ORMA: A High-Performance MAC Protocol for Fiber-optic LANsIMANs

network In this article, the author proposes a novel MAC-layer protocol, called Optical Reservation Multi stations to reserve transmission slots, which is attractive for use in fiber optic networks. Unlike conventional protocols, w is mostly done using software, ORMA performs its reservation using simple and effective optical circuits. Complete desc ORMA: A High-Performance MAC Protocol for Fiber-optic LANsIMANs Mounir Hamdi, Hong Kong University of Science and Technology ata and telecommunications are presently experiencD ing an evolutionary change. Technological progress promises the deployment of optical and electronic components with nearly unlimited transmission capacity and multiples of the processing speed of current systems. These advances facilitate the support of numerous new services by simultaneously giving access to a huge number of users. Concurrent to this evolution, an increased interest in realtime and multimedia applications can be seen in engineering, medicine, manufacturing, and entertainment. As a result, theie is an increasing demand for high-speed, highperformance fiber optic local and metropolitan area networks (LANs and MANs) to replace today’s dedicated communications systems by supporting a wide range of applications. Most of the networks proposed for this new broadband integrated services digital networking (B-ISDN) environment are based either on folded or dual unidirectional fiber optic bus technology [l, 21. With this design choice comes the challenge of designing medium access control (MAC) protocols for these networks. As a result, researchers are actively developing MAC protocols that will provide the performance and services expected of next-generation LANs and MANs. One reason for the importance of this research is that all higherlayer services are built on the fundamental packet transfer service, which is provided by the MAC sublayer, and it is the MAC protocol that determines the characteristics of this fundamental service. Hence, improvements to MAC services result in improved system performance, while the provision of new MAC services means that new applications can be developed. Using optical fiber as a transmission medium, which is This resenrch work I S suppoyt~d in part by a granf fvom the Hong Knng Research Grunt Council RGCIHKUST 619194E projected to have speeds beyond several gigabits per second and span distances of hundreds of kilometers, imposes more strict constraints on messageipacketislot processing times at the intermediate nodes, thereby providing a new challenge to MAC-level protocol designers. In particular, a MAC protocol for high-speed LANs/MANs should possess several basic characteristics. First, it must be simple enough to be implemented directly in hardware so that it can exploit the bandwidth capacity offered by optical fiber. Second, it must be fair; that is, the throughput of a station should be independent oC ils location within the network. In addition, a bursty station should not be served to the detri ment of other stations. In other words, the MAC protocol should not allow a single station to use all the available bandwidth inadvertently. However, the MAC protocol should be flexible enough to allocate bandwidth according to the applications’ demands. Thiid, the throughput of the MAC piotocol must be independent of the network’s size and transmission rate. This item is related to the well known a-parumeter.l Any MAC protocol which is sensitive to this parameter limits its usefulness to networks up to a certain size and rate. Fourth, the access delay of the stations should be bounded. This ensures that a process will always be able to transmit at regular intervals regardless of the current network load. This is