RFC2542 - Terminology and Goals for Internet Fax

Network Working Group L. Masinter
Request for Comments: 2542 Xerox Corporation
Category: Informational March 1999
Terminology and Goals for Internet Fax
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 (1999). All Rights Reserved.
Abstract
This document defines a number of terms useful for the discussion of
Internet Fax. In addition, it describes the goals of the Internet Fax
working group and establishes a baseline of desired functionality
against which protocols for Internet Fax can be judged. It
encompasses the goals for all modes of facsimile delivery, including
"real-time", "session", and "store and forward". Different levels of
desirability are indicated throughout the document.
Table of Contents
1. IntrodUCtion .................................................. 2
2. Definitions and Operational Modes ............................. 3
2.1 User model of fax ........................................... 3
2.2 Definition of Internet Fax .................................. 4
2.3 Internet Fax Roles .......................................... 5
2.4 Internet Fax Devices ........................................ 5
2.5 Operational modes ........................................... 8
3. Goals for Internet Fax ........................................ 8
4. Operational Goals for Internet Fax ............................ 9
4.1 Functionality ............................................... 9
4.2 Interoperability ............................................ 9
4.3 Confirmation ................................................ 10
4.4 Quick Delivery .............................................. 11
4.5 Capabilities ................................................ 12
4.6 Simplicity .................................................. 12
4.7 Security .................................................... 13
4.8 Reliability ................................................. 14
4.9 Fax-like use ................................................ 14
4.10 Legal ...................................................... 15
5. Functional Goals for Internet Fax ............................. 15
5.1 Goals for image data representation ......................... 15
5.2 Goals for transmission ...................................... 16
5.3 Goals for addressing ........................................ 16
5.4 Goals for security .......................................... 17
5.5 Goals for capability exchange ............................... 17
6. Security Considerations ....................................... 18
7. Acknowledgements .............................................. 18
8. Author"s Address .............................................. 18
9. References .................................................... 19
10. Full Copyright Statement ..................................... 20
1. Introduction
Facsimile (Fax) has a long tradition as a telephony application for
sending a document from one terminal device to another.
Many mechanisms for sending fax documents over the Internet have been
demonstrated and deployed and are currently in use. The general
application of using the Internet for facsimile is called "Internet
Fax".
This document defines a number of terms useful for the discussion of
Internet Fax. In addition, it describes the goals for Internet Fax and
establishes a baseline of desired functionality against which
protocols for Internet Fax can be judged. It encompasses the goals for
all modes of facsimile delivery, including "real-time", "session", and
"store and forward" (terms defined in Section 2 of this document).
1.1 Terminology used within this document
Within this document, different levels of desirability for a protocol
for Internet Fax are indicated by different priorities, indicated in
{braces}:
{1} there is general agreement that this is a critical
characteristic of any definition of Internet Fax.
{2} most believe that this is an important characteristic
of Internet Fax.
{3} there is general belief that this is a useful feature
of Internet Fax, but that other factors might override;
a definition that does not provide this element is
acceptable.
In addition, the following terms are used:
"service" An operational service offered by a service provider.
"application" A use of systems to perform a particular function.
"terminal" The endpoint of a communication application.
"goal" An objective of the standarization process.
2. Definitions and Operation Modes
This section defines some of the basic terms for Internet Fax.
2.1 User model of fax and basic operations
The phrase "traditional facsimile" or "G3Fax" is used to denote
implementations of [T.30]. Facsimile (fax) is a telephony application
for sending a document from one terminal device to another.
The telephone network is often referred to as the Public Switched
Telephone Network (PSTN) or Global Switched Telephone Network (GSTN).
Communication over the telephone network is accomplished using
modems. 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 of delivery (to give the sender assurance
that the final data has been received and processed.) Over time,
facsimile has been extended to allow for PCs using fax modems to send
and receive fax, to send data other than scanned facsimile images. In
addition, there have been many extensions to the basic image model,
to allow for additional compression methods and for representation of
images with grey-scale and color. Other delivery extensions have
included sub-addressing (additional signals after the call is
established to facilitate automated routing of faxes to desktops or
mailboxes), and enhanced features such as fax-back and polling.
