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Network Working Group K. Toyoda Request for Comments: 3965 H. Ohno Obsoletes: 2305 J. Murai Category: Standards Track WIDE Project

                                                               D. Wing
                                                         December 2004
           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 (2004).


 This specification provides for "simple mode" carriage of facsimile
 data using Internet mail.  Extensions to this document will follow.
 The current specification employs standard protocols and file formats
 such as TCP/IP, Internet mail protocols, Multipurpose Internet Mail
 Extensions (MIME), and Tagged Image File Format (TIFF) for Facsimile.
 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.
 This document is a revision of RFC 2305.  There have been no
 technical changes.

1. Introduction

 This specification defines 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 3965 A Simple Mode of Facsimile December 2004

 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 [15] 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

1.2. Cases

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

Toyoda, et al. Standards Track [Page 2] RFC 3965 A Simple Mode of Facsimile December 2004

1.3. Key Words

 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
 document are to be interpreted as described in [13].

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,

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.

Toyoda, et al. Standards Track [Page 3] RFC 3965 A Simple Mode of Facsimile December 2004

 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 [6] or
 similar mailbox access protocols.
 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 2822 and RFC 1123, 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 [5], also known as the S profile.   Such facsimile
 data are included in a MIME object by use of the image/TIFF sub-type
 [12].  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.

Toyoda, et al. Standards Track [Page 4] RFC 3965 A Simple Mode of Facsimile December 2004

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 [9].
 NOTE:  Internet mail transported via SMTP MUST contain a MAIL FROM
        address appropriate for delivery of return notices.  (See
        section 5.2.6.)

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.
 (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).

Toyoda, et al. Standards Track [Page 5] RFC 3965 A Simple Mode of Facsimile December 2004

 The telephone number format SHOULD conform to [7, 8].  Other formats
 MUST be syntactically distinct from [7, 8].

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) [5], which is also compatible with the
 specification for the minimum subset of TIFF-F in [14].  Receiving
 IFax devices MUST be able to read minimum set TIFF files.
 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.

Toyoda, et al. Standards Track [Page 6] RFC 3965 A Simple Mode of Facsimile December 2004

 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
 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.

Toyoda, et al. Standards Track [Page 7] RFC 3965 A Simple Mode of Facsimile December 2004

 Out-of-band communication of authorization information or use of
 encrypted data in special fields are the available non-standard
 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.

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]).

Toyoda, et al. Standards Track [Page 8] RFC 3965 A Simple Mode of Facsimile December 2004

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:

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), encrypted tunnels, 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.
 At the current time various protocols exist for performing the above
 functions, and are only mentioned here for information.  Such
 protocols are IPSec [17] and TLS [18].

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 can be used to provide end-to-end encryption.
 At the current time two protocols are commonly used for message
 encryption and are only mentioned here for information.  The two
 protocols are PGP-MIME [16] and S/MIME [19].

6. References

6.1. Normative References

 [1]  Klensin, J., Editor, "Simple Mail Transfer Protocol", RFC 2821,
      April 2001.
 [2]  Resnick, P., Editor, "Internet Message Format", RFC 2822, April

Toyoda, et al. Standards Track [Page 9] RFC 3965 A Simple Mode of Facsimile December 2004

 [3]  Braden, R., "Requirements for Internet hosts - application and
      support", STD 3, 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]  Buckley, R., Venable, D., McIntyre, L., Parsons, G., and J.
      Rafferty, "File Format for Internet Fax", RFC 3949, November
 [6]  Myers, J. and M. Rose, "Post Office Protocol - Version 3", STD
      53, RFC 1939, May 1996.
 [7]  Allocchio, C., "Minimal GSTN address format for Internet mail",
      RFC 3191, October 2001.
 [8]  Allocchio, C., "Minimal fax address format for Internet mail",
      RFC 3192, October 2001.
 [9]  Moore, K., and G. Vaudreuil, "An Extensible Message Format for
      Delivery Status Notifications", RFC 3464, January 2003.
 [10] Freed, N. and N. Borenstein, "Multipurpose Internet Mail
      Extensions (MIME) Part Two: Media Types", RFC 2046, November
 [11] Moore, K. "MIME (Multipurpose Internet Mail Extensions) Part
      Three: Message Header Extensions for Non-ASCII Text", RFC 2047,
      November 1996.
 [12] Parsons, G. and J. Rafferty, "Tag Image File Format (TIFF) -
      image/tiff MIME Sub-type Registration", RFC 3302, September
 [13] Bradner, S., "Key words for use in RFCs to Indicate Requirement
      Levels", BCP 14, RFC 2119, March 1997.

