Friday, September 17, 2010

SDF, QCI and Dedicated bearers

I had an interesting discussion with one of my friends regarding the dedicated bearers and QCI and thought of posting the same.

SDF- Service Data Flow- An aggregate set of packet flows that matches a set of filters.
QCI – QoS Class Identifier – A parameter that is typically associated to packet forwarding/scheduling etc treatments.

QCI values can be from 1 to 9. Since QCI is an 8 bit field it can have 255 values. Values 10 to 255 are operator specific. A bearer is always associated with a QCI. A UE can have a max of 11 bearers but QCI are from 1 to 9. Which means the QCI can be repeated for the bearers.

Each bearer is also associated with TFT. Yes, even the default bearer can be assigned a TFT after the recent spec changes. TFT can have multiple packet filters resulting in multiple SDFs. Now the confusion is with this statement - “Each Service Data Flow (SDF) is associated with one and only one QoS Class Identifier (QCI).”

Since two dedicated bearers can have same QCI the above statement leads to confusion. Reading the statement again makes sense. A bearer is associated with QCI and set of packet filters that will lead to multiple SDF’s. This means multiple SDF’s can be treated with same type of service but one SDF cannot be given multiple treatments. This also means that you cannot assign same packet filter to two dedicated bearers. Hence the above statement!

18 comments:

Asimananda said...

Nice 1...just wish it was a bit more detailed :)

Amit said...

santosh..which spec are u referring to when you say that with latest specs default bearer can be assigned a TFT?


Amit

Santosh said...

Please Refer to 3GPP CR 210 for 3GPP Spec 24.301.

CR can be found here:-

http://www.3gpp.org/ftp/tsg_ct/TSG_CT/TSGC_45_Seville/docs/CP-090653.zip

Anonymous said...

>>This also means that you cannot assign same packet filter to two dedicated bearers. Hence the above statement!

The overlapping filters can come in different SDFs (hence in diferen bearers). In those cases SDF (PCC Rule) Precedence decides which SDF filters to evaluate first.

//nice blog BTW

Anonymous said...

hello Santosh.

I have a doubt. In handover processes, when de target eNB do the admission control, this process is specified?or depend the implementation? what this process has on consideration?

Thanks

Santosh said...

Hi

Please refer to 3GPP TS 36.300 10.1.2.1.

Santosh

Anonymous said...

As seen, the admission control will be based on information from E-RAB QoS based on whether the target eNB may or may not provide this QoS, right? But my question is how does he see if you have the necessary resources or not, ie if there exists some process already defined for this check?

Thanks

Santosh said...

It is basically the core network that informs eNB about the E-RAB QoS, during the handover. So in case the target eNB doesnt have enough resources then it may partially accept the bearers during handover or may reject the handover itself.

It is the responsibility of eNB to see if it is congested or not.

Anonymous said...

Hello Santosh
Thank you very much for the information.
I have some Questions, Does the default bearer have a QCI? How is it treatment? Where can i see more about this?

Thank you very much

Santosh said...

Default bearer is assigned a QCI from 5 to 9.

Refer below for QoS treatments.

http://3g4g.blogspot.com/2009/06/lte-qci-and-end-to-end-bearer-qos-in.html

Anonymous said...

Value range for operator-defined QCIs starts at 128, not at 10.

Calvin said...

QCI5 can be used as the default bearer or not?

Santosh said...

Yes. QCI 5 can be used for default bearer.

A Beautiful life after marriage said...

So if assuming the same QCI is sent in the Bearer Resource command but the PCRF sends a different ARP will this trigger a dedicated bearer creation. I.e in a single pdn I can have bearers with same QCI and different arp ?. Any clarification on the same is very helpful

Santosh said...

I think the existing bearer should get updated with new ARP! Change in ARP alone shouldnt trigger a dedicated bearer.

Teo said...

Regarding QCi I saw that you can use values 1-8 for home PLMN and 9 for visiting subscribers. This is also specified in the TS.
Also GBR QCIs will not be allowed for default bearer.

I am involved in a trial now, but I am curious if anyone has seen the dedicated bearers @ work or not :)
Thanks!

Santosh said...

Yes, I have seen dedicated bearers in action :)

Anonymous said...

hi all...

I hope TFT in UL is different from the DL.