IMS far more mature than many realize, according to a newly published whitepaper from the MultiService Forum (MSF) that outlines the useful lessons learnt from the GMI 2006 interoperability event held in October. 
The conclusion of the whitepaper focuses on the main lessons learnt, and the way forward. Six key issues emerged:
- 1. The "Pre-conditions" mechanism for end-to-end QoS is not being consistently implemented by the industry. Current mechanisms, based on RFC 3312, exist but are not being widely embraced. The MSF will create a White Paper on this problem as input to the relevant standards bodies.
- 2. No P-CSCF tested had implemented an H.248 interface to directly control the D-SBG-NE. Some vendors assumed the presence of an intermediary function such as the SPDF of the ETSI TISPAN R1 architecture, whilst many Session Border Gateways (SBGs) combined both the S-SBG and D-SBG functions in a single element. The MSF will re-assess industry trends in this area and may revise the architecture and appropriate IAs (Implementation Agreements) accordingly.
- 3. There was a disappointing shortage of true IMS terminals, and much of the testing was done on SIP end points. Some of the IMS terminals might still be in the prototype stage, but the MSF considers that the industry missed a useful opportunity to put them to the trial.
- 4. Authentication proved a jungle -- there are so many options available that time was wasted and future users cannot be expected to find their way through such a proliferation of options without guidance. The MSF is looking for a way to sort this, and is evaluating the possibility of developing a new IA addressing authentication/authorization profiles.
- 5. The SBGs tested tended to focus on the UNI, or on the NNI in the interconnect scenarios. When deployed at the NNI to support roaming, the SBGs exhibited some attributes of a UNI, and some of an NNI. As a result, problems were encountered in the roaming scenarios, and the MSF has launched a work program to address this by developing a new IA.
- 6. No vendor supported the GMI roaming scenarios designed to provide testing of optimal routing of media. In all cases tested, the media followed the SIP signaling path back through the home networks, with a resulting QoS degradation. The MSF will liaise with appropriate industry bodies to address this issue.
However, the report's final conclusion is the one that will make the biggest impact. To quote: "Reality is closer than we thought. Most of the equipment worked straight away, almost out of the box. This makes it clear that it is appropriate for the MSF to take interworking to the next stage of rigour and explore implementing an industry wide certification program."
The whitepaper is available online.
http://www.msforum.org/interoperability/wp2006.shtml