Typically, the terminal device consists of a paper input device
(scanner), a paper output device (printer), with (a limited amount
of) processing power. Traditional facsimile has a simple user
operational model; the user
1) inserts paper into a device
2) dials a number corresponding to the destination
3) presses the "start" button on the device
4) the sending device connects to the receiving device using the
telephone network
5) the sending device scans the paper and transmits the image of
the paper
6) simultaneously, the remote device receives the transmission and
prints the image on paper
7) upon completion of transmission and successful processing by
the recipient, the sending user is notified of success
Although not usually visible to the user, the operation (5) of
transmission consists of
5a) negotiation: the capabilities of the recipient are oBTained,
and suitable mutually available parameters for the
communication are selected
5b) scanning: creating digitized images of pages of a document
5c) compression: the image data is encoded using a data
compression method
5d) transmission: the data is sent from one terminal to the other
In addition, the terminiation of operations (5d) and (6) may be
characterized as consisting of:
6a) completed delivery: the message has completed transmission
6b) completed receipt: the message has been accepted by the
recipient
6c) processing and disposition: the message has been processed
From a protocol perspective, the information conveyed in the
transmission consists of both "protocol" (control information,
capabilities, identification) and also "document content".
The document content consists primarily of the "document image" plus
additional metadata accompanying the image. The means by which an
image of a document is encoded within the fax content is the "image
data representation".
When the fax has been successfully transmitted, the sender receives a
"confirmation": an indication that the fax content was delivered.
This "confirmation" is an internal signal and is not normally visible
to the sending user, although some error messages are visible, to
allow a page to be retransmitted.
2.2 Definition of Internet Fax
The phrase "Internet Fax" is used to denote an application which
supports an approximation to the user model of fax (Section 2.1), but
where Internet protocols are used instead of the telephone network
for (some portion of) the transmission. The exact modes and
operations of traditional facsimile need not be duplicated exactly.
2.3 Internet Fax Roles
Internet Fax is a document transmission mechanism between various
different devices and roles. Those devices and roles might come in a
wide variety of configurations. To allow for a wide variety of
configurations, it is useful to separate out the roles, as they may
be made available separately or in combination. These roles are:
* Network scanner
A device that can scan a paper document and transmit the scanned
image via the Internet
* Network printer
A device that can accept an image transmission via the Internet
and print the received document automatically
* Fax onramp gateway
A device that can accept a facsimile telephone call and
automatically forward it via the Internet
* Fax offramp gateway
A device that can accept a transmission from the Internet and
forward it to a traditional fax terminal
In addition, other traditional Internet applications might also
participate in Internet Fax, including Internet mail users, Web
browsers, Internet printing hosts.
2.4 Internet Fax Devices
The Internet Fax roles may be embedded in a variety of combinations
and configurations within devices and larger applications. They may
be combined with other elements, e.g., a traditional T.30 fax device.
Many different configurations of applications and systems should {2}
be able to participate in Internet Fax; the specification should not
unnecessarily restrict the range of devices, applications and
services that can participate.
A device that supports Internet Fax might support any combination of
the roles defined in 2.3.
2.4.1 Gateway devices
A traditional fax terminal has a telephone line connection (GSTN)
with a fax modem used to connect over the telephone network. To
connect a fax terminal to the Internet requires a service which
offers connections on one side to the GSTN using standard fax
signals, and on the other side to the Internet. This role might be
performed by a "relay" (e.g., transmitting T.30 signals over real-
time controlled TCP connections) or a "gateway" (e.g., translating
T.30 to TIFF/email).
With these applications, the role of Internet Fax is to transport the
fax content across the Internet, e.g., with
[fax-term]-GSTNfax->[onramp]-Internet Fax->[recipient]
[sender]-Internet Fax->[offramp]-GSTNFax->[fax-term]
A onramp and/or offramp application may be local to a single fax
terminal. For example, the gateway application might exist within a
small device which has a telephone interface on one side and a
network connection on the other. To the fax machine, it looks like a
telephone connection, although it might shunt some or all connections
to Internet Fax instead (Such devices are called "Bump-in-cord.")
An onramp or offramp application may be a local facility serving many
fax terminals. For example, outgoing telephone fax calls through a
company telephone PBX could be rerouted through a local onramp. An
internet to telephone outbound connection could be part of a "LAN
Fax" package.
