One document matched: draft-ietf-fax-requirements-00.txt

		   Requirements for Internet Fax
 	        <draft-ietf-fax-requirements-00.txt>

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0. Introduction and Overview

Facsimile (Fax) has a long tradition of being a telephony application
from one terminal device to another, where the terminal device
consists of a paper input device (scanner), a paper output device
(printer), and a limited amount of processing power. The transmission
of data end-to-end is accompanied by negotiation (to ensure that the
scanned data can be rendered at the recipient) and confirmation (to
give the sender some assurance that the final data has been received
and processed.)

Over time, facsimile has been extended to allow for PCs connected
running software to send and receive fax, to send data other than
paper images, as well as many extensions to the basic image model,
e.g., recent ITU fax standards for color fax.

Many mechanisms for sending fax documents over the Internet have been
demonstrated and deployed.

This document attempts to summarize the many discussions in the
Internet Fax working group concerning requirements, and to establish a
baseline of agreed-to requirements against which any proposal for
Internet Fax can be judged.

It is the work of the author, but intended to be considered for moving
forward as the consensus view of the IETF Fax Working Group.  As such,
comments and counter-proposals are requested.

Summary of requirements:

 1. Interoperability: integrate with email
 2. Confirmation: ability to request a confirmation
 3. Quick Delivery: ability to ask for immediate delivery
 4. Capabilities: reliable, upgrade possible
 5. Simplicity: basic possible
 6. Security: Cause no harm, allow for privacy
 7. Reliability: avoid inconsistent operations

1. Interoperability

It is desirable that a standard for Internet Fax allow for the
interoperability of many kinds of terminal types.  There are three
primary terminal types considered for Internet Fax.

1a. Traditional fax terminals

A traditional fax terminal has a telephone line connection (PSTN) with
a fax modem used to connect over the telephone network. To connect a
fax terminal to the Internet requires a _gateway_: a service which
offers connections on one side to the PSTN using standard fax signals,
and on the other side to the Internet.

A standard for Internet Fax may address only the Internet side of the
connection, as the fax signals over PSTN are defined by T.30.
However, the Internet Fax protocol must accomodate requirements placed
by the nature of the gateway service.

A gateway which accepts fax telephone calls and makes an Internet
connection is called an 'Internet Fax onramp'. A gateway which accepts
Internet connections and makes fax telephone calls is called an
'Internet Fax offramp'.

[fax-term]-PSTNfax->[onramp]-Internet Fax->[recipient]
                    [sender]-Internet Fax->[offramp]-PSTNFax->[fax-term]

The gateway function may be local to a single fax terminal (a "bump in
the cord" device), to a local area network or local facility (a PBX
extension), or be offered by an Internet Service Provider (ISP).

1b. New "IFAX" terminals

Manufacturers of traditional facsimile devices may offer new devices
built out of similar components (scanner, processor, and printer),
which offer a similar functionality to a fax device, but which
connects to the Internet. These devices might also offer a traditional
fax modem capability, or might send documents exclusively through the
Internet.  Such devices might have a permanent Internet connection
(through a LAN connection) or might have occasional connectivity
through a (data) modem to an Internet Service Provider via PPP.

1c. Internet user

Normal Internet users with workstations or PCs who engage in messaging
should have the capability of sending and receiving fax messages
through the use of their ordinary software.

Fax messages might be received and displayed on the user's screen, or
even automatically printed when received, as with traditional fax
devices. Similarly, the fax messages originating from the user might
be the output of a software application which would normally 'print',
or specially constructed fax-sending software, or even from a scanner
attached to the user's terminal.

In some cases, the user might have a multi-function peripheral which
integrated scanner and printer, and which gave operability similar to
that of the stand-alone fax terminal.

1d. Mail processing systems

If Internet Fax is to use the Internet mail transport mechanisms, it
is important that it interoperate consistently with the deployed mail
environment. Internet Mail operates not only end-to-end, but also with
mailing list maintenance programs, mail archiving programs, mail firewalls
which scan incoming mail attachments for malicious viruses, etc.

