Bandwidth Management Page 53 of 258
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
Codec selection
For every Virtual Trunk call, a codec must be selected before the media path can be opened. When a call is set up or modified (that is, media redirection), one of two processes occurs:
•The terminating node selects a common codec and sends the selected codec to the originating node.
•The codec selection occurs on both nodes.
Each node has two codec lists: its own list and the far end’s list. In order to select the same codec on both nodes, it is essential to use the same codec selection algorithm on both nodes. Before the codec selection occurs, the following conditions are met:
•Each codec list contains more than one payload size for a given codec type (it depends on the codec configuration). Payload size must be set to 30 msec for proper functionality between the CS1000 and the SRG.
•Each codec list is sorted by order of preference (the first codec in the near end’s list is the near end’s most preferred codec, the first codec in the far end’s list is the far end’s preferred codec).
Codec selection algorithms
When the codec lists meet the above conditions, one of the following codec selection algorithms selects the codec to be used:
•H.323 Master/Slave algorithm
•“Best Bandwidth” codec selection algorithm
Main Office Configuration for Survivable Remote Gateway 50 Configuration Guide
