Subscription Data Format

I have become very concerned about making subscription requests work
through gateways between APEX and SIMPLE systems.

The subscription data format I proposed at

    http://simp.mitre.org/drafts/sdf.txt

was an attempt to make a concrete realization of what was in the CPIM
document that can be signed.  I spent some time reading the presence
proposals for APEX and SIMPLE.  The APEX proposal at

    http://www.ietf.org/internet-drafts/draft-ietf-apex-presence-06.txt

contains information exchanges that roughly follow the CPIM document,
so a common subscription data format based on CPIM should not be
difficult for APEX, however, the case for SIMPLE is quite different.
The SIMPLE documents include one that describes a subscription data
format in

    http://www.ietf.org/internet-drafts/draft-ietf-simple-winfo-format-02.txt

and describes its use in

    http://www.ietf.org/internet-drafts/draft-ietf-simple-winfo-package-02.txt

The SIMPLE subscription data format is designed to support a
subscription state machine that includes states that cannot be reached
using the CPIM model.  A SIMPLE client attempting to subscribe to an
APEX presentity might see surprising, and non-intuitive results.

It appears to me that the best way to ensure interoperability is to
define a core XML format used by all IMPP compliant protocols, much as
PIDF defines a common core.  Additional functionality would be
supported with extensions based on XML name spaces, as in PIDF.
Furthermore, the search for a common core might drive the CPIM model
of subscriptions to have more states, thereby better reflecting common
practice in instant messaging systems.  Of course, the other benefit
in a common format is that it can be signed.

John



  [reminder: [email protected] for non-technical discussions, please]