A recent spate of VoLTE launches has put the technology under the spotlight, but its lengthy absence on any meaningful scale – with the possible exception of South Korea – may seem troubling to some industry watchers.
When the original LTE specifications were drawn up, the circuit-switched (CS) domain used in 2G and 3G was dispensed with in favour of an all-IP environment. All well and good, but no provision was made as to how voice and texting – still the two mainstays of a mobile operator’s business – would be delivered over a spanking new all-IP data network.
Circuit-switched fallback (CSFB) is a possible ‘interim’ solution that WCDMA operators can deploy, but it’s hardly ideal. Lengthier call set-up times of around 1-2 seconds probably won’t upset high-spending LTE customers, but call-set up times may be longer if there’s no 3G signal and the call is then directed onto 2G. The 4G voice experience, in such scenarios, is worse than 3G.
Meanwhile, much effort (and ingenuity) has been expended in labs and trials to provide LTE customers with the same features they’ve long been used to on circuit-switched 3G voice, such as call forwarding and call waiting. SRVCC (single radio voice call continuity) technology has also been developed, allowing LTE users to maintain voice calls when moving out of LTE coverage and going within reach of either GSM or WCDMA networks. But SRVCC adds network complexity and expense.
VoLTE, at first glance, can seem little more than splashing around furiously just to keep still.
But there are potential rewards for VoLTE investment, which helps explain why AT&T, Bouygues Telecom, HKT, NTT Docomo, SingTel and T-Mobile US are among those declaring that they have either recently launched commercial VoLTE or are on the verge of doing so. They join South Korea’s three major network operators, and Metro PCS (now part of T-Mobile US), which were first out of the VoLTE traps back in August 2012.
One appeal of VoLTE is the freeing up of much-needed spectrum. According to Japan’s NTT Docomo, spectrum usage by VoLTE is three times more efficient than 3G circuit-switched voice.
Costs can also be reduced if operators shut down their CS domains as they move towards a packet-switched network. NTT Docomo has already shown this is possible, and on a large scale. With around 60 million subscribers, Japan’s biggest mobile operator completed the migration of 3G circuit-switched services onto an IMS core back in early 2011 (it shut down its circuit-switched 2G network in March 2012). Access gateways enable NTT Docomo to support 3G handsets using circuit-switched voice and video.
HD voice may also prove to be a competitive advantage, which IMS-based VoLTE makes easier to implement. Contributory reasons why 3G operators (with the notable exception of Orange) have been reluctant to offer HD voice are codec licensing costs, the time and expense needed to re-configure the network, and lack of bandwidth. IMS does not remove licensing cost issues, but much of the spadework needed to offer HD voice, according to the GSMA, is already done by implementing IMS architecture.
LTE also provides more bandwidth than 3G. Perhaps by exposing HD voice capabilities to other parties, such as gaming developers, operators can encourage greater service innovation.
Simultaneous voice and data calls over 4G could be another VoLTE attraction. One problem with CSFB is that incoming calls can break an LTE data session, bumping the connection down to 3G (providing a 3G network is available). If 3G is not available, 2G may not be able to support the data session and the connection is lost. Better video-conferencing, or sharing a video while still maintaining a voice call, are all possible revenue opportunities courtesy of VoLTE.
An indirect VoLTE benefit, and one not talked about as much by mobile operators, is improved indoor coverage. At least that’s the view of Kineto, which describes itself as a supplier of ‘telco-OTT’ solutions.
In a recent global survey undertaken by Kineto it was found that 16 per cent of mobile users in “key markets” said they had poor or no mobile voice coverage within their home. “While the delivery of voice services over LTE will not solve this challenge, the IP voice infrastructure that operators are putting in place to support VoLTE can, through Wi-Fi calling,” Ken Kolderup, Kineto’s CMO, told Mobile World Live.
The same survey discovered that 89 per cent of respondents with poor or no mobile voice coverage at home were also smartphone owners that had already configured their phone to connect automatically to a home Wi-Fi network. “To offer their voice and messaging services over Wi-Fi, operators need to put in place an IP voice and messaging infrastructure,” said Kolderup. “Fortunately, the core network equipment operators are putting in place to support VoLTE is exactly what’s needed to also enable VoWiFi.”
There’s more to VoLTE than perhaps meets the eye.