What are A and B Ethernet cable standards for?

[GamerGry123]

I mean ethernet cables that connect to the computer, what are the A and B standards for?

 

I do not mean standards such as foil or mesh screened.

I mean standards where cables are arranged according to colors.

 

Yet the ethernet cables are patchy, straight.
The patch is probably one RJ45 end connects to the computer and the other, where there is no RJ45 end, connects to the pachpanel?

Simple, is it probably where both ends are RJ45?

 

 

[Lurick]

It was/is to allow for crossover cables but with the advent of auto-mdix some 20-ish years ago the need for crossover cables has faded to near nothing. There are still applications where they are needed though.

A patch panel is nothing more than the termination point for wires either directly into the panel or via a connector end in instances where it's a female to female patch panel.

[mariushm]

As Lurick says, there are two color orders, to make it easy to create a crossover cable.

A crossover cable is a cable that makes a direct connection between two network cards, like how you could do with serial cables. The transmit pair is connected to the other card's receive and the receive pair is connected to the transmit on the other card so you have a loop between the two network cards.

 

On 100 mbps network cards, only 4 wires are used, wires 1, 2, 3 and 6.  Wires 4 and 5 (blue pair) was sometimes used for phones or for power over ethernet and the brown pair was not used.

 

On 1 gbps (and higher) network cards, all wires are used, and the ethernet standard requires network cards to support auto mdi-x , meaning auto detect pairs and recognize if user wants to use a regular cable as a crossover cable.

 

As for why that order, most manufacturers prefer one of those color orders because it has to do with how the wire pairs are twisted and then the four pairs of wires are twisted together (in cat5/cat5e standard) or separated (in cat6/cat6a and higher). 

I'm not sure where I've read but some claimed that arranging them in the order they used made for the least amount of untwisting and least number of wires crossing over other wires when flattened into the connector to be crimped.