Abstract-We study the problem of guaranteeing synchronous message deadlines in token ring networks where the timed to-ken medium access control protocol is employed. Synchronous bandwidth, defined as the maximum time for which a node can transmit its synchronous messages every time it receives the token, is a key parameter in the control of synchronous message transmission. To ensure the transmission of synchronous messages before their deadlines, synchronous capacities must be properly allocated to individual nodes. We address the issue of appropriate allocation of the synchronous capacities. Several synchronous bandwidth allocation schemes are analyzed in terms of their ability to satisfy deadline constraints of synchronous messages. We show that an inappropriate allocation of the syn-chronous capacities could cause message deadlines to be missed, even if the synchronous traffic is extremely low. We propose

We study the problem of guaranteeing synchronous message deadlines in communication networks where the timed token medium access control protocol is employed. Synchronous capacity, defined as the maximum time for which a node can transmit its synchronous messages every time it receives the token, is a key parameter in the control of synchronous message transmission. To ensure the transmission of synchronous messages before their deadlines, synchronous capacities must be properly allocated to individual nodes. In this paper, we develop and analyze an optimal synchronous capacity allocation scheme. An optimal scheme can allocate the synchronous capacities in such a way that the synchronous message deadlines are guaranteed if there exists any allocation scheme that can do so. The optimality of the allocation scheme proposed in this paper is formally proved and the bounds for its Worst Case Achievable Utilization are derived. Key Words: Hard Real-Time, Distributed System, FDDI, Timed Token...

This paper addresses issues related to guaranteeing synchronous messages with arbitrary deadline constraints in an FDDI network. We show that several network parameters must be set carefully if message deadlines are to be satisfied. First, message deadlines can only be met if sufficient synchronous bandwidth is allocated to each node. Thus, proper synchronous bandwidth allocation is essential if deadlines are to be guaranteed. Second, the target token rotation time (TTRT) determines both the speed of token circulation and the network utilization available to user applications. TTRT should also be chosen carefully to ensure that the token circulates fast enough while maintaining a high available utilization. Finally, sufficient buffer space must be provided for outgoing messages, otherwise messages could be lost due to buffer overflow. In this paper, we propose and analyze an integrated method for allocating the synchronous bandwidth and selecting TTRT so that the time constraints of sy...

Distributed multimedia applications require performance guarantees from the underlying network subsystem. Ethernet has been the dominant local area network architecture in the last decade, and we believe that it will remain popular because of its cost-effectiveness and the availability of higherbandwidth Ethernets. We present the design, implementation and evaluation of a software-based timed-token protocol called RETHER that provides real-time performance guarantees to multimedia applications without requiring any modifications to existing Ethernet hardware. RETHER features a hybrid mode of operation to reduce the performance impact on non-real-time network traffic, a race-condition-free distributed admission control mechanism, and an efficient token-passing scheme that protects the network against token loss due to node failures or otherwise. To our knowledge, this is the first software implementation of a real-time protocol over existing Ethernet hardware. Performance measurements f...

Ethernet has been the dominant local area network architecture in the last decade, and we believe that it will continue to be so because of its cost-effectiveness and the availability of higher-bandwidth Ethernets. We propose and evaluate a software-based protocol called RETHER (Real-time ETHERnet) that provides realtime performance guarantees to multimedia applications without modifying existing Ethernet hardware. RETHER features a hybrid mode of operation to reduce the performance impact on non-real-time network packets, a race-condition-free distributed admission control mechanism, and an efficient token-passing scheme that protects the network against token loss due to node failures. 1 Introduction With the rapid growth in distributed multimedia applications, it has become essential for the underlying systems to provide resource guarantees. Among the various types of media supported by multimedia information systems, digital audio and video, also known as continuous media, requi...

of the Dissertation The Design, Implementation and Evaluation of RETHER : A Real-Time Ethernet Protocol by Chitra Venkatramani Doctor of Philosophy in Computer Science State University of New York at Stony Brook 1996 The emergence of multimedia applications has created a need for support of guaranteed service for continuous media data such as audio and video over local area networks. Among LANs, Ethernet has been the dominant architecture in the last decade and we believe that it will continue to remain popular because of its cost-effectiveness and the availability of higher-bandwidth Ethernets. However, due to the lack of prioritization of traffic and the probabilistic nature of its medium access protocol, bandwidth guarantees cannot be built over conventional Ethernets. In this dissertation, we present the design, implementation and evaluation of a software-based timed-token protocol called RETHER that provides real-time performance guarantees to multimedia applications without req...

For fault-tolerant real-time distributed systems, the probability that a message is not delivered within its real-time deadline must be small enough that it does not adversely affect system reliability. We investigate the delivery of messages for the Totem Protocol, a reliable ordered broadcast protocol that we have developed for fault-tolerant distributed systems with physical broadcasts over a local-area network. The total order on broadcast messages, constructed by the Totem Protocol, supports the maintenance of consistency of replicated information as, for example, in a replicated database. We present a methodology for determining the probability of satisfying bounds on the latency from message origination to ordered delivery in the presence of communication faults.

This paper describes several existing data link layer protocols that provide real-time capabilities on wired networks, focusing on token-ring and Carrier Sense Multiple Access based networks. Existing modifications to provide better real-time capabilities and performance are also described. Finally the pros and cons regarding the At-Home Anywhere project are discussed.