波特率:即码元速率，单位是波特。CONTROLLING Communication services CONTROLLED STATION Link Link STATIONIND REQ RequestIND REQ Requestdata CON Respond RESP(no data)No dataRespond RESP(data)data CONCONTROLLING Communication services CONTROLLED STATION Link Link STATION IND_a REQ_a Request IND_b REQ_bData_b CON_a Respond RESP(no data)Respond RESP(data)data CON_b
