Nortel VoIP Gateway, Configuration Manual

Page: 205 / 220

Fax/Modem Settings 205
Norstar VoIP Gateway Configuration Guide
Configuring Fax/Modem ByPass Mode
When VxxTransportType=2 (FaxModemBypass, Vxx can be either V32/V22/V21/V34/Fax), then
when fax/modem is detected, the channel automatically switches from the current voice coder to a
high bit-rate coder, as defined by the User, with the FaxModemBypassCoderType configuration
parameter.
If fax relay is enabled for one of the modes, then the Answer Tone mode packets are relayed as fax
relay packets.
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 to be 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 is carried out, and bypass coder is switched to
regular voice coder.
Note:
For interoperability with other Nortel Networks endpoints, use only T.38 fax relay.
Note:
When Fax relay is enabled, V21TransportType must be set to disable (Transparent)
mode.