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!

Juniper MobileNext Platform

The number of subscribers using mobile network is on the rise day by day. It’s just not humans any more, its also machines. Machine-to-machine communication is expected to explode in the very near future. To support millions of subscribers and machines, there is serious need to build scalable networks right from the RAN all the way through to the core. It’s just not enough to build a scalable network, but also ensure the quality of experience. With machines the critical data is expected to make it to the servers on the other end of the mobile network without any loss. Imagine ATMs running on mobile networks!

Image Source

In this regards Juniper Networks has released a performance report for the MobileNext Broadband Gateway which seems very impressive. Juniper MobileNext GGSN/PGW was independently validated, for performance & scalability, by EANTC using Spirent tools. 

European Advanced Networking Test Center (EANTC) is internationally recognized as an objective test center. They provide vendor-neutral network performance test facilities for manufacturers, service providers and enterprise customers.

MobileNext is truly a distributed platform with clear control and data plane separation; enabling the GGSN/PGW to host millions of subscribers and simultaneously pump huge amounts of data traffic.  The numbers are clear in the below chart. Juniper claims that the MobileNext Broadband Gateway can host 8 Million Subscribers; transfer 434 Gbps of traffic with zero loss along with an activation rate of 48,000 sessions per second (168,000 transactions per second), all being done concurrently in a completely redundant system.  

Without redundancy MobileNext Broadband Gateway can host up to 12 Million Subscribers; transfer 551 Gbps of traffic with zero loss and handle 72K activations per second.  

Do we really need such a powerful device in the mobile core? Yes we do. Let’s take the direct tunnel case in 3G. If subscriber goes to idle mode, the direct tunnel is taken down by SGSN and when subscriber becomes active again a direct tunnel is created by SGSN. A Direct Tunnel create and delete leads to 2 transactions on GGSN. If there is charging trigger enabled for direct tunnel creation and deletion, count another 2 transactions. Now multiply that by the number of SGSNs/RNCs and subscribers. The number of transactions is quite significant, especially for a large operator.  Older generation hardware needs a gateway to be added every time there is an increase in transaction rate or data rate.

Another reason for need of high performance is machine to machine communication. Assume that smart meters are hooked on to the mobile network and are programmed to update the server at 6 in the morning in a location X. So at 6 in the morning there will be a bulk of create pdps followed by data transfer followed by delete pdp’s from location X. If we allocate different time slots for smart meters in different locations to update, there is constant pressure on the GGSN/PGWs to handle the high rate of transactions and data transfers throughout the day. Loss of data becomes a very critical, as a meter reading might be lost.

Small/Hybrid Cells and wifi offload is going to bring in many more subscribers and stress on the network. Not to forget the new devices and fancy applications that are melting the networks every day. Considering these aspects, the need for high performing and reliable mobile core is needed today and I believe we need these kind of platforms to build a scalable networks and ensure quality of experience.

3G to 4G

Its interesting to look at how operators would be migrating from 3G/2G to 4G. 3G/2G networks are here to stay for a long time. 4G is the one which is supposed to co-exist with the existing 3G/2G networks. 3G/2G inter-working with 4G might need few tweaks on the packet core of exiting 3G/2G networks and also of-course the whole new 4G network deployment itself. Below are few such change I can think of from packet core network perspective. (I am assuming here that there are no major upgrades done on 3G network, which means 3G network is still pre Rel 8)

GGSN & PGW integration:- This will be a big change but shouldn't be that complicated to an operator. I am assuming that LTE subscribers will be given a new APN that can be accessed over a 3G or 4G network. This would need GGSN and PGW to co-exist as there is need to share the APN along with user context
HLR/HSS:- HLR is database from 2G/3G. HSS is the new database in 4G. I would like these two entities to co-exist and share the data. We dont want to SGSN to contact one database and MME to contact other for authenticating the same imsi.

DNS integrations:- The same dns servers in 3G network should help MME in selecting SGW and PGW. Few entries need to be added and MME should be pointed to that DNS
SGSN configuration changes:- SGSN shoud be configured to point to new GGSN if users from LTE are moving to 3G network. This should not be a big problem as new subscribers mean new imsi and imsi can be mapped to a APN in SGSN (?) which in turn identifies the GGSN

Gn interface:- There is need for Gn interface between MME and SGSN to provision inter RAT handovers. If UE is moving from 4G to 3G then the Gn SGSN should be able to contact MME and pull out the UE context and vice versa.



Each point can taken up for discussion. Any more scenarios you can think of?

An observation!

There are bunch of office boys at the place I work. Since one year I have noticed them using big fat mobile phones while I carry a small GSM phone which can do nothing but voice and sms. So I talk to the boys and they tell me that these phones are made in China and apparently are very cheap. They also told me that these phones might stop working anytime or they might just keep working for years.

Later I observed them using GPRS and accessing WAP sites of service providers. They download a ringtone or a photo of an actress everyday. Now this made me wonder. People who have never used internet on a computer, or rather who have never used computer, have started using internet on mobile phone. So what happens when these guys realize the beauty of youtube. If 3G comes in and service providers start advertising youtube service on television, these guys are going to have a blast. Remember its the adds on television that made facebook so popular in India (Aircell advertisement?). This means India is directly moving to mobile internet, which is jumping over a step, skipping the internet revolution on PC. India is adding 10 million subscribers every month. Now with 3G coming and youtube like services rolling out just imagine how congested the networks are going to get!

Any thoughts?