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Interconnected Nets Offer Flexibility and Meet Increased Data Demands.

When it was impractical to develop a local-area network to support 60 buildings on the University of Southern California campus in Los Angeles, we built seven separate networks and interconnected them. And because of the way we did it, should we need to grow beyond our current 7500 interfaces, we can do so quite easily.

As a major research university with a budget of $250 million with over 25,000 students enrolled in a wide variety of undergraduate, graduate and professional programs, USC naturally requires extensive computer resources.

These resources are used to support highly sophisticated projects, including those of the Advanced Imaging Lab. In this lab, researchers have applied imaging techniques to the analysis of x-rays of lung disease and to the enhancement of photographs of the moon transmitted to earth by Surveyor.

There are also, of course, university administrative functions--such as admissions, financial aid and physical plant maintenance--whose efficiency is enhanced by the use of computers. The university's famed athletic and film programs benefit too; statistics for football, track and other sports stored on a central computer are available to users at the main athletic building, and a substantial electronic mail delivery system serves the film department, among others.

Student use of computers for turning in homework on line and for other tasks is increasing dramatically. This year, more than 3,000 of the university's students have their own accounts for computer time. And recently, we've made the university library's multi-million-card entry catalog available to every terminal on campus.

While most of the network's 2200 terminals are on the main University Park campus four miles south of downtown Los Angeles, there are also a number of terminals at the health science campus, seven miles from the main campus and at other locations up to 400 miles away.

We began the network in 1981 when we linked two Hewlett-Packard minicomputers at the school of business. That original network has now expanded to seven separate but interconnected local-area networks with more than 60 computer systems, most of which are on the University Park Campus.

While we anticipated a substantial amount of growth when we planned the network in 1981, its expansion to its present size exceeded our projections. Fortunately, the planning we did then was better than our estimating; it has enabled us to grow relatively painlessly.

We knew that whatever cable we needed would be installed with considerable difficulty. The very high density of buildings on campus and a substantial amount of wiring already installed in narrow crawl spaces and pipes left us precious little room for maneuvering. An extreme example of our cabling predicament was Olin Hall of Engineering. We would have liked to install at least 50 terminals there, but because both of Olin's two-inch-diameter conduits were already occupied by telephone cables, they could only support wiring for 15 terminals.

Keeping Cabling to a Minimum

Fortunately, a number of data communications devices have enabled us to keep cabling for Olin and other facilities to a minimum. Micom Systems' Instamux470 and Instatrunk480 allow us to transmit data from multiple terminals over twoinplace twisted-pair cables.

The Instamux470, designed for in-building or on-campus installation, permits up to eight "dumb" asynchronous terminals to be connected to an in-house comuter facility or to a data PBX using the same two twisted pairs of wires conventionally used to support only a single in-house terminal. It allows each terminal to operate as if it has its own dedicated link to the computer, and all terminals can operate simultaneously, without interference. It helps us divide our cabling requirements by eight. And since our data transmissions rarely exceed 2,000 feet when using our own in-place cables, the 470s' ability to transmit up to 5,000 feet is more than adequate for our needs.

These devices are particularly useful in academic departments, where we tend to get small clusters of terminals. At first, we thought that one terminal for the chairman would suffice for each department. However, the usefulness of these devices stimulated demand for them among department secretaries and administrative assistants and it is now common for three or more terminals to be attached to each local multiplexer in each department. The 60 muxes we already have installed can support up to 240 terminals. At less than $215 per connection, this is an economical and very convenient way to link terminals to computers. Recently, we found another use for the 470s--processing electronic mail between our different computer sites and systems.

The Instatrunk480 we have installed in Olin Hall enables us to connect up to 128 terminals over two twisted pairs. At present we are sending data from 80 terminals over this device, a great improvement over the 15 possible connections for terminals we had available before the 480 was installed.

Besides the problem of cabling costs and installation, we had to consider how best to manage our networks' traffic. Specifically, we needed to provide a means of controlling the traffic generated by our users, limit the number of expensive computer ports we require, and find a way to give users access to a number of computers without hardwiring each terminal to each computer it accesses.

