Explain SS7 Architecture ?

SS7 Architecture

SS7 Architecture consists of three different entities: 

1. SSP  (Service Switching Point)
2. STP (Signal Transfer Point)
3. SCP (Service Control Point)                                                                                                 

1.    1.) Service Switching Point (SSP)

The Service Switching Point (SSP) is the local exchange in the telephone network. An SSP can be a combination voice switch and SS7 switch, or an adjunct computer connected to the local exchange's voice switch. The SSP provides the functionality of communicating with the voice switch via the use of primitives and creating the packets, or signal units, needed for transmission in the SS7 network. The SSP function is to use the information provided by the calling party (such as dialed digits) and determine how to connect the call. A routing table will identify which trunk circuit to use to connect the call, and which exchange this trunk terminates at. An SS7 message must be sent to this adjacent exchange requesting a circuit connection on the specified trunk. There are very few features required of an SSP. The ability to send messages using the ISDN User Part (ISUP) protocol and the Transaction Capabilities Application Part (TCAP) protocol is the only requirement, other than the network management.

Summary:

• SSPs are switches in SS7 network.
• SSPs convert a dialed number from a subscriber line to SS7 signaling messages.
• SSPs setup, manage and release voice circuits required to make a call.
• SSPs send messages using the ISDN User Part (ISUP) and Transaction Capabilities Application Part (TCAP) protocols 
• SSP's function is to use a global title to determine how to connect a call using its   routing table.                                                                                                                                           

2.) Signal Transfer Point (STP)

STPs are packet switches, and act like routers in the SS7 network. Routes each incoming message to an outgoing signaling link, based on routing information contained in the SS7 messages and a pre-defined route table. It does not offer termination services. STPs are paired to ensure redundancy

There are three levels of STPs.

• ·        National Signal Transfer Point
• ·        International Signal Transfer Point
• ·        Gateway Signal Transfer Point

National STP exists within the national network

·        Protocol converters often interconnect a National and an International STP by converting from ANSI to ITU-TS.

International STP functions within an international network.

·        All nodes connecting to an International STP must use the ITU-TS protocol standard.

Gateway STP converts signaling data from one protocol to another.

·        Gateway STPs are often used as an access point to the international network.

·        Depending on its location, the Gateway STP must be able to use both the International and National protocol standards.

Summary:

•         An STP is a router and/or a gateway in the SS7 network.
•         Messages are not originated by an STP..
•         If an originating SSP does not know the address of a destination SSP, the STP must    provide it using Global Title Translation.
•         Gateway STPs serve as the interface into another network and they can provide protocol conversion.
•         STPs also provide traffic and usage measurements.

 3.) SCP (Service Control Point)

An SCP is usually a computer used as a front end to a database system. It is an interface to application-specific databases. The address of an SCP is a point code, and the address of the database it interfaces with is a subsystem number. The database is an application entity which is accessed via the TCAP protocol. It accepts a query for information from a subsystem at another node. SCP is used by STP to perform a function called global title translation