Network Working Group                                     T. Berners-Lee
Request for Comments: 1945                                       MIT/LCS
Category: Informational                                      R. Fielding
                                                               UC Irvine
                                                              H. Frystyk
                                                                 MIT/LCS
                                                                May 1996


                Hypertext Transfer Protocol -- HTTP/1.0(‘±‚«)

Status of This Memo(—ª)

IESG Note:(—ª)

Abstract(—ª)

1.  Introduction(—ª)

1.1  Purpose(—ª)

1.2  Terminology

   This specification uses a number of terms to refer to the roles
   played by participants in, and objects of, the HTTP communication.

   connection

       A transport layer virtual circuit established between two
       application programs for the purpose of communication.

   message

       The basic unit of HTTP communication, consisting of a structured
       sequence of octets matching the syntax defined in Section 4 and
       transmitted via the connection.

   request

       An HTTP request message (as defined in Section 5).

   response

       An HTTP response message (as defined in Section 6).

   resource

       A network data object or service which can be identified by a
       URI (Section 3.2).

   entity

       A particular representation or rendition of a data resource, or
       reply from a service resource, that may be enclosed within a
       request or response message. An entity consists of
       metainformation in the form of entity headers and content in the
       form of an entity body.

   client

       An application program that establishes connections for the
       purpose of sending requests.

   user agent

       The client which initiates a request. These are often browsers,
       editors, spiders (web-traversing robots), or other end user
       tools.

   server

       An application program that accepts connections in order to
       service requests by sending back responses.

   origin server

       The server on which a given resource resides or is to be created.

   proxy

       An intermediary program which acts as both a server and a client
       for the purpose of making requests on behalf of other clients.
       Requests are serviced internally or by passing them, with
       possible translation, on to other servers. A proxy must
       interpret and, if necessary, rewrite a request message before
       forwarding it. Proxies are often used as client-side portals
       through network firewalls and as helper applications for
       handling requests via protocols not implemented by the user
       agent.

   gateway

       A server which acts as an intermediary for some other server.
       Unlike a proxy, a gateway receives requests as if it were the
       origin server for the requested resource; the requesting client
       may not be aware that it is communicating with a gateway.
       Gateways are often used as server-side portals through network
       firewalls and as protocol translators for access to resources
       stored on non-HTTP systems.

   tunnel

       A tunnel is an intermediary program which is acting as a blind
       relay between two connections. Once active, a tunnel is not
       considered a party to the HTTP communication, though the tunnel
       may have been initiated by an HTTP request. The tunnel ceases to
       exist when both ends of the relayed connections are closed.
       Tunnels are used when a portal is necessary and the intermediary
       cannot, or should not, interpret the relayed communication.

   cache

       A program's local store of response messages and the subsystem
       that controls its message storage, retrieval, and deletion. A
       cache stores cachable responses in order to reduce the response
       time and network bandwidth consumption on future, equivalent
       requests. Any client or server may include a cache, though a
       cache cannot be used by a server while it is acting as a tunnel.

   Any given program may be capable of being both a client and a server;
   our use of these terms refers only to the role being performed by the
   program for a particular connection, rather than to the program's
   capabilities in general. Likewise, any server may act as an origin
   server, proxy, gateway, or tunnel, switching behavior based on the
   nature of each request.