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SS7 Overview
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Session Number
Presentation_ID
ITP Course
ITP Product Team
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Section 1SS7 Overview
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Objectives
Upon completing this module, you will be
able to:
Understand the role of SS7 in Telephony Networks.
Have a High Level understanding of SS7 MTP, SCCP,ISUP and TCAP Protocol Layers.
Get an General Introduction to SS7 NetworkArchitecture
SCCP is also overed in another Section
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Agenda
SS7 Architecture
SS7 Protocol and Standards
MTP L1, 2, 3
ISUP
SCCP
TCAP
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Signaling System 7 (SS7)
An international standard Protocol to provide highlyreliable message transfer without duplication or loss
for sending messages:Between switches for basic call control and callrelated services
Between switches and databases for network
based services (e.g.,free numbers ,portability)SS7 uses a logically separate, common channelpacket switched network .
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SS7 is widely deployed worldwide in Public
Switched Telephone Networks Adopted by Mobile Operators, who are
extensively implementing value added servicesusing SS7
SS7 is emerging as the common thread to tietogether different transport networks forconvergence
Signaling System 7 (SS7) Contd
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Many SS7 Protocol Standards
SS7 was originally defined in the ITU (C7) :
1980 Yellow Book
1984 Red Book
1988 Blue Book
1992 White Book
ANSI standard for US was developed from the Blue Book
Bellcores version is based on the ANSI standard and hastoday become the standard in the US (with someexceptions)
GR-246-CORE, Bell Communications ResearchSpecifications of SS7.
China, Japan have their own flavors
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Signaling Concept
Switch to Switch
Channel Associated Signaling
SS7 (ISUP)
Switch to Database
SS7 (TCAP)
Subscriber to Switch
Dial PulseDTMF
ISDN
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Common Channel Signaling
SSP CCSSO
STP
Conversation
Signaling
Channel Associated Signaling
EO EO
Signaling
Conversation
EO - End Office
STP - Signaling Transfer
Point
CCSSO - Common Channel
Signaling Switching office
SSP - Service Switching Poi
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Signaling - Call Setup
Switch SS7 Switch
off hook
dial tone
digits IAM IAM setupalertingACMACMring tone
off hookANMANMCONNECT
CONN ACK
DISCONN REL REL DISCONN
RELEASERLCRLCRELEASE
REL ACK
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SS7 versus - OSI Model
7 Application
3 Network
2 Data Link
1 Physical
ISUPTUP
NUP
MAP
TCAP
INAP
TCAP
SCCP
MTP
OMAP
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SS7 Network Hierarchy
Voice Trunks
Signaling Links
AINSCP
SCP1Region X Region Y
STP STP
SSP
SCP1
STP STP
CCSSO
STP - Signal Transfer Point
SSP - Service Switching Point
SCP - Service Control Point
AIN - Advanced Intelligent Network
CCSSO - Common Channel Signaling Switching Office
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F
The SS7 Terminology
Tandem
Switch
Tandem
Switch
CO
Switch
SEP
SSP = Service Switching Point
CO
Switch
SSP
STP
STP
SCP
SSPSSP
SCP SCP SCP
F
A A A A A A A A
C
B B B
A A A A
E
SCP = Service Control Point
STP = Signal Transfer Point
F
EE
STP
STP
C
STP
STP
C
BBSTP
STP
C
B
D D D
SEP = Signaling End Point
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Signaling Links
CCS Network Elements are connected with dedicated 64Kbpsdigital, bidirectional transmission facilities. Links areEngineered at 40% of capacity and use diverse routes.
Type of links:
Access Links (A-links)
Bridge Links (B-links)
Cross Links (C-links)
Diagonal Links (D-links)
Extended Links (E-links)
Fully Associated Links (F-links)
Links that combined any two nodes are referred as being in a linkset.The size of any linkset can range from one to sixteen links. Eachlink is defined by its Signaling Link Code (SLC)
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Signaling Links (Continued)
Associated - the signal links run directly in parallel with thebearer links. All connections are point-to-point, therefore routing
is not required.
Non-associated - there is a separate logical path for the signaland bearer links. Signal links generally go through multipleSTPs to get to their final destination.
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A
Linksets
F
SLC=0
SLC=1
SLC=0SLC=1
Combined
Linkset
SS7 Linksets & Link Codes
C
SLC=0
SLC=1
Linkset
STP
STP
SSP
SSP
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Signaling Transfer Point (STP)
STPs are the heart of the CCS network. High speed,ultra-reliable special purpose packet switch forsignaling message in the SS7 network.
They are responsible for routing messages.Messages can be routed in one of two ways:
Information within the message (SCCP/GTT)
Information within tables at the STP (MTP3 routing)
STPs are deployed as geographically separate matedpairs for reliability and optimally loaded for 40%capacity for dependability.
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ITU Signaling Point Code
Network ID (NID)
0--7(3bits)Cluster ID (CID)
0 -- 255(8bits)Member ID (MID)
0 7(3bits)
All CCS network elements are assigned a unique number
called a Point Code.ITU Point Codes are 14 bits, shown as decimal or 3-8-3 format
ANSI Point Codes are 24 bits, shown as 8-8-8 Format
Network ID are assigned by PTT- Authority
(ANCR,Offtel,IBTT,etc..) on demand .The same entity
from which the E164number ranges comes !!!
