Opinion: Delivering service parity for VoLTE

(Image Credit: iStockPhoto/Martin Dimitrov)

Most analysts are in agreement that mobile operators will be running a circuit switched and IP Multimedia Subsystem (IMS) network concurrently for many years, as they roll-out LTE network coverage and introduce Voice over LTE (VoLTE). Circuit switched networks, that deliver 2G and 3G services, are essential to provide service to users that haven’t yet upgraded to 4G, to fill-in where internet protocol (IP) coverage is poor and to support roamers.

During this period, operators are faced with the challenge of delivering a consistent and common set of  communication services across all generations of their networks, often referred to as ‘service parity’. Failure to do so will result in an incoherent experience for subscribers, receiving a different set of services depending on the network – 2G/3G or LTE – they are currently latched onto.

A legacy of services in the circuit switched network

In a traditional circuit switched network, the network switch provides basic call handling features such as call forwarding and call barring. Over the years, however, many new services and additional functionality have been developed and added to the circuit switch network – created on additional Intelligent Network platforms (IN) in the service layer. The IN platform has enabled operators to create value-added services to compliment their core telephony offerings. These services – such as voicemail, call screening, number translation, routing optimisation, and mobile roaming – make up the fabric of the operators’ service offering. In particular, services created for enterprise customers are in abundance, as many as fifty to one hundred in many networks, that are frequently used and highly valued.

In the IMS network, the ‘switch’ is just a router and does not provide any of the call-specific handling capabilities available in the circuit-switched switch. The Multimedia Telephony Application Server (MMTel TAS) provides call handling on the IMS network that is equivalent to that provided by a circuit-switched switch. However, the GSMA IR.92 VoLTE standard specifies the basic set of call handling capabilities required of an MMTel TAS. It does not address any of the additional services and functionality that have been added to the circuit switched network on IN platforms. This means IR.92 MMTel alone does not deliver service parity for VoLTE users, many of whom will be regular users of such IN services on the circuit-switched network.

Building from the ground up

Service parity for most services must be attained, and one way of accomplishing this is to re-implement all of the legacy services for the IMS network. However, this approach would take a long time; which is unlikely to be a viable option for those operators under pressure to rapidly migrate their subscribers to the IMS network in a race against the competition. Whilst operators will want to re-implement   most of their active legacy services in due course, doing it to an enforced, tight timetable is extremely costly. They need to minimise the upfront investment required to bring VoLTE services to market as quickly as possible. Re-implementation of their services, either as fully converged services or for IMS only, all prior to any significant subscriber migration to IMS, is a significant impediment to network transformation and the promised re-farming of spectrum. Operators need a solution that enables them to deliver service parity imminently, without breaking the bank.

Getting a head start

Fortunately, there is another approach that some operators are employing that makes it possible for operators to achieve service parity in a rapid, cost effective way. As a precursor to re-implementing each circuit switch service in the IMS network, some forward thinking operators are choosing to transform their networks to enable IMS users to use the services in the circuit switch network. They can do this by using an IMS switching function (IM-SSF), an adaption layer between the IMS core and the circuit switch network. This enables them to re-use the call handling intelligence that exists in the legacy switched IN infrastructure, to deliver a consistent user experience. The reverse capability can also be used so that newly developed IMS services can be made available to legacy network users. The result is that operators can re-use their services across IP and circuit-switched networks and therefore enhance basic VoLTE at a pace of their choosing without impacting the migration of subscribers to VoLTE and IMS.

Operators worldwide are rolling out VoLTE, with the intention of leveraging the efficiency benefits with the superior call quality and set-up times it offers subscribers. Whilst the benefits are clear, maximising the potential of VoLTE depends on a smooth, cost-effective transition to the new VoLTE services, and the IMS infrastructure needed to support them. The introduction of an adaption layer between the networks’ call-handling switches and the service control layer also streamlines the transition of services to VoLTE, now and for the future.

Do you agree with Jeff's thoughts on VoLTE? Let us know in the comments.

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