Avaya BCM 2.0 IP Telephony Manual de usuario descargar pdf (Pagina 38)

38 Engineering guidelines

Enterprise Edge 2.0 IP Telephony Configuration Guide P0911590 Issue 02

The G.723.1 codec uses a different compression method than the G.729 codec. The

G.723.1 method uses more DSP resources. Each MSPEC supports one G.723.1 call.

A G.711 call can run in the same MSPEC as a G.723.1 call. See the Enterprise Edge

Programming Operations Guide for additional information.

If the G.723.1 codec is the only possible codec for a call, a trunk can not be available

for the call if there are not enough DSP resources available. All VoIP Gateway

facilities can appear to be in use, although there are DSP resources available for

calls using other codec types.

Because most gateways support the G.711 codec, configure G.711 as a supported

codec. The G.711 codec does not compress audio or fax. The G.711 codec supports

two IP trunks on each MSPEC. See the Enterprise Edge Programming Operations

Guide for additional information.

G.711

This codec delivers “toll quality” audio at 64 kbit/s. This codec is best for speech

because it has the smallest delay, and is very strong to channel errors. However, the

G.711 codec uses the largest bandwidth. North America uses G.711 µ-LAW and

international markets use G.711 A-LAW.

Silence compression

G.723.1 and G.729, Annex B support Silence compression.

A key to VoIP Gateway’s in business applications is reducing WAN bandwidth use.

Beyond speech compression, the best bandwidth reducing technology is silence

compression, also known as silence suppression. Silence compression 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 36-40% of a full-duplex conversation is active. When one

person talks, the other listens (known as half-duplex). And there are important

periods of silence during speaker pauses between words and phrases.

By applying silence compression, full duplex bandwidth use is reduced by the same

amount, releasing bandwidth for other voice/fax or data communications. Figure 5

Silence compression shows how silence compression allows two conversations to

fit in the bandwidth otherwise used by one. This 50% bandwidth reduction develops

over a 20-30 second period as the conversation switches from one direction to

another.

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Avaya BCM 2.0 IP Telephony Manual de usuario Pagina 38