Page 188 of 770 Codecs
553-3001-365 Standard 3.00 September 2004
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.
Codec sorting
Before sending a codec list in FastStart and TCS messages, the codec list
must be sorted according to the BB or BQ policy. This is determined by the
following:
• the zone configuration of the IP Phone/DSP involved in the call
• the zone configuration of the virtual trunk used for the call
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