rfc2150.txt

著名的RFC文档,其中有一些文档是已经翻译成中文的的.

   at incredible speeds.  Unfortunately, there are many different ways
   of encoding information.  Computers that use different methods can be
   said to speak different languages.  In order for computers to talk to
   each other there must be a thing called a "Communication Protocol"
   that provides a set of procedures for talking and a common language
   to use.

   The Internet Protocol, or IP, is the Communication Protocol that all
   computers on the Internet must use and understand.  It allows
   computers to find each other, and to send packages, or "packets", of
   information back and forth.  Much like the Postal service reads your
   country code, city code, etc., but not the contents of your letter,
   the Internet Protocol does not care what is inside most of these
   packets of information.  This is a great thing because it means that
   other, higher level protocols may transmit any possible kind of
   information simply by stuffing it into a packet and handing it off to
   the software responsible for speaking IP.

   Another important protocol upon which the Internet is built is the
   Transmission Control Protocol, or TCP.  IP by itself provides a way
   of sending a message to another computer, but no guarantee that it
   will get through.  Since reliable communication is a necessity, the
   TCP protocol was invented which uses IP to send packets and
   guarantees their delivery by requiring the receiver to acknowledge
   the information received.  TCP and IP form the heart of a group of
   protocols aptly named the TCP/IP protocol suite.  This suite of
   protocols provides most of the functionality of the Internet.

   We will be mentioning these protocols throughout the rest of the
   document.  Information on IP and other Internet Protocols can be
   obtained through the resources referenced in Section 10.

4.1  Internet Addresses

   There are many things we would like to be able to find on the net,
   including people, information, and the computers themselves.  An
   important part of IP and other protocols is the way they label things
   so that the computers can find and identify them.  The U.S. Post
   Office finds people by their Postal Address, which is just a label
   containing information about who you are, and where you live.
   Likewise, the various protocols of the Internet have given computers,
   people, and information, addresses which can be used to find them.
   The following sections will describe several different kinds of
   addresses.





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4.1.1 Computer Addresses and Hostnames

   When speaking IP, computers locate each other using a thing called
   their IP Address.  Each computer on the Internet must have a unique
   IP Address.  Some programs allow or require you to use the IP Address
   directly, if so, it will appear as four groups of numbers separated
   by dots. (i.e., 123.123.123.123) Most of the time though, you will
   not need to worry about the actual IP Address number, because all
   computers have a "Host Name" to which the number is mapped.

   A computers hostname also comes in parts, separated by dots.  The
   first part is the name of the machine, and the second part is the
   name of the "domain" in which that computer is registered.

   For example, if I had a machine named "foo" registered in the
   commercial domain known as "com", my machine's hostname would be
   "foo.com".  When speaking out loud, this machine's address would be
   spoken as "foo dot com".

   A domain is just an abstract category to which machines and networks
   may be registered into in order to organize them.  Domains are
   organized in a hierarchy of top level domains and their subdomains.
   Top Level Domains include,

         .edu   for educational institutions
         .gov   for government sites
         .com   for commercial companies
         .org   for other organizations
         .net   for network infrastructure sites
         .us    for sites in the United States
         .ca    for sites in Canada
         .nl    for sites in the Netherlands
         .jp    for sites in Japan

   to name a few.  Domain names may be further subdivided by inserting
   one or more subdomain names before the top level domain, still
   separating everything with dots.  For example, "law.harvard.edu", for
   the Law School at Harvard University, and "la.ca.us" for computers in
   Los Angeles, California in the United States.

   More information about the Domain Naming System can be found in the
   documents referenced in Section 10.

4.1.2  Addresses of People on the Internet

   Every human being has a given name, or full name with which we
   address them.  When you begin to use a computer, you will be
   introduced to your "username".  Your username, sometimes called your



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   user i.d., may be your initials, your last name and first initial,
   your nickname, a number, or anything else that is just normal letter
   or number characters.  (Your username usually cannot contain
   "special" characters such as "&", or "%".)  Sometimes you get to
   choose your own username, and sometimes your service provider or
   system administrator will choose one for you.

   Your username is used when you connect to other computers, and to
   identify you in electronic mail. Your electronic mail, or Email
   Address, will consist of your username followed by the symbol "@",
   followed by your computers hostname.

   So, for Joe Cool, who has the username "jcool", and gets his Internet
   service from Dirigible Online, his email address might be
   "[e-mail]".  When spoken out loud, the "@" symbol is
   pronounced simply "at" so this would typically be spoken as "jcool at
   dirigible dot com".

   Email is moved around on the Internet using the Simple Mail Transfer
   Protocol, SMTP, over IP.  Information on SMTP can be found in the
   documents listed in Section 10.

