Monday, July 27, 2009

VoLGA: Take 1

This past weekend I was tired of doing exciting stuff so I decided to get a printout of VoLGA Requirements and started reading it. The stage 1 document is sweet and nicely written in 13 pages. Considering my small brain, here is what I could understand.

VoLGA: Voice over LTE Generic Access : - I will refer it as V. VoLGA is just too much to write every time.

The whole idea of V is to make SMS and circuit switched calls possible over LTE. Rocket science! Dah! There is so much fuss about LTE that people actually forgot the fact that mobile phones were first designed to make calls. Some how I am strangely "attracted" to V. I started reading every possible post on internet about V when it was launched. I myself checked the forum almost once every day to see if there was any draft. Then came the first draft and before I could download it there were reviews about it all over the web by industry pundits. Nevertheless this is what I could grasp from stage 1 doc.

V resembles the 3GPP Generic Access Network (GAN) of which I have no clue. So there is a new network element inserted between EPS and CS network. This device will make CS calls and SMS possible over LTE. For V, all signaling and user plane traffic is fully transparent to EPS access network. This means EPS will see all V traffic as normal user plane traffic over suitable EPS bearers. If there is a EPS bearer then it means there is a UE initial attach. Cool.

V can work with both Iu-Mode and A-Mode giving full access to 2G/3G CS network. V provides handover from E-UTRAN to GERAN/UTRAN CS network. Handover the other way is not supported in Phase 1. For V to work there has to be few changes in UE. First, UE shall support CS signaling over EPS bearers. UE needs to be capable of supporting V services with serving PLMN. UE will be able to use EPS default bearer or connectivity for V service discovery, or a dedicated PDN connection. The same applies to signaling and user traffic too. That means a UE can use default or dedicated bearer for V service discovery, CS signaling, SMS and user(voice) traffic. QoS for EPS bearers must be supported else the call quality might go bad.

VANC : VoLGA Access Network Controller : manages UE's connection to V service. It will interface with MSC using the standard A or Iu interface.

V doesn't impact EPS much. All it needs is proper QoS, charging policy and header compression on user plane(?).

I believe the above is what I could make out. I will start reading the stage 2 and post architecture and stuff soon.

Questions : Am I missing something here or no one is talking about it? How in the world does CDMA circuit switched calls work over LTE? I mean V is all about GSM evolution talking to LTE, then what about the CDMA networks? How will LTE and CDMA work together for CS calls and SMS?

Have anything to say, feel absolutely free to drop in a line.

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