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!

LTE: QoS (Part 2)

In the last post we understood TFT and QoS behavior in LTE. What's important to understand is bearers are all about achieving QoS. The whole concept of bearers is just to provide proper quality of service to user thus enhancing the quality of experience. So what we know at this point is a default bearer always exists once the UE is switched ON, until it is powered off. Any other bearer is a dedicated bearer which is associated with a TFT and QoS.

In this post lets try to understand few more terms like TAD and QCI (QoS Class Identifier). The concentration is on UE requested bearer creation/modification procedure.

Basically a UE may request for dedicated bearer. Lets say we are running a web browser on our mobile phone. Now UE wants to establish a dedicated bearer for that. So UE sends out a request for bearer creation procedure. MME here sends sends out a bearer resource command which includes LBI (Linked Bearer ID), PTI (Procedure Transaction ID), TAD (Traffic Aggregate Descriptor), QoS.

TAD is a partial TFT. It includes packet filters for a particular L7 activity. In our case as we are running HTTP, TAD will include packet filter for HTTP. Now MME will send this information to PGW. Now PGW understands that a dedicated bearer has to be created for running HTTP traffic. So it sends out a create bearer request with TFT (HTTP) and QoS. Here UE may request for particular QoS.

Lets look at QCI here. QCI field may be mapped to a diff serv. (Assured Forwarding?) . Say QCI value is set to 2 which indicates a particular class of assured forwarding, say AF12. We have MBR and GBR values in QoS which may be set to some value.

Once MME requests create bearer request it responds with a bearer response creating a dedicated bearer for HTTP activity with a QoS value (QCI: AF12). After this our mobiles should start displaying the web pages with a speed equal to Roger Federer's ace. :)

Now, you remember that your boss has asked something and you want to email him. So another dedicated bearer for this email? Ok... lets stop and understand this a bit clearly. If your http dedicated bearer QoS is fine for running email then we may just use it. But you need to indicate this to PGW. So we do a bearer modification (update?) procedure instead of bearer creation. MME here will send bearer resource command with TAD mapped to email traffic, say IMAP(?). But note here the QoS is same. (QCI still is AF12). PGW looks at this and thinks that may be I should update the dedicated bearer to include IMAP too. So it sends out Update bearer request with newly added TFT for IMAP. (We already have TFT for HTTP). MME responds to saying OK.

At this point we have two activities running on single dedicated bearer. That means when there is no QoS change a single bearer may be used to run various traffics. This brings us to square one where I said bearer is all about QoS. Once email is done, PGW may remove that TFT (IMAP) from dedicated bearer.

This was just a short post to look at things when no QoS is changed. I will try to analyze the whole QoS with various IE's in coming days.

I hope it was useful and as usual comments are greatly welcomed.

LTE : QoS

After a lot of brain storming I got close to understanding the QoS concepts in LTE. Over all QoS concept is clearly (?) defined in 3GPP TS 23.401 Clause 4.7. I wrote two posts some time back, one on Bearer lever QoS and other on EPS bearer. The idea is look at them together.

Before we proceed, there is term that needs to understood. TFT : Traffic Flow Template.

TFT is set of all packet filter associated with an EPS bearer. A packet filter may be associated with a protocol. A packet filter Identifier shall be used to identify a packet filter. For eg: lets say we have http traffic. Now we all know that destination port in Http is 80. So a packet filter can be created indicating destination port to 80 and this packet filter may associated with a ID which is nothing but packet filter ID. Now several packet filters can be combined to form a Traffic Flow Template. EBI+Packet filter ID gives us a "unique" packet filter Identifier. The following is the TFT for FTP protocol.

Let now try and understand the Bearer level QoS. Bearer level QoS is associated with a bearer and all traffic mapped to that will receive same bearer level packet forwarding treatment. Bearer level QoS parameter values of the default bearer are assigned by the network based on the subscription data received from HSS.

In LTE the decision to establish or modify a dedicated bearer is taken by EPC and bearer level QoS parameters are assigned by EPC. These values "shall" not be modified by MME but are forwarded transparently to EUTRAN. However MME may reject the establishment of dedicated bearer if there is any discrepancy.

Bearer QoS IE

Now we understand TFT and bearer QoS. A default bearer may or may not be associated with a TFT. But a dedicated bearer is always associated with TFT. So we have bearers, the qos values for them and TFT which indicate what type of application should run over them. This defines the LTE QoS. We have Uplink TFT and Downlink TFT which are used by UE and PDN in respective transmissions i.e uplink or downlink.

