Computer networks lab basic concepts

Generic script structure

1)      Create stimulator object

*Set ns [new stimulator]

Insert immediately after scheduler

*Trace packets on all links

Set nf[open out.nam w]

2)Turn on tracing(Tracing)  

                r:reciver

+:enquee

-:deque

d:drop

Create topology(create network)

1)Nodes

n0---àn2(Basic idea of two nodes)

*)set n0[$ns node]

*)set n1[$ns node]

2)Links and queing

                $ns duplex-link $n0 $n1 1mb 110ms RED

2)      To create a larger tpology

Use a for loop example

Setup packet loss,link dynamics

                Link failure

                                Hooks in routing module to reflect routing changes

Create routing agents(Create udp(Existing in forth layer the transport layer of the network) connection)

                Has to connect nodes cose there is so much nulls

Udp----n0------àn1---------null

Set udp[new Agent(Inheritedd)/UDP(base class)]

Create application and or traffic sources(On top of the UDP)

CBR tcp also doing the same function

                Set cbr[new Appliocation/Traffic/CBR]

                $cbr set packetssize_500

                Less number of intrevels means less number of packets.

Creating traffic(It is working on the top of TCP)

                Using ftp or telnet

Post-processing procedure(Nam, network animator)

Add a ‘finish’ procedure that closes the trace file and start nam

                Procfinish{}{

                Global ns nf

                $ns flush-trace

                Close $nf

                Exec nam out.nam &

                exit 0

}

Start stimulation

 *Schedule events

$ns at

·         Call finish

$ns at 5.0 “finish”

Run the stimulator

$ns run

Diffrence between switch and hub

Hub- it is a repeater

Switcher-layer three switch

Editors