复旦大学：《计算机网络 Computer Networking》课程电子教案（PPT课件讲稿）02 Protocol Stacks and Layering

Lecture 2 Protocol Stacks and Layering Dejian Ye Software School Fudan University Networking, Spring 2009

1 Lecture 2 Protocol Stacks and Layering Dejian Ye Software School Fudan University Networking, Spring 2009

Last time The Big picture y Goas Efficiency ilities"(scalability, manageability, availability) 3 Ease of creating applications 》 Challenges: Scale Geography Heterogeneity(** today' s focus A few specific details: 》 Circuits vs. packets >)Little bit about routing > Service model and how to construct services today !)

2 Last Time The Big Picture » Goals: – Efficiency – “ilities” (scalability, manageability, availability), – Ease of creating applications » Challenges: – Scale – Geography – Heterogeneity (** today’s focus!) A few specific details: » Circuits vs. packets » Little bit about routing » Service model and how to construct services (** today!)

Todav's Lecture ast time: "Big picture"(Design meeting system goals) Today >)General architectural principles for networks (Design for imlementation) >) Introduces a few concrete models examples Where we are going: >) Socket programming rev iew++ (for project >)Application examples( still high level) >)After that: Burrowing into the details, ground up Today' s specifics 》 What is a protocol 》 Protocol stacks 》 Some history > Standards organizations. 》 Application layer

3 Today’s Lecture Last time: “Big picture”(Design meeting system goals) Today: » General architectural principles for networks(Design for imlementation) » Introduces a few concrete models & examples Where we are going: » Socket programming review++ (for project) » Application examples (still high level) » After that: Burrowing into the details, ground up Today’s specifics: » What is a protocol. » Protocol stacks. » Some history. » Standards organizations. » Application layer

Why protocols and layering? No one can im plement such a huge system only by himself, and the system need to accommodate technology evolution, so we need the following >)Interoperability 》 Reuse >) Hiding underlying details Distributed components collaborate together, so > Some kind of agreement and collaboration between computing and communicaiton nodes

4 Why protocols and layering? No one can implement such a huge system only by himself, and the system need to accommodate technology evovlution. so we need the following: » Interoperability » Reuse » Hiding underlying details Distributed components collaborate together, so » Some kind of agreement and collaboration between computing and communicaiton nodes

What is a Protocol An agreement between parties on Friendly greeting how communication should take place. Protocols may have to define many aspects of the Muttered repl communication Syntax ) Data encoding, language, etc. Semantics. > Error handling, termination, ordering of Destination? requests, etc Protocols at hardware, software all levels! Shanghai Syntax: English, ascii, lines delimited by“ln Different layer protocol, e.g different communication method Thank you when a human grow up

5 What is a Protocol An agreement between parties on how communication should take place. Protocols may have to define many aspects of the communication. Syntax: » Data encoding, language, etc. Semantics: » Error handling, termination, ordering of requests, etc. Protocols at hardware, software, all levels! Syntax: English, ascii, lines delimited by “\n” Different layer protocol, e.g., different communication method when a human grow up Friendly greeting Muttered reply Destination? Shanghai Thank you

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