One Voice Initiative, Another IMS Success

By Manuel Vexler, IMS Forum

LTE (or Long Term Evolution) 4G standards are used to develop and deploy wireless technologies, delivering data rates comparable to VDSL and cable modems. Designed with high-speed data and voice over IP in mind, the standards don’t call for circuit switched voice, as for example, the ADSL standards do. As a result there were a number of proposals made for transitioning to LTE while continuing to support circuit-switched mobile voice (CS). Proposals required changes to the network architecture and additional functionality in the handsets to support CS and LTE interworking. While these proposals extend the life of the mobile circuit-switched voice, they also create a number of problems for operators.

Last year, in mid-November, operators from AT&T, Verizon, Vodafone and Telia Sonera agreed that the best path forward is to go directly to IMS-based voice over LTE. In their One Voice initiative, both suppliers and operators can leverage the LTE network functionality and deploy LTE without having to provide complex interworking architectures between 3G and 4G.

With LTE aggressively pursued by some of the largest operators, such as Verizon, it makes sense to simplify the network architecture and “byte” the bullet by executing a wholesale transition to LTE.

Besides the One Voice IMS voice over LTE approach, there are three other initiatives which propose first migrating CS voice to LTE and then following up by a second step where voice is migrated to IMS.

The initiatives are:

• VoLGA, or Voice over LTE via Generic Access. It requires special support to UE, and so far there is no migration path to IMS.
• CSFB, or Circuit Switched Fall Back. It is a 3GPP standard, however it requires development of UE chipsets and there is no simultaneous CS call and LTE data connection.
• CSoHS, or Circuit Switched over HSPA+. It is again a 3GPP standard, however, it also requires development of dedicated UE and, as its name indicates, applies only to HSPA and not to other mobile data technologies.

The One Voice initiative is one more proof that large operators are moving to IMS and the transition will be based on a business case which is both based on classical analysis (TCO and ROI) as well as on a competitive, leveled playing field sparked by the surge in demand for data due to the iPhone and Android platforms.

Manuel Vexler is the Technical Working Group Chair at the NGN IMS Forum. He can be reached at: mvexler@imsforum.org.