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rfc:rfc4160

Network Working Group K. Mimura Request for Comments: 4160 K. Yokoyama Category: Informational T. Satoh

                                                            C. Kanaide
                                          TOYO Communication Equipment
                                                          C. Allocchio
                                                       Consortium GARR
                                                           August 2005
                 Internet Fax Gateway Requirements

Status of This Memo

 This memo provides information for the Internet community.  It does
 not specify an Internet standard of any kind.  Distribution of this
 memo is unlimited.

Copyright Notice

 Copyright (C) The Internet Society (2005).

Abstract

 To allow connectivity between the General Switched Telephone Network
 facsimile service (GSTN fax) and the e-mail-based Internet Fax
 service (i-fax) an "Internet Fax Gateway" is required.  This document
 provides recommendations for the functionality of Internet Fax
 Gateways.  In this context, an "offramp gateway" provides facsimile
 data transmission from i-fax to GSTN fax; vice versa, an "onramp
 gateway" provides data transmission form GSTN fax to i-fax.  The
 recommendations in this document apply to the integrated service
 including Internet Fax terminals, computers with i-fax software on
 the Internet, and GSTN Fax terminals on the GSTN.

1. Introduction

 An Internet Fax Gateway provides connectivity and translation between
 the General Switched Telephone Network facsimile service (GSTN fax)
 and the e-mail-based Internet Fax service (i-fax).  This document
 defines the recommended behavior of an Internet Fax Gateway.  An
 Internet Fax Gateway can be classified as "onramp", when a facsimile
 is transferred from GSTN fax to the Internet Fax, and as "offramp",
 when a facsimile is transferred from Internet Fax to GSTN fax.  For a
 more detailed definition of "onramp" and "offramp" within i-fax
 service, see [1].

Mimura, et al. Informational [Page 1] RFC 4160 Internet Fax Gateway Requirements August 2005

 This document provides recommendations only for the specific case
 hereunder:
 1) the operational mode of the Internet Fax is "store and forward",
    as defined in Section 2.5 of [1].
 2) The format of image data is the data format defined by "simple
    mode" in [4].
 This document does not apply to the gateway functions for "real-time
 Internet Fax", as described and defined in [3].  Additional
 recommendations for optional functionality are described in [24].

1.1. Key Words

 The key words "MUST", "SHOULD", "SHOULD NOT", and "MAY" in this
 document are to be interpreted as described in [5].

2. Internet Fax Gateway Operations

 An onramp gateway receives a facsimile from a GSTN fax device (which
 may include an offramp gateway itself), and generates an Internet Fax
 over the Internet, which is sent to any Internet Fax device.
 An offramp gateway receives an Internet Fax over the Internet from
 any Internet Fax-capable device (which may include an onramp gateway
 or a PC), and generates a GSTN fax, which is sent to any GSTN fax
 device.
 In both of these cases, the Internet side of the gateway acts as an
 Internet Fax device, as described in [4], while the GSTN side of the
 gateway acts as a GSTN fax device, as described in [6].
 In this document we will only thus recommend the actions that occur
 while
 1) the onramp gateway converts a fax received from GSTN and forwards
    it to the Internet Fax service;
 2) the offramp gateway converts a fax received from the Internet and
    forwards it to the GSTN fax service.

Mimura, et al. Informational [Page 2] RFC 4160 Internet Fax Gateway Requirements August 2005

3. The Offramp Gateway Operations

 An offramp gateway MUST, as a minimal requirement, perform the
 following functions:
  1. address translation/mapping,
  2. image format conversion, and
  3. error/return notification handling
 and MAY also perform
  1. user authorization.

3.1. User Authorization

 An offramp gateway MAY have a user authorization function to confirm
 that a user is allowed to transmit its Internet Fax to the GSTN fax
 service.
 Because an Internet Fax is sent as a MIME e-mail message to the
 offramp gateway, digital signatures can be used to authenticate and
 authorize the user.  S/MIME is one example of a protocol that
 includes digital signature services.  S/MIME is described in
 [9][10][11][12][13].  Other methods of adding a digital signature to
 a mail message (such as OpenPGP [17] [25]) MAY also be used to
 authenticate and authorize the user.
 The agent sending the Internet Fax (which may include an onramp
 gateway) sends the digitally-signed S/MIME or OpenPGP Fax message to
 the offramp gateway.  The offramp gateway then compares the
 credentials of the user to determine if he/she is authorized to send
 faxes to the GSTN fax service.  If the authorization process fails,
 then the offramp gateway MUST generate an error delivery notification
 for the sender of the Internet Fax.

