Version 5.8 497 October 2009
SIP User's Manual 9. IP Telephony Capabilities
9.6.2.5 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:
îš„ Echo Canceller = on (or off, for modems)
îš„ Echo Canceller Non-Linear Processor Mode = off
îš„ Jitter buffering optimizations
To configure fax / modem transparent with events mode, perform the following
configurations:
îš„ IsFaxUsed = 0
îš„ FaxTransportMode = 3
îš„ V21ModemTransportType = 3
îš„ V22ModemTransportType = 3
îš„ V23ModemTransportType = 3
îš„ V32ModemTransportType = 3
îš„ V34ModemTransportType = 3
îš„ BellModemTransportType = 3
9.6.2.6 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:
îš„ Echo Canceller = off
îš„ Silence Compression = off
îš„ Echo Canceller Non-Linear Processor Mode = off
îš„ Dynamic Jitter Buffer Minimum Delay = 40
îš„ 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:
îš„ 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.
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