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MTP3-STP Message Routing
SS7 Link SS7 LinkSTP
IncomingMessages
OutgoingMessages
DPC
DPC X-Y-Z - Take Route 1
DPC A-B-C - Take Route 2
DPC is my own - Go to Global Title Translation Table
Routing Tables
DPC - Destination
Point Code
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MTP
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SS7 Protocol Stack
ISDN User
Part (ISUP)TCAP
INAPMAP
Non-Circuit Applications
SCCP
MTP
Enhanced addressing,
Connectionless/connection oriented services
Level 1
Level 2
Level 3
Null Presentation, Session, Transport
Application
MAPMobile Application Part
TCAP - Transaction Capabilities Application Part
ISUP - Integrated Services Digital Network User Part
Circuit-Related
Services
OSI Reference Model
Network
Message Discrimination/Distribution/Routing,
Network Management
Network
Data LinkLinkSU Delimitation/Alignment, Error detection/Correction,
retransmission, SUERM, Alignment, Flow Control
PhysicalData Link Link connection, bit rate, voltages
DTAP
SCCP - Signaling Connection Control Part
MTP - Message Transfer Part
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Protocol - Network Elements
ISUPTCAP
SCCP
MTP
Null
MTP L3
MTPL2
MTPL1
STP
SSP
SCCP
MTP
MTP L3
MTPL2
MTPL1
SCCP
MTP
MTP L3
MTPL2
MTPL1
SCCP
MTP
MTP L3
MTPL2
MTPL1
SCCP
MTP
MTP L3
MTPL2
MTPL1
ISUP
SCCP
MTP
MTP L3
MTPL2
MTPL1
TCAP
SCCP
MTP
Null
MTP L3
MTPL2
MTPL1
STP
SCP
STPSTP
CCSSO
STP
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MTP Level 1
There are two data channels in every link used for full duplextransmission. Common interface types are:
- V.35(USA)
-A single 64/56K channel (DS0) in a E1/T1 (DS1) interface
-The specification for MTP L1 can be found in recomandationITU-T Q702
- High-speed links
- IP links
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MTP Level 1
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 17 18 19 20 21 22 23 24 25 26 27 28 29 30 310
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 2324
SignalingFraming
E1
T1
16
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MTP 2
Signaling Unit delimitation
Error detection & correction
Initial Alignment
Flow Control
Signaling link Error monitoring
Level 2 provides reliable transfer of signaling
messages between two directly connectedpoints.
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MTP 2 (Signaling Unit Types)
MSU - Transfer user information
LSSU - Report change of linkstate
FISU - Filler when no other SU to
send
3 Types of Signaling Units
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LSSU
LSSULSSU
MSUMSU
MSU MSUFISU
FISU FISU
MTPL2 - SS7 Signal Units
Message Signal Unit (MSU) - used to transmit user data fromSCCP layer, ISUP layer, or Network Management.
Retransmitted if received in error
Link Status Signal Unit (LSSU) - used to carry link status
information between the two ends of a signaling link. LSSUs
are used to restore a failed link, handle receive congestion, and
communicate processor outage information to the far end
Fill-In Signal Unit (FISU) - transmitted when there are not any
MSUs or LSSUs. Used to maintain link integrity.
6 - 279 bytes per SU
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Message Formats
FLAG BSN/BIB FSN/FIB Length Status
FLAG BSN/BIB FSN/FIB Length CheckSvc Info Sig Info
Fill-in Signal Unit
Link Status Signal Unit
Message Signal Unit
1-2 bytes
8-272 bytes
BSN/BIBBBackward Sequence Number/Backward Indicator Bit
FSN/FIBForward Sequence Number/Forward Indicator Bit
LengthNumber of Octets Between Itself and the Check Sum
Svc InfoIs Used to Indicate the Type of Signaling Message that Follows
FLAG BSN/BIB FSN/FIB Length Check
Check
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MTPL2 Data
Flag = 0 1 1 1 1 1 1 0
0 0
PriorityN/I
Length Indicator
BIB
FIB
BSN
FSN
Service Indicator
Signaling
Information
Field
Check
Bits
MTPL2
Data
MTPL2
Data
Order of transmission
Sequence Numbers and Indicator Bits - used to
acknowledge the receipt of an MSU. Indicator
bits are used to indicate that an MSU was received
in error or has been retransmitted
The Length Indicator implies the type of signal
unit being transmitted:
If LI = 0 FISU
If LI = 1 or 2 LSSUIf LI > 2 MSU
Service Information Octet defines the message
priority, national or international indicator, and
the service indicator. The service indicator indicates
the upper level user who sent this information
The Signaling Information Field contains the user
data. This includes the following protocol layers:
TCAP, ISUP, SCCP, MTPL3
SIO
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MTPL2MSU - Service Information Octet
The SIO contains 3 fields:
Network Indicator- this says whether the messageconforms to National (2) or International (0) standards
Priority(only USA)- All MSUs are assigned one of fourpriorities (0-3) with 3 being the highest. Only usedduring congestion (0-2 can be discarded)
Service Indicator Code (SIC)- Upper level user
0 - Information and status message 2 - Messages related to call in progress
1 - Messages related to establishing a call 3 - Network Management messages
0 - MTP Network Management 2 - Link Testing & Maintenance 5 - ISUP
1 - Link Testing & Maintenance 3 - SCCP (TCAP, MAP, AIN)
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Leaky Bucket - Link Failure
A leaky bucket algorithm is used to fail a
signaling link.
