Which one of these standards will be adopted as global standard?

While VoLGA supporters still maintain that VOLGA will fulfil a useful role, the weight behind the One Voice initiative seems set to dictate the future direction to ensure voice over LTE interworking and roaming using 3GPP specifications for IMS. The specification includes E-UTRAN, evolved packet core, user equipment and IMS core features that the group considers essential to interoperable IMS voice. In the long run, support of voice and messaging in LTE over IMS remains the major target.

VOLGA supporters argue that there are numerous shortcomings with CSFB as an interim voice over LTE solution. CSFB requires modifications to existing elements within the network (MSCs) as well as specific support on new devices. The MSC modifications are also required for the SMS-over-SGs functionality as well as voice. Exact timing on the availability of these upgrades across the whole pool of current MSC implementations is unclear although SMS support is vital from day 1 for operational reasons even for data devices. The other shortcoming with CSFB is call set up latency which is a major factor in determining quality of experience when making a phone call. The concept of falling back to 2G or 3G from LTE has an obvious pre-requisite that there needs to be a suitable network with coverage available. In some cases this might not be case, for example operators that do not have 2G/3G networks. Another problem with CSFB is that is that it will likely drop any running LTE data connection when running concurrently with a CSFB call. There are also limitations in supporting SMS. There are costs associated with implementing CSFB. The costs are associated with both the network and handset even though there are also costs associated with other alternative approaches of voice over LTE. There is a problematic integration with CSFB and LTE femtocells. An LTE device connected to a femto would either need to fallback to 2G / 3G in the femto itself, or look for a macro cell-site instead. Adding 2G into femtos is very complex, while adding 3G increases cost, complexity and time-to-market.

As expected the supporters of CSFB have a different view from that of VOLGA supporters regarding CSFB. According to the supporteers of CSFB , CSFB is considered the preferred solution for the early stages of LTE network deployment as it represents a low-cost, low-risk approach. From the user perspective, it minimizes call establishment delay and supports smooth handoffs. For operators, the solution enables them to make full use of their existing networks to protect investments. The operators are able to re-use MSC interconnect, roaming agreements, charging and settlement processes. On 13 January 2011, ¬Huawei announced that they have successfully completed a CSFB voice call with an unnamed 3rd-party handset provider. “Conducted at Huawei's LTE and Evolved Packet Core (EPC) Interoperability Testing Lab in Shanghai, the call demonstrate that operators using LTE/EPC to provide pure data services will still be able to leverage its existing CS network to provide voice services”.

Moreover, VOLGA supporters are of the view that VOLGA should be the preferred interim solution for voice over LTE. They argue that on the network side, VoLGA only requires software enhancements to the circuit to packet gateways which already exist for GAN. No modifications are required on the MSC or the LTE core and access network nodes. This enables a rapid development and market introduction, especially in multi-vendor MSC network environments. Furthermore, VoLGA enables the use of SMS services over LTE without any modifications in the network. On the mobile device side, the protocol stack initially developed for GAN can also be re-used in large parts. The two main software additions required are to include the LTE access technology as a radio bearer together with a modified handover procedure, as the VoLGA approach allows for a smooth handover of ongoing voice calls to GSM or UMTS when the subscriber leaves the LTE coverage area.When supported by the visited network VOLGA enables a smooth introduction of global LTE roaming, all services can be delivered via the VoLGA circuit to packet gateway and the MSC in the visited network. In case where VoLGA is not supported, the VoLGA gateway and the Mobile Switching Centers in the home network may be used instead.

It seems there is a battle between VOLGA and CSFB on who will win the race as being the interim solution for voice over LTE. At the moment it is not clear as to which standard will be adopted between the two as the global standard. Considering that the skeptics of CSFB are of the view that CSFB in a sub- standard technically speaking based on the arguments discussed above and that the supporters of VOLGA are of the view that VOLGA is superior to CSFB. Then it should make sense that operators will adopt VOLGA. However, there are always politics and some decisions are taken on corridors during these standard development processes meetings. There are commercial issues at play and also limits on what can be discussed to avoid breaching competition laws. Sometimes, it is not about the technical superiority of the standard but it is about who backing the standard. According to GSA 56 % of LTE deployments will implement CSFB as their interim voice over LTE solution. So, I think CSFB will be the most successful interim solution for voice over LTE in that most operators will implement it. This is based on the fact that the major operators and equipment manufacturers are supporting CSFB. I think the long term solution for voice over LTE will be IMS. According to GSMA 94 % of LTE deployments will deploy IMS as their long term solution.

References
http://www.3gpp.org
http://www.volga-forum.com
http://www.cellular-news.com
http://www.gsa.com
http://www.gsmworld.com
http://www.disruptive-analysis.com