Why are fibers in a cross-over patch cord parallel?

Optical fibers run parallel in a cross-over patch cord. Are they really parallel or are they somehow flipped? 

Answer: From a physical perspective, the fibers run parallel. The connectors on both ends of the cord are installed in the same orientation: Connector A on the left, connector B on the right when being looked at from the front (please only look at the connectors after you have unplugged it, NEVER EVER look at them when the cord is plugged in somewhere – invisible laser light might damage the eye!). Because of the orientation mentioned above, connector A on one side is connected to connector B on the other side of the patch cord and vice versa. This is why there is a logical cross-over that is needed to connect transmit on one side and recieve on the other side and vice versa.

In order to avoid unnecessary confusion, network professionals refer to such patch cords as “A to B patch cords“. This makes it absolutely clear that connector A on one end is connected to connector B on the other end and so transmit and receive are connected properly.

Nobody knows everything. A comprehensive topic like IT cabling inevitably raises questions. This column gives answers to questions which reached Telegärtner’s Technical Helpdesk and which we consider interesting for everyone. Please do not hesitate to send us your questions, we will be happy to answer them. The questions will be published anonymously, of course.