Codec Negotiation - Avaya Nortel Communication Server 1000 Manual

222 Codecs
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Example 1
G.711 a-law, G.729A, G.729AB, and G.723.1 are configured.
The Voice Gateway registers G.711 a-law, G.711 mu-law, G.729A, and
G.729AB.
Example 2
G.711 mu-law, G.729A, and G.723.1 are configured.
The Voice Gateway registers G.711 a-law, G.711 mu-law, and G.729A.
Example 3
G.711 mu-law and G.723.1 are configured.
The Voice Gateway registers G.711 a-law, G.711 mu-law, and G.723.1.

Codec negotiation

For every virtual trunk call, a common codec must be selected for the call.
This is known as codec negotiation. Codec negotiation for virtual trunk
calls is performed through the H.323 FastStart and Terminal Capability
Set (TCS) messages.
For a call setup with the FastStart procedure, the originating node sends
its codec list in the FastStart element in the SETUP message to the
terminating node. For a call setup using the SlowStart procedure or for a
call modification (media redirection), each node sends its codec list in the
TCS message to the other node.
Copyright © 2003–2008, Nortel Networks
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T.38 and G.711 Clear Channel fax codecs are always registered.
G.711 Clear Channel is used for IP Trunk connections to Business
Communication Manager (BCM), which does not support T.38 fax.
A minimum of two codecs are registered if only G.711 was configured.
A maximum of four codecs can be registered - the G.711 a-law and
mu-law for BQ codec, and some BB codecs (defined by the following
rules).
— If the G.729A codec is configured, only the G.729A codec is
registered with the Call Server.
— If the G.729AB codec is configured, the G.729A codec and the
G.729AB codec are registered with the Call Server.
— If the G.723 codec is configured, the G.723 codec is registered with
the Call Server.
Nortel Communication Server 1000
IP Line Fundamentals
NN43100-500 02.02 Standard
Release 5.5 4 February 2008