An Introduction to OMNeT++

based on Documention from http://www.omnetpp.org/

Christian Timmerer and Mathias Lux

Klagenfurt University, Dept. of Information Technology (ITEC)

October 2007
 Organisatorisches
• Informationstechnik ∧¬ Betriebssysteme
– Einführung in die Welt der Prozesse & Threads
– Mittwoch (10.10. 2007) HS 4, 10-12 Uhr
 Outline
• Introduction
• OMNet++ in a Nutshell
– What does OMNeT++ provide then?
– OK. What does an OMNeT++ simulation model look like?
– How do I run this thing?
– OK! Now, how do I program a model in C++?
• Working with OMNet++: Flow Chart
• TicToc Tutorial
– Getting started
– Enhancing the 2-node TicToc
– Turning into a real network
– Adding statistics collection
– Visualizing the results with Plove and Scalars
• Conclusions

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 Introduction
• Discrete event simulator
– Hierarchically nested modules
– Modules communicate using messages through channels
• Written in C++
– Source code publicly available
– Simulation model for Internet, IPv6, Mobility, etc. available
• Free for academic use
– Commercial version of OMNESTTM
• Pros
– Well structured, highly modular, not limited to network
protocol simulations (e.g., like ns2)
• Cons
– Relatively young and only few simulation models
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Introduction
OMNet++ in a Nutshell:
What does OMNeT++ provide then?
• C++ class library
– Simulation kernel
– Utility classes (for random number generation, statistics collection, topology discovery etc.)

use to create simulation components (simple modules and channels)
• Infrastructure to assemble simulations
– Network Description Language (NED)
– .ini files
• Runtime user interfaces
– Tkenv
– Cmdenv
• Tools to facilitate creating simulations and evaluating results
– GNED
– Scalars
– Plove
• Tools to document large simulation models
– opp_neddoc
• Extension interfaces for real-time simulation, emulation, MRIP, parallel distributed
simulation, database connectivity and so on

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OMNet++ in a Nutshell:
OK. What does an OMNeT++ simulation model look like?

• OMNet++ provides component-based

architecture // Host with an Ethernet interface
• Models assembled from reusable module EtherStation
components = modules (can be combined in parameters: ...
various way like LEGO blocks) gates: ...
in: in; // for connecting to switch/hub,
• Modules can be connected with each other etc
through gates, and combined to form out: out;
compound modules submodules:
app: EtherTrafficGen;
// Ethernet CSMA/CD MAC llc: EtherLLC;
simple EtherMAC mac: EtherMAC;
parameters: connections:
address : string; // others omitted for brevity app.out --> llc.hlIn;
gates: app.in <-- llc.hlOut;
in: phyIn; // to physical layer or the network llc.macIn <-- mac.llcOut;
out: phyOut; // to physical layer or the network llc.macOout --> mac.llcIn;
in: llcIn; // to EtherLLC or higher layer mac.phyIn <-- in;
out: llcOut; // to EtherLLC or higher layer mac.phyOut --> out;
endsimple Timmerer, Lux / Klagenfurt University endmodule
/ Dept. of
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OMNet++ in a Nutshell:
How do I run this thing?

• Building the simulation program

– opp_makemake -N; make
– -N does not compile NED files into C++; are
loaded dynamically
– -I required in case subdirectories are used
• Run executable [General]
– Edit omnetpp.ini and preload-ned-files = *.ned
start ./<exec> network = etherLAN
– ./<exec> -f <name1>.ini –f <name2.ini>
[Parameters]
• By default, graphical user *.numStations = 20
interface, Tkenv **.frameLength = normal(200,1400)
**.station[0].numFramesToSend = 5000
– -u Tkenv oder -u Cmdenv **.station[1-5].numFramesToSend = 1000
**.station[*].numFramesToSend = 0

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OMNet++ in a Nutshell:
OK! Now, how do I program a model in C++?

