In the stream of updated drafts for the IETF meeting in december, I found a draft namedReal-time text interworking between PSTN and IP networks.This is work-in-progress in Asterisk svn trunk. We already have support for T.140 realtime text in the SIP channel, and support for US TDD phones in the Zap/PSTN channel driver. During this summer, I’ve assisted a developer who implemented a RTT gateway in Asterisk, so you could call with an old PSTN TDD phone and have a conversation with a modern SIP client with support for realtime text.This code will soon be implemented in Asterisk svn trunk, so Asterisk will become the reference implementation for this draft. How many xOIP acronyms do we have now? FOIP, VOIP, TOIP? I surely missed a few there… :-)From the abstract:

IP networks can support real-time text communication. SIP-based real- time text is called Text-over-IP or ToIP. PSTN networks support real-time text using textphones (or TTYs). When real-timetext is supported by different networks, gateways are needed to provide interoperability. Real-time text capable gateways may also support real-time voice.This specification describes procedures for interworking between ToIP and PSTN textphones using a real-time text capable gateway (RTT gateway). It also describes ways to route calls to RTT gateways for several call scenarios. Procedures that support the phased introduction of RTT gateways and procedures that support the invocation of text channels at any time during the call are included. Interworking of PSTN text phones thatdo not support simultaneity of voice and text with IP User Agents that support simultaneous voice and text is also described.