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

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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