The need for a low-cost, low-risk approach for bringing Voice to LTE deployments have lead to an initiative by T-Mobile Germany and some of the leading equipment vendors (Cisco, Kineto, Motorola, Ericsson, and Alcatel-Lucent etc.) to enable transmission of voice over LTE networks. The solution will enable the delivery of traditional circuit switched services such as voice, SMS and VMS over LTE. The overall objective is to enable GSM/UMTS operators to re-use existing equipment to deliver circuit based services over LTE and hence reduce costs.The advantage is that it will minimize the number of elements required to deploy VoIP over LTE. The architecture will also support handoff of circuit based services between GSM/UMTS and LTE networks. This means operators with legacy networks can migrate some of their network to LTE, still supporting legacy services in rural and suburban areas. It will also enable roaming between LTE and GSM/UMTS networks.
LTE (Long-Term Evolution) is shaping up as the choice of most mobile operators worldwide for next-generation networks, but it is not designed currently to carry voice or SMS traffic in the same way today's carrier networks do. This is basically because it uses a packet-based IP (Internet Protocol) data network. When looking at the options for ways of carrying voice over LTE, a number of possible solutions were arrived at. Equipment vendors and carriers have been lining up around two approaches to handle voice on LTE, called VoLGA (Voice over LTE via Generic Access) and One Voice.CSFB, Circuit Switched Fall Back is a less popular alternative.
Nokia Siemens Networks claims to have carried out a voice call over LTE networks at its research and development centers, recently. The call used the company's Fast Track VoLTE technology, which it said is aligned with the One Voice initiative. Meanwhile, Deutsche Telekom also claimed it had completed an LTE voice call using VoLGA technology, using independent VoLGA-based systems from Kineto Wireless and Alcatel-Lucent. Kineto has announced a new release of software for its access gateway that the company said supports the VoLGA Forum's specification.
The One Voice
The One Voice profile for Voice over LTE is proposed by a collaboration between over forty operators including: AT&T, Verizon Wireless, Nokia and Alcatel-Lucent. At the 2010 GSMA Mobile World Congress, GSMA announced that they were supporting the One Voice solution to provide Voice over LTE. VoLTE, Voice over LTE is an IMS-based specification. Adopting this approach will enable it to integrate into the suite of applications that will become available on LTE.
The VoLGA standard is based on the existing 3GPP Generic Access Network (GAN) standard. It aims at enabling LTE users to receive a consistent set of voice, SMS (and other circuit-switched) services as they transition between GSM, UMTS and LTE access networks.
CSFB, Circuit Switched Fall Back
The circuit switched fallback(CSFB) LTE has been standardised under 3GPP specification 23.272. LTE CSFB uses a variety of processes and network elements to enable the circuit to fall back to the 2G or 3G connection before a circuit switched call is initiated. It also allows for SMS to be carried since it is essential for set-up procedures for cellular telecommunications. The handset uses an interface known as SGs which allows messages to be sent over an LTE channel.
In the future, mobile operators with LTE will have to carry voice and SMS traffic alongside data on a single network using LTE. This will make more efficient use of radio spectrum. But the transition to that point is still very far!