Lets look at following paragraph carefully.

The UE routes uplink packets to the different EPS bearers based on uplink packet filters in the TFT's assigned to those EPS bearers. We have evaluation packet precedence index in packet filter which is used by UE to search for a match (to map the application traffic). Once the UE finds a match it uses that particular packet filter to transmit the data. If there is no match UE transmits the data on bearer to which no TFT has been assigned.

Let understand this with an example. Say UE wants to transmit a FTP and HTTP data. Say a dedicated bearer is created for transmitting HTTP data and say FTP is to be transmitted on default bearer. So dedicated bearer is associated with a TFT which has packet filter for HTTP. This packet filter has a evaluation precedence. So when UE wants to send HTTP data, it looks at the evaluation index. After that it matches if that packet filter is for HTTP or not. Once it finds a match it uses that bearer to send HTTP traffic. Note here that Packet filter is associated with TFT and TFT is associated with dedicated bearer and dedicated bearer QoS is set. So a proper traffic shaping/ forwarding mechanism will be used to transmit the HTTP data. And FTP is transmitted over default bearer as there is no packet filter associated for it.

Thus is the QoS mechanism in LTE. I hope the post is clear. Feel free to write to me in case of any clarification.

I hope I got it right else correct me. Comments are greatly welcomed.

LTE : Wishlist

Off-late work is keeping me busy and I am not finding time to do much except for logging and verifying bugs. :) I have jotted down few things which I feel are pretty important to understand LTE technology much better. I call it the "Wishlist". These are my priority now.

• QoS : QoS is top in my list. I had tried posting something before but I still need to work more. There are acronyms like TFT , TAD's to understand. I still have couple of questions from readers to answer.
• Dedicated Bearers: I still dont get the dedicated bearers completely. I am almost there. I wrote two posts on dedicated bearers sometime back and I almost understand how they work now. (Post 1 and Post 2)
• 3GPP Radius: I think I have got this one. There is not much difference in LTE and UMTS/GSM implementation of Radius authentication except for changes in few acronyms. If you pick up the free radius from freeradius.org you might just be able to authenticate user in GSM/UMTS domain as the dictionary for 3GPP is already available. But for LTE you might need to tweek something to make free radius work. I wrote something on Radius sometime back but more to follow.
• Interop with 3GPP/Non 3GPP: LTE is all about convergence. So lots of networks will be coming together. There is need to understand how this will happen. This is not a high priority on the list but interop with 3G is definitely on the charts.
• LTE Security aspects : I am still taking baby steps here. A lot needs to be done. :)

There is an event coming up on LTE. LTE World Summit in Germany from May 18th to 20th. Its one even that anyone working in LTE should watch out for. Unfortunately I cannot attend it. I am neither rich to afford a flight ticket nor my company is ready to sponsor. So attending one of these events is in my wish list too. :) There will be another LTE world summit in Asia, even that will be held in Hongkong in month september. It is very disheartening to see that nothing is happening in India. I know there are lot of people working on various LTE projects in India but 4G is not going to be deployed any sooner in India. I wish somebody takes up and initiative and arrange a meet in India where people from various companies can share their interests and show case their products. If I am unaware of any such events please enlighten me.

Having said 4G is far far away in India, 3G isn't coming any sooner too. THe spectrum auction again has been postponed. As elections are going on we might have to wait for the new government to form for spectrum to released. But BSNL has launched its 3G services which is not used by corporates. Lets hope we can have 3G at least by this year end.

I have a big question. Now that release 8 has free-zed how will any work on it will continue. Say something needs to changed in spec how will it be done. All changes go in Rel 9? That shouldn't be. Any ideas?

Right now all I can think of is LTE. But the question is pursuing it as career is a good idea? 3G took 7 years to deploy and work properly. LTE might 10 years. What after it? New technology? I dont know? Still thinking in that aspect as I have to move on with my career too.

I am in desperate need of tool using which I can make notes. I use windows PC in office and publish all my blogs from mac. So if I have to make a quick note on Mac which needs to be accessed on my office PC is getting difficult for me. I am right now using Google Notebook but I would really like to see some think like sticky which can used to make notes from any where and can be accessed any where. I am planning on buying a smart phone soon. So I will have three devices to make notes. I would really appreciate if any you know of any tool or service.

And finally I should say that my blog is not well maintained. Information is spread all over the blog and there is redundancy or lack of info in some posts. I apologize for that and will get better as the time passes by.

As always comments and emails are greatly welcome.