Performance of a Virtual Synchronization Mechanism in an Asynchronous Optical Network

Optical Packet Switched (OPS) ring Metropolitan Area Networks (MAN) are among the most promising solutions for Next Generation MAN architectures. However, a particular phenomenon is observed in optical ring networks with random access to the transmission medium, such as in asynchronous Optical Unslotted Carrier Sense Multiple Access with Collision Avoidance (OU-CSMA/CA). Due to the random moments of packet transmissions, the amount of bandwidth which is available for use, on each wavelength, becomes divided into many small pieces. This problem, also called bandwidth fragmentation, causes a waste of some transmission resources. In fact, free spaces which are smaller then the optical packet size are out of use for traffic insertion. The bandwidth fragmentation is reduced in synchronous networks, thanks to the better use of the transmission resources provided by these networks. This paper describes an access scheme that is proposed to improve the performance of the original OU-CSMA/CA applied to an asynchronous optical ring network. We propose a ldquovirtual synchronizationrdquo mechanism (VSC), which improves significantly the bandwidth utilization while being very simple to implement. We provide simulation works in order to validate the efficiency of the proposed mechanism. Numerical results show the improvement of performance provided by the VSC mechanism, compared to the original CSMA/CA protocol.