Despite its multimedia capabilities the IP Multimedia Subsystem (IMS) hasn't yet gotten a lot of opportunities to show its capabilities in wireless networks. One of the reasons for this is that current circuit switched mobile voice telephony works well and meets user expectations. Things, however, are improving for IMS.
With the introduction of the iPhone, more and more people are getting aware of multimedia and Internet capabilities of mobile devices. Thus, it might well be possible that multimedia enriched voice calls might also soon appear on the radar screen of users. On the network side many operators are upgrading their current 3G networks to 3.5G and with the first WiMAX networks rolled out now and LTE on the horizon there is sufficient bandwidth for such services. Additionally, WiMAX and LTE networks no longer have a circuit switched part and operators need a solution such as the IMS to be able to offer conversational services over their next generation networks. It thus seems inevitable, that the IMS will have a bright future.
In practice, however, things will be a bit more difficult since third party VoIP service providers such as Skype, Vonage and others could try to take a piece of the wireless market in a similar way as in fixed line networks today. After all, the application layer does not care whether IP packets traverse a DSL line or the air interface of a wireless network as long as there is enough bandwidth. From my own experience, SIP and proprietary VoIP services such as Skype work well over 3.5G wireless networks and even Skype video calls have excellent video quality in both directions.
Network operator based IMS systems, however, have a number of advantages over voice services provided by third parties if the play their cards right:
Network operators today sell both a mobile device and voice service. This means that the service works out of the box, no configuration required by the user. With pre-installed and pre-configured IMS applications such as voice, video calling, presence, etc. they have a head start over third party services for which applications have to be installed on mobile devices.
The IMS is also able to request a certain bandwidth for a session from the transport layer. In case there is congestion anywhere in the network, it will be made sure that multimedia sessions are not impacted.
The third advantage, which I think is a major one, is that IMS gives network operators with both fixed line (think DSL, cable) and wireless assets (think HSPA, WiMAX and LTE) the opportunity to converge their voice + multimedia service offerings both in the network and from the users point of view.
In the fixed line world the transition from analog telephony to VoIP over DSL or cable is already in full swing. The incentive for the user to switch to VoIP is usually a lower price for a combined voice service and Internet access over DSL or cable. When combined with mobile voice + Internet access, network operators can offer their clients Internet access + voice (and multimedia) telephony both at home, in the office or while roaming outside with a single device and a single telephone number.
The IMS also allows to have many devices registered to the same telephone number. This is great since at home it might be more convenient to use a dedicated phone, a notebook or even an IMS capable and connected television set to make a voice or video call.
With Voice Call Continuity (VCC) there is even the possibility that a mobile device automatically switches to Wifi when the user returns home or to his office thus reducing the load on the cellular network. Switching to Wifi at home also solves the issue of 3G/4G in-house coverage which in many regions of the world is inferior to 2G coverage due to the use of higher frequency bands.
And finally, the IMS has the capabilities to transfer a voice call from one device to the other. This is quite interesting in scenarios in which the user returns home and then transfers an ongoing voice call from his mobile phone to a television set and adding a live video stream to the call in the process.
It's clear that getting all of this right is not a trivial task. But if network operators want to retain their role as a service provider they have to go beyond what third party service providers could offer over a bit pipe.
As always, thoughts and comments are welcome!