Stage 2 Specification For Voice Over LTE from VOLGA Forum now available

From our friend Martin Sauter's blog:

Regular readers of this blog probably remember that I'm a fan of Voice over LTE via GAN (VOLGA). For those who don't, have a look here on more details on why I think it has a good chance of becoming THE voice solution for LTE. It's amazing how fast the Volga-Forum is pushing out the specifications. In May, they published the stage 1 specification document, which contains a high level architecture and the requirements. Now only a month later, a first version of the stage 2 specification is available. Stage 2 specifications as per 3GPP contain a detailed architecture description and all procedures required from connecting to the network, originating and terminating calls, doing handovers, etc.

While their speed is incredible, maybe it should not be that surprising, because VOLGA is based on the already existing 3GPP GAN (Generic Access Network, i.e. GSM over Wi-Fi) specification. That's a good thing because that means that VOLGA could thus be developed quite quickly as it's likely that existing products can be modified instead of being designed from scratch. In addition, this should also mean that the first version of the standard is already quite mature as many areas were already verified during implementation and rollout of GAN in current networks.

I did a quick comparison between the two stage 2 specs and as I expected, many parts are very similar. While the GAN stage 2 specification has 126 pages, the current VOLGA stage 2 specification has 87 pages. This is probably because VOLGA is simpler than GAN. There are fewer handover procedures and most of the handover details are part of the 3GPP Single Radio Voice Call Continuity (SR-VCC) specification (for IMS) so they don't have to be included in the VOLGA spec. In addition to fewer handover scenarios, handovers are a bit more simple with LTE from a VOLGA perspective, as the network takes care of it unlike with GAN, where the mobile has to force the network into a handover. Also, there's no need to support the packet switched part of the network which also significantly lowers the complexity.

Well done, I am looking forward to the stage 3 specification which will contain the details on all messages and information elements used.

I blogged about VoLGA last month here.

VoLGA: Bringing Voice to LTE

Voice is becoming an Important issue for seamless introduction of LTE services. Even though most people think that LTE will start with the Broadband Dongles, it is important to resolve the issue sooner rather than later.



VoLGA Forum is one such body proposing a solution and its backed by quite a few well known industry players.



In the LTE World Summit, Franz Seiser of T-Mobile Germany spoke about VoLGA. Here is a summary from his presentation:

In order to ensure LTE will be used as much as possible, voice-and messaging services need to be supported on LTE networks in high quality asearly as possible.

The main Drivers being:

• Ensure acceptance of LTE as an possible next generation PLMN
• Shift traffic to new network as fast as possible
• Avoid price competition with DSL
  

The industry needs a stable, scalable voice and SMS solution forLTE:

• delivering a seamless user experience (voice hand-over to existing 2G/3G networks)
• with proven, commercial quality
• availability in 2010 (SMS) /2011 (voice) latest

In a post earlier, I discussed about the possible voice options for LTE and that generated quite a discussion relating to GAN. Recently Dean Bubley and Martin Sauter have covered this VoLGA issue and in general Voice over LTE in far more detail than I have earlier or even in this post. Please see the links at the bottom to read their post details.

Specified 3GPP solutions for Voice/SMS in LTE do not meet all requirements because:

CS Fallback ruled out due to customer experience and non-LTE usage

• issues with customer experience (call set-up time increase >1.5sec., no parallel voice/data if legacy network is 2G w/o DTM)
• not using LTE radio for voice
• requires changes to Rel-4 architecture MSC-Servers
• has much more impacts than originally envisaged

IMS based solution has very high complexity; availability and stability notfeasible in time, roaming eco-system is not yet existent

• solution would consist of IMS platform, various application servers and a major upgrade/change to Rel-4 architecture MSC-Servers
• no eco-system in place yet for IMS voice/SMS roaming and interconnect (only GPRS data or CS eco-systems are available today)
• solution requires updates/changes to quite many IT systems and processes as well

Key Objectives for Voice/SMS over LTE Solution is to Re-use as much as possible of existing systems, mechanism and eco-system while avoiding proprietary extensions to 3GPP nodes

• build upon existing Rel-4 CS network and investments
• “do not touch the MSC”
• build upon fully 3GPP compliant Rel-8 EPC/LTE network
• re-use existing CS roaming/inter-connect regime
• minimise impact on UE, especially on user-interface

As a result, the simplest solution is “Voice over LTE Generic Access” or VoLGA

What is VoLGA?