3.2. Addressing

 An Internet Fax may contain multiple e-mail addresses, both as
 originators, and as recipients.  For its forwarding function to GSTN
 fax service, an offramp gateway MUST only consider those addresses
 which are explicitly itself, i.e., those where the right-hand side of
 the e-mail address corresponds to the offramp gateway.
 Because addresses on the Internet Fax service are e-mail addresses,
 in order to reach a destination in the GSTN fax service, the offramp
 gateway MUST convert e-mail addresses into GSTN addresses.

Mimura, et al. Informational [Page 3] RFC 4160 Internet Fax Gateway Requirements August 2005

 The GSTN destination address SHOULD normally be encoded inside the
 left-hand side of the e-mail address, according to [7].  However, an
 offramp gateway MAY use locally implemented translation rules to map
 left-hand side strings into GSTN addresses.
 In any case, the offramp gateway MUST process the resultant GSTN
 address and convert it to a "local-phone", in accordance with local
 dialing rules.
 "Global-phone" is defined in Section 2 of [7].  "Local-phone" is
 defined in Section 2 of [8].  "Exit-code" is defined in Section 2.1
 of [8].
 The offramp gateway SHOULD also have a function to apply translation
 to originator addresses and other addresses referred to into the
 Internet Fax, in order to ensure a possible return path from GSTN fax
 service to Internet Fax destinations, including other offramp
 gateways.  These functions MUST be compliant with the address
 handling of onramp gateways that is described in Section 4.2 of this
 document.

3.2.1. Examples of Local Dialing Rules Applied to GSTN Destination

      Addresses
 The first example shows how an offramp gateway converts a "global-
 phone" to a "local-phone" by removing the "+" and "44" (recognizing
 the international country code is local), and then knowing it can
 dial directly without an exit-code:
    global-phone:  +441164960348
 resulting in:
    local-phone:   1164960348
 The next example shows how an offramp gateway converts a "global-
 phone" to a "local-phone" by removing the "+" and "44" (recognizing
 the international country code is local), and then adding the exit-
 code "0" in front of the string:
    global-phone:   +441164960348
 resulting in:
    local-phone:   01164960348

Mimura, et al. Informational [Page 4] RFC 4160 Internet Fax Gateway Requirements August 2005

 The next example shows how an offramp gateway converts a "global-
 phone" to "local-phone" by removing the "+" and "44" (recognizing the
 international country code is local), and then adding the long
 distance "0" in front of the string:
    global-phone:   +441164960348
 resulting in:
    local-phone:    01164960348
 The last example shows how an offramp gateway converts a "global-
 phone" to a "local-phone" by removing the "+", recognizing the
 international country code is non-local, and adding the local
 international dialing prefix "00" in front of the string:
    global-phone:   +441164960348
 resulting in:
    local-phone:   00441164960348

3.2.2. Support for Subaddress

 An offramp gateway SHOULD support the subaddress.  If a subaddress is
 encoded into the left-hand side of the e-mail address [7], then it
 MUST be used by the offramp gateway, as specified in T.33 [15], to
 reach the final GSTN fax recipient.

3.3. Image Format Conversion

 An offramp gateway MUST convert the file format from TIFF Profile-S
 for Internet Fax (defined in [16]) into the GSTN fax image format.
 Other Internet Fax file formats are not considered in this document.

3.4. Error/Return Notification Handling

 An offramp gateway SHOULD have a function that allows it to send a
 return notice to the originator Internet Fax device (defined in [4])
 when a transmission error occurs over the GSTN fax service and the
 facsimile is not delivered to the destination.  The return notice
 MUST be in Message Delivery Notification (MDN) format and delivered
 by the offramp gateway over the Internet e-mail transport service
 used by Internet Fax.  The MDN disposition-type MUST be set as
 "processed", and the disposition-modifier MUST be set as an "error".

