According to the GSMA, there are now more than 279 commercial LTE networks around the world and more than 200 million active subscriptions. While most of these are data-only, things are changing rapidly. Operators need to activate voice services in their LTE networks rather than defaulting to circuit-switched fallback (CSFB) mode.
VoLTE provides a means of delivering high quality voice services in LTE networks. It delivers a more efficient use of radio spectrum and, in theory, will enable operators to offer enhanced voice services with better quality than OTT providers.
That’s all very well in theory, but there are considerable challenges associated with the deployment of VoLTE that must be addressed in order for its potential to be fulfilled. With VoLTE, all sessions are delivered via VoIP, managed through an IMS core. Unless LTE coverage is ubiquitous, user mobility means that individual subscribers will move between coverage areas.
A competitive voice service cannot exist in isolation only in areas covered by the LTE deployment: there must be a means of ensuring continuity as users move beyond coverage areas. In order to offer such seamless (and useful) voice services, the operator must manage sessions across multiple domains within its network, both VoIP in LTE networks and circuit switched in others, with no disruption as subscribers move from one to another. Without such continuity, operators risk losing more customers to OTT voice providers delivering services over data connections.
Moreover, operators offering VoLTE services must ensure that they can interconnect and support call delivery between their networks – this has implications both for national interconnection as well as for international interconnectivity. Customers that roam overseas must also be catered for.
Then there’s the legacy question. Voice calls must also be delivered to parties not in LTE networks. Interworking with legacy networks is not an option – it simply must be supported. While there is a solution to legacy interworking – Single Radio Voice Call Continuity (SRVCC) – operators need to be sure that SRVCC functions correctly and at scale. The result is that operators are confronted with a range of challenges not only for supporting VoLTE services but also for service continuity with legacy networks.
The situation is made more complex by the fact that many operators have selected several vendors for mobile core networks and may also select a new vendor for the IMS core. Their peers may have a different set of vendors. The resulting environment can be extremely complicated. Operators are confronted with the challenge of how to implement the new services and launch them successfully. End-to-end testing is essential to confirm interoperability between these heterogeneous networks.
In order to ensure successful interoperability with peers and legacy networks, operators need a solution that can support a wide range of test cases for the services they need to offer. They need a single solution that can scale for heavy user traffic.