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Diff-Serv over MPLS

  • From: Nabil Seddigh <nseddigh@tropicnetworks.com>
  • Date: Thu, 05 Apr 2001 11:16:51 -0400
  • CC: flefauch@cisco.com, liwwu@cisco.com, mpls@UU.NET
  • Organization: Tropic Networks




> A small doubt
>   Suppose PHBs related to a PSC have been assigned to
> different E-LSPs (say AF11 to one LSP and AF12 to
> another LSP)and first few (say 1-10)Packets belonging
> to a microflow have been assigned to AF11 and later
> packets (say 10-15) to AF12.
> Is it not possible for the packets in AF12 LSP to get
> transferred before the packets in AF11 LSP? 

The above is not possible if you want to maintain conformance
with RFC 2597. From section 2 of that document:

"A DS node MUST NOT reorder AF packets of the same microflow when they
 belong to the same AF class regardless of their drop precedence."
   
The means used to achieve the above are vendor-specific. 

One simple way is to ensure AF11 and AF12 packets are 
directed to the same physical queue. Of course, you
also ensure that a micro-flow's packets are only 
marked for treatment with PHBs from a single AF class.

---
Best,
Nabil Seddigh
nseddigh@tropicnetworks.com