Cisco Networking Simplified, Second Edition

Chapter . Voice over IP

Making Calls over the Web

Traditionally, voice traffic traveled across circuit-switched connections of the PSTN. Corporate customers often had so many phone lines that they often deployed their own telephone exchanges using private branch exchange (PBX) networks or networks of private lines and time-division multiplexers (TDM). Although they had trunks into the PSTN (trunks are PSTN connections that can carry dozens of calls), these traditional networks tended to be proprietary, closed systems that were expensive to maintain, upgrade, and scale.

Voice over IP (VoIP) provides voice services such as phones, call routing, and voice mail using the data network. Thus, both the data and voice networks can converge into a single ...