LTE, IMS and VoLTE
Voice and video over Mobile Broadband
Smartphone and tablet use grew dramatically in 2011 and 2012: the starting pistol has been fired and the race to implement LTE is underway. The telecom industry has identified Long Term Evolution (LTE) as the best way of delivering much more bandwidth at a better cost. Although originally focussed pretty much exclusively on efficient delivery of data, Voice is now being actively promoted as the “killer App” for LTE. Most industry experts agree: the best way to deliver voice on LTE is to use IMS. This also opens the door to HD voice and RCSe, both of which also require IMS.
As implementation of LTE requires an upgrade to the radio access network, it will be delivered incrementally on top of existing 2/3G networks and the LTE coverage and availability map will change incrementally over time. During this extended period, as users are truly mobile, this also means the infrastructure will need to be able to hand-over live calls/ video from one network seamlessly to another as the voice service is used.
In the case of LTE, the industry has identified Circuit-Switched Fall-Back (CSFB) and Voice over LTE (VoLTE) as the two mechanisms that will be adopted to provide this function. Both of which require additional capabilities in the handset and the network.
Mobile voice has been around now for over twenty years. Although still inferior to fixed-line voice in terms of the absolute user experience, the quality and availability of 2G and 3G networks for voice has improved to the point where it is now taking significant market share from fixed-line telephony. The fixed-mobile substitution tipping-point has been reached. Any next step for mobile voice must therefore deliver similar levels of utility and user experience.
Robust, reliable and seamless implementation of functionality to provide universal voice service whilst the LTE network coverage is evolving is therefore absolutely essential. Unlike “best efforts” OTT services, when voice provided by a telecommunications company – the user is paying and consequently there is an expectation of, and regulatory requirement for, full service availability, including emergency service access etc, 24-7 availability and to an acceptably high standard.
VoLTE potentially delivers real benefits to voice and video services: wide-band multi-rate codecs coupled with high bandwidth means it is possible to deliver a much higher definition service. But in addition to coverage and fall-back issues, heavy LTE traffic brings the risk of jitter and poor service. To deliver the same or superior quality of service to that which we enjoy today, and to do so 100% of the time, will require real-time management of time-sensitive services and careful management of LTE class-of-service.
VoLTE Service Layer
What place then, for a real-time Telecom Application Server (TAS) to provide signalling control logic for voice and video in the IMS/LTE service layer? There are three main application areas:
- Signalling control logic to handle the complexities of voice call continuity as the user moves between 2/3G and VoLTE networks. In the terminology of the 3rd Generation Partnership Project (3GPP) global initiative, this is known as Service Centralisation and Continuity (SCC) Application Server.
- Service Composition capabilities so that the standard set of supplementary services for voice (such as call divert, black-lists, white lists, call forwarding, prepaid calling etc) can be provided efficiently and cleanly during the migration to an all-VoLTE environment.
- The MMTel Application Server. MMTel (Multimedia Telephony) is defined in the 3GPP IP Multimedia Subsystem (IMS) specifications. It provides the means to deliver converged, fixed and mobile real-time multimedia communication using the multi-media capabilities. This includes voice, real-time video, text, file transfer and sharing of pictures, audio and video clips.
Summarising simply, a TAS can be used to (i) ensure that basic voice services function correctly across a patch-work of different networks (the first two areas), and also (ii) deliver a new generation of comms services making use of the multi-media capabilities of the IP network (the third area).
The SCC-AS is a key function for service continuity of VoLTE and for allowing sessions to be transferred between a user’s devices without undue disruption. The demanding requirements for real-time, high-volume and fault-tolerant behaviour make a real-time TAS particularly well-suited to deliver the SCC function.
The second area also holds much promise. In previous generations of networks, whilst a few supplementary services have been provided in the core network in the switch, most have been provided in the service layer in the Service Control Point (SCP). Typically, the range of supplementary services in the SCP becomes large and complex as each service combination and permutation needs to be handled. The current consensus in the industry is that the use of a Service Composition and Interaction Management (SCIM) function – a standard capability of a TAS – is the preferred way of isolating service logic from the complexities of such interaction logic. By using a SCIM function, OpCos will avoid the error-prone complexity and consequent impediment to service layer change. They will also be able to ensure standard supplementary service behaviour across all services, whether delivered on the VoLTE or 2/3G network.
Finally, a real-time TAS is also perfectly suited to the third area. Whereas supplementary services have traditionally been implemented on the switch and the SCP in legacy networks, in IMS, the switch has no knowledge of the service using the session. All service-specific function is delivered by the MMTel Application Server. If carriers are to compete with OTT providers, they will need to deliver basic service with similar levels of utility and user experience and then add new capabilities to this to deliver superior services. This will include HD voice, which the best efforts OTT services will not be able to do. It will also include making the services smarter – tailored to the users’ specific usage needs, to their location, their presence and taking account of their preferences and profiles. It will also involve the creation and delivery of multi-media comms services for business, for consumers and to address various market verticals with specific interactive visual requirements. In short, the realisation of the original IMS dream.Show Less…