FEATURE VOLTE
both following a CRFB transition path in the early stages of their LTE deployments. “LTE is used for data, legacy networks for voice,” he says. “It involves maintaining parallel networks, but you’re going to need to do that anyway until LTE coverage and device penetration is sufficient to switch them off.” Tommy Ljunggren, SVP of system develop- ment and mobility services at LTE pioneer TeliaSonera, has said that his firm’s 4G launch was made easier by the fact that TeliaSonera “focused on data only and wasn’t complicated by voice and voice integration with legacy systems and so on.” Meanwhile, Ericsson’s head of Mobile
Policies need to be put in place to ensure QoS for latency-sensitive services like voice and video, giving them priority and the bandwidth path they need.
Telephony Evolution, Eric Ericsson, says that the most common evolutionary path he sees operators choosing involves CSFB in some way, not least because it’s the industry choice for supporting inbound LTE roamers who don’t have IMS services or roaming capabili- ties. “We’re seeing operators introducing LTE with enabled handsets and then opting for CSFB in the initial stages while coverage is spotty,” he says. The natural progression for most of these operators will be to upgrade to VoLTE one-to-two years later, using SRVCC to manage handover between LTE and the circuit switched network. It’s an interim measure, yes, but as Ericsson points out, carriers have already invested heavily in their 3G networks. Given that a primary driver of LTE implemen- tation is cost rationalisation in core access, throwing the 3G baby out with the bathwater doesn’t currently make any sense. Ericsson says that many of the implemen-
tations his company is involved in re-use the existing legacy environment of the MSC, “breaking out to the legacy world so our ex- isting mobile media gateways remain in the network, even for VoLTE.” Ultimately, when LTE has broader reach, fallback will be onto the HSPA or 1xEVDO network— “that’s the all-IP scenario,” he says. “The availability of spectrum steers the technologies.” For Ericsson, it’s all about evolving the mobile core while maintaining a connection to the legacy, rather than replacing it completely. Some might not like it—the GSMA’s Warren, for example, says that interim steps between CS and IMS will be difficult to switch off in the long term—but with Ericsson predicting that “there will be circuit-switched users on the mobile side beyond 2020,” it’s clear that there is going to have to be some degree of pragmatism in operators’ LTE strategies going forward.
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While CSFB will be the way forward for
many operators transitioning to LTE, carriers that are pursuing a more aggressive path to the future, such as Verizon, are leaping with both feet into an all-IP future. Rather than looking at 100 per cent backwards compatibility, the telco is evolving straight into offering services that will compete with other OTT communica- tions services. Having demonstrated one of the world’s first VoLTE calls at this year’s Mobile World Congress on Samsung’s Revolution handset, the company is gearing up for the commercial launch of VoLTE-using-IMS in 2012. AT&T will follow suit by 2013; T-Mobile USA, according to Warren, will be sticking with HSPA+ for quite some time “because their last RAN investment gives them that evolutionary path via software but doesn’t allow for an LTE upgrade without a hardware investment.” Verizon’s more direct migration path can, in
some ways, be attributed to its existing CDMA network, which isn’t easily compatible with LTE. But it’s also likely to be part of a broader industry anxiety about OTT players and the damage that some observers believe they’ll be able to inflict on operators who spend too long hanging around on CSFB. Circuit-switched fall back sceptics like Kineto’s Steve Shaw say that, by implementing it, operators are open- ing the door to providers like Skype who can offer full video and audio calling over LTE’s super-fast, super-efficient technology. Shaw maintains that subscribers will simply stay on LTE, using OTT services for voice, get- ting annoyed with CSFB-induced delays and gradually eschewing carrier services for calls. For the GSMA’s Warren, however, it’s a glass-half-full/half-empty scenario. While he believes that it is unrealistic to even try to pre- tend that OTT voice is going to go away, there are plenty of drawbacks to voice offered on an OTT basis, not least quality of service. As Acme Packet director of solutions marketing, Kevin Mitchell says: “Left alone, IP networks treat every packet the same.” Policies need to be put in place to ensure
QoS for latency-sensitive services like voice and video, giving them priority and the band- width path they need. “Even though LTE gives us blazing-fast bandwidth, there are different constraints and choke points sill in place,” says Mitchell. “It doesn’t mean resources can’t be overloaded in the core network.” Engineering around that and implementing session border controllers can handle those issues, ensuring the QoS paths are there in a way that OTT players simply can’t.
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