Onramps and offramps may serve a wider area or broader collection of
users, e.g., services run by service bureaus, offering subscription
services; the telephone sender or the recipient might subscribe to
the service.
The target of an offramp may be a "hunt group": a set of telephone
numbers, each of which have a possibly different fax terminal
attached.
2.4.2 New "Internet Fax" devices
Manufacturers may offer new devices which support any combination of
the roles defined in setion 2.3. In particular, a device resembling a
traditional fax terminal, built out of similar components (scanner,
processor, and printer), could offer a similar functionality to a
traditional facsimile terminal, but be designed to connect to the
Internet rather than, or in addition to, a telephone line connection.
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.
2.4.3 Internet hosts
Internet users using Internet hosts with standard application suites
must {1} be able to exchange faxes with other participants in
Internet Fax, with minimum required enhancements to their operating
environment.
Interoperability with Internet mail users, either as Internet Fax
senders or recipients, is highly desirable {2}.
Internet users might receive faxes over the Internet and display them
on their screens, or have them automatically printed when received.
Similarly, the Internet 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 may be input
directly from a scanner attached to the user"s terminal.
The Internet Fax capability might be integrated into existing
fax/network fax software or email software, e.g., by the addition of
printer drivers that would render the document to the appropriate
content-type and cause it to be delivered using an Internet Fax
protocol.
In some cases, the user might have a multi-function peripheral which
integrated a scanner and printer and which gave operability similar
to that of the stand-alone fax terminal.
2.4.4 Internet messaging
In Internet mail, there are a number of components that operate in
the infrastructure to perform additional functions beyond mail
store-and-forward. Interoperability with these components is a
consideration for the store and forward profile of Internet Fax. For
example, mailing list software accepts mail to a single address and
forwards it to a distribution list of many users. Mail archive
software creates repositories of searchable messages. Mail firewalls
operate at organizational boundaries and scan incoming messages for
malicious or harmful mail attachments. Vacation programs send return
messages to the senders of messages when the recipient is on vacation
and not available to respond.
2.4.5 Universal messaging
Many software vendors are now promoting software packages that
support "universal messaging": a combined communication package that
combines electronic mail, voice mail, and fax.
2.5 Operational Modes for Internet Fax
Facsimile over the Internet can occur in several modes.
"Store and forward" Internet Fax entails a process of storing the
entire document at a staging point, prior to transmitting it to the
next staging point. Store and forward can be directly between sender
and recipient or can have a series of intermediary staging points.
The intermediate storage may involve an intermediate agent or
sequence of agents in the communication.
"Session" Internet Fax is defined such that delivery notification is
provided to the transmitting terminal prior to disconnection. Unlike
"store and forward", there is an eXPection that direct communication,
negotiation, and retransmission can take place between the two
endpoints.
"Real-time" Internet Fax allows for two [T.30] standard facsimile
terminals to engage in a document transmission in a way that all of
the essential elements of the [T.30] communication protocol are
preserved and there is minimal elongation of the session as compared
to Group 3 fax over the GSTN.
These modes are different in the end-user expectation of immediacy,
reliability, and in the ease of total compatibility with legacy or
traditional facsimile terminals; the modes may have different
requirements on operational infrastructure connecting sender and
recipient.
3. Goals for Internet Fax
Facsimile over the Internet must define the mechanisms by which a
document is transmitted from a sender to a recipient, and must {1}
specify the following elements:
- Transmission protocol: what Internet protocol(s) and extensions
are used? What options are available in that transmission?
- Data formats: what image data representation(s) are used,
appropriate, required, within the transmission protocol? What
other data representations are supported?
- Addressing: How are Internet Fax recipients identified? How may
recipient identification be represented in user Directories? How
are traditional fax terminals addressed?
- Capabilities: The capabilities of the sender to generate
different kinds of image data representations may be known to
the recipient, and the capabilities, preferences, and
characteristics of the recipient may be known to the sender. How
are the capabilities, preferences, and characteristics of
senders and recipients expressed, and communicated to each
other?
- Security: Faxes may be authenticated as to their origin, or
secured to protect the privacy of the message. How may the
authenticity of a fax be determined by the recipient? How may
the privacy of a message be guaranteed?
Specific goals for these elements are described in section 5.
