Signaling System 7
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Signaling System 7
Signaling System 7
Signaling system 7 (SS7) is a common-channel signaling standard developed in late 1970s by the ITU-T, formerly know as CCITT (Consultative Committee for International Telegraph and Telephone).
SS7 was derived from SS6. SS7 functionally include
Data base queries. Transaction. Network Operation. ISDN
Signaling System 7
SS7 Network Elements and Links.
SS7 Protocols Suite and Messages.
SS7 Examples and Call flow.
SS7 Network Architecture
SS7 contain three signaling elements.
Service Switching Point (SSP)
Signal Transfer Point
(STP)
Service Control Point
(SCP)
SS7 Network Architecture STP
STP
SCP
SCP
STP
SSP
STP
SSP
Service Switching Point
SSPs are end office or tandem switches that connect voice circuits and perform the necessary signaling function to originate and terminate calls.
Service Switching Point
The SSP uses the dialed number to complete the call.
It is an 800,888,900 or local number portability exchange (or is ported NXX).
In the latter case, a query is send to an SCP requesting the routing information (number) necessary to complete the call.
Service Switching Point
The following steps explain SSP uses to complete call
The SSP uses the called number from the calling party to routing number from the database query to begin circuit connection signaling message. Then the SSP user its routing table to determine the trunk group and circuit needed to connect the call. At this point, a signaling setup message is send to the destination SSP requesting a connection on the circuit specified by the originating SSP. The destination SSP responds with an acknowledgement.
Signal Transfer Protocol
The STP routes all the signaling message in the SS7 network based on.
Routing information Destination point code address
The STP looks at the global title dialed digits and through its own translator table to resolve the following
The point code address of the appropriate SCP for database. The subsystem number of the database
Signal Transfer Protocol
It also perform an intermediate global title translation by using its translation table to find another STP The intermediate STP then route the message to the other STP to perform the final global title translation.
STP Hierarchy
STP implementation can occur in multiple levels, such as
Local Signal Transfer Point Regional Signal Transfer Point National Signaling Transfer Point International Signaling Transfer Point Gateway Signaling Transfer Point
STP Hierarchy
Local, Regional, and national STPs transfer standards-based SS7 message within the same network
There STPs usually are not capable of converting or handling messages in different format or version.
International STPs provide international connectivity where the same ITU-T standards are deployed in both networks.
STP Hierarchy
Gateway STPs can provide the following
Protocol conversion from the national version to the ITU-T standard Network to network interconnection points Net work security features.
Service Control Protocol
The SCP provide access to the database for additional routing information used in call processing. SCP is the key element for delivering IN applications on the telephony network. The SCP provide the conversion between SS7 and X.25 protocols.
Service Control Protocol
The following databases are most common in the SS7 network
800 Database Line Information Database (LIDB) Home Location Register (HLR) Visitor Location Register (VLR)
Signaling Links
All signaling points in the SS7 network are connected by signaling links.
The signaling links are typically 56and 64-Kbps data network.
Signaling Modes
The SS7 has three mode of signaling
Associated Signaling
Nonassociated Signaling
Quasi-Associated Signaling
Associated Signaling
Signaling and voice path are directly connected between to signaling end points. Associated Signaling is common in Europe, where the signaling path is actually derived within the E1 trunk facilities.
Associated Signaling
S i g n a l i n g P a th SSP
SSP V o i c e P a th
Nonassociated Signaling
It uses a separate logical path for signaling and voice. The signaling message travel through multiple endpoints before reaching the final destination It is the most common form of signaling in SS7 network
NonAssociated Signaling STP
SSP
Signaling Path
Voice Path
STP
SSP
Quasi-Associated Signaling
Uses a separate logical path for signaling through the minimal number of transfer point to reach the final destination. Network delay is minimum. It is more costly them the Nonassociated method.
