[TCP/IP] Application Layer - Overview

Application Layer Overview

• Application layer of Models
  • OSI model: three layers of Application, Presentation, and Session
  • TCP/IP model: only Application layer
• Basic functions
  • the highest-level access to the network     #especially to TCP/IP model
  • the means for converting communication to data
• Application programs
  • run on different end systems
  • communicate over network
  • no need to write software for network-core devices <- P2P protocol

 

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API and Socket

• process: application program running within a host
• API: application programming interface between process and OS
• socket: network programming interface between process and the network protocols

 

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Applications' Requirements

• data integrity (loss)
  • some appes require 100% reliable data transfer
  • other apps can tolerate some loss
• timing (delay)
  • some apps require low delay to be "effective"
  • others can tolerate some delay
• throughput (bandwidth 대역폭)
  • some apps require minimum amount of throughput to be "effective"
  • other apps make use of whatever throughput they get
• security
  • encryption
  • data integrity

 

Need of Transport Services

• Network Layer of the Internet
  • based on datagram packet-switching technology (simple, but connecionless and unreliable)
  • each packet is treated independently by any practival route
    • out-of-order
    • loss
• Transprot Layer Protocols
  • UDP(User Datagram Protocol)
    • connectionless
    • unreliable
    • out-of-order
    • fast <- no  ACKs are used
    • less traffic
  • TCP(Transmission Control Protocol)
    • connection-oriented
    • reliable
    • in-order
    • congestion control
    • flow control
    • connection setup delay