Re: When route is changing....?

[K Sun <ksun@essex.ac.uk>]

Hello,

> Simulation is essentially an abstraction of the real world.  It is 
> difficult, if not impossible, to duplicate what exactly happen in
> the real world.  Usually, depending on what levels of details you care,
> you make sure the modules you're using capture the essence.  

   Yes. However, in certain sense, I would just like to investigate 
influence of route changing on network application. So, I hope the 
simulation can approach real network as much as I need. I think ns 
should be enough reflecting the situations in real network.
  
> Neither session routing nor DV work exactly like the real world in a sense
> that session routing ignores the dynamics that could happen in the
> transition of route changes and DV ignores processing time (and some other
> timer details furhter specified in PIM DM or DVMRP docs).  Nevertheless, 
> session routing and DV are already of great help to a significant set of
> research problems.  

   Actually, I concern DV more than session routing. About the 
processing time of DV, I feel, in ns, comprehensively, it does not 
ignore it. I am not sure of it.
Because when routing algorithm of DV is running in one node, the other 
nodes still deliver packets which transit them as the previous routing 
table. Just after the refresh message is coming to a specific node (it 
should includes the delay of delivery from nodes to nodes), 
re-caculating routing table will be in processing for the node which 
receive the refresh message. For DV, ns ignores the processing time in 
individual node. However, from the whole network routing, I feel it 
exactly simulates the situation of real network. I do not know whether 
my understanding above is correct or not. Hope more comments.

 
> And, the causality problem I thought (not sure if Lloyd agrees) was that
> session routing further abstracts away the transition details so that
> the timing/ordering of packets might be different from the results of
> DV.

   Thank you. I agree with you.

 
> hope this helps to clarify things a bit.

   Thanks a lot!
   
   Best Regards,

      Sun Kai