• A series of points are interconnected together via a communication path.
  • It makes communication between computer devices
  • In all data network consists of nodes
  • The physical connection between nodes are links
  • Links carry message between nodes

Need for computer networks:

  • File sharing
  • Data protection
  • Resource sharing
  • Remote access
  • Communication and collaboration

Network Characteristics:

  • Availability
  • Reliability
  • Security
  • Topology
  • Cost
  • Speed
  • Scalability

Devices to connect network:

  • Routers
  • Gateways
  • Repeaters
  • Bridges
  • Hub
  • Modem

Network Topologies:

  • Bus topology
  • Star topology
  • Mesh topology
  • Ring topology
  • Hybrid topology
  • Wireless topology

Factors for choosing network topology:

  • Topology defines the virtual structure of a network
  • Topology may be physical or logical
  • The main factors for choosing network topologies are,
  • Scale of your project -number of components to be connected
  • Amount of traffic expected on the network
  • Budget allotted for the network
  • Required response time

Criteria for choosing network type:

  • Size of the business
  • Level of security required
  • Type of activity
  • Skills of the administrators available
  • Volume of traffic over the network
  • Needs of the network’s users
  • Budget set aside for operating the network


#Create a simulator object
set ns [new Simulator]
#Open the NAM trace file
set nf [open o.nam w]
$ns namtrace-all $nf

# create nodes
set n0 [$ns node]
set n1 [$ns node]
set n2 [$ns node]
set n3 [$ns node]
set n4 [$ns node]
set n5 [$ns node]
set n7 [$ns node]
set n8 [$ns node]
set n10 [$ns node]
#Create links between the nodes
$ns duplex-link $n0 $n2 2Mb 10ms DropTail
$ns duplex-link $n1 $n2 2Mb 10ms RED
$ns duplex-link $n2 $n3 1.7Mb 20ms RED
$ns duplex-link $n4 $n5 2Mb 10ms RED
$ns duplex-link $n2 $n8 2Mb 10ms RED
$ns duplex-link $n4 $n10 2Mb 5ms DropTail
#Define a ‘finish’ procedure
proc finish {} {
global ns nf
$ns flush-trace
#Close the NAM trace file
close $nf
#Execute NAM on the trace file
exec nam o.nam &
exit 0}
#Call the finish procedure
$ns at 1.0 “finish”
#Run the simulation
$ns run