Re: asking the meaning of the content of movement scenario about mobile node

[Padmaparna Haldar <haldar@ISI.EDU>]

Kang,
     definiton of god and explanation of node-movement files are given
below. A tutorial for wireless simulations in ns is currently developed
and will be out soon. 

Quoted from CMU document on god, "God (General Operations Director) is the
object that is used to store global information about the state of the
environment, network or nodes that an omniscent observer would have, but
that should not be made known to  any participant in the simulation."
Currently, God object stores the total
number of mobilenodes and a table of shortest number of hops required to
reach from one node to an other. The next hop information is normally
loaded into god object from node-movement files, before simulation
begins, since calculating this on the fly during simulation runs can be
quite time consuming.

In node-movement file scen-3-test, we see node-movement commands like
<TABLE BGCOLOR="#eeeeee" CELLPADDING=5><TD><CODE><PRE>
$ns_ at 50.000000000000 "$node_(2) setdest 369.463244915743 \
170.519203111152 3.371785899154"
</PRE></CODE></TD></TABLE>

This, as described in earlier sub-section, means at time 50s, node2 starts
to move towards destination (368.4,170.5) at a speed of 3.37m/s.
We also  see other lines like
<TABLE BGCOLOR="#eeeeee" CELLPADDING=5><TD><CODE><PRE>
$god_ set-dist 1 2 2
</PRE></CODE></TD></TABLE>

These are command lines used to load the god object with the shortest hop
information. It means the shortest path between node 1 and 2 is 2 hops. By
providing this information, the calculation of shortest distance between
nodes by the god object during simulation runs, which can be quite
time-consuming, is prevented.
<P>
The path length information was used by CMU's Monarch Project to analyze
the path length optimality of ad hoc network routing protocols, and so
was printed out as part of the CMUTrace output for each packet.
</P>
<P>
Other uses that CMU has found for the information are:
<LI>Characterizing the rate of topology change in a movement pattern.
<LI>Identifying the frequency and size of partitions.
<LI>Experimenting with the behavior of the routing protocols if the
god information is used to provide them with ``perfect'' neighbor
information at zero cost.


Hope this helps,
--Padma.

> Hi, Senior
> 
> I'm a beginner of NS.
> I want the mobile-node to move as I wish. I can't under stand what it is
> when I read the example of movement scenario. It is followed
> 
> set god_ [God instance]
> $god_ set-dist  0 1 1
> $god_ set-dist  0 1 5
> .......
> .......
> .......
> ......
> 
> 
> I want to know  what "God" does, what "set-dist" is, and what the
> numbers mean.
> I look forward to your answer.
> 
> Thanks for your interest
> 
> 
> 
> 
> Kang, Yoonsik
> 
> armani@eeca1.sogang.ac.kr
> 
> 
> 

------------------------------------------------
Be true to your work, your word, and your friend.
--Thoreau

Padmaparna Haldar