In the sixties and early seventies, major activities in networking were focused on private and public data networks using either circuit and packet-switching technology or integrating both switching methods into a single network. In this time frame, manufacturers of main frames defined and implemented network architectures, ISO started work on the reference model of the Open-System Interconnect Architecture, and CCITT recommended the X-series of interfaces.Local-area communication networks (LAN's) represent a comparatively new field of activity which can be viewed as an extension to data networks for making high-speed packet-switching services available to the in-house domain. Currently, much research and development work is being pursued in this field, both at universities and in industry. The term local refers to communication on the users' premises, i.e., within a building or among a cluster of buildings.Local data and voice communication are not new. A typical example of a system widely used today for local data communication between hosts and display terminals is a star configuration where the terminals are attached to control units tightly coupled to a processor via I/O channels. The necessary terminal control functions are provided in the control unit and shared among a set of terminals. The most widely used local communication system is the Private Automatic Branch Exchange (PABX). Most PABX's installed today are optimised for real-time voice, and use analog technology.

Architecture, performance, transmission system, and wiring strategy of a token-ring local area network implemented at the IBM Zurich Research Laboratory are described. In the design of the system, particular emphasis was placed on high reliability, availability, and serviceability. To ensure robustness of the token-access protocol, we employ the concept of a monitor function which is responsible for fast recovery from access-related errors. Our protocol supports asynchronous transmission of data frames concurrently with full-duplex synchronous channels, e.g., for voice services or other applications requiring guaranteed delay. The delay-throughput performance of the token ring is shown to depend very little on data rate and distance. The transmission system of the ring is fully bit synchronous and allows insertion/removal of stations in/from the ring at any time. A mixed ring/star wiring strategy is used which provides the means for both fault detection and isolation, and system reconfiguration, and allows wiring of a building systematically.

The prime objective of the present paper is to analyze the performance of HDLC Balanced Class of Procedures, i.e., to quantitatively study the interaction among a multiplicity of parameters which are procedure specific, characterize the properties of the transmission medium, and identify the operational characteristics and requirements. The approach taken is to consider two kinds of operation: a saturated case characterized by maximum throughput as the most suitable measure of performance, and a nonsaturated situation for which waiting and transfer times are the appropriate measures. The analysis is performed by means of both simulation and analytic techniques. Within the simulation model, the information transfer phase of the HDLC procedure was implemented in full detail. The key idea of the analytic approach is to use a so-called virtual transmission time, a quantity comprising both the real constant transmission time of a message and the duration of recovery actions in case of transmission errors. It allows the performance measures to be represented by explicit and easily-computable expressions. The results provide a fundamental insight into how the most relevant parameters interact and determine performance.

The prime objective of the present paper is to analyze the throughput characteristics of a multi-processor configuration for packet switching-suggested in the context of an integrated network for circuit and packet switching-and to identify the major parameters on which it depends. The results provide a fundamental insight into how the most relevant system and traffic parameters determine throughput as a function of the number of packet-handling modules. In particular, it is shown that the proposed partitioning of the packet-handling function does indeed permit high throughput before saturation is encountered.

Based on the premise that flexibility is a primary objective for future data networks, it is proposed to integrate circuit switching (CS) and packet switching (PS) in a single network. This paper addresses the switching node in such a network. A novel node concept is presented, imposing PS on a CS structure. Connection management and node control functions on the one hand and packet processing/storing on the other are performed by two groups of modules. The modularity requirement leads to very small, simple processors built into storage modules for packet handling. Considering the high throughput requirement of about 1200 packets/s/node, configurations may exceed 30 packet-handling modules. The wellknown saturation effect of multiprocessor systems, i.e., decreasing incremental throughput with increasing number of processor modules, is overcome by a new concept of intermodule communications, taking advantage of the particular data-communications environment. Intermodule communications-and therefore overhead-have been significantly reduced. As a result, systems throughput for fixed processor module utilization is nearly a linear function of the number of modules, the deviation from linearity being less than 10 percent over the range considered.