Switching to VoIP

This is the Title of the Book, eMatter Edition

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

VoIP or IP Telephony

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a hub-based or wireless one. But for larger, critical VoIP implementations, your

choice of network infrastructure will be critical. For starters, using broadcast Ether-

net devices like hubs is a poor choice, as is using early-generation Ethernet switches

that lack quality-of-service features. Wide area equipment, like routers, will need to

support these features, too. (Quality-of-service features are covered in detail in

Chapter 9.)

Generally speaking, the faster your switches, routers, and network links are, the bet-

ter your VoIP network will perform. Nothing beats good ol’ speed for increasing the

performance of a wide area network, but sometimes a slow network link is an eco-

nomic or geographic necessity. VoIP is a speed-sensitive business, as you’ll find out.

The Layers of a VoIP Network

Like other networks, VoIP networking can be described using the Open Systems

Interconnect (OSI) reference model, a standardized way of describing the different

parts of the data communications process. The OSI model has seven layers that rep-

resent each part: physical, data link, network, transport, session, presentation, and

application. The purpose of the OSI model is to simplify connections between differ-

ent types of networks and to allow engineers who design network ...