Method, terminal and system for link parameter auto-negotiation based on HDLC (high-level data link control) protocol

The invention relates to a method, a terminal and a system for link parameter auto-negotiation based on an HDLC (high-level data link control) protocol. The method includes: a slave end sends an SUBME frame to a master end; the master end receives the SUBME frame, negotiates link parameters with the slave end according to the frame and returns the link parameters to the slave end through a UA frame; the slave end receives the UA frame, performs link parameter negotiation with the master end according to the UA frame, establishes link connection with the master end and sends the link parameters to the master end through a UE frame; and the master end receives the UE frame and establishes link connection with the slave end. Mutual entity symmetry is achieved by the aid of a three-handshaking mechanism established and linked by the HDLC protocol and by means of negotiating the link parameters by both communication sides and determining ARQ (automatic repeat request) types and size of a window used during data transmission. During normal working, optional parameters of a link are negotiated through unnumbered frames, so that link parameter auto-negotiation of the HDLC protocol is achieved, reliability and high efficiency of link transmission are improved, and implementation is simple.