Quasi-Associated Signaling
SSP
th Pa
Si gn a
lin
g
g lin na ig S
Pa th
STP
Voice Path
SSP
Signaling Links and Linksets B -Links
S TP Lin A-
ALin k
ks
n ks A -Li
inks
ks
E-L
STP
S CP
A - L in
SSP
B-Links
S TP
s
C -Links
B -Links
C -Links
S CP
STP
F-Links
SS P
Signaling Links and Linksets
A Links
Interaction between signaling end points (SSPs or SCPs) and STPs. The STP routes the A-link message received from the originating SCP Or SSP towards the destination.
Bridge Links (B-links)
Interaction between the mated pair of STPs
There mated STPs are peers operating at the same time hierarchical level and are interconnected through a quad of B-links.
B-links carry signaling message from the original to the intended destination
Signaling Links and Linksets
Cross Links (C-Links)
Interconnects a STP with its mate. C-links are use only when failure or congestion occurs. Under normal conditions, these links carry only management traffic.
Diagonal Links (D-links)
Interconnects mated STP pairs of one hierarchical level to meted STP pairs of another hierarchical level.
Diagonal Links STP
D-Links
STP
STP
SCP
SCP
STP
D-Links
STP
STP
Other Network SSP
SSP
Signaling Links and Linksets
Extended Links (E-links)
Interconnects SSP to an alternate STP More reliable
F-links
Used to directly interconnect two signaling end point. There links are used when STPs are not available or high traffic volume exits.
SS7 Protocol Stack OSI Model
Signaling Point Function
SS7 Level
Layer 7 Layer 6
TCAP
Layer 5 Layer 4 Layer 3 Layer 2 Layer 1
ISUP
TUP
Layer 4
SCCP MTP L3 MTP L2 MTP L1
Layer 3 Layer 2 Layer 1
SS7 Protocol Stack
MTP
ISUP
Telephone User Part
TCAP
ISDN User Part
TUP
Message Transfer Part
Transaction Capabilities Application Part
SCCP
Signaling Connection and Control Part
ISUP (ISDN User Part)
This user part is used to setup and tear down circuits for calls in PSTN. ISUP has replaced TUP (Telephone User Part). ISUP was designed to be compatible with ISDN signaling.
SCCP
SCCP is the Signaling Connection and Control Part
SCCP is used primarily to access databases in the entire network
Segmentation & Reassembly of TCAP messages. (TCAP provides transport capabilities to application entities) End to end addressing
SCCP
SCCP provides services on the top of MTP3 The combination of those two layers are the network service part. Topically uses SCCP to access database SCCP routing services enable the STP to perform global title translation using OPC subsection number
CIC (Circuit identification code)
Identifies the circuit being setup or reject for example.
IAM ACM ANM
TCAP
TCAP is the Transaction Capabilities Application Part
TCAP provides a protocol to enable transactions with a database and to invoke remote operations on a switch e.g. Call Back on Busy. All IN server access relies on TCAP. Example 800/900 call.
Access database
TCAP
TCAP uses SCCP and MTP protocols to route message end to end Different from ISUP, which pass message switch to switch. Two portions Transaction (begin or query) Component portions (error or reject)
Physical Layer – MTP L1
The physical layer (L1) of the MTP defines the physical and electrical characteristics of the signaling link. Also called MTP1, this SS7 protocol layer is virtually identical to OSI L1. Some possible MTP1 networks are.
T1, DS-0, E1, 56/64 Kbps and V.35
Data Layer – MTP L2
The data layer (L2) of the SS7 protocol is MTP L2, also called MTP2. The MTP2 protocol is used to create reliable point-to-point links between endpoint in the network MTP2 does not run across the network, therefore it is not connected with the final destination of the message.
Data Layer – MTP L2
MTP2 has the following mechanisms
Error detection and correction. Sequence of packet Link status indicator
Data Layer – MTP L2
Three type signal units provide MTP2 data layer function
Fill-in Signal Unit (FISU)
Link Status Signal Unit (LSSU)
Provide link error detection in SS7 network Provides link status on the link between two directly connected signaling element.