Mimura, et al. Informational [Page 5] RFC 4160 Internet Fax Gateway Requirements August 2005

 If the offramp gateway fails to transmit the MDN, the error
 information MAY be recorded to a log, and processing MAY end, or the
 administrator of the gateway system MAY be notified of these errors
 through a specific method (for example, by an e-mail message).
 The more complex case of Delivery Status Notification (DSN) requests
 handling is not considered in this document.

4. The Onramp Gateway Operations

 An onramp gateway MUST, as minimal requirement, perform the following
 functions:
  1. address translation/mapping,
  2. image format conversion, and
  3. error/return notification handling,
 and MAY also perform
  1. user authorization.

4.1. User Authorization

 An onramp gateway MAY have a user authorization function to confirm
 that the user is authorized to transmit a facsimile to the Internet
 fax service.  For example, user authorization may be accomplished by
 getting a user-ID and password received by Dual Tone Multi-Frequency
 (DTMF), or via a local authorization table based on the GSTN caller-
 ID.
 If the authorization process fails, then the onramp gateway MUST
 generate an error message/code for the sender of the GSTN Fax.

4.2. Address Translation/Mapping

 Addresses on Internet Fax service are e-mail addresses, thus a
 recipient of an Internet Fax might be either an e-mail user, an
 Internet Fax device with its own recipients/users, or an offramp
 gateway.  The onramp gateway SHOULD have a functionality in order to
 receive from GSTN (via DTMF) destination addresses.  However, there
 are two categories of destination addresses:
  1. e-mail users and Internet Fax recipient/users
  2. real GSTN addresses reached via an offramp gateway
 We define "indirect address mapping" as the functionality for the
 first category, and "direct address mapping" as the functionality for
 the second category.

Mimura, et al. Informational [Page 6] RFC 4160 Internet Fax Gateway Requirements August 2005

4.2.1. Indirect Address Mapping

 The onramp gateway MAY implement local address mapping mechanisms
 (via a table, directory lookup, or something similar) that permit
 translation from addresses (called "indirect address numbers")
 received from the GSTN fax sending device into e-mail addresses.  A
 single e-mail address or a list of e-mail addresses MAY correspond to
 a single indirect address number.
 Here is one mapping example:
 (1) An onramp gateway receives the indirect address number "1234"
     from the source GSTN facsimile by DTMF.
          1234
 (2) The destination address is looked up in the address mapping
     table.
          address mapping table
          1234 : ifax@example.com
 (3) An Internet Fax is sent to the address ("addr-spec")
          ifax@example.com
 "Addr-spec" is defined in Section 3.4.1 of [14].
 If the address mapping lookup fails, an error MUST be reported to the
 originating GSTN fax device.

4.2.2. Direct Address Mapping

 If the indirect address mapping specified in 4.2.1 is not
 implemented, then only "direct address mapping" can be used.  The
 GSTN sending device SHOULD send the full numeric destination address
 to the onramp gateway via DTMF.  Direct address mapping can also be
 used if indirect address mapping is implemented.
 An example:
 (1) An onramp gateway receives the destination telephone number
     "441164960348" from the source facsimile by DTMF.
          441164960348

Mimura, et al. Informational [Page 7] RFC 4160 Internet Fax Gateway Requirements August 2005

 (2) The destination number is encoded as a "global-phone", so "+" is
     added to the head of the string.
          +441164960348
 (3) "FAX=" is added in order to build the "fax-mbox" address item
          FAX=+441164960348
 (4) The destination address is completed, adding the specification of
     the appropriate offramp gateway, which is supposed to handle the
     delivery of the fax message to a global-phone address.
          FAX=+441164960348@example.com
 The procedure for choosing the domain name of an offramp gateway is
 defined in Section 4.3 ("Relay Function").
 "Global-phone", "fax-mbox", and "fax-address" are defined in Section
 2 of [7].  "Mta-I-fax" is defined in Section 3 of [7].  "Fax-email"
 is defined in Section 4 of [7].

