Internet Telephony Lecture Notes

10 July 2008 • Telephone Network Signaling

Outline

Signaling System Seven (SS7)

Signaling System Seven

Signaling System Seven (SS7) is the common-channel signaling (CSS) system for the phone network.
Evolved from the Common-Channel Signaling Six (CCS6).
An ITU standard with national variations.
- In the US, ANSI-SS7.

SS7 Network Components

The three main SS7 network components are

Service switching points (SSP) - the connection between the two networks.
Signal transfer point (STP) - the nodes in the CCS network.
Service control point (SCP) - software and databases defining services.

Service Switching Points

Translate to and from switch and SS7 signals.
Controls attached switches.
- Dialed-number look-up to establish the circuit route.

Signal Transfer Points

Routers in the SS7 network.
Access points for service control points.
Gateways for various versions of SS7 networks.

Service Control Points

Front-ends to telephone databases.
- Subscriber information, number translation (800 numbers), fraud data, calling cards.

SS7 Layers

Physical layer: Message transfer point level 1 (MTP1).
Link layer: MTP level 2.
Network layer (routing): MTP level 3.
Transport layer (global addressing, transport services): Signaling connection control point (SCCP).
Session layer (RPC): transaction capabilities application part (TCAP).
Application: Operations, administration, and management (OAM).

References

A Closer Look at SS7 (Chapter 8) in Signaling and Switching for Packet Telephony by Matthew Stafford, Artech House, 2004.

This page last modified on 17 June 2008.