ITG User’s Guide
4 2 1 4
11 2 1 11
Destination Table
The destination table maps a destination to a telephony port or the IP address of a remote
ITG.
Destination table sample
Dest id Mode Destination
-------------------------------------------------------
1 Local PORT = 0
3 Local PORT = 2
4 Local PORT = 3
11 H.323 Dest = 192.168.0.55/1720 TCP
3.6 DTMF Relay
Voice from PSTN is compressed by the ITG before sending across the IP network and then
decompressed by the destination ITG. The voice coders supported by the ITG are designed
for ideally compressing and decompressing human voice. If the compression / decompression
process is performed on DTMF tone which needs to be conveyed across
IP network, distortion might be too significant to be not cognizable in the receiving end. To
overcome the shortcoming that the voice coders can not perfectly encode DTMF tone, the
ITG encodes DTMF tone into special packets. The packets are then sent to the
destination ITG via a separate IP connection. The destination ITG decodes the packets,
generates the DTMF tone, and then sends the tone to the PSTN. The way the ITG
handles DTMF tone is so called DTMF relay.
The ITG handles DTMF relay per H.323 specifications. Certain third party VoIP devices
may handle DTMF relay per IMTC standard. For the ITG to interoperate with those VoIP
devices, users need to specify which remote VoIP devices uses IMTC conforming DTMF
relay technique. Refer to CLI command on Chapter 8 for detailed information on how
to select DTMF relay mode.
3.7 Voice Codecs
Voice codecs supported by the ITG include G.711, G.723.1 5.3kbps, G.723.1 6.3kbps and
G.729 AB. When setting up a call, two ITG automatically negotiate with each other until an
agreed upon codec is determined.
Configuring ITG from a Web Browser
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