terraces Each protocol offers an interface to its users and expects one from the layers on which it builds > Syntax and semantics strike again Data formats Interface characteristics, e.g. IP service model Protocols build upon each other 》 Add value E.g, a reliable protocol running on top of IP 》 Reuse E.g oS provides TCP, so apps don't have to rewrite 6
6 Interfaces Each protocol offers an interface to its users, and expects one from the layers on which it builds » Syntax and semantics strike again – Data formats – Interface characteristics, e.g. IP service model Protocols build upon each other » Add value – E.g., a reliable protocol running on top of IP » Reuse – E.g., OS provides TCP, so apps don’t have to rewrite
Protocol and Service levels application End-to-end Core Network
7 Protocol and Service Levels Application End-to-end Core Network
A Layered Network Model The Open Systems Interconnection(OSI)Model 7 Application Application pResentation 中 Presentation 5 Session Session tRansport Transport 3 Network Network Network 2 Data link Data link Data link 1 Physical Physical Physical 8
8 A Layered Network Model The Open Systems Interconnection (OSI) Model. Application Presentation Session Transport Network Data link 1 Physical 2 3 4 5 6 7 Network Data link Physical Application Presentation Session Transport Network Data link Physical
OSI Motivation standard way of breaking up a system in a set of components, but the com ponents are organized as a set of layers. > Only horizontal and vertical communication >)Components/layers can be implemented and modified in isolation Each layer offers a service to the higher layer, using the services of the lower layer Peer layers on different systems communicate via a protocol. > higher level protocols(e.g. TCP/IP, Appletalk) can run on multiple lower layers >)multiple higher level protocols can share a single physical network fts only a model! -tc/iP has been crazy successful and it's not based on a rigid osi model. But the osi model has been very successful at shaping thought 9
9 OSI Motivation Standard way of breaking up a system in a set of components, but the components are organized as a set of layers. » Only horizontal and vertical communication » Components/layers can be implemented and modified in isolation Each layer offers a service to the higher layer, using the services of the lower layer. “Peer” layers on different systems communicate via a protocol. » higher level protocols (e.g. TCP/IP, Appletalk) can run on multiple lower layers » multiple higher level protocols can share a single physical network “It’s only a model!” - TCP/IP has been crazy successful, and it’s not based on a rigid OSI model. But the OSI model has been very successful at shaping thought
OSI Functions (1)Physical: transmission of a bit stream (2)Data link: flow control, framing, error detection (3)Network: switching and routing (4)Trans port: reliable end to end delivery (5)Session: managing logical connections (6)Presentation: data transformations transter, telnet, network management, file (7 Application: specific uses, e.g. mai Multiplexing takes place in multiple layers 0
10 OSI Functions (1) Physical: transmission of a bit stream. (2) Data link: flow control, framing, error detection. (3) Network: switching and routing. (4) Transport: reliable end to end delivery. (5) Session: managing logical connections. (6) Presentation: data transformations. (7) Application: specific uses, e.g. mail, file transfer, telnet, network management. Multiplexing takes place in multiple layers