other messages in the A-interface up to the releasing of the SCCP connection are transmitted by using SCCP DT1 (Data Form 1) messages.
18. CIPHERING_MODE_COMMAND
Mobile Originated Call
The MSC asks the BSC start ciphering on the radio path. This message is sent in the A-interface in case the network wants to initiate ciphering over the radio interface. If the network uses ciphering then MS starts ciphering after receiving this message.
Mobile Originated Call
19. ENCRYPTION_COMMAND
The BSC stores the Encryption information to its memory and sends an Encryption command to the BTS to start ciphering mode operations.
20. CIPHERING_MODE_COMMAND
The BSS informs the MS about beginning of ciphering , and starts receiving in the ciphered mode.
21. CIPHERING_MODE_COMPLETE
Mobile Originated Call
The MS acknowledges ciphering command.
22. CIPHERING_MODE_COMPLETE
If ciphering is in use, this is the first ciphered message (by the MS) in the Air interface. The BSS acknowledges the Ciphering Command, informs the MSC that MS has started ciphering and starts sending information in ciphered mode.
23. TMSI_REALLOCATION_COMMAND
Mobile Originated Call
The purpose of the TMSI reallocation procedure is to provide identity confidentiality. Usually the TMSI reallocation is performed at least at each change of location area. MSC initiates the TMSI reallocation procedure by sending TMSI Reallocation command message to the MS. TMSI Reallocation Command message contains a new combination of TMSI and LAI allocated by the network or a LAI and the IMSI if the used TMSI shall be deleted. Usually the TMSI Reallocation Command message is sent to the MS by using a RR connection in ciphered mode.
24. TMSI_REALLOCATION_COMMAND
Mobile Originated Call
TMSI Reallocation Command is forwarded to the MS.
25. TMSI_REALLOCATION_COMPLETE
When the MS receives the TMSI Reallocation Command message, it stores the LAI in the SIM. If the received identity is the IMSI of the MS, it deletes any previously stored TMSI. If the received identity is a TMSI, the MS stores it in the SIM. In both cases the MS send a TMSI Reallocation Complete message to the network.
26. TMSI_REALLOCATION_COMPLETE
Mobile Originated Call
TMSI Reallocation Complete message is forwarded to the MSC.
Mobile Originated Call
27. SETUP
After authentication, Identification and Ciphering, the MS is in the SDCCH channel and ready to start real call setup signaling. The MSC sends a Setup message to the BSC to be forwarded to the MS.
28. SETUP
The BSC sends the Setup message to the MS via BTS in order to inform the MS about the incoming call.
Mobile Originated Call
29. CALL_PROCEEDING
The MS responds after having checked the compatibility with a requested bearer capability.
30. CALL_PROCEEDING
The information is forwarded to the MSC. This message indicates that the network has received all information that is required for call setup and no more such information will be accepted.
Mobile Originated Call
31. ASSIGNMENT_REQUEST
This message starts the TCH allocation. In the A- interface, MSC is the master and it hunts the circuit used for this call through the A- interface. This message can contain some optional information according to GSM- recommendations. This optional information is: Priority of the call, Downlink Discontinuous Transmission (DTX), Radio channel identity and Interference band to use.
32. PHYSICAL_CONTEXT_REQUEST
Mobile Originated Call
By using this message, the BSC interrogates the actual timing advance from the BTS in order to start TCH allocation through the Abis -interface.
33. PHYSICAL_CONTEXT_CONFIRM
BSC receives the timing advance information from the BTS and starts TCH reservation and allocation. This reservation & allocation procedure is similar to the case of the SDCCH -channel.
Mobile Originated Call
34. CHANNEL_ACTIVATION
After the BSC's internal channel reservation and allocation, it activates the TCH by sending this message towards the BTS. Contents: channel number, activation type, channel mode (DTX/No DTX), channel type (Speech / data: if speech, then GSM encoding algorithm included, if data, then information about transparency or non-transparency of the channel and data rate), channel identity, encryption information if received, BS & MS power levels as received in 'Physical context confirm' -message and timing advance.
