XI. Generating node-movement and traffic-connection files for large wireless scenarios

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We have used traffic-pattern and node-movement files available with the ns distribution for simulation examples in section IX and section X. In this section we will discuss how to use CMU's traffic and scenario generating scripts to create these files. This section is divided into 2 subsections. The first subsection talks about the traffic-pattern generating script, how it works and the random TCP and/or CBR flows it produces. The second subsection is about CMU's node-movement generator "setdest" which can be used to create random waypoint node movements for mobilenodes.

IMPORTANT: This tutorial chapter uses a revised version of setdest which is not available in the ns2.1b5 version. So please download the daily snapshot unless a release is made for version ns2.1b6 or higher. The current snapshot version is updated daily, so please check the validation results for that day before downloading, as these snapshots can sometimes be unstable due to ongoing changes made by ns-developers.

XI.1. Creating random traffic-pattern for wireless scenarios.

Random traffic connections of TCP and CBR can be setup between mobilenodes using a traffic-scenario generator script. This traffic generator script is available under ~ns/indep-utils/cmu-scen-gen and is called cbrgen.tcl. It can be used to create CBR and TCP traffics connections between wireless mobilenodes. In order to create a traffic-connection file, we need to define the type of traffic connection (CBR or TCP), the number of nodes and maximum number of connections to be setup between them, a random seed and incase of CBR connections, a rate whose inverse value is used to compute the interval time between the CBR pkts. So the command line looks like the following:
ns cbrgen.tcl [-type cbr|tcp] [-nn nodes] [-seed seed] [-mc connections]
[-rate rate]

The start times for the TCP/CBR connections are randomly generated with a maximum value set at 180.0s. Go through the tcl script cbrgen.tcl for the details of the traffic-generator implementation.

For example, let us try to create a CBR connection file between 10 nodes, having maximum of 8 connections, with a seed value of 1.0 and a rate of 4.0. So at the prompt type:
ns cbrgen.tcl -type cbr -nn 10 -seed 1.0 -mc 8 -rate 4.0 > cbr-10-test

From cbr-10-test file (into which the output of the generator is redirected) thus created, one of the cbr connections looks like the following:
# 2 connecting to 3 at time 82.557023746220864
set udp_(0) [new Agent/UDP]
$ns_ attach-agent $node_(2) $udp_(0)
set null_(0) [new Agent/Null]
$ns_ attach-agent $node_(3) $null_(0)
set cbr_(0) [new Application/Traffic/CBR]
$cbr_(0) set packetSize_ 512
$cbr_(0) set interval_ 0.25
$cbr_(0) set random_ 1
$cbr_(0) set maxpkts_ 10000
$cbr_(0) attach-agent $udp_(0)
$ns_ connect $udp_(0) $null_(0)
$ns_ at 82.557023746220864 "$cbr_(0) start"
Thus a UDP connection is setup between node 2 and 3. Total UDP sources (chosen between nodes 0-10) and total number of connections setup is indicated as 5 and 8 respectively, at the end of the file cbr-10-test.

Similarly TCP connection files can be created using "type" as tcp. An example would be:
ns cbrgen.tcl -type tcp -nn 25 -seed 0.0 -mc 8 > tcp-25-test
A typical connection from tcp-25-test looks like the following:
# 5 connecting to 7 at time 163.0399642433226
set tcp_(1) [$ns_ create-connection  TCP $node_(5) TCPSink $node_(7) 0]
$tcp_(1) set window_ 32
$tcp_(1) set packetSize_ 512
set ftp_(1) [$tcp_(1) attach-source FTP]
$ns_ at 163.0399642433226 "$ftp_(1) start"

XI.2. Creating node-movements for wireless scenarios.

The node-movement generator is available under ~ns/indep-utils/cmu-scen-gen/setdest directory and consists of setdest{.cc,.h} and Makefile. CMU's version of setdest used system dependent /dev/random and made calls to library functions initstate() for generating random numbers. That was replaced with a more portable random number generator (class RNG) available in ns. In order to compile the revised setdest.cc do the following:
1. Go to ns directory and run "configure" (you probably have done that already while building ns). This creates a makefile for setdest.
2.Go to indep-utils/cmu-scen-gen/setdest. Run "make" , which first creates a stand-alone object file for ~ns/rng.cc (the stand-alone version doesnot use Tclcl libs) and then creates the executable setdest.
3. Run setdest with arguments as shown below:
./setdest [-n num_of_nodes] [-p pausetime] [-s maxspeed] [-t simtime] \
      [-x maxx] [-y maxy] > [outdir/movement-file]

Lets say we want to create a node-movement scenario consisting of 20 nodes moving with maximum speed of 10.0m/s with an average pause between movement being 2s. We want the simulation to stop after 200s and the topology boundary is defined as 500 X 500. So our command line will look like:
./setdest -n 20 -p 2.0 -s 10.0 -t 200 -x 500 -y 500 > scen-20-test

The output is written to stdout by default. We redirect the output to file scen-20-test. The file begins with the initial position of the nodes and goes on to define the node movements.
$ns_ at 2.000000000000 "$node_(0) setdest 90.441179033457 44.896095544010
This line from scen-20-test defines that node_(0) at time 2.0s starts to move toward destination (90.44, 44.89) at a speed of 1.37m/s. These command lines can be used to change direction and speed of movement of mobilenodes.

Directives for GOD are present as well in node-movement file. The General Operations Director (GOD) object 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, the god object is used only to store an array of the shortest number of hops required to reach from one node to an other. The god object does not calculate this on the fly during simulation runs, since it can be quite time consuming. The information is loaded into the god object from the movement pattern file where lines of the form
$ns_ at 899.642 "$god_ set-dist 23 46 2"
are used to load the god object with the knowledge that the shortest path between node 23 and node 46 changed to 2 hops at time 899.642.

The setdest program generates node-movement files using the random waypoint algorithm. These files already include the lines to load the god object with the appropriate information at the appropriate time.

Another program calcdest (also available in ~ns/indep-utils/cmu-scen-gen/setdest) can be used to annotate movement pattern files generated by other means with the lines of god information. calcdest makes several assumptions about the format of the lines in the input movement pattern file which will cause it to fail if the file is not formatted properly. If calcdest rejects a movement pattern file you have created, the easiest way to format it properly is often to load it into ad-hockey and then save it out again. If ad-hockey can read your input correctly, its output will be properly formatted for calcdest.

Both calcdest and setdest calculate the shortest number of hops between nodes based on the nominal radio range, ignoring any effects that might be introduced by the propagation model in an actual simulation. The nominal range is either provided as an argument to the programs, or extracted from the header on the movement pattern file.

The path length information was used by the 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.

Other uses that CMU found for the information:

  • Characterizing the rate of topology change in a movement pattern.
  • Identifying the frequency and size of partitions.
  • Experimenting with the behavior of the routing protocols if the god information is used to provide them with ``perfect'' neighbor information at zero cost.

    Thus at the end of the node-movement file are listed information like number of destination unreachable, total number of route and connectivity changes for mobilenodes and the same info for each mobilenode.

    The revised (more portable) version of setdest ( files revised are: setdest{.cc,.h}, ~ns/rng{.cc,.h}, ~ns/Makefile.in ) should be available from the latest ns distribution. If not, you could download the daily snapshot version of ns from ns-build page.

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