Transition to a replacement for the text telephone (TTY) system...

years for getting the TTY replacement “commonly available,” three years until “no more legacy TTYs should be deployed,” and an additional six years until TTY support can cease, the subgroup said. That timeline can be sped up or slowed down depending on conditions in the overall transition from the public switched telephone network to Internet protocol, the subgroup said in the report. The subgroup recommended implementing the National Emergency Number Association i3Detailed Technical specification 08-003 and Internet Engineering Task Force (IETF) request for comment 6443 to achieve interoperability between service providers when at least one uses IETF Session Initiation Protocol (SIP) for call control. The default interoperability protocols include: IETF RFC 3261 SIP for call control, ITU-T Recommendation T.40 for real-time text presentation and IETF RFC 4103 for real-time text transport, as well as “suitable audio and wide-band audio codecs” commonly used in the implementation environment and supported by Next-Generation 911 (N-G9-1-1). For IMS, the profile specified in GSMA PRD ir.92, including its Annex B, specify a “similar set suitable” for TTY replacement, the subgroup said. That profile also recommends IETF RFC 3261 SIP for call control and IETF RFC 4103 for real-time text, but also requires 3GPP TS 26.114 IMS Multimedia Telephony Codec Considerations for audio. A “suitable combination” with video as specified in GSMA PRD ir.94 should be considered, the subgroup said. Other real-time text protocols can also be used within each service provider’s network or between service providers, provided the functional goals for TTY transition are still met and other protocols are supported as a fallback, the subgroup said. For interoperability of calls between PSTN’s TTY and the TTY replacement, the subgroup recommended placing gateways in the network -- and that calls that may contain text should automatically be routed through the gateway. Other alternatives should also be considered and further investigated, the subgroup said. Recommendation T6.3, which allows for conversion of TTY to IP-carried real-time text at the point of entry to IP networks, is the “realistic solution” for TTY access to N-G9-1-1, the subgroup said. There should be coordination with the U.S. Access Board, the Telecommunications Equipment Distribution Programs and the National Deaf-Blind Equipment Distribution Program, the subgroup said. TSR rules should be updated to “specifically support relay calls based on the protocols used in accessible interchange with N-G9-1-1,” including information requested in the NENA i3 technical specification, the subgroup said. Videophone and VRS service providers should implement TTY replacement features in combination with video, the subgroup said. NENA recommendations to provide 9-1-1 access to instant messaging users should be encouraged separately from TTY replacement activities “in order to provide 9-1-1 access for current users of these services related to both accessibility and general needs,” the subgroup said. The draft report includes two possible versions of a recommendation for a move toward TTY replacement in industry practice and FCC regulations, as the EAAC “could not come to an agreement” on a common version (http://bit.ly/Y5tvjC).