计算机网络体系结构 oS各层协议数据单元 Sending Y Receiving Process Process Data Application Application protocal AH Data Application aver Presentation Presentation protocol Presentation layer Data Session Session protocol SH Data Session layer Transport TH Data Transport layer protocol Network Data Network protocol +-------- Data link Dat IDT Data link Physical Bits Physical Actual data transmission pathOSI各层协议数据单元 计算机网络体系结构