35. CHANNEL_ACTIVATION_ACK.
Mobile Originated Call
The BTS returns current TDMA frame number and after that the TCH is activated through the Abis -interface.
36. ASSIGNMENT_COMMAND
The BTS delivers received information further on towards the MS. Contents: channel description, power levels, cell channel description, channel mode (Full / Half) and mobile allocation.
37. SABM (Set Asynchronous Balanced Mode)
Mobile Originated Call
This is Layer 2 message and contains some Layer 3 information. Content of this message: service request (look establishment cause!), ciphering key sequence, Mobile Station Classmark and Mobile Identity.
38. ESTABLISH_INDICATION
Establish indication -message has two uses. Firstly, when used this phase it points out that from the point of view of the BTS, the MS is now on the FACCH-channel. Thus, the BTS sends information back to the BSC that the MS is now on this kind of FACCH-channel which description is like this etc. Also the BTS identifies the link = main signaling channel and adds received
Mobile Originated Call
Layer 3 information into this message. This layer 3 information is coming from the MS, of course.
39. UA
UA is normal Level 2 acknowledgement when setting up the Layer 2 level link in LAPDm-protocol.
40. ASSIGNMENT_COMPLETE
The MS informs it is now on the TCH and everything is OK.
Mobile Originated Call
41. ASSIGNMENT_COMPLETE
The BSS acknowledges the channel seizure to the MSC.
42. CHANNEL_RELEASE
When MS has informed the network it is in the TCH, there is no need to use the SDCCH -channel for this call setup any more. By Channel Release procedure it is released.
43. CHANNEL_RELEASE_ACK.
Mobile Originated Call
The BTS acknowledges the Channel Release message.
44. ALERTING
The MS sends an Alerting message via BSS.
45. ALERTING
The MS informs that the subscriber has been alerted. This message can contain also so-called progress indicator IE, which tells that there are in-band announcements or other similar information to be received. In brief, this means
Mobile Originated Call
that the connection is not end-to-end ISDN connection. If the MS receives this element, it shall through-connect the speech path. In case it is not, the MS generates ringing tone in itself. This information can also be transferred in a Progress message.
46. CONNECT
The call is 'accepted' by MS user.
47. CONNECT
Mobile Originated Call
Connect -message is end-to-end message and when this message reaches the MSC, charging related to this call starts.
48. CONNECT_ACK.
By using this message, the MSC informs the MS that call is now connected through. Thus, the speech codecs can be opened in the MS, if not already opened, and the logical radio channel changes from FACCH to TCH.
49. CONNECT_ACK.
Mobile Originated Call
The message is forwarded to the MS.
50. MEASUREMENT_REPORT
When call is on, the MS sends measurement report concerning mainly the quality of the speech connection two times per second.
Mobile Originated Call
51. MEASUREMENT_REPORT/RESULT
If these measurement reports are preprocessed in the BTS then measurement results are sent towards the BSC. If the is no preprocessing in the BTS, then measurement reports are sent. In this phase, Nokia BTS does not make any preprocessing.
52. DISCONNECT
This request is sent by MS. Contents: clear end-to-end connection. This message stops the charging concerning this call connection.
Mobile Originated Call
53. DISCONNECT
The Disconnect message is forwarded to the MSC.
54. RELEASE
Actual release is coming from the MSC; real call is just about to end.
55. RELEASE
The Release message is forwarded to the MS.
Mobile Originated Call
56. RELEASE_COMPLETE
MS informs that it will release the transaction identifier, i.e. call release is proceeding.
57. RELEASE_COMPLETE
The Release Complete message is forwarded to the MSC.
58. CLEAR_COMMAND
Mobile Originated Call
This message is coming from the MSC and releases the associated dedicated resources, i.e. BSSAP connection concerning this call.
59. CHANNEL_RELEASE
Deactivation command of the used TCH. This is sent by the BSC towards the MS. Quite often this is also called '3rd layer disconnection'. In case of normal call setup case, the release cause is 'normal'.
60. DEACTIVATE_SACCH
Mobile Originated Call
By sending this message to downlink direction, the BSC inhibits system information message sending towards the MS. In fact, there is no use to send/receive any information in the SACCH channel any more, so it will be deactivated.
