帧格式 物理层 个 MAC MAC Destination Source Frame Control MAC Address MAC Address LLC PDU CRC 1octet 10r2 variable LLC PDU DSAP SSAP LLC Control Information 网络层 LLC IG DSAP value C/R SSAP value Address Fields LLC-Logical Link Control I/G Individual/Group C/R Command/Response PDU-Packet Data Unit DSAP-Destination Service Access Point SSAP-Source Service Access Point 12 SAP indicates the user12 帧格式 LLC - Logical Link Control PDU - Packet Data Unit DSAP - Destination Service Access Point SSAP - Source Service Access Point SAP indicates the user 网络层 物理层