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Problem Description

In the e911 industry there is still a small segment of the population that uses TTY devices for the hearing impaired.  These devices use specific tones called Baudot tones to communicate letters and characters via key presses on the keyboard of the TTY device. Although this has changed in today’s world using such technologies as SMS, TTY devices are still in use.  One differing capability is that SMS is not assured delivery nor real time whereas a TTY call is similar to a voice call and is real time communication as if you were speaking.

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1. An initial INVITE from IMG to SIP Server, any vocoder can be negotiated.

2. Upon detection of Baudot tone, the IMG shall send a Re-INVITE:

   1. SDP is the same as negotiated initially,

   2. R-URI will carry custom parameter “tty-ind”, indicating Baudot tone has been detected.

3. Application Server will send Re-INVITE to IMG

   1. SDP shall specify G711 codec in order to establish G711 voice path,

   2. SDP will specify information to establish media stream to the T.140/RFC4103 transcoder.

Note: The Baudot detection feature is available on PICASSO voice module only.

Note: The media received by the IMG, between the Baudot tone detection and the reception of the Re-INVITE from Application server, will not be sent to the T.140/RFC4103 transcoder.

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