Principles of Application Layer Protocols

Network Application Architecture

• Application communicating,distribute processes
  • hosts in "user spece"
  • exchange messages to implement application
• Application-layer protocols
  • define messages exchanged by apps and actions taken
  • user services provided by lower layer protocols

Processes Communicating

• Client
  • initiate contact with server (first)
  • typically requests service from server
• Server
  • provides requests service to client

Application-layer protocols

• defines interface between application and transport layer
• socket -> Internet API
  • two processes commiunicate by sending data to socket and reading data from socket

Services provided by Internet transport protocols

• TCP

  • connection-oriented: setup required between client and server
  • reliable transport: between sending and receiving process
  • flow control: sender won't overwhelm receiver
  • congestion control: throttle sender when network overloaded
  • Not provided:

    timing
    minimum bandwidth guarantees

• UDP

  • lightweight: unreliable data transfer between sending and receiving process
  • Not provided:

    connection setup
    reliability
    flow control
    congestion control
    timing
    any bandwidth guarantee