6.2. Informative References

 [14] Parsons, G. and J. Rafferty, "Tag Image File Format (TIFF) -- F
      Profile for Facsimile", RFC 2306, March 1998.
 [15] ITU-T (CCITT), "Standardization of Group 3 facsimile apparatus
      for document transmission", ITU-T (CCITT), Recommendation T.4.

Toyoda, et al. Standards Track [Page 10] RFC 3965 A Simple Mode of Facsimile December 2004

 [16] Callas, J., Donnerhacke, L., Finney, H., and R. Thayer, "OpenPGP
      Message Format", RFC 2440, November 1998.
 [17] Kent, S. and R. Atkinson, "Security Architecture for the
      Internet Protocol", RFC 2401, November 1998.
 [18] Hoffman, P., "SMTP Service Extension for Secure SMTP over
      Transport Layer Security", RFC 3207, February 2002.
 [19] Ramsdell, B., "S/MIME Version 3 Message Specification", RFC
      2633, June 1999.

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

Toyoda, et al. Standards Track [Page 11] RFC 3965 A Simple Mode of Facsimile December 2004

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.

Appendix B: List of edits to RFC 2305

 | No.| Section  |             Edit  July 27, 2001                 |
 | 1. |Copyright | Updated copyright from "1998" to "1999,2000"    |
 |    |Notice    |                                                 |
 | 2. |SUMMARY   | Changed the phrase "over the Internet" to       |
 |    |          |               "using Internet mail"             |
 | 3. |5         | Changed the paragraphs regarding to the         |
 |    |          | following references to make them very          |
 |    |          | non-normative.                                  |
 |    |          |  "OpenPGP Message Format", RFC 2440             |
 |    |          |  "Security Architecture for the IP", RFC 2401   |
 |    |          |  "SMTP Service Extensions for Secure SMTP over  |
 |    |          |   TLS", RFC 2487                                |
 |    |          |  "S/MIME Version 2 Message Specification",      |
 |    |          |   RFC 2311                                      |
 | 4. |REFERENCES| Removed the following references because they   |
 |    |          | are non-normative                               |
 |    |          |  "SMTP Service Extensions for Delivery Status   |
 |    |          |   Notifications", RFC 1891                      |
 |    |          |  "Internet Message Access Protocol", RFC 2060   |
 | 5. |REFERENCES| Separated REFERENCES to the normative and       |
 |    |          | non-normative                                   |
 | 6. |Appendix  | Changed the phrase from "NOT REQUIRED" to       |
 |    | A        | "not required"                                  |
 | 7. |Appendix  | Added "Appendix B  List of edits to RFC 2305"   |

Toyoda, et al. Standards Track [Page 12] RFC 3965 A Simple Mode of Facsimile December 2004

Authors' Addresses

 Kiyoshi Toyoda
 Panasonic Communications Co., Ltd.
 4-1-62 Minoshima Hakata-ku
 Fukuoka 812-8531 Japan
 Fax:   +81 92 477 1389
 Hiroyuki Ohno
 National Institute of Information and Communications Technology
 4-2-1, Nukui-Kitamachi, Koganei, Tokyo,
 184-8795, Japan
 Fax:   +81 42 327 7941
 Jun Murai
 Keio University
 5322 Endo, Fujisawa
 Kanagawa 252 Japan
 Fax:   +81 466 49 1101
 Dan Wing
 170 W. Tasman Drive
 San Jose, CA 95134 USA
 Phone: +1 408 525 5314

Toyoda, et al. Standards Track [Page 13] RFC 3965 A Simple Mode of Facsimile December 2004

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 retain all their rights.
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Toyoda, et al. Standards Track [Page 14]

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