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RFC2542 - Terminology and Goals for Internet Fax

王朝other·作者佚名  2008-05-31
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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.

10. Full Copyright Statement

Copyright (C) The Internet Society (1999). All Rights Reserved.

This document and translations of it may be copied and furnished to

others, and derivative works that comment on or otherwise explain it

or assist in its implementation may be prepared, copied, published

and distributed, in whole or in part, without restriction of any

kind, provided that the above copyright notice and this paragraph are

included on all such copies and derivative works. However, this

document itself may not be modified in any way, such as by removing

the copyright notice or references to the Internet Society or other

Internet organizations, except as needed for the purpose of

developing Internet standards in which case the procedures for

copyrights defined in the Internet Standards process must be

followed, or as required to translate it into languages other than

English.

The limited permissions granted above are perpetual and will not be

revoked by the Internet Society or its successors or assigns.

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 IMPLIED, INCLUDING

BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION

HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF

MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.

 
 
 
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