AudioCodes Mediant 2000, User Manual

Page: 355 / 418

Version 5.6 355 November 2008
SIP User's Manual 7. IP Telephony Capabilities
7.5.2.5 Fax / Modem Transparent with Events Mode
In this mode, fax and modem signals are transferred using the current voice coder with the
following automatic adaptations:
„ Echo Canceller = on (or off, for modems)
„ Echo Canceller Non-Linear Processor Mode = off
„ Jitter buffering optimizations
To configure fax / modem transparent with events mode, perform the following
configurations:
„ IsFaxUsed = 0
„ FaxTransportMode = 3
„
V21ModemTransportType = 3
„ V22ModemTransportType = 3
„ V23ModemTransportType = 3
„ V32ModemTransportType = 3
„ V34ModemTransportType = 3
„ BellModemTransportType = 3
7.5.2.6 G.711 Fax / Modem Transport Mode
In this mode, when the terminating device detects fax or modem signals (CED or AnsAM), it
sends a Re-INVITE message to the originating device requesting it to re-open the channel
in G.711 VBD with the following adaptations:
„ Echo Canceller = off
„ Silence Compression = off
„ Echo Canceller Non-Linear Processor Mode = off
„ Dynamic Jitter Buffer Minimum Delay = 40
„ Dynamic Jitter Buffer Optimization Factor = 13
After a few seconds upon detection of fax V.21 preamble or super G3 fax signals, the
device sends a second Re-INVITE enabling the echo canceller (the echo canceller is
disabled only on modem transmission).
A ‘gpmd’ attribute is added to the SDP according to the following format:
„
For G.711A-law:
a=gpmd:0 vbd=yes;ecan=on (or off, for modems)
„
For G.711 µ-law:
a=gpmd:8 vbd=yes;ecan=on (or off for modems)
The parameters FaxTransportMode and VxxModemTransportType are ignored and
automatically set to the mode called ‘transparent with events’.
To configure fax / modem transparent mode, set IsFaxUsed to 2.