Switching to VoIP

This is the Title of the Book, eMatter Edition

Copyright © 2007 O’Reilly & Associates, Inc. All rights reserved.

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Chapter 2: Voice over Data: Many Conversations, One Network

• Access interfacing, so that traditional phones and PBXs can participate in the

VoIP network by way of media conversion.

• Translation of audio encoding standards (codecs) in real time to facilitate calls

between endpoints that have different audio capabilities or between analog, digi-

tal, and IP endpoints.

When VoIP endpoints and servers are connected to the same IP network, VoIP

becomes the call-switching and voice-transmission mechanism, replacing the tradi-

tional PBX.

What differentiates VoIP servers from voice endpoints is whether they provide a user

interface for the telephony application. Phones do, so they are endpoints. Switches,

ATAs, PSTN gateway devices, and other specialized VoIP devices don’t, so they are

VoIP servers. Another differentiator between endpoints and servers is their abun-

dance on the network. Like the WWW, there are more endpoints than servers in a

VoIP system, sometimes even in thousands-to-one ratios.

Voice Endpoints

Endpoints that are TCP/IP aware (that is, they are valid hosts on the IP network) and

connect directly to a data link that carries TCP/IP (such as Ethernet) are usually

called IP phones. IP phones resemble feature-enriched business telephones but differ

in that they usually have ...