Message Signal Unit (MSU) • Provides the structure to carry the information massage in the SS7 network
Network Layer – MTP3
The MTP3 protocol routes SS7 messages and relies on the delivery of the message from MTP2. The MTP# protocol is divided in to two main function
Signaling message handling (SMH)
Route SS7 message during normal condition.
SNM – reroute link traffic duration network failure condition.
Application Services Elements ASE
TCAP
SCCP
MTP
Application Service Element
Basic Call Setup and Teardown Example STP1
SSP1
STP2
1
IAM
2
ACM
4
REL
3
ANM
5
RLC
1 IAM 4
REL
Voice Trunk
2
ACM
3
ANM
5
RLC
SSP2
Example
Organizing call
Collecting info
Analyzing info
Selecting route state
800 Database Query Example 800 STP2 SCP
SSP1
3
Response (End)
2
Query (Begin)
3
Response (End)
1
Query (Begin) STP1
Call Simulation (1) SS7 Network STP STP
STP
STP
IAM3
IAM2 IAM1
SP SP SP
SP
PSTN Switches Network
Call Simulation (2) SS7 Network STP STP
STP
STP
ACM1 ACM2 ACM3
SP SP
SP SP
PSTN Switches Network
Call Simulation (3) SS7 Network STP STP
STP
STP
ANM1 ANM2 ANM3
SP SP SP
SP
PSTN Switches Network
Call Simulation (4) SS7 Network STP STP
STP
STP
REL2
REL2
REL1
SP SP
SP SP
PSTN Switches Network
Call Simulation (5) SS7 Network STP STP
STP
STP
REL2
REL2
REL1
SP SP
SP SP
PSTN Switches Network
Call Simulation (6) SS7 Network STP STP
STP STP
RLC1 SP SP SP SP
PSTN Switches Network
Call Simulation (7) SS7 Network STP STP
STP STP
RLC2 SP SP SP SP
PSTN Switches Network
Call Simulation (8) SS7 Network STP STP
STP
STP
RLC3
SP SP SP
SP
PSTN Switches Network
Call Simulation (9) SS7 Network STP STP
STP STP
SP SP SP SP
PSTN Switches Network
Signaling System 7
Signaling system 7 (SS7) is a common-channel signaling standard developed in late 1970s by the ITU-T, formerly know as CCITT (Consultative Committee for International Telegraph and Telephone).
SS7 was derived from SS6. SS7 functionally include
Data base queries. Transaction. Network Operation. ISDN
Signaling System 7
SS7 Network Elements and Links.
SS7 Protocols Suite and Messages.
SS7 Examples and Call flow.
SS7 Network Architecture
SS7 contain three signaling elements.
Service Switching Point (SSP)
Signal Transfer Point
(STP)
Service Control Point
(SCP)
SS7 Network Architecture STP
STP
SCP
SCP
STP
SSP
STP
SSP
Service Switching Point
SSPs are end office or tandem switches that connect voice circuits and perform the necessary signaling function to originate and terminate calls.
Service Switching Point
The SSP uses the dialed number to complete the call.
It is an 800,888,900 or local number portability exchange (or is ported NXX).
In the latter case, a query is send to an SCP requesting the routing information (number) necessary to complete the call.
Service Switching Point
The following steps explain SSP uses to complete call
The SSP uses the called number from the calling party to routing number from the database query to begin circuit connection signaling message. Then the SSP user its routing table to determine the trunk group and circuit needed to connect the call. At this point, a signaling setup message is send to the destination SSP requesting a connection on the circuit specified by the originating SSP. The destination SSP responds with an acknowledgement.
Signal Transfer Protocol
The STP routes all the signaling message in the SS7 network based on.
Routing information Destination point code address
The STP looks at the global title dialed digits and through its own translator table to resolve the following
The point code address of the appropriate SCP for database. The subsystem number of the database
Signal Transfer Protocol
It also perform an intermediate global title translation by using its translation table to find another STP The intermediate STP then route the message to the other STP to perform the final global title translation.
