SS7 is an architecture for performing out of band signaling in support of the call establishment ,billing, routing, and information exchange function of the Public switched Telephone network (PSTN).It identifies functions to be performed by a signaling system network and a protocol to enable their performance.

SS7 Protocol Model:

The message transfer part (MTP) provides OSI level protocol model as level-1 data service, level-2 link service and level-3 network service

1) The full level-3 service is provided by the signaling connection control part (SCCP)

2) The SCCP provides an enhanced addressing capability that may be considered as level 3+ or close to level-4 The layer 4-6 in the OSI model don’t exist in SS7 protocol model

3) The transaction capability application part (TCAP) level and operations maintenance and administration (OMAP) part level are considered the same as the Application level-7 in the OSI

4) The application service element ASE is at the same level as the OMAP .

5) The TCAP includes protocol and services to perform remote operations .

6) The primary use of TCAP in these networks is for invoicing remote procedures in supporting IN service like, 800 services .

7) The OMAP provides the application protocols and procedures to monitor coordinate and control all the network resources which make communication based on SS7 possible

8) The ASE is for the MTP routing verification test (MRVT) which uses the connectionless services of TCAP

9) The MRVT is an important function on OMAP