Distributed-queue multiple-access (DQMA) and cyclic-reservation multiple-access (CRMA) access schemes for gigabit-per-second local and metropolitan area networks are described. These schemes are based on a slotted unidirectional bus structure, with both folded and dual-bus configurations. Like the distributed-queue dual-bus (DQDB) scheme, both the DQMA and the CRMA access schemes achieve full throughput independent of network speed and distance. They have two significant advantages over DQDB. They provide throughput fairness even at high speeds and large distances, where DQDB exhibits dramatic unfairness, and, by allowing reservation of multiple consecutive slots, they make segment labeling unnecessary and facilitate packet reassembly significantly.>

A model of commumcations protocols based on finite-state machines is investigated.The problem addressed is how to ensure certain generally desirable properties, which make protocols "wellformed," that is, specify a response to those and only those events that can actually occur.It is determined to what extent the problem is solvable, and one approach to solving it ts described.

The production of error-free protocols or complex process interactions is essential to reliable communications. This paper presents techniques for both the detection of errors in protocols and for prevention of errors in their design. The methods have been used successfully to detect and correct errors in existing protocols. A technique based on a reachability analysis is described which detects errors m a design. This "perturbation technique" has been implemented and has successfully detected inconsistencies or errors in existing protocol designs including both X.21 and X.25. The types of errors handled are state deadlocks, unspecified receptions, nonexecutable interactions, and state smbiguities. These errors are discussed and their effects considered. An interactive design technique is then described that prevents design errors. The technique is based on a set of production rules which guarantee that complete reception capability is provided in the interacting processes. These rules have been implemented in the form of a tracking algorithm that prevents a designer from creating unspecified receptions and nonexecutable interactions and monitors for the presence of state deadlocks and ambiguities.

This paper addresses the problem of protocol failures that are caused by logically incompletely specified designs. A design is logically complete if it specifies all occurrable event (message) receptions under normal operating conditions. A more stringent requirement is that of dual completeness. A design is dually complete if it neither contains unspecified event receptions nor unspecified event transmissions. Rules for creating dually-complete designs are established and a design methodology based on these rules is proposed. The problem of designing interactions that involve interrupt-masked computations is also treated.

A protocol is a set of rules which governs the interaction between processes. It is difficult to design protocols without errors because there are usually more interactions possible than anticipated. We are concerned with two-process protocols. A technique is described which identifies design errors in protocols. The technique is based on modeling a protocol as a pair of interacting graphs whereby interaction sequences are represented by path pairs (one path in each graph). The technique is currently limited to protocols that must revert to an initial or quiescent state after a finite number of interaction steps. The work represents a theory that can be automated on a digital computer.

One of the basic terminal-attachment configurations is the loop. As such, it is receiving substantial attention. But it has been pointed out that loop communication networks are relatively vulnerable and unreliable. This paper considers the single-loop reliability problem. Three loop reliability (availability) improvement techniques are investigated in detail. All three techniques are based on using an auxilliary transmission path parallel to the main loop. A comparative study shows the best techniques.

The rapidly growing interest in loop communication systems is accompanied by an increasing need to improve their reliability and reduce their vulnerability. This paper analyzes the reliability of multistage loop networks. Analytical expressions for topologies exhibiting maximum availability are obtained in terms of key-component down-time ratios. These optimal topologies are expressed in terms of terminal connections per subloop and subloops per higher level loops. The availability performance of these optimal topologies is investigated. Finally, the availability improvement obtainable by going to higher stage loop networks is investigated.