• Simple modules are C++ classes

– Subclass from cSimpleModule
– Redefine a few virtual member functions
– Register the new class with OMNet++ via Define_Module()
macro
• Modules communicate via messages (also timers=timeout
are self-messages)
– cMessage or subclass thereof
– Messages are delivered to handleMessage(cMessage *msg)
– Send messages to other modules: send(cMessage *msg, const
char *outGateName)
– Self-messages (i.e., timers can be scheduled):
scheduleAt(simtime_t time, cMessage *msg) and
cancelEvent(cMessage *msg) to cancel the timer
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OMNet++ in a Nutshell:
OK! Now, how do I program a model in C++? (cont’d)

• cMessage data members

– name, length, kind, etc.
– encapsulate(cMessage *msg), decapsulate() to facilitate
protocol simulations
• .msg file for user-defined message types
– OMNet++ opp_msgc to generate C++ class: _m.h and
_m.cc
– Support inheritance, composition, array members, etc.
message NetworkPacket {
fields:
int srcAddr;
int destAddr;
}
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OMNet++ in a Nutshell:
OK! Now, how do I program a model in C++? (cont’d)
• To simulate network protocol stacks, control_info may
carry auxiliary information to facilitate communication
between protocol layers
– cMessage's setControlInfo(cPolymorpic *ctrl) and
removeControlInfo()
• Other cSimpleModule virtual member functions
– initialize(), finish(), handleParameterChange(const char
*paramName)
• Reading NED parameters
– par(const char *paramName)
– Typically done in initialize() and values are stored in data
members of the module class
– Returns cPar object which can be casted to the appropriate type
(long, double, int, etc.) or by calling the object’s doubleValue()
etc. methods
– Support for XML: DOM-like object tree
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 Working with OMNet++: Flow Chart

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 Using OMNeT++ in our course
• OMNeT++ is installed at pl[00-03].itec.uni-
klu.ac.at.
– Connect there using SSH
• PuTTY on Windows:
http://www.chiark.greenend.org.uk/~sgtatham/putty/
– Use your Uni-Klu username & password
– Copy files using SCP
• WinSCP on Windows: http://winscp.net
 Using OMNeT++ in our course
• Displaying OMNeT++ Tkenv locally
– Install XMing on Windows and run it
• http://sourceforge.net/projects/xming
– Configure PuTTY the ‘right’ way
 Remote X11 using Linux ...
• Enable X11 forwarding with
– xhost +
• Connect with
– ssh –X –u <user> pl00.itec.uni-klu.ac.at
• Retrieve and edit files with Nautilus or
Konqueror
– <ctrl>-L and “ssh://pl00.itec.uni-klu.ac.at”
– enter fish://pl00.itec.uni-klu.ac.at
 TicToc Tutorial
• Short tutorial to OMNeT++ guides you through an
example of modeling and simulation
• Showing you along the way some of the
commonly used OMNeT++ features
• Based on the Tictoc example simulation:
samples/tictoc – much more useful if you actually
carry out at least the first steps described here
• http://www.omnetpp.org/doc/tictoc-tutorial/

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 Getting Started
• Starting point
– "network" that consists of two nodes (cf. simulation of telecommunications
network)
– One node will create a message and the two nodes will keep passing the same
packet back and forth
– Nodes are called “tic” and “toc”
• Here are the steps you take to implement your first simulation from
scratch:
1. Create a working directory called tictoc, and cd to this directory
2. Describe your example network by creating a topology file
3. Implement the functionality
4. Create the Makefile
5. Compile and link the simulation
6. Create the omnetpp.ini file
7. Start the executable using graphical user interface
8. Press the Run button on the toolbar to start the simulation
9. You can play with slowing down the animation or making it faster
10.You can exit the simulation program …
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 Describe your Example Network by creating a Topology File

// This file is part of an OMNeT++/OMNEST simulation example.

// Copyright (C) 2003 Ahmet Sekercioglu
// Copyright (C) 2003-2005 Andras Varga
// This file is distributed WITHOUT ANY WARRANTY. See the file
// `license' for details on this and other legal matters.
Txc1 is a simple module type, i.e., atomic
simple Txc1 on NED level and implemented in C++.
gates: Txc1 has one input gate named in, and one
in: in;
out: out;
output gate named out .
endsimple

