Today is a very nice day for me for blogging because I got a sigh of relief from some load of study ........I was surfing on the net and reading some basics about NS2 simulators.So, I thought this topic is interesting and why don't I share this with you some basics of Network Simulators.

Before knowing the NS2 , you must know what are Simulators ?

Simulation is the process of developing a virtual environment that can be a physical system or can be an object. Simulators are the combination of hardware and the software which runs on it to create the real experience.

Main purpose of Simulator : To understand the behavior of the system.

For example : The popular simulators are based on Games, where people who can't afford to purchase the real object;they can buy simulator and have the real game experience from home.

NS2 Simulator

It is event driven network simulator
   - Developed at UC Berkely
   - Implements network protocols
      1) TCP, UPD
      2) Traffic source mechanism:  FTP, TELNET, Web, CBR and VBR
      3) Router Queue management mechanism:  Drop Tail, RED, CBQ
      4) Routing Algorithm:  Dijkstra, and etc…
      5) Multicasting, Mac layer protocols for LAN

It is based on two languages( an object-oriented simulator (C++), and OTcl (object-oriented Tcl) interpreter.
It has rich library of network and protocol object
It has Compiled C++ hierarchy gives efficiency in simulation and faster execution times.
A network topology is simulated  With OTcl script provided by user.

Ns2 is event simulator where the advance of time depends on the timing of events maintained by a scheduler.
Event – an object in C++ hierarchy.
                  unique ID, Scheduled time,
                  pointer to an object

Scheduler – maintains ordered data structure with the events to be executed and fires them one by one, invoking the handler of the event.