Reader Forum: Calling the future of mobile voice

Editor’s Note: Welcome to our weekly Reader Forum section. In an attempt to broaden our interaction with our readers we have created this forum for those with something meaningful to say to the wireless industry. We want to keep this as open as possible, but maintain some editorial control so as to keep it free of commercials or attacks. Please send along submissions for this section to our editors at: [email protected] or [email protected].
All the chatter in the mobile telecom industry right now is about apps, smartphones and data services, but most ordinary people still use their mobile phones primarily for chatting. It can be easy to forget that voice services generate close to three-quarters of mobile operators’ service revenue worldwide and nearly every handset supports phone calls by default. People’s desire to make and receive voice calls wherever they are motivated the development of mobile telecommunications in the first place and, three decades on, voice is still the killer app.
It is, therefore, absolutely crucial that Long-Term Evolution (LTE) networks, which are now being tested and deployed in dozens of countries, also provide robust support for high-quality voice services, as well as lightning quick mobile data services. It is also critical that the operators running these LTE networks implement voice services in a consistent way. Let me explain why.
The extraordinary success of GSM is founded on a single approach to implementing voice services. As well as being deployed in a co-ordinated set of spectrum bands, GSM-based technologies all use the same single set of standards to support voice services. This uniformity means that handset manufacturers can produce mobile phones that will work on GSM networks across the world, enabling them to create a wide variety of models for a single global market and obtain massive economies of scale. A consistent approach to providing voice services also enables people to continue using their mobile phones and the same mobile number when they travel away from their home country. Today, business travellers and tourists alike enjoy the convenience of being contactable almost anywhere on the planet.
These reasons for the success of GSM are widely-accepted, so how did the same community put aside these principles when it came to defining a voice implementation for LTE?
One of the earliest decisions taken by the standards body 3GPP was that there would not be a circuit-switched domain in LTE. This was a fundamental change in approach. A circuit-switched domain, based on time-division multiplexing (TDM), has been the mechanism by which voice has been supported across all previous generations of mobile systems in the GSM family. The change was motivated by the desire to make LTE networks highly-efficient by moving all services on to a single IP-based transport system. However, there was also no explicit statement of what should replace the circuit-switched domain for voice. Instead, there was an implicit assumption that operators would provide voice services using an IP Multimedia Subsystem (IMS) and the related Multimedia Telephony Service (MMtel) standard.
MMtel was conceived in 2006 as a framework within which specific applications for person-to-person communication, including voice services, could be defined. But with 3GPP not prepared to define the specifics, and with little operator backing for IMS at that time, the assumption of an IMS-based voice implementation for LTE began to look like a weakness and so 3GPP began to define a circuit switched fall back (CSFB) approach as an “interim” or “migratory” solution. IMS was still widely-regarded as the ideal ultimate solution, but CSFB could fill the gap in the meantime. Having started this process, 3GPP then also began to study a further interim or migratory approach, known as circuit-switched over packet-system (CS over PS).
For many in the industry, this increasingly fragmented situation began to feel wrong. The problem with implementing any form of migratory solution is twofold. First, migratory solutions have a habit of sticking around for a long time. The network has to continue to support a migratory solution until the mobile operator has persuaded all of its customers with handsets that only support that solution to upgrade to new models.
Second, with two migratory solutions, plus a target IMS solution, and the need to continue to support circuit-switched domain voice services on existing networks, the long-standing and successful GSM principle of a single and consistent approach to voice was in danger of being broken. Could a CSFB device roam on a VoLGA network, or vice versa? Could either roam on an IMS network? These questions were posed in 3GPP and ultimately led to the CS over PS work being stopped, and then the establishment of the VoLGA Forum supporting the provision of voice over LTE using the GAN (Generic Access Network) standard.
The formation of the VoLGA Forum further highlighted the apparent fragmentation of voice over LTE and spurred action in two areas. Focusing on migratory solutions, the Next Generation Mobile Networks (NGMN) Alliance called for devices and networks to support CSFB to ensure the continuation of global roaming. At the same time, the One Voice group was formed to fully define an IMS-based solution. This group has since become the basis of the GSMA’s Voice over LTE initiative (VoLTE).
The goal of the VoLTE initiative is to not only define the end-to-end solution for an IMS-based voice solution for use with LTE, but also to accelerate the launch of that service and make the period during which migratory solutions are applicable as short as possible. Voice services work so well today because the number of options that exist are kept to the absolute minimum – that same principle must be rigorously applied to voice services in the IP world.
If we are serious about ensuring the continued success of mobile voice services, VoLTE needs to receive the full support of the industry, LTE spectrum needs to be aligned internationally as far as possible, and we need an IMS solution that also works with the fixed-line community. Fragmentation, multiple implementations and long-lived interim solutions would ultimately damage the mobile industry as a whole. In essence, the industry needs to follow the principles that made GSM so successful. That is why VoLTE exists, and why the industry will back it.