图2.2 0SI七层模型 Application 6 Presentation Session Transport Network Data link Physical 2.6
2.6 图 2.2 OSI 七层模型
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
Protocol Data Units (PDU) At each layer,protocols are used to communicate ■( Control information is added to user data at each layer Transport layer may fragment user data Each fragment has a transport header added ■Destination SAP ■Sequence number Error detection code This gives a transport protocol data unit
Protocol Data Units (PDU) At each layer, protocols are used to communicate Control information is added to user data at each layer Transport layer may fragment user data Each fragment has a transport header added Destination SAP Sequence number Error detection code This gives a transport protocol data unit
Protocol Data Units Application Data Transport Header Transport protocol data units Transport Header Network protocol data units (packets) Network Network Header Header
Protocol Data Units
OSI as Framework for Standardization Layer 7 (Application) Service to Layer N+1 Protocol Total Layer N Layer N with peer Communication entity Layer N Function Decompose (modularity, information-hiding) Service from Layer N-1 ● Layer I (Physical) OSI-wide standards (e.g.,network management,security)
OSI as Framework for Standardization