RE: [ns] question about the shortest path

["Wysocarski, Jeffrey" <Jeffrey.Wysocarski@itt.com>]

Hi,

I think what is happening is as follows (someone
please correct me if I'm wrong!).  When the 
scenario files are created using the CMU "setdest" 
file, the shortest path from source to destination 
is calculated using the assumption that radios 
that are <= 250 meters can communicate successfully.  
When the simulation is actually run, however, you
can have successful communication at distances a 
little bit larger than this, and so shorter paths 
to the destination can be found.  For example, you 
can look and see that radios that are a distance of 
250.003 meters apart can successfully communicate 
with each other, but the GOD data would say that 
since this distance is greater than 250 meters,
they are out of range.  You can also see this occasionally
when your network fragments (for which the GOD
data will indicate no path exists).

This will trigger the "Actual RT Length < Optimal" error 
if you run totals.pl on the output trace file.

hope this helps,

jeff
-----Original Message-----
From: Liang Qin [mailto:lqin@sce.carleton.ca]
Sent: Monday, August 21, 2000 12:16 PM
To: ns-users@ISI.EDU
Subject: [ns] question about the shortest path


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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