HTTP/1.1 200 OK Date: Tue, 09 Apr 2002 02:20:48 GMT Server: Apache/1.3.20 (Unix) Last-Modified: Mon, 19 Oct 1998 11:51:00 GMT ETag: "2ed975-6af8-362b27a4" Accept-Ranges: bytes Content-Length: 27384 Connection: close Content-Type: text/plain IETF Fax working group Graham Klyne Request for comments: nnnn 5GM/Content Technologies Category: Work-in-progress Lloyd McIntyre Xerox Corporation October 1998 Expires: April 1999 Content feature schema for Internet fax Status of this memo This document is an Internet-Draft. Internet-Drafts are working documents of the Internet Engineering Task Force (IETF), its areas, and its working groups. Note that other groups may also distribute working documents as Internet-Drafts. Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet-Drafts as reference material or to cite them other than as ``work in progress''. To view the entire list of current Internet-Drafts, please check the "1id-abstracts.txt" listing contained in the Internet-Drafts Shadow Directories on ftp.is.co.za (Africa), ftp.nordu.net (Northern Europe), ftp.nis.garr.it (Southern Europe), munnari.oz.au (Pacific Rim), ftp.ietf.org (US East Coast), or ftp.isi.edu (US West Coast). [[INTENDED STATUS: This document specifies an Internet standards track protocol for the Internet community, and requests discussion and suggestions for improvements. Please refer to the current edition of the "Internet Official Protocol Standards" (STD 1) for the standardization state and status of this protocol. Distribution of this memo is unlimited.]] Copyright Notice Copyright (C) The Internet Society 1998. All Rights Reserved. Abstract This document defines a content feature schema that is a profile of the media feature registration mechanisms [1,2,3] for use in performing capability identification between extended Internet fax systems [5]. Klyne/McIntyre Work-in-progress [Page 1] RFC nnnn Content feature schema for Internet fax October 1998 This document does not describe any specific mechanisms for communicating capability information, but does presume that any such mechanisms will transfer textual values. It specifies a textual format to be used for describing Internet fax capability information. Table of contents 1. Introduction ............................................2 1.1 Organization of this document 3 1.2 Terminology and document conventions 3 1.3 Revision history 3 1.4 Unfinished business 4 2. Fax feature schema syntax ...............................4 3. Internet fax feature tags ...............................4 3.1 Image Size 5 3.2 Resolution 5 3.3 Media type 6 3.4 Paper Size 6 3.5 Colour and greyscale 6 3.6 Coding 7 3.7 Colour model 8 3.8 Preferred units 8 4. Examples ................................................8 4.1 Simple mode Internet fax system 8 4.2 High-end black-and-white Internet fax system 9 4.3 Grey-scale Internet fax system 9 4.4 Full-colour Internet fax system (JPEG) 9 4.5 Full-colour Internet fax system (MRC) 9 4.6 Sender and receiver feature matching 9 5. Security considerations .................................12 5.1 Threats 12 6. Full copyright statement ................................12 7. Acknowledgements ........................................13 8. References ..............................................13 9. Authors' addresses ......................................15 Appendix A: Feature registrations ..........................15 1. Introduction This document defines a content feature schema that is a profile of the media feature registration mechanisms [1,2,3] for use in performing capability identification between extended Internet fax systems [5]. This document does not describe any specific mechanisms for communicating capability information, but does presume that any such mechanisms will transfer textual values. It specifies a textual format to be used for describing Internet fax capability information. Klyne/McIntyre Work-in-progress [Page 2] RFC nnnn Content feature schema for Internet fax October 1998 The range of capabilities that can be indicated are based on those covered by the TIFF file format for Internet fax [7] and Group 3 facsimile [6]. A companion document [4] describes the relationship and mapping between this schema and Group 3 fax capabilities. 