4G/LTE is gaining traction across APAC, providing opportunities for operators to launch VoLTE and thereby enhance the voice experience they provide for their customers. As operators move to an all-IP future, delivering VoLTE is the next natural step in their evolution.
The end goal for operators is to migrate all of their customers over to the LTE network using VoLTE. This will free up precious 3G spectrum, and eliminate the expense of running two separate networks (the LTE/IMS network, and the Circuit Switch (CS) network that is used for 2G and 3G services). However, most operators will need to continue running these networks in parallel for the next few years, until there is complete 4G coverage.
During this period of transition, they will need to support roamers and subscribers who still actively use 2G and 3G services – customers who provide operators with substantial revenue streams. Operators need to ensure that the legacy services that were developed on the CS network are all available to VoLTE subscribers on the IMS. If they cannot do so, users will receive a completely different and potentially lower quality experience, depending on the network they are using. This challenge is commonly referred to as ‘service parity’. It is proving to be a major hurdle for operators as they work to bring their VoLTE services to their subscribers quickly and economically.
The main challenge
IMS and CS networks have different call-handling protocols and consequently vary in the capabilities they can offer. This presents significant barriers to achieving service parity for 2G, 3G and 4G customers.
In CS networks, legacy switches handle most of the basic call functionality that we typically expect (for example, call forwarding and call barring). New services have been added via Intelligent Network (IN) platforms, rather than by making changes to the actual switches. This has enabled operators to create many value-adding services that extend and enhance their communications offerings.
These additional services, such as voicemail, number translation, and mobile roaming, now create the basic fabric of the network. They are used by businesses and consumers extensively. Furthermore, IN-enabled, bespoke services have been created that generate premium revenue streams for the enterprise market – sometimes over 100 on a single enterprise communications network. Operators need to make sure that all these services continue to be available for their customers when using VoLTE.
In the IMS network, the ’switch’ is a router that cannot provide the call-handling capabilities of a CS network switch. Instead, a Multimedia Telephony Telecom Application Server, or MMTel TAS, provides this capability. However, this presents another problem: the GSMA IR.92 VoLTE standard only outlines the set of call-handling requirements of the MMTel TAS; it doesn’t address any of the functionalities provided by legacy networks via IN platforms that are still being used today. This means that the various, legacy value-added services that consumers and businesses have become accustomed to are not automatically supported when using VoLTE.
For an operator eager to roll-out VoLTE, to compete with OTT players, this creates a difficult situation. All of their subscribers will expect the same experience of service availability and functionality, regardless of whether their devices latch onto 2G, 3G or 4G access networks. The need to have many, different generation access networks in parallel operation will persist for a few more years, even in relatively developed LTE markets, as 4G coverage is not yet ubiquitous, and networks must also support roamers who still actively use 2G and 3G services.
Overcoming this challenge and achieving service parity
Service parity must be achieved across both CS and IMS networks, yet the technical and financial challenges of implementing this are significant. So what can operators do about this?
One option is to re-implement all of the services from the legacy network again on the new IMS network, and vice-versa. But such duplication is slow and expensive. It is not suitable for operators that are under immense competitive pressure to bring their VoLTE services to market quickly. Although these services will all need to be re-implemented eventually, doing so to an urgent and rigid timetable is impractical and can be extremely costly. Any re-implementation before full subscriber migration is a risk and is not cost-effective. Furthermore, it can result in a severely negative impact on customers who can no longer access certain services – more than likely leading to significant churn.
Some of the world’s leading operators are beginning to take a different approach; a more cost-effective, efficient way to deliver service parity, and at the same time realize the spectrum re-farming benefits that LTE offers. They are choosing to transform their service layer, placing an IMS service switching function (IMS-SSF) between the IMS network and the legacy network. This enables them to re-use already existing call-handling technology without the need for duplication. Consequently legacy services can be available for VoLTE, and vice versa. This delivers a consistent user experience for both legacy and IMS customers. This approach means that operators can enhance their VoLTE offerings at their own pace, and migrate their subscribers to VoLTE in a cost-effective manner, without detriment to the user-experience they receive.
Operators across South and South-East Asia that are looking to offer VoLTE will need to look beyond the IR.92 standard if they want to avoid any negative repercussions for their subscribers. Fortunately, there are technologies available that will allow operators to offer their subscribers a smooth and consistent experience, with increased quality of calls and shortened set-up times, thereby reducing churn. Service parity is essential to ensure that efficiency and value are not compromised – for the operator and for the subscriber.
By :- Chris Haddock, Head of Marketing, OpenCloud