  A new method of estimating some statistical characteristics of TCP flows in
the Internet is developed in this paper. For this purpose, a new set of random
variables (referred to as observables) is defined. When dealing with sampled
traffic, these observables can easily be computed from sampled data. By
adopting a convenient mouse/elephant dichotomy also dependent on traffic, it is
shown how these variables give a reliable statistical representation of the
number of packets transmitted by large flows during successive time intervals
with an appropriate duration. A mathematical framework is developed to estimate
the accuracy of the method. As an application, it is shown how one can estimate
the number of large TCP flows when only sampled traffic is available. The
algorithm proposed is tested against experimental data collected from different
types of IP networks.
