Hy Guys,
In this post i will tell you about Signaling System No. 7 [SS7]. I am not going to this post longer. I will give you short & informative knowledge in this post.
WHAT IS SS7 ?
SS7 is a global network infrastructure for cellular phones. Signaling System No. 7 (SS7) is a series of telephony signaling protocols. Also known as CCS7 (Common Channel Signaling System 7) or CCIS7 (Common Channel Interoffice Signaling 7).
SS7 History
In 1975, a series of protocols was developed to connect one cellular network to another cellular network to exchange information between calls and text messages, and this is called SS7.
WHY WE USE SS7 ?
š Routes calls and messages between different networks.
š (SMS) Short Messaging Service
š Information Exchange functions (Dial Tone, Call-Waiting Tone, Voice Mail, etc)
š Switching from one Cell Tower to another
š Prevents Call drops without the decrease in quality
š Allows users to roam on another when traveling in a different location
š Number Translation
š Local Number Portability
š Prepaid Billing
Signaling System No. 7 is a global standard for telecommunications defined by the International Telecommunication Union (ITU) Telecommunication Standardization Sector.
SS7 is used in as many as 800+ telecommunication companies around the world.
SS7 also Helps Banks in confirming the presence of their customer’s phone in a specific country to authorize their transactions and prevent fraudulent activities.
Short Explanation of SS7 Protocols:-
1.a Signaling Links
SS7 messages are exchanged between network elements over 56 or 64 kilobit per second (kbps) bidirectional channels called signaling links. Signaling occurs out-of-band on dedicated channels rather than in-band on voice channels. Compared to in-band signaling, out-of-band signaling provides:
š Faster call setup times (compared to in-band signaling using multi-frequency (MF)
signaling tones)
š More efficient use of voice circuits
š Support for Intelligent Network (IN) services, which require signaling to network
elements without voice trunks (e.g., database systems)
š Improved control over fraudulent network usage
1.b Singaling Points
Each signaling point in the SS7 network is uniquely identified by a numeric point code. Point codes are carried in signaling messages exchanged between signaling points to identify the source and destination of each message. Each signaling point uses a routing table to select the appropriate signaling path for each message.
There are three kinds of signaling points in the SS7 network.
SSP (Service Switching Point)
STP (Signal Transfer Point)
SCP (Service Control Point)
1.c Singaling Link Types
SS7 signaling links are characterized according to their use in the signaling network.
š A Link
š B Link
š C Link
š D Link
š E Link
š F Link
2. SS7 Protocol Stack
The hardware and software functions of the SS7 protocol are divided into functional abstractions called “levels.” These levels map loosely to the Open Systems Interconnect (OSI) 7-layer model defined by the International Standards Organization (ISO).
2.a Message Transfer Part
The Message Transfer Part (MTP) is divided into three levels.
The lowest level, MTP Level 1, is equivalent to the OSI Physical Layer.
MTP Level 2 ensures accurate end-to-end transmission of a message across a signaling link.
MTP Level 3 provides message routing between signaling points in the SS7 network.
2.b ISDN User Part (ISUP)
The ISDN User Part (ISUP) defines the protocol used to set-up, manage and release trunk circuits that carry voice 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. However, calls that originate and terminate at the same switch do not use ISUP signaling.
2.c Telephone User Part (TUP)
In some parts of the world, the Telephone User Part (TUP) is used to support basic call setup and tear-down. TUP handles analog circuits only. In many countries, ISUP has replaced TUP for call management.
2.d Signaling Connection Control Part (SCCP)
SCCP provides connectionless and connection-oriented network services and global title translation (GTT) capabilities above MTP Level 3. A global title is an address (e.g., a dialed 800 number, calling card number or mobile subscriber identification number) that is translated by SCCP into a destination point code and subsystem number. A subsystem number uniquely identifies an application at the destination signaling point. SCCP is used as the transport layer for TCAP-based services.
2.e Transaction Capabilities Applications Part (TCAP)
TCAP supports the exchange of non-circuit related data between applications across the SS7 network using the SCCP connectionless service. Queries and responses sent between SSPs and SCPs are carried in TCAP messages.
3. Message Transfer Part
The Message Transfer Part (MTP) is divided into three levels:
3.a MTP Level 1
The lowest level, MTP Level 1, is equivalent to the OSI Physical Layer. MTP Level 1 defines the physical, electrical and functional characteristics of the digital signaling link.