1. When the signaling link is placed in service the bucket is
empty.
2. When a bad message is received (based on CRC), atoken is added to the bucket
3. When 256 messages are received (good or bad), a tokenis removed from the bucket
4. When the number of tokens in the bucket is equaled to 64the link is failed.
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MTP 2 (LSSU)
SIOS - Out of Service
SIO - Out of Alignment
SIN - Normal Alignment
SIE - Emergency Alignment
SIPO - Process Outage
SIB - Busy (Level 2 Congestion)
Status Field Indicators
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MTP 2 (Link Alignment)
T2 Start
T2 Stop
SIO
SIO
Not Aligned
T3 Start
T3 Stop
SIN or SIE
Aligned
SIN or SIE
SIOS
Start Link Proving PeriodT4 Start
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MTP 3
Level 3 is responsible for the reliable transfer of
messages between SS7 network nodes.
The Signaling Network functions fall into two
major categories
Signaling Message Handling
Signaling Network Management
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MTP 3 (Routing Label)
MSU
SIF Field
SIO
Routing Label
SIF
User Specific Information
Signaling Link
Selector
Origination Point
Code
Destination Point
CodeRouting Label
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MTP Level 3 - Routing Label
4 octets field right after the SIO
It is made of:
Destination Point Code (DPC) - Identifies the node that the
MSU is bound for. Not necessarily the ultimate destination ornext node-14 bits
Originating Point Code (OPC) - Identifies the node that theMSU came from. Not necessarily the originator or previousnode14 bits.
Signaling Link Selection (SLS) - Used to select a link andlinkset so that traffic is evenly distributed- 4 bits
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STP STP
STP STP
A
B
C
D
E
F
Load Sharing
LS 1
LS 0
LS 1
LS 0
LS 1
LS 0
1. Node A assigns a unique 4 bit SLS code XXXX
2. Node A uses the Bit number3(03) (LSB) to do the decision on link selection
0->LS0 and 1->LS1 .The bit used for selection is configurable at each node.
3 Node B and C will need to have make the decision on other bit (bit 2) to conserve
the load sharing
SLSXXXX
SLSXXX1
SLS -SLSXXX0 SLSXX00
SLSXX10
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Routesets
3-3-21-1-31-1-2
1-1-1
3-3-0
2-2-1
2-2-0
Alias 2-2-2
1 2 3 4
5
6
7
1-1-0
Point Code Linkset Cost
1-1-1 LS1 00
LS5 01
1-1-2 LS2 00
LS5 011-1-3 LS3 00
LS5 01
3-3-2 LS4 00
LS5 01
3-3-0 LS5 00
2-2-0 LS6 00
LS5 012-2-1 LS7 00
LS5 01
2-2-2 LS6 00
LS7 00
LS5 01
Once a destination is known to an STP
routing tables are consulted to determine the
least cost route to get there.
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MTP 3 (SNM)
Signaling Network Management
Signaling Traffic Management
Signaling Link Management
Signaling Route Management
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MTPL3 - Network Management
Traffic Management
Slows or diverts traffic from or to an affected link or route
Link Management
Activates, deactivates or restores signaling links in response tofailures or changes in link status
Route Management
Distribute information about signaling network status
Congestion Control (only used in USA)
Control traffic based on message priority
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MTP 3 (SNM)
Signaling Traffic Management
Changeover
Changeback
Forced Rerouting
Controlled Rerouting
Management Inhibiting
Signaling traffic flow control
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Traffic Management
Slows or diverts traffic from or to an affected link or route
Forced Rerouting - done when signaling route becomesunavailable. Procedure involves diverting traffic from one link
set to another one. Result of TFP(Transfer Prohibited).Controlled Rerouting - used to divert traffic to a more efficient
route. Result of TFR (Transfer Restricted).
MTP Restart - used to avoid flooding node when it is goingthrough a restart. UsesTRW (Traffic Restart Waiting) and
TRA(Transfer Allowed)
Management Inhibiting - allows maintenance personnel toprevent MSUs from being transmitted on a link
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Link Management
Activates, deactivates or restores signaling links in response tofailures or changes in link status
Signaling Link Activation - once a link is aligned and haspassed the link test, it is considered activated and ready tocarry traffic
Signaling Link Changeover - diverts traffic from anunavailable link to one or more link without message loss,
mis-sequencing or duplication. COO(Change Over Order) issent and COA(Change Over Acknowledgement) is returned.
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Link Management (Cont)
Activates, deactivates or restores signaling links in response tofailures or changes in link status
Signaling Link Changeback - diverts traffic back to originallink. CBD ( Change Back Declaration) is sent and CBA(Change Back Acknowledge) is returned.
Signaling Link Tests - done after initial alignment, periodicallybetween 2 nodes (30-90sec). SLTM (Signaling Link Test
Message) is sent and SLTA (Signaling Link TestAcknowledge) is returned.
