AudioCodes Mediant 3000 User Manual page 170

When using T.38 mode, you can define a redundancy feature to improve fax transmission
over congested IP networks. This feature is activated using the 'Fax Relay Redundancy
Depth' parameter
Redundancy Depth' parameter (FaxRelayEnhancedRedundancyDepth). Although this is a
proprietary redundancy scheme, it should not create problems when working with other
T.38 decoders.
13.2.2.1.1 Switching to T.38 Mode using SIP Re-INVITE
In the Switching to T.38 Mode using SIP Re-INVITE mode, upon detection of a fax signal
the terminating device negotiates T.38 capabilities using a Re-INVITE message. If the far-
end device doesn't support T.38, the fax fails. In this mode, the 'Fax Transport Mode'
parameter (FaxTransportMode) is ignored.

To configure T.38 mode using SIP Re-INVITE messages:
1. In the SIP General Parameters page (Configuration tab > VoIP menu > SIP
Definitions > General Parameters), set the 'Fax Signaling Method' parameter to T.38
Relay (IsFaxUsed = 1).
2. In the Fax/Modem/CID Settings page, configure the following optional parameters:
•
'Fax Relay Redundancy Depth' (FaxRelayRedundancyDepth)
•
'Fax Relay Enhanced Redundancy Depth'
(FaxRelayEnhancedRedundancyDepth)
•
'Fax Relay ECM Enable' (FaxRelayECMEnable)
•
'Fax Relay Max Rate' (FaxRelayMaxRate)
Note:
13.2.2.1.2 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:
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, set the 'Fax Transport Mode' parameter to
RelayEnable (FaxTransportMode = 1).
3. Configure the following optional parameters:
•
'Fax Relay Redundancy Depth' (FaxRelayRedundancyDepth)
•
'Fax Relay Enhanced Redundancy Depth'
(FaxRelayEnhancedRedundancyDepth)
•
'Fax Relay ECM Enable' (FaxRelayECMEnable)
•
'Fax Relay Max Rate' (FaxRelayMaxRate)
User's Manual
(FaxRelayRedundancyDepth)
The terminating gateway sends T.38 packets immediately after the T.38
capabilities are negotiated in SIP. The originating device sends no-op T.38
packets after the T.38 capabilities are negotiated in SIP. For this feature to
function, no-op packets must be enabled (NoOpEnable = 1).
and the
170
Mediant 3000
'Fax Relay Enhanced
Document #: LTRT-89729