TCP/IP Tutorial and Technical Overview - IBM Redbooks

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Request
A request message from a client to a server includes the method to be applied to
the resource, the identifier of the source, and the protocol version in use. A
request message field is as follows:
Request = Request-Line
*( general-header | request-header | entity-header )
CRLF
[ message-body ]
Refer to RFC 2616 for detailed information.
Response
An HTTP server returns a response after evaluating the client request. A
response message field is as follows:
Request = Request-Line
*( general-header | request-header | entity-header )
CRLF
[ message-body ]
Refer to RFC 2616 for detailed information.
Entity
Either the client or server might send Entity in the request message or the
response message, unless otherwise indicated. Entity consists of the following:
► Entity header fields
► Entity body
Persistent connections
A significant difference between HTTP 1.1 and earlier versions of HTTP is that
HTTP 1.1 uses a persistent connection as the default. In earlier version
implementations, a separate TCP connection is established for each URL and
clients have to make multiple requests for images and associated data on the
same URL. This approach was causing congestion and performance problems in
the network. Persistent HTTP connections have a number of advantages, most
notably the reduction in TCP connections and subsequently, of waiting times.
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