3.b MTP Level 2
MTP Level 2 ensures accurate end-to-end transmission of a message cross a signaling link. Level 2 implements flow control, message sequence validation and error checking. MTP Level 2 is equivalent to the OSI Data Link Layer.
3.c MTP Level 3
MTP Level 3 provides message routing between signaling points in the SS7 network. MTP Level 3 is equivalent in function to the OSI Network Layer. MTP Level 3 routes messages based on the routing label in the signaling information field (SIF) of message signal units.
3.d Signaling Link Selection (SLS)
The selection of outgoing link is based on information in the DPC and Signaling Link Selection field.
4. ISDN User Part
The ISDN User Part (ISUP) defines the protocol and procedures used to set-up, manage and release trunk circuits that carry voice and data calls over the public switched telephone network (PSTN). ISUP is used for both ISDN and non-ISDN calls. Calls that originate and terminate at the same switch do not use ISUP signaling.
5. Telephone User Part
In some parts of the world the Telephone User Part (TUP) supports basic call processing. TUP handles analog circuits only – digital circuits and data transmission capabilities are provided by the Data User Part.
6. Signaling Connection Control Part
SCCP provides connectionless and connection-oriented network services above MTP Level 3. While MTP Level 3 provides point codes to allow messages to be addressed to specific signaling points, SCCP provides subsystem numbers to allow messages to be addressed to specific applications (called subsystems) at these signaling points. SCCP is used as the transport layer for TCAP-based services such as free phone (800/888), calling card, and local number portability, wireless roaming and personal communications services (PCS).
7. Transaction Capabilities Application Part
TCAP enables the deployment of advanced intelligent network services by supporting non-circuit related information exchange between signaling points using the SCCP connectionless service. The SCP uses TCAP to return a response containing the routing number(s) (or an error or reject component) back to the SSP. Calling card calls are also validated using TCAP query and response messages. When a mobile subscriber roams into a new mobile switching center (MSC) area, the integrated visitor location register requests service profile information from the subscriber’s home location register (HLR) using mobile application part (MAP) information carried within TCAP messages. TCAP messages are contained within the SCCP portion of an MSU. A TCAP message is comprised of a transaction portion and a component portion.
In this post i will tell you about Signaling System No. 7 [SS7]. I am not going to this post longer. I will give you short & informative knowledge in this post.
SS7 is a global network infrastructure for cellular phones. Signaling System No. 7 (SS7) is a series of telephony signaling protocols. Also known as CCS7 (Common Channel Signaling System 7) or CCIS7 (Common Channel Interoffice Signaling 7).
In 1975, a series of protocols was developed to connect one cellular network to another cellular network to exchange information between calls and text messages, and this is called SS7.
š Routes calls and messages between different networks.
š (SMS) Short Messaging Service
š Information Exchange functions (Dial Tone, Call-Waiting Tone, Voice Mail, etc)
š Switching from one Cell Tower to another
š Prevents Call drops without the decrease in quality
š Allows users to roam on another when traveling in a different location
š Number Translation
š Local Number Portability
š Prepaid Billing
Signaling System No. 7 is a global standard for telecommunications defined by the International Telecommunication Union (ITU) Telecommunication Standardization Sector.
SS7 is used in as many as 800+ telecommunication companies around the world.
SS7 also Helps Banks in confirming the presence of their customer’s phone in a specific country to authorize their transactions and prevent fraudulent activities.
1.a Signaling Links
SS7 messages are exchanged between network elements over 56 or 64 kilobit per second (kbps) bidirectional channels called signaling links. Signaling occurs out-of-band on dedicated channels rather than in-band on voice channels. Compared to in-band signaling, out-of-band signaling provides:
š Faster call setup times (compared to in-band signaling using multi-frequency (MF)
signaling tones)
š More efficient use of voice circuits
š Support for Intelligent Network (IN) services, which require signaling to network
elements without voice trunks (e.g., database systems)
š Improved control over fraudulent network usage
1.b Singaling Points
Each signaling point in the SS7 network is uniquely identified by a numeric point code. Point codes are carried in signaling messages exchanged between signaling points to identify the source and destination of each message. Each signaling point uses a routing table to select the appropriate signaling path for each message.
There are three kinds of signaling points in the SS7 network.
