Nortel Networks NN43001-307

Codec negotiation 97

SRG 50 does not support G.723 codec.

ATTENTION

If the payload sizesare sethigher 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 conversionis performed between systems with differentlaws.

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 betweenan IPPhone 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

VoiceActivity 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 adifferent 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 forSRG 50

NN43001-307 02.02 Standard

Release 5.0 3 December 2007