A Cheap Solution to the "Rat's Nest of Cable" Problem: Part 3

by Lee Hudspeth

TNPC subscriber Darren Pilgrim took the time to submit a detailed rejoinder to two of the suggestions from my previous cabling article. It was so nicely put together that I wanted to share it with you.

Darren says, "In response to the suggestion that you run everything through data switches:

This can work well, however there are three caveats:

First, some cables are very sensitive to EMI (electromagnetic interference) and RF (radio frequency) interference. Macintosh SCSI cables (DB25), long parallel cables (over 4 meters), and video cables (HDDB15 cables are the worst). Every time you add a break in the cable to add a port connection (there's at least two at the data switch) you add interference to the cable.

Second, some cables should never be switched. Network and SCSI cables, digital audio cables (SPDIF or Sony Philips Digital Interface Format), and any serial or parallel cable with a live connection on it (i.e., null modem networks and parallel Zip drives) all do real-time communication over the line. Breaking that line can cause problems on both ends of the cable, even damage whatever device the cable is attached to.

Third, some interfaces, while they can be switched, sometimes do not respond well to being switched. Disconnecting the mouse or keyboard can crash a system, or hang the mouse or keyboard driver. You can even do permanent damage to a PS/2 mouse or keyboard hardware controller by switching the mouse or keyboard while the power is on. With video, if you have a monitor with PnP enabled, disconnecting the monitor can make Windows do strange things, such as try to detect a new monitor when reconnected. A good electronic KVM (keyboard, video, and mouse) switch will hold the connection and generate the signals needed to make the disconnected computer think that the keyboard, mouse, and video are still connected, preventing crashes and driver hangs.

In response to the twisted pair network cable warning:

UTP (Unshielded Twisted Pair) is designed to handle relatively large amounts of interference. The levels of interference generated by house-current power cables and normally-operating video cable isn't enough (by far) to disrupt the signals on UTP cable. Any interference with the network link you get is likely the result of a UTP cable not meeting Category 5 specifications. (Category 5 provides for specifications on signal bandwidth up to 100 MHz and greater.)"

Thanks for the write-up, Darren!