Supporting V.34 Faxes - 3Com VCX V7122 User Manual

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 is carried out, and bypass coder is
switched to regular voice coder.

Supporting V.34 Faxes

V.34 fax machine support is available only in bypass mode (fax relay is not supported) when
the channel is configured in one of the configurations described below:
FaxTransportMode = 2 (Bypass)
V34ModemTransportType = 2 (Modem bypass)
In this configuration, both T.30 and V.34 faxes work in Bypass mode
Or
FaxTransportMode = 1 (Relay)
V34ModemTransportType = 2 (Modem bypass)
In this configuration, T.30 faxes use Relay mode (T.38) while V.34 Fax uses Bypass mode.
In order to use V.34 fax in Relay mode (T.38), you must configure:
FaxTransportMode = 1 (Relay)
V34ModemTransportType = 0 (Transparent)
V32ModemTransportType = 0
V23ModemTransportType = 0
V22ModemTransportType = 0
This configuration forces the V.34 fax machine to work in T.30 mode.
210 3Com VCX V7122 SIP VoIP Gateway User Manual