Avaya BCM 4.0 Networking Guide de configuration télécharger pdf (Page 399)

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Chapter 43 VoIP overview 399

BCM 4.0 Networking Configuration Guide

LAN

A Local Area Network (LAN) is a communications network that serves users within a confined

geographical area. For BCM, a LAN is any IP network connected to a LAN card on the BCM

system. Often, the LAN can include a router that forms a connection to the Internet. A BCM can

have up to two LAN connections.

Key VoIP concepts

The following explains four commonly used VoIP terms.

QoS

QoS (Quality of Service) is technology that determines the quality of the VoIP connection. BCM

and network routers use QoS to ensure that real time critical IP packets, such as voice packets, are

given higher routing and handling priority than other types of data packets.

Silence suppression

Silence suppression also referred to as VAD (Voice activated detection) technology identifies the

periods of silence in a conversation, and stops sending IP speech packets during those periods.

Telco studies show that in a typical telephone conversation, only about 36% to 40% of a

full-duplex conversation is active. When one person talks, the other listens. This is half-duplex.

There are important periods of silence during speaker pauses between words and phrases. By

applying silence suppression, average bandwidth use is reduced by the same amount. This

reduction in average bandwidth requirements develops over a 20-to-30-second period as the

conversation switches from one direction to another. Also refer to “Silence suppression” on

page 703.

Codecs

The algorithm used to compress and decompress voice over IP networks and VoIP trunks is

embedded in a software entity called a codec (COde-DECcode).

Refer to “Codec rates” on page 721 for a listing of the supported codes and their transmission

rates.

• The G.711 Codec samples the voice stream at a rate of 64kbps (kilobits per second), and is the

Codec to use for maximum voice quality. Choose the G.711 Codec with the companding law

(alaw or ulaw) that matches your system requirements.

• The G.729 Codec samples the voice stream at 8 kbps. The voice quality is slightly lower using

a G.729 but it reduces network traffic by approximately 80%.

• The G.723 Codec should be used only with third party devices that do not support G.729 or

G.711.

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