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The Voice Over LTE Challenge

Steve Shaw of Kineto Wireless looks at the options for providing Voice over LTE including VoLGA, VoLTE and CSFB.

Long-term evolution (LTE) has been on the radar of industry leaders for a number of years, with mobile operators embracing LTE as the basis for the next-generation mobile internet. Twenty-two carriers are due to roll-out LTE commercially this year, but despite the demand for the technology and mobile operators making tracks towards its deployment, data in LTE remains the only service offered. The industry lacks a clear strategy for supporting voice over LTE.

Ericsson reported in March that data traffic had overtaken voice traffic for the first time in the mobile industry's 25-year history, and yet voice services still remain the predominant revenue generator. The Tomi Ahonen Almanac 2010 reports that the voice market generated $615 billion dollars globally in 2009 and is still growing. Though mobile VoIP hasn't been the disruptive technology it was expected to be, if operators fail to offer a voice service over their new IP-based LTE network, it still has strong potential to threaten the voice market's overall revenue.

LTE offers an opportunity for operators to blend voice and internet services and deliver new converged multimedia services. Delivering integrated voice services over LTE is not only critical in delivering on established subscriber expectations; it is also an opportunity for operators to fully capitalise on new developing macro-networks and realise an adequate return on investment.

The majority of the current mobile market implements voice in roughly the same way. However, in the move to LTE, and migration away from the Circuit Switched (CS)-domain, voice emerges as a greater challenge. In moving away from a set domain, the industry faces problems of interoperability and fragmentation in voice services which will be unable to maintain the freedom of roaming and capability to make off-net and no-SIM emergency calls we have now.

IMS within LTE

The IP Multimedia Subsystem (IMS) has emerged as a common target solution to combat the potential risks associated with an array of voice solutions. IMS telephony is set to offer carriers a single, enhanced-services architecture for delivering any service, using any media, to reach any customer, regardless of how they connect to the network.

Earlier this year, the GSMA adopted the work of a group of companies, known collectively as the 'One Voice' initiative, which had set out to provide a framework for IMS telephony. One Voice had begun to create a basic set of capabilities and parameters to simplify IMS telephony. The GSMA is now leading developments of VoLTE via IMS (voice over LTE) specifications that will enable interconnection and international roaming between LTE networks in the future.

Though IMS has emerged as the preferred path for voice over LTE, it is far from ready for deployment. The movement to IMS will involve substantial financial and infrastructure commitments from operators. Its deployment will require operators to realign their operational and business support systems for this new IP environment.

Carriers not wishing to move to IMS at an early stage do however have an alternative when it comes to deploying an interim solution before committing to a full IMS investment. These interim solutions fall into two camps: CS Fall Back and Voice over LTE via Generic Access, or VoLGA.

Circuit Switched Fall Back (CSFB)

With the CSFB approach, LTE handsets drop the existing LTE connection to revert, or 'fall back', to the 2G or 3G radio network whenever the user needs to make or receive a call. Upon ending the call the device will re-associate and register with the LTE network.

Clearly this approach does not deliver voice services natively over LTE. In falling back onto the 2G/3G network the user cannot expect an enhanced user experience offered by a next-generation network technology, instead receiving a legacy voice service that is inconsistent with the rest of the LTE user experience.

The movement towards LTE has been fuelled by users wanting increased capabilities, at higher speeds, with lower latency. With CSFB, for every voice call made or received the LTE handset must perform a handover to the 2G/3G network, attach to that network to conduct the call and then move back to the LTE network on ending the call. The delay caused by this necessary fall-back, and following re-alignment with the LTE network, would decrease rather than enhance the user experience received today in the GERAN or UTRAN.

Not only does CSFB fail to meet standards demanded by LTE, it also requires new feature investment in the 'legacy' of 2G/3G network, burdening the LTE environment with functions that have no synergy with any aspect of an IMS voice service. While CSFB has received some publicity, it remains an ill-conceived and costly interim step with an investment in backward-looking technology providing no logical path towards IMS.

VoLGA (Voice over LTE via Generic Access)

In March 2009, the VoLGA Forum was initiated. The forum is comprised of leaders in the wireless industry, including Deutsche Telekom (T-Mobile), Alcatel Lucent, HTC, Huawei, LG, Motorola, Research in Motion, Samsung, Starent/Cisco, ZTE and Kineto Wireless, working to enable mobile operators to deliver mobile voice and messaging services over LTE access networks based on the existing 3GPP Generic Access Network (GAN) standard.

VolGA's specifications support existing circuit services, as well as IMS and other combinational services. Unlike CSFB, VoLGA offers a clear roadmap towards LTE and does not require further costly investment in legacy technologies.

Tests carried out earlier this year confirm that VoLGA outperforms current 3G network call-setup times by nearly 40 percent. The testing, conducted with Deutsche Telekom's next generation mobile test network using VoLGA systems from Kineto Wireless and Alcatel Lucent, delivered call-setup times up to 65 percent faster than CSFB. The lower latency, offered by LTE, enables high-speed exchanges between the handset and network. VoLGA is able to outperform even standard UMTS based call-setup times.

Harnessing capabilities offered by the network is a key selling point for operators wishing to rollout LTE. Users will not subscribe or pay premium rates for an equal - let alone inferior- service. VoLGA takes full advantage of emerging LTE technology to help operators offer compelling, high-speed performance, compared to those on the 3G network.

The group has completed development of the VoLGA specifications which are designed to provide subscribers a consistent set of voice, SMS (and other circuit-switched) services as they transition between GSM, UMTS and LTE access networks.

VoLGA solutions require no modifications or upgrades to an operator's existing 2G/3G core network, and investments made in the LTE network for VoLGA are equally relevant investments for voice support in the IMS.


Customers expect LTE services to exceed those offered by today's technologies. CSFB is not able to offer a user experience compatible with expectations. In subscribing to LTE, users will expect services to outperform current network offerings.

With IMS as the clear target for voice services over LTE, it is imperative for operators to invest in technology with a clear roadmap toward full IMS services. CSFB has no potential for re-use when the operator introduces voice support in the IMS. Operators simply do not wish to operate multiple costly parallel systems.

The VoLGA Forum is supportive of the 'One Voice' (now GSMA's VoLTE) initiative, recognising VoLGA as an interim solution, a key step on the path towards IMS. The GSMA equally recognise the place for a migratory solution, ahead of IMS deployment. VoLGA is a necessary step for those operators moving quickly towards LTE who need a voice solution faster than the GSMA VoLTE are able to provide, or for operators not yet ready to invest in a migration to IMS for voice.

VoLGA is able to offer a much richer user experience than CSFB, at a lower cost and with fewer risks. Building on a ready-made ecosystem of vendors to provide a complete range of VoLGA-based products, mobile operators are presented with a clear path to revenue generating services and making voice a central element of their LTE strategy.

Steve Shaw VP Corporate Marketing Kineto WirelessSteve Shaw is vice president of corporate marketing for Kineto Wireless and is responsible for the market development and corporate communication strategies of Kineto's product lines. A frequent speaker, blogger and general evangelist for the fixed-mobile convergence and UMA/GAN industries, Mr. Shaw has nearly 20 years experience in product, marketing, and business development roles with telecommunications companies.. Steve holds a bachelor of science in computer science from the University of Southern Californi.

Kineto is a privately held, venture-backed company committed to enabling mobile operators to fully embrace the cost and performance advantages of IP-based broadband access networks. Kineto provides standards-based products and services to major wireless infrastructure and device vendors in order to develop products compatible with the latest 3GPP standards for Smart Offload and Voice over LTE.

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