# CAT5E and T568A vs. T568B

Homework Helper
Gold Member
Searching "t568" doesn't bring up any matches: presumably the topic ain't been covered.

As far as stringing ethernet cables, T568A and T568B connector standards for CAT5E are transparent to the hardware being connected so long as one preserves the standard (and gender?) at both ends of a cable run. Net sites discussing A & B include caveats regarding mixing; A won't work with B, and vice versa, with comments that video goes to hell, or other nagging problems, intermittents, sensitivity to phases of the moon, you name it.

The questions: has anyone ever had such problems; and, does anyone know physically what's happening to signals?

## Answers and Replies

Homework Helper
Gold Member
OK. thankee.

For the interested, U. S. recommends A for residential wiring, B is the common use item, and B is what you get at the village drugstore when you ask for ethernet patch cords.

A on one end, B on the other, same gender both ends works for tying two computers together.

Hermaphrodites (different genders on ends of cable) are what causes trouble in "mixed" systems.

although I don't follow you completely, I would like to specify a couple things that confused me. t568A and t568B are 2 different wiring standards used in cat-5 cable. Normally, t568B wiring is used, but t568a wiring also works.
If you use a cable with t568B on one end and t568A on the other, you'd have
an ethernet crossover cable, used for a NIC2NIC network connection.
I would assume that with just switching the wiring on one end of a cat-5 cable to the other type, you can make a cat-5 cable act as an ethernet crossover cable, however, I have not tried myself (I have used a prefab ethernet crossover cable between 2 NICs and it worked)

The colours mean nothing as long as you have the correct pin outs at both ends...

Code:
100BaseTX RJ-45 Connector

The Fast Ethernet RJ-45 port actively terminates wire pair 4 and 5 and wire pair 7 and 8. Common-mode termination reduces electromagnetic interference (EMI) and susceptibility to common-mode sources.

The table below shows the pin and corresponding signal for the RJ-45 connector pinouts.

RJ-45 Connector Pinout

Pin

Signal

1 TX+

2 TX-

3 RX+

6 RX-

http://www.cisco.com/en/US/products/hw/routers/ps133/products_tech_note09186a00801f5d9e.shtml