ns (simulator)

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ns-3 Network Simulator
Developer(s) ns-3 project[note 1]
Initial release June 30, 2008; 9 years ago (2008-06-30)[1]
Stable release
3.27 / October 12, 2017; 28 days ago (2017-10-12)[3]
Preview release
Mercurial repository[2]
Repository code.nsnam.org
Development status Active
Written in C++ (core) Python (bindings)
Operating system Linux, FreeBSD, macOS
Platform IA-32, x86-64
Type Network simulator
License GPLv2
Website www.nsnam.org

ns (from network simulator) is a name for a series of discrete event network simulators, specifically ns-1, ns-2 and ns-3. All of them are discrete-event computer network simulators, primarily used in research[4] and teaching. ns-3 is free software, publicly available under the GNU GPLv2 license for research, development, and use.

The goal of the ns-3 project is to create an open simulation environment for computer networking research that will be preferred inside the research community:[citation needed]

  • It should be aligned with the simulation needs of modern networking research.
  • It should encourage community contribution, peer review, and validation of the software.

Since the process of creation of a network simulator that contains a sufficient number of high-quality validated, tested and maintained models requires a lot of work, ns-3 project spreads this workload over a large community of users and developers.



The first version of ns, known as ns-1, was developed at Lawrence Berkeley National Laboratory (LBNL) in the 1995-97 timeframe by Steve McCanne, Sally Floyd, Kevin Fall, and other contributors. This was known as the LBNL Network Simulator, and derived in 1989 from an earlier simulator known as REAL by S. Keshav.


Ns-2 began as a revision of ns-1. In 1995 ns development was supported by DARPA through the VINT project at LBL, Xerox PARC, UCB, and USC/ISI. In 2000, ns-2 development was support through DARPA with SAMAN and through NSF with CONSER, both at USC/ISI, in collaboration with other researchers including ACIRI.

Ns-2 incorporates substantial contributions from third parties, including wireless code from the UCB Daedelus and CMU Monarch projects and Sun Microsystems. For documentation on recent changes, see the version 2 change log.


In 2006, a team led by Tom Henderson, George Riley, Sally Floyd, and Sumit Roy, applied for and received funding from the U.S. National Science Foundation (NSF) to build a replacement for ns-2, called ns-3. In the process of developing ns-3, it was decided to completely abandon backward-compatibility with ns-2. The new simulator would be written from scratch, using the C++ programming language. Development of ns-3 began in July 2006.

The first release, ns-3.1 was made in June 2008, and afterwards the project continued making quarterly software releases, and more recently has moved to three releases per year. ns-3 made its twenty first release (ns-3.21) in September 2014.

Current status of the three versions is:

  • ns-1 development stopped around 2001. It is no longer developed nor maintained.
  • ns-2 development stopped around 2010. It is no longer developed nor maintained.
  • ns-3 is under development (but not compatible for work done on ns-2)


ns-3 is built using C++ and Python with scripting capability. The ns-3 library is wrapped by Python thanks to the pybindgen library which delegates the parsing of the ns-3 C++ headers to gccxml and pygccxml to automatically generate the corresponding C++ binding glue. These automatically-generated C++ files are finally compiled into the ns-3 Python module to allow users to interact with the C++ ns-3 models and core through Python scripts. The ns-3 simulator features an integrated attribute-based system to manage default and per-instance values for simulation parameters.

Simulation workflow[edit]

The general process of creating a simulation can be divided into several steps:

  1. Topology definition: To ease the creation of basic facilities and define their interrelationships, ns-3 has a system of containers and helpers that facilitates this process.
  2. Model development: Models are added to simulation (for example, UDP, IPv4, point-to-point devices and links, applications); most of the time this is done using helpers.
  3. Node and link configuration: models set their default values (for example, the size of packets sent by an application or MTU of a point-to-point link); most of the time this is done using the attribute system.
  4. Execution: Simulation facilities generate events, data requested by the user is logged.
  5. Performance analysis: After the simulation is finished and data is available as a time-stamped event trace. This data can then be statistically analysed with tools like R to draw conclusions.
  6. Graphical Visualization: Raw or processed data collected in a simulation can be graphed using tools like Gnuplot, matplotlib or XGRAPH.


NS is often called as Nightmare Software because modelling is so very complex and time-consuming. It has no GUI and users need to learn TCL, AWK, Python, C++ and more.

Unlike commercial tools which come with a GUI and results dashboard, users need to learn tcl scripting for scenario creation, and subsequently use AWK scripts for manually calculating the result from massive trace files. The source code is in C++ and since there is no supporting debugging environment.

See also[edit]


  1. ^ Tom Henderson, Mathieu Lacage, George Riley, Mitch Watrous, Gustavo Carneiro, Tommaso Pecorella and others.


  1. ^ Henderson, Tom (2012-06-09). "upcoming ns-3.1 release" (Mailing list). ns-3 GSoC 2015 students. Retrieved 2013-05-31. 
  2. ^ "ns-3-dev". ns-3 project. Retrieved 26 December 2012. 
  3. ^ "ns-3.26 released". ns-announce. 
  4. ^ http://www.nsnam.org/overview/publications/

External links[edit]