III. AGGREGATED NETWORK TRAFFIC CHARACTERISTICS ON SERVER
In this section, we evaluate the aggregated network band-
width usage as on the Microsoft Office Communications
Server. Initially, we investigate the overall traffic characteris-
tics for the three periods September, November and December.
We illustrate the different traffic for the server view in Figure 1
for the timescales of 1, 10 and 60 seconds. We observe that
most of the traffic in bps remains under a 10 Mbps level, with
exceptions that occur sporadically for all measurement periods.
Once aggregated and smoothed, we observe that in aggregates
of 10 seconds, the traffic sparingly reaches 100 Mbit, with
most of the traffic being under 10 Mbit per ten seconds. We
furthermore note that the traffic for the November measure-
ment exhibits the highest “spikes” of network activities. With
additional traffic aggregation to minutes, we observe that the
November trace exhibits distinctive and sustained periods of
extreme traffic, whereby for multiple minutes (and even up to
hours) the overall traffic is more than 60 Mbit/minute.
We illustrate the autocorrelation coefficient characteristics
for the aggregated server traffic in Figures 2 for the timescales
of 1, 10 and 60 seconds. We observe that the November
measurement exhibits a significant level of self-similarity (as
measured by the autocorrelation) for the bandwidth per second
and ten seconds, and a slightly reduced level for the minute
time scales. For the September and December measurements,
on the other hand, we note an initially sharp decline in the
autocorrelation coefficient, which rises again after about one
minute in the bandwidth per second evaluation. Although
the December level of autocorrelation is slightly higher than
observed for the September one, both are close in their overall
behavior. Similar observations can be made for the time scales
of ten seconds and one minute, whereby we observe that the
autocorrelation exhibits (i) an oscillating decline for the time
scale of ten seconds and (ii) a nearly exponential decline
indicating the absence or low level of self-similarity for the
time scale of one minute.