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ISSUE
Fixed Network Curriculum
Development Section
OAA000008 Call Control Protocol --SS7
2.0
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2
Objective
SS7 system principle
Message transfer part (MTP) principle
ISDN user part (ISUP) message and
application
After this session, you will learn:
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References
Product Manual -- Technical Manual -- Signaling and
Protocols Chapter 5 SS7
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Contents
Section 1 MTP
Section 2 ISUP
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Signaling System No.7 (SS7)
Signaling is used for connection control, work
coordination and session between communication
devices
SS7 is formulated by CCITT and is widely applied inswitched circuit networks (e.g. PSTN).
SoftX3000 supports SS7 and implements interworking
with the existing switched circuit networks.
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SS7 Functional Structure in SoftX3000
MACMTP1
MTP2
MTP3
SCCP
TCAP
TUP
ISUP
M3UA
IP
INAP
User part
MessageTransfer Part
M2UASCTP
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SoftX3000 SS7 Functional Structure
SS7 has two parts:
User Part (UP)
Message Transfer Part (MTP).
MTP : enables reliable transfer of signaling messages
between user functions.
SS7 messages can be transmitted over
narrowband TDM transmission network (i.e. MTP),
over broadband IP network (the protocol used for transmitting SS7
over IP network is SIGTRAN.)
UP :
the independent user part of different users
it is the functional entity for various call services
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MTP
Overview, MTP1, MTP2
MTP3
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MTP - Overview
The main function
to provide reliable signaling message transfer in the
signaling network
Feature : has measures to avoid or reduce
message loss
repetition
loss of sequence
MTP consists of three function levels:
signaling data link (MTP1)
signaling link function (MTP2)
signaling network function (MTP3).
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MTP1
MTP1 definition:
Defining the physical, electric and functional characteristics
of signaling data link, as well as access methods.
Equivalent to the physical layer of OSI seven-layer protocol
structure, and used to generate and receive the signals
over physical channels
Signaling Data Link :
A bidirectional transmission channel for a signaling.
Composed of two-way data channels.
The standard bit-rate is 64kbit/s
which also can be applied to the transmission link with lower rate
(such as 4.8kbit/s) or that with higher rate (2048kbit/s)
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MTP2
MTP2 definition:
Having Signaling link function .
It is used to transmit signaling to data link, and cooperates with MTP1
to ensure reliable signaling link between two directly connected
signaling points.
Signaling link function can be sub-divided into
signaling unit delimitation
signaling unit location
error detection
error correction,
initial location
processor failure
level-two flow control
and signaling link error rate monitoring functions.
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MTP
Overview, MTP1, MTP2
MTP3
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MTP3
Definition : Network layer
It implements the functions of the third layer of OSI
used to transmit management messages to ensure reliable
transmission of signaling messages in case of faults in
signaling link or signaling transfer point
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Functions
Message
allocation
Signal message processing
Message
identificationMessage
routing
Out
In
Signal Traffic
management
Signal network management
Signal route
management
Signal link
management
Signal network functions
The fourth level The third-level MTP The second level
Test and maintenanceSignal message stream
Indication and control
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Signaling Message Processing
Message routing function:
To determine the outgoing signaling link for transmitting
messages to destination point
Message identification function:
To check whether the destination signaling point in
received message is a local office signaling point
Message allocation function:
To distribute received messages (sent to the point) to
corresponding UPs
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Signaling Network Management
Signaling service management:
To transfer signaling service from one link or route to one
or multiple different links or routes, reset MTP in a signaling
point or slow down the traffic in case of congestion
Signaling link management:
To recover faulty signaling link, activate idle (non-arranged)
links, and deactivate arranged signaling links.
Signaling route management:
To distribute the messages related to signaling network
status, block or unblock signaling routes
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Message Format
MTP has three basic signaling unit formats:
Message Signaling Unit (MSU)
To transmit messages of respective UPs, signaling network
management messages as well as signaling network test and
maintenance messages.)
