Application Protocols and Layers


Application Layer

  • Web Services
    • HTTP
      • Hyper Text Transfer Protocol
      • Supports web services
      • Uses port number 80
      • The secure version is HTTPS
      • HTTPS uses port number 443
      • Transfers text, images, and hyper links
    • HTTPS
  • File Sharing Services/File transfer
    • FTP
      • File Transfer Protocol
      • Uses port number 21
      • Built=in in MS Windows Operating Systems
      • Many 3rd party programs
      • Web browser works as FTP client
    • TFTP
    • Network File System
  • Mail Services
    • SMTP
      • Common language used by the majority of mail servers
      • Send messages back and forth to other mail servers or email clients
    • POP3 “Post Office Protocol version 3”
      • Collects email messages from the mail server
      • Download messages on the machine
      • User can work offline
      • Saves quota on the server
    • IMAP4 “Internet Message Access Protocol version 4”
      • Retrieves the message header only
  • DNS Services
    • Domain Name System DNS resolves Domain Name into IP Address


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