SSP (Service Switching Point)
STP (Signal Transfer Point)
SCP (Service Control Point)
1.c Singaling Link Types
SS7 signaling links are characterized according to their use in the signaling network.
š A Link
š B Link
š C Link
š D Link
š E Link
š F Link
2. SS7 Protocol Stack
The hardware and software functions of the SS7 protocol are divided into functional abstractions called “levels.” These levels map loosely to the Open Systems Interconnect (OSI) 7-layer model defined by the International Standards Organization (ISO).
2.a Message Transfer Part
The Message Transfer Part (MTP) is divided into three levels.
The lowest level, MTP Level 1, is equivalent to the OSI Physical Layer.
MTP Level 2 ensures accurate end-to-end transmission of a message across a signaling link.
MTP Level 3 provides message routing between signaling points in the SS7 network.
2.b ISDN User Part (ISUP)
The ISDN User Part (ISUP) defines the protocol used to set-up, manage and release trunk circuits that carry voice 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. However, calls that originate and terminate at the same switch do not use ISUP signaling.
2.c Telephone User Part (TUP)
In some parts of the world, the Telephone User Part (TUP) is used to support basic call setup and tear-down. TUP handles analog circuits only. In many countries, ISUP has replaced TUP for call management.
2.d Signaling Connection Control Part (SCCP)
SCCP provides connectionless and connection-oriented network services and global title translation (GTT) capabilities above MTP Level 3. A global title is an address (e.g., a dialed 800 number, calling card number or mobile subscriber identification number) that is translated by SCCP into a destination point code and subsystem number. A subsystem number uniquely identifies an application at the destination signaling point. SCCP is used as the transport layer for TCAP-based services.
2.e Transaction Capabilities Applications Part (TCAP)
TCAP supports the exchange of non-circuit related data between applications across the SS7 network using the SCCP connectionless service. Queries and responses sent between SSPs and SCPs are carried in TCAP messages.
3. Message Transfer Part
The Message Transfer Part (MTP) is divided into three levels:
3.a MTP Level 1
The lowest level, MTP Level 1, is equivalent to the OSI Physical Layer. MTP Level 1 defines the physical, electrical and functional characteristics of the digital signaling link.
3.b MTP Level 2
MTP Level 2 ensures accurate end-to-end transmission of a message cross a signaling link. Level 2 implements flow control, message sequence validation and error checking. MTP Level 2 is equivalent to the OSI Data Link Layer.
3.c MTP Level 3
MTP Level 3 provides message routing between signaling points in the SS7 network. MTP Level 3 is equivalent in function to the OSI Network Layer. MTP Level 3 routes messages based on the routing label in the signaling information field (SIF) of message signal units.
3.d Signaling Link Selection (SLS)
The selection of outgoing link is based on information in the DPC and Signaling Link Selection field.
4. ISDN User Part
The ISDN User Part (ISUP) defines the protocol and procedures used to set-up, manage and release trunk circuits that carry voice and data calls over the public switched telephone network (PSTN). ISUP is used for both ISDN and non-ISDN calls. Calls that originate and terminate at the same switch do not use ISUP signaling.
5. Telephone User Part
In some parts of the world the Telephone User Part (TUP) supports basic call processing. TUP handles analog circuits only – digital circuits and data transmission capabilities are provided by the Data User Part.
6. Signaling Connection Control Part
SCCP provides connectionless and connection-oriented network services above MTP Level 3. While MTP Level 3 provides point codes to allow messages to be addressed to specific signaling points, SCCP provides subsystem numbers to allow messages to be addressed to specific applications (called subsystems) at these signaling points. SCCP is used as the transport layer for TCAP-based services such as free phone (800/888), calling card, and local number portability, wireless roaming and personal communications services (PCS).
7. Transaction Capabilities Application Part
TCAP enables the deployment of advanced intelligent network services by supporting non-circuit related information exchange between signaling points using the SCCP connectionless service. The SCP uses TCAP to return a response containing the routing number(s) (or an error or reject component) back to the SSP. Calling card calls are also validated using TCAP query and response messages. When a mobile subscriber roams into a new mobile switching center (MSC) area, the integrated visitor location register requests service profile information from the subscriber’s home location register (HLR) using mobile application part (MAP) information carried within TCAP messages. TCAP messages are contained within the SCCP portion of an MSU. A TCAP message is comprised of a transaction portion and a component portion.