61. DISC
The MS send Layer 2 frame DISConnect to uplink direction in order to inform the BTS it is stopping the traffic in the TCH/FACCH.
62. UA
Mobile Originated Call
The BTS acknowledges DISC -frame. Consequences: the MS starts to listen BCCH -channel again and all the Air interface resources are released.
63. RELEASE_INDICATION
The BTS informs the BSC that the MS has no more any dedicated Air interface resources (i.e. TCH/FACCH) in use.
64. RF_CHANNEL_RELEASE
The BSC tells the BTS to release the rest of the radio resources.
Mobile Originated Call
65. RF_CHANNEL_RELEASE_ACK.
All the rest of the radio resources have been released; BTS send an acknowledgment to BSC. These radio resources are: TCH/FACCH and SACCH.
66. CLEAR_COMPLETE
This is acknowledgement to the message SCCP Data (Clear Command). Now the BSC informs the MSC that all radio resources related to this call are released.
Mobile Originated Call
67. SCCP_RELEASED
When all radio resources are released, BSSAP connection concerning this call is not needed any more. This message tells the BSC to release this SCCP connection. The message is sent as RLSD message.
68. SCCP_RELEASED_ACK.
BSC informs MSC that now the dedicated SCCP connection concerning this call is released. The message is sent as RLC message.
Mobile Originated Call
3. LOCATION UPDATE
Mobile Originated Call
MSC BSC BTS MSVLR
Channel Required
Channel Activation
Channel Activation Ack.
Immediate Assigment Command.
Channel Request ( RACH )
Immediate Assigment ( AGCH ).
Location Update Request
Establish IndicationProcess Access Request
AuthenticateDT1Authentication Request
Authentication Request ( SDCCH )
Authentication Response ( SDCCH )DT1 Authentication Response
Authentication Response
Set Ciphering ModeDT1 Cipher Mode Command
Encryption Command
Ciphering Mode Command ( SDCCH )
Ciphering Mode Complete ( SDCCH )DT1Cipher Mode Complete
Access Request Accepted
DT1 Location Update Accepted
Location Update Accepted
TMSI reallocation CompleteDT1TMSI Reallocation Complete
DT1 Clear Command
Channel Release ( SDCCH )
Deactivate SACCHDISC ( FACCH )
UA ( FACCH )Release Indication
RF Channel Release
RF Channel Release Ack.DT1 Clear Complete
RLSD (SCCP Released)
RLC (SCCP Released Ack.)
CR Location Update Req.Request Request UA ( SDCCH )
Identity RequestCC Identity Request
Identity Request ( SDCCH )
Identity Response ( SDCCH )DT1 Identity ResponseIdentity Response
12
34
56
78
910
1112
1314
1516
1718
1920
21
2223
2425
2627
2829
3031
3233
34
3536
3738
RADIOACCESSPART
IDENTIFICATIONANDAUTHENTICATIONPROCEDURES
CHANNELRELEASE
LOCATIONUPDATEREQUEST
CIPHERING ANDENCRYPTIONPART
LOCATIONUPDATE
Location Update RequestRequest Request SABM (SDCCH)
Mobile Originated Call
Mobile Originated Call
1. CHANNEL_REQUEST
The MS requests a channel by sending a random access burst on a RACH channel via one BTS. Channel request -message contains the establishment cause. This can be 'Answer for paging', 'emergency call', 'other services (Mobile Originated Call, Short Message Service)' or 'Other', like location update. In addition to, this message contains Random Reference. This is 5 bits randomly selected by MS. The usage of random reference is: when two MSs are accessing to the network exactly the same time, the network can separate these Mobile Stations by using this random reference.
Mobile Originated Call
2. CHANNEL_REQUIRED
The BTS sends a channel required message to the BSC. By using this message, BTS delivers further on towards the BSC the channel request generated by MS. In practice Channel Required contains the same information as above but the BTS adds some information into it also. BTS numbers always the channels. In this case, the number of the Uplink CCCH (RACH -burst) is included. Request reference is directly coming from Channel request -message. Then, the first timing advance estimate called Access Delay is added into this message by the BTS.
