Equality: Service parity for VoLTE


By Jonathan Bell, VP marketing at OpenCloud

In the circuit switched network for 2G and 3G, operators have generated a wide range of value added services to complement their existing vanilla voice offerings. Over time, these services have become the very fabric of operators’ voice offerings: voicemail, number translation, and mobile roaming all play their part.

Perhaps more importantly, operators have been developing various bespoke services for their enterprise customers, with as many as 100 services deployed in today’s networks. These services are still used and generate revenue, supporting roamers and subscribers that actively use these cheaper services.

Rolling out LTE for VoLTE

Meanwhile operators are now focussing their attention and money on the ongoing project of rolling out LTE as they move to an all-IP future. Voice over LTE (VoLTE) hosted on IP multimedia subsystem (IMS) is the preferred technology for voice and video services on LTE networks. But VoLTE only delivers the core, vanilla voice calling capabilities that were formerly delivered by the mobile switch, and none of the additional services created.

This presents a major challenge; to avoid a service downgrade operators must offer the same set of value added services that are available on their 2G and 3G networks on the LTE network for VoLTE, often referred to as ‘service parity’. If this doesn’t happen, depending on their location (and therefore, which network they are currently using,) when using the voice service, subscribers will have different service capabilities and receive a different user experience, which is likely to be confusing, perhaps irritating and could ultimately lead to customer churn.

Complex network of networks

The challenge facing operators in achieving service parity is that the circuit switch network and the IMS network, work differently in terms of call handling capabilities for new services and functions.

In 2G and 3G networks, in order to limit changes to the network switch, value added services were created on additional intelligent network (IN) platforms. These IN platforms provide the call handling capabilities of all today’s voice services. On an LTE network, the IMS provides the base networking platform for such services; VoLTE then runs on top of the IMS. The core voice services (those in the switch in 2G and 3G such as call forwarding, call barring, etc,) are provided by the Multimedia Telephony Application Server (MMTel TAS) in VoLTE.

Mirroring the separation in 2G and 3G networks, any services beyond those provided by the MMTel TAS are to be provided by additional IMS TASs. In essence, this means that any service that is currently delivered by an IN platform will be missing from the VoLTE voice service unless it is re-implemented on a separate IMS TAS. Operators therefore face the challenge of working out how and when to re-implement these services and so remove the impediment of subscriber migration to VoLTE.

Service delivery, a choice to be made

As operators look for a solution for the VoLTE service parity challenge, some are considering re-implementing all of the legacy services in the IMS for VoLTE. But this approach would take a considerable amount of time and cost, both of which cannot be afforded when operators want to bring VoLTE to market rapidly to stay competitive. Whilst these services will need to be re-implemented over time, doing so within a tight timeframe is not cost effective, and will have significant impact on network transformation going forward. Operators need a risk-free solution that gives them service parity, urgently.

A number of key operators are taking advantage of an alternative approach that makes it possible to deliver service parity rapidly, but also cost effectively, rapidly and with reduced risk. By using a combination of an agile, flexible TAS and an IMS service switching function (IM-SFF) between the IMS and circuit switch networks, they are able to access and use call handling intelligence functionality within the pre-existing IN platforms. By doing this, users on the IMS network have the same set of services that are available on the circuit switch networks. If required, it may be possible for operators to also deliver the reverse (R-IM-SFF) and make any new VoLTE service available for 2G and 3G customers.

The capabilities provided by a TAS and an IM-SSF mean that operators can focus on moving customers over to the IMS network independent of their timetable for service re-implementation on IMS. Then, as they re-implement their services on IMS, they can retire legacy services and platforms that are no longer needed.

Ultimately, they will be able to re-farm their valuable 2G and 3G spectrum. If they select an open IMS TAS for re-implementation of these services, besides replication of what already exists, they will be able to move their focus to competitive differentiation and service innovation as was originally envisaged when IMS was first designed.

VoLTE and IMS need to deliver more than a modern version of the closed systems with the same pre-baked services we have been using for the past twenty five years. Delivering VoLTE service parity doesn’t have to be an obstacle to IMS migration, but only if operators select the right technology to aid them in that journey.

Used by 60-plus operators globally, OpenCloud’s open, extendable products transform the real time communications service layer to enable competitive and economically sustainable evolution of IN, GSM, IMS and VoLTE services.


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