Fax/Modem Bypass Mode - AudioCodes Mediant 800B User Manual


To configure fax fallback mode:

In the SIP General Parameters page (Configuration tab > VoIP menu > SIP
Definitions > General Parameters), set the 'Fax Signaling Method' parameter to Fax
Fallback (IsFaxUsed = 3).

13.2.2.4 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 'Fax/Modem Bypass Coder Type' parameter (FaxModemBypassCoderType). The
channel is also automatically reconfigured with the following fax / modem adaptations:

Disables silence suppression

Enables echo cancellation for fax

Disables echo cancellation for modem

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 following parameters:

'Fax Bypass Payload Type' (FaxBypassPayloadType)

ModemBypassPayloadType (ini file)
During the bypass period, the coder uses the packing factor, configured by the 'Fax/Modem
Bypass Packing Factor' parameter (FaxModemBypassM). The packing factor determines
the number
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:
1. In the SIP General Parameters page (Configuration tab > VoIP menu > SIP
Definitions > General Parameters), set the 'Fax Signaling Method' parameter to No
Fax (IsFaxUsed = 0).
2. In the Fax/Modem/CID Settings page, do the following:
a. Set the 'Fax Transport Mode' parameter to Bypass (FaxTransportMode = 2).
b. Set the 'V.21 Modem Transport Type' parameter to Enable Bypass
(V21ModemTransportType = 2).
c. Set the 'V.22 Modem Transport Type' parameter to Enable Bypass
(V22ModemTransportType = 2).
d. Set the 'V.23 Modem Transport Type' parameter to Enable Bypass
(V23ModemTransportType = 2).
e. Set the 'V.32 Modem Transport Type' parameter to Enable Bypass
(V32ModemTransportType = 2).
f. Set the 'V.34 Modem Transport Type' parameter to Enable Bypass
(V34ModemTransportType = 2).
3. Set the ini file parameter, BellModemTransportType to 2 (Bypass).
4. Configure the following optional parameters:

'Fax/Modem Bypass Coder Type' (FaxModemBypassCoderType).

'Fax Bypass Payload Type' (FaxBypassPayloadType) - in the RTP/RTCP
Settings page (Configuration tab > VoIP menu > Media > RTP/RTCP Settings).

ModemBypassPayloadType (ini file).

FaxModemBypassBasicRTPPacketInterval (ini file).

FaxModemBypasDJBufMinDelay (ini file).
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