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rfc:rfc2305

Network Working Group K. Toyoda Request for Comments: 2305 H. Ohno Category: Standards Track J. Murai

                                                         WIDE Project
                                                              D. Wing
                                                                Cisco
                                                           March 1998
           A Simple Mode of Facsimile Using Internet Mail

Status of this Memo

 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.

SUMMARY

 This specification provides for "simple mode" carriage of facsimile
 data over the Internet.  Extensions to this document will follow.
 The current specification employs standard protocols and file formats
 such as TCP/IP, Internet mail protocols [1, 2, 3], MIME [4, 16, 17],
 and TIFF for Facsimile [5,6,19].  It can send images not only to
 other Internet-aware facsimile devices but also to Internet-native
 systems, such as PCs with common email readers which can handle MIME
 mail and TIFF for Facsimile data.  The specification facilitates
 communication among existing facsimile devices, Internet mail agents,
 and the gateways which connect them.
 The key words "MUST", "SHOULD", "SHOULD NOT", and "MAY" in this
 document are to be interpreted as described in [7].

1 SCOPE

 This specification defines a message-based facsimile communication
 over the Internet.  It describes a minimum set of capabilities,
 taking into account those of typical facsimile devices and PCs that
 can generate facsimile data.

Toyoda, et. al. Standards Track [Page 1] RFC 2305 Simple Mode of Facsimile March 1998

 A G3Fax device has substantial restrictions due to specifications in
 the standards, such as for timers. This specification defines a
 profile for Internet mail, rather than creating a distinct "facsimile
 over the Internet" service.  The semantics resulting from the profile
 are designed to be compatible with facsimile operation over the
 general switched telephone network, so that gateways between
 facsimile and Internet mail can operate with very high fidelity.
 The reason for developing this capability as an email profile is to
 permit interworking amongst facsimile and email users.  For example
 it is intended that existing email users be able to send normal
 messages to lists of users, including facsimile-based recipients, and
 that other email recipients shall be able to reply to the original
 and continue to include facsimile recipients.  Similarly it is
 intended that existing email software work without modification and
 not be required to process new, or different data structures, beyond
 what is normal for Internet mail users.  Existing email service
 standards are used, rather than replicating mechanisms which are more
 tailored to existing facsimile standards, to ensure this
 compatibility with existing email service.

1.1 Services

 A facsimile-capable device that uses T.4 [8] and the general switched
 telephone network (GSTN) is called a "G3Fax device" in this
 specification.  An "IFax device" is an Internet- accessible device
 capable of sending, receiving or forwarding Internet faxes.  A
 message can be sent to an IFax device using  an Internet mail
 address. A message can be sent to a G3Fax device  using an Internet
 mail address; the message MAY be forwarded via an IFax offramp
 gateway.

1.2 Cases

 This specification provides for communication between each of the
 following combinations:
 Internet mail             =>  Network printer
 Internet mail             =>  Offramp gateway (forward to
                               G3Fax)
 Network scanner           =>  Network printer
 Network scanner           =>  Offramp gateway (forward to
                               G3Fax)
 Network scanner           =>  Internet mail

Toyoda, et. al. Standards Track [Page 2] RFC 2305 Simple Mode of Facsimile March 1998

2 COMMUNICATION PROTOCOLS

 The set of conventions necessary to achieve facsimile- compatible
 service covers basic data transport, document data formats, message
 (document) addressing, delivery confirmation, and message security.
 In this section, the first 4 are covered.  The remainder are covered
 in following sections, along with additional details for addressing
 and formats.

2.1 Transport

 This section describes mechanisms involved in the transport between
 IFAX devices.

2.1.1 Relay

 Data transfer MAY be achieved using standard Internet mail transfer
 mechanisms[1, 3].  The format of addresses MUST conform to the RFC
 821 <addr-spec> and RFC 822 <mailbox> Internet mail standards [1, 2,
 3].

