rfc2531.txt

著名的RFC文档,其中有一些文档是已经翻译成中文的的.

         (| (& (paper-size=A4) (ua-media=[stationery,transparency]) )
            (& (paper-size=B4) (ua-media=continuous) ) )
         (image-coding=[MH,MR,JBIG]) )

   Turning to the document itself, assume it is available to the sender
   in three possible formats, A4 high resolution, B4 low resolution and
   A4 high resolution color, described by:

      (& (dpi=300) (dpi-xyratio=1)
         (color=Binary)
         (paper-size=A4)
         (image-coding=[MMR,JBIG]) )

      (& (dpi=200) (dpi-xyratio=200/100)
         (color=Binary)
         (paper-size=B4)
         (image-coding=[MH,MR]) )

      (& (dpi=300) (dpi-xyratio=1)
         (color=Mapped) (color-levels<=256)
         (paper-size=A4)
         (image-coding=JPEG) )

   These three image formats can be combined into a composite capability
   statement by a logical-OR operation (to describe format-1 OR format-2
   OR format-3):





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      (& (dpi=300) (dpi-xyratio=1)
         (color=Binary)
         (paper-size=A4)
         (image-coding=[MMR,JBIG]) )
      (& (dpi=200) (dpi-xyratio=200/100)
         (color=Binary)
         (paper-size=B4)
         (image-coding=[MH,MR]) )
      (& (dpi=300) (dpi-xyratio=1)
         (color=Mapped) (color-levels=42)
         (paper-size=A4)
         (image-coding=JPEG) ) )

   This could be simplified, but there is little gain in doing so at
   this point.

   The composite document description can be matched with the receiver
   capability description, according to the rules in [2], to yield the
   result:

      (& (dpi=300) (dpi-xyratio=1)
         (color=Binary)
         (paper-size=A4)
         (ua-media=[stationery,transparency])
         (image-coding=JBIG) )
      (& (dpi=200) (dpi-xyratio=200/100)
         (color=Binary)
         (paper-size=B4)
         (ua-media=continuous)
         (image-coding=[MH,MR]) ) )

   Points to note about the feature matching process:

   o  The color document option is eliminated because the receiver
      cannot handle either color (indicated by '(color=Mapped)') or JPEG
      coding (indicated by '(image-coding=JPEG)').

   o  The high resolution version of the document with '(dpi=300)' must
      be send using '(image-coding=JBIG)' because this is the only
      available coding of the image data that the receiver can use for
      high resolution documents.  (The available 300dpi document codings
      here are MMR and JBIG, and the receiver capabilities are MH, MR
      and JBIG.)

   o  The low-resolution version of the document can be sent with either
      MH or MR coding as the receiver can deal with either of these for
      low resolution documents.




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   o  The high resolution variant of the document is available only for
      A4, so that is the paper-size used in that case.  Similarly the
      low resolution version is sent for B4 paper.

   o  Even though the sender may not understand the 'ua-media' feature
      tag, and does not mention it, the matching rules preserve the
      constraint that the B4 document is rendered with '(ua-
      media=continuous)', and the A4 document may be rendered with '
      (ua-media=[stationery,transparency])'.

   Finally, note that when matching an MRC document description, the
   description of each component sub-image must match the capabilities
   of the intended receiver.

5. IANA Considerations

   Appendix A of this document calls for registrations of feature tags
   in the "IETF tree", as defined in section 3.1.1 of "Media Feature Tag
   Registration Procedure" [1] (i.e. these feature tags are subject to
   the "IETF Consensus" policies described in RFC 2434 [21]).

   ASN.1 identifiers should be assigned for each of these registered
   feature tags and replaced in the body of the registration.

6. Security Considerations

   The points raised below are in addition to the general security
   considerations for extended Internet fax [5], and others discussed in
   [2,8,11,12,13]

6.1 Capability descriptions and mechanisms

   Negotiation mechanisms reveal information about one party to other
   parties.  This may raise privacy concerns, and may allow a malicious
   party to make better guesses about the presence of specific security
   holes.

   Most of these concerns pertain to capability information getting into
   the hands of someone who may abuse it.  This document specifies
   capabilities that help a sender to determine what image
   characteristics can be processed by the recipient, not mechanisms for
   their publication.  Implementors and users should take care that the
   mechanisms employed ensure that capabilities are revealed only to
   appropriate persons, systems and agents.







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6.2 Specific threats

   1.  Unsolicited bulk mail:  if it is known that a recipient can
       process certain types of images, they may be targeted by bulk
       mailers that want to send such images.

7. Acknowledgements

   The authors gratefully acknowledge the contributions of the following
   persons who commented on earlier versions of this memo: James
   Rafferty, Dan Wing, Robert Buckley, Mr Ryuji Iwazaki.  The following
   contributed ideas upon which some of the features described here have
   been based: Larry Masinter, Al Gilman, Koen Holtman.

8. References

   [1]  Holtman, K., Mutz, A. and T. Hardie, "Media Feature Tag
        Registration Procedure", BCP 31, RFC 2506, March 1999.

   [2]  Klyne, G., "A Syntax for Describing Media Feature Sets", RFC
        2533, March 1999.