4. Operational Goals for Internet Fax
This section lists the necessary and desirable traits of an Internet
Fax protocol.
4.1 Functionality
Traditionally, images sent between fax machines are transmitted over
the global switched telephone network. An Internet Fax protocol must
{1} provide for a method to accomplish the most commonly used
features of traditional fax using only Internet protocols. It is
desirable {3} for Internet Fax to support all standard features and
modes of standard facsimile.
4.2 Interoperability
It is essential {1} that Internet Fax support interoperability
between most of the devices and applications listed in section 2, and
desirable {3} to support all of them. To "support interoperability"
means that a compliant sender attempting to send to a compliant
recipient will not fail because of incompatibility.
Overall interoperability requires {1} interoperability for all of the
protocol elements: the image data representations must be understood,
the transport protocol must function, it must be possible to address
all manner of terminals, the security mechanism must not require
manual operations in devices that are intended for unattended
operation, and so forth.
Interoperability with Internet mail user agents is a requirement {1}
only for the "store-and-forward" facsimile, although it would be
useful {3} for "session" and "real-time" modes of delivery of
Internet Fax.
The requirement for interoperability has strong implications for the
protocol design. Interoperability must not {1} depend on having the
same kind of networking equipment at each end.
As with most Internet application protocols, interoperability must
{1} be independent of the nature of the networking link, whether a
simple IP-based LAN, an internal private IP networks, or the public
Internet. The standard for Internet Fax must {1} be "global": that
is, a single specification which does not have or require special
features of the transport mechanism for local operations.
If Internet Fax is to use the Internet mail transport mechanisms, it
must {1} interoperate consistently with the current Internet mail
environment, and, in particular, with the non-terminal devices listed
in section 2.4.4. If Internet Fax messages might arrive in user"s
mailboxes, it is required {1} that the protocol interoperate
successfully with common user practices for mail messages: storing
them in databases, retransmission, forwarding, creation of mail
digests, replay of old messages at times long after the original
receipt, and replying to messages using non-fax equipment.
It is desirable {3} that the Internet Fax standard support and
facilitate universal messaging systems described in section 2.4.5.
If Internet Fax requires additions to the operational environment
(services, firewall support, gateways, quality of service, protocol
extensions), then it is preferable {3} if those additions are useful
for other applications than Fax. Features shared with other messaging
applications (voice mail, short message service, paging, etc.) are
desirable {3}, so as not to require different operational changes for
other applications.
4.3 Confirmation
In almost all applications of traditional fax, it is considered very
important that the user can get an assurance that the transmitted
data was received by a terminal at the address dialed by the user.
This goal translates to the Internet environment. The "Internet Fax"
application must {1} define the mechanisms by which a sender may
request notification of the completion of transmission of the
message, and receive a determinate response as to whether the message
was delivered, not delivered, or that no confirmation of delivery is
possible.
Originally, fax "confirmation" implied that the message was received
and processed, e.g., delivered to the output paper tray of the
recipient fax device. In reality, this implication was relying upon
a signal produced by the receiving terminal that the incoming page
had been inspected and was determined to be of reasonable (or
unacceptable) quality, via an unspecified algorithm.
In later devices which support error correction mode, the ECM method
(per [T.30]) enabled error checking via a specific algorithm,
providing a more exact indication that the bits within the compressed
image were not corrupted during transmission. With the addition of
memory buffering, PC-based fax modems and the more common use of
error correction mode, traditional fax confirmation still implies
some assurance of processability; (e.g., a fax modem would not be
able to receive an incoming fax if it required compression mechanisms
that were not supported) without reporting on whether the image has
been printed or viewed.
Consequently, the fax confirmation is not the same as a confirmation
that the message was "read": that a human had confirmed that the
message was received. It is desirable {3}, but not required, that
Internet Fax support confirmation that a message has been read (above
and beyond the confirmation that the message has been delivered).
4.4 Quick Delivery
In many cases, fax transmission is used for delivery of documents
where there is a strong user requirement for timeliness, with some
guarantees that if transmission begins at all, it will complete
quickly. For example, it is a common practice to fax documents for
discussion to other participants in a telephone conference call prior
to the call.
Internet Fax should {2} allow the sender of a document to request
immediate delivery, if such delivery is possible. In such cases, it
should {2} be possible for the sender of a message to avoid sending
the message at all, if quick delivery is not available for a
particular recipient.
