IETF fax WG G. Klyne, Content Technologies
Internet draft [[[et al]]]
22 October 1999
Expires: April 2000
Timely Delivery for Facsimile Using Internet Mail
<draft-ietf-fax-timely-delivery-00.txt>
Status of this memo
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Copyright Notice
Copyright (C) The Internet Society 1999. All Rights Reserved.
Abstract
This proposal is to describe a way to accomplish timely delivery of
e-mail messages, with deterministic service quality guarantee,
while preserving the traditional roles and responsibiltiies of the
agents involved in e-mail transfers.
It is essentially a profile of the DSN and DELIVERBY extentions for
ESMTP, [[[and possibly]]] a new extension for establishing the
deerministic service guarantee.
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NOTE: This is a first and very preliminary version of
specification, rapidly drafted to indicate a possible way forward
to achieve the timely delivery requirement for full mode Internet
fax. The content is very rough, and the intent at this time is to
indicate just the outline of a mechanism. Please address comments
to major structural and semantic issues.
Table of contents
1. Introduction.............................................2
1.1 Structure of this document ...........................2
1.2 Document terminology and conventions .................2
1.3 Discussion of this document ..........................3
2. Background and goals.....................................3
2.1 Background ...........................................3
2.2 Goals for timely delivery ............................4
3. Framework for timely delivery............................4
3.1 Transmitting a message for timely delivery ...........4
3.2 Relaying a message ...................................5
3.3 Accepting a message by the final MTA .................6
4. Compliance-required ESMTP extension......................7
5. DSN reporting extensions.................................7
6. Notes....................................................7
7. Examples.................................................7
8. IANA Considerations......................................8
9. Internationalization considerations......................8
10. Security considerations.................................8
11. Acknowledgements........................................8
12. References..............................................8
13. Authors' addresses......................................9
Appendix A: Amendment history...............................9
Full copyright statement....................................9
1. Introduction
1.1 Structure of this document
[[[TBD]]]
1.2 Document terminology and conventions
[[[TBD]]]
NOTE: Comments like this provide additional nonessential
information about the rationale behind this document.
Such information is not needed for building a conformant
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implementation, but may help those who wish to understand
the design in greater depth.
[[[Editorial comments and questions about outstanding issues are
provided in triple brackets like this. These working comments
should be resolved and removed prior to final publication.]]]
1.3 Discussion of this document
Discussion of this document should take place on the content
negotiation and media feature registration mailing list hosted by
the Internet Mail Consortium (IMC):
Please send comments regarding this document to:
ietf-fax@imc.org
To subscribe to this list, send a message with the body 'subscribe'
to "ietf-fax-request@imc.org".
To see what has gone on before you subscribed, please see the
mailing list archive at:
http://www.imc.org/ietf-fax/
2. Background and goals
2.1 Background
Traditional e-mail [2] is open-loop. The sender of a message
normally has no certainty if or when a message is delivered. (A
separate memo [6] contains a discussion of some open- and closed-
loop issues in e-mail.)
To be more than just a hint to the message transfer system, timely
delivery requires a deterministic confirmation mechanism, to close
the loop. This is provided by DSN [4].
Three kinds of timeliness can be identified:
(a) timely delivery to the receipient
(b) timely notification to the sender of delivery
(c) timely notification to the sender that the message has been
processed
This proposal focuses on (a) and (b). A separate proposal is under
consideration to address the final case (c).
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The DELIVERBY extension [5] provides a mechanism to ensure timely
delivery of a message.
From the sender's point of view, timely confirmation of delivery is
the most desirable requirement.
[[[Need to consider how timely confirmation (i.e. delay in the
return path transfer of the confrmation) is handled]]]
2.2 Goals for timely delivery
The primary goal is to provide a mechanism that allows a consenting
parties to establish a relationship with guarenteed delivery within
a specified time, or notification that the delivery was not
achieved.
