Switching to VoIP

This is the Title of the Book, eMatter Edition

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

QoS Past and Present

|

191

Quantizing

Like the G.711 (PCM) codecs used in traditional telephony, all forms of quanti-

zation produce distortion. This is basically unavoidable, though this chapter

describes how best to select codecs that minimize signal distortion.

Using an IP network as a transport for voice can indeed impair the sound signal, and

this is where network QoS measures come into play. Since IP networks weren’t origi-

nally designed for “reliable,” real-time, and connection-oriented transmission the

way the PSTN is, QoS measures can make up for IP’s shortcomings and make for a

network that is actually more resource-sparing than the PSTN could ever be.

QoS is Two Things

Quality of Service is both a network design concept and a set of standards for band-

width reservation on the network. The QoS concept deals with fundamental detrac-

tors from quality—like packet loss and latency—and their cure: sound network

design. This means providing enough bandwidth and proper physical and geo-

graphic organization of network traffic. Indeed, most network engineers, when faced

with bottlenecks, instinctively seek to add more bandwidth. There’s nothing wrong

with that—it’s just not the most elegant or cost-effective way of dealing with the

problem. As a result, many network engineers overbuild ...