  This paper aims to identify the operational region of a link in terms of its
utilization and alert operators at the point where the link becomes overloaded
and requires a capacity upgrade. The number of active flows is considered the
real network state and is proposed to use a proxy for utilization. The Gaussian
approximation gives the expression for the confidence interval on an
operational region. The easy rule has been formulated to display the network
defects by means of measurements of router loading and number of active flows.
Mean flow performance is considered as the basic universal index characterized
quality of network services provided to single user.
