SS7

SS7 is a signaling network and protocol that is used to bring telecommunications networks to life. Calls, roaming and messaging, and converged voice/data services, call Waiting, are few of the vast number of services that SS7 is used in the communications network.

There are many combinations of protocol stacks. It depends on whether SS7 is used for cellular-specific services or intelligent network services, whether transportation is over IP or is controlling broadband ATM networks instead of time-division multiplexing (TDM) networks, and so forth. SS7 stack is comprised of following protocols.

• Message Transfer Parts (MTP 1, 2, and 3)
• Signaling Connection Control Part (SCCP)
• Transaction Capabilities Application Part (TCAP)
• Telephony User Part (TUP)
• ISDN User Part (ISUP)

ss7 Stack

MTP

This comprises the functions to transport information from one Service Point to another. The MTP transfers the signaling message, in the correct sequence, without loss or duplication, between the Service Points that make up the SS7 network.

MTP3

MTP3 performs two functions:

• Signaling Message Handling (SMH)— Delivers incoming messages to their intended User Part and routes outgoing messages toward their destination.

• Signaling Network Management (SNM)— Monitors linksets and route sets, providing status to network nodes so that traffic can be rerouted when necessary.

TUP and ISUP

TUP and ISUP sit on top of MTP to provide circuit-related signaling to set up, maintain, and tear down calls.

SCCP

The addition of the SCCP provides a more flexible means of routing and provides mechanisms to transfer data over the SS7 network. Such additional features are used to support noncircuit-related signaling, which is mostly used to interact with databases (SCPs).

Enhanced routing is called global title (GT) routing. It keeps SPs from having overly large routing tables that would be difficult to provision and maintain.

TCAP

TCAP allows applications to communicate with each other (over the SS7 network) using agreed-upon data elements. These data elements are called components. Components can be viewed as instructions sent between applications.