It is desirable {3} to have the protocol for requesting quick
delivery be the same as, or similar to, the protocol for delayed
delivery, so that two separate mechanisms are not required.
For real-time fax delivery, immediate delivery is the norm, since the
protocol must guarantee that when the session connecting sender to
recipient has terminated, the message has been delivered to the
ultimate recipient.
4.5 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
increasingly offered additional capabilities (higher resolution,
color) as options.
The use of fax has grown in an evolving world (from "Group 1" and
"Group 2", to "Group 3" facsimile) because of two elements: (a) a
useful baseline of capabilities that all terminals implemented, and
(b) the use of capabilities exchange to go beyond that.
To accommodate current use as well as future growth, Internet Fax
should {2} have a simple minimum set of required features that will
guarantee interoperability, as well as a mechanism by which higher
capability devices can be deployed into a network of lower capability
devices while ensuring interoperability. If recipients with minimum
capabilities were, for example, to merely drop non-minimum messages
without warning, the result would be that no non-minimum message
could be sent reliably. This situation can be avoided in a variety of
ways, e.g., through communication of recipient capabilities or by
sending multiple renditions.
The exchange of capabilities in Internet Fax should {2} be robust. To
accomplish this, recipients should {2} be encouraged to provide
capabilities, even while senders must {1} have a way to send messages
to recipients whose capabilities are unknown.
Even minimum-capability recipients of messages should {2} be required
to provide a capability indication in some reliable way. This might
be accomplished by providing an entry in a directory service, by
offering automatic or semi-automatic replies, or by sending some
indication of in a reply to a message with multiple renditions, or as
an addition to a negative acknowledgement requiring retransmission.
On the other hand, for reliability, senders cannot rely on capability
information of recipients before transmission. That is, for
reliability, senders should {2} have an operational mode which can
function when capabilities are not present, even when recipients must
always provide capabilities.
4.6 Simplicity
Internet Fax should not {2} require terminals to possess a large
amount of processing power, and a base level implementation must {1}
interoperate, even if it does not offer complex processing.
Internet Fax should {2} allow interoperability with recipient 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.
Different operational modes (real-time, session, store and forward)
might use different protocols, in order to preserve the simplicity of
each.
It is preferable {3} to make as few restrictions and additions to
existing protocols as possible while satisfying the other
requirements. It is important {2} that it be possible to use
Internet Fax end-to-end in the current Internet environment without
any changes to the existing infrastucture, although some features may
require adoption of existing standards.
4.7 Security: Cause No Harm, Allow for privacy
The widespread introduction of Internet Fax must {1} not cause harm,
either to its users or to others. For example, an automatic mechanism
for returning notification of delivery or capabilities of fax
recipients by email must {1} not expose the users or others to mail
loops, bombs, or replicated delivery. Automatic capability exchange
based on email might not be sufficiently robust and, without
sufficient precautions, might expose users to denial of service
attacks, or merely the bad effects of errors on the part of system
administrators. Similar considerations apply in these areas to those
that have been addressed by work on electronic mail receipt
acknowledgements [RFC2298].
Internet Fax should {2} not, by default, release information that the
users consider private, e.g., as might be forthcoming in response to
a broadcast requests for capabilities to a company"s Internet fax
devices. Public recipients of Internet Fax (e.g., public agencies
which accept facsimile messages) should {2} not be required to
broadcast messages with capability statements to all potential
senders in order to receive facsimile messages appropriate for the
capabilities of their device.
The possibility for "causing harm" might be created by a combination
of facilities and other features which individually may be viewed as
harmless. Thus, the overall operation of a network full of Internet
Fax devices must {1} be considered.
Interoperation with ITU defined T.30 fax security methods, as well as
standard Internet e-mail security methods is desirable {3}.
4.8 Reliability
The Internet Fax protocol should {2} operate reliably over a variety
of configurations and situations.
In particular, operations which rely on time-delayed information
might result in inconsistent information, and the protocol should be
robust even in such situations.