2.1.2 Gateway

 A gateway translates between dissimilar environments.  For IFax, a
 gateway connects between Internet mail and the T.4/GSTN facsimile.
 Gateways can service multiple T.4/GSTN facsimile users or can service
 only one.  In the former case, they serve as a classic "mail transfer
 agent" (MTA) and in the latter as a classic "mail user agent" (UA).
 An onramp is a gateway which connects from T.4/GSTN facsimile to
 Internet mail.  An offramp is a gateway which connects from Internet
 mail to T.4/GSTN facsimile. Behavior of onramps is out of scope for
 this specification.
 This specification describes the Internet mail service portion of
 offramp addressing, confirmation and failure notification.  Details
 are provided in later sections.

2.1.3 Mailbox protocols

 An offramp gateway that operate as an MTA serving multiple users
 SHOULD use SMTP; a gateway that operates as a UA serving a single
 mail recipient MAY use a mailbox access protocol such as POP or IMAP
 [9, 10].

Toyoda, et. al. Standards Track [Page 3] RFC 2305 Simple Mode of Facsimile March 1998

 NOTE: An offramp gateway that relays mail based on addressing
 information needs to ensure that it uses addresses supplied in the
 MTA envelope, rather than from elsewhere, such as addresses listed in
 the message content headers.

2.2 Formats

2.2.1 Headers

 IFax devices MUST be compliant with RFC 822 and RFC1123, which define
 the format of mail headers.  The header of an IFax message SHOULD
 include Message-ID and MUST include all fields required by [2, 3],
 such as DATE and FROM.

2.2.2 MIME

 IFax devices MUST be compliant with MIME [4], except as noted in
 Appendix A.

2.2.3 Content

 The data format of the facsimile image is based on the minimum set of
 TIFF for Facsimile[6], also known as the S profile.   Such facsimile
 data are included in a MIME object by use of the image/TIFF sub-type
 [19].  Additional rules for the use of TIFF for Facsimile, for the
 message-based Internet facsimile application, are defined later.

2.2.4 Multipart

 A single multi-page document SHOULD be sent as a single multi- page
 TIFF file, even though recipients MUST process multipart/mixed
 containing multiple TIFF files. If multipart content is present and
 processing of any part fails, then processing for the entire message
 is treated as failing, per [Processing failure] below.

2.3 Error Handling

2.3.1 Delivery failure

 This section describes existing requirements for Internet mail,
 rather than indicating special requirements for IFax devices.
 In the event of relay failure, the sending relay MUST generate a
 failure message, which SHOULD be in the format of a DSN. [14,15]
      NOTE:  Internet mail transported via SMTP MUST contain a MAIL
      FROM address appropriate for delivery of return notices [Also
      see section 5.2.6]

Toyoda, et. al. Standards Track [Page 4] RFC 2305 Simple Mode of Facsimile March 1998

2.3.2 Processing failure

 IFax devices with limited capabilities might be unable to process the
 content of a message.  If this occurs it is important to ensure that
 the message is not lost without any notice. Notice MAY be provided in
 any appropriate fashion, and the exact handling is a local matter.
 (Also see Appendix A, second bullet.)

3 ADDRESSING

3.1 Classic Email Destinations

 Messages being sent to normal Internet mail recipients will use
 standard Internet mail addresses, without additional constraints.

3.2 G3Fax Devices

 G3Fax devices are accessed via an IFAX offramp gateway, which
 performs any authorized telephone dial-up.

3.3 Address Formats Used by Offramps

 When a G3Fax device is identified by a telephone number, the entire
 address used for the G3fax device, including the number and offramp
 host reference MUST be contained within standard Internet mail
 transport fields, such as RCPT TO and MAIL FROM [1, 3].  The address
 MAY be contained within message content fields, such as <authentic>
 and <destination> [2, 3], as appropriate.
 As for all Internet mail addresses, the left-hand-side (local- part)
 of an address is not to be interpreted except by the MTA that is
 named on the right-hand-side (domain).
 The telephone number format SHOULD conform to [11, 12].  Other
 formats MUST be syntactically distinct from [11, 12].