Further goals are:
o Deterministic behaviour.
[[[TBD]]]
3. Framework for timely delivery
Timely delivery is achieved through a number of ESMTP extensions
used in concert:
- Deivery Status Notification ("DSN") [RFC 1891]
- Deliver-by ("DELIVERBY") []
- Compliance-required [[[NEW!]]] [[[if needed: deliver-by looks
nearly sufficient.]]]
The confirmation loop for succesful delivery looks something like
this. The path through MTAs taken by the confirmation response is
not defined, and may be different from the forward path of the
original message.
+-----------+ +--------+ +--------+ +---------+
|Originating|-->--|Relaying| ... |Relaying|-->--|Receiving|
| MTA | | MTA | | MTA | --| MTA |
+-----------+ +--------+ +--------+ | +---------+
| | |
+-------------+ | +---------+
| Originating |--<-- ... .... ... --<-- |Receiving|
| MUA | | MUA |
+-------------+ +---------+
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3.1 Transmitting a message for timely delivery
A transmitted message for which timely delivery is required MUST
include the following:
- an ENVID parameter on the MAIL command, per DSN [4]
- a NOTIFY=SUCCESS,FAILURE parameter on the corresponding RCPT
command, per DSN [4]
- an ORCPT parameter on the MAIL command, per DSN [4]
- a 'BY' parameter on the corresponding RCPT command, per [5]
- a COMPLIANCE-REQUIRED parameter on the corresponding RCPT, as
described below
The message MUST NOT be transmitted to any MTA that does not
indicate support for all of these extensions in its response to the
EHLO command. In this case, a negative delivery status report MUST
be generated indicating the non-compliant MTA, the extensions that
it does not support, and the name of the reporting MTA (per DSN,
using the non-compliance reporting extensions noted below).
3.2 Relaying a message
An MTA that relays a message for timely delivery MUST support all
of the ESMTP extensions noted above, otherwise it should not
receive the message in the first place. When a relaying MTA
accepts a message (by its 2xx status response to receipt of the
message data), it becomes responsible for its onward delivery,
including satisfying all of the options associated with the
message.
In order to relay a message, an MTA must note when the message was
received, note the time when the attempt to transmit the message to
the next MTA is initiated, and reduce accordingly the time interval
used for the 'deliver-by' parameter (see note below on handling
fine-grained timing requirements).
If the deliver-by interval is reduced to less than zero, (or less
than some system-configurable value indicating that delivery within
the indicated interval is unlikely to be achieved) then the message
MUST NOT be relayed. Instead, a negative delivery status report
MUST be generated indicating that the time for delivery of the
message has expired, and the reporting MTA (per DSN, using the
deliver-by extensions and/or non-compliance reporting extensions
noted below).
[[[Remove duplication between above and DELIVERBY spec]]]
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If the first attempt to relay a message fails, the relaying MTA MAY
assume that delivery within the desired time will not be achieved,
and immediately indicate a delivery failure, indicating the name of
the next-hop MTA. Alternatively, the relaying MTA may wait and
retry the transmission, provided that the retry attempt will be
performed within the remaining deliver-by period; if the
transmission cannot be completed after one or more such retries
then a negative DSN should be generated as noted above.
In all cases, any DSN generated should indicate the number of
retries attempted (where 0 means no retries).
The choice to retry or not retry is installation dependent.
Effectively, when a relay does not retry, any reposibility for
overcoming the delivery failure is passed back to the original
sender. This strategy may be appropriate for cases where very
rapid delivery is required or expected.
[[[Need to limit the number and/or frequency of retries?]]]
3.3 Accepting a message by the final MTA
The MTA that accepts final delivery of a message has responsibility
for passing the message to a Mail User Agent. The exact mechanism
by which this is achieved is a local matter, and not defined here
or by the Internet e-mail specifications. The final MTA is also
responsible for generating any successful DSN message.
