1. OMNeT++ and MiXiM Framework
Introduction

2. 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.

3. 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

4. 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

5. Important issues in a discrete event simulation environment
Pseudorandom generators
Flexibility
Programming model
Model management
Support for hierarchical models
Debugging, tracing, and experiment specifications
Documentation
Large scale simulation
Parallel simulation

6. Flexibility Core framework for discrete event simulation.
Different add-ons for specific purposes.
Fully implemented in C++.
Functionality added by deriving classes following specified rules.

7. OMNET++ Programming model
Eyes - energy efficient sensor networks
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

8. Hierarchical models
Node
Application
Network
Nic
MAC
Phy
Decider
Analog Model
Network interface card, a compound module consisting of a simple module MAC and a compound module Phy

9. Build models and combine like LEGO blocks
Model management
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

10. Debugging and tracking
Eyes - energy efficient sensor networks
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.

11. Simulation Model building
Add behavior
for (int i=0;i<10;i++) { }
...
Analyze
[General]
network=test_disk
[Parameters]
...
Run
Set up parameters
Model structure
Compile

12. Module behavior C++ code
Build process
Network description
nedtool compiler
Simulation kernel libraries
User interface libraries
Generated C++ code
Module behavior C++ code
C++ compiler
C++ compiler
Linker
Simulation program

13. NED Overview
The topology of a model is specified using the NED language.
Edit it with GNED or other text editor.

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

15. Import directives import "ethernet"; // imports ethernet.ned import
"Router",
"StandardHost",
"FlatNetworkConfigurator";

16. Channel definitions
channel LeasedLine delay // sec error 1e-8 datarate // bit/sec endchannel

17. Simple module definitions
simple TrafficGen parameters: interarrivalTime, numOfMessages : const, address : string; gates: in: fromPort, fromHigherLayer; out: toPort, toHigherLayer; endsimple
Application Layer
TrafficGen
MAC Layer

18. Compound module definitions
module CompoundModule parameters: //... gates: //... submodules: //... connections: //... endmodule

19. Compound module definitions - submodules
module CompoundModule //... submodules: submodule1: ModuleType1 parameters: //... gatesizes: //... submodule2: ModuleType2 endmodule

20. Assigning values to submodule parameters
module CompoundModule parameters: param1: numeric, param2: numeric, useParam1: bool; submodules: submodule1: Node p1 = 10, p2 = param1+param2, p3 = useParam1==true ? param1 : param2; //... endmodule

21. Connections
module CompoundModule parameters: //... gates: //... submodules: //... connections: node1.output --> node2.input; node1.input <-- node2.output; //... endmodule

22. Network definitions
network wirelessLAN: WirelessLAN parameters: numUsers=10, httpTraffic=true, ftpTraffic=true, distanceFromHub=truncnormal(100,60); endnetwork

23. 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

24. 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;
… }

25. Running a model #> opp_makemake --deep #> make
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) Andras Varga [....] <!> Error during startup: Cannot open ini file `omnetpp.ini'

26. Running a model (omnetpp.ini)
[General] network = etherLAN *.numStations = 20 **.frameLength = normal(200,1400) **.station[0].numFramesToSend = **.station[1-5].numFramesToSend = **.station[*].numFramesToSend = 0
One 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.

27. 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

28. 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

29. MiXiM

30. 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

31. 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 radios can be modeled

32. 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.)

33. 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

34. 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

35. Example BaseNetwork.ned BaseHost.ned BaseNic.ned config.xml
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

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

37. BaseNode.ned BaseUtility is a mandatory module
BaseArp is used for address resolution
IBaseMobility 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.

38. BaseNetwork.ned Path inside MiXiM directory Module parameters
ConnectionManager
checks if any two hosts can hear each other
updates 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

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

40. omnet.ini

41. 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

42. 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.

43. 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

44. 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.

45. 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.

46. 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.

47. 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.

48. 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.

49. 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()":

50. Writing your own MAC layer
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.
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

51. 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.

52. 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

53. Links and readings http://mixim.sourceforge.net
“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, ICIEA rd 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

54. Questions?

55. OMNeT++ and MIXIM Framework
Installation