Thursday, February 18, 2010

3GPP Specs

As we know there are hundreds of 3GPP specs. But when coming to the implementation will all that is written in the spec will be implemented. Of-course not. I think the specs give an detailed view of the architecture and how things should work . But there are some many things that are outside the specifications scope and mind you they can happen in the real world.

Ambiguous scenarios, negative scenarios, collision scenarios and what not. When coming to LTE I pity eNB and MME. They are most vulnerable to take a beating from various handsets. More over the interpretation of specifications from one engineer to other may be different, so the product might seem different. Hence IOTs are needed.

The wireless world is so different from the regular networking at Layer 2 and Layer 3. The IEEE standards and RFCs are clearly written, so the implementation is very clear. The thing to notice here is there are not many end user to it. Who would be running BGP or OSPF or MPLS? Most of the traffic in the internet is at Layer 7 and hence I feel difficulty is a bit less in internet. But I do agree at there are very complex protocols involved in the internet. But in wireless, the whole network is at the customers stake. A fake UE can bring down the back-end devices. So the equipment manufactures do implement lot of things that are outside the scope of the 3GPP specs. Just a thought.

Tuesday, February 9, 2010

LTE Tidbits-II

Few more things are LTE below. Find part 1 here.

UE network attach:

We all know how important IMSI is and we wouldn't want to spill it out anytime. This requirement brings in a second type of attach procedure in LTE. Usually attach request from UE contains IMSI so that network can validate the same. Once network knows the UE's IMSI, it will generate a Globally Unique Temporary Identifier (Find details here) and assign it to UE. So for further communication UE can use GUTI instead of IMSI.

Why this? The Attach Request sent to the network is not encrypted. Security procedures are done only after network receives Attach Request. This means if IMSI is sent in Attach Request its susceptible to be known to outsider. To avoid this UE may send Old GUTI to network in Attach Request(The term "Old" is used here because it is assumed that UE is moving from one MME to other MME). Once the network receives that GUTI it will map the IMSI from it. Problem solved. What if the network doesn't know the GUTI, then it will have to ask the UE to send its IMSI. Network sends out an Identity Request to UE asking for its IMSI, to which UE will respond with Identity Response with its IMSI. Note that this message is not encrypted.

GUTI is assigned by the network. Which means UE should send its IMSI to network at-least once. If UE moves from one MME to other then its responsibility of MME to get the UE's IMSI from other MME based on the GUTI which UE has sent. Identity Request (for IMSI) should be sent only if MME fails to retrieve the IMSI.

Inter Rat Handovers:

There is special section in 3GPP TS 23.401 which we tend to ignore. Appendix. :-) If we look at inter handover requirements it is quite clear that SGSN's should be upgrade with new version of GTP protocol. But this Appendix has a different information altogether. Refer to Appendix 5 in the spec. Checkout the Routing and Tracking Area update procedures. They both speak of GTPv1 rather than GTPv2. This means MME has to support GTPv1 too. This sucks. Anyway, I still have my fingers crossed about inter RAT handovers. Hope they will be seems less.

More later. Comments/Corrections are welcome.

Saturday, February 6, 2010

I will NOT be at Mobile World Congress this year!

I will NOT be at MWC this year. :-) Neither was I last year nor the year before. :-D

But I am close follower of the event. Last year was all about mobile devices. HTC unveiled their new phone and so did other brands. Nokia N97 was announced just ahead of MWC. All in all last year was more of devices.

However this year I am guessing most of the attention would be towards LTE and HSPA+. Now the devices are in the market and we need speed. I want to see more of LTE demos, chipsets and handsets. Also an announcement regarding voice over LTE would be sweet.

With so much action in Barcelona its disheartening to see no 3G in India. I see an add today which says TV over Mobile phone. Cool! But dah! Network is still running GPRS. Considering a city like Bangalore in India this application makes no sense. Any way hope to see 3G soon in India.

I wish all visiting Barcelona for MWC a good luck and hope to see some live blogging from there. May be I will get a chance sometime in future to visit Barcelona :-)