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Signaling Route Management
Transfer Restricted (TFR)
Transfer Prohibited (TFP)
Transfer Allowed (TFA)
Signaling Routeset Test (RST)
Transfer Controlled (TFC)
Signaling Routeset Congestion Test (RCT)
Route Management
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Route Management(cont)
Distributes information about signaling network status
Transfer-Restricted (TFR) - Notify a node to avoid sending messages tothe indicated PC through the STP that sent TFR
Transfer-Prohibited(TFP) - Notify a node that an adjacent STP is unableto route to a specific signaling point in network
Transfer-Allowed (TFA) - Notify a node that a signaling point is nowavailable through the STP that sent TFA
Signaling-Route-Set-Test (RST) - Sent in response to a restricted or
prohibited message (every 30 seconds)
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Link Failure and Restoral
STP1 STP2
SSP1 SSP2
SCP1 SCP2
Sequence of Level 3 events
for Out of service link andrestoral
1. Link goes Status Indicator Out
of Service (SIOS)
SLC=1
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STP1 STP2
SSP1 SSP2
SCP1 SCP2
Sequence of Level 3 eventsfor Out of service link and
restoral
1. Link goes Status Indicator Out
of Service (SIOS)
2. Change Over Order (COO) sent from
STP1 to SSP2 via STP2 with SLC=1
SLC=1
COO
COO
Link Failure and Restoral
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STP1 STP2
SSP1 SSP2
SCP1 SCP2
Sequence of Level 3 events
for Out of service link and
restoral
1. Link goes Status Indicator Out
of Service (SIOS)
2. Change Over Order (COO) sent from
STP1 to SSP2 via STP2 with SLC=1
3. Change Over Acknowledge (COA) sentfrom SSP2 to STP1 via STP2 with SLC=1
SLC=1
COA
COA
Link Failure and Restoral
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STP1 STP2
SSP1 SSP2
SCP1 SCP2
Sequence of Level 3 events
for Out of service link andrestoral
1. Link goes Status Indicator Out
of Service (SIOS)
2. Change Over Order (COO) sent from
STP1 to SSP2 via STP2 with SLC=1
3. Change Over Acknowledge (COA) sent
from SSP2 to STP1 via STP2 with SLC=1
4. Transfer Restricted (TFR) sent for SSP2
to all signaling point connected to STP1
SLC=1
TFR
TFR
TFR
TFR
Link Failure and Restoral
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STP1 STP2
SSP1 SSP2
SCP1 SCP2
Sequence of Level 3 events
for Out of service link andrestoral
1. Link goes Status Indicator Out
of Service (SIOS)
2. Change Over Order (COO) sent from
STP1 to SSP2 via STP2 with SLC=1
3. Change Over Acknowledge (COA) sent
from SSP2 to STP1 via STP2 with SLC=1
4. Transfer Restricted (TFR) sent for SSP2
to all signaling point connected to STP1
5. Transfer Prohibited (TFP) sent by STP1
to STP2
SLC=1
TFP
Link Failure and Restoral
i i
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STP1 STP2
SSP1 SSP2
SCP1 SCP2
Sequence of Level 3 events
for Out of service link andrestoral
1. Link goes Status Indicator Out
of Service (SIOS)
2. Change Over Order (COO) sent from
STP1 to SSP2 via STP2 with SLC=1
3. Change Over Acknowledge (COA) sentfrom SSP2 to STP1 via STP2 with SLC=1
4. Transfer Restricted (TFR) sent for SSP2
to all signaling point connected to STP1
5. Transfer Prohibited (TFP) sent by STP1
to STP2
6. Route Set Test Restricted (RSR) sent for
destination SSP2 to all signaling point to
STP1 every 30 seconds
SLC=1
RSR
RSR
RSR
RSR
Link Failure and Restoral
Li k F il d R l
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STP1 STP2
SSP1 SSP2
SCP1 SCP2
Sequence of Level 3 events
for Out of service link and
restoral
1. Link goes Status Indicator Out
of Service (SIOS)
2. Change Over Order (COO) sent from
STP1 to SSP2 via STP2 with SLC=1
3. Change Over Acknowledge (COA) sentfrom SSP2 to STP1 via STP2 with SLC=1
4. Transfer Restricted (TFR) sent for SSP2
to all signaling point connected to STP1
5. Transfer Prohibited (TFP) sent by STP1
to STP2
6. Route Set Test Restricted (RSR) sent for
destination SSP2 to all signaling point toSTP1 every 30 seconds
7. Link 1 is restored and aligned
8. Change Back Declaration (CBD) send
by STP1 and SSP2SLC=1
CBD CBD
Link Failure and Restoral
Li k F il d R l
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STP1 STP2
SSP1 SSP2
SCP1 SCP2
Sequence of Level 3 eventsfor Out of service link and
restoral
1. Link goes Status Indicator Out
of Service (SIOS)
2. Change Over Order (COO) sent from
STP1 to SSP2 via STP2 with SLC=1
3. Change Over Acknowledge (COA) sentfrom SSP2 to STP1 via STP2 with SLC=1
4. Transfer Restricted (TFR) sent for SSP2
to all signaling point connected to STP1
5. Transfer Prohibited (TFP) sent by STP1
to STP2
6. Route Set Test Restricted (RSR) sent for
destination SSP2 to all signaling point to
STP1 every 30 seconds7. Link 1 is restored and aligned
8. Change Back Declaration (CBD) send
by STP1 and SSP2
9. Change Back Acknowledge (CBA) sent
by STP1 and SSP2SLC=1
CBA
CBA
Link Failure and Restoral
Li k F il d R t l
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STP1 STP2
SSP1 SSP2
SCP1 SCP2
Sequence of Level 3 events
for Out of service link andrestoral
1. Link goes Status Indicator Out
of Service (SIOS)
2. Change Over Order (COO) sent from
STP1 to SSP2 via STP2 with SLC=1
3. Change Over Acknowledge (COA) sent
from SSP2 to STP1 via STP2 with SLC=14. Transfer Restricted (TFR) sent for SSP2
to all signaling point connected to STP1
5. Transfer Prohibited (TFP) sent by STP1
to STP2
6. Route Set Test Restricted (RSR) sent for
destination SSP2 to all signaling point to
STP1 every 30 seconds
7. Link 1 is restored and aligned8. Change Back Declaration (CBD) send
by STP1 and SSP2
9. Change Back Acknowledge (CBA) sent
by STP1 and SSP2
10. TFA sent by STP1 to all signaling
points. RSR test suspended
SLC=1
TFA
TFA TFA
TFA
Link Failure and Restoral
3 (S )
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Signaling Link Management
Signaling link activation,
restoration and deactivation
Link set activation
Automatic allocation of STs and
data links
MTP 3 (SNM)
MTP 3 (SNM)
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Link Inhibiting
Link Inhibit (LIN)
Link Inhibit Ack (LIA)Link Uninhibit (LUN)
Link Uninhibit Ack (LUA)
Link Force Uninhibit (LFU)
Link Local Inhibit Test (LLI)
Link Remote Inhibit Test (LRI)
MTP 3 (SNM)
MTP 3 (SNM)
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S.S.P.
