AudioCodes Media Pack MP-112, User Manual

Page: 401 / 486

Version 5.8 401 September 2009
SIP User's Manual 9. IP Telephony Capabilities
9.5.2.5 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
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:

For G.711A-law:

a=gpmd:0 vbd=yes;ecan=on (or off, for modems)
For G.711 µ-law:
The parameters FaxTransportMode and VxxModemTransportType are ignored and
automatically set to the mode called ‘transparent with events’.
a=gpmd:8 vbd=yes;ecan=on (or off for modems)
To configure fax / modem transparent mode, set IsFaxUsed to 2.