Authorized Self-Study Guide Cisco Voice over IP (CVOICE), Third Edition

Chapter 4 Performing Call Signaling over Digital Voice Ports

Enterprise networks often use digital circuits, in contrast to analog circuits, when interconnecting their Voice over IP (VoIP) network to traditional telephony environments, such as the public switched telephone network (PSTN) or a private branch exchange (PBX). One major advantage of using digital circuits is the economies of scale made possible by transporting multiple conversations over a single circuit. For example, a digital T1 circuit using Channel Associated Signaling (CAS) (which is described in this chapter) can carry 24 simultaneous voice conversations on a single circuit.

Many enterprises also have the need to interconnect PBX systems, and these PBXs might be from different ...