Asynchronous measurement of CDV in ATM networks using OAM cells

Abstract

The synchronisation between source and destination clocks at network nodes to a common reference time of day is important in order to achieve accurate measurements of cells delays in ATM networks. Otherwise, direct measurement of the cell transfer delay and cell delay variation using time-stamped OAM cells would be inaccurate. In this work, a method for the accurate measurement of cell delay variation using OAM cells, which does not rely on synchronised clocks at the measurement points is presented. This is achieved by assuming that each ATM switch has the capability to process and to modify the information contained in the OAM cells. The system presented here was modelled by means of a block-oriented network simulator (BONeS), which is a graphically-oriented, general-purpose simulation language for modelling and simulating communications networks, including ATM networks. The measurements of the cell delay variation were carried out on a VBR video source generated by a real MPEG-2 encoder with a fixed quantizer step size. The simulation results obtained show that measurements of the cumulative cell delay variation carried out without synchronised clocks at the measurement points were very closed to those obtained using synchronised clocks at the measurement points.