Re: [manet] Comments on "Problem Statement for OSPF Extensions ..." draft

["Charles E. Perkins" <charliep at iprg.nokia.com>]

Hello Justin,

Your observation is very important to understanding
how to improve MPR flooding.  We have, indeed,
measured a drop in packet delivery ratio when the
number of broadcasts is kept to the theoretical
minimum.  This occurs because broadcasts are not
reliable, and when some are lost during MPR flooding
their absence is more damaging than with blind flooding
(I assume not totally blind!).

More comments inline below...

Justin Lipman wrote:

> What is your definition of "reliable" flooding?
>  
I thought it meant that a broadcast source gets an acknowledgement
from each of its neighbors that its broadcast was received.  This
acknowledgement can come in various forms, of course.  If I am
using the term in some way that is not compatible with the discussion
about OSPF extensions, I hope someone will tell me what the correct
meaning should be.

> Blind flooding can be seen as reliable and my own work shows it performs very well (if one ignores the broadcast storm).
Why is it legitimate to ignore the broadcast storm?  That's the
entire motivation anyway for trying to create a better broadcast
mechanism.  Congestion due to broadcast can significantly
degrade packet delivery ratios in many scenarios.

> Sadly, MPR and other optimised 
> flooding algorithms do not perform well at all!
>  
I thought it depended on the scenario!

Regards,
Charlie P.



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