VOIP and TTY

TTY (Teletype) and the later term TDD (Telecommunications Device for the Deaf) is a technology used by the hearing impaired to communicate over the phone. In the USA support of TTY is required in some public places (call centres, hotels, etc).

Asterisk has some basic Alpha level code (as of December 2006) with support for TTY.

There is some additional information available at tdd mode. Asterisk svn trunk has support for T.140 Real-time text and improvements on the TDD mode in zaptel. TDD support is being developed in SIP too as well as a TDD gateway between zaptel (analog devices) and SIP/T.140 real time text in RTP.

See Also

• ipTTY is a good example of an application that supports TTY over IP Product Site
• TTY & TTD Over VoIP: Dispelling the “Packet Loss” Myth – Cisco
• TDD/TTY – Information at Assistive Technology.