// Two instances (tic and toc) of Txc1 connected both ways. Tictoc1 is a compound module assembled
// Tic and toc will pass messages to one another.
from two sub-modules tic and toc
module Tictoc1 (instances from a module type called
submodules: Txc1).
tic: Txc1;
toc: Txc1; Connection: tic’s output gate (out) to toc’s
connections: input gate and vice version w/ propagation
tic.out --> delay 100ms --> toc.in; delay 100ms.
tic.in <-- delay 100ms <-- toc.out;
endmodule
Define a network tictoc1 which is an
network tictoc1 : Tictoc1
instance of the module type TicToc1.
endnetwork
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 Implement the Functionality
Txc1 simple module
#include <string.h> represented as C++ class Txc1;
#include <omnetpp.h>
subclass from cSimpleModule.
class Txc1 : public cSimpleModule { Need to redefine two methods from
protected: // The following redefined virtual function holds the algorithm. cSimpleModule: initialize() and
virtual void initialize(); handleMessage().
virtual void handleMessage(cMessage *msg);
};
Define_Module(Txc1); // The module class needs to be registered with OMNeT++

void Txc1::initialize() {
// Initialize is called at the beginning of the simulation. To bootstrap the tic-toc-tic-toc process, one of the modules needs
// to send the first message. Let this be `tic‘. Am I Tic or Toc?
if (strcmp("tic", name()) == 0) {
// create and send first message on gate "out". "tictocMsg" is an arbitrary string which will be the name of the message
object.
cMessage *msg = new cMessage("tictocMsg");
send(msg, "out");
} Create cMessage and send it to
} out on gate out.
void Txc1::handleMessage(cMessage *msg) {
// The handleMessage() method is called whenever a message arrives at the module.
// Here, we just send it to the other module, through gate `out'.
// Because both `tic' and `toc' does the same, the message will bounce between the two.
send(msg, "out"); Send it back.
}
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 Create the Makefile, Compile, and Link the Simulation

• Create Makefile: opp_makemake

– This command should have now created a
Makefile in the working directory tictoc.
• Compile and link the simulation: make

If you start the executable now, it will complain

that it cannot find the file omnetpp.ini

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 Create the omnetpp.ini File
• … tells the simulation program which network you want to
simulate
• … you can pass parameters to the model
• … explicitly specify seeds for the random number
generators etc.
# This file is shared by all tictoc simulations.
# Lines beginning with `#' are comments

[General]
preload-ned-files = *.ned
network = tictoc1 # this line is for Cmdenv, Tkenv will still let you choose from a dialog

[Parameters]
tictoc4.toc.limit = 5
# argument to exponential() is the mean; truncnormal() returns values from
# the normal distribution truncated to nonnegative values
tictoc6.tic.delayTime = exponential(3)
tictoc6.toc.delayTime = truncnormal(3,1)
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Start the Executable, Run, Play, Exit
• ./tictoc shall start the simulation environment
• Hit Run button to start the actual simulation
• Play around, e.g., fast forward, stop, etc.
• Hit File->Exit to close the simulation

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 Enhancing the 2-node TicToc
• Step 2: Refining the graphics, and adding
debugging output
• Step 3: Adding state variables
• Step 4: Adding parameters
• Step 5: Modeling processing delay
• Step 6: Random numbers and parameters
• Step 7: Timeout, cancelling timers
• Step 8: Retransmitting the same message

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 Step 2: Refining the Graphics, and Adding Debugging Output

submodules:
tic: Txc2;
display: "i=block/process,cyan"; // Note "i=<icon>,<color>”
toc: Txc2;
display: "i=block/process,gold"; // Here too
connections:

Debug messages
• ev << "Sending initial message\n";
• ev << "Received message `" << msg->name() << "', sending it out again\n";

Run the simulation

in the OMNeT++
GUI Tkenv.

