Single fiber SFPs are always deployed in matched pairs, sometimes referred to as “A-end” and “B-end” modules. These paired modules use complementary wavelengths. For instance, if the local SFP transmits at 1310nm and receives at 1550nm, the remote SFP must transmit at 1550nm and. Therefore the module must be used in pairs, with matched BiDi wavelengths (e., one end TX1310/RX1550, the other end TX1550/RX1310). Single-fiber optical modules operate with the largest savings in fiber resources. Two fiber connections are required. Different prices. The majority of optical networks require a pair of fibers to achieve full duplex operation.