USA Local area n e t w o r k s - are they almost almost here?

Since 1970, there has been a tremendous increase in our depen- dence on computers for a myriad of applications. There has also been a trend toward smaller and cheaper computers, both for standalone, personal computing, and for distri- buted-processing applications. These developments have led to a perceived need for lower cost, higher bandwidth ways to intercon- nect a number of machines within a small area.

Long-haul intercommunication networks are now well established: they are included in computer manufacturers' product lines, sup- ported by a variety of interface equipment manufacturers, stan- dardized by international bodies, and used, at least for limited pur- poses, by a substantial percentage of the computer community. How- ever, the technology used in these nets is not quite the optimum solu- tio for local interconnection, as users and manufacturers are well aware. The major issue in the design of communications networks has been the efficient cost-effective use of shared transmission facilities; it is common knowledge how much faster computing costs are dropping compared to communications costs. In a local environment, within the user's building or building com- plex, this is not the case. In fact, it is easy to acquire a large bandwidth (Mbit/s) just by ordering cable; the trick is to get those bits transferred between machines, without sinking in the cost of switches or expensive computer interfaces.

Local networks designed to take advantage of the cheap bandwidth have been around for several years. The two favourite approaches have been the ring net and the bus net. Both use cable as a broadcast

medium, with each node able to send and receive messages from all other notes, and with no specialized packet or circuit switching ele- ments. The major difference be- tween these approaches is that each interface in a ring net acts as an active repeater for 'through traffic'; in a bus, the interfaces are passive taps, unless the node is transmitting its own messages. Within these approaches, there have been varia- tions in modulation schemes, pro- tocols for sharing the cable band- width etc. There are also wide differ- ences in application and per- formance among local net imple- mentations: bandwidths go from about I Mbit/s to about 50 Mbit/s, and interface costs from hundreds of dollars to tens of thousands of dollars per interface.

Most of the local networks are still laboratory experiments. There are a few products, such as ISl's process control network, and Network Sys- tem Corporation's fast and expen- sive Hyperchannel; but off-the-shelf hardware, and especially systems, are not yet available for efficient local networking of small and medium sized machines. In 1979, there was a tremendous increase in local net interest, standardization, and product development; 1980 promises delivery of interface hard- ware and even complete systems from several sources.

Probably the best known local network in existence is Xerox's Ethernet. While this began at their Palo Alto Research Center as an experiment, it is now in such wide use, both at Xerox and at various universities and nonprofit com- panies, that it has demonstrated both the feasibility, and also the real usefulness, of local networking. The research Ethernet links personal

minicomputers, called Altos, with each other, and with larger service computers, by a bus running at about 3 Mbit/s. Recently, Xerox announced a local network product that links, not the Altos, but their Xeros 360 word processor. Deliver- ies of this packaged local network system will begin in Autumn 1980.

The Xerox product announce- ment was only part of the activity in the field. For one thing, 1979 was a year of conferences and conference sessions on local nets. Mitre and the US National Bureau of Standards sponsored a three day symposium in Boston in May 1979, which was devoted entirely to local area com- munications networks. Attendance was about 200 people, and the program included everything from military shipboard networks through automated offices. In October 1979, the 4th Annual Con- ference on Local Networks was held in Minneapolis. This meeting, spon- sored by the University of Minne- sota, had previously been quite small and rather exclusive. It had been dominated by the large com- puter centre people and by their most useful local network product: Network Systems Corporation's Hyperchannel. In 1978, there was an evening session at the confer- ence that included a debate on 'what is a local network', and con- cluded that 'if you think you have a local network, then you do.' Pro- posed definitions in 1978 included everything from processor-peri- pheral buses to satellite networks, if they were owned by a single com- pany. In 1979, the conference was jointly sponsored by the university and by the IEEE, speakers came from all over the US and from Europe as well, and the presentations were far more varied, including both big computer nets and small-scale ter- minal networking efforts. Besides these conferences devoted entirely to the subject, it seemed that every computer conference of any size was required to devote at least one session to local network issues.

Lately, there has been great interest in standardization of local network interfaces, probably re-

Vol 3 no 3 june 1980 143

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lated to the imminent product announcements. An IEEE standards group has been organized, and had its first meeting in San Francisco just after Compcon in February, 1980. This meetingwas attended by about 70-80 people from laboratories, computer manufacturers, peri- pheral manufacturers and systems houses. The group's stated intent is to arrive at a standard which will 'pro- mote compatibi l i ty between equip- ment made by different manufac: turers'. The initial suggested direc- tion, put forward by organizer Maris Graube, of Tektronix, is a bus net- work some-what similar to Ethernet running at bus speeds of at least 1 Mbit/s, and using a layered protocol approach to facilitate I nternetwork connections. Other standards acti- vity includes increased interest by some of the American National Standards Institution task groups in both the data communications and computer interface areas.

The local network developers and standardizers are aware of the more mature packet-switched network technology, and are looking to net- work architectures which can incor- porate both kinds of interconnec- tion. Xerox has already developed a protocol architecture, PUP, for Ethernet and packet-switching net- works, and this will allow its announced office products net great f lexibil i ty in connecting on- and off-premise equipments. The Defense Research Projects Agency (DARPA) is also connecting local, satellite and packet-switching nets, together with its essentially similar internet, which standardizes proto- cols at the host-host internet data- gram layer, and permits lower levels to take advantage of the characteri- stics of particular communications media.

Even more recent than the Xerox 360 announcement, have been several announcements of OEM

local networks. The offerers of these product lines provide the local net- work interface hardware, interface controllers (which are usually micro- processors) and varying amounts of software support, network control, development support, etc. Once the local network basics are avail- able as real off-the-shelf products, it is likely that development of user- oriented systems will fol low rather quickly.

In summary, it looks like 1980 will see the delivery of the Xerox 360 local network product, the availa- bility of several OEM products for integration by systems developers, and the formation of more stan- dards groups. Real progress on stan- dardization, and integrated network products from computer manufac- turers, are coming - - but later.

Ruth Nelson

Human Interaction with Computers H.T. Smith and T .R.G. Green Apri l 1980, viii + 370pp. Hardback: £12.40 (UK only) /~29.00, O. 12.652850.0 Paperback: £6.40 (UK only) /~15.00, o. 12.652852.7

Despite the proliferation of computer systems we do not yet know how to use them fluently. They are rigid and unyielding, unable to accomodate themselves to the looser habits of their users. Even the most sophisticated systems designed for the user with no special training have unexpected problems. Many people from many disciplines are struggling to narrow the gap between the computer and the user. This book aims to provide a focus for efforts in different areas. Despite the common problems there is no substantial agreement about solutions, only about the appropriate criteria to apply. Frequently the problems are many-faceted, that is they are problems of sociology as well as of technology. The simple faith that computers could easily be absorbed must now be abandoned; cooperation and communication is needed between the different disciplines.

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