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Data Communication & networking

This blog is for undergraduate/graduate students who require some basic information about their subjects or any other topic related to data communication.

Sunday 27 March 2011

OSI Model

OSI MODEL:
The open systems interconnection (OSI) model was developed by the International Organization for Standardization (ISO) as a model for a computer communications architecture and as a framework for developing protocol standards. It consists of seven layers:
  •  Application
  •  Presentation
  •  Session
  •  Transport
  •  Network
  •  Data Link
  •  Physical
  
Function of OSI Layers

Layer # 1 (Physical Layer)
  • Physical characteristics of interfaces and media.
  • Representation of bits (types of encoding)
  • Date rate (transmission rate (duration of bits))
  • Synchronization of bits
  • Line configuration (point-to-point configuration, multipoint configuration)
  • Physical topology (mesh, ring, bus topology etc)
  • Transmission mode (simplex, half/full duplex)
Layer # 2 (Data Link Layer)
  • Frames
  • Framing
  • Physical addressing (source/destination address)
  • Flow control (prevent overwhelming)
  • Error control
  • Access control
Layer # 3 (Network Layer)
  • Packets
  • Source to destination delivery of packets
  • Logical addressing
  • Routing
Layer # 4 (Transport Layer)
  • Segment
  • Source to destination (end-to-end) delivery of entire message
  • Service point addressing
  • Segmentation and reassembly
  • Connection control (connection oriented / connection less)
  • Flow control (perform end to end)
  • Error control (perform end to end)
Layer # 5 (Session Layer)
  • Establish, maintain, synchronize and terminates session between two
  • communication systems
  • Dialog control
  • Synchronization
Layer # 6 (Presentation Layer)
  • Translation
  • Encryption / decryption
  • Compression
Layer # 7 (Application Layer)
  • Network virtual terminal
  • File transfer, access and management (FTAM)
  • Mail services
  • Directory services

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