1.1 Organization of this document Section 2 specifies the overall syntax for fax feature descriptions by reference to the media feature registration and syntax documents [1,2]. Section 3 enumerates the feature tags that are to be recognized and processed by extended Internet fax systems, according to their capabilities. Appendix A contains additional feature tag registrations for media features that are specific to fax and for which no applicable registration already exists. These are presented in the form prescribed by the media feature registration procedure [1]. 1.2 Terminology and document conventions The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in [RFC2119]. The term "eifax system" is used to describe any software, device or combination of these that conforms to the specification "Extended Facsimile Using Internet Mail" [5]. NOTE: Comments like this provide additional nonessential information about the rationale behind this document. Such information is not needed for building a conformant implementation, but may help those who wish to understand the design in greater depth. 1.3 Revision history 00a 28-Sep-1998 Initial draft. 01a 12-Oct-1998 Incorporated review comments. Described feature tag for differential x/y resolution ratio. Klyne/McIntyre Work-in-progress [Page 3] RFC nnnn Content feature schema for Internet fax October 1998 1.4 Unfinished business - Review terminology (especially eifax). - Finalize feature set - Supply examples - Supply new feature registrations 2. Fax feature schema syntax The syntax for the fax feature schema is described by "A syntax for describing media feature sets" [2]. This in turn calls upon media feature tags that may be registered according to the procedure described in "Media Feature Tag Registration Procedure" [1]. NOTE: Media feature registration provides a base vocabulary of features that correspond to media handling capabilities. The feature set syntax provides a mechanism and format for combining these to describe combinations of features that may be handled by eifax systems. 3. Internet fax feature tags This section enumerates and briefly describes a number of feature tags that are defined for use with Extended Internet Fax (eifax) systems and applications. These tags may be used also by other systems and applications that support corresponding capabilities. The feature tags presented below are those that an eifax system is expected to recognize its ability or non-ability to handle. Definitive descriptions of feature tags are indicated by reference to their registration per the 'conneg' registration procedure [1] (some of which are appended to this document) NOTE: The presence of a feature tag in this list does not mean that an eifax system must have that capability; rather, it must recognize the feature tag and deal with it according to the capabilities that it does have. Further, an eifax system is not prevented from recognizing and offering additional feature tags. The list below is intended to provide a minimum vocabulary that all eifax systems can use in a consistent fashion. If an unrecognized or unused feature tag is received, the feature set matching rule (described in [2]) operates so that tag is effectively ignored. Klyne/McIntyre Work-in-progress [Page 4] RFC nnnn Content feature schema for Internet fax October 1998 3.1 Image Size Feature tag name Legal values ---------------- ------------ pix-x (>0) pix-y (>0) Reference: "Media Features for Display, Print, and Fax" [3]. [[[GK: The use of pixels as a measure of fax image size is currently under discussion: should we use pixels or some physical unit of measure? In my opinion, we should use physical dimensions rather than pixels, because when a device (like a fax) offers a range of resolutions, these are not generally reflected in the physical image size, though they would affect the pixel size. Thus, using physical dimensions, it is not necessary to specify a different image size with each resolution option.]]] 