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OSI Model Layers


OSI Model Layers


The following table compares the functions
performed at each OSI model layer.




























Layer Description and Keywords Protocols Devices Encapsulation
Application

  • User interface
  • Communication partner identification

  • HTTP
  • Telnet
  • FTP
  • TFTP
  • SNMP

 Messages and Packets
Presentation

  • Data format (file formats)
  • Encryption, translation, and compression
  • Data format and exchange

  • JPEG, BMP, TIFF, PICT
  • MPEG, WMV, AVI
  • ASCII, EBCDIC
  • MIDI, WAV

 Packets
Session

  • Keeps data streams separate (session identification)
  • Set up, maintain, and tear down communication
    sessions

  • SQL
  • NFS

  • ASP
  • RPC
  • X window



    Packets


    Transport


    • Reliable (connection-oriented) and unreliable
      (connectionless) communications
    • End-to-end flow control
    • Port and socket numbers
    • Segmentation, sequencing, and combination




    • TCP (connection-oriented)
    • UDP (connectionless)



    Segments, Datagrams, and Packets


    Network


    • Logical addresses
    • Path determination (identification and selection)
    • Routing packets




    • IP
    • IPX
    • AppleTalk
    • DECNET


    Router
    Packets and Datagrams


    Data Link
    Logical Link Control (LLC)


    • Convert bits into bytes and bytes into frames
    • MAC address, a.k.a. burned in address (BIA),
      hardware address
    • Logical network topology
    • Media access
    • Flow control

    • Parity and CRC





    • LAN protocols: 802.2 (LLC), 802.3 (Ethernet),
      802.5 (Token Ring), 802.11 (Wireless)
    • WAN protocols: HDLC, PPP, Frame Relay, ISDN,
      ATM


    NICs

    Switches
    Bridges
    Frames


    Media Access Control (MAC)


    Physical


    • Move bits across media
    • Cables, connectors, pin positions
    • Electrical signals (voltage, bit synchronization)
    • Physical topology (network layout)




    • EIA/TIA 232 (serial signaling)
    • V.35 (modem signaling)
    • Cat5
    • RJ45


    Cable

    Connectors

    Hubs and repeaters
    Bits