Open separate output windows for tic and

toc by right-clicking on their icons and
choosing Module output from the menu –
useful for large models.
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 Step 3: Adding State Variables
#include <stdio.h> #include <string.h> #include <omnetpp.h>
class Txc3 : public cSimpleModule {
private:
int counter; // Note the counter here
protected:
virtual void initialize();
virtual void handleMessage(cMessage *msg);
};
Define_Module(Txc3);
void Txc3::initialize() {
counter = 10;
/* The WATCH() statement below will let you examine the variable under Tkenv. After doing a few steps in the simulation,
double-click either `tic' or `toc', select the Contents tab in the dialog that pops up, and you'll find "counter" in the list. */
WATCH(counter);
if (strcmp("tic", name()) == 0) {
ev << "Sending initial message\n“;
cMessage *msg = new cMessage("tictocMsg");
send(msg, "out");
}
}
void Txc3::handleMessage(cMessage *msg) {
counter--; // Increment counter and check value.
if (counter==0) { /* If counter is zero, delete message. If you run the model, you'll find that the simulation will stop at this point
with the message "no more events“. */
ev << name() << "'s counter reached zero, deleting message\n“;
delete msg;
} else { ev << name() << "'s counter is " << counter << ", sending back message\n"; send(msg, "out"); }
}
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We'll turn the "magic number" 10 into a
parameter
Step 4: Adding Parameters
• Module parameters have to be declared in the NED file: numeric, string, bool, or
xml
simple Txc4
parameters:
limit: numeric const; // declare the new parameter
gates:
• Modify the C++ code to read the parameter in initialize(), and assign it to the
counter.
counter = par("limit");
• Now, we can assign the parameters in the NED file or from omnetpp.ini.
Assignments in the NED file take precedence.
module Tictoc4
submodules:
tic: Txc4;
parameters:
limit = 8; // tic's limit is 8
display: "i=block/process,cyan“;
toc: Txc4; // note that we leave toc's limit unbound here
display: "i=block/process,gold";
connections:
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 Step 4: Adding Parameters (cont’d)
• … and the other in omnetpp.ini:
– tictoc4.toc.limit = 5
• Note that because omnetpp.ini supports wildcards,
and parameters assigned from NED files take
precedence over the ones in omnetpp.ini, we could
have used
– tictoc4.t*c.limit = 5
• or
– tictoc4.*.limit = 5
• or even
– **.limit = 5
• with the same effect. (The difference between * and
** is that * will not match a dot and ** will.)
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 Step 5: Modeling Processing Delay
• Hold messages for some time before sending it back
timing is achieved
by the module sending a message to itself (i.e., self-messages)
class Txc5 : public cSimpleModule {
private:
// pointer to the event object which we'll use for timing
cMessage *event;
// variable to remember the message until we send it back
cMessage *tictocMsg;
public:

• We "send" the self-messages with the scheduleAt() function

scheduleAt(simTime()+1.0, event);

• handleMessage(): differentiate whether a new message has arrived via the

input gate or the self-message came back (timer expired)
if (msg==event) or if (msg->isSelfMessage())

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 Step 5: Modeling Processing Delay (cont’d)
void Txc5::handleMessage(cMessage *msg) {
// There are several ways of distinguishing messages, for example by message
// kind (an int attribute of cMessage) or by class using dynamic_cast
// (provided you subclass from cMessage). In this code we just check if we
// recognize the pointer, which (if feasible) is the easiest and fastest
// method.
if (msg==event) {
// The self-message arrived, so we can send out tictocMsg and NULL out
// its pointer so that it doesn't confuse us later.
ev << "Wait period is over, sending back message\n";
send(tictocMsg, "out");
tictocMsg = NULL;
} else {
// If the message we received is not our self-message, then it must
// be the tic-toc message arriving from our partner. We remember its
// pointer in the tictocMsg variable, then schedule our self-message
// to come back to us in 1s simulated time.
ev << "Message arrived, starting to wait 1 sec...\n";
tictocMsg = msg;
scheduleAt(simTime()+1.0, event);
}
}

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 Step 6: Random Numbers and Parameter
• Change the delay from 1s to a random value :
// The "delayTime" module parameter can be set to values like
// "exponential(5)" (tictoc6.ned, omnetpp.ini), and then here
// we'll get a different delay every time.
double delay = par("delayTime");

ev << "Message arrived, starting to wait " << delay << " secs...\n";
tictocMsg = msg;
scheduleAt(simTime()+delay, event);

• "Lose" (delete) the packet with a small (hardcoded) probability:

if (uniform(0,1) < 0.1) {
ev << "\"Losing\" message\n";
delete msg;
}

• Assign seed and the parameters in omnetpp.ini:

