Method A uses straight-through MPO array cables to map the fibers the same way on each end of the link. They are connected by Type A adapters or cassettes, which have a “key-up/key-down” orientation. Polarity in fiber optic networks refers to the alignment of transmit (Tx) and receive (Rx) signals between interconnected devices. Although it may seem obvious, fiber optic polarity is a frequent source of confusion and. Below are 6 fundamental rules for managing fiber optic polarity in fiber optic networks, covering design, deployment, and troubleshooting. Because of this B to A and A to B connection, it is referred to as Cross-Over since the A position crosses over to the B, and vice versa.