Nortel Networks Remote Gateway 50 Law and mu-law interworking, Bandwidth management and codecs

Page 52 of 258 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 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

553-3001-207 Standard 2.00 January 2006