VS Peripheral Connections Getting to there from here
From "VS Workshop",  Access 88, January 1988
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Last month I briefly reviewed connection options for VS peripherals as they relate to site planning. Since that time I have had many discussions with VS users and have found that most do not have a clear understanding of the options available to them to connect their workstations and printers. Thus, I will continue my discussion of these concepts in more detail. This month we'll cover the synchronous approach (the 928 CONNECTION), and cover asynchronous devices next month.

First, some terms. Let's assume that the functional divisions of the system (the TOPOLOGY) consist of PROTOCOL, the DISTRIBUTION NETWORK, and the APPLICATION ENVIRONMENT.

Protocol: Synchronous versus Asynchronous transmissions

In data communications terminology, PROTOCOL refers to the format and timing rules both sides must observe for message interchange. A SYNCHRONOUS device is one that receives CLOCK information from the central processer and sends data bits at a fixed rate (i.e. synchronized). ASYNCHRONOUS devices transmit characters at unequal intervals and rely on START and STOP BITS to isolate the data portion of the transmission. Two important points should emerge about synchronous devices: first, they are likely to be faster since fewer bits are transmitted; second, the central processor and peripheral are actively sending timing signals whether data is being sent or not.

Like many manufacturers, Wang decided early to use the synchronous approach - probably due to it's inherent speed and reliability. (By the way, the parallel terminals discussed last month were only available for the VS 50/60/80 processer line, and comparatively few were sold.) Public demand and improvements in error-correcting data transmission algorithms have made it important for Wang to support asynchronous devices, and their async product offerings have increased steadily over the last two years.

Distributing data to synchronous peripherals

The DISTRIBUTION NETWORK consists of the physical cable, network controllers, and system software required to get the data to the peripherals. For synchronous devices, I divide distribution options into two subdivisions: cable and cable substitutes, and the Peripheral Band of WangNet.

The most obvious synchronous connection consists simply of a dual-coaxial cable connected to the back of the CPU. From what I have seen, most shops use this approach for the majority of their peripheral connections. While the dual-coax cable is costly to purchase and install, its use at least guarantees that there will be little or no interference or other degradation. Wang recommends that cables run a maximum of 2000 feet, but lengths of 3000 are common.

The easiest way to improve the cost of such an installation is through the use of Coaxial-to-twisted-pair adapters (CXTPs). These small devices translate the signal of a coaxial cable set to phone-type twisted-pair wire, and then back again at the peripheral end. I repeat, YOU NEED TWO OF THEM TO MAKE A CONNECTION. Priced between $60 and $100 apiece, they are of great benefit if your building has excess telephone wiring since you can usually separate two pairs to make a new connection. The maximum length varies from 600 to 1500 feet. I have found these little devils to be reliable and extremely cost-effective in our use.

A lesser-known option for cable substitution is the use of a cable multiplexor. These devices take advantage of the excess signal capability of a coaxial cable by "squeezing" 8 or 16 signals onto a single cable. Most units were made for the IBM 3270 world and consist of only one cable, so you will have to hope that the two coax cables remain redundant. Again, in our use these multiplexers have been relatively trouble-free.

CXTPs and cable multiplexers work by mimicking uninterrupted coax cable. The last option - the Peripheral Band of WangNet - catapults you into the realm of networking. P-band, as it is sometimes known, requires different controllers, additional communications equipment, and careful configuration. In brief, P-band sends all data through a special coaxial cable at extremely high frequency. Communications controllers (NETMUXs) near the peripheral listen for data streams intended for their devices and route them when necessary. The primary advantage is that there are far fewer coax cables to pull between floors.

In many cases, you can combine elements of the above approaches to achieve even better cost reductions. For example, our firm uses WangNet's P-band network in combination with CXTPs, with peripheral connections made through excess phone wire. Similarly, we also use CXTPs in combination with non-Wang cable multiplexers. There are limits to our bravery, however; I doubt we would attempt to combine WangNet and non-Wang multiplexers in the same connections.

Effects to VS applications

None of the options mentioned above affect the configuration of the final device, so they have little impact on the applications used. In some cases, there is some degradation of workstation speed or other side effects, but this is rare. By contrast, the controller options for asynchronous connections can significantly affect the type of applications allowed - primarily due to whether or not the controller will support the loading of microcode. (More on this next month.)

Summary: synchronous peripherals on the VS

What does all this mean? Simply that there are several options to consider in planning an installation or expansion and you should consider a few. There are significant cost advantages to be had in many installations; there is also a potential for support issues and the finger-pointing typical in any multi-vendor environment. In the experience of almost everyone I have talked to, the benefits realized from these options far outweigh the effort required to implement and support them.

Old Business: Resolutions and Corrections

As this is the start of a new year, I feel obliged to reveal a few errors from past columns that, for one reason or another, I did not mention before. Belated thanks to all of you that strive to keep me honest through your criticism. Please do your part by expressing your opinion.

Tim Barwick, Data Processing Manager for WCRB in Waltham, MA, wrote to tell me I was all wet regarding the RPGII menu option of EZFORMAT (see ACCESS, October 1987; page 16). He's used it successfully for over three years and many menus. Well, I have to admit that I haven't had much call to use RPGII, don't have a RPGII compiler, and couldn't remember WHICH utility didn't work right with RPGII. Any way, my apologies.

I also received an anonymous letter castigating me for referring to defunct Multi-Station software names in the MWSEDIT procedure column (see ACCESS, June, 1987; page 12). Yes, I admit that my employer and I were (ARE?) still using older versions of the MWS software - specifically, PERSON instead of WSPERSON and MWSRSTR instead of WSRSTR. Point given, though I maintain that the differences between the products are insignificant.

Welcome to starship Wang for another year. Again, I look forward to your comments and suggestions.

Glossary

Term	Description
928 connection	A proprietary interface used by most Wang SERIAL devices. Uses two coaxial cables and allows MICROCODE to be sent to the peripheral along with the data stream.
application environment	Those portions of a data communications environment that are visible or controllable by the user.
asynchronous transmission	A data transmission in which characters are sent at random intervals, separated by additional control data. (see also START BIT and STOP BIT)
distribution network	The physical and logical elements that move data from the central processer to peripherals. May include system software, network controllers, and the physical cabling environment.
parallel connection	A data transmission in where seven or more bits are sent simultaneously over individual channels. Opposite of SERIAL CONNECTION.
protocol	Rules governing the format and timing of message interchange.
serial connection	A data transmission in which the individual bits are sent in order, one at a time. Opposite of PARALLEL CONNECTION.
synchronous transmission	A data transmission in which characters are sent at timed intervals, with transmitter and receiver synchronized.