4.2.3. Sender Address Handling

 The onramp gateway SHOULD gather information about the GSTN fax
 sender address (for example, via Caller-ID, if available) and encode
 it as the sender of the Internet Fax, using the direct address
 mapping (see Section 4.2.2 of this document).  The sender address
 SHOULD be completed using the onramp gateway address, unless the
 onramp gateway has additional information with which to specify a
 different return path.
 If the onramp gateway does not have any sender address information,
 the Internet Fax sender address SHOULD be set to either a "no-reply"
 address or an appropriate default mailbox.

4.2.4. Support for Subaddress

 An onramp gateway SHOULD support the subaddress.  In the case of
 direct address mapping, the subaddress is specified using the T.33
 [15] specification, and encoded as given in [7].  In the case of
 indirect address mapping, the subaddress MAY be contained inside the
 address mapping table.

Mimura, et al. Informational [Page 8] RFC 4160 Internet Fax Gateway Requirements August 2005

4.3. Relay Function

 The onramp gateway SHOULD provide functionality for choosing the
 destination offramp gateway by analyzing a destination fax number.  A
 possible method to expand or acquire information from the onramp
 gateway about offramp gateways MAY include keeping cached information
 about sender addresses that was sent by other onramp gateways.

4.4. File Format Conversion

 An onramp gateway MUST convert the file format from a facsimile over
 the GSTN to the file format TIFF Profile-S for Internet Fax, as
 defined in [16].

4.6. Return Notice Handling

 When an onramp gateway receives and analyzes a return notice from the
 Internet Fax destination, it MAY have the functionality to send the
 delivery status to a suitable facsimile device on the GSTN through an
 appropriate offramp gateway.  The generated notice sent via GSTN fax
 SHOULD contain both the human-readable notice information, and the
 original delivery codes.
 If the onramp gateway fails in the transmission of the return notice
 back to GSTN fax service, the information MAY be recorded into a log,
 and processing MAY end.  As an alternate, the administrator of the
 gateway system MAY be notified of this notice with a specific method
 (for example, by sending an e-mail message to a mailbox).

5. Security Considerations

 Refer to Section 3.1 ("User Authorization") for authentication for an
 offramp gateway.  OpenPGP [17] [25] can be used to provide
 authorization services instead of S/MIME.  Refer to Section 4.1
 ("User Authorization") for authentication for an onramp gateway.
 S/MIME and OpenPGP can also be used to encrypt a message.  A signed
 or encrypted message is protected while transported along the
 network; however, when a message reaches an Internet Fax Gateway,
 either onramp or offramp, this kind of protection cannot be applied
 anymore.  Here, security must rely on trusted operations of the
 gateway itself.  A gateway might have its own certificate/key to
 improve security operations when sending Internet Faxes, but, as with
 any gateway, it breaks the end-to-end security pattern of both S/MIME
 and PGP.
 Other security mechanisms, like IPsec [18][19][20][21][2] or TLS [23]
 also do not ensure a secure gateway operation.

Mimura, et al. Informational [Page 9] RFC 4160 Internet Fax Gateway Requirements August 2005

 Denial-of-service attacks are beyond the scope of this document.
 Host compromise caused by flaws in the implementation is beyond the
 scope of this document.

6. References

6.1. Informative References

 [1]  Masinter, L., "Terminology and Goals for Internet Fax", RFC
      2542, March 1999.
 [2]  Thayer, R., Doraswamy, N., and R. Glenn, "IP Security Document
      Roadmap", RFC 2411, November 1998.

6.2. Normative References

 [3]  "Procedures for real-time Group 3 facsimile communication over
      IP networks", ITU-T Recommendation T.38, June 1998.
 [4]  Toyoda, K., Ohno, H., Murai, J., and D. Wing, "A Simple Mode of
      Facsimile Using Internet Mail", RFC 3965, December 2004.
 [5]  Bradner, S., "Key words for use in RFCs to Indicate Requirement
      Levels", BCP 14, RFC 2119, March 1997.
 [6] "Procedures for document facsimile transmission in the general
      switched telephone network", ITU-T Recommendation T.30, April
      1999.
 [7]  Allocchio, C., "Minimal FAX address format in Internet Mail",
      RFC 3192, October 2001.
 [8]  Allocchio, C., "GSTN Address Element Extensions in E-mail
      Services", RFC 2846, June 2000.
 [9]  Housley, R., "Cryptographic Message Syntax (CMS)", RFC 3852,
      July 2004.
 [10] Rescorla, E., "Diffie-Hellman Key Agreement Method", RFC 2631,
      June 1999.
 [11] Ramsdell, B., "Secure/Multipurpose Internet Mail Extensions
      (S/MIME) Version 3.1 Certificate Handling", RFC 3850, July 2004.
 [12] Ramsdell, B., "Secure/Multipurpose Internet Mail Extensions
      (S/MIME) Version 3.1 Message Specification", RFC 3851, July
      2004.

