[ns] Problem - Throughput greater than link bandwith

[Giuseppe Tringali <gtringali@katamail.com>]

Hi NS users,

I have modified the script sat_repeater.tcl that comes with NS.

The script takes 2 argument:
first argument in the error rate in % (0 <--> 100) of the error model
second argument is:
         the number of TCP Agents and FTP traffic sources
         the number uf UDP Agents and CBR traffic sources
         the bandwith of the link in Mb/s

(You can find the complete script below my signature)

With a simple awk script, I sum the size (in bytes) of all the packets 
received by node2 (node2 in the trace file), I convert it to Mb and then 
divide it by the length of the data transfer.

Now I try to explain my problem with an example:

ns script_name.tcl 0 2

so the error rate is 0.0 and I have 2 TCP agents and so on ... and a 
bandwith of 2 Mb/s (or at least I think) .

The awk script gives me a value of about 3.5 (Mb/s I think). How is it 
possible?
Could someone  tell me where is my error?

Thanks in advance,
Giuseppe Tringali

#
# Copyright (c) 1999 Regents of the University of California.
# All rights reserved.
#
# Redistribution and use in source and binary forms, with or without
# modification, are permitted provided that the following conditions
# are met:
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#    notice, this list of conditions and the following disclaimer.
# 2. Redistributions in binary form must reproduce the above copyright
#    notice, this list of conditions and the following disclaimer in the
#    documentation and/or other materials provided with the distribution.
# 3. All advertising materials mentioning features or use of this software
#    must display the following acknowledgement:
#       This product includes software developed by the MASH Research
#       Group at the University of California Berkeley.
# 4. Neither the name of the University nor of the Research Group may be
#    used to endorse or promote products derived from this software without
#    specific prior written permission.
#
# THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
# ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
# IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
# ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
# FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
# DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
# OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
# HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
# LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
# OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
# SUCH DAMAGE.
#
# Contributed by Tom Henderson, UCB Daedalus Research Group, June 1999
#
# Modified by Giuseppe Tringali, 03-09-2001
# The script takes 2 argument:
# first argument in the error rate in % (0 <--> 100) of the error model
# second argument is:
#       the number of TCP Agents and FTP traffic sources
#       the number uf UDP Agents and CBR traffic sources
#       the bandwith of the link in Mb/s


if {$argc != 2} {
puts "ERROR! ns called with wrong number of arguments!($argc)"
exit 1
} else {
set arg [lindex $argv 0]

set NN [lindex $argv 1]
set bw [expr $NN*1e6]

set max 100.0
set rate [expr $arg/$max]

global ns
set ns [new Simulator]
$ns rtproto Dummy; # Using C++ routing agents and objects

# Global configuration parameters

global opt
set opt(chan)           Channel/Sat
set opt(bw_up)          bw; # Uplink bandwidth-- becomes downlink bw also
set opt(phy)            Phy/Sat
set opt(mac)            Mac/Sat
set opt(ifq)            Queue/DropTail
set opt(qlim)           1000
set opt(ll)             LL/Sat


# XXX This tracing enabling must precede link and node creation
set f [open out_p($arg)_n($NN).tr w]


$ns trace-all $f

# Set up satellite and terrestrial nodes

# GEO satellite at 95 degrees longitude West
set n1 [$ns satnode-geo-repeater -95 $opt(chan)]

# Two terminals: one in NY and one in SF
set n2 [$ns satnode-terminal 40.9 -73.9]; # NY
set n3 [$ns satnode-terminal 37.8 -122.4]; # SF

# Add GSLs to geo satellites
$n2 add-gsl geo $opt(ll) $opt(ifq) $opt(qlim) $opt(mac) $opt(bw_up) \
     $opt(phy) [$n1 set downlink_] [$n1 set uplink_]
$n3 add-gsl geo $opt(ll) $opt(ifq) $opt(qlim) $opt(mac) $opt(bw_up) \
     $opt(phy) [$n1 set downlink_] [$n1 set uplink_]

# Add an error model to the receiving terminal node
# and sets its packet error rate to $rate

set em_ [new ErrorModel]
$em_ unit pkt
$em_ set rate_ $rate
$em_ ranvar [new RandomVariable/Uniform]
$n3 interface-errormodel $em_

$ns trace-all-satlinks $f

for {set counter 1} {$counter <= $NN} {incr counter} {

global ns n2 n3

# Attach agents for FTP
set tcp($counter) [$ns create-connection TCP/Newreno $n2 TCPSink $n3 $counter]

# set windows size to 100 packets
$tcp($counter) set window_ 100

# set packet size to 500 bytes
$tcp($counter) set packetSize_ 500

set ftp($counter) [$tcp($counter) attach-app FTP]

$ns at 1.0 "$ftp($counter) start"

# Attach agents for CBR traffic generator
set udp($counter) [new Agent/UDP]
$ns attach-agent $n2 $udp($counter)
set cbr($counter) [new Application/Traffic/CBR]
$cbr($counter) attach-agent $udp($counter)

# set packet size to 500 bytes
$udp($counter) set packetSize_ 500

# set flow id to counter
$udp($counter) set fid_ $counter

# set rate to 1 Mbps
$cbr($counter) set rate_ 1Mb

set sink($counter) [new Agent/LossMonitor]
$ns attach-agent $n3 $sink($counter)

$ns connect $udp($counter) $sink($counter)

$ns at 1.0 "$cbr($counter) start"
}


# We use centralized routing
set satrouteobject_ [new SatRouteObject]
$satrouteobject_ compute_routes

$ns at 100.0 "finish"

proc finish {} {
         global ns f f0 f1
         $ns flush-trace
         close $f

       exit 0
}

$ns run
}
}