Q & A on 100BaseT and 10BaseT Cabling,

Q: Can 100-Base-T ethernet cables be used with 10-Base-T cables? In which case, some pairs are just ignored?

A: There are two parts to the answer. First, as long as the cable meets the standard (i.e., category 5), the same type of cable can indeed be used for either. Second, twisted pair Ethernet uses RJ-45 connectors (8-pin modular connectors that are larger versions of 4-wire connectors used on a conventional telephone). As long as all eight wires are connected, the same connector can be plugged into either 10 or 100 Mbps equipment.

As a practical matter, most network interface cards are now called ``10/100 cards'' because the hardware automatically senses whether it has been connected to a 10Base-T hub or a 100Base-T hub. The same cable can be used between the computer and the hub in each case. In our lab, for example, when we ask students to measure 10 and 100 Mbps Ethernet, they switch computers from one to the other merely by changing the hub -- the same cable is used.