MPLS QOS Diffserv Models Qn

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Jul 17th, 2008
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Hi All

Maybe someone can explain to me the difference between Pipe and short pipe Model with regards to the Egress LSR actions.

This is the way i understand it, not really understanding, confused more less

With Pipe model, the egress LSR forwards Packets based on the LSP Diffserv Information, right ? MPLS per hop (exp bits and EXP bits are not propagated to IP Precedence.

Short pipe, the Egress LSR forwards the ip packet based on the tunneled Diffserv information

My question is ? With pipe model, at the egress LSR, how is the packet forwarded based on LSP Diffserv information ? This is the egress LSR, doesnt that mean that before the packet is forwarded to the output interface, the Label is stripped so, its now IPV4 therefore with original DSCP ? So what does the forwarding based on LSP Diffserv mean ? I can understand the Short pipe model as forwarding is based on the tunneled Diffserv information, original DSCP from the customer

As i said, am confused, someone put me right please



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lee.reade Fri, 07/18/2008 - 03:32
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Well you are 100% correct!

The answer to your question is however, when the MPLS VPN label is sent into the PE router from the P router, a policy map is configured inbound on the interface (P-PE), this will then set the qos-group value, so that the value of the MPLS EXP is 'remembered' in memory, then on the outbound PE-CE link another policy-map, will be configured, with a class-map that matches the previously defined qos-group, and then sets the OOS settings as required.

Here is a link describing mpls qos.



devang_etcom Mon, 07/21/2008 - 15:28
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In pipe mode you can have an advantage of Explicit null label. That particular label's main use is to carry the MPLS EXP value when it is needed. and you can configure router to advertise Explicit null label too. you can get more information about the same from the link given in previous post.


Devang Patel


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