Link Status Signaling Unit (LSSU)
LSSU provides the link status information to perform the connection
and recovery of signaling links
Fill-In Signaling Unit (FISU)
FISU is used to maintain normal operation of the signaling link and
implement fill-in function when no MSU or LSSU is transmitted over
the signaling link.
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Message Format
MSU F CK SIF SIO LI FIB FSN BIB BSN F
8 16 8N(N2) 8 2 6 1 7 1 7 8
Message signaling unit format
First transmitted bit
LSS U F CK SF LI FIB FSN BIB BSN F
8 16 816 2 6 1 7 1 7 8
Link status signaling unit format
First transmitted bit
FISU F CK LI FIB FSN BIB BSN F
8 16 2 6 1 7 1 7 8
Fill-in signal unit format
First transmitted bit
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Mandatory Part for MTP Processing
This part mainly includes the following fields:
flag (F)
forward sequence number (FSN)
forward indicator bit (FIB)
backward sequence number (BSN)
backward indicator bit (BIB)
length indicator (LI)
check bit (CK)
status field (SF)
service information octet (SIO).
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Mandatory Part for MTP Processing
Meanings of SF status indication:
SF CBA Indicator Indication Meaning
000 SIO Status indication
"O"
Loss of alignment
001 SIN Status indication
"N"
Normal alignment
010 SIE Status indication
"E"
Emergency
alignment
011 SIOS Status indication
"OS"
Break of Service,
100 SIOP Status indication
"OP"
Processor fault
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Mandatory Part for MTP Processing
Service Information Octet SIO
SISSF
MeaningDCBA
International
network message
Reserved
(International)
Domesticmessage
Reserved
(Domestic)
0 0 0 0
0 1 0 0
1 0 0 0
1 1 0 0
MeaningDCBA
Signaling network management message
Signaling network test and maintenance messages
Reserved
Signaling connection control part
Telephone user partISDN user part
Data user part
Reserved
0 0 0 0
0 0 0 1
0 0 1 0
0 0 1 1
0 1 0 00 1 0 1
0 1 1 0
0 1 1 1
1 0 0 0
1 1 1 1
F CKSIF SIO
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SIF to be Processed by UP
F CK SIF FIBLI FSNSIO BIB BSN
Management messages SLC OPC DPC
Type A: Signaling network
management message
Type B TUP message
Type C ISUP message
Type D SCCP message
Signaling messageCIC
OPC DPCSLS
Signaling message OPC DPCCIC SLC
F
SSCP subscriber data SLS OPC DPC
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Assignment of Signaling Network Management
Message Label Codes
MessageGroup
H1
H00000 0001 0010 0011 0100 0101 0110 0111 1000
0000
CHM 0001 COO COA CBD CBA
ECM 0010 ECO ECA
FCM 0011 RCT TFC
TFM 0100 TFP * TFR TFA *
RSM 0101 RST RSR
MIM 0110 LIN LUN LIA LUA LID LFU LLT LRT
TRM 0111 TRA
DLM 1000 DLC CSS CNS CNP
1001
UFC 1010 UPU
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Signaling procedure
Message routing
Changeover
Changeback
Signaling link activation
Signaling link recovery
Signaling link deactivation
Signaling route manager Transfer prohibited
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Contents
Section 1 MTP
Section 2 ISUP
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ISUP Signaling
Overview
Message structure
Call process
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ISUP - Overview
ISUP is one of UPs of Common Channel Signaling
System No.7.
It provides necessary signal functions for supporting
basic bearer services and supplementary services ofvoice and non-voice purposes in the Integrated Service
Digital Network (ISDN).
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Applications in SoftX3000
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Protocol Stack
MACMTP1
MTP2
MTP3
ISUP
M2UA
M3UA
IP
SCTP
User part
Message transfer part
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ISUP Signaling
Overview
Message structure
Call process
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Message Type Codes
Co
de
Abbre
viation
Meaning
0000
0001
IAM Initial address message: A message sent in the forward direction to
initiate occupancy of an outgoing circuit and to transmit number and
other information relating to the routing and handling of a call.
