Fax / Modem Transport Mode; Fax Fallback - AudioCodes Mediant 2000 User Manual

SIP User's Manual

Jitter buffering optimizations
To configure fax / modem transparent with events mode, perform the following
configurations:

IsFaxUsed = 0
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FaxTransportMode = 3
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V21ModemTransportType = 3

V22ModemTransportType = 3
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V23ModemTransportType = 3
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V32ModemTransportType = 3
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V34ModemTransportType = 3
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BellModemTransportType = 3
9.5.2.6 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:
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For G.711A-law:
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For G.711 µ-law:
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.
9.5.2.7

Fax Fallback

In this mode, when the terminating device detects a fax signal, it sends a Re-INVITE
message to the originating device with T.38. If the remote device doesn't support T.38
(replies with SIP response 415 'Media Not Supported'), the device sends a new Re-INVITE
with G.711 VBD with the following adaptations:

Echo Canceller = on

Silence Compression = off

Echo Canceller Non-Linear Processor Mode = off
Version 5.8
a=gpmd:0 vbd=yes;ecan=on (or off, for modems)
a=gpmd:8 vbd=yes;ecan=on (or off for modems)
415
9. IP Telephony Capabilities
October 2009