VoLTE Takes Off at Mobile Asia Congress 2010

People expect their mobile phones to be capable of delivering ubiquitous high-bandwidth services. To provide a better experience for their customers and to gain a competitive advantage, mobile operators are now testing and deploying LTE. LTE standardization was completed by 3GPP in December 2008, and the first commercial LTE network was launched in 2009. It is expected that over 20 operators will offer live commercial LTE services by 2011.

Presently, voice remains the dominant revenue-generating service in mobile communications. Revenue from voice calls amounted to $615 billion USD in 2009. Voice over LTE (VoLTE) is the next step in developing a standard way of delivering voice for LTE. Although high-speed data, not voice, is the key driving force for LTE, VoLTE is crucial for operators because it can generate a lot of revenue. As LTE has all-IP network architecture and is designed to support voice in the packet domain, circuit switched (CS) core networks are no longer supported in the LTE specifications.

Single Radio (SR) mode is used in LTE, and it is impossible to deploy services on both LTE and UTRAN/GERAN. There are requests for voice handoff and CS access, especially when LTE is initially deployed as hotspot islands. One approach is to instruct an LTE handset to fall back to the CS network when a voice call is required. Another approach is to adopt Single Radio Voice Call Continuity (SRVCC), which uses an IMS system for call anchoring and handover and is based on a third party call control mechanism.

The main driving force that will bring IMS into the wireless market is LTE. An IMS-based solution is now universally accepted as the key for VoLTE service deployment. SRVCC is the preferred choice for most operators, and IMS acts as a unified control platform for voice and multimedia services. IMS-based SRVCC provides QoS control, flexible charging, and better user experience.

At the Mobile Asia Congress 2010 (MAC 2010) held in Hong Kong, GSMA, CSL, and ZTE successfully made an IMS-based VoLTE call on CSL’s LTE network and also on its existing mobile networks. The call was made using conventional 2G/3G handsets and was crystal clear. This was the first time a VoLTE call had been made using interoperable LTE and 2G/3G networks.

The VoLTE call was made between IMS clients located at the GSMA booth and ZTE booth (see Figure 1). A call was also made from an IMS client to a recipient using a 2G/3G handset. Supplementary services such as call forwarding and call waiting were also demonstrated.

By showcasing its IMS-based solutions and leveraging its expertise in LTE, ZTE demonstrated how voice will be incorporated into next generation networks. The VoLTE demonstration at MAC 2010 builds on the deep relationship between ZTE and CSL. ZTE employed Uni-CORE (EPC and IMS) solutions to build an intelligent, converged, and high-performance core network for CSL. These solutions enabled full convergence of CSL’s 2G, 3G and 4G networks. ZTE’s MMTel AS (or ZXUN SSS) based on the ETCA hardware platform provides VoIP related PSTN Simulation Service (PSS) and PSTN/ISDN Emulation Service (PES) together with ZXUN CSCF, as illustrated in Figure 2. IMS-based broadband voice demonstrated at MAC 2010 serves as a good reference for mobile voice service to evolve from legacy to LTE networks. This demonstration will boost operators’ confidence to deploy and operate LTE networks.

“Implementing VoLTE is one of the biggest challenges for operators as they deploy LTE networks. ZTE is cooperating with CSL to research this area and to gain valuable experience in voice applications over the LTE network. This lays the foundation for CSL in terms of future IMS-based LTE and also provides a significant reference for other operators,” said Xu Ziyang, president of ZTE’s Core Network products.