Achieving voice service parity for VoLTE subscribers
However, for operators to deliver these benefits requires a smooth transition of the services in the circuit switch network to the IP Multimedia Subsystem (IMS) network. Jonathan Bell, VP Marketing at OpenCloud, discusses how an evolutionary transformation of the service layer is required for operators to transition to VoLTE with no negative effect on the subscriber.
In a traditional circuit switched network used to deliver 2G and 3G services, the switch provides a lot of the basic call handling functionality such as call forwarding and call barring. Over the years, most new services and additional functionality have been added to the circuit switched network. They have been developed on additional Intelligent Network (IN) platforms rather than by making changes to the switch. The IN platform has enabled operators to create value-added services which complement their existing core telephony and communication service offerings. These are services that businesses and consumers worldwide often take for granted as the basic fabric of the network itself, such as voicemail, number translation, least-cost routing and mobile roaming. Most importantly, operators have developed premium revenue generating business services for the enterprise market. There are countless variations of such service implementations and most operators have fifty to a hundred different services being used and valued by enterprises and consumers alike.
In the IMS network, the ‘switch’ is just a router and does not provide any of the call handling capabilities that are provided by a circuit switched telephony switch. The Multimedia Telephony Telecom Application Server (MMTel TAS) provides the equivalent call handling on the IMS network. The GSMA IR.92 VoLTE standard specifies the set of basic call handling capabilities required of an MMTel TAS. IR.92.However, the standard does not address any of the additional functionality that has been added to all legacy networks on IN platforms and is still being used to deliver services today.
Operators will be running circuit switched and IP networks concurrently for many years as they roll-out network coverage, providing service to users that are happy with their current mobile device and to support roamers. During this period, operators are faced with the challenge of delivering a common and consistent set of value-added services across both networks (commonly referred to as achieving “service parity”). A user’s device will latch on to a 2G, 3G or 4G network depending on the prevailing coverage, and they will expect the same customer experience in terms of service availability and operation. Most industry analysts agree users will be using a variety of networks for at least the next three years in the UK despite it being a relatively developed LTE market.
Service parity must be achieved and one way of accomplishing this is to systematically re-implement all of the services on the legacy network again on the IMS network. However, this approach will take a lot of time and is not feasible for those operators under pressure to rapidly bring their VoLTE services to market in a race against their competitors. Whilst operators will want to re-implement most of these services in due course, an urgent and enforced timetable is extremely costly. Re-implementation of their services – either as fully convergent 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.
However, there is another approach that some operators are employing that makes it easier and less expensive to deliver service parity. As a precursor, some operators are choosing to transform their service layer to enable IMS users to use the services in the circuit switch network. Operators can use an IMS service switching function (IM-SSF) between the IMS core and the legacy network. This enables them to re-use the call handling intelligence that already exists in the legacy switch IN infrastructure where needed and deliver a consistent customer user experience. The reverse capability can also be used, so that new IMS services, as they become available, can be made available to legacy network users. The result is that operators can re-use their legacy services and enrich and enhance basic VoLTE at a pace of their choosing without impacting the migration of subscribers to VoLTE and IMS.
The spectrum efficiency benefits together with the superior call quality and set-up times of VoLTE make it an attractive proposition for users and operators alike. Without service parity with their existing service offerings, there is a serious impediment to subscriber migration to the IP network. Operators must look beyond the IR.92 standard for VoLTE and deploy technology that gives them the ability to offer subscribers a smooth, consistent experience. Subsequently any future changes to switching or other service requirements on the IMS network can be easily accommodated, maximising efficiency and value for operators.
About the Author
Jonathan Bell, VP Marketing at OpenCloud, has worked in VC-funded software product companies in the telecommunications industry for more than 35 years. Jonathan was a founder and member of the executive team at Geneva Technology, a VC-funded telecoms billing start-up company from 1995-2002. He was responsible for the original conception and design of the company’s convergent real-time billing system. Bell continued as VP product strategy for Convergys post Geneva’s acquisition in 2001.
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