[ns] bug in wireless implementation?

[Vikram Kanodia <kanodia@ece.rice.edu>]

Hi,

i have noticed the following bug while running a "very simple
simulation" using mac-802.11 implementation of ns.

try running any simulation under a heavy CBR load case (eg just two nodes
in a single broadcast environment, CBR traffic, pkt size 512, interval say
.0025, )....

one would not expect the sequence numbers of the packets received (
note..sequence numbers not uid...) to be out of order (at the agt
level trace) since mac-802.11 takes packets from the ifq in FIFO order
right ? wrong!!!

i have attached a copy of my wireless1.tcl file below ....let me know
whether i am doing something wrong or is there a serious bug in mac-802.11
implementation....

when you run the simulation as defined in the attached file, the sequence
number of the first packet received by node 1 is 0 and the SECOND PACKET
SEQUENCE NUMBER IS 6----sequence number 1 comes much later.

 -Vikram


####################### wireless1.tcl ###################

# A simple example for wireless simulation

# ======================================================================
# Define options
# ======================================================================

set val(chan)       Channel/WirelessChannel
set val(prop)       Propagation/TwoRayGround
set val(netif)      Phy/WirelessPhy
set val(mac)        Mac/802_11
set val(ifq)        Queue/DropTail
set val(ll)         LL
set val(ant)        Antenna/OmniAntenna
set val(x)              670   ;# X dimension of the topography
set val(y)              670   ;# Y dimension of the topography
set val(ifqlen)         50            ;# max packet in ifq
set val(seed)           0.0
set val(adhocRouting)   DSR
set val(nn)             2           ;# how many nodes are simulated
set val(stop)           200.0           ;# simulation time

# =====================================================================
# Main Program
# ======================================================================

#
# Initialize Global Variables
#

# create simulator instance
set ns_		[new Simulator]

# setup topography object
set topo	[new Topography]

# create trace object for ns and nam
set tracefd	[open wireless1-out.tr w]
$ns_ trace-all $tracefd

# define topology
$topo load_flatgrid $val(x) $val(y)

#
# Create God
#
set god_ [create-god $val(nn)]

#
# define how node should be created
#

# Create channel #1 
set chan_1_ [new $val(chan)]

#global node setting
$ns_ node-config -adhocRouting $val(adhocRouting) \
                 -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 OFF \
                 -macTrace OFF \
		 -channel $chan_1_

#
#  Create the specified number of nodes [$val(nn)] and "attach" them
#  to the channel. 

for {set i 0} {$i < $val(nn) } {incr i} {
	set node_($i) [$ns_ node]	
	$node_($i) random-motion 0		;# disable random motion
}

#setting initial positions of the nodes
#nodes are stationary for throughout the simulation
$node_(1) set Z_ 0.000000000000
$node_(1) set Y_ 0.0
$node_(1) set X_ 200.0

$node_(0) set Z_ 0.000000000000
$node_(0) set Y_ 0.00
$node_(0) set X_ 0.00

#creating a CBR flow from node 0 to node 1

set udp_(0) [new Agent/UDP]
$ns_ attach-agent $node_(0) $udp_(0)
set null_(0) [new Agent/Null]
$ns_ attach-agent $node_(1) $null_(0)
set cbr_(0) [new Application/Traffic/CBR]
$cbr_(0) set packetSize_ 512
$cbr_(0) set interval_ .0025
$cbr_(0) set random_ 2
$cbr_(0) set maxpkts_ 10000
$cbr_(0) attach-agent $udp_(0)
$ns_ connect $udp_(0) $null_(0)
$ns_ at 5.00 "$cbr_(0) start"


# Tell nodes when the simulation ends

for {set i 0} {$i < $val(nn) } {incr i} {
    $ns_ at $val(stop).0 "$node_($i) reset";
}

$ns_ at  $val(stop).0002 "puts \"NS EXITING...\" ; $ns_ halt"

puts "Starting Simulation..."
$ns_ run