OMNET++ AND MIXIM FRAMEWORK

Introduction

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What is OMNeT++? OMNeT++ is a component-based, modular and

open-architecture discrete event network simulator.

OMNeT++ represents a framework approach Instead of containing explicit and hardwired support

for computer networks or other areas, it provides an infrastructure for writing such simulations

Specific application areas are catered by various simulation models and frameworks, most of them open source.

These models are developed completely independently of OMNeT++, and follow their own release cycles.

OMNET++ Frameworks Partial list of OMNeT++-based network simulators and simulation

frameworks: Mobility Framework -- for mobile and wireless simulations INET Framework -- for wired and wireless TCP/IP based simulations Castalia -- for wireless sensor networks MiXiM -- for mobile and wireless simulations

More specialized, OMNeT++-based simulators: OverSim -- for overlay and peer-to-peer networks (INET-based) NesCT -- for TinyOS simulations Consensus Positif and MAC Simulator -- for sensor networks SimSANs -- for storage area networks CDNSim -- for content distribution networks ACID SimTools -- for simulation of concurrency control, atomic commit

processing and recovery protocols X-Simulator -- for testing synchronization protocols FIELDBUS -- for simulation of control networks (fieldbuses) PAWiS -- Power Aware Wireless Sensor Networks Simulation Framework

What is MiXiM? MiXiM project

MiXiM (mixed simulator) is a simulation framework for wireless and mobile networks using the OMNeT++ simulation engine

MiXiM is a merger of several OMNeT++ frameworks written to support mobile and wireless simulations

The predecessors of MiXiM are: ChSim by Universitaet Paderborn Mac Simulator by Technische Universiteit Delft Mobility Framework by Technische Universitaet

Berlin, Telecommunication Networks Group Positif Framework by Technische Universiteit Delft

Important issues in a discrete event simulation environment

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Pseudorandom generators Flexibility Programming model Model management Support for hierarchical models Debugging, tracing, and experiment

specifications Documentation Large scale simulation Parallel simulation

Flexibility6

Core framework for discrete event simulation. Different add-ons for specific purposes.

Fully implemented in C++.

Functionality added by deriving classes following specified rules.

OMNET++ Programming model Simulated objects are represented by modules

Modules can be simple or composed (depth of module nesting is not limited)

Modules communicate by messages (sent directly or via gates)

One module description consists of: Interface description (.NED file) Behavior description (C++ class)

Modules, gates and links can be created: Statically - at the beginning of the simulation (NED

file) Dynamically – during the simulation

Hierarchical models Network interface

card, a compound module consisting of a simple module MAC and a compound module Phy

Model management9

Clear separation among simulation kernel and developed models.

Easiness of packaging developed modules for reuse.

No need for patching the simulation kernel to install a model.

Build models and combine like LEGO blocks

Debugging and tracking Support is offered for:

Recording data vectors and scalars in output files Random numbers (also from several distributions) with

different starting seeds Tracing and debugging aids (displaying info about the

module’s activity, snapshots, breakpoints) Simulations are easy to configure using .ini file Batch execution of the same simulation for

different parameters is also included Simulations may be run in two modes:

Command line: Minimum I/O, high performance. Interactive GUI: Tcl/Tk windowing, allows view

what’s happening and modify parameters at run-time.

Simulation Model building11

for (int i=0;i<10;i++) {}...

[General]network=test_disk

[Parameters]...

Model structure

Add behavior

Set up parameters

Compile

Run

Analyze

Build processNetwork

description

Generated C++ code

Module behavior C++

code

Simulation kernel

libraries

User interface libraries

Simulation

program

NED Overview The topology of a model is specified

using the NED language. Edit it with GNED or other text editor.

Components of a NED description Import directives Channel definitions Simple and compound module

definitions Network definitions

Import directives import "ethernet"; // imports

ethernet.ned import "Router", "StandardHost", "FlatNetworkConfigurator";

Channel definitionschannel LeasedLine

delay 0.0018 // sec error 1e-8 datarate 128000 // bit/sec

endchannel

Simple module definitionssimple TrafficGen

parameters: interarrivalTime, numOfMessages : const,

address : string; gates:

in: fromPort, fromHigherLayer; out: toPort, toHigherLayer;

endsimple

Application Layer

TrafficGen

MAC Layer

Compound module definitions module CompoundModule

parameters: //... gates: //... submodules: //... connections: //...

endmodule

Compound module definitions - submodulesmodule CompoundModule

//... submodules:

submodule1: ModuleType1 parameters: //... gatesizes: //...