S.T.P.
S.S.P.
S.T.P.
Link Inhibit
LIN
LIA
MTP 3 (SNM)
MTP 3 (SNM)
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S.S.P.
S.T.P.
S.S.P.
S.T.P.
Link Uninhibit
LUN
LUA
MTP 3 (SNM)
MTP 3 (SNM)
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S.S.P.
S.T.P.
S.S.P.
S.T.P.
Routing
ControlledUninhibiting
LUN
(2)LUA
(3)
LFU(1)
MTP 3 (SNM)
MTP 3 (SNM)
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Network Congestion
Transmit Buffer Congestion (L3)
3 Congestion Level Thresholds
Handled by TFC,RCT messages
Receive Buffer Congestion (L2)
Congested/Not Congested (no levels)
Handled by SIB LSSU
MTP 3 (SNM)
MTP 3 (SNM)
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S.S.P.
B
S.T.P.
S.S.P.
A
S.T.P.
Routeset
Congestion (L3)
MSU(B)
Priority 1
TFC(B)
Priority 2
Congestion
Level 2
MTP 3 (SNM)
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ISUPCall Controll
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ISDN User Part (ISUP)
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ISDN User Part (ISUP)
The ISDN User Part (ISUP) defines the protocol used toset-up, manage, and release trunk circuits that carryvoice and data between terminating line exchanges (e.g.,between a calling party and a called party).
ISUP is used for both ISDN and non-ISDN calls.
Calls that originate and terminate at the same switch do
not use ISUP signaling. The specification for ISUP can be found in ITU-T
recomandations Q761-Q764
ISUP M F t
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MSU
SIF Field
SIO
Routing Label
SIF
ISUP Message
Optional
Part CIC
Message
Type
Mandatory
Variable Part
Mandatory Fixed
Part
ISUP Message Format
Basic Tr nk Signaling
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Basic Trunk Signaling
Call Processing
Software
MTP L1, L2, L3
ISUP
Call Processing
Software
MTP L1, L2, L3
ISUP
MTP L1, L2, L3
STP
LEC Switch IXC Switch
Voice Trunk
A-LinkA-Link
ISUP Message Format
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ISUP Message Format
Pointer to Variable Parameter 1
Pointer to Variable Parameter n
Pointer to Start of Optional Parameter
Length of Variable Parameter 1
Variable Parameter 1
Length of Variable Parameter n
Variable Parameter n
Name of Optional Parameter m
Length of Optional Parameter m
Optional Parameter m
Name of Optional Parameter 1
Length of Optional Parameter 1
Optional Parameter 1
End of Optional Parameter
Routing Label
Trunk Circuit Identification Code (2)
Message Type
Mandatory Parameter 1
Mandatory Variable Parameters
Optional Parameters
MTP
MTP
ISUP
Data
Mandatory Parameter p
ISUP (Si l C ll)
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ISUP (Simple Call)
OriginateIAM
ACM
ANM
Speech
Ringback Ring
SpeechREL
Onhook
RLC
Sending an Initial Address Message
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Sending an Initial Address Message
STP STP
SSP 1 SSP 2
IAM
1. SSP 1Connects via D-link
SSP 1 Originated
SSP 1 will set a time (TIAM20-30 seconds)
and wait for a response
2. SSP 2SSP will identify and busy the incoming trunk
Translate the dialed digits
(check the status of the called partys line)
Encode and transmit an Address Complete Message (ACM)
If a Continuity Check is to be done on the trunk, the ACM is delayed
SS7 Voice Trunk
Initial Address Message Format
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SIODPC - OPC - SLS
Circuit Identification Code
Message Type (IAM)
Nature of Connection Indicators
Forward Call Indicators
Calling party's Category
Pointer to User Service Info
Pointer to Called Party Number
Length Indicator Called Party Number
Pointer to Optional Part
Length Indicator USI
User Service Information
Called Party Number
Routing Label
Mandatory Fixed Part
Mandatory VariablePart
End of Opt Parms
Opt Parms
Initial Address Message Format
Initial Address Message
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Initial Address Message
Parameter Type Length
Message Type
Nature of Connection Indicators
Forward Call Indicators
Calling Partys Category
User Service Information
Called Party Number
Calling Party Number
Charge Number
Originating Line Information
Transit Network Selection
Carrier SelectionService Code
Carrier Identification
Original Called Number
Redirecting Number
Redirection Number
F
F
F
F
V
V
O
O
O
O
OO
O
O
O
O
1
1
1
2
4
4
2-11
6-12
3-9
33
3
5
5
6-9
6-9
Nature of Connection Indicators - Contains satellite
indicator, continuity check indicator
Forward Call Indicators - Information concerning
the type of signaling used to this point (interworking
or all SS7), and end to end transfer options
Calling Partys Category- information concerningthe service category (ordinary/test) of the calling
party
User Service Information - describes the nature of
the communication (i.e., voice, data, etc.)