4 IMAGE FILE FORMAT

 Sending IFax devices MUST be able to write minimum set TIFF files,
 per the rules for creating minimum set TIFF files defined in TIFF for
 Facsimile (the S profile) [6], which is also compatible with the
 specification for the minimum subset of TIFF-F in [5].  Receiving
 IFax devices MUST be able to read minimum set TIFF files.

Toyoda, et. al. Standards Track [Page 5] RFC 2305 Simple Mode of Facsimile March 1998

 A sender SHOULD NOT use TIFF fields and values beyond the minimum
 subset of TIFF for Facsimile unless the sender has prior knowledge of
 other TIFF fields or values supported by the recipient.  The
 mechanism for determining capabilities of recipients is beyond the
 scope of this document.

5 SECURITY CONSIDERATIONS

5.1 General Directive

 This specification is based on use of existing Internet mail.  To
 maintain interoperability with Internet mail, any security to be
 provided should be part of the of the Internet security
 infrastructure, rather than a new mechanism or some other mechanism
 outside of the Internet infrastructure.

5.2 Threats and Problems

 Both Internet mail and G3Fax standards and operational services have
 their own set of threats and countermeasures.  This section attends
 only to the set of additional threats which ensue from integrating
 the two services. This section reviews relevant concerns about
 Internet mail for IFax environments, as well as considering the
 potential problems which can result of integrating the existing G3Fax
 service with Internet mail.

5.2.1 Spoofed sender

 The actual sender of the message might not be the same as that
 specified in the Sender or From fields of the message content headers
 or the MAIL FROM address from the SMTP envelope.
 In a tightly constrained environment, sufficient physical and
 software controls may be able to ensure prevention of this problem.
 The usual solution is through encryption-based authentication, either
 for the channel or associated with the object, as discussed below.
 It should be recognized that SMTP implementations do not provide
 inherent authentication of the senders of messages, nor are sites
 under obligation to provide such authentication. End-to-end
 approaches such as S/MIME and PGP/MIME are currently being developed
 within the IETF. These technologies can provide such authentication.

5.2.2 Resources consumed by dialout

 In addition to the resources normally consumed for email (CPU cycles
 and disk), offramp facsimile causes an outdial which often imposes
 significant resource consumption, such as financial cost. Techniques

Toyoda, et. al. Standards Track [Page 6] RFC 2305 Simple Mode of Facsimile March 1998

 for establishing authorization of the sender are essential to those
 offramp facsimile services that need to manage such consumption.
 Due to the consumption of these resources by dialout, unsolicited
 bulk email which causes an outdial is undesirable.
 Offramp gateways SHOULD provide the ability to authorize senders in
 some manner to prevent unauthorized use of the offramp. There are no
 standard techniques for authorization using Internet protocols.
 Typical solutions use simple authentication of the originator to
 establish and verify their identity and then check the identity
 against a private authorization table.
 Originator authentication entails the use of weak or strong
 mechanisms, such as cleartext keywords or encryption-based data-
 signing, respectively, to determine and validate the identify of the
 sender and assess permissions accordingly.
 Other control mechanisms which are common include source filtering
 and originator authentication.  Source filtering entails offramp
 gateway verification of the host or network originating the message
 and permitting or prohibiting relaying accordingly.

5.2.3 GSTN authorization information

 Confidential information about the sender necessary to dial a G3Fax
 recipient, such as sender's calling card authorization number, might
 be disclosed to the G3Fax recipient (on the cover page), such as
 through parameters encoded in the G3Fax recipients address in the To:
 or CC: fields.
 Senders SHOULD be provided with a method of preventing such
 disclosure.  As with mechanisms for handling unsolicited faxes, there
 are not yet standard mechanisms for protecting such information.
 Out-of-band communication of authorization information or use of
 encrypted data in special fields are the available non-standard
 techniques.
 Typically authorization needs to be associated to specific senders
 and specific messages, in order to prevent a "replay" attack which
 causes and earlier authorization to enable a later dial-out by a
 different (and unauthorized) sender.  A non-malicious example of such
 a replay would be to have an email recipient reply to all original
 recipients -- including an offramp IFax recipient -- and have the
 original sender's authorization cause the reply to be sent.