STP Hierarchy
STP implementation can occur in multiple levels, such as
Local Signal Transfer Point Regional Signal Transfer Point National Signaling Transfer Point International Signaling Transfer Point Gateway Signaling Transfer Point
STP Hierarchy
Local, Regional, and national STPs transfer standards-based SS7 message within the same network
There STPs usually are not capable of converting or handling messages in different format or version.
International STPs provide international connectivity where the same ITU-T standards are deployed in both networks.
STP Hierarchy
Gateway STPs can provide the following
Protocol conversion from the national version to the ITU-T standard Network to network interconnection points Net work security features.
Service Control Protocol
The SCP provide access to the database for additional routing information used in call processing. SCP is the key element for delivering IN applications on the telephony network. The SCP provide the conversion between SS7 and X.25 protocols.
Service Control Protocol
The following databases are most common in the SS7 network
800 Database Line Information Database (LIDB) Home Location Register (HLR) Visitor Location Register (VLR)
Signaling Links
All signaling points in the SS7 network are connected by signaling links.
The signaling links are typically 56and 64-Kbps data network.
Signaling Modes
The SS7 has three mode of signaling
Associated Signaling
Nonassociated Signaling
Quasi-Associated Signaling
Associated Signaling
Signaling and voice path are directly connected between to signaling end points. Associated Signaling is common in Europe, where the signaling path is actually derived within the E1 trunk facilities.
Associated Signaling
S i g n a l i n g P a th SSP
SSP V o i c e P a th
Nonassociated Signaling
It uses a separate logical path for signaling and voice. The signaling message travel through multiple endpoints before reaching the final destination It is the most common form of signaling in SS7 network
NonAssociated Signaling STP
SSP
Signaling Path
Voice Path
STP
SSP
Quasi-Associated Signaling
Uses a separate logical path for signaling through the minimal number of transfer point to reach the final destination. Network delay is minimum. It is more costly them the Nonassociated method.
Quasi-Associated Signaling
SSP
th Pa
Si gn a
lin
g
g lin na ig S
Pa th
STP
Voice Path
SSP
Signaling Links and Linksets B -Links
S TP Lin A-
ALin k
ks
n ks A -Li
inks
ks
E-L
STP
S CP
A - L in
SSP
B-Links
S TP
s
C -Links
B -Links
C -Links
S CP
STP
F-Links
SS P
Signaling Links and Linksets
A Links
Interaction between signaling end points (SSPs or SCPs) and STPs. The STP routes the A-link message received from the originating SCP Or SSP towards the destination.
Bridge Links (B-links)
Interaction between the mated pair of STPs
There mated STPs are peers operating at the same time hierarchical level and are interconnected through a quad of B-links.
B-links carry signaling message from the original to the intended destination
Signaling Links and Linksets
Cross Links (C-Links)
Interconnects a STP with its mate. C-links are use only when failure or congestion occurs. Under normal conditions, these links carry only management traffic.
Diagonal Links (D-links)
Interconnects mated STP pairs of one hierarchical level to meted STP pairs of another hierarchical level.
Diagonal Links STP
D-Links
STP
STP
SCP
SCP
STP
D-Links
STP
STP
Other Network SSP
SSP
Signaling Links and Linksets
Extended Links (E-links)
Interconnects SSP to an alternate STP More reliable
F-links
Used to directly interconnect two signaling end point. There links are used when STPs are not available or high traffic volume exits.
SS7 Protocol Stack OSI Model
Signaling Point Function
SS7 Level
Layer 7 Layer 6
TCAP
Layer 5 Layer 4 Layer 3 Layer 2 Layer 1
ISUP
TUP
Layer 4
SCCP MTP L3 MTP L2 MTP L1
Layer 3 Layer 2 Layer 1
SS7 Protocol Stack
MTP
ISUP
Telephone User Part
TCAP
ISDN User Part
TUP
Message Transfer Part
Transaction Capabilities Application Part
SCCP
Signaling Connection and Control Part
ISUP (ISDN User Part)
This user part is used to setup and tear down circuits for calls in PSTN. ISUP has replaced TUP (Telephone User Part). ISUP was designed to be compatible with ISDN signaling.
