Instant Messaging and Presence - the IMPP working group
The IMPP is the standards committee behind the IM world, chief contributors being AOL, Microsoft et al.
Much confusion surrounds the efforts to standardise on an IM protocol. Different IM communities have appeared and, other than some work to make AOL and Microsoft interoperate with ICQ, little progress had been made until recently. IMPP has now established the requirements for a standard protocol and, in CPIM (a Common Profile for Instant Messaging) it sets out an architecture and discusses server-to-server interoperability in a multi-protocol environment.
SIP is one of three proposed protocols in the IETF's IMPP working group - the others being PRIM and APEX (formerly IMXP).
PRIM and APEX are both designed specifically for the needs of IM whereas SIP would require some extensions to fulfil the requirements of the IMPP working group. PRIM takes as its starting point the idea that a standard protocol should be based on the existing proprietary architectures for IM; APEX does IM and presence on top of a BEEP (Blocks Extensible Exchange Protocol) mesh - an XML protocol.
Due to the obvious need for presence to be used in voice communications, SIP is a strong contender as the mechanism by which users and applications communicate their presence data to and from the network. The PRIM group have acknowledged this and allow the possibility of interfacing with SIP for voice applications. The strongest argument for SIP is probably that of convergence: the other initiatives require an IM-specific infrastructure. SIP, of course, can also be used for many other purposes. Significant in this respect is the decision by Microsoft to adopt SIP for real-time communications on the .NET framework.
The CPIM document shows that some consensus is being reached. A likely outcome, however, is that each of the groups will pursue their own protocol but will support base-level interoperability.
Further information can be found on the IMPP Products and Services