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|| The TCP/IP Guide|
9 TCP/IP Application Layer Protocols, Services and Applications (OSI Layers 5, 6 and 7)
9 TCP/IP Key Applications and Application Protocols
9 TCP/IP File and Message Transfer Applications and Protocols (FTP, TFTP, Electronic Mail, USENET, HTTP/WWW, Gopher)
9 TCP/IP World Wide Web (WWW, "The Web") and the Hypertext Transfer Protocol (HTTP)
9 TCP/IP Hypertext Transfer Protocol (HTTP)
9 HTTP Entities, Transfers, Coding Methods and Content Management
HTTP Content Negotiation and "Quality Values"
(Page 1 of 3)
Many Internet resources have only
one representation, meaning a single way in which they are stored or
made available. In this situation, a client request to a server is an
all or nothing proposition. The client may specify conditions
under which it would like the server to send the resource, using the
If- series of request
headers. If the condition is met, the
resource will be sent in the servers response in the one form
in which it exists; if the condition is not met, no entity will be returned.
Other resources, however, may have
multiple representations. The most common example would be a document
that is available in multiple languages, or that is stored using more
than one character set. Similarly, a graphical image might exist in
two different formats: one a Tagged Image File Format (TIFF) file for
those wanting maximum image quality despite the large size of TIFF images;
and a more compact JPEG file for those who need to see the image quickly
and dont care as much about its quality level.
Content Negotiation Techniques
To provide flexibility in allowing
clients to obtain the best version of resources that exist in multiple
forms, HTTP/1.1 defines a set of features that are collectively called
content negotiation. The standard defines two basic methods by
which this negotiation may be performed:
- Server-Driven Negotiation: In this technique,
the client includes headers in its request that provide guidance to
the server about its desired representation for the resource. The server
uses an algorithm that processes this information and provides the version
of the resource that it feels best matches the clients preferences.
- Agent-Driven Negotiation: This method
puts the client in charge of the negotiation process. It first sends
a preliminary request for the resource to the server. If the resource
is available in multiple forms, the server typically sends back a 300
(Multiple Choices) response, which contains a list
of the various representations in which the resource is available. The
client then sends a second request for the one that it prefers.
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Table Of Contents - Contact Us
The TCP/IP Guide (http://www.TCPIPGuide.com)
Version 3.0 - Version Date: September 20, 2005
© Copyright 2001-2005 Charles M. Kozierok. All Rights Reserved.
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