0000
0010
SAM Subsequent address message: A message that may be sent in the
forward direction following an initial address message, to convey
additional called number information.
0000
0011
INR Information request: A message sent by an exchange to request for
channel associated information of a call.
0000
0100
INF Information: A message sent to convey channel associated
information of a call, which may have been requested in an
information request message.
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Message Type Codes (Cont.)
Cod
e
Abbrevia
tion
Meaning
0000
0101
COT Continuity message: A message indicating whether or
not there is continuity on the preceding circuit as well
as of the selected circuit to the following exchange,including verification of the communication path
across the exchange with the specified degree of
reliability.
0000
0110
ACM Address complete message: A message indicating that
all the address signals required for routing the call to
the called party have been received.
0000
0111
CON Connect message: A message indicating that all the
address signals required for routing the call to the
called party have been received and that the call has
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Message Type Codes (Cont.)
Code Abbreviation Meaning
0000
1000
FOT Forward transfer: A message sent in the forward
direction on semi-automatic calls when the outgoing
international exchange operator wants the help of an
operator at the incoming international exchange. The
message will normally serve to bring an assistance
operator into the circuit if the call is automatically set
up at the exchange.When the call is completed via an
operator at the incoming international exchange, the
message should preferably cause this operator to be
recalled.
0000
1001
ANM Answer message: it indicates that the call has been
answered. In semi-automatic phone set, this message
has a supervisory function. In automatic phone set,
this message is used in conjunction with charging
information.
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Message Type Codes (Cont.)
Code Abbreviatio
n
Meaning
0000
1100
REL Release message: A message sent in either forward or
backward direction to indicate that the circuit is being
released due to the cause supplied and is ready to be put
into the idle state on receipt of the release complete message.
Where the call is to be redirected the message will also carry
the redirection number.
0000
1110
RES Resume message: A message sent in either direction
indicating that the calling or called party, after having been
suspended, is reconnected.
0001
0000
RLC Release complete message: A message sent in either
direction in response to the receipt of a release message, or
if appropriate, to a reset circuit message, when the circuit
concerned has been brought into the idle condition.
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Message Type Codes (Cont.)
Code Abbre
viation
Meaning
0001
0001
CCR Continuity check request message: A message sent by an
exchange for a circuit on which a continuity check is to be
performed, to the exchange at the other end of the circuit,
requesting for continuity checking equipment to be attached.
0001
0010
RSC Reset circuit message: A message sent to release a circuit, due
to memory failure or other causes.
0001
0011
BLO Blocking: A message sent only for maintenance purposes to the
exchange at the other end of a circuit, to cause an engaged
condition of that circuit for subsequent calls outgoing from that
exchange. When a circuit is used in the dual-circuit mode of
operation, an exchange receiving the blocking message must be
capable of accepting incoming calls on the concerned circuit
unless it has also sent a blocking message. Under certain
conditions, a blocking message is also a proper response to a
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Message Type Codes (Cont.)
Cod
e
Abbre
viatio
n
Meaning
0001
0101
BLA Blocking acknowledgement: A message sent in response
to a blocking message, indicating that the circuit has beenblocked.
0001
0111
GRS Circuit group reset: A message sent to release an identified
group of circuits.
00011000
CGB Circuit group blocking message: A message sent to theexchange at the other end, indicating the specified circuit
group has been blocked.
0001
1001
CGU Circuit group unblocking: A message sent to the exchange
at the other end of an identified group of circuits to cause
cancellation in that group of circuits of an engaged
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Message Type Codes (Cont.)
Code Abbre
viation
Meaning
0001
1010
CGBA Circuit Group Blocking Acknowledgement: A message
sent in response to a circuit group blocking message
to indicate that the requested group of circuits has
been blocked.
