Saturday, May 30, 2009


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.tiff
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.

Sunday, May 24, 2009

LTE : Tunnel Identifiers (GTPv2)

From my LTE mind map in the last post, understanding bearers is the most important thing. I must agree with one my readers who pointed out that "MindMap" looks horrific and ugly. I know. I am very bad with sketches and that was the main reason for me to drop off from choosing medical sciences. :) Rest apart, lets get going.

First step in understanding bearers is tunnels. How are tunnels identified? I want to elaborate this post with complete LTE call flow where two activities are running on mobile phone, one is using default bearer and other is using dedicated bearer.

The trick is not to understand the whole message in single gulp. Divide the message into IE's and take up the activity of each IE separately. Note that we are only dealing with mandatory and conditional IE's here. The concentration is on TEID and FTEID fields.


The above call flow is self explanatory and is pretty simple. We see two fields TEID and FTEID. TEID is the field present in the GTP-C header and using which the tunnel is identified. FTEID is Fully Qualified Tunnel End Point Identifier. This IE is used to send TEID/GRE Key and IP info of sending entity.

Create Session Request is always sent with TEID value set to zero. There are bunch of other messages where TEID value is set to zero and sent. Refer to spec for details. The S-FTEID is senders FTEID. MME sends this field with a TEID value say 0x111 and IP address of it to S-GW.

Once S-GW receives this message it learns the IP address of MME and TEID field to be used in the response. S-GW creates create session Response message with TEID value 0x111 and S-FTEID. S-FTEID value here contains the TEID value,say 0x222, to be used by MME and IP address of the S-GW.

At this stage the control plane for communication between MME and SGW is set. MME uses TEID: 0x222 for sending any control plane info to S-GW and S-GW uses TEID 0x111 to send any control plane info to MME.

Once the control plane is set traffic has to flow. Modify Bearer Request is used to indicate the S1-U interface of eNB. So S-FTEID (S1-U eNB FTEID) value is set to say 0x0a + IP address and sent to S-GW. S-GW replies with its S1-U interface FTEID. At this stage the TEID for the user plane are set. User plane traffic will flow using the TEID's exchanged. Thus the traffic flows on default bearer.


Bearer Resource Command is used by MME to request for a dedicated bearer. Once S-GW receives bearer resource command it initiates a Create Bearer request. Observe that same TEID field is used which was negotiated earlier. In create bearer request S-GW includes S1-U SGW F-TEID for user plane traffic.

MME sends a Create Bearer Response message with the S1-U eNB FTEID. At this point the a dedicated bearer is created and user plane traffic tunnel is negotiated. Dedicated bearer user plane traffic flows using the TEID's exchanged.

The interface described above is S11. This interface is mapped to S5/S8 and S1-MME interfaces. TEID are used to identify and map the tunnels in various interfaces.

There have been significant changes in the messages from Dec spec to March spec. The above details are with respect to March spec (3GPP 29.274 v8.1.1). I hope I got them correct. Else please correct me.

In next posts I want to look at the EBI fields and QoS. Comments are greatly welcomed.

Tuesday, May 19, 2009

LTE Mind Map

I tried to plot a mind map of LTE. The major links are set and we need to start looking at individual thread and plot a granular map. I honestly accept that I am not an artist and ... here is how it looks (Definitely shabby).

If any of you are interested in working out more maps for individual threads, please write to me. I would be very glad.

Flickr link to the image here.


Sunday, May 17, 2009

LTE : Open Technology

One fine evening I was browsing through books in shopping mall. I saw this book called "What Would Google Do?" . I already knew about this, so i picked up a copy and started reading it. I am half way through. Amazon link here

Its an amazing book written by Jeff Jarvis. The book talks of google as a platform, as an elegant organization, as a paradigm shift to many. I totally agree with it. As I read the book I started comparing LTE to Google. Sounds strange but yes I started doing it.

Lets start with Google. Google started as a search engine crawling millions of sites. Slowly google became a platform to so many things. Google shared it revenue with its user by AdSense. Google very intelligently directs the users to their destination. Google takes inputs from users and gets better with every click. Google gave out the APIs to the developers to write applications over it. Google started to become a converging point.

