ns2

Network Simulator 2, commonly known as ns-2, is a discrete-event network simulator used for research and education. It provides a framework to model packet-switched networks and to evaluate the behavior of networking protocols and architectures in a controlled, repeatable environment. ns-2 is widely cited in academic literature for studying routing, transport protocols, and network performance.

Architecture and design

ns-2 combines a core simulation engine written in C++ with a scripting interface based on OTcl (a Tcl extension). The OTcl layer is used to build and configure simulations, while the C++ backend implements the actual protocol models and event handling. The design is modular, enabling researchers to extend or replace protocol components, queueing disciplines, and link models by adding new classes or modifying existing ones.

Features and applicability

The simulator supports both wired and wireless networking scenarios. It includes implementations of several transport and network layer protocols, such as TCP variants, UDP, IP, and common routing protocols. The wireless extension adds features for 802.11 MAC, mobility models, and ad hoc routing protocols like AODV and DSR, among others. ns-2 produces trace files that log events such as packet transmissions, receptions, drops, and state changes, allowing detailed performance analysis with external tools.

Usage and status

ns-2 runs primarily on Unix-like systems and is distributed as open-source software. It has historically been used in classrooms and research labs to test hypotheses before real-world deployment. Development of ns-2 has slowed as ns-3 emerged as its successor, but ns-2 remains in use for legacy research and instructional purposes.