Asynchronous time-division multiplex communication medium virtual

Abstract

A device evaluates the throughput of virtual circuits conveying cells and using an asynchronous time-division multiplex transmission medium. It comprises a store in which each virtual circuit is assigned a context containing a set of data defining the conditions for evaluating the throughput of the virtual circuit and data obtained from previous such evaluations. A clock supplies a current time and a processor unit reads the context of the respective virtual circuit when each cell is received. This context contains a start time which was the current time observed and stored when a previous cell of the virtual circuit in question was received. The start time is subtracted from the current time and the time difference obtained in this way together with the number of cells observed between that for which the start time was recorded and the present cell provide a basis for evaluating the throughput. The device comprises a unit for scanning the contexts cyclically and, during this cyclic scanning, incrementing for each context the content of a scan cycle counter having an initial position. The device also comprises a unit for identifying virtual circuits guaranteeing a minimal throughput and a processor unit comparing for each identified virtual circuit the content of the scan cycle counter for the identified virtual circuit with a predetermined threshold value to produce a cut off call detection signal if the content of the counter reaches the predetermined threshold value.