Mimura, et al. Informational [Page 10] RFC 4160 Internet Fax Gateway Requirements August 2005

 [13] Hoffman, P., "Enhanced Security Services for S/MIME", RFC 2634,
      June 1999.
 [14] Resnick, P., "Internet Message Format", RFC 2822, April 2001.
 [15] "Facsimile routing utilizing the subaddress", ITU recommendation
      T.33, July 1996.
 [16] Buckley, R., Venable, D., McIntyre, L., Parsons, G., and J.
      Rafferty, "File Format for Internet Fax", RFC 3949, February
      2005.
 [17] Callas, J., Donnerhacke, L., Finney, H., and R. Thayer, "OpenPGP
      Message Format", RFC 2440, November 1998.
 [18] Kent, S. and R. Atkinson, "Security Architecture for the
      Internet Protocol", RFC 2401, November 1998.
 [19] Kent, S. and R. Atkinson, "IP Authentication Header", RFC 2402,
      November 1998.
 [20] Ramakrishnan, K., Floyd, S., and D. Black, "The Addition of
      Explicit Congestion Notification (ECN) to IP", RFC 3168,
      September 2001.
 [21] Piper, D., "The Internet IP Security Domain of Interpretation
      for ISAKMP", RFC 2407, November 1998.
 [23] Blake-Wilson, S., Nystrom, M., Hopwood, D., Mikkelsen, J., and
      T. Wright, "Transport Layer Security (TLS) Extensions", RFC
      3546, June 2003.
 [24] Mimura, K., Yokoyama, K., Satoh, T., Watanabe, K., and C.
      Kanaide, "Guidelines for Optional Services for Internet Fax
      Gateways", RFC 4161, August 2005.
 [25] Elkins, M., Del Torto, D., Levien, R., and T. Roessler, "MIME
      Security with OpenPGP", RFC 3156, August 2001.

Mimura, et al. Informational [Page 11] RFC 4160 Internet Fax Gateway Requirements August 2005

Authors' Addresses

 Katsuhiko Mimura
 TOYO Communication Equipment CO., LTD.
 2-1-1 Koyato, Samukawa-machi, Koza-gun
 Kanagawa, Japan
 Fax: +81 467 74 5743
 EMail: mimu@miyabi-labo.net
 Keiichi Yokoyama
 TOYO Communication Equipment CO., LTD.
 2-1-1 Koyato, Samukawa-machi, Koza-gun
 Kanagawa, Japan
 Fax: +81 467 74 5743
 EMail: keiyoko@msn.com
 Takahisa Satoh
 TOYO Communication Equipment CO., LTD.
 2-1-1 Koyato, Samukawa-machi, Koza-gun
 Kanagawa, Japan
 Fax: +81 467 74 5743
 EMail: zsatou@t-ns.co.jp
 Chie Kanaide
 TOYO Communication Equipment CO., LTD.
 2-1-1 Koyato, Samukawa-machi, Koza-gun
 Kanagawa, Japan
 Fax: +81 467 74 5743
 EMail: icemilk77@yahoo.co.jp
 Claudio Allocchio
 Consortium GARR
 Viale Palmiro Togliatti 1625
 00155 Roma, Italy
 Fax: +39 040 3758565
 EMail: Claudio.Allocchio@garr.it

Mimura, et al. Informational [Page 12] RFC 4160 Internet Fax Gateway Requirements August 2005

Full Copyright Statement

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 contained in BCP 78, and except as set forth therein, the authors
 retain all their rights.
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Acknowledgement

 Funding for the RFC Editor function is currently provided by the
 Internet Society.

Mimura, et al. Informational [Page 13]

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