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In computer network research, network simulation is a technique whereby a software program models the behavior of a network by calculating the interaction between the different network entities (routers, switches, nodes, access points, links etc.). Most simulators use discrete event simulation - the modeling of systems in which state variables change at discrete points in time. 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 / protocols would behave under different conditions.
A network simulator is software that predicts the behavior of a computer network. Since communication networks have become too complex for traditional analytical methods to provide an accurate understanding of system behavior, network simulators are used. In simulators, the computer network is modeled with devices, links, applications etc. and the network performance is reported. Simulators come with support for the most popular technologies and networks in use today such as Wireless LANs, mobile ad hoc networks, wireless sensor networks, vehicular ad hoc networks, cognitive radio networks, LTE / LTE- 5G, Internet of Things (IoT) etc.
Most of the commercial simulators are GUI driven, while some network simulators are CLI driven. The network model / configuration describes the network (nodes, routers, switches, links) and the events (data transmissions, packet error etc.). Output results would include network level metrics, link metrics, device metrics etc. Further, drill down in terms of simulations trace files would also be available. Trace files log every packet, every event that occurred in the simulation and are used for analysis. 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.
Network emulation allows users to introduce real devices and applications into a test network (simulated) that alters packet flow in such a way as to mimic the behavior of a live network. Live traffic can pass through the simulator and be affected by objects within the simulation.
The typical methodology is that real packets from a live application are sent to the emulation server (where the virtual network is simulated). The real packet gets 'modulated' into a simulation packet. The simulation packet gets demodulated into a real packet after experiencing effects of loss, errors, delay, jitter etc., thereby transferring these network effects into the real packet. Thus it is as-if the real packet flowed through a real network but in reality it flowed through the simulated network.
Emulation is widely used in the design stage for validating communication networks prior to deployment.
List of network simulators
There are both free/open-source and proprietary network simulators available. Examples of notable network simulators / emulators include:
- TETCOS NetSim
Both commercial tools are available at deeply discounted prices to universities for network lab experimentation and network R&D.
Uses of network simulators /emulators
Network simulators provide a cost-effective method for
- Network design validation for enterprises / data centers / sensor networks etc.
- Network R & D (More than 70% of all Network Research paper reference a network simulator)
- Defense applications such as HF / UHF / VHF Radio based MANET Radios, Naval communications, Tactical data links etc.
- LTE, LTE-Adv, IOT, VANET simulations
- Education - Lab experimentation and R & D. Most universities use a network simulator for teaching / R & D since its too expensive to buy hardware equipment
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
- Model the network topology specifying the nodes on the network and the links between those nodes
- Model the application flow (traffic) between the nodes
- Providing network performance metrics as output
- Visualization of the packet flow
- Technology / protocol evaluation and device designs
- Logging of packet/events for drill down analyses / debugging
- Channel model
- Mobility model
- Network emulation
- Network topology
- Network traffic simulation
- Queueing theory
- Traffic generation model
- Wireless sensor network simulators