SS7/IP Interworking Tutorial

Introduction

Telephone companies offload voice calls from public switched telephone networks (PSTNs) to voice-over-Internet Protocol (VoIP) networks because it is cheaper to carry voice traffic over Internet Protocol (IP) networks than over switched circuit networks. In the future, IP telephony networks are expected to enable innovative new multimedia services while working seamlessly with legacy telephone networks.

A VoIP network carries voice traffic cheaper than a switched circuit telephone network because IP telephony networks make better use of available bandwidth. In a public switched telephone network, for example, a dedicated 64 kilobits per second (kbps) end-to-end circuit is allocated for each call. In a VoIP network, digitized voice data is highly compressed and carried in packets over IP networks. Using the same bandwidth, a VoIP network can carry many times the number of voice calls as a switched circuit network with better voice quality. The savings realized in using VoIP networks are often passed onto users in the form of lower costs.

In addition to voice data, signaling data is exchanged between switched circuit telephone networks and VoIP networks. Signaling information is used to setup, manage and release voice calls, and support telephony services such as caller ID, toll-free calling, and mobile authentication and roaming services.

The remainder of this tutorial introduces the topic of interworking the public switched telephone network and next-generation VoIP networks to support voice calls and telephony services.

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