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RE: [ns] question about the shortest path



Ya Xu-

By "ad hoc routing" did you mean the 'actual' hop count 
achieved by the selected routing protocol when the simulation
is run, or the 'optimal' hop count predetermined by the
Floyd-Warshall algorithm in the setdest.cc file?

I thought the Floyd-Warshall Algorithm calculated the least 
cost paths for source-destination pairs using a connectivity matrix.  
If so, then the problem below is that the routing protocol 
in the ns run is finding a path that is shorter than the one
determined via the Floyd-Warshall algorithm with perfect
knowledge of the network connectivity.

thanks,

jeff


-----Original Message-----
From: Ya Xu [mailto:[email protected]]
Sent: Thursday, August 24, 2000 1:40 PM
To: Liang Qin
Cc: [email protected]
Subject: Re: [ns] question about the shortest path


yes. ad hoc routing does not always give you the shortest path

On Mon, 21 Aug 2000, Liang Qin wrote:

> Hi ns-users,
> 
> I'm running wireless ad-hoc examples from CMU by using their scenario
> files. I got a problem when I reading the trace file:
> 
> --------
> s 50.922355194 _2_ AGT  --- 383 cbr 64 [0 0 0 0] ------- [2:1 3:0 32 0]
[114] 0 4
> r 50.922355194 _2_ RTR  --- 383 cbr 64 [0 0 0 0] ------- [2:1 3:0 32 0]
[114] 0 4
> s 50.922355194 _2_ RTR  --- 383 cbr 100 [0 0 0 0] ------- [2:1 3:0 32 28]
[114] 0 4
> r 50.923452437 _28_ RTR  --- 383 cbr 100 [a2 1c 2 800] ------- [2:1 3:0 32
28] [114] 1 4
> f 50.923452437 _28_ RTR  --- 383 cbr 100 [a2 1c 2 800] ------- [2:1 3:0 32
34] [114] 1 4
> r 50.925142474 _34_ RTR  --- 383 cbr 100 [a2 22 1c 800] ------- [2:1 3:0
32 34] [114] 2 4
> f 50.925142474 _34_ RTR  --- 383 cbr 100 [a2 22 1c 800] ------- [2:1 3:0
32 3] [114] 2 4
> r 50.926412899 _3_ RTR  --- 383 cbr 100 [a2 3 22 800] ------- [2:1 3:0 32
3] [114] 3 4
> r 50.926412899 _3_ AGT  --- 383 cbr 100 [a2 3 22 800] ------- [2:1 3:0 32
3] [114] 3 4
> -------
> parameters: cbr-50-10-4-64  and scen-1500x300-50-30-1-1
> 
> from above info we can see the shortest path(optimal hop count) is 4, but
> actually the hop count is 3, better than the shortest path. Is it
possible?
> 
> Thank you in advance!
> 
> 
> Liang Qin 
> 

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