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Network Performance and Quality of Service 7. Network Simulation Contents RQ12 Why use simulation Systematic simulation study Types of simulations Simulation validation and verification Confidence level of simulation results Simulation with self similar traffic Simulation tools 2 Why Use Simulation Predict performance for proposed network Allow performance evaluation under a wide variety of network conditions Compare alternative architectures under identical and repeatable conditions Simulation can incorporate more details than analytical modeling, thus produce results closer to reality Validate analytical results RQ12 3 Systematic Simulation Study Pre-software stage Define problem/objective Design network model and select fixed parameters Select performance metrics Select variable parameters RQ12 4 Systematic Simulation Study Software stage Model construction Simulation configuration Simulation execution/Data collection Result presentation RQ12 5 Systematic Simulation Study (Cont.) Software stage RQ12 Model construction Simulation configuration Simulation execution/Data collection Result presentation 6 Types of simulations Continuous vs. discrete event Terminating vs. steady state Synthetic vs. trace-driven RQ12 7 Continuous vs. discrete event The state of the system model can be … continuous (concentration of substance in chemical system) discrete (queues of packets in packet switching system) A discrete event simulation (DES) uses a discrete state model of a system Each event has an associated time value indicating the time to execute the event RQ12 8 Terminating vs. steady state Terminating simulation is to study network system for a well-defined period of time or number of events. If we are interested in steady-state behaviour of a network system, we cannot use terminating simulations Must continue until it reaches steady state RQ12 9 Synthetic vs. trace-driven In many simulations, input traffic is synthetically generated using random traffic generators. Actual network traces can be used as simulation input Results can be more convincing RQ12 10 Simulation Validation and Verification Validation: Make sure that the assumptions are realistic Verification: Make sure that the model implements assumptions correctly Guidelines to follow Look for “surprise” in output Employ analytical modeling Compare with real network data RQ12 11 Confidence Level Relative precision formula for 95% confidence Confidence level in terminating simulation RQ12 Repeat the entire simulation many times with different random numbers (or seeds) 12 Self Similar Traffic Poisson model does not capture the burstiness of TCP/IP traffic TCP/IP traffic usually exhibits self similar property Generated by superimposing many ON/OFF sources with Pareto distribution RQ12 14 Classification of Simulation Tools RQ12 GPPL: General Purpose Programming Language PSL: “Plain” Simulation Language SP: Simulation Package 15 Network simulators Commercial OPNET QualNet Open Source RQ12 NS2 NS3 OMNeT++ SSFNet J-Sim 16 OPNET RQ12 Developed by OPNET Technologies Inc. Commercial SP Object-oriented Totally menu-driven package Built-in model libraries contain most popular protocols and applications Simulation task made easy 17 OPNET RQ12 Lot of component library with source code Object-oriented modeling Hierarchical modeling environment Scalable wireless simulations support Customizable wireless modeling Discrete Event, Hybrid, and Analytical simulation 32-bit and 64-bit parallel simulation kernel Realistic Application Modeling and Analysis Integrated, GUI-based debugging and analysis Open interface for integrating external component libraries 18 OPNET RQ12 19 OPNET Platform Supported OPNET Modeler OPNET IT Guru (Academic Edition) RQ12 Microsoft Windows (32 and 64 bit) Red Hat Enterprise Linux Fedora Linux Microsoft Windows 20 NS-2 Simulator Discrete Event Simulator Packet level Modeling Network protocols Collection of Various protocols at multiple layers RQ12 TCP(reno, tahoe, vegas, sack) MAC(802.11, 802.3, TDMA) Ad-hoc Routing (DSDV, DSR, AODV, TORA) Sensor Network (diffusion, gaf) Multicast protocols, Satellite protocols, and many others 21 NS-2 Simulator Object-oriented Written in C++ and object-oriented tcl (Otcl) Network components are represented by classes From the user’s perspective, NS−2 is an OTcl interpreter that takes an OTcl script as input and produces a trace file as output. RQ12 22 NS-2 Platforms supported Most UNIX and UNIX-like systems Windows RQ12 FreeBSD Linux Solaris Cygwin required Some work, some doesn’t 23 OMNET++ OMNeT++ is a component-based, modular and open-architecture discrete event network simulator. OMNeT++ represents a framework approach RQ12 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. 24 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 X-Simulator -- for testing synchronization protocols RQ12 25 OMNET++ RQ12 26 OMNET++ Platform Supported RQ12 Microsoft Windows Linux Mac OS X other Unix-like systems 27 Important issues in a discrete event simulation environment RQ12 Pseudorandom generators Flexibility Programming model Model management Support for hierarchical models Debugging, tracing, and experiment specifications Documentation Large scale simulation Parallel simulation 28 Selecting the Right Tool RQ12 Built-in libraries Credibility User-Friendliness Technical support Level of Details Resource consumption Cost 29