Tuesday, April 24, 2012

Fallback to older RAT for throttling

We all are, painfully, aware of service providers applying fair usage policy, beyond a certain limit of data usage, by throttling mobile data speeds. Typically this is done using a PCRF/OCS. With latest revisions of 3GPP (Release 9) we can achieve FUP just by using PCRF. However I want to put forth another way of doing this. Push the LTE subscribers to UMTS after a data threshold; similarly push UMTS subscribers to GPRS/EDGE. Don’t kill me; I am just stating another feature of 3GPP :-).
Few years back we had GPRS/EDGE widely deployed, with UMTS coming in a new network was deployed along side of GPRS/EDGE. Also LTE is going to co-exist with UTRAN/GERAN. As of now most of the devices that do data are 3G capable and are always hooked on to UMTS/HSPA. The numbers of 3G/4G capable devices are on the rise leaving the GPRS/EDGE network least used. What if we push the 3G subscribers to GPRS/EDGE after a certain limit? This way we could still utilize the GERAN.
I am not sure of limitations on radio side, but from core network it seems like a simple feature. HLR/HSS store information about subscriber and can dictate which Radio Access Technology (RAT) a UE can connect to. Refer to 3GPP TS 29.272 and look for “Access Restriction Data”. The AVP has values like “UTRAN Not Allowed”, “GAN Not Allowed”, “E-UTRAN Not Allowed” etc. Based on these values MME/SGSN will either allow or block the UE from accessing a corresponding RAT. Typically blocking a RAT will lead to an “Attach Reject” with definite “Cause” towards an UE. Assume a UE is blocked from E-UTRAN, so when that UE tries to gain E-UTRAN access, MME rejects the Attach with Cause “EPS services not allowed”. This will stop UE from connecting to E-UTRAN, until it is switched off and switched on. Similarly we can achieve this over UTRAN and make UE fallback to GERAN.
Downsides
  • Identify the subscribers whose data threshold are hit and re-program the HSS/HLR to block access. Once billing cycle is complete re-program the HSS/HLR again to allow access.
  • What happens when the coverage for the enforced RAT is not present? Assume the subscriber is pushed to GERAN and he/she is in a location where GERAN is not available.
This is pretty lousy solution to implement, but achievable. Nice way to implement is rate limit the subscriber using PCRF.  We could still use this feature to block certain users from accessing a RAT all-together, which is reasonable.
This shows the amount of control a mobile network can have over a subscriber!

6 comments:

supert0nes said...

Currently the 3g networks are full and lte networks only 5% capacity, so this will not help the wireless providers for a few years as adoption increases. In the mean time it will only hurt subscribers

Santosh Kumar Dornal said...

Many Nations are seeing 3G now with 2G widely deployed.

Call me crazy, but we can push the 3G heavy users to 2G, after threshold, to make some room.

Anonymous said...

Wow, come on, remember you go to GERAN it will be for both CS and PS... And in GERAN if you are making data traffic there will be no MT calls for you (unless Gs/DTM is used, still very limited in real-life networks)... And it will be loading further the GERAN... Not long ago it was the UTRAN used to make the offload the GERAN for voice hehe :) Things sort of swap now...

A 3G heavy user not able to receive voice calls, I want to see how happy he will be :)))

In addition you need to *again* re-think the per-subs. policing as we moved it from HLR/RADIUS to PCRF, now moving back to HLR/HSS, not really trivial I am afraid...

This is a really old feature since the first days of UMTS, when OpCos were trying to charge more for 3G service :) It did not work, it won't work... The radio tech. should be independent... this is the main idea behind SAE and the EPC :)

Santosh Kumar Dornal said...

Wow..thank you! Eye opener! :)

Anonymous said...

You'd be wrong there.

A GERAN user will be able to receive calls. He'll receive the paging request from the CS and put the PS on hold for the duration of the CS call.

Don't you think there would have been an outcry 10 years ago if people surfing with GPRS around the world suddenly stopped getting CS calls?

mah said...

hi I am new to this blog can you suggest a link for the PS call in UMTS which can describe the PDP context clearly