0001
1011
CGUA Circuit group unblocking acknowledgement: A
message sent in response to a circuit group
unblocking message to indicate that the requested
group of circuits has been unblocked.
0001
1111
FAR Facility request: A message sent from an exchange to
another exchange to request for activation of a facility.
0010
0000
FAA Facility accepted: A message sent in response to a
facility request message indicating that the requested
facility has been activated
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Message Type Codes (Cont.)
Code Abbre
viatio
n
Meaning
0010
0001
FRJ Facility rejected: A message sent in response to a facility request
message to indicate that the facility request has been rejected.
0010
0100
LPA Loop-back acknowledgement message: A message sent in the
backward direction in response to a continuity check request
message indicating that a loop (or transceiver in the case of a 2-
wire circuit) has been connected.
00101000
Handoffs
0010
1001
GRA Circuit group reset acknowledgement: A message sent in response
to a circuit group reset message and indicating that the requested
group of circuits has been reset.The message also indicates the
maintenance blocking state of each circuit.
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Message Type Codes (Cont.)
Code Abbreviation
Meaning
0010
1010
CQM Circuit group query message: A message sent on a
routine or demand basis to request the far-end exchange
to give the states of all circuits in a particular range.
0010
1011
CQR Circuit group query response: A message sent in
response to a circuit group query message to indicate
the states of all circuits in a particular range.
0010
1100
CPG Call progress: A message sent in either direction during
the set-up or active phase of the call, indicating that an
event, which is of significance, and should be relayed to
the originating or terminating access, has occurred.
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Message Type Codes (Cont.)
Code Abbre
viation
Meaning
0010
1111
CFN Confusion message: A message sent in response to
any message (other than a confusion message) if the
exchange does not recognize the message or detects
a part of the message as being unrecognized.
0011
0000
OLM Overload message: A message sent in the backward
direction, on non-priority calls in response to an IAM,
to invoke temporary trunk blocking of the circuit
concerned when the exchange generating the
message is subject to load control.
0011
0001
CRG Charging information: Information sent in either
direction for accounting and/or call charging purposes.
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Message Type Codes (Cont.)
Code Abbre
viation
Meaning
00110010 NRM Network resource management message: A
message sent in order to modify network
resources associated with a certain call.The
message is sent along an established path in
any direction in any phase of the call.
00110011 FAC Facility: The message is sent at any stage of
a call in the forward or backward direction to
request for an action at the peer end. This
message is used to carry the previous
request result, error or rejected information.
00110110 Identification request
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Message Type Codes (Cont.)
Code Abbre
viation
Meaning
00110111 Identification response
00111000 SGM Segmentation message: A message thatmay be sent in the forward direction
following an initial address message, to
convey additional called party number
information.
00011101 Reserved
00011100
00011110
00100111
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ISUP Signaling
Overview
Message structure
Call process
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Successful Call Setup
Calling PartyOriginationg
ExchangeTransit
Destination
ExchangeCalled Party
Setup IAMIAM
Setup
Address Complete
(no indication)
Address Complete
(no indication)
Alerting
Alerting
Call Progress
(Alerting)Call Progress
(Alerting)
ANM
ANMConnect
Connect Answered(off hook)
Dial
Ring
Ring
Connect Ack
Connect Ack
Speech or Data
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Successful Call Release (1)
Calling Party Originationg
ExchangeTransit Destination
ExchangeCalled Party
Disconnect
REL REL
RLC
Release
RLC
RLC
DisconnectOnHook
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Successful Call Release (2)
Calling Party OriginationgExchange
Transit DestinationExchange
Called Party
DisconnectREL REL
RELEASEDisconnectRLC
RLC
OnHook
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Summary
SS7 signaling includes two parts: Message Transfer Part
(MTP) and User Part (UP).
The MTP consists of MTP1, MTP2 and MTP3
ISUP is one of UPs of SS7. It provides necessary signalfunctions for supporting basic bearer services and
supplementary services of voice and non-voice purposes
in the integrated service digital network.
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