Because the number of truly different local network configurations  is manageably small,  a  comparative analysis of local network performance is possible. The question of performance is of concern in the design. or selection of a local network for a specific application. Given a certain c,ollection of devices, with certain traffic characteristics, a fundamental requirement is that the local network has adequate capacity for the expected load. Table I, based on studies by the IEEE 802 Local Network Standards Committee, indicates the type of load that may be offered to a local network by various devices. We would like the local network to be able to sustain a throughput that keeps up with the load, and does so without undue delays. This paper aims to show which factors are significant in determining  local  network.  performance' and to summarize recent comparative studies. The first section below shows that two basic characteristics of a local network, propagation delay and data rate, set an upper bound on  performance independent of the  mediumaccess control protocol. Next, some simple models are developed for comparing three protocols: CSMA/CD, token bus, and token ring. These are protocols for which standards have been developed [2], and it is likely that most local network products will use a variant of one of them. Finally, some comparative studies are summarized. The results cover CSMA/CD, token bus, and token ring, as weil as two other ring protocols slotted ring and register insertion.

Local network performance

Local area networks are expected to provide the communications base for interconnecting computer equipment and terminals over the next decade. The primary objective of a local area network (LAN) is tpor ovide high-speed data transfer among a group of nodes consisting of data-processing terminals, controllers, or computers within the confines ofa building or campus environment. The network should be easily accessible, extremely reliable, and extendible in both function and physical size. The rapid advances in computing and communications technology over the last two decades have led to several different transmission schemes and media types that could be used in these networks. The star/ring wiring topology with token-access control has emerged as a technology that can meet all of these objectives. The requirements of small networks with just a few nodes, as well as those of very large networks with thousands of nodes, can be achieved through this one architecture. This paper is a tutorial of the fundamental aspects of the architecture, physical components, and operation of a token-ring LAN. Particular emphasis is placed on the fault detection and isolation capabilities that are possible, as well as the aspects that allow for mtwork expansion andgrowth. The role of the LAN relative to IBM's Systems Network Architecture (SNA) is also discussed.

A local communications network based on interconnected token-access rings: a tutorial

Unlimited asynchronism is intolerable in real physically distributed computer systems. Such systems, synchronous or not, use clocks and timeouts. Therefore the magnitudes of elapsed absolute time in the system need to satisfy the axiom of Archimedes. Under this restriction of asynchronicity logically time-independent solutions can be derived which are nonetheless better (in number of message passes) than is possible otherwise. The use of clocks by the individual processors, in elections in a ring of asynchronous processors without central control, allows a deterministic solution which requires but a linear number of message passes. To obtain the result it has to be assumed that the clocks measure finitely proportional absolute time-spans for their time units, that is, the magnitudes of elapsed time in the ring network satisfy the axiom of Archimedes. As a result, some basic subtilities associated with distributed computations are highlighted. For instance, the known nonlinear lower bound on the required number of message passes is cracked. For the synchronous case, in which the necessary assumptions hold a fortiori, the method is -asymptotically- the most efficient one yet, and of optimal order of magnitude. The deterministic algorithm is of -asymptotically- optimal bit complexity, and, in the synchronous case, also yields an optimal method to determine the ring size. All of these results improve the known ones.

Distributed elections in an Archimedean ring of processors

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Distributed elections in an archimedean ring of processors

This paper examines the system design considerations of metropolitan area networks utilizing cable television networks for the delivery of a variety of services to residential customers. Specifically, this paper focuses on the technology, marketplace, and regulatory aspects of this new and expanding market.

Cable-Based Metro Area Networks

In February 1980 a group of people met in San Francisco, CA, USA, to form Project 802: Local Area Network Standards, sponsored by the IEEE Computer Society. The subcommittee held two open meetings, each followed by circulation of a draft report for comment. All claims had to have enough evidence to allow independent verification. Such evidence included source code plus data for all simulation results, all numbers and formulas for analytic results, and complete experimental conditions and measurement procedures for data analysis on actual systems. This article summarizes the subcommittee's focus on calculating the maximum mean data rate. The best available evidence, based on this study and related studies, is as follows. Token passing via a ring is the least sensitive to workload, offers short delay under light load, and offers controlled delay under heavy load. Token passing via a bus has the greatest delay under light load, cannot carry as much traffic as a ring under heavy load, and is quite sensitive to the bus length (through the propagation time for energy to traverse the bus). Carrier sense collision detection offers the shortest delay under light load, is quite sensitive under heavy load to the workload, and is sensitive to the bus length (the shorter the bus the better it performs) and to message length (the longer the packet the better it does). While this evidence is currently being examined by those actually building local area networks, other independent testing of these plots for confirmation is sought and encouraged.

Stuck

Papers

Calculating te maximum mean data rate in local area networks