Next-generation networks are expected to support a wide variety of services. Some services such as video, voice, and plant control traffic have explicit timing requirements on a per-message basis rather than on the average. In this paper, we develop a general model of dual-link networks to support real-time communication. We examine the desirable properties of this network and the difficulties in achieving these properties. We then introduce the concept of coherence and develop a theory of coherent dual-link networks. We show that a coherent dual-link network can be analyzed as though it is a centralized system. We then discuss practical considerations in implementing a dual-link network, and implications of this work to address problems observed in the IEEE 802.6 metropolitan area network standard.

This paper develops necessary and sufficient conditions for analyzing the schedulability of fixed priority algorithms on resources with limited priority levels. We introduce the degree of schedulable saturation (S/sub max/) as an objective function. A multimedia task set is used to demonstrate how S/sub max/ can be used to optimize the grouping of tasks to priority levels.>

This paper develops a unified framework for reasoning about timing correctness of packet-switched networks. The unification is in the form of a set of consistent scheduling models for a variety of network architectures and protocols. The unification is important as it allows heterogeneous network types to be analyzed using a consistent methodology and facilitates scheduling over multihop networks where each link is a different type of network. To demonstrate the framework, a scheduling model for a dual-link network, IEEE 802.5 token ring, and FDDI, is presented. The use of this framework to select paths in multi-hop networks is also demonstrated.>

We address issues in determining FIFO sizes necessary for high-performance, in an integrated high-speed network interface, using a 100 Mbps Fast Ethernet controller as an example. A detailed analytical model is developed which accounts for system design choices, in addition to network parameters such as packet size and rate. The model yields insight into the impact of system parameters, such memory latency and maximum DMA transfer size, on the size of FIFOs required. The model also shows that the worst-case, in terms of receive-FIFO required, is not necessarily when back-to-back minimum size packets are received, but depends on the system parameters such as maximum DMA transfer size. We also study the possibility of FIFO underflows for the transmit direction.>

Real-time computing systems are used to control telecommunication systems, defense systems, avionics, and modern factories. Generalized rate-monotonic scheduling theory, is a recent development that has had large impact on the development of real-time systems and open standards. In this paper we provide an up-to-date and self-contained review of generalized rate-monotonic scheduling theory. We show how this theory can be applied in practical system development, where special attention must be given to facilitate concurrent development by geographically distributed programming teams and the reuse of existing hardware and software components.>

A fast packet-switched network is considered that transmits fixed-sized packets or cells and provides connection-oriented services. A number of rate-based service disciplines that offer timing guarantees have recently been proposed. These disciplines work well for connections which exhibit low burstiness or whose burstiness can be managed by admission control. However, some messages have irregular arrival patterns, but must be delivered with low delay. These aperiodic messages include connection set-up/tear-down messages, link-slate updates, and other status or alarm messages. The authors propose techniques that significantly minimize aperiodic message delay without jeopardizing guarantees made to existing connections. Simple hardware implementations of these techniques that can be embedded in output queues of fast packet-switches are also described.>

The authors develop a general model of reservation-based dual-link networks to support real-time communication. They examine the desirable properties of this network and the difficulties in achieving these properties. They then introduce the concept of coherence and develop a theory of coherent dual-link networks. It is shown that a coherent dual-link network can be analyzed as though it is a centralized system. It is also shown that a coherent dual-link network can be analyzed similarly to an equivalent centralized system in terms of its schedulability for periodic message traffic.>