RJ45 green vs orange????
RJ45 green vs orange????
The orange and green pairs serve different roles in the wiring, but they’re not interchangeable. The orange pair typically carries the data signal, while the green pair often provides power or ground. T568A and T568B are standards that define the order of connections to ensure consistency across devices. Electricity itself isn’t affected by color—it’s the wiring configuration that matters.
Electrically the sequence doesn't matter as long as both ends are identical. Using T568-A at one end and T568-B at the other forms a cross-over cable. Prior to Auto-MDIX, similar devices like computers, switches, or routers needed a cross-over connection to swap transmit and receive pairs for proper communication. Only straight-through cables were suitable for different devices such as router to switch or switch to PC. Now with Auto-MDIX, separate T568-A and B standards aren't necessary. In fact, most modern cables today adhere solely to the B standard.
The MDI/MDIX connections determine if a signal crosses or stays within a channel. For example, MDI chooses pins 1 and 2 as transmitters, while the wiring simply transports electrons. I’m still puzzled about how the various 568 configurations arise.
It’s a common mistake people make that they overlook. Using A on one end and B on the other makes a crossover cable suitable for 100Mb connections, but it won’t work with gigabit devices since only two of the four pairs are crossed over. If neither device supports Auto-MDIX (like in some Cisco 2950 switches), they’ll either fail to connect or be forced to operate at 100Mb. When both support Auto-MDIX, they keep switching endlessly because they can’t find a correct match for half the pairs in each direction. I’ve seen this firsthand—modern networks rarely need these old tricks anymore.
If you're asking not why the standards exist but why the NIC developers created their adapters to work this way then I can't say. It may very well have been an after thought. Seems I should have mentioned I was already aware of this. Yes. It creates a 100Mbit cross-over cable. It's quite the misconception because you don't really hear about or see in stores how to make a crossover cable with all four pairs. There's a standard for it but you won't see it written on the back of a pack of RJ-45 ends.
This standard aims to keep backward compatibility for those upgrading from 100-BASE-T that previously used crossover cables (many offered Auto-MDIX) to 1000-BASE-T, where a crossover cable is no longer needed. The diagrams for 1000-BASE-T are often confusing, especially for users unfamiliar with how Gigabit Ethernet fundamentally differs from earlier versions.
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