submodule2: ModuleType2 parameters: //... gatesizes: //...

endmodule

Assigning values to submodule parameters module CompoundModule

parameters: param1: numeric, param2: numeric, useParam1: bool; submodules: submodule1: Node parameters: p1 = 10, p2 = param1+param2, p3 = useParam1==true ? param1 : param2; //...

endmodule

Connections module CompoundModule

parameters: //... gates: //... submodules: //... connections:

node1.output --> node2.input; node1.input <-- node2.output; //...

endmodule

Network definitions network wirelessLAN: WirelessLAN

parameters: numUsers=10, httpTraffic=true,

ftpTraffic=true, distanceFromHub=truncnormal(100,60);

endnetwork

Simulation Model //

// Ethernet CSMA/CD MAC // simple EtherMAC {

parameters: string address; // others omitted for brevity

gates: input phyIn; // to physical layer or the

network output phyOut; // to physical layer or

the network input llcIn; // to EtherLLC or higher layer output llcOut; // to EtherLLC or higher layer

} Modules can be connected with each other via gates  and combined to form compound modules. Connections are created within a single level of module hierarchy: a submodule can be connected with another, or with the containing compound module. Every simulation model is an instance of a compound module type. This level (components and topology) is dealt with in NED files

Simulation Model //

// Host with an Ethernet interface // module EtherStation {

parameters: ... gates: ...

input in; // connect to switch/hub, etc

output out;submodules:

app: EtherTrafficGen; llc: EtherLLC; mac: EtherMAC;

connections: app.out --> llc.hlIn; app.in <-- llc.hlOut; llc.macIn <-- mac.llcOut; llc.macOout --> mac.llcIn; mac.phyIn <-- in; mac.phyOut --> out;

}

Simple modules which, like EtherMAC, don't have further submodules and are backed up with C++ code that provides their active behavior, are declared with the simple keyword; compound modules are declared with the module keyword. To simulate an Ethernet LAN, you'd create a compound module EtherLAN and announce that it can run by itself with the network keyword:

network EtherLAN { submodules: EtherStation;…

}

Running a model #> opp_makemake --deep

creates a makefile with the appropriate settings #> make To run the executable, you need

an omnetpp.ini file.  Without it you get the following error: #> ./etherlan

OMNeT++/OMNEST Discrete Event Simulation (C) 1992-2005 Andras Varga [....] <!> Error during startup: Cannot open ini file `omnetpp.ini'

Running a model (omnetpp.ini) [General]

network = etherLAN *.numStations = 20 **.frameLength = normal(200,1400) **.station[0].numFramesToSend = 5000 **.station[1-5].numFramesToSend = 1000 **.station[*].numFramesToSend = 0One function of the ini file is to tell which network to simulate. You can also specify

in there which NED files to load dynamically, assign module parameters, specify how long the simulation should run, what seeds to use for random number generation, how much results to collect, set up several experiments with different parameter settings, etc.

Why use separate NED and ini files? NED files define the topology of

network/modules It is a part of the model description

Ini files define Simulation parameters Results to collect Random seeds

This separation allows to change parameters without modifying the model E.g. no need to recompile, experiments can be

executed as a batch

Output of a simulation The simulation may write output vector and output scalar

files omnetpp.vec and omnetpp.sca The capability to record simulation results has to be explicitly

programmed into the simple modules An output vector file contains several output vectors

series of pairs timestamp, value They can store things like:

queue length over time, end-to-end delay of received packets, packet drops or channel throughput

You can configure output vectors from omnetpp.ini you can enable or disable recording individual output vectors, or limit

recording to a certain simulation time interval Output vectors capture behaviour over time

Output scalar files contain summary statistics number of packets sent, number of packet drops, average end-to-

end delay of received packets, peak throughput

MiXiM

MiXiM World utility module provides global

parameters of the environment (size, 2D or 3D) Objects are used to model the environment

ObjectHouse, ObjectWall Objects influence radio signals and the mobility of

other objects ObjectManager decides which objects are

interfering ConnectionManager dynamically manages

connections between objects Signal quality based on interference Signal quality based on mobility

Node Modules Application, network, MAC,

and physical layers MAC and physical layers are

grouped into a single Nic module

A node with multiple Nic modules can be defined A laptop with bluetooth, GSM,

and 802.11 radios can be modeled

Node Modules Mobility module is responsible for the

movements of an object Battery module used for modeling the

energy reserve of nodes Communication, processing, mobility related

energy consumption can be modeled Utility module is used for easy statistical

data collection and inter-modular data passing (location, energy level etc.)

