Use of Multiple Networks in the Xerox Network System

Managing information is an integral part of today's office, and Xerox's Network System is a distributed office information system that provides tools for doing this. With these tools, office personnel can create, store, retrieve, display, modify, reproduce, and share information in ways that encourage creativity and increase productivity. Workstations like Star help to simplify creation, modifiying, and displaying information. I Electronic filing, printing, database, and mail systems simplify storing, retrieving, reproducing, and sharing information. With the continuing improvements in the price/performance ratio of computing and communications, the structure of computerized office information systems is changing. We no longer need large centralized systems to realize economies of scale. Instead, we can push intelligence back into the workstation, and decentralize resources by function into dedicated servers to create a system that is a collection of loosely coupled elements tied together by a communication network. The Network System is just such a system, in which expensive resources are shared and information is exchanged among users. Within an organization, we typically find natural localities of activity and interaction. Interaction between localities generally decreases as they are farther apart. While the nature and characteristics of the interaction between close and distant stations are different, both are essential to the functioning of an organization. The Ethernet local computer network24 provides digital transmission of data, and satisfies most of the requirements for local office communications. The Ethernet, however, was designed in the context of an overall network architecture and is viewed as one component of an internetwork communication system that serves many diverse devices connected to many different kinds of networks.5-8 An internetwork architecture allows the communication system to be reconfigured to satisfy the immediate and future requirements of the user. For example, the Network System may have only one Ethernet initially and then be expanded (without software modification) to contain two or more Ethernets, which are interconnected directly or via other communication media, whose choice depends on the volume, frequency, and dispersion ofcommunications. Public and private packet-switching facilities can be used to carry higher dispersions of low-volume office communication, and as facilities for lower cost, higher rate, modemless digital transmission become available, they can be used to carry higher volumes of data. Of concern in this article are the major features of the Network System's internetwork communication system, in particular, its ability to use different kinds of networks (Figure 1). Protocol layers above the internetwork communication system permit different kinds of office services to be added as the need arises, thereby allowing an organization to minimize the initial purchase cost and to control any system expansion. The article also describes how the Network System can be connected to systems (network-based or stand-alone) from other vendors that obey different protocols by using protocol conversion gateways at different levels.