In a previous post What is IP Multimedia Subsystem (IMS) I had mentioned a few use cases for IMS in order to explain how it could be used. I followed that post up with a question on LinkedIn asking the community to share any other interesting use cases they might have thought of or come across.
Alexander Sevastyanov clarified that most of the use cases given by me were possible via the internet without IMS and listed “true” end-user differentiators of IMS and the reasons why these values are not playing yet:
1) IMS subscription makes end-user universally accessible by SIP services as GSM has done it for circuit switched voice – unfortunately current technology requests for constantly active PDP context and some signalling traffic via IMS APN. With the future evolution of 3G this will be overcome and PDP attach will be enough for on-line status in IMS.
2) Two and more IMS users (irrespective of roaming status and home operators) can establish peer-to-peer SIP application session – unfortunately IMS and SIP multivendor compatibility is still in the roadmaps, while H.324M standard easily allows two 3G phones to establish multimedia session inside 64 kbit/sec circuit switched channel (e.g. 3G video call) already now.
3) IMS is a one SIP Registrar with one SIP subscription for all SIP services – same problem with SIP compatibility. Usually SIP Application servers request for usage of own SIP clients, so that to use IMS as external SIP Registrar a dedicated SIP client has to be developed (who said that you can just add SIP applications on top of your infrastructure?).
4) IMS provides mobility management for your SIP services – same problem with IMS multivendor compatibility complemented by the fact that preferred way of GPRS roaming is via home GGSN, so all IMS mobility management with Proxy-, Interrogating-CSCF is never used.
Usually the list of IMS values is longer, but I put here only differentiators – the ones, that cannot be offered by some Internet Registrar or Application server (e.g. Skype, MSN, ICQ, ISP-mails etc.). And the main technical problem is compatibility and standardization. So overall impression is that the reason why IMS is not flying so good as GSM is that it has started being sold in too row condition – try to guess how successful would be GSM if first sold without roaming, SMS, mobility management and even simple and compatible handsets!
In the last twenty years Telecom has gone from national regulated era, via deregulation phase to finally commoditized state. The business model of successful mobile services deployment was formed in the years of deregulation, when competition gave rise to good solutions, but the profitability of vendors was still high to allow for good R&D and complete and fast go-to-market. Now that all vendors are balancing at the edge of profitability it is hard to expect that they can invest into fast IMS spreading in mobile world (look at 3G history). But operators should also adopt their mentality and approaches to commoditized reality – why they still dream about “killing VAS like it was with SMS”?