Wednesday, September 30, 2009

LTE: QoS and Bandwidth

I want to touch base on two concepts here. I am quite not clear on things at this moment, may be some one can help!

Concept 1:

LTE QoS: Default bearers, Dedicated bearers, TFT and Bearer QoS (QCI, ARP, MBR, GBR) are the QoS variables in LTE (any more?). I am very much aware how these behave in EPC, but I am unable to map the same with UE. Assume a default bearer has been established. Note that there is no TFT associated with default bearer, but there is a bearer level QoS present in default bearer creation. This QoS might limit the bit rate on the network side. And these QoS values are indicated to the UE through a NAS message (Activate Default Bearer Context Request?). So far so good. Now UE wants to have a dedicated bearer for particular application. UE requests for a dedicated bearer using Bearer Resource Allocation NAS message which contains the TFT, or to say traffic flow aggregates. Once this message reaches EPC, PGW consults PCRF and allocates a QoS value to this particular TFT. The QoS allocated for the TFT is signaled to UE in Activate Dedicated Bearer Context Request NAS message. Now UE has the QoS values. The big confusion is how are these QoS values limiting the data flow from UE?

My theory: Basically there is QoS concept in air interface (what?). All the QoS rules are imposed by eNB, which means the bandwidth is controlled on the eNB side. So even if the UE gets all the spectrum it will not be able to do much as the bandwidth on the network side is limited. I believe the QoS for TFT is indicated to UE so that it can also regulate the usage of spectrum. Right? Totally out of mind?

Concept 2:

Considering the above "my theory" to be correct lets try and understand how service provider can offer services. In India there is no 3G yet (except for BSNL) on mobile phones. How ever there are mobile operators whose networks are 3G ready and have started offering 3G speeds over USB sticks (TATA and Reliance). When I spoke to their customer care executives I was told the USB sticks come with a limited data plan. They also told me that this restriction was imposed by the government. The restriction can be explained using "my theory". If we start offering unlimited data service over USB sticks people might start consuming all the spectrum all the time leaving nothing for others to use. Base stations are always throttling. This can be avoided by placing data usage limit or time limit. Good move.

On the other hand, all the Blackberry's in my office run on EDGE. These handsets are provided with unlimited data usage plans. This means I can connect a Blackberry to laptop and start using it as a modem and get unlimited access to internet. Only problem as of now is these devices are running on EDGE which means low speeds.

The authorizing body is imposing data limit usage on USB sticks while allowing unlimited access on mobile phones. What will happen when a 3G phone arrives? If the network is 7.2 Mbps ready and so is the device then people can get unlimited access using mobile phone at high rates. Its just a matter of USB cable which can give high rates on laptop too. So what will the plans be when 3G arrives here? I ask my boss, "Hey with 3G you will get 3 Mbps speed but you will be able to do only 3 GB per month". This actually surprised him and he said I would rather stay on EDGE and get unlimited access. People using blackberry's dont want to fall into limited usage schemes as its frustrating to keep monitoring how much data they have used all the time. These things seem quite contradictory.

I have no idea how things are going to turn up. Can anybody enlighten me? Thanks!


Anonymous said...

Hey santosh,

I have been following your blogs from last several weeks and it is very informative and useful.

Regarding question on Concept your understanding is corrct.eNB is controller of radio resources and based on QOS variables (QCI, ARP, GBR and radio conditions of UE) eNB does Radio Admission Control to allocate the radio resources for uplink and downlink.

Santosh said...

Hey, Thanks!

It would be interesting what would be the strategy for 3G then.