Command Reference Guide

3Com Router 5000 Family and Router 6000 Family fax protocol ● 161
Command Reference
Description Use the fax protocol command to configure the protocol for intercommunication
with other devices or enable the fax Passthrough mode, and configure the number of
redundant packets sent via the T.38 fax protocol. The argument standard-t38
indicates the standard T38 negotiation mode specified by H323 or SIP adopted.
Use the undo fax protocol command to restore the default number of
redundant packets and disable the fax Passthrough.
This command is only applied to IP Fax.
Low-speed data refers to the V.21 command data, and high-speed data refers to the
TCF and graphic data.
To intercommunicate with the mainstream fax terminals of the industry, the
mainstream fax protocol must be used. Likewise, to intercommunicate with other fax
terminals supporting the T.38 protocol, the T.38 protocol must be adopted. As the
mainstream devices do not support local training mode for fax, the end-to-end
training mode must be adopted in order to implement intercommunication with the
mainstream devices of the industry.
Increasing the number of redundant packets will improve reliability of network
transmission and reduce packet loss ratio. A great amount of redundant packets,
however, can increase bandwidth consumption to a great extent and thereby, in the
case of low bandwidth, affect the fax quality seriously. Therefore, the number of
redundant packets should be selected properly according to the network bandwidth.
The fax Passthrough is easily influenced by such factors as loss of packet, jitter and
delay, so the clock on both sides of the communication must be kept synchronous. At
present, only G.711Alaw and G.711μlaw compression methods are supported, and
the voice activity detection (VAD) function should be disabled for fax Passthrough.