AudioCodes Media Pack MP-124, User Manual

Page: 149 / 584

Version 6.6 149 MP-11x & MP-124
User's Manual 13. Media
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.711 A-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 following parameters are ignored and automatically set to Events Only :

'Fax Transport Mode' (FaxTransportMode)

'Vxx ModemTransportType' (VxxModemTransportType)

To configure fax / modem transparent mode:

In the SIP General Parameters page ( Configuration tab > VoIP menu > SIP
Definitions > General Parameters ), set the 'Fax Signaling Method' parameter to
G.711 Transport (IsFaxUsed = 2).
13.2.1.3 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

Dynamic Jitter Buffer Minimum Delay = 40

Dynamic Jitter Buffer Optimization Factor = 13
When the device initiates a fax session using G.711, a ‘gpmd’ attribute is added to the SDP
according to the following format:

For G.711A-law:
a=gpmd:0 vbd=yes;ecan=on

For G.711 µ-law:
a=gpmd:8 vbd=yes;ecan=on
In this mode, the 'Fax Transport Mode' (FaxTransportMode) parameter is ignored and
automatically set to
Disable (transparent mode).

To configure fax fallback mode:

In the SIP General Parameters page ( Configuration tab > VoIP menu > SIP
Definitions > General Parameters ), set the 'Fax Signaling Method' parameter to Fax
Fallback (IsFaxUsed = 3).
13.2.1.4 Fax/Modem Bypass Mode
In this proprietary mode, when fax or modem signals are detected, the channel
automatically switches from the current voice coder to a high bit-rate coder, according to
the 'Fax/Modem Bypass Coder Type' parameter (FaxModemBypassCoderType). The
channel is also automatically reconfigured with the following fax / modem adaptations:

Disables silence suppression