I'll be happy send you some links if you have an extra $3,000 to $5,000 to spend. Simple continuity testers, which are relatively inexpensive ($30-$50, or probably less at Radio Shack, etc.), send a tone down the line or perform a roundtrip DC resistance test. They do not measure impedance/line capacitance loading or noise at RF frequencies. They are not adequate tests for certifying cables and do not guarantee, by any means, that an Ethernet cable will operate at Ethernet speeds. Your Ethernet adapters automatically perform a better test than continuity testers as they send multiple pulses down the line and Link LEDs on them will not light-up unless the cables are wired so that the correct Ethernet transmitter pins are connected to the correct Ethernet Receiver pins. However, the Link LEDs can be lit and the cable may still not work. Short of expensive test equipment, the best test I know of is to copy and time the 100 Mbytes as I stated. If it sends the 100 Mbytes in a reasonable time, you will have a cable that can send many files in the installed environment without excessive retransmissions caused by corrupted packets. If you don’t have a network, then first check the Link LEDS, and then perform the copy test. I have done this many times. My cable tester has been gathering dust. LarryQ. Why would the Link (or LNK) LEDs be on solid, if there is a faulty cable connecting two Ethernet devices?
A. Solid Link LEDs usually indicate a good network connection between two network adapters connected by a crossover cable or between a PC and hub or switch connected by straight-thru cable, but not always...
10BASET and 100BASE-TX Ethernet interfaces have two transmit pins (+ and -) and two receive pins (+ and -). The rest of the pins are unused. Transmit + pins must be connected to receive + pins, etc.
Solid LINK (or LNK) LEDs on two 10/100 Ethernet devices (network interface card--NIC, hub, switch, etc.) that are connected together indicates that the two transmit pins are connected to the correct receive pins. It does not, however, guarantee that the cable is made properly, is made with the correct cable and connectors, and that will reliably transmit data. For example, the Ethernet standard specifies that the transmit pins be connected to corresponding receive pins with wires from the same twisted pair. It is certainly possible to connect a set of pins using one wire from one pair and another wire from a different pair. The reason it is possible to get solid LINK LEDs and unreliable data transfers is that link determination is made with a link integrity test pulse which is transmitted at a much slower rate than the actual Ethernet signals that transfer data. Broken, disconnected, improperly terminated (coax), or miswired cables are responsible for over 70% of all LAN problems.