For example, in a store-and-forward message environment, the
capabilities and preferences of a fax recipient might be used by the
sender to construct an appropriate message, e.g., sending a color fax
to a color device but a black and white fax to a device that does not
have color capability. However, the information about recipient
capabilities must be Accessible to the sender even when the recipient
cannot be contacted directly. Thus, the sender must access recipient
capabilities in some kind of storage mechanism, e.g., a directory. A
directory of recipient capabilities is a kind of distributed
database, and would be 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. The
Internet Fax protocol should {2} be robust in these situations;
messages should {2} not be lost or misprocessed even when the
sender"s knowledge of recipient capabilities are wrong, and robust
mechanisms for delivery of recipient capabilities should {2} be used.
4.9 User Experience
The primary user experience with fax is:
immediate delivery
delivery confirmation
ease of use
The primary user experience with email is:
delayed delivery
no delivery confirmation
ability to reply to sender
easy to send to multiple recipients
An Internet Fax standard should {2} attempt to reconcile the
differences between the two environments.
4.10 Legal
An Internet Fax standard should {2} accomodate the legal requirements
for facsimile, and attempt to support functionality similar to that
legally required even for devices that do not operate over the public
switched telephone network.
The United States Federal Communication Commission regulations
(applicable only within the USA) state:
Identification Required on Fax Messages
The FCC"s rules require that any message sent to a fax machine
must clearly mark on the first page or on each page of the
message:
* the date and time the transmission is sent;
* the identity of the sender; and
* the telephone number of the sender or of the sending fax
machine.
All fax machines manufactured on or after December 20, 1992 and
all facsimile modem boards manufactured on or after December 13,
1995 must have the capability to clearly mark such identifying
information on the first page or on each page of the
transmission."
5. Functional Goals for Internet Fax
These goals for specific elements of Internet Fax follow from the
operational goals described in section 4.
5.1 Goals for image and other data representations
Interoperability with Internet Mail or other transmission mechanisms
that cause data files to appear in Internet terminal environments
requires {1} that Internet Fax use a format for images that is in
wide use.
Interoperability with Internet Mail requires {2} that Internet Fax
recipients handle those message types that are common in the email
environment, including a minimum set of MIME mail formats.
Interoperability with traditional fax terminals requires {1} that the
data format be capable of representing the commonly used compression
mechanisms defined for traditional facsimile; support for _all_
standard formats defined for traditional facsimile is highly
desirable {2}. In addition, interoperability with "private use"
facsimile messages suggests {3} that the standard accommodate
arbitrary bit sequences.
5.2 Goals for transmission
It is necessary {1} that Internet Fax to work in the context of the
current Internet, Intranet, and the combination across firewalls.
A single protocol with various extensions is preferable {3} to
multiple separate protocols, if there are devices that might require,
at different times and for different recipients, different protocols.
5.3 Goals for addressing
Interoperability with the terminal types in section 2 requires {1}
the ability to address each of the kinds of recipient devices. The
address of a recipient must give sufficient information to allow the
sender to initiate communication.
Interoperability with offramps to legacy fax terminals requires {1}
that the message contain some way of addressing the final destination
of facsimile messages, including telephone numbers, various ISDN
addressing modes, and facsimile sub-addresses.
Interoperability with Internet Mail requires {1} that it be possible
to address Internet Fax to any email address. Interworking with
Internet mail also requires {1} that the addressing is in the email
addressing headers, including mail transport envelope [RFC1123] and
RFC822 headers, as appropriate. The information must {1} appear
nowhere else.
Sending devices might not have local storage for directories of
addresses, and addresses might be cumbersome for users to type in.
For these reasons, Internet Fax devices may require configuration to
locate directories of recipients and their capabilities.
The source of a fax message must {1} be clearly identified. The
address of the appropriate return message (whether via fax or via
email) should {2} be clearly identified in a way that is visible to
all manner of recipients. In the case of Internet Fax delivered by
email, it should {2} be possible to use the normal "reply" functions
for email to return a message to the sender.
Traditionally, it is common for the first page of a fax message sent
to a facsimile terminal to contain an (image) representation of the
name, address, return number, etc. of the sender of the document.
Some legal jurisdictions for facsimile require an identification of
the sender on every page. The standard for Internet Fax should {2}
cover the issues of sender and recipient identification in the cases
where fax messages are re-routed, forwarded, sent through gateways.