Toyoda, et. al. Standards Track [Page 7] RFC 2305 Simple Mode of Facsimile March 1998

5.2.4 Sender accountability

 In many countries, there is a legal requirement that the "sender" be
 disclosed on a facsimile message.  Email From addresses are trivial
 to fake, so that using only the MAIL FROM [1, 3]  or From [2, 3]
 header is not sufficient.
 Offramps SHOULD ensure that the recipient is provided contact
 information about the offramp, in the event of problems.
 The G3Fax recipient SHOULD be provided with sufficient information
 which permits tracing the originator of the IFax message.  Such
 information might include the contents of the MAIL FROM, From, Sender
 and Reply-To headers, as well as Message-Id and Received headers.

5.2.5 Message disclosure

 Users of G3Fax devices have an expectation of a level of message
 privacy which is higher than the level provided by Internet mail
 without security enhancements.
 This expectation of privacy by G3Fax users SHOULD be preserved as
 much as possible.
 Sufficient physical and software control may be acceptable in
 constrained environments.  The usual mechanism for ensuring data
 confidentially entail encryption, as discussed below.

5.2.6 Non private mailboxes

 With email, bounces (delivery failures) are typically returned to the
 sender and not to a publicly-accessible email account or printer.
 With facsimile, bounces do not typically occur.  However, with IFax,
 a bounce could be sent elsewhere (see section [Delivery Failure]),
 such as a local system administrator's account, publicly-accessible
 account, or an IFax printer (see also [Traffic Analysis]).

5.2.7 Traffic analysis

 Eavesdropping of senders and recipients is easier on the Internet
 than GSTN.  Note that message object encryption does not prevent
 traffic analysis, but channel security can help to frustrate attempts
 at traffic analysis.

5.3 Security Techniques

 There are two, basic approaches to encryption-based security which
 support authentication and privacy:

Toyoda, et. al. Standards Track [Page 8] RFC 2305 Simple Mode of Facsimile March 1998

5.3.1 Channel security

 As with all email, an IFax message can be viewed as it traverses
 internal networks or the Internet itself.
 Virtual Private Networks (VPN) which make use of encrypted tunnels,
 such as via IPSec technology [18] or transport layer security, can be
 used to prevent eavesdropping of a message as it traverses such
 networks.   It also provides some protection against traffic
 analysis, as described above.

5.3.2 Object security

 As with all email, an IFax message can be viewed while it resides on,
 or while it is relayed through, an intermediate Mail Transfer Agent.
 Message encryption, such as PGP-MIME [13] and S/MIME, can be used to
 provide end-to-end encryption.

6 REFERENCES

 [1]  Postel, J., "Simple Mail Transfer Protocol", STD 10, RFC
      821, August 1982.
 [2]  Crocker, D., "Standard for the Format of ARPA Internet
      Text Messages", STD 11, RFC 822, August l982.
 [3]  Braden, R., 1123 "Requirements for Internet hosts -
      application and support", RFC 1123, October 1989.
 [4]  Borenstein, N., and N. Freed, " Multipurpose Internet
      Mail Extensions (MIME) Part Five:  Conformance Criteria and
      Examples ", RFC 2049, November 1996.
 [5]  Parsons, G., and J. Rafferty, "Tag Image File Format
      (TIFF) -- F Profile for Facsimile", RFC 2306, March 1998.
 [6]  McIntyre, L., Zilles, S., Buckley, R., Venable, D.,
      Parsons, G., and J. Rafferty, "File Format for Internet Fax",
      RFC 2301, March 1998.
 [7]  Bradner, S., "Key words for use in RFCs to Indicate
      Requirement Levels", RFC 2119, March 1997.
 [8]  ITU-T (CCITT), "Standardization of Group 3 facsimile
      apparatus for document transmission", ITU-T (CCITT),
      Recommendation T.4.

