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Ch2 Application Layer

Created: 2025-11-29
Updated: 2025-11-29

2.1 Principles of Network Applications

  • application architecture:
    • client-server architecture: HTTP, IMAP, FTP
      • server: always-on host, permanent IP address, often in data center for scaling
      • client: contact with server, may be intermittently connected, may have dynamic IP
    • peer-to-peer architecture: P2P file sharing
      • arbitrary end systems directly communicate → peers request/provide services from/to peers
      • peers are intermittently connected, change IP address → complex management
      • self scalability → but people are selfish
      • cost effective ∵ no server infrastructure and server bandwidth
      • challenges of security, performance, and reliability ∵ decentralized structure
  • process := program running within a host
    • within same host: IPC (inter-process communication) defined by OS
    • in different host: by exchanging messages (via socket)
    • client process: process that initiates communication
    • server process: process that wait to be contacted
    • P2P architecutres also have client & server process

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