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Comprehensive Overview of Computer Networks: Applications, Hardware, and Protocol Design

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This text provides an in-depth exploration of computer networks, covering various applications in business, home, and mobile contexts. It highlights the client-server model and peer-to-peer systems, demonstrating how networks facilitate access to information, communication, entertainment, and e-commerce. The classification of network types such as LANs, MANs, WANs, and wireless networks is discussed, along with essential network hardware. Furthermore, it delves into protocol hierarchies, design issues, and the interaction between layers, ensuring a thorough understanding of network architecture and functionality.

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Comprehensive Overview of Computer Networks: Applications, Hardware, and Protocol Design

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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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