Telecommunications Industry Association
Newport Beach, CA February 19 – 21, 2003
Technical Committee TR-30 Meetings
SOURCE: Gallaudet University
CONTACT: Fred Lucas
3421 Buttonwood Court
Reisterstown, MD 21136-4401
TITLE: Requirements for TIA-825 over IP
DISTRIBUTION: Members of TR-30.1
This contribution builds upon TR-30.1/02-12-154, Some User Considerations for ToIP, presented at the December meeting of TR-301. It provides a non-exhaustive list of Requirements for the interim standard for TIA-825 over IP.
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The purpose of the TR-30.1 work to develop an interim standard for the reliable transport of TIA-825 over IP in a network where 2 TDD’s are connected to the PSTN which incorporates VoIP links. This interim standard will define the necessary capabilities in the gateways between the PSTN and IP networks for the transport of TIA-825 signaling. It is the intent of this Interim Standard to make the presence of the VoIP links transparent to the TDD (i.e. not require new procedures for the TDD user).
The following are a list of requirements for the gateway function for TIA-825 over IP. This list is not exhaustive and input on additional requirements is sought.
1. Reliable transport of TIA-825 over the IP network.
With ITU-T V.150.1 now approved, it would appear that extensions of that Recommendation would be the logical approach.
2. Transport of DTMF tones over the IP network.
3. Text and Voice alternating in opposite directions
Under this requirement are 2 different modes of operation. Both are essentially the same scenario for the standard with voice in one direction and text in the other.
3a. Voice Carry-Over (VCO) where the deaf person is speaking and receiving responses via the TTY.
3b. Hearing Carry-Over (HCO) where a person with a speech disability is using text to transmit and is receiving voice responses.
4. Text and voice in one direction
Under this requirement are again 2 different modes of operation.
4a. Network Voice announcements may be preceded by a short burst of TTY (TIA-825). Following the voice announcement a longer TTY (TIA-825) message will be seen.
4b. When Interactive Voice Response (IVR) systems are involved voice and TTY (TIA-825) messages appear in one direction with DTMF tones in the other.
5. Transport of TTY (TIA-825) text character by character
In many cases the user of the TTY device will be typing very slowing (hunt and peck). Normal operation over the PSTN will send each character typed across the network without waiting for some form of end of line or end of message character. The gateway function should operate in a similar manner.
6. TTY calls are silent at call set-up
Generally TTYs are silent until the called party answers and responds with a TTY message. Therefore the gateway cannot rely on being aware that a call will require the conversion features defined in this IS during the initial call set-up.
7. TTYs are always on but tones are not
TTYs are always on but the FSK tones, defined in ANSI/TIA/EIA-825-A, are only present when keys are being depressed. . There is no unique calling/answering tone which identifies when the TTY is being used. The gateway function must be capable of detection without character loss.