Toyoda, et. al. Standards Track [Page 9] RFC 2305 Simple Mode of Facsimile March 1998

 [9]  Myers, J., and M. Rose, "Post Office Protocol - Version
      3", STD 53, RFC 1939, May 1996.
 [10] Crispin, M., "Internet Message Access Protocol - Version
      4Rev1", RFC 2060, December 1996.
 [11] Allocchio, C., "Minimal PSTN address format for Internet
      mail", RFC 2303, March 1998.
 [12] Allocchio, C., "Minimal fax address format for Internet
      mail", RFC 2304, March 1998.
 [13] Elkins, M., "MIME Security with Pretty Good Privacy
      (PGP)", RFC 2015, October 1996.
 [14] Moore, K., and G. Vaudreuil, "An Extensible Message
      Format for Delivery Status Notifications", RFC 1894, January
      1996.
 [15] Moore, K., "SMTP Service Extension for Delivery Status
      Notifications", RFC 1891, January 1996.
 [16] Freed, N., and N. Borenstein, "Multipurpose Internet
      Mail Extensions (MIME) Part Two: Media Types", RFC 2046,
      November 1996.
 [17] Moore, K., "Multipurpose Internet Mail Extensions (MIME)
      Three: Representation of Non-ASCII Text in Internet ge Headers",
      RFC 2047, November 1996.
 [18] Atkinson, R., "Security Architecture for the Internet
      Protocol", RFC 1825, Naval Research Laboratory, August 1995.
 [19] Parsons, G. and Rafferty, J. "Tag Image File Format
      (TIFF) -- image/TIFF: MIME Sub-type Registration", RFC 2302,
      March 1998.

7 ACKNOWLEDGEMENTS

 This specification was produced by the Internet Engineering Task
 Force Fax Working Group, over the course of more than one year's
 online and face-to-face discussions.  As with all IETF efforts, many
 people contributed to the final product.
 Active for this document were: Steve Huston, Jeffrey Perry, Greg
 Vaudreuil, Richard Shockey, Charles Wu, Graham Klyne, Robert A.
 Rosenberg, Larry Masinter, Dave Crocker, Herman Silbiger, James
 Rafferty.

Toyoda, et. al. Standards Track [Page 10] RFC 2305 Simple Mode of Facsimile March 1998

8 AUTHORS' ADDRESSES

 Kiyoshi Toyoda
 Matsushita Graphic Communication Systems, Inc.
 2-3-8 Shimomeguro, Meguro-ku
 Tokyo 153 Japan
 Fax: +81 3 5434 7166
 Email: ktoyoda@rdmg.mgcs.mei.co.jp
 Hiroyuki Ohno
 Tokyo Institute of Technology
 2-12-1 O-okayama, Meguro-ku
 Tokyo 152 Japan
 FAX: +81 3 5734 2754
 Email: hohno@is.titech.ac.jp
 Jun Murai
 Keio University
 5322 Endo, Fujisawa
 Kanagawa 252 Japan
 Fax: +81 466 49 1101
 Email: jun@wide.ad.jp
 Dan Wing
 Cisco Systems, Inc.
 101 Cooper Street
 Santa Cruz, CA 95060 USA
 Phone: +1 408 457 5200
 Fax: +1 408 457 5208
 Email: dwing@cisco.com

Toyoda, et. al. Standards Track [Page 11] RFC 2305 Simple Mode of Facsimile March 1998

9 APPENDIX A: Exceptions to MIME

  • IFax senders are NOT REQUIRED to be able to send

text/plain messages (RFC 2049 requirement 4), although IFax

      recipients are required to accept such messages, and to process
      them.
  • IFax recipients are NOT REQUIRED to offer to put results

in a file. (Also see 2.3.2.)

  • IFax recipients MAY directly print/fax the received

message rather than "display" it, as indicated in RFC 2049.

Toyoda, et. al. Standards Track [Page 12] RFC 2305 Simple Mode of Facsimile March 1998

10 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.
 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.

Toyoda, et. al. Standards Track [Page 13]

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