3.2 Resolution Feature tag name Legal values ---------------- ------------ dpi (>0) dpi-xyratio (>0) Reference: "Media Features for Display, Print, and Fax" [3], and this document appendix A. If 'dpi-xyratio' is present and not equal to 1 then the horizontal resolution (x-axis) is indicated by the 'dpi' feature value, and the vertical resolution (y-axis) is the value of 'dpi' divided by 'dpi-xyratio'. For example, the basic Group 3 fax resolution of 200*100dpi might be indicated as: (& (dpi=200) (dpi-xyratio=200/100) ) [[[Handling of differential x- and y- resolutions is currently under discussion.]]] Klyne/McIntyre Work-in-progress [Page 5] RFC nnnn Content feature schema for Internet fax October 1998 3.3 Media type Feature tag name Legal values ---------------- ------------ ua-media screen screen-paged stationery transparency envelope envelope-plain continuous Reference: "Media Features for Display, Print, and Fax" [3]. NOTE: Where the recipient indicates specific support for hard copy or soft copy media type, a sender of colour image data may wish to adjust the colour components (e.g. per the related rules of ITU recommendation T.42 [9]) to improve rendered image quality on that medium. 3.4 Paper Size Feature tag name Legal values ---------------- ------------ paper-size A4 A3 B4 letter legal Reference: "Media Features for Display, Print, and Fax" [3]. 3.5 Colour and greyscale Feature tag name Legal values ---------------- ------------ grey (Typically 2,16,256,65536,16777216) color (Typically 16,256,65536,16777216) Reference: "Media Features for Display, Print, and Fax" [3]. NOTE: a bi-level (i.e. black-and-white only) fax image or capability is indicated by the feature value 'grey=2'. This is indicates the rendering capabilities of a recipient or requirements of a document, and does not of itself indicate a coding scheme. Klyne/McIntyre Work-in-progress [Page 6] RFC nnnn Content feature schema for Internet fax October 1998 3.6 Coding Feature tag name Legal values ---------------- ------------ image-coding MH MR MMR JBIG-2-Level (bi-level) JBIG-M-Level (multi-level) JPEG MRC strip-size image-interleave Strip Plane color-subsampling MRC-level [1-7] The 'strip-size' feature may be used with JBIG and MRC coding, and indicates the maximum number of scan lines in an image strip. For JBIG receivers the legal constraints are: (strip-size=128) (strip-size>=0) The later being equivalent to no restriction. For MRC coded image receivers, the legal constraints are: (strip-size=[0..256]) (strip-size>=0) For a receiver that can handle both JBIG and MRC images, the strip- size constraints may need to be related to the image coding, as in this example: (| (& (image-coding=JBIG-2-LEVEL) (strip-size=128) ) (& (image-coding=JBIG-M-LEVEL) (strip-size=128) ) (& (image-coding=MRC) (strip-size=[0..256]) ) Where it may vary, the actual maximum strip size for a given file is indicated in the image data. The 'MRC-level' feature is used only if the 'image-coding' feature includes MRC. Reference: this document, appendix A. [[[GK: color subsampling is proposed to be changed to a token, thus allowing subsampling capabilities other than 4:1:1.]]] Klyne/McIntyre Work-in-progress [Page 7] RFC nnnn Content feature schema for Internet fax October 1998 3.7 Colour model Feature tag name Legal values ---------------- ------------ color-space CIELAB (per T.42 [9]) Palette (per T.43 [10]) custom-illuminant custom-gamut Reference: this document, appendix A. 3.8 Preferred units Feature tag name Legal values ---------------- ------------ preferred-unit metric inch NOTE: this feature is really provided for interactions that involve legacy fax machines. TIFF images used for Internet fax (per RFC 2301 [7]) always contain inch-based measurements. The value of this feature does not affect in any way the units used for expressing other feature values; e.g. resolution is always measured in dots per inch. Reference: this document, appendix A. 4. Examples Some of the examples contain comments introduced by '--...'