As most of you probably already know there are standards bodies for everything in telecommunications and data communications. So if IMS is suppose to span all technologies and networks then how are standards being set. To understand this we will start were IMS started. The first standard body we need to look at is the ITU(International Telecommunication Union). The ITU created IMT-2000(International Mobile Telecommunications-2000) which is the global standard for 3G network. A collaboration of standards bodies make up the the IMT-2000. Inside the IMT-2000 there are two standards bodies that are the main focus for IMS: 3GPP(Third Generation Partnership Project) and 3GPP2. 3GPP delas with UMTS networks and 3GPP2 deals with CDMA networks. Both have created standards for IMS, but most will refer to the 3GPP standards. There are other groups in IMT-2000 working on IMS, but these two groups are the main focus of IMS. 3GPP introduced packet switched voice services in a standard called R4. IMS was introduced in standards R5/R6.
In R5 the standard calls for the use of SIP and IP has a basis for IMS. Hence this is were the IETF(Internet Engineering Task Force) comes in to play. IETF is responsible for SIP and other IP protocols. SIP is a good protocol but needed to be extended to fit the 3GPP needs. So 3GPP and IETF started working on extending the standards for SIP.
At the same time other groups like CableLabs(Cable Companies standards) started defining IMS support in DOCSIS(Data over Cable Services Interface Specification) 2.0. Also wireline groups ETSI(European Telecommunications Standards Institute) TISPAN(Telecoms & Internet converged Services & Protocols for Advanced Networks) defining (EMEA) wireline extensions to IMS. For North Ameica, ATIS(Alliance for Telecommunications Industry Solutions) is developing IMS specs for NA market.
As you can imagine these groups all have special needs of SIP and this also gets pushed back into the IETF. Within the IETF, there are working groups that have areas. One of the areas was SIP. Once IMS chose SIP has a basis it became clear that the SIP group was going to be over worked. So to help with the problem the IETF created a new working group call SIPPING. The purpose of SIPPING is to gather SIP requirements from all areas and prioritize work before it goes to the SIP working group.
I have given a brief of descriptions and standards bodies and their roles in IMS. There is one more body that I would like to mention. Even though this group does not define any IMS specification it does deal with applications that will ride on top of the IMS architecture. This group is OMA(Open Mobile Alliance). To date they have defined Push to Talk and IM for IMS architectures.
Hopefully this has been helpful in understanding all the different industries and standards bodies that are working on IMS. I have include a diagram below to summarize this topic. Below the diagram I have also listed links to the various standards bodies.
Standards Bodies Links