• A technological approach for delivering voice and SMS services over LTE access networks
• Leverages a mobile operator’s existing core voice network
• Derived from the existing 3GPP GAN standard

What is the VoLGA Forum?

A group of companies working to…

• Leverage collective technical skills to define VoLGA specifications
• Publish proposed specifications via the VoLGA Forum web site (coming soon)
• Facilitate the easy adoption of VoLGA technology by other vendors and operators

The group is open to interested parties in the mobile community

• See http://www.volga-forum.com/ for more information about joining

The main Highlights of VoLGA are:

• Full service transparency

Supports all circuit services over LTE

Supports IMS RCS and combinational services (CS+IMS) over LTE

Supports handover of active calls between LTE and GSM/UMTS

Supports expected LTE femtocell deployments

• Low risk, low investment

• Based on well proven 3GPP GAN standard

  Requires no change to existing MSCs and operational systems

  Conserves existing, extensive voice interconnection regime

To keep things simple, VoLGA is the best option available at the moment.

Further Reading:

• VoLGA Forum
• VoLGA Specifications
• Voice - Bearer Aware, Bearer Adaptive or Bearer Agnostic?
• The Volga-Forum: Taking the Quest For Voice over LTE out of 3GPP
• VoLGA - reinventing UMA for Voice-over-LTE
• LTE, mobile broadband & SMS - VoLGA vs. IMS

You can search multiple blogs (including mine) in a single search via the 3G4G search here. (Search at the bottom of the page).

Solving the LTE voice dilemma

Continuing the discussion from LTE World Summit, this is something that has been discussed in the past by myself and other blogs as well. We know that there is no out of the box solution for voice calls in Release 8 but there are some solutions that are being standardised for this problem. Dr. Howard Benn, Director of Cellular Standards, Motorola Mobile Devices gave an interesting presentation on this topic titled, "Voice –how to talk over LTE". Here is the summary of his presentation along with some more information:
As we know, IMS was introduced in Rel 5 but even till today, there has been no major IMS rollouts. There are some operators working on deploying the IMS solution but in reality its not been as successful as it should have been. If IMS is available then the problem of voice call on LTE goes away. The problem can be solved using Voice Call Continuity or VCC. Infact there is a bunch of specifications on IMS Centralized Services (ICS) and network Centric VCC for solving this and other similar problems.

So with IMS not being available, the first alternative for this problem is Circuit Switched Fallack (CSFB). In this, as can be seen from the MSC above, the user is attached to an LTE network. MSC can send Paging to the UE and if the user accepts the voice call then he is handed over to 2G/3G network. The big problem with this approach is additional time required to establish the voice call and the PS services might get disrupted, depending on how its handled.

The second solution is to have a Generic Access Network (GAN... previously known as UMA) based solution. This is similar solution to the ones used by some Femtocells. This would mean that the UE's would require GAN chipsets and GAN is known to be power hungry so it can impact the battery life significantly.

China Mobile's, Bill Huang in a recent interview mentioned that “We could carry voice over UMA” and “We will have an LTE network that supports voice…”. He was referring to this approach mentioned above.

Finally there are always proprietary options like Skype that can be used along with the data services to solve the voice problem.

Infact a service like Vonage, modified for mobiles, can solve this problem easily. You can connect a VoIP client from your phone or device to Vonage and you are given a landline number that you can pass to others. When calls are received on this number, the client in the mobile rings and you answer the call normally.

Nick Yamasaki from KDDI mentioned that KDDI will roll out LTE with CS fallback option for voice initially but then SRVCC (Single Radio VCC) solution will be adopted in future.