Nortel Networks Remote Gateway 50 - Manual (Page 52)

Page 52 of 258 Bandwidth Management
553-3001-207 Standard 2.00 January 2006
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) 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 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 (RDB) (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
(553-3001-213) 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 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