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Computer Network

4122102 :. Computer Network. & Distributed. Computer Network and Distributed. Rachphat Sriprom. Rajabhat Institute Chandrakasem. Computer Network. A network is a set of devices (nodes) connected by media links A node can be a computer, printer, etc.

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Computer Network

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  1. 4122102 : Computer Network & Distributed Computer Network and Distributed Rachphat Sriprom Rajabhat InstituteChandrakasem

  2. Computer Network • A network is a set of devices (nodes) connected by media links • A node can be a computer, printer, etc. • The links are called communication channels

  3. Simplified Network Model

  4. LAN : Local Area Network

  5. WAN : Wide Area Network

  6. WAN : Dial On Demand-PSTN

  7. WAN : Leased line - PSTN

  8. WAN : PSDN

  9. WAN : ISDN

  10. Enterprise Network

  11. Network Criteria

  12. Performance The performance of a network depends on a number of factors ; • Number of users • Type of transmission medium • Hardware • Software

  13. Reliability • Frequency of failure • Recovery time of a network after failure • Catastrophe

  14. Security • Unauthorized access • For a network to be useful, sensitive data must be protected from unauthorized access. Protection can be accomplished at a number of levels • Viruses • A good network is protected from viruses by hardware and software designed specifically for that purpose.

  15. Computer Networks &Computer Communications • Computer Networks: two or more computer interconnected via a communication network • Computer Communications: the exchange of information between two computers for purpose of cooperative action

  16. Transmission system utilization Interfacing Signal generation Synchronization Exchange Management Error detection and correction Flow control Addressing Routing Recovery Message formatting Security Network management Communications Tasks

  17. Protocols • Protocol - a set of rules governing the exchange of data between two entities in a system • Must speak the same language • Entities • User applications • e-mail facilities • terminals • Systems • Computer • Terminal • Remote sensor

  18. Key Elements of a Protocol • Syntax • Data formats • Signal levels • Semantics • Control information • Error handling • Timing • Speed matching • Sequencing

  19. Protocol Data Unit (PDU)

  20. Protocol Data Unit (PDU) • The sending application generates a block of data and passes this to the transport layer • Each of these blocks the transport layer appends a transport header, containing protocol information • The combination of data from the next higher layer and control information is known as a protocol data unit (PDU)

  21. Encapsulation in PDU • Addition of control information to data • Address information • Error-detecting code • Protocol control

  22. Protocol Data Unit (PDU)

  23. Standard or Nonstandard

  24. OSI Model • The Open Systems Interconnection model is a layered framework for the design of network systems that allows for communication across all types of computer systems • It consists of seven separate but related layers • An ISO standard ISO is the organization. OSI is the model.

  25. OSI seven layers • Application layer • Presentation layer • Session layer • Transport layer • Network layer • Data Link layer • Physical layer

  26. OSI layers

  27. The OSI Environment Headers are added to the data at layers 6, 5, 4, 3, and 2. Trailers are usually added only at layer 2.

  28. Functions Of The Layers • Physical Layer • Physical interface between devices • Information Transmission • Medium & Signal • Mechanical (Connector)

  29. Data Link Layer • Control the information transfer over Physical link • Physical addressing • Framing • Flow control • Error control • Synchronization • Access control

  30. Data Link Layer Figure shows Framing

  31. Data Link Layer Example

  32. Network Layer • The network layer is responsible for the source-to-destination delivery of a packet possibly across multiple networks (links) • Switching & Routing • Logical Addressing • Higher layers do not need to know about underlying technology • Not needed on direct links

  33. Network Layer Example

  34. Network Layer Example

  35. Transport Layer • Control for information transfer between end user system • Segmentation & Reassembly • In sequence • Connection control • Flow control • Error control • Quality of service (QoS)

  36. Transport Layer

  37. Transport Layer Example

  38. Session Layer • Control of dialogues between applications in end systems • Dialogue discipline (full duplex or half duplex) • Grouping • Recovery

  39. Presentation Layer • The presentation layer is concerned with the syntax and semantics of the information exchanged between two systems • Data formats and Encoding • Data compression • Encryption (senders transforms the original information to another from and sends it out over the network)

  40. Presentation Layer

  41. Application Layer • The application layer provides user interface and support for services such as electronic mail, remote file access and transfer, shared database management, etc. • Network virtual terminal (allows a user to log on to a remote host) • File transfer, access, and management (FTAM) • Mail services • Directory services

  42. Application Layer

  43. Summary of Layer Functions

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