Telecommunications leaders such as AT&T and Verizon have jointly backed a standard for LTE voice and SMS services, called One Voice (pdf). It helps guarantee international roaming and interoperability for LTE voice and SMS services. LTE’s packet-based network doesn’t support legacy circuit-switched traffic, so traditional voice and SMS service would have to be shunted to older networks.
The profile is based on the IP Multimedia Subsystem (IMS), for transitioning from circuit-switched telelphony to IP-based LTE. It defines an optimal set of existing 3GPP-specified functions that all industry stakeholders can use to offer compatible LTE voice solutions.
AT&T, Orange, Telefonica, TeliaSonera, Verizon, Vodafone, Alcatel-Lucent, Ericsson, Nokia Siemens Networks, Nokia, Samsung, and Sony Ericsson have backed One Voice as the preferred way to ensure the smooth introduction and delivery of voice and SMS services on Long Term Evolution (LTE) networks worldwide.
A number of alternative solutions have been studied to be the successor to the circuit switched voice architecture by the 3G Partnership Project (3GPP). They include:
- CSFB, or Circuit Switched Fallback, essentially allows devices to revert to GSM or UMTS for incoming and outgoing voice calls.
- The VoLGA Forum (Voice over LTE via Generic Access), supported by companies like Alcatel-Lucent, HTC, LG, Motorola, Samsung, ZTE, and Deutsch Telekom. The VoLGA concept, advanced by T-Mobile and vendors like Ericsson and Kineto Wireless, essentially “tunnels” circuit voice over a packet-based radio connection.
- IP Multimedia Subsystem (IMS): An architectural framework for delivering Internet Protocol (IP) multimedia services. To ease the integration with the Internet, IMS uses IETF protocols wherever possible, e.g. Session Initiation Protocol (SIP). One Voice is based on IMS, and uses IETF protocols wherever possible, such as Session Initiation Protocol (SIP) for voice. Integrating voice, video and data into an IP Multimedia System also makes synchronized voice and data easier
3GPP has specified CS fallback, reverting to earlier GSM or UMTS standards for voice. Many network operators are hoping for IMS in the long-term, which will carry voice and video on the IP network. However both leave LTE exposed on the voice front at least over the next couple of years. VOLGA (pdf), it is thought, could deliver voice over LTE more quickly and with less overhead than IMS.
The VoLGA Forum includes forum members like Alcatel-Lucent, Ericsson, Huawei, Kineto Wireless, LG Electronics, Mavenir, Motorola, Nortel, Samsung, Starent Networks, T-Mobile International and ZTE. Kineto Wireless, the company behind voice over WiFi handsets promoted its technology for LTE. Originally ratified into 3GPP Release 6, the UMA/GAN specification, promoted by Kineto, defines how mobile circuit, packet and IMS-based services are extended generically over fixed-IP access networks like DSL and cable.
Instead of shunting voice to a parallel infrastructure, One Voice is based on the IP Multimedia Subsystem (IMS). It integrates voice, video and data and uses IETF protocols wherever possible, such as Session Initiation Protocol (SIP) for voice.
With the backing of large carriers like AT&T, Vodafone and Orange, infrastructure manufacturers like Alcatel-Lucent, Nokia, Ericsson and handset manufactures like Samsung, Nokia and Sony, is expected to go a long way in establishing One Voice as an industry standard for voice over LTE. Verizon Wireless, and its Vodafone partner, are planning to rollout LTE service commercially next year in the U.S.
Related Dailywireless articles include; Voice over LTE Gets a Spec: VoLGA, Sweden Tests LTE, and WiMAX: Passive/Aggresive?.
