4G / LTE is gaining signification traction and being rolled out across Asia and the rest of the world. As this happens, telecom operators are equally enthusiastic to implement VoLTE, which is emerging as the preferred solution to support voice.
VoLTE is deployed over the IP Multimedia Subsystem (IMS) network, a system that is connected directly to the underlying LTE network.
The operator’s end goal is to migrate all of their customers over to the LTE network using VoLTE, to free up the precious 3G spectrum, and the expense of running two separate networks – the LTE/IMS network and the circuit switch, which is used for 2G and 3G services. However, most telecom operators will still be running both networks in parallel for the next couple of years to come, until there is complete 4G coverage, and also to support roamers and subscribers who still actively use 2G and 3G services.
During this period, telecom operators need to ensure that the legacy services that were developed on the circuit switch are all available to VoLTE subscriber on the IMS, otherwise users will receive a completely different experience, depending on the network they are using. This challenge is commonly referred to as service parity and is proving to be a major hurdle for operators as they look to bring their VoLTE services to market quickly and efficiently.
Services that rely on different networks
The main challenge of service parity lies in the fact that the IMS and the circuit switch currently work differently in terms of their call handling capabilities for new services and functionality.
In the circuit switch, the switch itself provides a lot of the basic call handling functionalities like call forwarding and call barring. As time has progressed, most new services and capabilities have been added to the circuit switch network through Intelligent Network (IN) platforms, rather than by making changes to the switch. This has enabled operators to create value added services which complement their pre-existing communications offerings. Businesses and consumers use these services extensively, but also take them for granted.
Voicemail, number translation, and mobile roaming are all part of this, and create the basic fabric of the network. Perhaps most importantly, bespoke services have also been created to provide premium revenue generating services for the enterprise market – in many cases over 100 have been developed. Operators must ensure that these services are available now and in the IP networks of tomorrow.
However, in the IMS network, the “switch” is merely a router and cannot provide call handling capability that the circuit switched telephony switch does. The Multimedia Telephony Telecom Application Server, or MMTel TAS, provides this instead. But therein lies a problem, the GSMA IR.92 VoLTE standard only makes the set of call handling capabilities needed by the MMTel TAS, it doesn’t address any of the functionalities to do with the pre-existing legacy networks using IN platforms that are crucially still being used today.
For an operator eager to roll-out VoLTE to compete, this is going to be a particularly poignant challenge. As their subscribers devices will latch onto pre-existing 2G, 3G and now 4G access networks depending on operator coverage, all users will expect the same experience in terms of service availability and function. The need for multiple, concurrently run access networks is here to stay for at least the near future, even in relatively developed LTE markets.
Accomplishing service parity
Service parity must be achieved across both networks, however the challenge of implementing it is still very present – so what can operators do? One option is to systematically re-implement all of the services from the legacy circuit switch network again on the new IMS network. But this is slow, expensive, and not feasible as operators are under immense pressure to bring their VoLTE services to market quickly and stay in the race with their competitors.
Whilst these services will need to be re-implemented in due course, doing so to a rigid and urgent timetable is extremely costly. On top of that, any re-implementation and deactivation of these services when subscriber migration is not significantly achieved will result in tremendous negative impact on subscribers, who will no longer have access to these services and will more than likely lead to significant churn. Network transformation cannot be instant, as much as operators would like it to be. Doing so instantly would significantly impede reputation, and also the re-farming of spectrum that LTE offers and indeed promises.
But there is another approach that some leading operators across the globe are already beginning to employ, a more cost effective, efficient way to deliver service parity. These operators are choosing to transform their service layer, to enable IMS users to employ the services from the circuit switch network.
An IMS service switching function (IMS-SSF) is being used by some operators between the IMS network and the legacy network, enabling them to re-use already existing call-handling intelligence technology in the IN network when needed. This will deliver a consistent customer user experience, whilst also being capable of doing the reverse so new IMS services can be available to legacy network users as they become available. By using an IMS-SSF, operators can re-use their legacy services, enhance VoLTE at their own pace, and cost effectively migrate their subscribers to VoLTE without affecting the experience they receive.
Operators across Asia who are looking to offer VoLTE without any negative effect on the subscriber, will need to look beyond the IR.92 standard for VoLTE. A technology that gives them the ability to offer subscribers a smooth and consistent experience is needed; reducing churn and increasing the quality of calls, and set-up times. Achieving Service Parity is essential to ensure that efficiency and value is not compromised, for the operator or the subscriber.
Chris Haddock, head of Marketing, OpenCloud
