Technical Summary
This document describes how to invoke transcoding services using the
conference bridge model. This way of invocation meets the
requirements for SIP regarding transcoding services invocation to
support deaf, hard of hearing and speech-impaired individuals.
The Framework for Transcoding with SIP describes how two SIP
UAs (User Agents) can discover imcompatibilities that prevent them
from establishing a session (e.g., lack of support for a common
codec or for a common media type). When such incompatibilities are found,
the UAs need to invoke transcoding services to successfully
establish the session. The transcoding framework introduces two models to
invoke transcoding services: the 3pcc (third-party call control)
model and the conference bridge model. This document specifies
the conference bridge model.
In the conference bridge model for transcoding invocation, a
transcoding server that provides a particular transcoding service
(e.g., speech-to-text) behaves as a B2BUA (Back-to-Back User Agent)
between both UAs and is identified by a URI. The UAs do not exchange
any traffic (signalling or media) directly between them
Working Group Summary
This document was developed in the SIPPING working group, in large
part to address requirements raised by related work dealing with
conferencing for the hearing-impaired. The document was initially
presented as an individual contribution, was adopted by the WG, and
went through several iterations as a working group document before
being formally reviewed in a working-group last call and developing a
consensus on publication.
Protocol Quality
This document was reviewed for the IESG by Jon Peterson. There are
believed to be several implementations of this approach either in-use or
demonstrated at interoperability events.