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Network Models

OSI Model

  • Open Systems Interconnection Model
  • Developed by ISO in 1980
  • Became standard at 1984
  • Properly designed
  • Academic and theoretical only
  • 7 layers
    • Application
    • Presentation
    • Session
    • Transport
    • Network
    • Data link
    • Physical

TCP/IP Model

  • Developed by DARPA for ARPANET in 1969
  • Became standard by 1983
  • Not properly designed
  • But used throughout internet
  • 4 layers
    • Network Access (Link) => Ethernet, WiFi
      • Merges Physical and Data link layer in OSI model
    • Internet => Logical addressing & routing (IP, ARP)
      • same as Network layer in OSI Model
    • Transport => End-to-end delivery (TCP, UDP)
      • same as Transport layer in OSI Model
    • Application => All high level protocols (HTTP, FTP, SMTP, DNS)
      • Merges Application, Presentation and Session layer in OSI Model
  • Error and flow control in Data link layer is moved to Transport layer
  • Application layer is in User space
  • Transport, Internet and Network Access (Link) layer is in Kernel space
  • No layer is in hardware

In OSI model since routers and switches have Data link layer, error and flow control is done through out the path, but in TCP/IP, its done only in the destination device

Header which we pass includes, Port No (16 bit), IP Address (32 bit), MAC Address (48 bit) of both the sender and receiver Therefore, there will be a overhead of (16 + 32 + 48) * 2 = 192 bits