Called Party Number - contains address information
for the calls destination
Sending an Address Complete Message
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STP STP
SSP 1 SSP 2
IAM
SS7 Voice Trunk
Sending an Address Complete Message
ACM
4. Local Exchange will stop timer TIAM20-30
3. SSP SSP sends the ACM in the backwards direction to indicate to the
originating switch that all of the routing information required to
complete the call has been received
Address Complete Message
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Address Complete Message
Optional Backward Call IndicatorsCause Indicators O
O5-6
Parameter Type Length
Message Type
Backward Call Indicators F
F
2
1
3
Backward Call Indicator - information consisting of the charge indicator, called partys status, interworking
indicator
Optional Backward Call Indicator - information of relevance to the originating exchange or calling party and
consisting of the in-band information indicator and call forwarding may occur indicator
Cause Indicators - information consisting of coding standard, location (international network, local private
network, ), cause value (no route to destination, subscriber absent, ), and diagnostics.
Sending an Answer Message
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STP STP
SSP 1 SSP 2SS7 Voice Trunk
Sending an Answer Message
IAM
ACM
6. SSP 1SSP 1 will begin any required billing
on receipt of an ANM.
Conversation begins
5. SSP 2When called subscriber answers SSP 2 sends and answer message ANM .
ANM
Answer Message
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Parameter Type Length
Message Type
Backward Call Indicators O
F
2
1
Answer Message
Backward Call Indicator - information consisting of the charge indicator, called partys status, interworking
indicator
Release (REL) and Release Complete (RLC)
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SSP 1 SSP 2
STP STP
SS7 Voice Trunk
Release (REL) and Release Complete (RLC)
1 or 2. SSP 1 or 2A REL message can be sent in either direction
to indicate that the specified circuit (CIC) is being
released from the connection. The circuit is
released before the REL is sent but it not idleduntil a RLC is received
2 or 1. SSP 1 or 2The RLC is sent in response to an REL to confirm that the indicated circuit has been
placed in an idle state. The switch sets a guard timer (0.5 to 1 second). It will not seize
that circuit until the guard timer expires.
IAM
ACM
ANM
RELRLC
ISUP (REL Message Format)
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ISUP (REL Message Format)
SIO
DPC - OPC - SLS
Circuit Identification Code
Message Type (REL)
Pointer to Cause Indicators
Pointer to Optional Part
Length Indicator for Cause Indication
Cause Indicators
First Opt Parameter Name
Length Ind. Last Optional Parm
Length Ind. 1st Optional Parm
1st Optional Parm
Last Optional Parameter Name
Last Optional Parm
Routing Label
Optional Part
Mandatory VariablePart
End of Opt Parms
Release and Release Complete Messages
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Parameter Type Length
Message Type
Cause Indicators V
F
3-4
1
Release and Release Complete Messages
Release (REL)
Parameter Type Length
Message Type F 1
Release Complete (RLC)
Other messages, like the Reset Circuit (RSC) can also trigger an RLC
Cause Indicators - information consisting of coding standard, location (international network, local private
network, ), cause value (no route to destination, subscriber absent, ), and diagnostics.
Sending a Continuity Check (COT)
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Sending a Continuity Check (COT)
STP STP
SSP 1 SSP 2
COT
1. SSP 1The Nature of Connections Indicators in the IAM
indicates whether a Continuity check is to be
performed on this circuit, or if a Continuity check
is being performed on some previous circuit
2. SSP 2SSP 2 will not send an ACM until it has an indication that either:
No Continuity checks are being done, or
Any and all Continuity checks are successful.
SS7 Voice Trunk
IAM
COT - a test used to verify that an SS7 bearer circuit is functioning correctly
it generally involves a combination of tone generation, tone detection, and
loopback circuitry to verify physical continuity of a circuit
Continuity Message
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Parameter Type Length
Message Type
Continuity Indicators F
F
1
1
Continuity Message
Continuity check indicators - the value of the parameter is continuity check failed
or continuity check successful
Subscriber Busy
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SSP 1 SSP 2
STP STP
SS7 Voice Trunk
Subscriber Busy
2. SSP 1The SSP will release the outgoing trunk, send an
RLC to the distant end
1. SSP 2Upon receiving an IAM the called partys line is checked for its busy/idle status.
In the event that the called partys line is busy, a busy signal is returned to the
calling party. The busy signal can be played from the terminating, intermediate, or
originating switch
The SSP releases the trunk that was indicated in the IAM. It sends a REL with a
cause indicator of subscriber busy
IAM
REL
RLC
Release Message
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Parameter Type Length
Message Type
Cause Indicators V
F
3-4
1
Release Message
Diagnostic (if any)
8
1
ext
0/1
ext
Coding Standard Spare General
Location
Cause Value
(class) (value in class)
1234567
Cause Indicators - information consisting of coding standard, location (international network, local private
network, ), cause value (no route to destination, subscriber absent, ), and diagnostics.
