Nortel Networks SRG 50 NN43001-307 - Manual (Page 97)

Codec negotiation 97
SRG 50 does not support G.723 codec.
ATTENTION
If the payload sizes are set higher than the default values (for example, to support
a third-party gateway), then the local IP calls are affected by higher latency.
This is because the codec configuration applies to both IP Peer calls and local
IP (IP Line) calls.
G.711 A-law and mu-law interworking
In case the far end uses a different Pulse Code Modulation (PCM) encoding
law for its G.711 codec, systems that are configured as G.711 A-law also
include G.711 mu-law on their codec preferences list. Systems configured
as G.711 mu-law include G.711 A-law as their last choice. Therefore,
encoding law conversion is performed between systems with different laws.
Bandwidth management and codecs
Bandwidth management defines which codecs are used for intrazone calls
and interzone calls.
Bandwidth management enables administrators to define codec preferences
for IP Phone to IP Phone calls controlled by the same CS 1000 system in
the same zone. These calls are known as intrazone calls. This is different
than the codec preferences for calls between an IP Phone on the CS 1000
system to a Virtual Trunk (potentially an IP Phone on another CS 1000
system) or calls to IP Phones in another zone. These calls are known as
interzone calls.
For example, you may prefer high quality speech (G.711) over high
bandwidth within one system, and lower quality speech (G.729AB plus
Voice Activity Detection [VAD]) over lower bandwidth to a Virtual Trunk.
Such a mechanism can be useful when a system is on the same LAN as
the IP Phones it controls, but the other systems are on a different LAN
(connected through a WAN).
The Virtual Trunk usage of bandwidth zones is different than IP Phone
bandwidth usage. For Virtual Trunks, a zone number is configured in the
Route Data Block (RDB) (LD 16). The zone number determines codec
selection for interzone and intrazone calls (that is, Best Bandwidth or
Best Quality). See IP Peer Networking Installation and Commissioning
(NN43001-313) for information on configuring the RDB zone.
Bandwidth usage for Virtual Trunks is accumulated in its zone in order
to block calls that exceed the bandwidth availability in a specific zone.
However, the amount of bandwidth that is required to complete a given
Nortel Communication Server 1000
Main Office Configuration Guide for SRG 50
NN43001-307 02.02 Standard
Release 5.0 3 December 2007
Copyright © 2005-2007, Nortel Networks
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