5.4 Goals for Security
Users typically use GSTN-based fax for confidential document
transmission, assuming a similar or higher level of confidentiality
and protection from both deliberate and inadvertent eavesdropping as
holds for telephone conversations; the higher level of
confidentiality arising from the requirement for non-standard
equipment to intercept and interpret an overheard fax transmission.
Similarly, in traditional fax there is an expectation (and, in some
contexts, a legally recognized assurance) that the received fax is
unaltered from the document originally transmitted.
It is important {2} that Internet Fax give users a level of assurance
for privacy and integrity that is as good or better than that
available for telephone-based fax. The Internet Fax standard should
{2} specify how secure messages can be sent, in an interoperable
fashion. The Internet Fax protocol should {2} encourage the
introduction of security features, e.g., by requiring that minimum
capability devices still accept signed messages (even if ignoring the
signature.)
In the case where the sender is responsible for payment for offramp
services in a remote location, it is desirable {3} to provide for
authentication and authorization of the sender, as well as enable
billing related information from the offramp to be transferred
securely.
5.5 Goals for capabilities exchange
Traditional fax supports a wide range of devices, including high
resolution ("Superfine"); recent enhancements include methods for
color and a variety of compression mechanisms. Fax messaging includes
the capability for "non-standard frames", which allow vendors to
introduce proprietary data formats. In addition, facsimile supports
"binary file transfer": a method of sending arbitrary binary data in
a fax message.
To support interoperability with these mechanisms, it should {2} be
possible to express a wide variety of fax capabilities.
Capability support has three elements: expression of the capabilities
of the sender (as far as a particular message is concerned),
expressing the capabilities of a recipient (in advance of the
transmission of the message), and then the protocol by which
capabilities are exchanged.
The Internet Fax standard should {2} specify a uniform mechanism for
capabilities expression. If capabilities are being sent at times
other than the time of message transmission, then capabilities should
{2} include sufficient information to allow it to be validated,
authenticated, etc.
The Internet Fax standard may {3} include one or several methods for
transmission, storage, or distribution of capabilities.
A request for capability information, if sent to a recipient at any
time other than the immediate time of delivery of the message, should
{2} clearly identify the sender, the recipient whose capabilities are
being requested, and the time of the request. Som kind of signature
would be useful, too.
A capability assertion (sent from recipient to sender) should {2}
clearly identify the recipient and some indication of the date/time
or range of validity of the information inside. To be secure,
capability assertions should {2} be protected against interception
and the substitution of valid data by invalid data.
6. Security Considerations
This document describes the goals for the Internet Fax protocol,
including the security goals. An Internet Fax protocol must {1}
address the security goals and provide adequate measures to provide
users with expected security features.
7. Acknowledgements
The author gratefully acknowledges the contributions of Graham Klyne,
Vivian Cancio, Dan Wing, Jim Dahmen, Neil Joffe, Mike Lake, Lloyd
McIntyre, Richard Shockey, Herman Silbiger, Nadesan Narenthiran,
George Pajari and Dave Crocker for their valuable comments on this
document.
8. Author"s Address
Larry Masinter
Xerox Corporation
3333 Coyote Hill Road
Palo Alto, CA 94304
http://www.parc.xerox.com/masinter
Fax: (650) 812-4333
EMail: masinter@parc.xerox.com
9. References
[T.30] "Procedures for Document Facsimile Transmission in the
General Switched Telephone Network", ITU-T (CCITT),
Recommendation T.30, July, 1996.
[F.185] "Internet facsimile: Guidelines for the support of the
communication of facsimile documents", ITU-T (CCITT),
Recommendation F.185, 1998.
[T.37] "Procedures for the transfer of facsimile data via store-
and-forward on the Internet", ITU-T (CCITT), Recommendation
T.37, 1998.
[T.38] "Procedures for real time Group 3 facsimile communication
between terminals using IP Networks", ITU-T (CCITT),
Recommendation T.38, 1998.
[RFC2305] Toyoda, K., Ohno, H., Murai, J. and D. Wing, "A Simple Mode
of Facsimile Using Internet Mail", RFC2305, March 1998.
[RFC2298] Fajman, R., "An Extensible Message Format for Message
Disposition Notifications", RFC2298, March 1998.
[RFC1123] Braden, R., "Requirements for Internet hosts - Application
and Support", STD 3, RFC1123, October 1989.
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