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In This Issue - August 1996 Volume 46 Issue 4

CURRENT ISSUE - August 1995 Volume 46 Issue 4 Most local area networks (LANs) today have the same bandwidth, or maximum data transfer rate, as ten years ago-10 to 16 megabits per second. In the same time period the speed of computers and the size of files created by sophisticated applications have increased a hundredfold. As we might expect, the result is a rising level of user complaints about long response times, symptomatic of network congestion caused by too many users and a high volume of data-intensive applications such as database access, image analysis, desktop publishing, network printing, and computer-aided design. Multimedia applications demand even more bandwidth and will only make the situation worse unless the bandwidth of these LANs can be increased. An increase in the data rate to 100 megabits per second would be a major improvement. Because existing local area networks already represent major investments in wiring, it would be ideal if the increased bandwidth were made available over existing twisted-pair building wiring, with fiber-optic cabling an option. The ideal technology would also be compatible with existing network protocols, topologies, and software, and would offer guarantees that such multimedia applications as real-time video would not experience unacceptable delays because of congestion. In 1992, HP Laboratories in Bristol, England and the HP Roseville Networks Division in California established teams to work on this challenge. Official approval of their solution, the proposed IEEE 802.12 demand priority local area network standard, is expected soon. This new networking technology, called 100VG-AnyLAN by HP, is introduced in the article on page 6. It offers an affordable upgrade path for congested LANs based on the IEEE 802.3 (Ethernet) and IEEE 802.5 (token ring) standards, as most existing LANs are. It provides a 100-megabit-per-second data rate with guaranteed bandwidth and bounded delay for time-critical applications such as interactive video. Perhaps best of all, a large proportion of network owners won't have to rewire their buildings to convert to it. The demand priority protocol, which is explained in the article on page 13, is implemented by intelligent hubs, or repeaters as they're called in the standard. The hubs use a round-robin technique to give all of the nodes in the network a fair opportunity to transmit data. Two priority levels make it possible to give priority service to time-critical applications. For transmission over common unshielded twisted-pair building wiring, the standard's quartet signaling technique takes advantage of the four-pair cable used in most buildings, transmitting at a rate of 25 megabits per second over each pair (see the article on page 18). Techniques for transmission over 25-pair cable, shielded twisted-pair cable, and fiber-optic cable are also specified in the standard. A spectrally efficient coding method called a 5-bit/6-bit block code (page 27) makes it possible to transmit at 25 megabits per second over unshielded cable without exceeding electromagnetic interference regulations. The coding scheme also provides the needed levels of error detection and correction. The article on page 33 tells how 100VG-AnyLAN meets the needs of multimedia applications, and the article on page 39 describes the design of an intelligent hub based on special repeater and transceiver chips.

Optical character recognition or OCR is the process of scanning a hard-copy page and turning it into computer editable text. It's harder than you'd think. Many documents a human can read easily simply can't be converted accurately by an ordinary OCR program. Small or closely spaced text, thin lines, multiple columns, and graphics can mean major trouble for an OCR program. HP AccuPage technology (page 43) provides image processing transforms that are used in OCR software to provide much more accurate text conversion and the ability to capture text and pictures at the same time. HP AccuPage techniques include adaptive threshold determination and upscaling of small text.

The HP S1010A flat panel display is a color liquid crystal display (LCD) monitor that's designed as a lighter, lower-power, smaller-footprint direct replacement for conventional computer monitors-you can unplug a conventional monitor and plug in the HP S1010A. The article on page 51 tells how the analog red-green-blue signals from the computer are converted to digital signals to drive the LCD, and how the 256-level colors from the computer are converted to noise-free 8-level colors for the LCD.

An application software package is typically composed of many components. Each component requires a design decision: to buy or to build. Experts at HP Laboratories who advise HP product divisions in such decisions have been recommending the use of third-party software whenever it makes sense economically. In the article on page 61, Wes Higaki of HP Laboratories proposes an improved economic model for buy-or-build decisions. The model extends an existing model with an extensive list of costs and benefits, net present value calculations, and estimation techniques for costs and benefits.

If you're a designer of an application-specific integrated circuit (ASIC), your choice of a supplier is critical. Choosing one with unrealistic performance claims can lead to failure, while choosing one with overly conservative claims leads to higher costs than necessary. For an objective way to evaluate ASIC suppliers' performance claims, HP procurement engineers have been using two benchmark circuits. As described in the article on page 66, they collect supplier sample data for the two circuits, calculate technology constants for various parameters, and plot the results to spot optimistic or conservative claims.

R.P. Dolan

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