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Generate a series packet sizes for network testing
Lists example from a Well House Consultants training course
More on Lists [link]

This example is described in the following article(s):
   • Generating traffic for network testing - [link]

Source code: pk4.tcl Module: T206

# Setting traffic in small medium and large packets
# where we know the proportion of BYTES in packets of each size

#############################

proc maketraffic {perc size rez} {

# First parameter - percentage of traffic in packets of each size (a list)
# Second parameter - size of each of the packet types (a list)
# Third parameter - the NAME of a variable to use for a returned list

# We want to output a list of packet sized from this proc, which we
# do via the regular "return". However, we may also want to pass
# back a table of percentages for each packet size which we'll do
# via the third parameter

upvar $rez tealeaves

set ecount [llength $perc]
set totrat 0

# Work out the number of packets of each size for a megabit of data

for {set i 0} {$i < $ecount} {incr i} {
        set nprop [expr 1000000 * [lindex $perc $i] / 100. / [lindex $size $i]]
        lappend prop $nprop
        set totrat [expr $totrat + $nprop]
        }

# Work out the PROPORTION of each size of packet to get the required
# proportion of traffic

set ratiosofar 0
for {set i 0} {$i < $ecount} {incr i} {
        set nprop [expr [lindex $prop $i] / $totrat]
        set ratiosofar [expr $nprop + $ratiosofar]
        lappend ratios $ratiosofar
        lappend c 0
        }

# Use the randomiser to choose which packet to send

for {set counter 0} {$counter < 10000} {incr counter} {
        set trigger [expr rand()]
        for {set i 0} {$i < $ecount} {incr i} {
        if {$trigger < [lindex $ratios $i]} {
                set c [lreplace $c $i $i [expr 1 + [lindex $c $i]]]
                lappend stream [lindex $size $i]
                break
                }
        }
}

# Go work out how much traffic in each size of packet

set tottra 0
for {set i 0} {$i < $ecount} {incr i} {
        set thistraffic [expr [lindex $c $i] * [lindex $size $i]]
        lappend traffic $thistraffic
        set tottra [expr $tottra + $thistraffic]
        }

# And reduce that to a percentage

for {set i 0} {$i < $ecount} {incr i} {
        lappend tperc [expr 100 * [lindex $traffic $i] / $tottra ]
        }

# Use the upvar variable to return the statistics

set tealeaves $tperc

# And return the relating list of packet sizes

return $stream

}

#############################

# Seed the random number generator (default is actually
# clock seconds - we have added here explicitly to show
# how to do it)

puts [clock seconds]
expr srand([clock seconds])

# Set up some sample patterns

set cellular_pc "80 5 15"
set cellular_sz "64 576 1518"

set data_pc "30 10 60"
set data_sz $cellular_sz

set sophie_pc "60 10 7 2 6 15"
set sophie_sz "64 99 150 237 576 1518"

# Generate and test those patterns

set generate [maketraffic $cellular_pc $cellular_sz tlevs]
# puts $generate
puts $tlevs

set generate [maketraffic $cellular_pc $cellular_sz tlevs]
# puts $generate
puts $tlevs

set generate [maketraffic $data_pc $data_sz tlevs]
# puts $generate

set generate [maketraffic $sophie_pc $sophie_sz twiddle]
puts $tlevs
puts $twiddle


Learn about this subject
This module and example are covered on the following public courses:
 * Learning to program in Tcl
 * Tcl Programming
 * Tcl Programming
Also available on on site courses for larger groups

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Other Examples
This example comes from our "Lists" training module. You'll find a description of the topic and some other closely related examples on the "Lists" module index page.

Full description of the source code
You can learn more about this example on the training courses listed on this page, on which you'll be given a full set of training notes.

Many other training modules are available for download (for limited use) from our download centre under an Open Training Notes License.

Other resources
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