pin 6

snipped-for-privacy@gmail.com schrieb:

Mike,

it is important to use twisted pairs of wires in the cable for balanced transmission lines. The standard wiring scheme "A" *) is:

Pair No. 1 is connected to pins 4 and 5. Pair No. 2 is connected to pins 3 and 6. Pair No. 3 is connected to pins 1 and 2. Pair No. 4 is connected to pins 7 and 8.

Pair No. 1 is used for telephone lines. Ethernet and Fast Ethernet use Pairs 2 and 3. Gigabit Ethernet needs all four pairs.

If you try to use pins 3 and 4 you will get what we call split pairs with excessive crosstalk resulting in high bit error rates or no link at all.

Thomas

Sideways compatibility.

The RJ style jacks are also used for telephone wiring, where, in an 8 pin jack the primary phone line is on pins 4,5, and the secondary phone line on 3,6.

It is required for ethernet, and a very good idea for phone lines to use twisted pairs. That is, the two wires used for a given signal should be twisted together.

Compatibility with one and two line phones meant pairing (4,5) and (3,6). The electrical characteristics of (1,2) and (7,8) are better than (2,7) and (1,8) as used by three and four line phones. It seems that the latter was considered rare enough not to worry about.

Not using (4,5) for pre-gigabit ethernet reduces problems plugging into the wrong jack.

-- glen