Communication method, apparatus and system

A communication method is disclosed. The method includes: a technical specification indicated by a user instruction is downloaded from a server according to the user instruction, and the technical specification is sent to an Optical Network Unit (ONU) through an out-of-band management channel; the technical specification is configured; a control message is sent to the ONU through the out-of-band management channel in order to indicate the ONU to configure the technical specification; on the basis of the mode supported by the technical specification, communication with the ONU is performed through an in-band data channel. With the solution, the dynamic reconstruction of the physical layer or the MAC layer can be implemented; according to user requirements and application scenarios, PON systems with different standards are defined by using different software and without changing hardware; the flexibility of the PON deployment is greatly increased, and the cost of deployment and maintenance is reduced.