Triplett TVR10/100/1000 - Manual (Page 43)

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some devices are programmable, allowing you to "force" their speed
and duplex. "Forced" devices, likewise, may not send link pulses.
Because the TVR1000 uses link pulses to determine the speed and
duplex, if there is no link pulse, no speed LEDs will light. This does
not mean that the devices cannot communicate. It means that the
TVR1000 cannot detect the details about the device. Fortunately,
most LAN devices constantly provide link pulses.
Common cable problems: The cable category (Cat 5, Cat
5E, etc.), the number of twisted pairs in a cable and the correct
fabrication of the cable all affect the communication capability of a
network. For instance, 10Base-T only requires two pair cables. Two
standards exist for 100Base-T. One requires two pair cables and the
other requires four wire pair cables. 1000Base-T requires 4 pairs.
If a two pair cable is used when four pair cables is required, a slow
connection will be permanently established. Another common cable
problem is caused by inverted pairs: A pair exists but the pins are
inverted (e.g. 1,2 is 2,1). Make sure you use the proper cable type.
Cat 5E cable is required for 100 MB/s and 1000 MB/s speeds.
LAN type Cable Pairs Required
10Base-T 1,2 3,6
100Base-T (Type 1 or TX) 1,2 3,6
100Base-T (Type 2 or T4) 1,2 3,6 4,5 7,8
1000Base-T 1,2 3,6 4,5 7,8
As is shown in the above table, 10Base-T or 100Base-T (Type 1 or
TX) LAN ports use two pair cables. 100Base-T (Type 2 or T4) and
1000Base-T LANs require all four pairs. It is best to use a minimum
of Cat 5E cables with all four pairs to insure compatibility with all
three types of Base-T LANs.