Mobile Originated Call
3. CHANNEL_ACTIVATION
The BSC sends a Channel Activation message to the BTS. After receiving channel required from the BTS, the BSC starts to search and allocate SDCCH -channel for this call on certain terms, the most important is of course which BTS and then the channel configuration of this SDCCH. Parameters: DTX control, channel ID & description & mobile allocation, maximum power levels of the MS and BS and finally, the first timing advance concerning this access calculated by the BSC.
4. CHANNEL_ACTIVATION_ACK.
Mobile Originated Call
A response to the channel activation message. When BTS has received this message it starts to send and receive SACCH -channel. The reference used in this case is the power levels received in Channel Activation message.
5. IMMEDIATE_ASSIGNMENT_COMMAND
The BSC tells the BTS about the SDCCH channel to be used.
Mobile Originated Call
6. IMMEDIATE_ASSIGNMENT
The BSS informs the MS on AGCH channel about the SDCCH channel to be used. In practice, this message is an order from the network to the MS to move to the SDCCH -channel defined before. Page mode, SDCCH channel description, associated SACCH and hopping frequency are included as a parameters. In addition, request reference (same as establishment cause), initial timing advance and frequency allocation if frequency hopping applies are also included.
7. LOCATION_UPD_REQ
Mobile Originated Call
The Location Update Request message is sent by the MS to the network to request update of its location file.
8. ESTABLISH_INDICATION
BTS acknowledges the Immediate Assignment Command by returning Establish Indication message. Establish indication -message has two uses. Firstly, when used in this phase it points out that from the BTS point of view, the MS is now on the SDCCH-channel. Thus, the BTS sends information back to the BSC that the MS is now on this kind of SDCCH-channel which
Mobile Originated Call
description is like this etc. Also the BTS identifies the link = main signaling channel and adds received Layer 3 information into this message.
9. LOCATION_UPD_REQ
The Location Update Request message is forwarded to the MSC as a CR (Connection Request) message.
10. UA
Mobile Originated Call
UA is normal Layer 2 level acknowledgement when setting up the Layer 2 level link in LAPDm -protocol.
11. IDENTITY_REQUEST
Actually this is an Identification procedure used for IMEI -checking. IMEI = International Mobile Equipment Identity. This kind of request is generated by Equipment Identity Register in order to control MS Hardware Parts. Normally, this is not made in every call setup; quite typical value (set inside the VLR) is that IMEI is checked every 20th time when MS is making call setup. The network may also require IMSI of the subscriber in case it cannot be obtained
Mobile Originated Call
from the network side. An example is that MS tries to establish a call with TMSI, but the network has lost TMSI. In this case the network has no other possibility to identify the subscriber than to ask the MS. The Identity Request message is sent as a CC (Connection Confirm) message.
Mobile Originated Call
12. IDENTITY_REQUEST
The BSS forwards the Identity Request message to the MS.
13. IDENTIFICATION_RESPONSE
The MS sends a response to the Identity Request containing its mobile identity information.
14. IDENTIFICATION_RESPONSE
Mobile Originated Call
The message is forwarded to the MSC.
15. AUTHENTICATION_REQUEST
As a DT1 (Data Form 1) message, the MSC sends an Authentication Request message to the BSC. The message contains the RAND.
16. AUTHENTICATION_REQUEST
The BSC forwards the message via the BTS to the MS.
Mobile Originated Call
17. AUTHENTICATION_RESPONSE
The MS responds to the Authentication Request with the Signed Response SRES. The Authentication Response is sent to the BSC via the BTS.
In the MS Authentication procedure, two algorithms, A3 and A8 are used. In the SIM -card (In MS), both of these algorithms and 32 -digit key are stored) and the very same information can be found in Authentication Centre (AuC) also. When MS Authentication is requested by the network, AuC/VLR sends 32 -digit RANDom Number to the MS. MS calculates then Signed Response (SRES and returns that back to the VLR. VLR makes a comparison if received
Mobile Originated Call
SRES is same than it has received inside of the Authentication triplet from the AuC before. If these two SRESs are the same, authentication went OK and MS can continue the call setup.
