Switching to VoIP

This is the Title of the Book, eMatter Edition

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

Key Issues: Voice over Data: Many Conversations, One Network

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Key Issues: Voice over Data: Many

Conversations, One Network

• VoIP can replace traditional telephony, but quality-of-service measures are

required in order to make it as reliable as old-school gear.

• The OSI network model breaks down VoIP in terms of layers. The networking

aspects run at the lower layers, and the application aspects run at the higher

layers.

• VoIP media streams are delivered by connectionless UDP datagrams, and not

TCP packets. This is because, in telephony and other real-time media applica-

tions, there’s no point in error correction. VoIP administrators would rather

strive for full error abatement. This means designing an IP network to carry

voice, not just data.

• Most IP phones allow simple calls to be made directly to each other, dialed by IP

address, without the need for a VoIP PBX server as an intermediary. The job of

the server, among other things, is to provide a human-friendly addressing

scheme and other features that the phones alone can’t provide.

• Traditional telephony networking is characterized by client/server or mainframe-

like tendencies. VoIP networks are characterized by distributed or fat-client ten-

dencies.

• Most IP endpoints sit at the proverbial “edge” of the network, where PCs ...