Connection Modeling In wireless simulations the channel connecting two

nodes is the air A broadcast medium that can not be represented with a

single connection Theoretically a signal sent out by a node affects all other

nodes in the simulation Since the signal is attenuated by the channel, as the

distance to the source is increased the interference becomes negligible

MiXiM sends all simultaneous signals to the connected nodes to let them decide on the final signal quality

Maximal interference distance decides on the connectivity

Definition of connection: All nodes that are not connected, definitely do not

interfere with each other

Utility module Modules can publish observed parameters

to the blackboard, a globally accessible service Other modules can subscribe to these

published parameters to implement different data analysis methods for gathering results

Dynamic parameters like location of a node or the energy levels can also be published so that other modules can change their behaviors accordingly

Example BaseNetwork.ned

contains the simulation network BaseHost.ned

contains the compound module defining the hosts for the network

BaseNic.ned contains the compound module defining the

network interface card of the hosts config.xml

contains configuration for the physical layers decider and analogue models

omnetpp.ini contains configuration for the simulation

BaseNic.nedMiXiMs provides two MAC layer implementations CSMAMacLayer and Mac80211. If you use only MiXiMs Decider and AnalogueModel implementations you can use the PhyLayer module.

BaseNode.nedBaseUtility is a mandatory moduleBaseArp is used for address resolutionIBaseMobility is a mandatory module which defines current position and the movement pattern of the node. IBaseApplLayer, IBaseNetwLayer and BaseNic define the network stack of this host. IBaseApplLayer is the module for the application layer to use. You can implement you own by sub classing MiXiMs "BaseApplLayer".INetwLayer is the module for the network layer to use. Sub-class your own network layer from MiXiMs BaseNetwLayer.

BaseNetwork.ned

Path inside MiXiM directory

Module parameters

ConnectionManagerchecks if any two hosts can hear each otherupdates their connections accordingly. If two hosts are connected, they can receive something from each other

BaseWorldUtility contains global utility methods and parameters node[numNodes]: BaseNode

defines the hosts/nodes of our simulation.

The baseNetwork example defines a network and an application layer on top of a NIC

config.xml

The Decider section defines the Decider to use as well as its parameters. You can find all of the already implemented Deciders under "modules/phy/".You can set the XML file which defines the Decider and AnalogueModels of a physical layer by setting the "analogueModels" and "decider" parameter of it in omnetpp.ini

The AnalogueModels section defines the analogue models to use.. You can find all of the already implemented AnalogueModels under "modules/analogueModel/".

omnet.ini

Example II The MAC layer we want to implement

will only implement the basic sending and receiving process

Since implementing a Mac layers requires a lot message handling and state changing, it needs a lot of rather boring glue code, so we will only explain the interesting parts of the code

Tasks of the MAC layer Define start, duration, TX power mapping and

bit-rate mapping of the Signal: BaseMacLayer provides the convenience method

“createSignal()” for simple signals Takes start, duration, TX power and bit-rate as

parameters Returns a new Signal with a mapping representing

the passed (constant) TX power and the passed (constant) bit-rate

To define non constant TX power and / or bit-rate over time one will have to set the Mappings of the Signal manually.

Tasks of the MAC layer Channel sensing:

“getChannelState()” - phy module method for instantaneous channel sensing.

Control message of kind “MacToPhyInterface::CHANNEL_SENSE_REQUEST” sent to phy module

Requests the phy to sense the channel over a period of time

Takes a timeout and a sense mode value UNTIL_TIMEOUT: is used to sense for the specified amount of

time. UNTIL_IDLE: is used to sense until the channel is idle or until the

timeout. UNTIL_BUSY: is used to sense until the channel is busy or until

the timeout. both methods return a “ChannelState” object with an idle

flag and the current RSSI value

Tasks of the MAC layer Switch radio:

“setRadioState()” - phy module method used to switch the radio.

Takes the state to switch to as argument “Radio::TX” “Radio::RX” “Radio::SLEEP” Returns the duration the switching will need. Control message of kind

“RADIO_SWITCHING_OVER” from the physical layer indicates that the switching is over.

Write your own MAC layer class MyMacLayer : public BaseMacLayer {

protected: cPacket* packetToSend;enum MacState{ RX, CS, TX }; int macState; ChannelSenseRequest* chSense;

} "packetToSend" stores the packet from the upper layer

we currently want to send down to the channel. "macState" will store the current state our MAC layer

is in "chSense" hold a "UNTIL_IDLE"-channel sense request

which we will use to wait for the channel to turn idle.