Should you notice, the first 8 digits of the KI are used for Authentication and SRES calculation, the rest 24 are reserved for Ciphering Key calculation.
18. AUTHENTICATION_RESPONSE
Inside of this message, the SRES value from the MS is forwarded back to the VLR in order to finalize authentication procedure.
Mobile Originated Call
This and all other messages in the A-interface up to the releasing of the SCCP connection are transmitted by using SCCP DT1 (Data Form 1) messages.
Mobile Originated Call
19. CIPHERING_MODE_COMMAND
The MSC asks the BSC start ciphering on the radio path. This message is sent in the A-interface in case the network wants to initiate ciphering over the radio interface. If the network uses ciphering then MS starts ciphering after receiving this message.
20. ENCRYPTION_COMMAND
The BSC stores the Encryption information to its memory and sends an Encryption command to the BTS to start ciphering mode operations.
Mobile Originated Call
21. CIPHERING_MODE_COMMAND
The BSS informs the MS about beginning of ciphering , and starts receiving in the ciphered mode.
22. CIPHERING_MODE_COMPLETE
The MS acknowledges ciphering command.
23. CIPHERING_MODE_COMPLETE
Mobile Originated Call
If ciphering is in use, this is the first ciphered message (by the MS) in the Air interface. The BSS acknowledges the Ciphering Command, informs the MSC that MS has started ciphering and starts sending information in ciphered mode.
24. LOCATION_UPD_ACC
The MSC sends the Location Updating Accep message to the MS to indicate that updating has been completed.
25. LOCATION_UPD_ACC
Mobile Originated Call
The Location Updating Accept message is forwarded to the MS by the BSS.
26. TMSI_REALLOC_COMPL
The TMSI Reallocation Complete message is sent to the network to indicate, that reallocation of new TMSI has taken place.
27. TMSI_REALLOC_COMPL
The TMSI Reallocation Complete message is forwarded to the MSC.
Mobile Originated Call
28. CLEAR_COMMAND
This message is coming from the MSC and releases the associated dedicated resources, i.e. BSSAP connection concerning this call.
Mobile Originated Call
29. CHANNEL_RELEASE
Deactivation command of the used TCH. This is sent by the BSC towards the MS. Quite often this is also called '3rd layer disconnection'. In case of normal call setup case, the release cause is 'normal'.
30. DEACTIVATE_SACCH
Mobile Originated Call
By sending this message to downlink direction, the BSC inhibits system information message sending towards the MS. In fact, there is no use to send/receive any information in the SACCH channel any more, so it will be deactivated.
31. DISC
The MS send Layer 2 frame DISConnect to uplink direction in order to inform the BTS it is stopping the traffic in the TCH/FACCH.
32. UA
Mobile Originated Call
The BTS acknowledges DISC -frame. Consequences: the MS starts to listen BCCH -channel again and all the Air interface resources are released.
33. RELEASE_INDICATION
The BTS informs the BSC that the MS has no more any dedicated Air interface resources (i.e. TCH/FACCH) in use.
34. RF_CHANNEL_RELEASE
The BSC tells the BTS to release the rest of the radio resources.
Mobile Originated Call
35. RF_CHANNEL_RELEASE_ACK.
All the rest of the radio resources have been released; BTS send an acknowledgment to BSC. These radio resources are: TCH/FACCH and SACCH.
36. CLEAR_COMPLETE
This is acknowledgement to the message SCCP Data (Clear Command). Now the BSC informs the MSC that all radio resources related to this call are released.
Mobile Originated Call
37. SCCP_RELEASED
When all radio resources are released, BSSAP connection concerning this call is not needed any more. This message tells the BSC to release this SCCP connection. The message is sent as RLSD message.
Mobile Originated Call
38. SCCP_RELEASED_ACK.
BSC informs MSC that now the dedicated SCCP connection concerning this call is released. The message is sent as RLC message.
Mobile Originated Call
4. INTERNAL HANDOVER, INTRA CELL
Mobile Originated Call
BSC BTS MSMSC
Receiver Ready ( FACCH )
Measurement Report ( SACCH )Measurement Report/Result
DT1 ( HO Performed )
RF Channel Release
RF Channel Release Ack.
