CHAPTER 3: LITERATURE REVIEW 3.1 NEED FOR SIMULATION ENVIRONMENT IN WSN

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1 26 CHAPTER 3: LITERATURE REVIEW 3.1 NEED FOR SIMULATION ENVIRONMENT IN WSN Due to the continuous research progress in the field of WSN, it is essential to verify the new hardware and software design and the modifications in existing design. This verification in terms of correctness, effectiveness, and the ability to be used in different WSN application scenario, is required. But it is not practically feasible to verify the modifications done on existing protocols or new proposed implementation using real WSN hardware as it requires more efforts of time and costs. One option for testing is to use simulation environments to simplify this process instead of implementing everything on real hardware sensor nodes. Hence, simulation of WSNs is essential for any real time WSN application development. In general, simulation environment is used for evaluating the performance of new protocols, algorithms, and new mechanisms. WSN simulation environment is very much essential to study the performance of various protocols and other parameters such as number of nodes, data rate, deployment strategies etc., apriori to real time deployment in a WSN application design. Contrasting to wired and traditional wireless networks, WSNs have certain requirements, which has to be considered for the choice of a simulator [20]. As WSN consists of hundreds up to thousand nodes, the major requirement is scalability. In order to simulate WSN realistically, the simulator software should provide energy model, propagation modelling, physical environment modelling, and the tools for analyzing the simulation results to tune the parameters.

2 EXISTING SIMULATION SOFTWARE FOR WSN SIMULATION There are many simulation environments which can be used for WSN simulation. These simulation environments differ significantly in their structure and the provided features such as models and protocols Network Simulator (NS) Network Simulator [21-22] is an object-oriented discrete event simulator. At the beginning NS supported wired network simulations, later wireless support was added. This simulator is open source and provides online document. NS is also often referred to as NS-2 due to its current major version number. NS-2 is written in C++ and OTcl, an object-oriented version of Tool Command Language (Tcl). The source code, licensed under GPL2, is freely available. Hence NS-2 is very extensible and thus widely used in academia. Advantages of NS-2 1) NS-2 can support a considerable range of protocols in all layers. For example, the Adhoc and WSN specific protocols are provided by NS-2. 2) The open source model saves the cost of simulation, and online documents allow the users to modify and improve the codes easily. Disadvantages of NS-2 1) User should be familiar with scripting language and modeling technique 2) Use of NS-2 is more complex and time-consuming than other simulators to model a desired application. 3) NS-2 does not provide Graphical User Interface (GUI).

3 28 4) As the code is unclear due to its continuous change and evolution in open forum, the results may not be reliable. Limitations of NS-2 with respect to WSN simulation 1) NS-2 cannot simulate unique characteristics of WSN such as bandwidth, and energy model. 2) NS-2 has scalability problem with respect to WSN simulation. As the number of nodes is increased, the tracing file in NS-2 becomes too large to manage Global Mobile Simulator Software (GloMoSim) GloMoSim [23-25] is a scalable simulation environment for wireless and wired network systems. GloMoSim uses the parallel discrete-event simulation capability provided by Parsec [26], a C-based simulation language for sequential and parallel execution of discrete-event simulation models. GloMoSim uses the idea of the OSI reference model and Application Programming Interface (API) is used for communication between layers. Hence new protocols can be developed and integrated with GloMoSim using these APIs. In GloMoSim, a JAVA GUI is provided for the creation and configuration of scenarios as well as the playback of simulations and the results obtained through the simulations. But GloMoSim is a text based simulator meaning that no GUI facility exists to configure the parameters for the application simulation. GloMoSim offers basic functionality such as Adhoc On Demand Distance Vector (AODV) and Dynamic Source Routing (DSR) protocol support to simulate wireless

4 29 Table 3.1 Model/Protocol support of GloMoSim Layers Layer Model/Protocol Physical (Radio Propagation) Free space, Two-Ray Data Link (MAC) CSMA, MACA, TSMA, IEEE Network (Routing) Bellman-Ford, FSR, OSPF, DSR, WRP, LAR, AODV Transport TCP, UDP Application Telnet, FTP networks and adhoc networks. The current version of GloMoSim does not offer any sensor network specific features in the default package. This implies that without any further efforts no WSNs can be simulated meaningfully. The models / protocols supported by GloMoSim [25] in each of the layer is shown in Table 3.1. Limitations of GloMoSim with respect to WSN simulation 1. No GUI support 2. No support for WSN Protocol in data link layer 3. Non availability of library of WSN routing protocol 4. No energy model support for lifetime estimation 5. No tool for viewing necessary application level statistics 6. No charting utility for lifetime analysis QualNet [27] is the commercial derivate of GloMoSim 2.0, the last version of GloMoSim released under an academic license. The current version 5.0 of QualNet supports a new sensor network library for ZigBee, network security library, parallel updates, and battery and energy models.

