Nortel Networks Remote Gateway 50 - Manual (Page 51)

Bandwidth Management Page 51 of 258
Main Office Configuration for Survivable Remote Gateway 50 Configuration Guide
By default, the G.711 codec must be supported at both ends of a call. Codec
configuration is performed for each node and is independent of the signaling
gateway that is used on the node.
Note: The payload size on the CS 1000 must be set to 30 msec in order
to work with the SRG.
IP Peer Networking performs codec negotiation by providing a list of codecs
that the devices can support. Use CS 1000 Element Manager to configure the
list of codec capabilities. Refer to IP Peer Networking: Installation and
Configuration (553-3001-213) for instructions on configuring codecs.
The codec preference sequence sent over H.323 depends on the bandwidth
policy selected for the Virtual Trunk zone and the involved telephones. For
“Best Quality”, the list is sorted from best to worst voice quality. For “Best
Bandwidth”, the list is sorted from best to worst bandwidth usage.
The G.711 codec delivers “toll quality” audio at 64 kbit/s. This codec is
optimal for speech quality, as it has the smallest delay and is resilient to
channel errors. However, the G.711 codec uses the largest bandwidth.
The G.729A codec provides near toll quality voice at a low delay. The
G.729A codec uses compression at 8 kbit/s. The G.729AB codec also uses
compression at 8 kbit/s.
The G.723.1 codec provides the greatest compression.
Note 1: SRG50 does not support G.723 codec.
Note 2: Payload default values need to be changed if the customer wants
to communicate with a third-party gateway that does not support the
above default payload sizes. Otherwise, IP Peer calls to or from the
third-party gateway are not successful.
Note 3: 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.