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Blog address. soloeng.wordpress.com. Data Communication & Computer Networks. Comp421. Chapter 1-Introduction To Networking. A Communication Model Message/Data Source generates data to be transmitted Medium Transports the data Destination Takes incoming data.

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  1. Blog address • soloeng.wordpress.com

  2. Data Communication & Computer Networks Comp421

  3. Chapter 1-Introduction To Networking • A Communication Model • Message/Data • Source • generates data to be transmitted • Medium • Transports the data • Destination • Takes incoming data

  4. Some of Key Communications Tasks • Transmission System Utilization • Signal Generation • Error detection and correction • Addressing and routing • Message formatting • Security

  5. Data Communication Networks • At least two communicating devices needed • Conventional concept • Central computer: a computer serving all of the organization’s computational needs. • Not suited for communication over a long distance • Point to point communication not usually practical. • Devices are too far apart • Large set of devices would need impractical number of connections • Solution is communications network • an connected collection of autonomous computers. Resource sharing, high reliability, cost saving, ...etc..

  6. Terminology • Guided • Transmission in the form of EMW • The waves are guided along a physical path. • Examples: TP, Coaxial cable, and optical fibers • Unguided • Provides a means for transmitting EMW • But don’t guide them • Ex: Propagation through air, vacuum, and sea water

  7. Terminology… • Direct link • signals propagate directly from transmitter to receiver • No intermediate devices other than amplifiers or repeaters • This can apply to both guided and unguided medium • In Direct link • Systems connected through a switched communication network • Point-to-Point guided transmission medium • Direct link between two devices • And those are the only devices sharing the medium • Multi-Point Guided configuration • More than two devices share the same medium

  8. Terminology… • Simplex • Communication can only flow in one direction and never flow back the other way • Half-duplex • bidirectional communication but signals can only flow in one direction at a time • Duplex/Full-duplex • both ends of the communication can send and receive signals at the same time

  9. Terminology… • Server • A central computer in the network • Stores data or software that can be accessed by clients • Client • Service requestor • Circuit • The pathway through which messages travel

  10. Types of Computer Networks • Why networking? • Sharing of resources • Data, Hardware, Software • Communication • E-mail, video conferencing, etc • LAN • Local Area Network • Smaller scope • Building or small campus • Usually owned by same organization • Data rates much higher • Now some switched systems and ATM are being introduced

  11. Types of Computer Networks… • MAN • Short for Metropolitan Area Network • a data communication network designed for a town or city • Larger than LANs • Characterized by very high-speed connections

  12. Types of Computer Networks… • WAN • Short for Wide Area Network • Large geographical area • Alternative technologies • Circuit switching • Packet switching • Frame relay • Asynchronous Transfer Mode (ATM)

  13. Protocols • Used for communications between entities in a system • Entities: • Any thing capable of Sending/Receiving • User applications • e-mail facilities • DBMSs • etc. • Systems • Physically distinct object that contains one or more entities

  14. For two entities to communicate successfully: • Must speak the same language • Mutually acceptable Convention is required • What is communicated? • How it is communicated? • When it is communicated?

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

  16. Protocol Architecture • Task of communication broken up into modules • For example file transfer could use three modules • File transfer application • Communication service module • Network access module

  17. Simplified File TransferArchitecture

  18. A Three Layer Model • Network Access Layer • Transport Layer • Application Layer

  19. Network Access Layer • Exchange of data between the computer and the network • Sending computer provides address of Destination • May invoke levels of service • Dependent on type of network used (LAN, packet switched etc.)

  20. Transport Layer • Reliable data exchange • Independent of network being used • Independent of application

  21. Application Layer • Support for different user applications • E.g. e-mail, file transfer

  22. Addressing Requirements • Two levels of addressing required • Each computer needs unique network address • Each application on a (multi-tasking) computer needs a unique address within the computer • The service access point or SAP

  23. Protocol Architectures andNetworks

  24. Protocols in SimplifiedArchitecture

  25. Protocol Data Units (PDU) • At each layer, protocols are used to communicate • Control information is added to user data at each layer • Transport layer may fragment user data • Each fragment has a transport header added • Destination SAP • Sequence number • Error detection code • This gives a transport protocol data unit

  26. Network PDU • Adds network header • network address for destination computer • Facilities requests

  27. Operation of a ProtocolArchitecture

  28. TCP/IP Protocol Architecture • Developed by the US Defense Advanced Research Project Agency (DARPA) for its packet switched network (ARPANET) • Used by the global Internet • No official model but a working one. • Application layer • Host to host or transport layer • Internet layer • Network access layer • Physical layer

  29. Physical Layer • Physical interface between data transmission • device (e.g. computer) and transmission • medium or network • Characteristics of transmission medium • Signal levels • Data rates • etc.

  30. Network Access Layer • Exchange of data between end system and network • Destination address provision • Invoking services like priority

  31. Internet Layer (IP) • Systems may be attached to different networks • Routing functions across multiple networks • Implemented in end systems and routers

  32. Transport Layer (TCP) • Reliable delivery of data • Ordering of delivery

  33. Application Layer • Support for user applications • e.g. http, SMPT

  34. TCP/IP Protocol ArchitectureModel

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