Uniform Resource Locator Parts

The general form of an URL has four parts

  1. A scheme followed by a colon.
    • Invokes a TCP/IP-based application level protocol
    • Schemes are: http, https, ftp, news, mailto, file, telnet.

  2. A server name.
    • A // followed by the host name or IP address of the server
    • Not needed if the server is the default
      • news server
      • mail server

  3. An optional port number. Standard or default port numbers are:
      ftp *
      ssh 22
      telnet 23
      smtp 25
      gopher 70
      http 80
      nntp 119
      SSL 443

  4. A path.
    • Consisting of folders and/or files.
    • May include a file extension which identifies the type of document.
    • May also include a QUERY_STRING with arguments.

    * Ftp uses port 20 for data and port 21 for flow control.

I understand the parts of an URL. What is a service?