Physical Context Request
Physical Context Confirmed
Channel Activation
Channel Activation Ack.
Assignment Command (FACCH )
SABM ( FACCH )Establish Indication
UA ( FACCH )
Assignment Complete ( FACCH )
12
3
4
5
6
7
8910
111213
1415
NEWTCHRESERVATIONANDACTIVATION
OLDTCHRELEASE
HOMEASUREMENTS
PHYSICALCONTEXTINFORMATION
SIGNALLING ONFACCH NEW
SIGNALLINGON FACCH OLD
Mobile Originated Call
1. MEASUREMENT_REPORT
When call is on, the MS sends measurement report concerning mainly the quality of the speech connection two times per second.
2. MEASUREMENT_REPORT/RESULT
Mobile Originated Call
If these measurement reports are preprocessed in the BTS then measurement results are sent towards the BSC. If the is no preprocessing in the BTS, then measurement reports are sent.
3. PHYSICAL_CONTEXT_REQUEST
4. PHYSICAL_CONTEXT_CONFIRM
5. CHANNEL_ACTIVATION
Mobile Originated Call
The BSC sends a Channel Activation message to the BTS. After receiving Handover Request from the MSC, the BSC starts to search and allocate TCH for this call on certain terms, the most important is of course which BTS and then the channel configuration of this BTS. Parameters: DTX control, channel ID & description & mobile allocation, maximum power levels of the MS and BS and finally, the first timing advance concerning this access calculated by the BSC.
Mobile Originated Call
6. CHANNEL_ACTIVATION_ACK.
A response to the Channel Activation message. When BTS has received this message it starts to send and receive TCH/SACCH. The reference used in this case is the power levels received in Channel Activation message.
7. ASSIGNMENT_COMMAND
8. SABM (Set Asynchronous Balanced Mode)
Mobile Originated Call
This is Layer 2 message and contains some Layer 3 information. Content of this message: service request (look establishment cause!), ciphering key sequence, Mobile Station Classmark and Mobile Identity.
9. ESTABLISH_INDICATION
BTS acknowledges the Immediate Assignment Command by returning Establish Indication message. Establish indication -message has two uses. Firstly, when used in this phase it points out that from the BTS point of view, the MS is now on the new TCH. Thus, the BTS sends information back to the BSC that the MS is now on this kind of TCH which description is like this etc.
Mobile Originated Call
Also the BTS identifies the link = main signaling channel and adds received Layer 3 information into this message.
10. UA
UA is normal Layer 2 level acknowledgement when setting up the Layer 2 level link in LAPDm -protocol.
11. ASSIGNMENT_COMPLETE
Mobile Originated Call
This message is sent by the MS to the network to indicate, that the MS has established the main signalling link successfully.
12. RR
The BTS sends a Receive Ready message to the MS.
13. HO_PERFORMED
Mobile Originated Call
The Handover Complete message is forwarded to the MSC. When the Handover Complete message is received, the network releases the old channels.
14. RF_CHANNEL_RELEASE
When MS has informed the network it is in the TCH, there is no need to use the old TCH for this call setup any more. By Channel Release procedure it is released.
15. RF_CHANNEL_RELEASE_ACK.
Mobile Originated Call
The BTS acknowledges the Channel Release message.
Mobile Originated Call
5. INTERNAL HANDOVER, INTER CELL
Mobile Originated Call
BSC BTS 2 BTS 1 MSMSC
Handover Command
Handover Detect
HO Command ( FACCH )
HO Access ( FACCH )
Establish Indication
Physical Info ( FACCH )
SABME ( FACCH )
Handover Complete
Handover Complete ( FACCH )
UA ( FACCH )
Receiver Ready ( FACCH )
Measurement Report ( SACCH )Measurement Report/Result
Channel Activation
Channel Activation Ack.
DT1 ( HO Performed )RF Channel Release
RF Channel Release Ack.
12
45 6
789
1011
1314
3
15
12
1617
18
TCHRESERVATION ANDACTIVATION IN BTS2
HO MEASUREMENTS
SIGNALLINGON FACCH IN BTS1
SIGNALLINGON FACCH IN BTS2
TCH RELEASE INBTS1
Mobile Originated Call
1. MEASUREMENT_REPORT
When call is on, the MS sends measurement report concerning mainly the quality of the speech connection two times per second.
