Reconciling the Intervals and the Final

The main reason for extracting the interval sums is so that you can perform time-series analysis. If you try and re-calculate the final bandwidths with these intervals, however, you will find that the values don’t match. This is because iperf is both rounding the times and reserving the last transfer from the intervals (but adding it to the final sums). This is an exploration of how much of a difference it can make.

# this package
from iperflexer.iperfparser import IperfParser
from iperflexer.sumparser import SumParser
from iperflexer.unitconverter import UnitConverter
from iperflexer.unitconverter import UnitNames as d_names
from iperflexer.unitconverter import BinaryUnitNames as b_names
from iperflexer.unitconverter import BinaryUnitconverter

d_converter = UnitConverter()
b_converter = BinaryUnitconverter()

The Data

The iperf session was run over wifi with four threads, a buffer size of 128 Kilobytes and reporting at one second intervals. We’ll use the server output as the baseline and the client output to reconcile the final sums and the interval sums.

server_voodoo = IperfParser(units='bits', threads=4)
server_sums = SumParser(units='bits', threads=4)
client_voodoo = IperfParser(units='bits', threads=4)
client_sums = SumParser(units='bits', threads=4)

with open('server_p4_128K.csv') as reader:
    for line in reader:
        server_voodoo(line)
        server_sums(line)

with open('client_p4_128K.csv') as reader:
    for line in reader:
        client_voodoo(line)
        client_sums(line)

Now we can compare the values for each different method.

mbits = d_converter[d_names.bits][d_names.mbits]
server_final = server_sums.last_line_bandwidth
server_final_mbits = server_sums.last_line_bandwidth*mbits
recalc = sum(server_voodoo.bandwidths)/float(len(server_voodoo.intervals)) * mbits
client_final = client_sums.last_line_bandwidth * mbits
client_recalc = sum(client_voodoo.bandwidths)/float(len(client_voodoo.intervals))
client_recalc_mbits = client_recalc * mbits

Comparisons

Source	Value	Difference from Server Final
Server Final	10.002708	0
Server Recalculated	10.0002203279	0.00248767213115
Client Final	10.08557	-0.082862
Client Recalculated	10.1362346667	-0.133526666667

The link was obviously very bad. Let’ see how much of a difference the case with the largest difference from the server’s true bandwidth (re-calculated client data) was.

proportion = (client_recalc - server_final)/float(server_final)
print(proportion)

0.0133490517435