What is SS7 ?

SS7 (Common Channel Signaling System No. 7/Short Signalling 7/Signalling System Number 7/ C7)


1.) SS7 Definition
2.) SS7 Functionality 
2.) SS7 Architecture
3.) SS7 Link Interface
4.) SS7 Signalling Protocols


1.) SS7 Definition :  
Signalling System Number 7 (SS#7 or C7) is the protocol used by the telephone companies for interoffice signalling. SS7 is a critical component of modern telecommunications systems. SS7 is a communications protocol that provides signaling and control for various network services and capabilities. Every call in every network is dependent on SS7. Likewise, every mobile phone user is dependent on SS7 to allow inter-network roaming. SS7 is also the "glue" that sticks together circuit switched (traditional) networks with Internet protocol based networks.


2.) SS7 Functionality:

The SS7 network and protocol are used for:

• basic call setup, management, and tear down
• wireless services such as personal communications services (PCS), wireless roaming, and mobile subscriber authentication
• local number portability (LNP)
• toll-free (800/888) and toll (900) wireline services
• enhanced call features such as call forwarding, calling party name/number display, and three-way calling
• efficient and secure worldwide telecommunication

3.) SS7 Architecture:

There are three kinds of signaling points in the SS7 network as shown 

• SSP  (Service Switching Point)
• STP (Signal Transfer Point)
• SCP (Service Control Point)

4.) SS7 Link Interface

• Access Link (A Link) 
• Bridge Link (B Link) 
• Cross Link (C Link) 
• Diagonal Link (D Link) 
• Extended Link (E Link) 
• Fully Associated Link (F Link)

5.) SS7 Signalling Protocols

This is just an brief overview of the SS7 network layout.