Configuring Fax/Modem Bypass Mode; Supporting V.34 Faxes; Using Bypass Mechanism For V.34 Fax Transmission; Using Relay Mode For Both T.30 And V.34 Faxes - AudioCodes Mediant 1000 User Manual

8.3.3

Configuring Fax/Modem Bypass Mode

When VxxTransportType= 2 (FaxModemBypass, Vxx can be one of the following:
V32/V22/Bell/V34/Fax), then on detection of fax/modem, the channel automatically
switches from the current voice coder to a high bit-rate coder (G.711 or G.726), as defined
by the user, with the FaxModemBypassCoderType configuration parameter.
During the bypass period, the coder uses the packing factor (by which a number of basic
coder frames are combined together in the outgoing WAN packet) set by the user in the
FaxModemBypassM configuration parameter. The network packets generated and
received during the bypass period are regular voice RTP packets (per the selected bypass
coder) but with a different RTP Payload type.
When fax/modem transmission ends, the reverse switching, from bypass coder to regular
voice coder, is carried out.
8.3.4

Supporting V.34 Faxes

V.34 faxes don't comply with the T.38 relay standard. We therefore provide the optional
modes described under Sections
Note that the CNG detector is disabled (CNGDetectorMode=0) in all the following
examples.
8.3.4.1

Using Bypass Mechanism for V.34 Fax Transmission

In this proprietary scenario, the media gateway uses a high bit-rate coder to transmit V.34
faxes, enabling the full utilization of its speed.
Refer to the following configurations:
FaxTransportMode = 2 (Bypass)
V34ModemTransportType = 2 (Modem bypass)
V32ModemTransportType = 2
V23ModemTransportType = 2
V22ModemTransportType = 2
In this configuration, both T.30 and V.34 faxes work in Bypass mode.
Or
FaxTransportMode = 1 (Relay)
V34ModemTransportType = 2 (Modem bypass)
V32ModemTransportType = 2
V23ModemTransportType = 2
V22ModemTransportType = 2
In this configuration, T.30 fax uses T.38 Relay mode while V.34 fax uses Bypass mode.
8.3.4.2

Using Relay mode for both T.30 and V.34 faxes

In this scenario, V.34 fax machines are compelled to use their backward compatibility with
T.30 faxes; as a T.30 machine, the V.34 fax can use T.38 Relay mode.
Refer to the following configuration:
FaxTransportMode = 1 (Relay)
V34ModemTransportType = 0 (Transparent)
V32ModemTransportType = 0
V23ModemTransportType = 0
V22ModemTransportType = 0
Both T.30 and V.34 faxes use T.38 Relay mode. This configuration forces the V.34 fax
machine to operate in the slower T.30 mode.
H.323 User's Manual
8.3.4.1 and 8.3.4.2:
262
Mediant 1000
Document #: LTRT-83401