Re: Draft on constraint-based routing

"Guo, Liang" <guol@ccs.neu.edu> Fri, 05 February 1999 01:47 UTC

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Date: Thu, 4 Feb 1999 20:41:18 -0500 (EST)
From: "Guo, Liang" <guol@ccs.neu.edu>
To: Yao-Min Chen <ychen@fla.fujitsu.com>
cc: braja@ccrl.nj.nec.com, qosr@newbridge.com
Subject: Re: Draft on constraint-based routing
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On Thu, 4 Feb 1999, Yao-Min Chen wrote:

> It seems reasonable to run in parallel best-effot and 
> QoS routing protocols.  The mechanism described 
> in the proposal is described as "overlay" because 
> QoS routing relies on link state info collected by the 
> best effort routing protocol.  The info is used to 
> compute the MST.  It seems that the proposal chose 
> MST instead of other types of spanning trees because 
> nodes can individually compute but the computations 
> will lead to exactly the same tree, which is important
> to the correct operation of the proposal. Other than this,
> is there any strong empirical or analytical reason 
> why MST should be used?  Another type of spanning tree 
> may be a min-hop one where the max number 
> of hops between any pair of nodes along the tree is 
> minimized.  Since the draft requires reliable 
> transmission between neighboring nodes at the QoS 
> routing layer, per-hop delay may be significant.
> By reducing number of hops one can 
> reduce the latency when some routing update
> needs to be propagated along the tree to all nodes.  
>  
> Rgds,
> Yao-Min  
> 

A good reason could be the simplicity of the MST algorithm,
it's impractical to use a steiner tree or "min-diameter" tree
to transmit control messages since both these trees are hard
to compute, heuristics to these trees are usually time-consuming.

Guo, Liang

guol@ccs.neu.edu                   College of Computer Science,
(617)373-7920 (O)                  161 Cullinane Hall,
(617)859-8879 (H)                  Northeastern University.
http://www.ccs.neu.edu/home/guol   MA 02115.