Avaya Communication Manager Administrator's Manual page 1136

Screen Reference
Valid entries
relay
pass-through
Redundancy
Valid entries
0 to 3
TDD/TTY Mode
Valid entries
off
US
UK
pass-through
1136 Administrator Guide for Avaya Communication Manager
Usage
For users in regions using this codec, use relay mode for modem
transmissions over IP network facilities. Avaya V.32/FNBDT Modem
Relay is supported when using modem relay mode.
Note: Modem over VoIP in relay mode is currently available only for use
by specific analog telephones that serve as Secure Telephone Units
(STUs). Contact your Avaya technical support representative for more
information.
For users in regions using this codec, use pass-through mode for modem
transmissions over IP network facilities. Avaya V.8 Modem Pass-Thru is
supported when using modem pass-through mode.
Usage
Enter the number of duplicate or redundant packets that are sent in
addition to the primary packet for all Modes except pass-through and
Clear-channel. The default is 0.
Usage
Turn off special TTY handling when using this codec set. In this case, the
TTY transmission is treated like an ordinary voice call.
With a codec set that uses G.711, this setting is required to send TTY calls
to non-Avaya systems. However, there might be errors in character
transmissions.
For users in regions using this codec, use U.S. Baudot 45.45 mode for
TTY transmissions over IP network facilities. This is the default for new
installations and upgrades to Communication Manager R2.1.
For users in regions using this codec, use U.K. Baudot 50 mode for TTY
transmissions over IP network facilities.
For users in regions using this codec, use pass-through mode for TTY
transmissions over IP network facilities.