General FAQs about parallel printer switches

+S Last Update: 15.12.2004 Close

Why use printer sharers when I already have a network?
The widespread use of networks seemed to many to mark the demise of the printer sharer. This assumption is based on the misconception that printer sharers and networks are competing systems. In reality, they complement each other. 95 % of LEUNIG printer sharers, for example, are used in large networks. There are several important reasons for this:

• Over the past ten years, the data volume of the average print job has increased 1000-fold, which has lead to a significant increase in network traffic.
• Printing over a network is still prone to errors and relatively unstable compared to local printing.
• Printing locally through the printer port is usually faster than printing over a network.
• many cases, document printouts are too important to rely on the network.
• In most cases, printers are located near the workstations using them. Why, therefore, put up with the above disadvantages? Taking into account the expense of routing printer cables to the nearest hub or switch, even the cost advantage of using the network tends to become insignificant. Printing locally through the printer port is usually faster than printing over a network.
  

Why, then, the are there fewer and fewer of these devices available?
It is true that sales and availability of this product have dropped. This is only partly due to a reduced breadth of application of these products, the main reason being that this type of device has gained a bad reputation.

Why is that?
In the early to mid-nineties, Taiwanese companies started to flood the market with cheap printer switches that cost only a fraction of the established brand products and were touted to have the same functionality. In reality, the Taiwanese manufacturers had neither the required knowledge of the problems associated with parallel ports nor the necessary development resources. Most manufacturers of quality products gave up trying to compete when the bidirectional IEEE 1284 interface began to establish itself in 1994. This standard made a clean implementation of bidirectionality and automatic printer sharing impossible.
Some manufacturers still make bidirectional printer sharers without pointing out the basic problems, which does little for the reputation of these devices.

The issue of bidirectionality

Introduction
All printer ports are "bidirectional" in the sense that Paper Out and other error messages are reported back to the computer. Today, the term is usually applied to true communication between the two devices. This development was driven by the availability of parallel port devices such as tape drives, all-in-one printing devices (combined fax machine, printer and scanner) and the desire for simpler printer designs with fewer buttons. The main reason, however, was the central management of printers through networks, which marked the inception of IEEE 1284. This new standard resulted in widespread interest in bidirectionality, which - due to technical problems - has now largely subsided.

Most of the LEUNIG printer sharers are not bidirectional. Why is that?
Making a bidirectional printer sharer does not, in itself, present any technical problems. 4Print2, for example, supports bidirectionality, but we do not use this feature in the product because bidirectional printer sharing presents some fundamental problems.
However, in the conventional sense, all our products are bidirectional, so that paper jams, etc. are reported to the PC.

So what's the problem?
The problem does not lie with the switchboxes, but in the communication between PC and printer. A switchbox - regardless of whether it is automatic or manual - must, by its very nature, interrupt the connection between printer and PC to establish a connection with another PC. In doing so, it must also interrupt all communications between the two devices.
The printer then communicates with a different computer without knowing it, and the PC is unaware that the printer is no longer available to it and - believing it to be still connected - continues trying to print to it.

What problems can occur?
There are no general rules. The answer to this question depends on the printer model and can even vary with the printer driver version being used (the communication protocol between printer and PC is proprietary and depends on the printer manufacturer). Other factors are the volume of printed data and how often the printer is changed. Error messages may occur several times a day or not at all.

Will these problems be solved by the IEEE 1284 standard or by EPP or ECP?
No. IEEE 1284 actually gave rise to the problem, since it allows for a connection of up to 64 peripherals to a single PC, but not of multiple PCs to one peripheral.

Does USB not present a solution?
No. Like IEEE 1284, USB has a "1 - n" or "single-host" topology, which means that a PC can communicate with many peripherals, but not the other way round. There are workarounds, but USB does not solve the basic bidirectionality problem.

So what do you recommend for parallel ports?
Disable bidirectionality in the printer driver. Because of the problems mentioned earlier, all reputable printer manufacturers provide this option. Some printer drivers even have bidirectionality disabled by default. The loss of convenient features is minimal for most printers. There are, of course, special-purpose and multifunction printers that only work with bidirectional communications enabled, and these do not allow printer sharing.