2. MEASUREMENT_REPORT/RESULT
Mobile Originated Call
If these measurement reports are preprocessed in the BTS then measurement results are sent towards the BSC. If the is no preprocessing in the BTS, then measurement reports are sent.
3. CHANNEL_ACTIVATION
The BSC sends a Channel Activation message to the BTS. After receiving Handover Request from the MSC, the BSC starts to search and allocate a TCH for this call on certain terms, the most important is of course which BTS and then the channel configuration of this BTS. Parameters: DTX control, channel ID & description & mobile allocation, maximum power levels of the MS and
Mobile Originated Call
BS and finally, the first timing advance concerning this access calculated by the BSC.
4. CHANNEL_ACTIVATION_ACK.
A response to the Channel Activation message. When BTS has received this message it starts to send and receive TCH/SACCH. The reference used in this case is the power levels received in Channel Activation message.
Mobile Originated Call
5. HO_COMMAND
Handover Command message is sent from the BSC to the BTS to change the dedicated channel configuration and timing adjustment needeed.
6. HO_COMMAND
The BTS forwards the message to the MS.
7. HO_ACCESS
Mobile Originated Call
The MS sends a Handover Access message in random mode to the new BTS.
8. HO_DETECT
The new BTS informs the BSC, that it has detected a handover access message.
9. PHYSICAL_INFO
The Physical Information message contains various physical layer related information, allowing a proper transmission by the MS.
Mobile Originated Call
10. SABM (Set Asynchronous Balanced Mode)
This is Layer 2 message and contains some Layer 3 information. Content of this message: service request (look establishment cause!), ciphering key sequence, Mobile Station Classmark and Mobile Identity.
11. ESTABLISH_INDICATION
BTS acknowledges the Immediate Assignment Command by returning Establish Indication message. Establish indication -message has two uses. Firstly, when used in this phase it points out that from the BTS point of view,
Mobile Originated Call
the MS is now on the new TCH. Thus, the BTS sends information back to the BSC that the MS is now on this kind of TCH which description is like this etc. Also the BTS identifies the link = main signaling channel and adds received Layer 3 information into this message.
12. UA
UA is normal Layer 2 level acknowledgement when setting up the Layer 2 level link in LAPDm -protocol.
13. HO_COMPLETE
Mobile Originated Call
This message is sent by the MS to the network to indicate, that the MS has established the main signalling link successfully.
Mobile Originated Call
14. RR
The BTS sends a Receive Ready message to the MS.
15. HO_COMPLETE
The Handover Complete message is sent to the BSC.
16. HO_PERFORMED
Mobile Originated Call
The Handover Complete message is forwarded to the MSC. When the Handover Complete message is received, the network releases the old channels.
17. RF_CHANNEL_RELEASE
When MS has informed the network it is in the new TCH, there is no need to use the old TCH for this call setup any more. By Channel Release procedure it is released.
18. RF_CHANNEL_RELEASE_ACK.
Mobile Originated Call
The BTS acknowledges the Channel Release message.
Mobile Originated Call
6. EXTERNAL HANDOVER
Mobile Originated Call
BSC1 BTS 2 BTS 1 MSMSC
Handover Detect
HO Command ( FACCH )
HO Access ( FACCH )
Establish Indication
Physical Info ( FACCH )
SABME ( FACCH )
Handover Complete
Handover Complete ( FACCH )
UA ( FACCH )
Receiver Ready ( FACCH )
Measurement Report ( SACCH )Measurement Report/Result
Channel Activation
Channel Activation Ack.
DT1 ( HO Detection )
RF Channel Release
RF Channel Release Ack.
12
45
6
7
89
1011
13
1415
12
16
18
TCHRESERVATION ANDACTIVATION IN BSS2
HOMEASUREMENTSANDDECISION
DISCONNECTIONAND TCH RELEASEIN BSS1
BSC2
3
CC ( HO_Req.Ack )
CR ( HO_Request )
DT1 ( HO Required )
DT1
17
19DT1 ( HO Complete)20
Handover Command
2122
DT1 Clear Command
23
24DT1 ( Clear Complete)
Mobile Originated Call
1. MEASUREMENT_REPORT
When call is on, the MS sends measurement report concerning mainly the quality of the speech connection two times per second.
