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Network Simulator

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Network Simulator

In communication and computer network research, network simulation is a technique where a program models the behavior of a network either by calculating the interaction between the different network entities (hosts/packets, etc.) using mathematical formulas, or actually capturing and playing back observations from a production network. The behavior of the network and the various applications and services it supports can then be observed in a test lab; various attributes of the environment can also be modified in a controlled manner to assess how the network would behave under different conditions. When a simulation program is used in conjunction with live applications and services in order to observe end-to-end performance to the user desktop, this technique is also referred to as network emulation.

Network simulator

A network simulator is of software or hardware that predicts the behavior of a networks, without an actual network being present. A network simulator is a software program that imitates the working of a computer network. In simulators, the computer network is typically modelled with devices, traffic etc. and the performance is analysed. Typically, users can then customize the simulator to fulfill their specific analysis needs. Simulators typically come with support for the most popular protocols / networks in use today, such as WLAN, Wi-Max, TCP, WSN, Cognitive radio etc

Simulations

Most of the commercial simulators are GUI driven, while some network simulators are CLI driven. The network model / configuration describes the state of the network (nodes,routers, switches, links) and the events (data transmissions, packet error etc.). An important output of simulations are the trace files. Trace files log every packet, every event that occurred in the simulation and are used for analysis. Network simulators can also provide other tools to facilitate visual analysis of trends and potential trouble spots.

Most network simulators use discrete event simulation, in which a list of pending "events" is stored, and those events are processed in order, with some events triggering future events—such as the event of the arrival of a packet at one node triggering the event of the arrival of that packet at a downstream node.

Some network simulation problems, notably those relying on queueing theory, are well suited to Markov chain simulations, in which no list of future events is maintained and the simulation consists of transiting between different system "states" in a memoryless fashion. Markov chain simulation is typically faster but less accurate and flexible than detailed discrete event simulation.

Simulation of networks is a very complex task. For example, if congestion is high, then estimation of the average occupancy is challenging because of high variance. To estimate the likelihood of a buffer overflow in a network, the time required for an accurate answer can be extremely large. Specialized techniques such as "control variates" and "importance sampling" have been developed to speed simulation.[1][2]

Examples of network simulators

There are many both open-source and commercial network simulators.Examples of notable network simulation software are, ordered after how often they are mentioned in research papers:

  1. ns2/ns3
  2. OPNET
  3. NetSim

Uses of network simulators

Network simulators serve a variety of needs. Compared to the cost and time involved in setting up an entire test bed containing multiple networked computers, routers and data links, network simulators are relatively fast and inexpensive. They allow engineers, researchers to test scenarios that might be particularly difficult or expensive to emulate using real hardware - for instance, simulating a scenario with several nodes or experimenting with a new protocol in the network. Network simulators are particularly useful in allowing researchers to test new networking protocols or changes to existing protocols in a controlled and reproducible environment. A typical network simulator encompasses a wide range of networking technologies and can help the users to build complex networks from basic building blocks such as a variety of nodes and links. With the help of simulators, one can design hierarchical networks using various types of nodes like computers, hubs, bridges, routers, switches, links, mobile units etc.

Various types of Wide Area Network (WAN) technologies like TCP, ATM, IP etc. and Local Area Network (LAN) technologies like Ethernet, token rings etc., can all be simulated with a typical simulator and the user can test, analyze various standard results apart from devising some novel protocol or strategy for routing etc. Network simulators are also widely used to simulate battlefield networks in Network-centric warfare

There are a wide variety of network simulators, ranging from the very simple to the very complex. Minimally, a network simulator must enable a user to represent a network topology, specifying the nodes on the network, the links between those nodes and the traffic between the nodes. More complicated systems may allow the user to specify everything about the protocols used to handle traffic in a network. Graphical applications allow users to easily visualize the workings of their simulated environment. Text-based applications may provide a less intuitive interface, but may permit more advanced forms of customization.

Reliability issues with Network Simulators and Simulation Based Research

The ride for Network Simulators has however, remained bumpy due the to consistent revelations about inaccuracies/inconsistencies in their results. The questions about credibility of network simulator and the simulation based research have always engrossed the minds of researchers.Essentially, the aim of questioning the credibility of network simulators is to make sure that irrespective of the simulation model, every simulation configured in a similar set of environment variables should conform to similar results. The variation in the credibility of every simulator directly affects the end results and also affects the repeatability of a simulation experiment when conducted using a different package. In order for a scientific experiment to be considered factual, it should be repeatable. However, even if we exclude the credibility factors of the network simulators most of the simulation based research cannot be independently repeatable. Lack of description of experiment design, the input parameters, and lack of rigorous testing can cause problems in repeating the same experiment by another research group. Such problems in repeatability also cast doubts about the viability of the outcomes of scientific experiments even if the simulation package is highly credible. Many of the popular simulators provide features that when properly tuned can close the gap between the simulators and actual measurements.

See also

References

[Reliability of Network Simulators & Simulation Based Reserach, IEEE PIMRC 2013 Conference paper]

External links

  • List of Network Simulation Tools

[Reliability of Network Simulators & Simulation Based Reserach, IEEE PIMRC 2013 Conference paper]

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