A powerful grouping of major operators and equipment vendors have put their combined weight behind an initiative to agree a common method for handling voice and SMS traffic over LTE. Labelled One Voice, the group is looking to promote its preferred specifications for providing interoperable voice over LTE with the intention of convincing the GSMA and 3GPP to formally recommend its adoption.
Notably absent from the One Voice group - which includes AT&T, Orange, Telefonica, TeliaSonera, Verizon, Vodafone, Alca-Lu, Ericsson, NSN, Nokia, Samsung and Sony Ericsson, is T-Mobile. The operator has been a firm advocate for VoLGA (Voice over LTE via Generic Access) which was proposing an interim LTE voice concept that tunnelled circuit-switched voice traffic through the packet-based LTE network.
However, while VoLGA supporters still maintain that the concept will fulfil a useful role, the weight behind the One Voice initiative seems set to dictate the future direction to ensure voice over LTE interworking and roaming using 3GPP specifications for IMS. The specification includes E-UTRAN, evolved packet core, user equipment and IMS core features that the group considers essential to interoperable IMS voice.
However, One Voice assumes that operators and vendors have taken it as read that moving to LTE and SAE in the RAN and core network will also mean moving to IMS in the control plane. According to Sandro Tavares, converged core marketing manager at NSN, operators could migrate by using a method such as NSN's Fast Track, which introduces IMS functionality to non-IMS elements. Tavares said that Fast Track was completely compliant with the One Voice profile, while operators who wish to use LTE purely as a data network could still use CS Fallback to handle voice and SMS traffic to LTE devices.
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