In the code segment given below, contention based MAC Maccon is used in which each node randomly selects the channel from available channels. Collision occurs due to the independent random selection of the channels by the nodes and the selected channel information is attached in packet header and passed to PHY layer.
| set val(chan) | Channel/WirelessChannel | ; #Channel Type |
| set val(prop) | Propagation/TwoRayGround | ; #Radio propagation model |
| set val(netif) | Phy/WirelessPhy | ; #Network interface type |
| set val(ant) | Antenna/OmniAntenna | ; #Antenna model |
| set val(rp) | AODV | ;#Routing Protocol |
| set val(ifq) | Queue/DropTail/PriQueue | ;# interface queue type |
| set val(ifqlen) | 50 | ;# max packet in ifq |
| set val(mac) | Mac/Maccon | ;# MAC type |
| set val(ll) | LL | ;# link layer type |
| set val(nn) | 6 | ;# number of mobilenodes |
| set val(channum) | 3 | ;# number of channels per radio |
| set val(cp) | ./topo4.tcl | ; # topology traffic file |
| set val(stop) | 50 | ;# simulation time |
# ==================================================================
# Main Program
# ======================================================================
# Initialize Global Variables
set ns_ [new Simulator]
set tracefd [open test.tr w]
$ns_ trace-all $tracefd
# set up topography object
set topo [new Topography]
$topo load_flatgrid 1000 1000
#create nam
set namtrace [open test.nam w]
$ns_ namtrace-all-wireless $namtrace 1000 1000
# Create God
set god_ [create-god $val(nn)]
# configure node
$ns_ node-config -adhocRouting $val(rp) -llType $val(ll) -macType $val(mac) -ifqType $val(ifq) -ifqLen $val(ifqlen) -antType $val(ant) -propType $val(prop) -phyType $val(netif) -topoInstance $topo -agentTrace ON -routerTrace ON -macTrace ON -movementTrace ON
for {set i 0} { $i < $val(channum)} {incr i} {
set chan_($i) [new $val(chan)]
}
for {set i 0} {$i < $val(channum) } {incr i} {
$ns_ add-channel $i $chan_($i)
}
#Configure for channels
$ns_ node-config -channel $chan_(0) -ChannelNum $val(channum)
for {set i 0} {$i < $val(nn) } {incr i} {
set node_($i) [$ns_ node]
$node_($i) set recordIfall 1
$node_($i) random-motion 0 ;# disable random motion
}
source $val(cp) ; #source topology and traffic file generated by others