. These are not part of the allowed capability description syntax. They are included here to explain some of the constructs used. <<> 4.1 Simple mode Internet fax system This example describes the capabilities of a typical simple mode Internet fax system. Note that TIFF application S is required to be supported by such a system. (& ( dpi=200 ) ( dpi-xyratio=[200/100,200/200] ) ( grey=2 ) ( paper-size=A4 ) ( image-coding=MH ) ( ua-media=stationery ) ) Klyne/McIntyre Work-in-progress [Page 8] RFC nnnn Content feature schema for Internet fax October 1998 4.2 High-end black-and-white Internet fax system This would include support for B/W JBIG and be equivalent to what is sometimes called "Super G3", except that Internet fax functionality would be added. (& (| (& (dpi=200) (dpi-xyratio=200/100) ) -- 200*100 (& (dpi=200) (dpi-xyratio=1) ) -- 200*200 (& (dpi=300) (dpi-xyratio=1) ) -- 300*300 (& (dpi=400) (dpi-xyratio=1) ) ) -- 400*400 ( grey=2 ) ( paper-size=[A4,B4] ) ( image-coding=[MH,MR,MMR,JBIG-2-LEVEL] ) ) 4.3 Grey-scale Internet fax system This is the previous example extended to handle grey scale multi- level images. In keeping with Group 3 fax, this capability requires equal x- and y- resolutions for a multi-level image. (& (| (& (dpi=200) (dpi-xyratio=200/100) (grey=2) ) (& (dpi=200) (dpi-xyratio=1) ) (& (dpi=300) (dpi-xyratio=1) ) (& (dpi=400) (dpi-xyratio=1) ) ) ( grey<=256 ) ( paper-size=[A4,B4] ) ( image-coding=[MH,MR,MMR,JBIG-2-LEVEL,JPEG,JBIG-M-LEVEL] ) ) 4.4 Full-colour Internet fax system (JPEG) <<>> 4.5 Full-colour Internet fax system (MRC) <<>> 4.6 Sender and receiver feature matching This example considers sending a document to a high-end black-and- white fax system with the following capabilities: (& (| (& (dpi=200) (dpi-xyratio=200/100) ) -- 200*100 (& (dpi=200) (dpi-xyratio=1) ) -- 200*200 (& (dpi=300) (dpi-xyratio=1) ) -- 300*300 (& (dpi=400) (dpi-xyratio=1) ) ) -- 400*400 ( grey=2 ) (color=0) (| (& (paper-size=A4) (ua-media=[stationery,transparency]) ) (& (paper-size=B4) (ua-media=continuous) ) ) ( image-coding=[MH,MR,JBIG-2-LEVEL] ) ) Klyne/McIntyre Work-in-progress [Page 9] RFC nnnn Content feature schema for Internet fax October 1998 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 colour, described by: (& ( dpi=300 ) ( dpi-xyratio=1 ) ( grey=2 ) ( paper-size=A4 ) ( image-coding=[MMR,JBIG-2-LEVEL] ) ) (& ( dpi=200 ) (dpi-xyratio=200/100) ( grey=2 ) ( paper-size=B4 ) ( image-coding=[MH,MR] ) ) (& ( dpi=300 ) ( dpi-xyratio=1 ) ( color<=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): (| (& ( dpi=300 ) ( dpi-xyratio=1 ) ( grey=2 ) ( paper-size=A4 ) ( image-coding=[MMR,JBIG-2-LEVEL] ) ) (& ( dpi=200 ) (dpi-xyratio=200/100) ( grey=2 ) ( paper-size=B4 ) ( image-coding=[MH,MR] ) ) (& ( dpi=300 ) ( dpi-xyratio=1 ) ( color=42 ) ( paper-size=A4 ) ( image-coding=JPEG ) ) ) This could be simplified, but there is little gain in doing so at this point. Klyne/McIntyre Work-in-progress [Page 10] RFC nnnn Content feature schema for Internet fax October 1998 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 ) ( grey=2 ) ( paper-size=A4 ) ( ua-media=[stationery,transparency] ) ( image-coding=JBIG-2-LEVEL ) ) (& ( dpi=200 ) (dpi-xyratio=200/100) ( grey=2 ) ( paper-size=B4 ) ( ua-media=continuous ) ( image-coding=[MH,MR] ) ) ) Points to note about the feature matching process: o The colour document option is eliminated because the receiver cannot handle either colour (indicated by '(color=0)') or JPEG coding. o The high resolution version of the document with '(dpi=300)' must be send using '(image-coding=JBIG-2-LEVEL)' because this is the only available coding of the image data that the receiver can use for high resolution documents. 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. 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])'. Klyne/McIntyre Work-in-progress [Page 11] RFC nnnn Content feature schema for Internet fax October 1998 5. 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] 5.1 Threats 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 considerations pertain to capabilities information getting into the hands of someone who wanted to abuse it. This document specifies a list of capabilities which will help a sender determine what image files characteristics can be processed by the recipient, not mechanisms for their publication. Implementors and users should try to ensure that these capabilities are provided to appropriate persons, systems and agents. 