Before generating a DSN message, the final MTA must ensure that all
of the conditions for delivery of the message have been achieved.
Specifically, it should ensure that final delivery to the MTA will
be completed within the deliver-by interval indicated. Exactly
what constitutes final delivery to the MTA may depend somewhat on
the nature of the MTA: in the simplest case, depositing the
message in a local mailbox probably constitutes final delivery; a
more complex case would be that of a fax offramp: in this case it
may be reasonable for final delivery to be completion of a
successful outdial and transmission of the fax.
[[[DISCUSS: In environments where the timing of final delivery of
the message is outside the control of the final MTA (e.g. the time
required for an outdial, or waiting for a client to collect the
message), an interim DSN report may be generated indicating that
the message has been received pending final delivery. This report
bshould be clear whether final delivery is dependent on the
receiving user (e.g. mail collection) or some other unknown
infrastructure delay (e.g. fax out-dial or external e-mail
environment).]]]
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[[[I think the above is verging on trying to be too clever, getting
too far into MDN teritory]]]
4. Compliance-required ESMTP extension
[[[TBD]]]
Essentially, the semantics will be to REQUIRE conformance to any
SMTP extensions used for delivery to be successfully completed.
[[[I am thinking the required extensions should be listed in the
RCPT command; e.g. COMPLIANCE=DSN,DELIVER-BY]]]
5. DSN reporting extensions
- Extension not supported
- Delivery time exceeded
- Delivered for further transmission: final confirmation pending
[[[???]]]
- Delivered for collection by user: final confimation pending
[[[???]]]
6. Notes
[[[These are placeholders for further discussion]]]
- Use of alternative port (e.g. like message submission).
- Scalability analysis. Required state information -- all at the
edges?
- Discussion of race conditions. Indeterminacy in time for status
response to reach sender. Message duplication as the worst case.
- Return path different from forward path.
- Handling fine-grained timing requirements (deliver-by
modification and implementation techniques). Must assume deliver-
by interval is large relative to normal network transit times.
- Partial non-delivery: failure to some recipients. Must be
handled, since all-or-nothing cannot be imposed within the SMTP
transfer environment.
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7. Examples
[[[TBD]]]
8. IANA Considerations
[[[TBD: ESMTP and DSN extension registrations]]]
9. Internationalization considerations
[[[TBD?]]]
10. Security considerations
[[[TBD]]]
11. Acknowledgements
[[[TBD]]]
12. References
[1] RFC 2542, "Terminology and Goals for Internet Fax"
L. Masinter, Xerox Corporation
March 1999.
[2] RFC 821, "Simple Mail Transfer Protocol"
Jonathan B. Postel, ISI/USC
August 1982.
[3] (SMTP extensions)
[4] RFC 1891, "SMTP Service Extension for Delivery Status
Notifications"
K. Moore, University of Tennessee
January 1996.
[5] DELIVERBY: <draft-newman-deliver-02.txt>
[6] <draft-ietf-fax-content-negotiation-00.txt>
[7] RFC 2234, "Augmented BNF for Syntax Specifications: ABNF"
D. Crocker (editor), Internet Mail Consortium
P. Overell, Demon Internet Ltd.
November 1997.
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13. Authors' addresses
Graham Klyne (editor)
Content Technologies Ltd.
1220 Parkview,
Arlington Business Park
Theale
Reading, RG7 4SA
United Kingdom.
Telephone: +44 118 930 1300
Facsimile: +44 118 930 1301
E-mail: GK@ACM.ORG
[[[et. al. TBD]]]
Appendix A: Amendment history
00a 22-Oct-1999 Memo initially created.
TODO:
Full copyright statement
Copyright (C) The Internet Society 1999. All Rights Reserved.
This document and translations of it may be copied and furnished to
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other than English.
The limited permissions granted above are perpetual and will not be
revoked by the Internet Society or its successors or assigns.
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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
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Klyne, et al Internet draft [Page 10]