Trunk Release Procedure
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SSP 1 SSP 2
STP STP
SS7 Voice Trunk
Trunk Release Procedure
1. SSPA REL has been sent, the SSP expects an RLC as a confirmation from the far end.
The trunk is maintained in a software busy until an RLC is received.To guard against possibility of a lost RLC, 2 timers are started when the REL is sent.
These are the TREL(4-6 seconds) and the TREL, 1(1minute).
If timer TREL,1 expired before an RLC is received, the trunk will be removed from
service and maintenance will be notified.
An RSC is sent to the far end at one minute intervals until an RLC is received, or
maintenance intervenes.
REL
RSC
REL
REL
Glare
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Glare
STP STP
SSP SSP
IAM
Two-way trunks are subject to occasional simultaneous seizures at both ends.
This is called dual-seizure or glare.
Switches have a glare bit in memory for each two-way trunk. The purpose of
the glare bit is to determine which switch is in control and which switch must
yield. Agreements between network operators need to be in place to determine
control offices
SS7 Voice Trunk
IAM
ISUP Call Set-up Example
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Setup
Call Proceeding
Transit Exchange Destination ExchangeOriginating Exchange
SU Ca Set up a p e
ISUP Call Set-up Example
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Setup
Call Proceeding
Transit Exchange Destination ExchangeOriginating Exchange
IAM1IAM2
Setup
p p
ISUP Call Set-up Example
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Setup
Call Proceeding
Transit Exchange Destination ExchangeOriginating Exchange
IAM1IAM2
Setup
Call Proceeding
AlertingConnectACM1
ANM1ACM1
ANM1
Connect
Alerting
End to End Connection
p p
ISUP Call Set-up Example
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p p
Setup
Call Proceeding
Transit Exchange Destination ExchangeOriginating Exchange
IAM1IAM2
Setup
Call Proceeding
Alerting
ConnectACM1
ANM1ACM1
ANM1
Connect
Alerting
End to End Connection
DisconnectREL2
REL1Disconnect
RLC2RLC1
RELREL
RLC RLC
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SCCP
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SCCP
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SCCP provides routing and management
functions to subsystem instances.
Connectionless Services
Connection-oriented Services
SCCP (Connectionless Services)
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SCCP(Connectionless Services)
Connection Class 0 & 1
Unitdata (UDT)
Unitdata Service (UDTS)
Signaling Connection ControlPart (SCCP)
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Part (SCCP)
The primary function is to support the transfer of TCAPand OMAP data between network nodes. It also
performs:Connectionless Transfer of Data - Class 0 and 1
Specialized Routing Functions - Global TitleTranslation (GTT)
Subsystem Management - record status of all primaryand secondary SCPs
SCCP Routing
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E800 TCAP CLASS TCAPACCS TCAP AIN TCAP
SCCP
MTP
Routes with Point Code
Routes with
SubsystemNumbers
Specialized Routing
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p g
SSPSTP STP
GTT Changes DPC
GTT Could change other MTP/SCCP Values
GTT Does not change Calling Party Address or TCAP
DPC is the STP where GTT will be done
Service Indicator is a Value of 3 (SCCP)
SCCP Routing Detail
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Global TitleIndicatorRtgIndicator Point CodeindicatorNatl'/Int'lIndicator SSNIndicator
CDPA & CGPA Address Indicator
SCCP Routing Example
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S.T.P. AS.S.P. A S.C.P. A
S.T.P. B
Destination Point Code =2-2-2Route on GT
Destination Point Code = 3-3-3
SSN = 254
Route on PC/SSN
E800(254)
Global TitleTranslations performed
at STP
1-1-1 2-2-1
2-2-0
3-3-3
Alias
2-2-2
SCCP Management
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SCCP Management
Messages
Subsystem Allowed (SSA)
Subsystem Prohibited(SSP)
Subsystem Status Test (SST)
Subsystem Out of Service Request (SOR)
Subsystem Out of Service Grant (SOG)
Subsystem Backup Routing (SBR)
Subsystem Normal Routing (SNR)
Subsystem Routing Status Test (SRT)
SCCP Management
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S.T.P.
S.T.P.
S.C.P.
ACCS
PVN
E800
CLAS
AIN
S.C.P.
1. SSP(E800)
2. SST(E800)
SCCP Management
SCCP Data
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MTP Level 3 Data
Options/Protocol Class
SCCP Message Type
SCCP
Data
MTP Level 3 Data
Routing Label
Pointers
Called Party Address
Calling Party Address
Length of Data
Optional SCCP Parameters
SIFSCCP
Data
Message Type - There are 4 types
UnitDaTa (UDT)
UnitDaTa Service (UDTS)eXtended UnitDaTa (XUDT)
eXtended UnitDaTa Service (XUDTS)
The UDTS and XUDTS are options to return
messages on error. XUDTS is similar to UDT
but allow for optional SCCP parameters.
