信息帧控制域格式（以2字节为例) N(S):the sequence of this data .N(R):the sequence of data should be received next time from DSAP DSAP SSAP Control Field Message Send Count-NS)P/F Receive Count-N(R) 2345 6 8 10 11121314 15 1515 信息帧控制域格式（以2字节为例）