2. MEASUREMENT_REPORT/RESULT
Mobile Originated Call
If these measurement reports are preprocessed in the BTS then measurement results are sent towards the BSC. If the is no preprocessing in the BTS, then measurement reports are sent.
3. HO_REQUIRED
The BSC informs the MSC, that according to the measurement results, a handover is needed.
4. HO_REQUEST
Mobile Originated Call
The MSC sends a Handover Request message to the new BSC, which starts channel activation.
Mobile Originated Call
5. CHANNEL_ACTIVATION
The BSC sends a Channel Activation message to the BTS. After receiving Handover Request from the MSC, the BSC starts to search and allocate a TCH for this call on certain terms, the most important is of course which BTS and then the channel configuration of this BTS. Parameters: DTX control, channel ID & description & mobile allocation, maximum power levels of the MS and BS and finally, the first timing advance concerning this access calculated by the BSC.
6. CHANNEL_ACTIVATION_ACK.
Mobile Originated Call
A response to the Channel Activation message. When BTS has received this message it starts to send and receive TCH/SACCH. The reference used in this case is the power levels received in Channel Activation message.
7. HO_REQUEST_ACK
After channel activation the new BSC sends a Handover Request Acknowledge message to the MSC to indicate, that the channel activation procedure is executed.
8. HO_COMMAND
Mobile Originated Call
Handover Command message is sent from the MSC to the BSC to change the dedicated channel configuration and timing adjustment needeed.
9. HO_COMMAND
The BSC forwards the message via the BTS to the MS.
10. HO_ACCESS
The MS sends a Handover Access message in random mode to the new BTS.
Mobile Originated Call
11. HO_DETECT
The new BTS informs the BSC, that it has detected a handover access message.
12. HO_DETECTION
The new BSC sends a Handover Detection message to the MSC, which starts channel establishment procedure on the new BSS.
13. PHYSICAL_INFO
Mobile Originated Call
The Physical Information message contains various physical layer related information, allowing a proper transmission by the MS.
Mobile Originated Call
14. SABM (Set Asynchronous Balanced Mode)
This is Layer 2 message and contains some Layer 3 information. Content of this message: service request (look establishment cause!), ciphering key sequence, Mobile Station Classmark and Mobile Identity.
15. ESTABLISH_INDICATION
BTS acknowledges the Immediate Assignment Command by returning Establish Indication message. Establish indication -message has two uses. Firstly, when used in this phase it points out that from the BTS point of view,
Mobile Originated Call
the MS is now on the new TCH. Thus, the BTS sends information back to the BSC that the MS is now on this kind of TCH which description is like this etc. Also the BTS identifies the link = main signaling channel and adds received Layer 3 information into this message.
16. UA
UA is normal Layer 2 level acknowledgement when setting up the Layer 2 level link in LAPDm -protocol.
17. HO_COMPLETE
Mobile Originated Call
This message is sent by the MS to the network to indicate, that the MS has established the main signalling link successfully.
18. RR
The BTS sends a Receive Ready message to the MS.
19. HO_COMPLETE
Mobile Originated Call
The Handover Complete message is forwarded to the MSC. When the Handover Complete message is received, the network releases the old channels.
20. CLEAR_COMMAND
This message is coming from the MSC and releases the associated dedicated resources, i.e. BSSAP connection concerning this call.
21. RF_CHANNEL_RELEASE
Mobile Originated Call
When MS has informed the network it is in the TCH, there is no need to use the old TCH for this call setup any more. By Channel Release procedure it is released.
22. RF_CHANNEL_RELEASE_ACK.
The BTS acknowledges the Channel Release message.
Mobile Originated Call
23. CLEAR_COMPLETE
This is acknowledgement to the message SCCP Data (Clear Command). Now the BSC informs the MSC that all radio resources related to this call are released.
Mobile Originated Call