Re: [ns] question about the shortest path

[Satish Kumar <kkumar@ISI.EDU>]

Just a guess but it seems like the transmission range specified in setdest.cc 
(by the RANGE variable, I think) may be different from the transmission range 
used in the simulations (which is computed from the propagation model).

Satish


> 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:yaxu@ISI.EDU]
> Sent: Thursday, August 24, 2000 1:40 PM
> To: Liang Qin
> Cc: ns-users@ISI.EDU
> 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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