When a new connection request is received at the network, the CAC function determines whether the network has sufficient remaining capacity to accept the new connection, without spoiling the service being given to existing connections. Most CAC algorithms use parametric modeling of traffic types to estimate the bandwidth requirement of existing connections. Parametric modeling is unsatisfactory because of the wide variety of traffic types offered to the network, the difficulties in modeling burstiness and the time required to fit parameters. LD Theory is a recently developed branch of probability theory - a sophisticated version of the law of averages. It is used to estimate the frequency of rare events.
Actuaries use it to calculate safe premiums.
Teletraffic engineers use it to calculate safe buffer-sizes. Both use parametric modeling to estimate the LD rate-function. Chemical engineers do not use parametric models to determine entropy functions - they measure them directly. Preliminary investigations by the DIAS group on the measurement of LD rate-functions of teletraffic, published in the IEEE Journal on Selected Areas in Communications in 1995, were sufficiently promising to persuade Telia, the Swedish telecom, and Cambridge University Computer Laboratory to join DIAS in pursuing the idea. Telia own a public ATM network.