5 OPNET OPNET [28-30] is a commercial modelling and simulation tool for wireless networks. The OPNET provides an object-oriented modelling approach and a hierarchical modelling environment. Three tired hierarchy of OPNET uses three domains such as network, node, and process. The network domain consists of nodes, links, and subnets. A node represents a network device and groups of devices. Process domain consists of state transition diagrams, blocks of C-code, OPNET Kernel Procedures (KPs) as well as state and temporary variables. The graphical editor interface can be used to build network topology and entities from the application layer to the physical layer. An advantage of OPNET is that all these domains can be accessed using graphical editors that are integrated in a common GUI, which provides debugging and analysis features. OPNET offers different propagation and modulation techniques at physical layer level and IEEE ZigBee [31] support at MAC layer level. Limitations of OPNET with respect to WSN simulation 1. No routing protocol support for WSN simulation 2. Simulation requires a lot of processing power and can be more time consuming for network with a large number of nodes 3. Lack of energy model support OMNET++ Object Oriented Modular Network Testbed (OMNeT++) is an object-oriented modular discrete event network simulation framework. An OMNeT++ model consists

6 31 of modules that communicate with message passing. The active modules are termed simple modules and are written in C++, using the simulation class library. Simple modules can be grouped into compound modules. The whole model, called network in OMNeT++, is itself a compound module. Messages can be sent either via connections that span modules or directly to other modules. The main features of OMNET++ [32] are the following: 1. Modules, which are instances of module types 2. Hierarchically nested modules 3. Modules communicate with messages through channels 4. Flexible module parameters 5. Topology description language The simulation frameworks which enable OMNeT++ to be used for wireless sensor networks are Mobility Framework [32-33] and MiXiM [34-35]. The Mobility Framework provides the basic support for mobile and wireless networks. The MAC protocols supported by this framework are Aloha and CSMA and flooding is the network layer protocol. MiXiM is a merger of several OMNeT++ frameworks to support mobile and wireless simulations. It uses the mobility support, the connection management, and the general structure from the Mobility Framework, the radio propagation models from the CHannelSIMulator, and the protocol library from the MAC simulator, the Positif framework [36], and the Mobility Framework. CSMA and IEEE are the MAC protocol support given by this framework.

7 32 Table 3.2 Comparison of Existing Software/Framework Simulator / Framework Features License WSN Support GUI Support Programming Language Lifetime Estimation NS-2 Yes GPL (Unclear) No C++/OTCL No Yes GloMoSim Open Source No No C/JAVA No No Qualnet Commercial Yes Yes C++/JAVA No Yes OPNET Commercial Yes Yes No Yes OMNET++ LSU Sensor Simulator Mannasim Academic Public License Charting Facility Limited Yes C++/JAVA No Yes Open Source Yes Yes C++/JAVA No Yes GPL Yes No except for Script Generation tool C++/JAVA No Yes Prowler GNU Limited Yes Matlab/Java No Yes J-SIM Academic Free License Limited Yes JAVA No No JIST Free for non- Commercial Limited Yes JAVA/CSIM No Yes Use Cooja Open Source Limited Yes JAVA No No TOSSIM Open Source BSD License Yes Yes Nes C No Yes Sensor Simulator [37] is another framework developed on OMNeT++ at Louisiana State University, intended to support Sensor Network Simulations. The framework provides basic modules that can be derived in order to implement application specific modules. Using this concept a programmer can easily develop own protocol implementations for the Sensor Simulator framework without having to deal with the necessary interface and interoperability issues. The protocol support provided by this framework for WSN simulation are IEEE and Directed Diffusion with GEAR.

8 COMPARISON OF EXISTING SIMULATOR SOFTWARE / FRAMEWORK FOR WSN The various simulator software and framework used for WSN simulation is compared and shown in Table 3.2. From the table, it is seen that no simulator software is supporting lifetime estimation facility. Also, software providing essential facilities for WSN simulation is not an open source. This motivated us to develop a Simulator Framework with required facilities for WSN simulation such as GUI support, energy model based lifetime estimation, and charting facility for plotting the results obtained from the simulation. 3.4 SIMULATION PROCEDURE IN GLOMOSIM AN OVERVIEW The important three files used for simulating wireless adhoc networks in GloMoSim are config.in, nodes.input, and app.conf. The configuration parameters for setting up a scenario are defined in config.in file. The parameters to be set in config.in file [25] are shown in Table 3.3. The various node placement strategies, mobility model, MAC protocols, and routing support by GloMoSim are shown in Table 3.4. The values for all the parameters can be set by specifying the values against the parameter. For example, SIMULATION-TIME 10M SEED 1 TERRAIN-DIMENSIONS (1000, 1000) NUMBER-OF-NODES 20 set the simulation time to 10 minutes, the seed value used for the simulation is 1, the simulation terrain dimension is 1000 x 1000, and the number of nodes used in the simulation is 20. Similarly, the values for all other parameters such as PROPAGATION LIMIT, PROPAGATION-PATHLOSS, RADIO FREQUENCY, RADIO BANDWIDTH, etc., can also be set in config.in file.

