[강의정리] 데이터통신과네트워크 Application Layer

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Principles of network applications

Application architectures

• client-server
• peer-to-peer

Client-server architecture

• server:

  • always-on host
  • permanent IP address

• clients:

  • communicate with server
  • may be intermittently connected
  • do not communicate directly

P2P architecture

• No always-on server

Processes communicating

• Process: program running within a host
  • 같은 host 에서, inter-process communication을 통하여 두개의 프로세스가 통신

Sockets

• Process sends/receives messages to/from its socket
• Socket analogous to door

Addressing processes

• Identifier includes both IP address and port numbers associated with process on host.

Example port numbers:

• HTTP server: 80

• mail server: 25

• to send HTTP message to usaint web server:

• IP address: 203.253.31.114

• port number: 80

App-layer protocol defines

• Types of messages exchanged,
  • E.g., request, response
• Message syntax
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