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. <<>> 6. Full copyright statement Copyright (C) The Internet Society 1998. All Rights Reserved. This document and translations of it may be copied and furnished to others, and derivative works that comment on or otherwise explain it or assist in its implementation may be prepared, copied, published and distributed, in whole or in part, without restriction of any kind, provided that the above copyright notice and this paragraph are included on all such copies and derivative works. However, this document itself may not be modified in any way, such as by removing the copyright notice or references to the Internet Society or other Internet organizations, except as needed for the purpose of developing Internet standards in which case the procedures for copyrights defined in the Internet Standards process must be followed, or as required to translate it into languages other than English. The limited permissions granted above are perpetual and will not be revoked by the Internet Society or its successors or assigns. Klyne/McIntyre Work-in-progress [Page 12] RFC nnnn Content feature schema for Internet fax October 1998 This document and the information contained herein is provided on an "AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET ENGINEERING TASK FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE. 7. Acknowledgements The authors gratefully acknowledge the following persons who made comments on earlier versions of this memo: James Rafferty, Dan Wing, [[...]]. 8. References [1] "Media Feature Tag Registration Procedure" Koen Holtman, TUE Andrew Mutz, Hewlett-Packard Ted Hardie, NASA Internet draft: Work in progress, July 1998. [2] "A syntax for describing media feature sets" Graham Klyne, 5GM/Content Technologies Internet draft: " Work in progress, September 1998. [3] "Media Features for Display, Print, and Fax" Larry Masinter, Xerox PARC Koen Holtman, TUE Andrew Mutz, Hewlett-Packard Dan Wing, Cisco Systems Internet draft: Work in progress, September 1998. [4] "Internet fax feature mapping from Group 3 fax" Lloyd McIntyre, Xerox Corporation Graham Klyne, 5GM/Content Technologies Internet draft: Work in progress, August 1998. [5] "Extended Facsimile Using Internet Mail Larry Masinter, Xerox Corporation Dan Wing, Cisco Systems Internet draft: Work in progress, September 1998. Klyne/McIntyre Work-in-progress [Page 13] RFC nnnn Content feature schema for Internet fax October 1998 [6] "Procedures for document facsimile transmission in the general switched telephone network" ITU-T Recommendation T.30 International Telecommunications Union July 1996 [7] RFC 2301, "File format for Internet fax" L. McIntyre, R. Buckley, D. Venable, Xerox Corporation S. Zilles, Adobe Systems, Inc. G. Parsons, Northern Telecom J. Rafferty, Human Communications March 1998. [8] RFC 2305, "A Simple Mode of Facsimile Using Internet Mail" K. Toyoda H. Ohno J. Murai, WIDE Project D. Wing, Cisco Systems March 1998. [9] T.42 (custom illuminant, gamut) [10] T.43 (JBIG for colour/grey) [11] "Scenarios for the Delivery of Negotiated Content" T. Hardie, NASA Network Information Center Internet draft: Work in progress, November 1997. [12] "Requirements for protocol-independent content negotiation" G. Klyne, Integralis Ltd. Internet draft: Work in progress, March 1998. Klyne/McIntyre Work-in-progress [Page 14] RFC nnnn Content feature schema for Internet fax October 1998 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. Telephone: +44 1491 641 641 +44 118 930 1300 Facsimile: +44 1491 641 611 +44 118 930 1301 E-mail: GK@ACM.ORG Lloyd McIntyre Xerox Corporation Mailstop PAHV-305 3400 Hillview Ave. Palo Alto, CA 94304 USA Telephone: +1-650-813-6762 Facsimile: +1-650-845-2340 E-mail: Lloyd.McIntyre@pahv.xerox.com Appendix A: Feature registrations [[[This appendix contains registrations of media features, that are specific to fax and for which no applicable registration already exists.]]] Klyne/McIntyre Work-in-progress [Page 15]