   [3]  Masinter, L., Holtman, K., Mutz, A. and D. Wing, "Media Features
        for Display, Print, and Fax", RFC 2534, March 1999.

   [4]  McIntyre, L. and G. Klyne, "Internet fax feature mapping from
        Group 3 fax", Work in Progress.

   [5]  Masinter, L. and D. Wing, "Extended Facsimile Using Internet
        Mail", RFC 2532, March 1999.

   [6]  "Procedures for document facsimile transmission in the general
        switched telephone network", ITU-T Recommendation T.30 (1996),
        International Telecommunications Union, July 1996.

   [7]  McIntyre, L., Buckley, R., Venable, D., Zilles, S., Parsons, G.
        and J. Rafferty, "File format for Internet fax", RFC 2301, March
        1998.

   [8]  Toyoda, K., Ohno, H., Murai, J. and D. Wing, "A Simple Mode of
        Facsimile Using Internet Mail", RFC 2305, March 1998.

   [9]  "Continuous-tone color representation method for facsimile"
        ITU-T Recommendation T.42 (1996), International
        Telecommunications Union, (Covers custom illuminant, gamut).






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   [10] "Colour and gray-scale image representation using lossless
        coding scheme for facsimile", ITU-T Recommendation T.43 (1997),
        International Telecommunications Union. (Covers JBIG for
        colour/grey images).

   [11] Hardie, T., "Scenarios for the Delivery of Negotiated Content",
        Work in Progress.

   [12] Klyne, G., "Requirements for protocol-independent content
        negotiation", Work in Progress.

   [13] "Standardization of Group 3 facsimile terminals for document
        transmission", ITU-T Recommendation T.4 (1996), International
        Telecommunications Union, (Covers basic fax coding formats: MH,
        MR).

   [14] "Facsimile coding schemes and coding control functions for Group
        4 facsimile apparatus", ITU Recommendation T.6, International
        Telecommunications Union, (Commonly referred to as the MMR
        standard; covers extended 2-D fax coding format).

   [15] "Mixed Raster Content (MRC)", ITU-T Recommendation T.44,
        International Telecommunications Union.

   [16] "Information technology - Digital compression and coding of
        continuous-tone still image - Requirements and guidelines",
        ITU-T Recommendation T.81 (1992) | ISO/IEC 10918-1:1993,
        International Telecommunications Union, (Commonly referred to as
        JPEG standard).

   [17] "Information technology - Coded representation of picture and
        audio information - Progressive bi-level image compression",
        ITU-T Recommendation T.82 (1993) | ISO/IEC 11544:1993,
        International Telecommunications Union, (Commonly referred to as
        JBIG1 standard).

   [18] "Application profile for Recommendation T.82 - Progressive bi-
        level image compression (JBIG1 coding scheme for facsimile
        apparatus)", ITU-T Recommendation T.85 (1995), International
        Telecommunications Union, (Covers bi-level JBIG).

   [19] "Colorimeter, 2nd ed.", CIE Publication No. 15.2, 1986.
        (Defines CIELAB color space;  use with fax is further
        constrained by T.42 [9].)







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   [20] Tag Image File Format, Revision 6.0, Adobe Developers
        Association,
        <ftp://ftp.adobe.com/pub/adobe/devrelations/devtechnotes
        /pdffiles/tiff6.pdf>, June 1992.

   [21] Narten, T. and H. Alvestrand, "Guidelines for Writing an IANA
        Considerations Section in RFCs", BCP 26, RFC 2434, October 1998.












































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9. Authors' Addresses

   Graham Klyne
   5th Generation Messaging Ltd.    Content Technologies Ltd.
   5 Watlington Street              Forum 1, Station Road
   Nettlebed                        Theale
   Henley-on-Thames, RG9 5AB        Reading, RG7 4RA
   United Kingdom                   United Kingdom.

   Phone:     [phone]      [phone]
   Facsimile: [phone]      [phone]
   EMail:     [e-mail]


   Lloyd McIntyre
   Xerox Corporation
   Mailstop PAHV-121
   3400 Hillview Ave.
   Palo Alto, CA 94304 USA

   Phone:     [phone]
   Facsimile: [phone]
   EMail: [e-mail]




























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RFC 2531        Content Feature Schema for Internet Fax       March 1999


Appendix A: Feature registrations

A.1 Image size

   -  Media Feature tag name(s):

         size-x
         size-y

   -  ASN.1 identifiers associated with these feature tags:

         1.3.6.1.8.1.7
         1.3.6.1.8.1.8

   -  Summary of the media features indicated:

         These feature tags indicate the size of a displayed, printed or
         otherwise rendered document image;  they indicate horizontal
         (size-x) and vertical (size-y) dimensions.

         The unit of measure is inches (to be consistent with the
         measure of resolution defined by the feature tag 'dpi').

         Where the actual size is available in millimetres, a conversion
         factor of 10/254 may be applied to yield an exact inch-based
         value.

   -  Values appropriate for use with these feature tags:

         Rational (>0)

   -  The feature tag is intended primarily for use in the following
      applications, protocols, services, or negotiation mechanisms: