Introduction to networking - Ch.3.0 Application Layer, Principle of network application

Submitted by keithyau on Thu, 01/07/2010 - 16:36

Principle of network application

Application layer protocols
  1. Http
  2. FTP
  3. SMTP / POP / IMAP
  4. DNS
  • Define messages exchanged by applications and actions taken
  • Is one "piece" of an application
Aspects of network
  1. Transport-layer service models
  2. Client-server paradigm 範例
  3. peer-to-peer paradigm
Some network applications 應用
  1. email
  2. web
  3. instant messaging
  4. remote login
  5. p2p file sharing
  6. multi-user network games
  7. streaming stored videos
  8. VoIP
  9. video conferencing 會議
  10. ...
Application architectures
  1. Client-server
  2. Peer-to-peer(p2p)
  3. Client-server + p2p
Client-server architecture

server
  • Always-on
  • Permanent IP address
  • Server farms for scaling
Clients
  • communicate with server
  • Do not directly communicate with each other
  • May have dynamic IP addresses
P2P architecture
  1. no always-on server
  2. arbitrary end systems directly communicates
  3. Peers are intermittently connected and change IP addresses
  4. * Highly scalable 鄺展性 but difficult to manage
Client-server + P2P
  1. Skype - Central server to find address of remote party
  2. Instant messaging - central server to presence client detection/location, login

Processes 程序 communicating
  1. Client process: Process that initiates communication
  2. Server process: Process that waits to be contacted

  3. to receive messages, process must have identifier


  4. identifier includes both IP address and port numbers associated 一齊 with process on host.


  5. process sends/receives messages to/from its socket



Application layer protocol defines

  1. Types of messages exchange e.g., request, response
  2. Message syntax: what fields in messages & how fields are delineate 描述
  3. Message semantic: meaning of information in field
  4. Rules for when and how processes send & respond to messages


TCP & UDP

TCP

  1. connection-oriented 連線主要: setup required between client and server processes

  2. reliable transport between sending and receiving process
  3. flow control: sender won’t overwhelm receiver
  4. congestion control: throttle 節流 sender when network overloaded
  5. does not provide: timing, minimum bandwidth guarantees

UDP

  1. unreliable 不可靠 data transfer between sending and receiving process
  2. does not provide:connection setup,reliability, flow control,congestion 阻塞 control, timing,or bandwidth guarantee 保證


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