Mechanical design of the HP 4980 Network Advisor - protocol analyzer - Technical

Hewlett-Packard Journal, Oct, 1992 by Kenneth R. Krebs

The package design for the Network Advisor was guided by the electrical. mechanical, and ergonomic requirements of a PC-based protocol analyzer.

The HP 4980 Network Advisor package consists of 31 injection-molded parts, 15 sheet-metal parts, 19 cables, nine printed circuit boards, two custom-machined parts, a custom power supply, flexible and hard disk drives, a color or monochrome LCD (liquid-crystal display), and numerous other custom and standard parts. Its hinged, fold-up, flatpanel display and fold-down keyboard are designed to make it easy to use the Network Advisor either on a desktop (see Fig. 1 on page 6) or in a floor-standing position (see Fig. 1), while providing maximum portability when closed. It has interchangeable network interface modules that mount to the underside of the instrument. The overall package measures 5.9 inches high by 14.3 inches wide by 16.8 inches deep and weighs 25 pounds fully loaded.

Design Decisions

Mechanical design for the Network Advisor was driven by several major decisions made very early in the product definition phase of the project. The first of these was to make the instrument DOS-compatible and, therefore, PC-based. Because of the dominance of the DOS operating system in the LAN testing market, our customers demanded DOS compatibility in our products.

While we did not intend to market the Network Advisor as a PC that does protocol analysis, but rather as a protocol ana* lyzer with an embedded PC, we did feel that the ability to run standard PC applications (e.g., word processors and spreadsheets) would be a marketing benefit. Therefore, we needed a full-screen, 80-coluum display. Since the VGA standard was emerging as the choice of the future, we chose it for our instrument. A second result of the DOS decision was the requirement for a full-function, full-size PC keyboard and internal flexible and hard disk drives.

A second decision (a result of the first design decision) was the need to be able to install at least one and preferably two standard, off-the-shelf, full-length, low-profile PC cards.

The third major decision was the choice of a flat-panel technology over a CRT. The VGA decision dictated a CRT too bulky and heavy to meet our portability requirements. Also, CRTs have some manufacturing disadvantages we wished to avoid (e.g., pincushioning, alignment, high voltages, and shielding). We also felt that the market perception of flat panels as a leading-edge technology would be beneficial.

We investigated several flat-panel technologies including electroluminescent, gas plasma, and liquid-crystal. Electroluminescent and plasma displays were costly, had high power dissipation and lacked sufficient grayscale shades. After investigating several types of LCD, we chose a cold-cathode, backlighted, film-compensated LCD as having the best combination of brightness, contrast ratio, cost, and weight. Just before our tooling release, Sharp Inc. introduced a 10.4-inchdiagonal, TFr (thin-film transistor) active matrix, color LCD, which is larger and thicker than the monochrome LCD we had chosen. After a redesign effort to accommodate the larger display, the display housing injection mold was de* signed with inserts to allow for both color and monochrome versions.

Because there are several different networking technologies (e.g., token ring network, Ethernet, fiber distributed data interface (FDDI)), our instruments need different hardware sets for data acquisition and analysis and different external connector types for connection to the network. In the past we accomplished this by offering different interface modules (pods) cabled to the base instrument (mainframe). Considering how to handle different network technologies led to our fourth major design decision which was to integrate the pods into the mainframe so that nothing external would be required or would hang off the instrument and get in the way during operation. These integral pods needed to be easy to install and remove. The difference in networking technologies also required that the network line and event status LEDs on the front panel (up to 12 pairs with each pair consisting of one red and one green LED) be easy to relabel since different network types have different numbers and types of lines and different nomenclatures.

Another important design constraint was the requirement that the user be able to operate the instrument conveniently on a desktop and on the floor. Frequently our customers need to make their network connections in a small control room, a closet, or around the back of a patch panel where tabletop space is unavailable.

Since many of our customers are third-party network service providers who travel with the instrument to their customers' sites, the instrument had to be truly portable and rugged. This meant that it had to fit under an airline seat and weigh less than 33 lb (we set a target of 20 lb and achieved 25 lb with a fully configured instrument). This also meant that we needed a carrying case not only for the instrument but also for appurtenances such as interface cables and different interface modules.