4.1.3  Information Addresses, Uniform Resource Locators, or URLs.

   In order to retrieve information from the Internet, you need to be
   able to find it and know how to ask for it.  This is the job of the
   Uniform Resource Locator, or URL which functions as an address for
   information.  Every file or document intended to be accessible
   through the Internet has a URL.

   URLs (or simplified versions of them) are now appearing frequently in
   TV, billboard, and magazine advertising as a company's Internet
   Address; basically the hostname of their web site.

   In previous sections we've identified IP Addresses, hostnames and
   email addresses; a URL contains more information.  Not only does it
   tell you what the information is, and where to find it, it also tells
   you precisely which protocol you need to use to retrieve it.

   A URL is a machine readable, and hence somewhat cryptic, text string,
   in a form such as "http://www.something.com/location/filename.ext".
   This string can be broken down into the following pieces.

    http    is the name of the communications protocol which can be used
            to access the information.  In this case, it identifies the
            HyperText Transfer Protocol, which is used in the World Wide
            Web, and will be described later.  Other protocols are
            described in Section 4.3.



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      :     separates the protocol from the hostname

     //     indicates that what is to follow is the hostname

   www.something.com  is the hostname of the computer on which the
            document resides.  In this case, the "www" indicates that
            it is a machine named for the fact that it is running a
            World Wide Web server.  "something.com" is the domain in
            which that server is registered.  Typically the "something"
            part is the name of the organization running the server.

     /      separates the hostname from directory on the machine in
            which the information resides.

   location is the location of the information on the machine
            something.com.

   filename is the first part of the file name of the information you
            are retrieving.

     .      a dot separates the filename from its extension

     ext    the extension, or file "type" actually says a great deal
            about the file, how to handle it, and how to present it.

   The URLs you see will usually be simpler than this.  The people at
   something.com assume you are going to use a modern web browser to
   access the information, so they may leave off the protocol
   information, "http://",  because this is probably your web browsers
   default protocol.  Also, if they configure their server to have a
   default homepage to display, they can leave off everything after the
   hostname part of the URL.  This puts it into the form that is most
   commonly seen, www.something.com.

   URLs can specify any file and most protocols.  In this example, the
   URL is using the protocol for moving HyperText, the HyperText
   Transfer Protocol, HTTP, over IP.  More information on HyperText and
   HTTP can be found in the next section, and in the Resources section.

4.2 How Does the World Wide Web Work?

   Web pages are computer files written in a format called HTML, the
   HyperText Markup Language.  HTML is the protocol for putting specific
   strings of letters and symbols (such as parentheses) into an ordinary







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   text document which can specify that words link to other pages, or be
   viewed in a particular type font, or display images, or many other
   things when viewed with the appropriate software.  The appropriate
   software would generally be a web browser.  More information about
   software tools is provided in Section 6.2.

   HTML is simple enough that most people can learn to use it, but rich
   enough in possibility that there will always be a thriving community
   of people making web pages for others.

   Links within a hypertext documented are implemented using references
   to the URL of the information to be linked to.

   In order to download information from distant places in the web, your
   computer will typically be using a protocol called HTTP, the
   HyperText Transfer Protocol.  HTTP was designed to allow web browser
   software to connect to web server software on other machines and
   request the transmission of a web page in the form of an HTML
   document and any associated images, audio, video, etc.  The latest
   version of the HTTP can actually tell what type of browser is
   connecting and the server is now able to better customize its default
   homepage to its audience.

   More information on HTML, HTTP, and hypertext can be found in Section
   7.3, and through the references listed in the Resources section.

4.3  Other Higher Level Protocols on the Internet.

   There are many other higher level protocols built on top of IP.
   We've provide examples throughout the document, but we'll mention a
   few here to make you more familiar with them.

      telnet: a protocol for providing remote terminal service.  Telnet
            software allows you to log in to remote computers across the
            net by giving you a virtual terminal on that computer.

      ftp: the File Transfer Protocol.  FTP allows diverse machines to
            send simple files back and forth.  FTP is usually used by
            archive sites to allow multiple users to download files
            simultaneously.

      smtp: the Simple Mail Transfer Protocol.  The SMTP specification
            allows electronic mail to be sent, stored, and forwarded,
            around the Internet.  SMTP does not specify how a mail
            "reader" operates, just the transmission of email.






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      nntp: the Network News Transfer Protocol.  NNTP specifies how
            Internet News is passed, stored and forwarded around the
            Internet.

      gopher: the Gopher protocol creates linkages, much like the web,
            which is called, "gopherspace".  The specification allows