3Com VCX V7122 SIP, User Manual

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3Com VCX V7122/SIP VoIP Gateway User Manual
relay mode. The UseT38orFRF11 configuration parameter defines either T.38-compliant
network packets or proprietary FRF.11-based packets (the last mode should be used mostly
for backward-compatibility with older software versions).
When fax transmission ends, the reverse is carried out, and fax relay switches to voice. This
mode switch occurs automatically, both at the local and remote endpoints.
You can limit the fax rate using the FaxRelayMaxRate parameter and can enable/disable
ECM fax mode using the FaxRelayECMEnable parameter.
When using T.38 mode, you can define a redundancy feature to improve Fax transmission
over congested IP network. This feature is activated by FaxRelayRedundancyDepth and
EnhancedFaxRelayRedundancyDepth parameters. Although this is a proprietary redundancy
scheme, it should not create problems when working with other T.38 decoders.
When using FRF.11 mode, only FaxRelayRedundancyDepth parameter can be used.
T.38 mode currently supports only the T.38 UDP syntax.
Configuring Fax/Modem ByPass Mode
When VxxTransportType=2 (FaxModemBypass, Vxx can be either
V32/V22/V21/Bell/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.
When Fax relay is enabled, V21TransportType must be set to disable
(Transparent) mode.
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 following configurations:
FaxTransportMode = 2 (Bypass)
V34ModemTransportType = 2 (Modem bypass)