SCCP
SCCP is the Signaling Connection and Control Part
SCCP is used primarily to access databases in the entire network
Segmentation & Reassembly of TCAP messages. (TCAP provides transport capabilities to application entities) End to end addressing
SCCP
SCCP provides services on the top of MTP3 The combination of those two layers are the network service part. Topically uses SCCP to access database SCCP routing services enable the STP to perform global title translation using OPC subsection number
CIC (Circuit identification code)
Identifies the circuit being setup or reject for example.
IAM ACM ANM
TCAP
TCAP is the Transaction Capabilities Application Part
TCAP provides a protocol to enable transactions with a database and to invoke remote operations on a switch e.g. Call Back on Busy. All IN server access relies on TCAP. Example 800/900 call.
Access database
TCAP
TCAP uses SCCP and MTP protocols to route message end to end Different from ISUP, which pass message switch to switch. Two portions Transaction (begin or query) Component portions (error or reject)
Physical Layer – MTP L1
The physical layer (L1) of the MTP defines the physical and electrical characteristics of the signaling link. Also called MTP1, this SS7 protocol layer is virtually identical to OSI L1. Some possible MTP1 networks are.
T1, DS-0, E1, 56/64 Kbps and V.35
Data Layer – MTP L2
The data layer (L2) of the SS7 protocol is MTP L2, also called MTP2. The MTP2 protocol is used to create reliable point-to-point links between endpoint in the network MTP2 does not run across the network, therefore it is not connected with the final destination of the message.
Data Layer – MTP L2
MTP2 has the following mechanisms
Error detection and correction. Sequence of packet Link status indicator
Data Layer – MTP L2
Three type signal units provide MTP2 data layer function
Fill-in Signal Unit (FISU)
Link Status Signal Unit (LSSU)
Provide link error detection in SS7 network Provides link status on the link between two directly connected signaling element.
Message Signal Unit (MSU) • Provides the structure to carry the information massage in the SS7 network
Network Layer – MTP3
The MTP3 protocol routes SS7 messages and relies on the delivery of the message from MTP2. The MTP# protocol is divided in to two main function
Signaling message handling (SMH)
Route SS7 message during normal condition.
SNM – reroute link traffic duration network failure condition.
Application Services Elements ASE
TCAP
SCCP
MTP
Application Service Element
Basic Call Setup and Teardown Example STP1
SSP1
STP2
1
IAM
2
ACM
4
REL
3
ANM
5
RLC
1 IAM 4
REL
Voice Trunk
2
ACM
3
ANM
5
RLC
SSP2
Example
Organizing call
Collecting info
Analyzing info
Selecting route state
800 Database Query Example 800 STP2 SCP
SSP1
3
Response (End)
2
Query (Begin)
3
Response (End)
1
Query (Begin) STP1
Call Simulation (1) SS7 Network STP STP
STP
STP
IAM3
IAM2 IAM1
SP SP SP
SP
PSTN Switches Network
Call Simulation (2) SS7 Network STP STP
STP
STP
ACM1 ACM2 ACM3
SP SP
SP SP
PSTN Switches Network
Call Simulation (3) SS7 Network STP STP
STP
STP
ANM1 ANM2 ANM3
SP SP SP
SP
PSTN Switches Network
Call Simulation (4) SS7 Network STP STP
STP
STP
REL2
REL2
REL1
SP SP
SP SP
PSTN Switches Network
Call Simulation (5) SS7 Network STP STP
STP
STP
REL2
REL2
REL1
SP SP
SP SP
PSTN Switches Network
Call Simulation (6) SS7 Network STP STP
STP STP
RLC1 SP SP SP SP
PSTN Switches Network
Call Simulation (7) SS7 Network STP STP
STP STP
RLC2 SP SP SP SP
PSTN Switches Network
Call Simulation (8) SS7 Network STP STP
STP
STP
RLC3
SP SP SP
SP
PSTN Switches Network
Call Simulation (9) SS7 Network STP STP
STP STP
SP SP SP SP
PSTN Switches Network
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