Guidelines for Optional Services for Internet Fax Gateways
RFC 4161

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Network Working Group                                         K. Mimura
Request for Comments: 4161                                  K. Yokoyama
Category: Informational                                        T. Satoh
                                                            K. Watanabe
                                                             C. Kanaide
                                           TOYO Communication Equipment
                                                            August 2005

       Guidelines for Optional Services for Internet Fax Gateways

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 guidelines for the optional 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 from 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.

   This document supplements the recommendation for minimal features of
   an Internet Fax Gateway.  In particular, it covers techniques for
   dropping duplicated fax messages, automatic fax re-transmission,
   error, return notice, and log handling, and possible authorization
   methods by DTMF (Dual Tone Multi-Frequency) for onramp gateways.

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RFC 4161      Optional Services for Internet Fax Gateways    August 2005

1.  Introduction

   An Internet Fax Gateway can be classified as either an offramp
   gateway or an onramp gateway.  This document provides guidelines for
   optional services and examples of Internet Fax Gateway operations.
   In particular, it covers techniques for dropping duplicated fax
   messages, automatic fax re-transmission, error, return notice, and
   log handling, and possible authorization methods by DTMF (Dual Tone
   Multi-Frequency) for onramp gateways.

   A more detailed definition of onramps and offramps is provided in
   [1].  Recommended behaviors for Internet Fax Gateway functions are
   defined in [15].

   This document provides recommendations only for the specific cases
   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 [16].

   This document does not apply to the gateway functions for "real-time
   Internet Fax", as described and defined in [18].

1.1.  Key Words

   The key words "MUST", "SHOULD", "SHOULD NOT", and "MAY" in this
   document are to be interpreted as described in [17].

2.  Optional Services for an Offramp Gateway

2.1.  Drop Duplicated GSTN Fax Transmission

   Electronic mail transport agents (MTA) deliver an Internet Fax
   message into either the recipient's mailbox or an offramp gateway
   mailbox.  Hence, the message is retrieved for further action, which
   in the case of the offramp gateway, will result in its delivery to
   the GSTN fax service.

   The offramp gateway mailbox will thus receive all messages which the
   gateway will process, regardless of their final, distinct GSTN
   destinations.  As such, addresses like

      Fax=+12224567654@example.com
      Fax=+38155234578@example.com
      Fax=+3904567437777@example.com

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RFC 4161      Optional Services for Internet Fax Gateways    August 2005

   will all end up in the offramp gateway mailbox corresponding to the
   "example.com" domain.

   However, the handling of e-mail messages (including those of Internet
   Faxes) that contain more than one recipient, but are directed to the
   same final MTA, can be different, depending on the MTA configuration
   or features.  A single message with multiple recipients in the SMTP
   envelope [19] is likely to be the most common case on the mail
   transport system, but it may happen that multiple copies of the same
   message are transmitted, one per recipient.  Or it may happen that
   the final MTA is set to deliver a separate copy of the message per
   recipient into the final mailbox, supposing it is delivering messages
   to real mailboxes of distinct endusers.

   Thus, it may happen that the offramp gateway receives multiple copies
   of the same Internet Fax message that is to be delivered to different
   GSTN destinations, which are listed together and repeatedly in the