RE: [TE-wg] TE use in today's networks

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

Jennifer/Randy:


   First of all my apologies for not clear about my concerns:

   Please look at my inline comments:

-> In the OSPF case, the second issue could involve basic recomputation
-> of paths using the existing weights.  In many cases, the resulting
-> paths are not all that bad.  In some cases, some weights may need to
-> be changed to move to a better set of paths for the prevailing
-> traffic; in practice, it is sufficient to change one or two weights,
-> and these changes can be precomputed.  Yes, this does require a
-> network management system (or person) to effect the changes.  That is
-> a definitely a disadvantage, as you mention.  But, how significant is
-> this disadvantage?

   As a developer of OSPF (without any knowledge of customer real networks)
   I think, manual "Optimization" of weights (even small number if weights)
   based on the huge topology is a real disadvantage. But I supposed, 
   this disadvantage can be eliminated by incorporating "dynamic"
"optimized"
   weight selections based on constraints/policies is possible. This 
   needs sufficient changes to the existing routing protocols, which 
   I didn't find any developments/deployments. Am I correct?


-> The details of the MPLS case really depend on what MPLS features are
-> in use.  
-> 
->   * On one extreme, you could imagine having precomputed backup
->     paths (or even backup subpaths to replace individual 
->     link failures).
->     Something has to trigger the failover to these backup paths.  In 
->     theory, this can all be done without intervention by a network
->     management system.  But, are MPLS implementations and deployments
->     this mature yet?  Are the backup paths precomputed -- by 
->     the routers themselves or by an external management system?  

    As you mentioned this is "dynamic" without intervention by a network
    management system. There are many implementation and progress I 
    can see in IETF. (In my opinion these implementations are going to
    be mature in foreseeable future). 
 

->   * Another possibility is dynamic recomputation of routes based on
->     dynamic link weights (set based on the prevailing traffic).  This
->     requires the edge router to learn about the failure, 
->     compute a new path, and signal this path.  In fact, a single failure 
->     may cause a bunch of edge routers to compute a bunch of new paths.
->     What kind of signaling load does this introduce?  Are the local 
->     decisions made by each router (as the system moves to the new state) 
->     good for the global traffic load?

     This is another possibility MPLS fast reroute. Your questions are 
     valid in this case:
     
         What kind of "signaling" load does this introduce?
         Are the local decisions made by each router (as the system moves 
         to the new state) good for the global traffic load?

     My questions are:

         What kind of "routing" load does weight changes introduce in OSPF
         and with what added complexity and/or extra benefits?
         Won't the local decision is based on the global topology?
         Consider PNNI/RSVP-TE signaling, even the local decision 
         is made about the PATH. Isn't that based on global topology data
base?!?
         

-> In either case, the key question is whether or not this complexity is
-> warranted.  I don't doubt at all that the full-fledged deployment of
-> MPLS opens up additional possibilities (in addition to the existing
-> IGP mechanisms) for more efficient failover (both in terms of routing
-> efficiency and convergence delay).  But, how much, and at what added
-> complexity?  

   I agree complexity is one issue but with what extra benefits?

   Let me very clear, I am not against any of the proposals.
   These are the questions just I have in mind, please don't mind!


--Venkata Naidu