The Return of IMS?
Posted by Vince Lesch on Tue, Feb 16, 2010 @ 05:26 PM
This is my first in what will become regular contributions to the Tekelec SIP Blog. In addition to covering SIP from a purely technical perspective, I will look at some of the traction and activities in the market. This installment focuses on the adoption of IMS, and hence SIP, by mobile operators as the foundation for supporting voice and SMS in LTE environments.
IMS, like many new technologies, has gone through a tremendous "hype cycle". There has been the typical name bashing - with claims such as IMS means "I Must Sell" new technologies and the ups and downs of "everyone is moving to IMS" and then "no one is moving to IMS". While initially developed by the mobile industry in 3GPP, it was widely adopted as a standard by the wireline and cable communities as well. At this point in time the number of commercial deployments of IMS has been modest by any measure and my guess is that there are probably more commercial wireline deployments of IMS then there are commercial wireless deployments. However, over the next few years that may all change.
On November 4th 2009, a relatively simple press release was made by a collection of mobile operators on the work that they had collaborated on to create an IMS profile that they named "One Voice". Simply put, this profile was created to help the industry secure a common standardized IMS voice (and SMS) solution. To do this, they defined a "profile" or specification that defines a common, recommended feature set from the 3GPP IMS specifications when multiple options exist for a single functionality. The goal of One Voice was in essence to have a common IMS profile to support Voice and SMS in an LTE environment.
Since then there has been considerable collaboration between the GSMA and participating One Voice companies to enable the profile work to be handed over to the GSMA to take the lead moving forwards. On February 15, 2010, GSMA announced that it had chosen to adopt the One Voice initiative and has given it its full backing. Having adopted the One Voice profile, the GSMA has opened the work to its entire membership (820+ operators and 220+ vendors) and will work with all interested companies to define protocols needed for LTE voice connectivity. It will also work to define the interfaces and functional architecture required to enable international roaming and establish interconnection policies between mobile operators, using the One Voice profile as the basis of that work. This will all result in the definition of end-to-end service principles for Voice over LTE. The sum total of work will be completed under the name of Voice over LTE, or VoLTE.
This work will hopefully benefit the entire operator and vendor community and move towards broadening the deployment of SIP and IMS-based technologies. The worldwide penetration of mobile phones greatly exceeds that of wireline phones so the adoption of IMS in wireless networks will greatly expand the use of SIP. Of course, the work will take time and LTE will not be deployed over night, although there appears to be growing momentum for LTE in large part driven by the huge uptake in mobile data.
In the mean time, what do I expect to see? Well, many operators today have deployed VoIP in their core network as part of their R4 soft switch deployments. However, when the 3GPP R4 specifications were adopted they selected BICC - or Bearer Independent Call Control - as the signaling protocol because of the relative immaturity of SIP at the time. Over the last 12-18 months we have begun to see some of the R4 soft switches (or MSS) in mobile networks evolve to support SIP in addition to BICC and of course SIP has become the "winner" for next generation signaling. Recently we have also seen interest in BICC-to-SIP functionality to help mobile operators cost effectively transition to SIP and interwork with other SIP based networks (e.g., international transit networks) from their BICC-based mobile core.
So will IMS happen in mobile networks as part of the deployment of LTE? More than likely the answer is yes based on the current direction being pushed by the mobile operators behind the VoLTE initiative. Of course many other questions remain, including: over what time frame will this happen, what is the evolution path, and how long will hybrid 3G-4G networks exist and what challenges will these hybrid networks create for operators? I will likely address these and other topics in future posts.
Vince Lesch
Tekelec CTO