Network simulation
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In computer network research, network simulation is a technique where a program simulates the behavior of a network. The program performs this simulation either by calculating the interaction between the different network entities (hosts/routers, data links, packets, etc) using mathematical formulas, or actually capturing and playing back network parameters from a production network. Using this input, the behavior of the network and the various applications and services it supports can be observed in a test lab. Various attributes of the environment can also be modified in a controlled manner to asses these behaviors 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.
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[edit] Uses
Network simulators are used to predict the behavior of networks and applications under different situations. Researchers use network simulators to see how their protocols would behave if deployed. It is typical to use a network simulator to test routing protocols, MAC (Medium Access Control) protocols, transport protocols, applications etc. Companies use simulators to design their networks and/or applications to get a feel for how they will perform under current or projected real-world conditions.
[edit] Simulators
The simulator (or network simulator) is the program in charge of calculating how the network would behave. They may be distributed in source form (software) or provided in the form of a hardware appliance. Users can then customize the simulator to fulfill their specific analysis needs. The simulators come with support for the most popular protocols implemented (such as IPv4, IPv6, UDP, and TCP).
[edit] Open Source Simulators
Free/open source network simulators in research include NS-2, OMNet++ and GloMoSim (the later no longer under active development), which run on Linux, FreeBSD, SunOS, Solaris, Microsoft Windows and other operating systems. NS-2 and GloMoSim are widely used in universities.
[edit] Proprietary Simulators
Commercial network simulators include OPNET, Shunra, QualNet (formerly GloMoSim), NetSim, Itheon Network Emulator,
[edit] Simulations
Some network simulators require input scripts or commands (network parameters) and produce trace files. The network parameters describe the state of the network (node placement, existing links) and the events (data transmissions, link failures, etc). Trace files can document every event that occurred in the simulation and are used for analysis. Some simulators incorporate or provide visualization tools for the trace files. NAM, for example, displays how a network looks and animates the packet transmissions. Network simulators can also capture this type of data directly from a functioning production environment. This data capture may be done at various times of the day, week, month, in order to reflect average, worst-case, and best-case conditions. Network simulators can also provide other tools to facilitate visual analysis of trends and potential trouble spots.
[edit] Other
Network simulation (or network modeling) is also used to describe a computer simulation of a network of pipes or cables used in pipeline transport (e.g. of natural gas, oil, water, etc.) electric power transmission and electricity distribution.
