Method of using communication apparatus to select communication protocol

A method for selecting communication protocols by communication devices is used in a communication system containing equipments A and B carrying out communications characterizing that A sends a data packet to B, which receives the data packet of A to judge if it can select communication protocols based on said data packet, if not, it selects a communication protocol and operates it at the interface, in which, every physical interface can select communication protocols automatically and guarantees the correctness of the negotiation on the protocol.