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NS Simulator for beginners

NS Simulator for beginners. Chapter 2 & 3. ns Simulator Preliminaries 2009-09-02 Thiep M. Ha thiep03@yahoo.com. Contents. Initialization and termination Definition of a network of links and nodes Agents and applications Scheduling events Visualisation: using nam Tracing

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NS Simulator for beginners

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  1. NS Simulator for beginners Chapter 2 & 3. ns Simulator Preliminaries 2009-09-02 Thiep M. Ha thiep03@yahoo.com

  2. Contents • Initialization and termination • Definition of a network of links and nodes • Agents and applications • Scheduling events • Visualisation: using nam • Tracing • Random variables

  3. Initialization and termination • An ns simulation starts with the command • Creating output files (trace files or nam files)

  4. Initialization and termination • The termination of the program • At the end of the ns program we should call the procedure “finish” and specify at what time the termination should occur.

  5. Definition of a network of links and nodes • Definition of a node • Definition of a link • In NS, an output queue of a node is implemented as a part of each link whose input is that node. • Definition of the buffer capacity of the queue related to each link

  6. Definition of a network of links and nodes • Form of a simplex link • Duplex link is constructed from two parallel simplex links.

  7. Definition of a network of links and nodes • Defining nodes, links and assigning queue size

  8. Agents and applications • FTP over TCP

  9. Agents and applications • CBR over UDP

  10. Scheduling events • The Tcl script defines when event should occur. • Format • Examples • The scheduler is started when running ns, i.e. through the command $ns run.

  11. Visualisation: using nam • Giving node position (for NAM)

  12. Tracing • Tracing objects in a simplex link • EnqT registers information concerning a packet that arrives and is queued at the input queue of the link. • DrpT handles the information concerning the dropped packet. • DeqT registers information at the instant the packet is dequed. • RecvT gives us information about packets that have been received at the output of the link.

  13. Tracing • Structure of trace files • Event: event type. • r: receive (at the output of the link) • +: enqueued • -: dequeued • d: dropped • Time: the time at which the events occurs. • From node: givens the input node of the link at which the events occurs. • To node: gives the output node of the link at which the events occurs. • Pkt id: unique id of the packet

  14. Tracing • Example • Tracing a subset of events

  15. Random variables • Seeds and generators • The seed value of 0 results in the generation of a new random variable each time we run the simulation. • In contrast, if we use other seeds then each time we run the simulation, the same sequence of random variables that are generated in a simulation will be generated. • Creating random variables • Creating a new generator • When actually creating a random variable, we have to define its distribution type and its parameters.

  16. Random variables

  17. Random variables

  18. Random variables

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