So google is an open technology and every one is making money out of it.

Long Term Evolution. The vision of LTE is convergence. Single global standard for mobile communication. LTE is providing a platform for all the technologies to coexist and converge. Mark Zuckerberg of Face book once said "Communities already exists. They are looking for a platform to communicate better. Its a foolish thought to start/control a community". Facebook later opened to developer who wrote numerous applications over it thus increasing the popularity of facebook. This has made lot of money not only to Facebook but also to the developers. Same is the case with IPhone. So many apps over IPhone and apple is benefitting so are developers. These all are open technologies/platforms where every one is benefitted.

Similar to this LTE is giving a platform to 2G/3G Wimax, Wlan networks to converge. Thus helping user move from one technology to other seamlessly. I would say LTE is a open technology not controlled by single entity. Its becoming a platform for all the techonolgies/users/companies/developers. With high speeds are emerging devices. With emerging devices are emerging applications. With applications, developers are emerging. In this process a lot of money is flowing. So every one is earning. More and more people are opening up. The one who doesnt open up are gone. For example yahoo. Yahoo tried to control the media for a long and now its going no where.

When I started reading LTE 8 months back I found no technical information about it in the internet except for the 3GPP specs. Then I decided to start a blog and write about how LTE works. I am not an expert but I try to publish what I read. Later I saw people reading the blog and posting their comments. Now, people working on LTE are already there. My blog is just providing a way to communicate. So blog is an open platform. If I start controlling the platform I will loose my readers.

The future is Open. Ajit Jaokar of Open Gardens writes a lot about Open technologies and systems. I encourage you to read the blog regularly.

To conclude, get hold of the above book. Read it and try to see if your business fits in that line.

Comments are greatly welcome

Thursday, May 7, 2009

Who Makes What: LTE Equipment

Very interesting article by Light Reading. Must read.

Wednesday, May 6, 2009

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 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.

Friday, May 1, 2009

LTE: Few thoughts

I have jotted down few things about LTE that were going through my mind.

Backhaul: With LTE wireless bandwidths shooting sky high there is a need for more stronger backhaul. To say we need a intelligent backhaul. Many proposed MPLS but still there is work to do.

Second biggest challenge is making the customer to move to LTE. At present we have 2G and 3G. With LTE there will three technologies running together and making the customers to move to LTE will be a hard task. To the customer technology doesn't matter. All consumer will ask for a high speed and ensured quality of service no matter if it is LTE or HSPA or HSPA+.

LTE has excellent data capabilities. But voice on LTE is still to be finalized. No matter how much bandwidth you give to a consumer voice is a must. Voice will stay. Is Volga just doing that?

From the operators perspective the timing has to be right to move to LTE. With the whole world on HSPA now, operator has tough time choosing the technology they want to move to. Should they move to HSPA+ or wait and move to LTE.

Migrating is one challenge, data plans and charging is other. With LTE how will be the data plans and charging. Cost per MB of data should go down else it doesn't make any sense to go to LTE.

LTE as a technology is challenge in itself. The specification are not clear yet. More over there is LTE Advance coming. Technology has to mature which will definitely take time. There were some issues with roaming when 3G was deployed. Such issues should be handled with LTE.

Making devices is a big challenge.

LTE shouldnt be deployed too early nor too late. The timing has to be proper.

Spectrum: Getting spectrum is tough task. I am not much aware of the spectrum issues and at what spectrum LTE is planned to deploy. Could some one enlighten me in this area please? :)

With LTE I feel there will be convergence and open devices will emerge. Take the latest skype integration in Iphone or N97 for example. With skype integration dependence on operator for voice call will fade away. For me using conference bridges in US through skype is free. So with the latest skype integration I can do a skype call from my device. This will reduce the dependence on laptop for skype call. Isnt it a nice Idea. Do keep your eyes open in this "Open Cloud" area. Share with me similar ideas.

Finally LTE is not only a technology, its business. Every has to share and eat. If single person eats everything he will die of indigestion and others die of starvation. Co existence is must.

Free free to post your thoughts here or email me.