Fortunately, Micom's Micro600 data PBX handles all these functions quite nicely. The data switch allows the user to select the "class" of computer port they would like to access, a "class" being a group of ports associated with a uniquely definable computing resource, such as a specific data base. If any one of the computer ports dedicated to that data base is available when the user requests access, the data PBX makes the connection; if all ports are busy, the user is so informed and the switch offers to queue the user for connectionwhen a port does become available.

The dial-up capability of the data PBX makes connections simple for users at locations off campus, some as far as 400 miles away. For example, some users access our network from terminals at the health center campus, the site of the medical school and school of pharmacy, and faculty, staff and studens can even access the network from their homes. The switch enables these users, like those on the main campus, to consult a number of computers on a single call.

Researchers on the imaging lab projects mentioned earlier are among those who are able to work at home on terminals by dialing their application through the switch. These reseachers do their software development through the network. Among the projects for which they developed software was the enhancement of photographs of the moon transmitted to earth by Surveyor. The lab has also applied advanced imaging techniques to the analysis of medical x-rays, particularly in the field of lung diseases.

Preventing Unauthorized Access

While the data PBX greatly simplifies access for authorized users, such as those in the imaging lab, it can also prevent unauthorized access to the networks and sensitive fileS. It provides the computer manager with complete control over computer access, and supplies a time-and-date stamped record of every connection, every disconnection, every failure to connect along with its cause and every entry into the wait queue.

The contention feature of the data PBX, along with its statistics log that keeps track of the origins of each request for access to a class, have enabled us to achieve significant savings.

Despite periods of intense demand for computer ports, such as end-of-semester exams, we know from the switch's statistics log that we can maintain a seven-to-five ratio of terminals to ports and still provide a high level of service.

The log also informs us that the typical session of an undergraduate user lasts 20 minutes, that of graduate students 30 minutes, while researchers and certain users in administration are often on-line virtually all day--important facts to know in balancing port usage. The log also confirms that sessions on the IBM systems are longer than those on DEC systems, a reasonable conclusion considering the 4341s and the 3081 are used for research and administrative applications. Our software staff is developing programs to help us make even better use of the data the statistics log provides.

The data PBX offers a great deal of flexibility in building networks for reasons beyond its switching, port contention and statistics features. First, the number of bays in the switch may be expanded to 12, allowing it to serve up to 1,504 lines/ports and to maintain 489 simultaneous connections. The ability to add up to 11 bays, each serving 120 or 128 ports, is a decided advantage when a network is growing as fast as ours. The seven switches we now have range in size from 3 to 12 bays to reflect the number of lines/ports they need to serve.

These devices promote ease in building networks because they may be interconnected. It is this feature that made it possible to join our seven separate data PBXs and solve our local-networking dilemma. In fact, it is possible to gain access to a resource by going through most of the interconnected switches.

The amount of communications through specific channels is reflected in the number of trunks between the switches. There are 192 trunks between the engineering computer lab and the university computing center, eight trunks between the school of business and the engineering computer lab, 32 trunks between the financial services and the engineering computer lab, 64 trunks between parking structure D and financial services, eight trunks between KUSC and the university computing center, 32 trunks between financial services and the university computing center, and 16 between the business school and UCC.

There are other means of telecommunications we are exploring. In addition to expanding our use of multiplexers and port selectors, we have installed a 256 channel (TIC) GE Gemlink Microwave, which at present is accessed through the engineering computer lab and university computing center switches. We are also using the Telenet network, which also is accessed through a data PBX.

New projects in the imaging lab, such as teaching robots to respond to changes in colors and textures, the search for new ways to employ the communications equipment we already have, and the ever-increasing number of students who need access to computers, are certain to provide us with plenty of challenges in the future. We are confident, though, that our network has the flexibility to continue to grow to meet our increasing needs.
COPYRIGHT 1985 Nelson Publishing
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Copyright 1985 Gale, Cengage Learning. All rights reserved.

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Author:Wiedel, J.
Publication:Communications News
Date:Dec 1, 1985
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