Writing your own MAC layer

• During initialization we set the initial state of our MAC layer to receiving and we initialize or "UNTIL_IDLE"-request. • The first parameter to the constructor is the name for our message and the second is the kind, which has to be "MacToPhyInterface::CHANNEL_SENSE_REQUEST" for every ChannelSenseRequest.• We further set the mode and the timeout (in seconds) of our request.

Writing your own MAC layer

This is only a part of the actual "handleUpperMsg()" method it is called on reception of a packet which should be sent down to the channel.

We store the packet for further processing and then we ask the phy module to do an instantaneous channel sense to see if the channel is currently idle. "getChannelState()" returns a ChannelState instance which provides an "isIdle()"

and "getRSSI()" method. Both of the values are defined by the Decider of the phy module and especially the

meaning of "isIdle()" depends on the used Decider but in most cases it should indicate that we can send something to the channel without interfering with another transmission.

If the channel is idle we can start the transmission process, if not we will need to start an "UNTIL_IDLE“ request to wait for it to turn back idle.

Writing your own MAC layer

We set the MAC layers state to carrier sensing and send our "UNTIL_IDLE“ request over the control channel down to the phy module.

The phy module will hand it to its Decider and when the Decider says that the channel is idle again or the timeout is reached it will set the "ChannelState“ member of the request and send it back up to our MAC layer.

Writing your own MAC layer

The ChannelSenseRequest we get back from the phy module will be the same which we sent down but with the result of the sensing stored in its "ChannelState" member. If the result says that the channel is back idle we can start the transmission process, which is done in "transmitpacket()":

Writing your own MAC layer

As soon as the switching process is over the phy module will send us a message of kind "RADIO_SWITCHING_OVER" over the control channel. As soon as the radio is in TX mode we can start sending the packet to the channel which we do in "handleRadioSwitchedToTX()“

Here the packet we got from the upper layer is encapsulated into a MacPkt and then sent down to the physical layer which will send it to the channel. During encapsulation the Signal for the packet is created and attached to it

We see that we do not yet start transmitting the packet because we have to switch the radio to TX mode first. We do this by calling the phy modules "setRadioState()" method

The method will return the time the switching process is over. The time it takes to switch from one radio state to another can be set as parameters of the phy module.

Writing your own MAC layer

The actual encapsulation is handled by BaseMacLayers "encapsMsg()" method. Our MAC layer is only responsible for creating and attaching the Signal. Since we will use a constant bit-rate and sending power for the whole transmission we can use the "createSignal()" method provided by BaseMacLayer. It takes the start and the length of the signal to create as well as its sending power and bit-rate. The method then creates a constant mapping for the power and bit-rate, stores them in a new Signal and returns it to us. If you want to use a more complex power or bitrate mapping you'll have to create the signal and the Mappings by yourself. You can take a look at the implementation of the "createSignal()" method to see how this basically works.

The Signal then is added to the MacPkts control info. Note: Since the MAC layer has to create the Signal it has to know the whole length of the

packet, including the phy header (if there is one). The phy module itself does not change the length of the packet sent to it.

Writing your own MAC layer After the transmission of the packet is over the phy module will

send us a message of kind "TX_OVER" over the control channel. When this happens our MAC layer has to switch the radio back to RX state phy->setRadioState(Radio::RX);

Again the phy module will send us a "RADIO_SWITCHING_OVER" message as soon the switching process is over which we handle in "handleRadioSwitchedToRX()":

Now the whole transmission process is over and our MAC layer goes back to receiving state

Links and readings http://mixim.sourceforge.net http://www.omnetpp.org/ “The OMNeT++ discrete event simulation system”, Varga

A. Proceedings of the European Simulation Multiconference (ESM 2001), Prague, Czech Republic, 6–9 June 2001

“Comparison of OMNET++ and other simulator for WSN simulation”, Xiaodong Xian; Weiren Shi; He Huang Industrial Electronics and Applications, 2008. ICIEA 2008. 3rd IEEE Conference on

“Simulating wireless and mobile networks in OMNeT++ the MiXiM vision”, Proceedings of the 1st international conference on Simulation tools and techniques for communications, networks and systems Marseille, France, 2008

Questions?

OMNET++ AND

MIXIM FRAMEWORKInstallation

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