[RAI] How to exchange metadata about the media streams established with a SIP session

[Gonzalo Camarillo <[e-mail]>]

Folks,

I am sending this email to the RAI list because it is about an
architectural issue that affects more than one WG.

Both the CLUE and SIPREC WGs have identified the need to exchange
metadata about media streams that have been established using SIP. Both
groups need to transport such metadata between SIP UAs.

In CLUE, they are studying how to transport their metadata, as
documented in:
http://tools.ietf.org/html/draft-wenger-clue-transport-01

In SIPREC, they are planning to piggyback the metadata in SIP UPDATEs as
an XML-encoded body part. When they need to send a request for full
state (as opposed to partial state), they use an UPDATE request with a
particular body type, as documented in:
http://tools.ietf.org/html/draft-ietf-siprec-protocol-02

The best way to exchange metadata within a SIP session depends on the
type of metadata and on how the UAs need to interact with each other
(e.g., a UA simply pushing information to the other UA or a more
complicated protocol). Given that SIPREC and CLUE have different
metadata and interactions, it may well be that we decide to use a
different mechanism in each group. Nevertheless, I think both groups
would benefit from architecturally-inclined RAI people having a look at
their work. Please, continue this discussion focusing on their specific
requirements on either the CLUE list or the SIPREC list.

Somewhat related to this issue, the RTCWeb group discussed the use of
SCTP over UDP as a reliable NAT-friendly way to exchange data between
endpoints.

Cheers,

Gonzalo