9 34 Table 3.3 Parameters to be set in Config.in and its description Parameter SIMULATION-TIME SEED Description Maximum simulation time. For example, 100NS means simulation time to be set is 100 nanoseconds. Similarly, 100M means 100 minutes, 100H means 100 hours, and 100D means 100 days It is a random number used to initialize part of the seed of various randomly generated numbers in the simulation Terrain Area simulated in meters TERRAIN- DIMENSIONS NUMBER-OF-NODES Number of nodes being simulated NODE-PLACEMENT Represents the node placement strategy RADIO-TYPE Radio model to transmit and receive packets RADIO-FREQUENCY Frequency in Hertz ANTENNA-GAIN MOBILITY Represents the mobility model. PROPAGATION- Signals below this parameter (in dbm) are not delivered. LIMIT This value must be smaller than RADIO-RX-. SENSITIVITY +RADIO-ANTENNA-GAIN of any node in the model. Otherwise, simulation results may be incorrect. Lower value should make the simulation more precise, but it also makes the execution time longer. PROPAGATION- Specifies the path loss model PATHLOSS TEMPERATURE Temperature of the environment (in K) RADIO- BANDWIDTH RADIO-RX-TYPE RADIO- RADIO-TX-POWER RADIO-RX- SENSITIVITY RADIO-RX- THRESHOLD MAC-PROTOCOL PROMISCUOUS- MODE NETWORK- PROTOCOL ROUTING- PROTOCOL Bandwidth in bits per second Specifies the packet reception model Radio transmission power (in dbm) Antenna Gain (in db) Sensitivity of the radio (in dbm) Minimum power for received packet (in dbm) Definition of Medium Access Protocol It is set to YES if nodes want to overhear packets destined to the neighbouring node. The option needs to be set to YES only for DSR. Definition of the Network Protocol Definition of the Routing Protocol

10 35 Table 3.4 Node Placement, Mobility, and Protocol support in GloMoSim Parameter NODE-PLACEMENT MOBILITY MAC-PROTOCOL NETWORK-PROTOCOL ROUTING-PROTOCOL Support Random Grid, Uniform, and File Random Way Point Model CSMA, MACA, TSMA, and IEEE IP BELLMANFORD, AODV, DSR, LAR1, WRP, FISHEYE, and ZRP The X, Y, and Z positions of the nodes are specified in nodes.input file. The general syntax to specify the node position is nodeaddr 0 (x, y, z). The parameter following nodeaddr specifies the mobility. MOBILTY parameter in config.in file is used for specifying mobility. If the value of this parameter is NONE, it specifies that there is no node movement. The application configuration file specifies the types of data traffic that will be used in the simulations. GloMoSim provides FTP, Telnet, HTTP, and CBR (Constant Bit Rate) data traffic. In WSN simulations, CBR traffic can be used which sends data packets at regular time intervals. The general syntax to use CBR is as follows: CBR <src> <dest> <items to send> <item size> <interval> <start time> <end time> For example, the statement CBR ms 0S 70S in app.conf specifies that node 1 sends node 0 fifty items of 512 bytes each at the start of the simulation up to 70 seconds into the simulation. The inter-departure time for each item is 5 milliseconds. If the fifty items are sent before 70 seconds elapsed, no other items are sent.

11 36 Further the statement CBR ms 0S 0S specifies that node 3 continuously sends node 0 items of 512 bytes each at the start of the simulation up to the end of the simulation. The inter-departure time for each item is 5 milliseconds. After specifying the values in config.in, nodes.input, and app.conf files, the following command is used to get output file called glomo.stat which contains all the statistics generated. glomosim config.in > a.trace The Visualization Tool of GloMoSim is a platform independent tool used for debugging and verifying the models and scenarios simulated using GloMoSim. Simulations can be viewed, stopped, and resumed easily through this tool and step by step execution is also possible. It shows packet transmissions, mobility groups in different colours, and statistics. To initialize the Visualization tool the following steps to be executed: 1. Copy the trace file in java_gui folder of GloMoSim 2. Go to java_gui folder 3. Compile GlomoMain.java file 4. Run GlomoMain file Java Development Kit (JDK) version 1.2 or higher version need to be installed o use visualization tool. Also the compiled source files of GloMoSim must be available in the appropriate folder.

12 SUMMARY WSNs are having several common aspects with wireless adhoc networks [38] and in many cases WSNs are considered as a special case of adhoc networks. This leads to incorrect conclusions, when protocols and algorithms designed for Adhoc networks are used in WSN. The main features of WSNs to be considered while designing real time applications are the following: scalability with respect to the number of nodes in the network, self-organization, self-healing, energy efficiency, a sufficient degree of connectivity among nodes, low-complexity, low cost, and size of nodes [39]. To test the performance of all these parameters and to change the values to get better design before going for real environment, the simulation environment is used. The simulation software or framework used for WSN application design should be an open source (free of cost) and should provide all necessary facilities to simulate WSN. The essential features required for effective WSN simulation are sophisticated GUI to configure the parameters, lifetime estimation which is considered as heart of WSN research, support for various hardware used in WSN, and charting tool to plot the results obtained using the simulation.