数据链路层协议的位置 network actual PDU flow d d Router R1 ph phph applicatio app ication transport sport network net vork data lin network network data link data link 物理层提供physical protocol p可3ica 不可靠的比 ph ph p ph Host H1 ph 特传输服务 network Host H2 Router R2 Router R3 ph Router ph:physical Layer Router R4 dl:data link layer Data link Routing PDU:Protocol Data Unit layer process process (message at application 端口 layer,packet at network ■■ 3 layer,frame at dl,and bit Data link Frames Packets protocol at ph) here here 数据链 路层协议 端口 Transmission 6 line to a router数据链路层协议的位置 6 ph: physical Layer dl: data link layer PDU: Protocol Data Unit (message at application layer, packet at network layer, frame at dl, and bit at ph) 物理层提供 不可靠的比 特传输服务 端口 端口 数据链 路层协议