Shepherd writeup

Shepherd writeup for draft-ietf-stox-7248bis-05

1. Summary

The document shepherd is Saúl Ibarra Corretgé.

The responsible Area Director is Ben Campbell.

This document describes bidirectional protocol mappings for the
exhcnage of pressence information between SIP (Session Initiation
Protocol) and XMPP (eXtensible Messaging and Presence Protocol)
endpoints. RFC 7247 provided the basic architectural concepts for
interworking between the two protocols, and this document is
dedicated to describe to apply such concepts in the context of
presence exchange.

RFC 7248 was already published when some important problems were
found in draft-ietf-stox-groupchat, which also applied to RFC 7248.
This problems were related to the diagrams describing the architecture
of the system, hence the need for a -bis RFC.

The requested publication type is Standards Track, as it provides
normative guidance for interwork gateway designers.

2. Review and Consensus

Presence is one of the key components in the context of instant messaging.
Throughout time both SIP and XMPP grew the capability to exchange presence
information. Because these two protocols are widely deployed and presence
is used, it makes sense to try and interwork between the two.

The STOX WG was created to tackle the task of producing the necessary
specifications for SIP - XMPP interoperability. Presence was part of this
work and the result was published as RFC 7248.

Unfortunately, some issues raised by Ben Campbell during the review
of draft-ietf-stox-groupchat also applied to draft-ietf-stox-presence, but
it was already a published RFC. The issues raised where specifically:

- innacuracy of diagrams regarding SIP traffic
- confusing double-gateway model

The original email that kickstarted the discussing can be seen here:

The consensus was to create a new document rather than submitting
errata since the changes are significant.

Some other issues were raised during the review of the former RFC 7248 and
the current -bis version: the architectural assumptions were not correct. In
SIP, presence servers handle SUBSCRIBE requests for the user and communicate
this via the 'presence.winfo' package as specified in RFC 3857. The described
architecture also considered the use of 2 gateways on the same setup, but that's
highly unlikely in real deployments (which we have knowledge of), so they have
been adjusted to consider the case where the core infrastructure is SIP and there
is a gateway to XMPP and vice versa.

The architectural assumptions and diagrams have been adjusted to match this model.

During the review of this document, special attention was directed at the diagrams
and signalling flows, which were throroughly reviewed by Markus Isomaki and
Ben Campbell. Some vestiges of RFC 7248 were still present in the text, which the
author corrected as per the received feedback. Diagrams were also further adjusted
to better express the single gateway model (RFC 7248 used a dual-gateway
architecture, as mentioned above). Last, terminology was clarified in order
to better express the responsibilities of the involved signalling entities on the
SIP side: 'SIP Proxy' replaced 'SIP server' and the role of a possibly separate
SIP presence server was also clarified.

All issues raised have been addressed and the document shepherd is
not aware of any further standing problems with the document moving

3. Intellectual Property

Each author has confirmed conformance with BCP 78/79. There are no IPR disclosures on the document.

4. Other Points

The document obsoletes RFC 7248.