[Olsr-users] XL routing protocol

Hannes Gredler (spam-protected)
Wed Sep 3 13:43:16 CEST 2008

Bob Keyes wrote:
> I don't know how many of you have seen this paper from a group at UCSD 
> (University of California at San Diego) which presents a new method of 
> discerning which route updates to forward to a given node.
> http://ccr.sigcomm.org/online/files/p15-levchenko.pdf
> Some of the content of the paper is stating the obvious, but other parts 
> of it are rather formal logic which I don't have the necessary skills to 
> interpret. I am giving it a close read to see what I can learn from it.
> I am interested to read the opinions and reviews of some of the rest of 
> you. Does anything presented in this paper provide anything of value for 
> future versions of OLSR?

when i saw this (constrained flooding) first time my first impression was
that this is a solution in search of a problem.

what *is* the problem -

is it CPU load because of SPF calculation ?

observation #1:

-the CPU power of route processors have outpaced the average growth of
  routing nodes in a network. today on a mobile-pentium 2Ghz class of CPU
  a SPF calculation of a node with 10000 nodes can be performed in less than 40ms.
  on a MIPS equivalent CPU computation of 500 nodes is finished after app. 20ms.

is it network traffic because of flooding ?

observation #2
-the authors assume that a link-state protocol has some form of reliable
  transport to make sure that a necessary update reaches all corners of the
  network. - the issue with OLSR is that such a reliable transport does not
  exist. what OLSR does is retransmitting its TC messages such that despite of high
  loss a TC update message is seen by everybody else. this is neither optimal
  nor desirable, however unless we get some semi reliable transport in OLSR
  there is no way to implement constrained flooding.

so IMO its not worth pursuing now - perhaps if we get a reliable transport.


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