SIP User's Manual 494 Document #: LTRT-12801
MP-500 MSBG
9.6.2.1.2 Automatically Switching to T.38 Mode without SIP Re-INVITE
In the Automatically Switching to T.38 Mode without SIP Re-INVITE mode, when a fax
signal is detected, the channel automatically switches from the current voice coder to
answer tone mode, and then to T.38-compliant fax relay mode.
To configure automatic T.38 mode, perform the following configurations:
îš„ IsFaxUsed = 0
îš„ FaxTransportMode = 1
îš„ Additional configuration parameters:
• FaxRelayEnhancedRedundancyDepth
• FaxRelayRedundancyDepth
• FaxRelayECMEnable
• FaxRelayMaxRate
9.6.2.2 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 parameter FaxModemBypassCoderType). In addition, the channel is automatically
reconfigured with the following fax / modem adaptations:
îš„ Disables silence suppression
îš„ Enables echo cancellation for fax
îš„ Disables echo cancellation for modem
îš„ Performs certain jitter buffering optimizations
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
(according to the parameters FaxBypassPayloadType and ModemBypassPayloadType).
During the bypass period, the coder uses the packing factor, which is defined by the
parameter FaxModemBypassM. The packing factor determines the number of coder
payloads (each the size of FaxModemBypassBasicRTPPacketInterval) that are used to
generate a single fax/modem bypass packet. When fax/modem transmission ends, the
reverse switching, from bypass coder to regular voice coder is performed.
To configure fax / modem bypass mode, perform the following configurations:
îš„ IsFaxUsed = 0
îš„ FaxTransportMode = 2
îš„ V21ModemTransportType = 2
îš„ V22ModemTransportType = 2
îš„ V23ModemTransportType = 2
îš„ V32ModemTransportType = 2
îš„ V34ModemTransportType = 2
îš„ BellModemTransportType = 2
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