RADVision L2W-323 User Manual page 38

Overview
Default Extension
The default extensions can be any endpoint on the LAN and all calls not routed via one of
the above incoming call routing methods, are forwarded to this endpoint. Default extensions
can be defined per WAN port.
Incoming Call Routing Logic
The Gateway routes an incoming call from the WAN according to the routing methods
enabled for the WAN port during configuration, following this order of priority:
MSN → TCS4 → IVR → Default Extension
If any of the methods fail, the Gateway automatically tries to route the call via the next
routing method in the priority line. If all methods fail, the call is disconnected. The call may
also be disconnected if the Gateway routes the call to the requested endpoint but the
endpoint is busy or not available.
Supported Audio Transcoding
When an audio transcoding card is installed on the Gateway, the Gateway can perform
transcoding between the following types of audio protocols.
!" G.711 (WAN) to G.723.1 (LAN) / G.723.1 (LAN) to G.711 (WAN)
!" G.728 (WAN) to G.711 (LAN) / G.711 (LAN) to G.728 (WAN)
The audio protocols differ in the quality and bit rate of the audio they provide. G.711
provides toll quality audio at 64 Kbps, G.728 provides near toll quality audio at 16 Kbps,
and G.723.1 provides voice quality audio at 5.3 or 6.3 Kbps.
Usually, WAN endpoints have G.711 and G.728 codecs while LAN endpoints have G.711
and G.723.1 codecs. By performing transcoding between these audio protocols, the Gateway
can optimize the audio bandwidth usage either on the LAN (G.723.1↔G.711) or on the
WAN (G.728↔G.711). Transcoding is particularly useful for WAN codecs, where
bandwidth can be limited to 128 Kbps for a video call. For example, when G.728↔G.711
transcoding takes place the audio bandwidth usage is compressed to 16 Kbps, leaving an
additional 40 Kbps for the video stream on the WAN. This will largely improve the quality
of the video on the WAN.
You can define a preferred transcoding setting for the Gateway. This does not mean the
Gateway always performs the preferred transcoding. If this transcoding cannot be performed
due to WAN/LAN endpoint restrictions, the Gateway may use a different transcoding
method. For example, if you set the preferred transcoding to G.728-G.711 and the call is a
voice call, the Gateway uses the G.711-G.723.1 method instead in an effort to optimize the
LAN bandwidth usage.
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