Internet Fax software should not be disruptive in such an environment
and preferably should interoperate well.

2. Confirmation

Traditional fax applications are often used for important business
correspondence, where some amount of assurance is available that the
transmitted data was actually recieved at the intended terminal.

In Internet Fax, it should be possible for a sender to request
acknowledgement of the completion of transmission of the message, and
to receive a determinate response as to whether the message was
delivered, not deliveried, or that confirmation was denied.

3. Quick Delivery

In many (if not most) cases, fax transmission is used for urgent
delivery of documents, with some guarantees that if transmission
begins at all, it will complete quickly. EMail doesn't normally have
this characteristic.

The Internet Fax standard should allow the sender of a document to
request immediate delivery, and to have a mechanism for accomplishing
that, and to avoid sending a document only to accomplish indeterminate
delivery times.

4. Capabilities: reliable, upgrade possible

Traditionally, facsimile has guaranteed interworking between senders
and recipients, by having a strict method of negotiation of the
capabilities between the two devices. The image representation of
facsimile originally was a relatively low resolution, but has offered
higher resolution, and color capabilities as options.

The standard for Internet fax should not require fax terminals to
support all capabilities, but there should be a mechanism by which
transmission can be reliably accomplished. This might be because there
is a facility by which the sender might determine the capabilities of
the recipient with reasonable reliability in advance of transmission,
by sending multiple renditions, or by relying on negative
acknowledgement and retransmission.

5. Simplicity

The Internet Fax standard should not require terminals to possess a
large amount of processing power, and a base level implementation
should interoperate, even if it does not offer complex processing.

The Internet Fax standard should allow interoperability with fax
terminal devices which have limited buffering capabilities, and cannot
buffer an entire fax message prior to printing, or cannot buffer an
entire set of fax pages before beginning transmission of scanned
pages.

6. Security: Cause No Harm, Allow for privacy

The widespread introduction of any standard mechanism for Internet Fax
must not cause harm, either to its users or to others. It is
important, for example, that no automatic mechanism for returning
acknowledgements of receipt or capabilities of fax recipients expose
the users or others to mail loops, bombs, or replicated
delivery. Similar considerations apply in these areas to those that
have been addressed by work on electronic mail receipt
acknowledgements [RECEIPT].

Automatic capability exchange based on email is not robust and may
expose its users to denial of service attacks, or merely the bad
effects of errors on the part of system administrators.  While manual
configuration and confirmation are awkward, the alternative (exposing
users to unreliable or disruptive operations) is less acceptable.

If a request for capabilities is sent via email, then the rules for
responding to it have the same requirements as the rules for read
receipts: only with the recipient's explicit confirmation.

Protocols should not subject users to release of private information,
such as might be accomplished by broadcast requests for capabilities
to a company's Internet fax devices.  Public recipients of Internet
Fax should not be required to broadcast capability statements in order
to receive quality faxes.

Interoperation with ITU defined T.30 fax security methods, as well
as standard Internet e-mail security methods is desirable.

7. Reliability: Avoid inconsistent operations

Insofar as there is information about the capabilities of recipients
in a store-and-forward message environment, the capabilities and
preferences of the recipient must be known by the sender prior to the
construction and transmission of the message. Because this information
must be accessible by the sender even when the recipient cannot be
contacted directly, the sender must access capabilities in some kind
of storage mechanism. Most commonly these stored capabilities will be
in a directory of some kind.  This directory of capabilities is, in
fact, a distributed database, and is subject to all of the well-known
failure modes of distributed databases. For example, update messages
with capability descriptions might be delivered out of order, from old
archives, might be lost, non-authenticated capability statements might
be spoofed or widely distributed by malicious senders.

Unfortunately, the mechanisms by which a distributed database of
directory information may be maintained and updated reliably are not
yet widely deployed in the Internet environment, but an asyncronous
and delayed distribution of capability information is not robust.

8. References

[] <<omitted this draft>>