One Voice initiative looks to make IMS more usable for LTE

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One Voice initiative looks to make IMS more usable for LTE

By CAROLINE GABRIEL

Published: 5 November, 2009

One of the trickiest issues for early LTE deployers is uncertainty over how voice and SMS services - still the key cash cows for most operators - can be supported. Eventually, all these services will be carried over IP, using the IMS (IP Multimedia Subsystem) standard, but only a few carriers, like Verizon Wireless, are looking to deploy all-IP from day one. However, there is pressure to accelerate the process and reduce the cost and risk of LTE/IMS for carriers, and this is the objective of the new One Voice initiative.

Some operators believe they will initially deploy LTE as a data-only network, but most want to support voice and, even more importantly, SMS (which underpins many cellco processes and customer communications). Faced with the risk that large players might delay their plans until they have a strong route to voice, One Voice has defined a profile based on existing 3GPP standards for IMS-enabled voice.

The work has initially emerged from Nokia Siemens, which was previously trying to get wide industry support for its own interim voice over LTE solution, VoLTE (which only worked with its own softswitches). The company's convergent core marketing manager, Sandro Tavares, said One Voice should ease fears over how voice will be deployed by resolving roaming and interworking issues at an early stage. It is not creating a new standard, but aims to ensure compatibility between networks and devices by creating a common profile, which defines an optimal set of existing 3GPP functionalities for use by vendors and operators. "There is no new standard," added Tavares. "It's just using what is there already."

NSN is already producing LTE equipment that complies with the new profile, and so has a headstart in offering an important feature to early triallists - which could boost its so-far low profile in LTE tests, dominated by Ericsson and Huawei. However, the vendor will now hand its work to the 3GPP and GSM Association so that other companies can work on and adopt the profile. So far, it has signed support from most of the key operators that tend to wield influence over cellular standards, apart from DoCoMo and China Mobile - AT&T, Orange, Telefonica, TeliaSonera, Verizon Wireless and Vodafone are there, plus a strong line-up of vendors. These are Alcatel-Lucent and Ericsson on the infrastructure side and Nokia, Samsung and Sony Ericsson for devices. The group needs to get the Chinese vendors on board to complete the set, as well as Motorola.

The supporters of the initiative say this is their "preferred path" for voice over LTE, though for carriers that do not want to move to IMS at an early stage, there are other options available - namely open web-based voice; the stopgap solution of Circuit Switch Fallback (also enshrined in 3GPP standards), where the handset is forced off the LTE network onto 2G or 3G for voice calls; and variations on the theme of using circuit switch over packet techniques. There are two main approaches to this - MSC Voice, which is tied to a switch, with NSN's VoLTE the most prominent example; and VoLGA, which is architecture independent, and uses the UMA/GAN (Unlicensed Mobile Access/Generic Access Network) protocol. This Kineto originated technology was originally adopted for Wi-Fi/3G fixed-mobile convergence and as such did find its way into the 3GPP. VoLGA does not require modifications in the LTE RAN or core, or the MSC, but uses a separate gateway controller.

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