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Command Reference Guide
t38
Use the t38 command to enable T.38 fax operation on the Media Gateway Control Protocol (MGCP)
endpoint. Use the no form of this command to disable this feature.
The modem-passthrough command must be enabled for T.38 operation to work. Refer to
modem-passthrough on page 3238
Syntax Description
No subcommands.
Default Values
By default, T.38 is disabled.
Command History
Release 16.1
Release A2
Usage Examples
The following example enables T.38 on MGCP endpoint 1:
(config)#voice mgcp-endpoint 1
(config-mgcp-1)#t38
Technology Review
T.38 is an International Telecommunication Union (ITU) specification that allows Group-3 Fax (T.30) data to
be transported over the Internet. It is similar to dual tone multi-frequency (DTMF) relay (RFC 2833) in that
the digital signal processor (DSP) decodes tones and demodulated fax data and converts them into
packets. A similar device on the other end takes the packets/tones and remodulates them so that an
analog fax machine on the other end can receive the fax. AOS's previous support (revisions 12 through 15)
for fax/modem signals was simply detecting a tone and forcing the coder-decoder (CODEC) into G.711 and
disabling/enabling echo cancellers based on the tones detected. When packet loss becomes high, sending
faxes over G.711 becomes problematic, due to dropped messages and timeouts/retrains.
T.38 can be used in conjunction with various call-control schemes, such as H.323, Session Initiation
Protocol (SIP), and MGCP. AOS only supports SIP as the call-control method. This is typically referred to
T.38/Annex-D. Annex-D describes the Session Initiation Protocol/Session Description Protocol (SIP/SDP)
call establishment procedures.
60000CRG0-35E
for more information.
Command was introduced.
Command was added to the MGCP endpoint configuration.
Copyright © 2012 ADTRAN, Inc.
MGCP Command Set
3247
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