Re: Proposed XMPP Extension: Jingle Synchronized Real-Time Text

Thanks Marvin, I agree with these points. I opened PR #1548 to address them.

The update clarifies that XEP-0167 already supports RTP/T.140 without 
rtt-sync,
moves grouping to XEP-0338, removes lang/sync-group/sync-reference from 
rtt-sync,
adds RFC 8864/RFC 8373 as open mapping work, and includes an 
illustrative SIP/SDP
RTP/T.140 example so we can discuss the mapping target more concretely.


mvg,

Edward Tie


Op 3-6-2026 om 08:29 schreef Marvin W. via Standards:
> On Tue, 2026-06-02 at 19:41 -0500, Stephen Paul Weber wrote:
>>> Reason that 911NG/112NG are using standaard T.140 via gateway SIP.
>>> It must
>>> be same data without delay.
>> Any gateway could easily convert the format though, no?
> Only if the gateway is a MITM gateway, requiring server resources and
> increasing latency. Using the T.140 standard via standard RTP (RFC
> 4103) and WebRTC Data Channels (RFC 8865) seems sensible for better
> end-to-end real-time interop.
>
> XEP-0167 already supports RTP/T.140 out of the box, the only addition
> in this specification is the rtt-sync metadata element. It's thus
> important that the specification points out that other implementations
> may use RTP/T.140 without the rtt-sync element.
>
> RFC 8865 uses the dcmap and dcsa attributes from RFC 8864. We don't
> have a mapping for RFC 8864 at this point. Rather than only specifying
> the use of RFC 8865, it would be more sensible to add an RFC 8864
> mapping, which implies compatibility with RFC 8865 in the same way as
> XEP-0167 supports RTP/T.140.
>
> The sync-group/-reference/-name rtt-sync attributes should use the
> existing XEP-0338 instead.
>
> The lang rtt-sync attribute should be transported using a mapping of
> RFC 8373 SDP, which we don't have yet, but would potentially also be
> useful for other Jingle media.
>
> As you already explained that SIP gateways are a target usecase, I am
> interested in seeing an example SDP as it would be on the SIP side, so
> we can together figure what is the best way to map these. I am not a
> subject matter expert of RTT over SIP, but I believe the SDP likely is
> to refer to IANA registered SDP attributes, which typically have RFC or
> other standard documents referred, which could be very useful to
> discover both the most reasonable SDP mapping for XMPP and for more
> specification of the meaning of certain attribute values. If the SDP
> does include attributes that are not well defined in any existing
> specification documents at applicable standards organizations (IETF,
> ITU, 3GPP), it may be useful to specify them with any of them first, so
> we can build our XMPP/Jingle on top of those.
>
> Marvin
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