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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