[General] seed-0-mt=532569 # or any other 32-bit value

tictoc6.tic.delayTime = exponential(3)
tictoc6.toc.delayTime = truncnormal(3,1)
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 Step 7: Timeout, Cancelling Timers
• Transform our model into a stop-and-wait simulation

void Tic7::handleMessage(cMessage *msg) {

if (msg==timeoutEvent) {
// If we receive the timeout event, that means the packet hasn't
// arrived in time and we have to re-send it.
ev << "Timeout expired, resending message and restarting timer\n";
cMessage *msg = new cMessage("tictocMsg");
send(msg, "out");
scheduleAt(simTime()+timeout, timeoutEvent);
} else { // message arrived
// Acknowledgement received -- delete the stored message
// and cancel the timeout event.
ev << "Timer cancelled.\n";
cancelEvent(timeoutEvent);

// Ready to send another one.

cMessage *msg = new cMessage("tictocMsg");
send(msg, "out");
scheduleAt(simTime()+timeout, timeoutEvent);
}
}
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 Step 8: Retransmitting the Same Message

• Keep a copy of the original packet so that we can

re-send it without the need to build it again:
– Keep the original packet and send only copies of it
– Delete the original when toc's acknowledgement
arrives
– Use message sequence number to verify the model
• generateNewMessage() and sendCopyOf()
– avoid handleMessage() growing too large

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Step 8: Retransmitting the Same Message (cont’d)

cMessage *Tic8::generateNewMessage() {
// Generate a message with a different name every time.
char msgname[20];
sprintf(msgname, "tic-%d", ++seq);
cMessage *msg = new cMessage(msgname);
return msg;
}

void Tic8::sendCopyOf(cMessage *msg) {

// Duplicate message and send the copy.
cMessage *copy = (cMessage *) msg->dup();
send(copy, "out");
}

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 Turning it into a real network

• Step 9: More than two nodes

• Step 10: Defining our message class

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 Step 9: More Than Two Nodes
simple Txc9
gates:
in: in[]; // declare in[] and out[] to be vector gates
out: out[];
endsimple

module Tictoc9
submodules:
tic: Txc9[6]; // we'll have 6 Txc modules
display: "i=block/process";
connections:
tic[0].out++ --> delay 100ms --> tic[1].in++;
tic[0].in++ <-- delay 100ms <-- tic[1].out++;

tic[1].out++ --> delay 100ms --> tic[2].in++;

tic[1].in++ <-- delay 100ms <-- tic[2].out++;

tic[1].out++ --> delay 100ms --> tic[4].in++;

tic[1].in++ <-- delay 100ms <-- tic[4].out++;

tic[3].out++ --> delay 100ms --> tic[4].in++;

tic[3].in++ <-- delay 100ms <-- tic[4].out++;

tic[4].out++ --> delay 100ms --> tic[5].in++;

tic[4].in++ <-- delay 100ms <-- tic[5].out++;
endmodule Timmerer, Lux / Klagenfurt University / Dept. of
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Step 9: More Than Two Nodes (cont’d)
• tic[0] will generate the message to be sent around
– done in initialize()
– index() function which returns the index of the module
• forwardMessage(): invoke from handleMessage() whenever a message arrives

void Txc9::forwardMessage(cMessage *msg) {

// In this example, we just pick a random gate to send it on.
// We draw a random number between 0 and the size of gate `out[]'.
int n = gate("out")->size();
int k = intuniform(0,n-1);

ev << "Forwarding message " << msg << " on port out[" << k << "]\n";
send(msg, "out", k);
}

• When the message arrives at tic[3], its handleMessage() will delete the message

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 Step 10: Defining our Message Class
• Destination address is no longer hardcoded tic[3] – add destination address to
message
• Subclass cMessage: tictoc10.msg
message TicTocMsg10 {
fields:
int source;
int destination;
int hopCount = 0;
}
• opp_msgc is invoked and it generates tictoc10_m.h and tictoc10_m.cc
• Include tictoc10_m.h into our C++ code, and we can use TicTocMsg10 as any other
class
#include "tictoc10_m.h"

TicTocMsg10 *msg = new TicTocMsg10(msgname);

msg->setSource(src);
msg->setDestination(dest);
return msg;

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 Step 10: Defining our Message Class (cont’d)
• Use dynamic cast instead of plain C-style cast ((TicTocMsg10 *)msg) which is not safe

void Txc10::handleMessage(cMessage *msg) {

TicTocMsg10 *ttmsg = check_and_cast<TicTocMsg10 *>(msg);

if (ttmsg->getDestination()==index()) {
// Message arrived.
ev << "Message " << ttmsg << " arrived after " << ttmsg->getHopCount() << " hops.\n";
bubble("ARRIVED, starting new one!");
delete ttmsg;

