MPLS DS-TE Class type

Answered Question
Aug 2nd, 2010

Hi Guys,

A quick question on DS-TE Class-Type (CT) - Cisco IOS only supports CT0 (global pool) and CT1 (sub-pool). This means that all traffic is mapped to either CT0 or CT1, essentially, EF PHB and best-effort PHB. These CTs and setup priorities are then mapped to TE classes.

However, my question is- is this enough to support DiffServ on MPLS TE as ideally all traffic is classified as EF or BE? Junos supports 4 class types (0-3).

Thanks.

Amit.

I have this problem too.
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Correct Answer by jcozzupoli about 6 years 5 months ago

Hi Amit,

Yes 8 Class-Types. There are two models used for DS-TE bandwidth allocations within each class, Russian Doll and Maximum Allocation Bandwidth. For more information on these read up on Russian Doll model (RFC 4127) and Maximum Allocation Bandwidth model (RFC4125). With RDM you are able to use Tunnel Preemption for each of the CT and they both support up to 8 CTs.

HTH.

Joe.

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jcozzupoli Tue, 08/03/2010 - 01:47

Hi Amit,

I'd say its enough. SP's nowadays have voice services as a product seperate to data but running in the same core. So having one Tunnel for EF and one for non-EF would be fine using DS-TE would be fine. Think of it as MPLS-TE + MPLS-DiffServ, where TE contraints are aware of DiffServ.

The advantage of DS-TE is that it takes into account engineering contraints (give x traffic 40% of the link bandwidth) and bandwidth availablity of each class (ensuring there is enough bandwidth for servicing the queues).

I hope this brief insight has helped.

Joe.

amit.bhagat Tue, 08/03/2010 - 23:34

Hi Joe,

This helps but what I interpret from this is that the SP then only classifies traffic into EF and BE PHB. Hence, every customers' voice traffic is given equal priority. Is that correct?

So the question arises what can a customer do to ensure his voice/video (RTP) traffic is given most importance by SP as compared to others when there is a congestion in SP network?

Regards,

Amit.

amit.bhagat Wed, 08/04/2010 - 17:55

I think I have figured it out. I was thinking more in terms of Class Types than TE Classes. The SP can definitely take advantage of 8 TE Classes which is a combination of Class Types and Setup Priority. Hence, upto 8 DS-TE tunnels can be setup which is more than enough to classify traffic into different PHBs.

Regards,

Amit.

Correct Answer
jcozzupoli Wed, 08/04/2010 - 18:54

Hi Amit,

Yes 8 Class-Types. There are two models used for DS-TE bandwidth allocations within each class, Russian Doll and Maximum Allocation Bandwidth. For more information on these read up on Russian Doll model (RFC 4127) and Maximum Allocation Bandwidth model (RFC4125). With RDM you are able to use Tunnel Preemption for each of the CT and they both support up to 8 CTs.

HTH.

Joe.

jcozzupoli Wed, 08/04/2010 - 23:11

Hi Amit,

I'll have a look at that link when I get a chance.

Yes if you look at it from the view of TE Classes then its clear. Also, think about which Bandwidth Contraint model suits the SP needs. RDM has the advantage of simultaneously enure both bandwidth efficiency and protect against QoS class degredation of all the CTs, while MAM does not and can only do this for the premium QoS class.

Cheers.

Joe.

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