Correlations between FTP & Ping
Two common ways to measure the data rates (kilo bytes/second or kB/s) between
two nodes are to use the Internet File Transfer
Protocol (FTP) and ping. Though FTP is closer to what may be expected
by the user, it is also more complex to use, more intrusive on the
network, and more dependent on end node loading.
Ping is much more simple, it simply measures the round-trip
response time for a given number of bytes. In order to get an idea
of how well a ping measurement of data rate would correlate with an
FTP measurement, we have measured the data rates by both methods to several
sites and plotted the results below.
We derive the ping data rate in two ways:
These two ping measures are plotted against the FTP data rate here:
Measure the average ping response time (t) for a packet of 1000 bytes. The
average is taken over a 10 week interval on working days with 5 measurements
every 3 minutes. The throughput = 2000 bytes / t. There are 2000 bytes since
the packet has to go out and back. We call this the Ping Data Rate
Measure the average ping response times (t100 and t1000) for packets of
100 bytes and 1000 bytes over the same 10 week interval. The byte rate
is then = (2000 - 200) bytes / (t1000 - t100). We call this the
Ping Thruput measure.
It can be seen that there is a strong correlation. It is not clear which ping
gives the better correlation. Since the Ping Data Rate method is
to calculate, less dependent on anomalies due to say t100 being > t1000),
we tend to use the Data Rate method. More details as to which node saw what
response can be seen below where the ping throughput is plotted in log form.
Owner: Les Cottrell