The efficiency of protocols coordinating the data transmission between the transmitter and receivers in a network of stations connected using a passive star coupler, equipped with fixed transmitters and tunable receivers, and using wavelength-division multiplexing is discussed. Two reservation-based protocols with varying degrees of signaling complexity are proposed: the dynamic allocation scheme (DAS), which dynamically assigns slots on a packet-by-packet basis, and the hybrid time-division-multiplexing (TDM) scheme (HTDM), which combines the TDM and the DAS scheme and allows both preassigned and dynamic slot assignment. Analytical results are derived for the delay performance of the two schemes and compared with that of TDM. It is shown that the performance of DAS under ideal conditions is close to optimal, but its signaling costs are exorbitantly high. On the other hand, HTDM has lower signaling needs, but has higher delays when compared to DAS.>

A network with N stations connected via a passive star coupler using wavelength division multiplexing (WDM) is considered. Each station is equipped with a transmitter, transmitting at a fixed frequency, and a tunable receiver, capable of receiving frequencies over the entire transmitting spectrum. Two reservation-based protocols are proposed for a local area network (LAN) environment: the dynamic allocation scheme (DAS), which dynamically assigns slots on a packet-by-packet basis, and the hybrid TDM scheme (HTDM) which is a combination of TDM and the DAS, allowing both preassigned slot and dynamic slot assignment. Analytical results are derived for the delay performance of the two schemes and these results are compared with that of the TDM. It is shown that the performance of DAS is close to optimal when the propagation delay is zero. However, it requires a large signaling bandwidth. On the other hand, HTDM has lower signaling needs, provides lower delays when compared to TDM (particularly under nonuniform traffic conditions), and is capable of handling bursty data traffic. Thus, HTDM offers a more practical solution for implementation for LANs.>

The performance of several policies for scheduling real-time and non-real-time messages in a statistical multiplexer is examined. The performance metric for the real-time traffic is the percentage of messages not transmitted within their deadlines; the performance metric for the non-real-time traffic is the average delay. The scheduling policies are: (1) first-come first-served (FCFS); (2) head of the line priority, in which real-time packets are given priority; (3) minimum-laxity threshold (MLT) policy; and (4) queue-length threshold (QLT) policy. Under the MLT policy, priority is given to the real-time traffic when the minimum laxity is below some threshold. The QLT policy gives priority to the non-real-time traffic whenever the number of queued non-real-time packets is above some threshold. Results show that the FCFS policy causes relatively high losses for the real-time traffic while providing relatively low message delays for the non-real-time traffic; the converse holds true for the strict priority discipline. Both the MLT and QLT disciplines allow the designer to explicitly trade off the performance realized by each traffic class by using an appropriately chosen value for the threshold parameter. Little difference is observed in the performance tradeoffs available, so it is concluded that the QLT policy is more practical, as it is simpler to implement.>

in soft real-time distributed computer stems, a job submitted at a node in the network must complete execution within a specified time constraint, otherwise it is considered lost. When a single node occasionally experiences an overload of jobs, it may still be possible to execute some of the otherwise lost jobs by invoking a load sharingnode algorithm to distribute the local overload to other system nodes. We examine several relatively simple approaches to load sharing and show that these simple real-time load sharing algorithms may often perform as well as their more complex counterparts. Approximate analytic performance models are developed and validated through simulation. The performance results suggest that, over a relatively wide range of system parameters, the performance of these simple approaches is substantially better than the case of no load sharing and often close to that of a theoretically optimum algorithm.