Syntax extensions for abbreviating media feature sets with URLs

Document Type Expired Internet-Draft (conneg WG)
Author William Newman 
Last updated 1999-03-01
Stream Internet Engineering Task Force (IETF)
Intended RFC status (None)
Expired & archived
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Stream WG state WG Document
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IESG IESG state Expired
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This Internet-Draft is no longer active. A copy of the expired Internet-Draft can be found at


Other Internet Drafts from the CONNEG working group describe a syntax[SYNTAX] and vocabulary[FEATURES] for negotiating media feature sets which can be used for transmission of a message. For example, a feature set may specify that full color output up to 800x600 pixels is supported, or that output can have up to 300 dots per inch. These feature sets can be arbitrarily complex, and typical feature set expressions may be hundreds of bytes in length. It would be relatively costly to transmit such long feature set expressions, and this cost could be a significant obstacle to the use of the CONNEG standard to negotiate capabilities for Internet transactions. The problem is likely to particularly severe for low-bandwidth wireless connections to the Internet. This document describes an extension to the CONNEG syntax[SYNTAX] which allows a feature set expression to be represented as an absolute URL, which can then be looked up over another channel, which is not necessarily the channel between the negotiating parties. By using this extension, content negotiation between two parties can proceed with a relatively small exchange of data over the channel between them. Of course, the contents of the URL must still be found through some channel. However, the channel used to find the contents of the URL may have greater bandwidth than the channel between the negotiating parties, and may further benefit from HTTP or other caching mechanisms. This extended syntax is only applicable when the receiver of the feature set has the capability to fetch the contents of absolute URLs. In contrast, the base, unextended syntax[SYNTAX] is applicable to any transmission channel, without requiring any external resources for the feature set transmitter or the feature set receiver.


William Newman (

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