A protocol configuration method for use by a substation to be coupled to a main station in an optical access network is described. The configuration method comprises the following steps: predefining for the substation a plurality of predefined types of protocol for use by the substation of one of the types of protocol during operation; and after being coupled to the main station, determining with a first determiner, a bit-rate and a line-coding for a bit-stream being received from the main station, thereby providing a downstream line-rate and a downstream line-coding; and based upon at least anyone of the downstream line-rate, the downstream line-coding and the bit-stream, selecting with a selector according to predefined rules and conditions a type out of the plurality of predefined types of protocol for the bit-stream, the predefined rules and condition are based upon one or more distinguishing marks between the plurality of predefined types of protocol; and activating the selected type for further operation and thereby enabling the substation to communicate with the main station according to the selected type of protocol.