Protocol Class - indicates the type of informationtransfer that is being requested:
Protocol Class 0 - connectionless service without
need for sequencing
Protocol Class 1 - connectionless service with
sequencing
Protocol Class 2,3,4 - associated with connection
oriented service
CdPA - contains information about the destination
node and the database or application for which
the message is destined
CgPA - contains information about the node that
originated the transaction
Options: The only available option is to return the
message on error
Routing Indicator
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MTP Link Level DataRouting Label
SCCP Message Type
Options/Protocol Class
Pointers
Called Party Address
Calling Party Address
Length of Data
SIF
MTP Link Level Data
Length Indicator
Address Type
ABCDEFGH
0
1
Route on DPC in routing
label and SSN in CdPA
Route on Global Title
Bit G of the Address Type is the Routing
Indicator (RI). If the RI is set to zero,
routing is based on the Global Titledigits. If the RI is set to one, routing is
based on the DPC in the routing label
and the SSN in the CdPA field.
Global Title Translations (GTTs)
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Global Title Translations allow for easy management of the network and flexibility in routing.
Routing changes can be done at the STP pair, eliminating the need for knowing network
addresses and applications at each network elements (SSPs).
Global Title
316285-316287
316288-316292
316230-316239
3162599
PPC - 1-1-5
SPC - 1-1-6PPC-1-2-0
SPC-1-2-1
2-1-0
0-50-5
0-50-1
Point Code SSN
6
6
6
6
6
6
6
RI
D
D
D
D
G
PPC - Primary Point Code
SPC - Secondary Point Code
RI - Routing Indicator
D - Route on DPC/SSN
G - Route on Global Title
The application requesting GTT will indicate
to the STP what table (Translation Table) to
go to.
The STP will go to the proper table and index
the global title digits. Within that 6 or 10
digit number (or range) will be the routing
information required to send this message
on its way.
316240-316249
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TCAP
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TCAP (Message Format)
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MSU
SIF Field
SIO
Routing Label
SIF
SCCP
Parameter
Info Package Type
Transaction
InfoOperation Info Component Info
TCAP
TCAP Message Format
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TCAP messages consist of two parts
Transaction portion
Component portion
TCAP (Component Types)
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Invoke (Last/Not Last)
Return Result (Last/Not Last)
Return Error
Reject
Transaction CapabilitiesApplication Part (TCAP)
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Application Part (TCAP)
TCAP is an application level of the protocol Documents describing TCAP are specific to a
particular service. TCAP follows guidelinesthat can be found in ITU-Q771-Q775, and
Recommendation T1.114.1-5 (ANSI) All TCAP messages consist of 2 portions:
Transaction Portion - contains protocol controlinformation
Component portion - contains protocol controlinformation and data concerning the particularapplication
TCAP (Messaging)
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( g g)
Node A Node B
Response
Simple Query
Query with
Permission
Node B
Response
ConversationQuery with
Permission
Node A
Conversation with
Permission
Conversation withPermission
TCAP Transaction Portion
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MTP
MTP
SCCP
Transaction
Portion
Component
Portion
TCAP Package Type
Total Length
Transaction ID Identifier
Transaction ID Length
Transaction ID
Component Sequence Identifier
Component Sequence Length
Package type - spells out what type of dialogue will
exist between these 2 applications. There are 6 types:
Unidirectional - One way, no reply expectedQuery With Permission - Sent from originating
application. Will not send more than one message for
transaction. Terminating application has permission
to terminate
Query Without Permission - Sent from originating
application. Will send more messages for transaction.
Response With Permission - Sent by terminating
application In response to Query with or without
Permission
Response Without Permission - Sent by terminating
application In response to Query with or without
Permission
Abort - Defined for use if protocol errors are
received
Transaction ID - Application use this unique
random number to correlate messages within
same transaction.
TCAP Component Portion
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MTP
MTPSCCP
Transaction
Portion
Component
Portion Component Type IdentifierComponent Length
Component ID Identifier
Component ID Length
Component IdsOperation Code Identifier
Operation Code Length
Operation Code
Parameter Set Identifier
Parameter Set Length
Parameters
800 Service - Query
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STPSSP
GTT STP800 SCP
DPC = STP Alias
OCP = SSP
SCCP
CdPA
Route on GT
TT = 254SSN = 0
GTA = 800234
CgPA
Route on Destination
SSN = 254
SPC = SSP
TCAP
Query with Permission
Invoke
8002341111
ANI
LATA
OST
MTP
DPC = 800 SCP
OCP = STP
SCCP
CdPA
Route on Destination
TT = 254SSN = 254
GTA = 800234
CgPA
Route on Destination
SSN = 254
SPC = SSP
TCAP
Query with Permission
Invoke
8002341111
ANI
LATA
OST
MTP
800 Service - Response
5/26/2018 SS7 Overview
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112112112 2001, Cisco Systems, Inc. All rights reserved.Presentation_ID
STPSSP
GTT
800 SCP
DPC = SSP
OCP = SCP
SCCP
CdPA
Route on Destination
SSN = 254
CgPA
Route on Destination
SSN = 254
TCAP
Response
Invoke
Carrier ID
Routing Number
AMA Call type
MTP
DPC = 800 SCP
OCP = STP
SCCP
CdPA
Route on Destination
SSN = 254
CgPA
Route on Destination
SSN = 254
TCAP
Response
Invoke
Carrier ID
Routing Number
AMA Call type
MTP
No GTTs are
necessary
5/26/2018 SS7 Overview
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End Section
Thank You
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