SS7 Protocols

Signaling System Number 7 (SS7) is a set of telephony signaling protocols which are used to set up most of the world's public switched telephone network telephone calls.
CCITT developed SS7 specification. SS7 is a common channel signalling system.

SS7 protocols:

• MTP-2 Message transfer Part Level 2
• MTP-3 Message transfer Part Level 3
• SCCP: Signalling Connection Control Part
• DUP: Data User part
• ISUP: ISDN User Part
• TUP: Telephone User PA\art
• TCAP: Transaction Capabilities Application Part
• MAP: Mobile Applicatin Part

MTP-3
it transfers messges between the nodes of the signalling network. Used to perform message distribution and in some cases to perform message routing.

MTP-2
It provides reliable transfer of signallingmessages between two directly connected signalling points.

SCCP:
Offers enhancements to MTP-3 to provide connectionless and connection-oriented network services, as well as to address translation capabilities.

DUP:
defines the necessary call control, facility registration, and cancellation realted elements, for international common channel signalling, by using SS7 for circuit-switched data transmission services.
The data signalling messages are divided into two categories:

1. Call and circuit related messages.
2. Facility registration and cancellation related messages.
   

ISUP:
ISUP defines the protocol and procedures used to setup, manage, and relaese trunk circuits that carry voice and data calls over the public switched telephone network. ISUP is used for both ISDN and non-ISDN calls.ISDN User part messages are carried on the signalling link by means of signal units.

TUP:
TUP messages are carried on the signalling data link by means of signal unit.

TCAP:
enables the deployment of advanced intelligent network services by supporting non-circuit related information exchange between signalling points using the SCCP connectionless service. TCAP messages are contained within the SCCP portion of an MSU.

MAP:
MAP messages sent between mobile switches and databases to support user authentication, and roaming, are carried by TCAP in mobile networks. When a mobile subsciber roams into a new MSC area, the integrated VLR requests profile information from the subscribers HLR using MAP info carried over TCAP messages.