A backward compatible frame reuse mechanism that allows new information to be defined a reused frame without causing any incorrect operation in a legacy receive device. To generate a reused frame, a portion of the frame in the first format is masked with a predetermined masking sequence (PMS) and thereby redefined as new fields in a second format. When a device that supports the reuse scheme receives a frame that possible is a reused frame, the device checks the potentially reused portion according to the first format after de-masking and also checks according to the second format without de-masking. Based on the check results, the device selects a format to resolve the frame. A legacy device receiving the reused frame only checks the reused portion without de-masking, which results in a certain check error and makes the device discard the frame without any harmful operation.

A backward compatible frame reuse mechanism that allows new information to be defined a reused frame without causing any incorrect operation in a legacy receive device. To generate a reused frame, a portion of the frame in the first format is masked with a predetermined masking sequence (PMS) and thereby redefined as new fields in a second format. When a device that supports the reuse scheme receives a frame that possible is a reused frame, the device checks the potentially reused portion according to the first format after de-masking and also checks according to the second format without de-masking. Based on the check results, the device selects a format to resolve the frame. A legacy device receiving the reused frame only checks the reused portion without de-masking, which results in a certain check error and makes the device discard the frame without any harmful operation.

A system and method for carrying a downstream optical signal and an upstream optical signal on a fiber optic link is disclosed. The system and method includes a first transceiver unit that receives an input communication signal from at least one external communication device at an electrical input port, a transmitter that converts the input communication signal into an optical signal and transmits the optical signal as an downstream optical signal on a fiber optic link, a receiver at the second transceiver unit that receives the downstream optical signal and converts the downstream optical signal into an electrical communication signal, and a first circuit in the second transceiver unit that determines whether the second transceiver couples the electrical communication signal to a two wire intercom circuit or a four wire intercom circuit.