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Introduction

Introduction. Chapter 1. Uses of Computer Networks. Business Applications Home Applications Mobile Users Social Issues. Business Applications of Networks. A network with two clients and one server. Business Applications of Networks (2).

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Introduction

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  1. Introduction Chapter 1

  2. Uses of Computer Networks • Business Applications • Home Applications • Mobile Users • Social Issues

  3. Business Applications of Networks • A network with two clients and one server.

  4. Business Applications of Networks (2) • The client-server model involves requests and replies.

  5. Home Network Applications • Access to remote information • Person-to-person communication • Interactive entertainment • Electronic commerce

  6. Home Network Applications (2) • In peer-to-peer system there are no fixed clients and servers.

  7. Home Network Applications (3) • Some forms of e-commerce.

  8. Mobile Network Users • Combinations of wireless networks and mobile computing.

  9. Network Hardware • Local Area Networks • Metropolitan Area Networks • Wide Area Networks • Wireless Networks • Home Networks • Internetworks

  10. Classification • Types of transmission technology • Broadcast links • Point-to-point links

  11. Classification(2) • Classification of interconnected processors by scale.

  12. Local Area Networks • Two broadcast networks • (a) Bus • (b) Ring

  13. Metropolitan Area Networks • A metropolitan area network based on cable TV.

  14. Wide Area Networks • Relation between hosts on LANs and the subnet.

  15. Wide Area Networks (2) • A stream of packets from sender to receiver.

  16. Wireless Networks • Categories of wireless networks: • System interconnection • Wireless LANs • Wireless WANs

  17. Wireless Networks (2) • (a) Bluetooth configuration • (b) Wireless LAN

  18. Wireless Networks (3) • (a) Individual mobile computers • (b) A flying LAN

  19. Home Network Categories • Computers (desktop PC, PDA, shared peripherals • Entertainment (TV, DVD, VCR, camera, stereo, MP3) • Telecomm (telephone, cell phone, intercom, fax) • Appliances (microwave, fridge, clock, furnace, airco) • Telemetry (utility meter, burglar alarm, babycam).

  20. Network Software • Protocol Hierarchies • Design Issues for the Layers • Interfaces and services • Connection-Oriented and Connectionless Services • Service Primitives • The Relationship of Services to Protocols

  21. Network SoftwareProtocol Hierarchies • Layers, protocols, and interfaces.

  22. Protocol Hierarchies (2) • The philosopher-translator-secretary architecture.

  23. Protocol Hierarchies (3) • Example information flow supporting virtual communication in layer 5.

  24. Design Issues for the Layers • Addressing • Transfer rule • Error Control • Flow Control • Disassemble and reassemble • Multiplexing • Routing

  25. Design Issues for the LayersAddressing • Each layer needs a mechanism for identifying senders and receivers • Sender: a process on a machine • Receiver: a process on another machine

  26. Design Issues for the LayersTransfer rule • Simplex • Half-duplex • Full-duplex

  27. Design Issues for the LayersError Control • Physical lines are not perfect • Error-detecting or error-correcting codes • How the receiver tells the sender which messages have been correctly received and which have not • Messages may be out of sequence • How the sender numbers the messages, how the receiver deals with the messages arrive out of order

  28. Design Issues for the LayersFlow control • A fast sender may swamp a slow receiver with data • Method 1: some kind of feedback from the receiver to announce it’s current situation • Method 2: limit the sender’s transmission rate

  29. Design Issues for the LayersDisassemble & Reassemble • Each layer could have different message size • Lower layer may disassemble upper layer’s message into several smaller messages reassembled by receiving peer • Lower layer may gather several small messages into a single large message to improve efficiency

  30. Design Issues for the LayersMultiplexing • The underlying layer may use the same connection for multiple, unrelated conversions • The multiplexing and demultiplexing must be done transparently

  31. Design Issues for the LayersRouting • When multiple paths exist, a route must be chosen

  32. Interfaces and services • Entity: active elements in a layer, software entity or hardware entity • Peers: entities in the same layer on different machines • Service provider and service user: the entities in layer n implement a service used by layer n+1, layer n is called the services provider, layer n+1 is called service user • SAPs: Service Access Points, the layer n SAPs are the places where layer n+1 can access the services offered • IDU: Interface Data Unit, the information elements exchanged between neighboring layers via SAP

  33. Interfaces and services(2) • SDU: Service Data Unit, the information passed across the network to the peer entity and then up to layer n+1,it is filled into user data part of layer n PDUs • PDU: Protocol Data Unit, the information exchanged between two peers • ICI: Interface Control information, the control information in IDU • PCI: Protocol Control Information, the control information in PDU

  34. Interfaces and services(3)

  35. Connection-Oriented and Connectionless Services • Six different types of service.

  36. Service Primitives • Requests: an entity wants the service to do some work • Indication: an entity is to be informed about an event • Response: an entity wants to respond to an event • Confirm: The response to an earlier request has come back

  37. Service Primitives (2) SYSTEM A SYSTEM B 服务用户 （N+1） 服务提供者 （N） 服务提供者 （N） 服务用户 （N+1） Request PDU Indication confirmed Response Confirm Request unconfirmed Indication

  38. Service Primitives (3)Example • CONNECT.request - request a connection to be established • CONNECT.indication - signal the called party • CONNECT.response - used by the callee to accept/reject calls • CONNECT.confirm – tell the caller whether the call was accepted • DATA.request – request that data be sent • DATA.indication – signal the arrival of data • DISCONNECT.request – request that a connection be released • DISCONNECT.indication – signal the peer about the request

  39. Service Primitives (3)Example(2)

  40. Services to Protocols Relationship • The relationship between a service and a protocol.

  41. Reference Models • The OSI Reference Model • The TCP/IP Reference Model • A Comparison of OSI and TCP/IP • A Critique of the OSI Model and Protocols • A Critique of the TCP/IP Reference Model

  42. *Reference Models The OSI reference model.

  43. *Reference Models (2)

  44. *Reference Models (3) • The TCP/IP reference model.

  45. *Reference Models (4) • Protocols and networks in the TCP/IP model initially.

  46. *Comparing OSI and TCP/IP Models • Concepts central to the OSI model • Services • Interfaces • Protocols

  47. A Critique of the OSI Model and Protocols • Why OSI did not take over the world • Bad timing • Bad technology • Bad implementations • Bad politics

  48. Bad Timing • The apocalypse of the two elephants.

  49. A Critique of the TCP/IP Reference Model • Problems: • Service, interface, and protocol not distinguished • Not a general model • Host-to-network “layer” not really a layer • No mention of physical and data link layers • Minor protocols deeply entrenched, hard to replace

  50. Hybrid Model • The hybrid reference model to be used in this book.

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