The MPLS-OPS Archive

["Naidu, Venkata" <Venkata.Naidu@Marconi.com>]

Ashwin:

   Please look at my inline comments...

-> The priority/preemption is a task of MPLS Management 
-> module. I would like to know why the 8 priority levels 
-> are provided in the OSPF Extension? 

   OSPF (for that matter any IGP) job is to flood the TE
   information throughout the area (at present) for TE
   purpose. The 8 priority levels for unreserved bw is 
   nothing to do with OSPF calculations. Just flood the info!

-> What i was thinking is this 8 priority levels is used by 
-> the CSPF for the computation of the routes. If so, why 
-> is it Unreservable Bandwidth for the 8 priority levels ? 

   Yes! After flooding the TE information, ingress LERs do 
   CSPF to prune links (which are not met the requested 
   bw, priority, preemption etc) to find the best path to egress.

-> does it mean that on a link we configure the Bandwidth 
-> for different priority levels ? 
->        (Like Priority 0 -> 30 % bandwidth etc ) 
->        Or this is ment for some other purpose ? 

   It is not that simple, please look at Kompella's paper
   draft-kompella-tewg-bw-acct-00.txt (and nested references)

->        As i found the draft draft-katz-yeung-ospf-traffic-04 
-> not mentioning it clearly. 

   As I said, draft-katz-yeung-ospf-traffic-04 is nothing to do
   with configuration of priority levels. 

--Venkata Naidu


-> -----Original Message----- 
-> From: Naidu, Venkata [mailto:Venkata.Naidu@Marconi.com] 
-> Sent: Tuesday, August 14, 2001 7:37 PM 
-> To: 'Ashwin C. Prabhu'; mpls@UU.NET; mpls-ops@mplsrc.com 
-> Subject: FW: Traffic Engineering TLV 
-> 
-> 
-> Prabhu: 
-> ->             Can anyone please tell me what are these 8 
-> -> priority levels and what for these 
-> ->             used ? 
->   There are no set of semantics for each priority level. 
->   The different levels provide an ordering that can be 
->   used to determine preemption during the establishment 
->   of LSPs. They can also be used by an implementation 
->   as a means of ordering LSP computation and setup. 
->   How to use these priority levels? Look at: 
->   CR-LDP draft-ietf-mpls-cr-ldp-05.txt and 
->   RSVP-TE draft-ietf-mpls-rsvp-lsp-tunnel-08.txt 
-> -> why we need this. 
->   The need for priority levels is specified in 
->   RFC 2702. There is a consensus of eight protocols 
->   being sufficient.  
->   In Dan's terms... 
->   "The priority attribute defines the relative importance of traffic 
->    trunks.  If a constraint-based routing framework is used 
-> with MPLS, 
->    then priorities become very important because they can be used to 
->    determine the order in which path selection is done for traffic 
->    trunks at connection establishment and under fault scenarios. 
->    Priorities are also important in implementations  permitting 
->    preemption because they can be used to impose a partial 
-> order on the 
->    set of traffic trunks according to which preemptive 
-> policies can be 
->    actualized." 
-> --Venkata Naidu 
-> 

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