// Generate another one.

ev << "Generating another message: ";
TicTocMsg10 *newmsg = generateMessage();
ev << newmsg << endl;
forwardMessage(newmsg);
} else {
// We need to forward the message.
forwardMessage(ttmsg);
}
}

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 Adding statistics collection

• Step 11: Displaying the number of packets

sent/received

• Step 12: Adding statistics collection

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 Step 11: Displaying the Number of Packets Sent/Received

• Add two counters to the module class: numSent and

numReceived
• Set to zero and WATCH'ed in the initialize() method
• Use the Find/inspect objects dialog (Inspect menu; it is also
on the toolbar)

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 Step 11: Displaying the Number of Packets Sent/Received (cont’d)

• This info appears above the module icons using the

t= display string tag

if (ev.isGUI())
updateDisplay();

void Txc11::updateDisplay(){
char buf[40];
sprintf(buf, "rcvd: %ld sent: %ld", numReceived, numSent);
displayString().setTagArg("t",0,buf);
} Timmerer, Lux / Klagenfurt University / Dept. of
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Step 12: Adding statistics collection
• Example: average hopCount a message has to
travel before reaching its destination
– Record in the hop count of every message upon
arrival into an output vector (a sequence of
(time,value) pairs, sort of a time series)
– Calculate mean, standard deviation, minimum,
maximum values per node, and write them into a
file at the end of the simulation
– Use off-line tools to analyze the output files

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 Step 12: Adding statistics collection (cont’d)

• Output vector object (which will record the data into omnetpp.vec) and a
histogram object (which also calculates mean, etc)
class Txc12 : public cSimpleModule {
private:
long numSent;
long numReceived;
cLongHistogram hopCountStats;
cOutVector hopCountVector;

protected:
• Upon message arrival, update statistics within handleMessage()
hopCountVector.record(hopcount);
hopCountStats.collect(hopcount);
• hopCountVector.record() call writes the data into omnetpp.vec (will be
deleted each time the simulation is restarted)

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 Step 12: Adding statistics collection (cont’d)

• Scalar data (histogram object) have to be recorded manually, in the finish()

function

void Txc12::finish() {
// This function is called by OMNeT++ at the end of the simulation.
ev << "Sent: " << numSent << endl;
ev << "Received: " << numReceived << endl;
ev << "Hop count, min: " << hopCountStats.min() << endl;
ev << "Hop count, max: " << hopCountStats.max() << endl;
ev << "Hop count, mean: " << hopCountStats.mean() << endl;
ev << "Hop count, stddev: " << hopCountStats.stddev() << endl;

recordScalar("#sent", numSent);
recordScalar("#received", numReceived);
hopCountStats.recordScalar("hop count");
}

• recordScalar() calls in the code below write into the omnetpp.sca file
• omnetpp.sca not deleted between simulation runs; new data are just appended –
allows to jointly analyze data from several simulation runs
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 Step 12: Adding statistics collection (cont’d)

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 Visualizing the results with Scalars
• Scalars tool can be used to visualize the contents of the
omnetpp.sca file: bar charts, x-y plots (e.g. throughput
vs. offered load), or export data
$ scalars omnetpp.sca

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 Visualizing the results with Plove
$ plove omnetpp.vec

The left pane displays vectors

that are present in the
omnetpp.vec file. (You can load
further vector files as well.)

To plot, you have to copy some

vectors to the right pane, select
one or more of them (shift+click
and ctrl+click works), and click the
Plot icon on the toolbar.

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 Visualizing the results with Plove (cont’d)

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 Visualizing the results with Plove (cont’d)

• Turned off connecting the data points

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 Visualizing the results with Plove (cont’d)

• Apply a filter which plots mean on [0,t).

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 Conclusions
• OMNeT++: discrete event simulation system
• OMNeT++ is a
– public-source,
– component-based,
– modular and open-architecture simulation
environment
– with strong GUI support and
– an embeddable simulation kernel

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 Thank you for your attention

... questions,
comments, etc. are
welcome …

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