12.3. 10base2 (thin coax) Ethernet Cabling

10base2 is an ethernet cabling standard that specifies the use of 50 ohm coaxial cable with a diameter of about 5 millimeters. There are a couple of important rules to remember when interconnecting machines with 10base2 cabling. The first is that you must use terminators at both ends of the cabling. A terminator is a 50 ohm resistor that helps to ensure that the signal is absorbed and not reflected when it reaches the end of the cable. Without a terminator at each end of the cabling you may find that the ethernet is unreliable or doesn't work at all. Normally you'd use `T pieces' to interconnect the machines, so that you end up with something that looks like:

|==========T=============T=============T==========T==========| | | | | | | | | ----- ----- ----- ----- | | | | | | | | ----- ----- ----- -----

where the `|' at either end represents a terminator, the `======' represents a length of coaxial cable with BNC plugs at either end and the `T' represents a `T piece' connector. You should keep the length of cable between the `T piece' and the actual ethernet card in the PC as short as possible, ideally the `T piece' will be plugged directly into the ethernet card.