Nortel Networks NN43001-314 - Manual (Page 58)

58 Bandwidth Management
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
within 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) 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).
Virtual Trunks usage of bandwidth zones is different than IP Phone
bandwidth usage. For Virtual Trunks, a zone number is configured in the
Route Data Block (LD 16). The zone number determines codec selection
for interzone and intrazone calls (that is, Best Bandwidth or Best Quality).
Refer to IP Peer Networking: Installation and Configuration (NN43001-313)
for information on configuring the RDB zone.
Bandwidth usage for Virtual Trunks is accumulated in its zone to block
calls that exceed the bandwidth availability in a specific zone. However,
the amount of bandwidth that is required to complete a given call is not
known until both call endpoints have negotiated which codec to use.
The bandwidth used for calculating the usage of a Virtual Trunk call is
determined by the preferred codec of the device that connects to the Virtual
Trunk. If the device is an IP Phone, the bandwidth calculations use the
preferred codec of the IP Phone, based on the codec policy defined for
the zones involved (that is, Best Bandwidth or Best Quality). Likewise, the
bandwidth calculations use the preferred codec of the Voice Gateway Media
Card for connections between a circuit-switched device (for example, a PRI
trunk) and a Virtual Trunk.
Nortel Communication Server 1000
Branch Office Installation and Commissioning
NN43001-314 01.02 Standard
Release 5.0 20 June 2007
Copyright © 2007, Nortel Networks
.