图2.3 0SI模型层次间的相互作用 Device Device A B 相邻两层之间的接口是服务访问点SAP Peer-to-peer protocol(7th layer) Application Application 7-6 interface 7-6 interface Peer-to-peer protocol(6th layer) Presentation Presentation 6-5 interface 6-5 interface Peer-to-peer protocol(5th layer) Session Session 5-4 interface 5-4 interface Peer-to-peer protocol(4th layer) Transport Transport 4-3 interface 4-3 interface 3rd 3rd 3rd Network Network Network Network 3-2 interface 3-2 interface 2d, 2nd Data link Data link Data link 2nd Data link 2-1 interface 2-1 interface 1st 1st 1st Physical Physical Physical Physical Physical communication 2.7 2.7 图 2.3 OSI 模型层次间的相互作用 相邻两层之间的接口是服务访问点SAP