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Network Working Group M. Rose
Request for Comments: 1486 Dover Beach Consulting, Inc.
C. Malamud
Internet Multicasting Service
July 1993
An Experiment in Remote Printing
Status of this Memo
This memo defines an Experimental Protocol for the Internet
community. It does not specify an Internet standard. Discussion and
suggestions for improvement are requested. Please refer to the
current edition of the "IAB Official Protocol Standards" for the
standardization state and status of this protocol. Distribution of
this memo is unlimited.
Table of Contents
1. Introduction .......................................... 1
1.1 The Advantage of a General-Purpose Infrastructure..... 2
2. Procedure ............................................. 2
2.1 Naming, Addressing, and Routing ...................... 3
2.2 The application/remote-printing Content-Type ......... 4
2.3 Usage Example ........................................ 5
2.4 Remote Printing without MIME ......................... 6
3. The Experiment ........................................ 7
3.1 Infrastructure ....................................... 8
3.1.1 Zones .............................................. 8
3.1.2 MX records ......................................... 8
3.2 Accounting and Privacy ............................... 9
3.3 Mailing list ......................................... 9
3.4 Prototype Implementation ............................. 10
4. Future Issues ......................................... 11
5. Security Considerations ............................... 11
6. Acknowledgements ...................................... 11
7. References ............................................ 11
8. Authors' Addresses..................................... 12
A. The image/tiff Content-Type .......................... 13
B. Uniform Addressing ................................... 13
1. Introduction
Although electronic mail is preferable as a means of third-party
communication, in some cases it may be necessary to print
information, in hard-copy form, at a remote location. The remote
output device may consist of a standard line printer, a printer with
Rose & Malamud [Page 1]
RFC 1486 An Experiment in Remote Printing July 1993 multiple fonts and faces, a printer that can reproduce graphics, or a facsimile device. Remote output may be accompanied by information that identifies the intended recipient. This memo describes a technique for "remote printing" using the Internet mail infrastructure. In particular, this memo focuses on the case in which remote printers are connected to the international telephone network. Furthermore, it describes an experiment in remote printing. 1.1. The Advantage of a General-Purpose Infrastructure The experiment in remote printing is about "outreach"; specifically, integrating the e-mail and facsimile communities. By providing easy access to remote printing recipients, enterprise-wide access is enhanced, regardless of kind of institution (e.g., commercial, educational, or government), or the size of institution (e.g., global, regional, or local). This approach at outreach allows an organization to make it easier for the "outside world" to communicate with the personnel in the organization who are users of facsimile but not e-mail; e.g., the sales person, the university registrar, or the (elected) official. The ease in which the Internet mail infrastructure can be used to provide this facility is (yet) another example of the power of a general-purpose infrastructure. 2. Procedure When information is to be remotely printed, the user application constructs an RFC 822 [1] message, containing a "Message-ID" field along with a "multipart/mixed" content [2] having two parts, the first being a "application/remote-printing" content-type, and the second being an arbitrary content-type corresponding to the information to be printed. The message is then sent to the remote printer server's electronic mail address. It should be noted that not all content-types have a natural printing representation, e.g., an "audio" or "video" content. For this reason, the second part of the "multipart/mixed" content should be one of the following: text/plain, message/rfc822, application/postscript image/tiff (defined in Appendix A), any multipart Note that: (1) With the "text/plain" content-type, not all character sets may be available for printing. (2) With the "message" content-type, the subordinate content will be processed recursively. Rose & Malamud [Page 2]
RFC 1486 An Experiment in Remote Printing July 1993 (3) With the "application/postscript" content-type, the remote printer server should evaluate the contents in a safe execution environment. (4) With the "multipart" content-type the subordinate contents will be processed recursively: for a "multipart/mixed" or "multipart/digest" content, each subordinate content will start on a new page, whilst for a "multipart/parallel" content, all subordinate contents will, if possible, start on the same page. Naturally, when processing a "multipart/alternative" content, only one subordinate content will be printed. When the remote printer server finishes its processing, a message is returned to the originator, indicating either success or failure. 2.1. Naming, Addressing, and Routing A printer is identified by a telephone number which corresponds to a G3-facsimile device connected to the international telephone network, e.g., +1 415 968 2510 where "+1" indicates the IDDD country code, and the remaining string is a telephone number within that country. This number is used to construct the address of a remote printer server, which forms the recipient address for the message, e.g., remote-printer@0.1.5.2.8.6.9.5.1.4.1.tpc.int That is, the local-part of the remote printer server's address is ALWAYS "remote-printer", and the domain-part is constructed by reversing the telephone number, converting each digit to a domain- label, and being placed under "tpc.int." The message is routed in exactly the same fashion as all other electronic mail, i.e., using the MX algorithm [3]. Since a remote printer server might be able to access many printers, the wildcarding facilities of the DNS [4,5] are used accordingly. For example, if a remote printer server residing at "dbc.mtview.ca.us" was willing to access any printer with a telephone number prefix of +1 415 968 then this resource record might be present *.8.6.9.5.1.4.1.tpc.int. IN MX 10 dbc.mtview.ca.us. Rose & Malamud [Page 3]
RFC 1486 An Experiment in Remote Printing July 1993 Naturally, if several remote printer servers were willing to access any printer in that prefix, multiple MX resource records would be present. It should be noted that the presence of a wildcard RR which matches a remote printer server's address does not imply that the corresponding telephone number is valid, or, if valid, that a G3-facsimile device is connected at the phone number. 2.2. The application/remote-printing Content-Type (1) MIME type name: application (2) MIME subtype name: remote-printing (3) Required parameters: none (4) Optional parameters: none (5) Encoding considerations: 7bit preferred (6) Security considerations: none The "application/remote-printing" content-type contains originator and recipient information used when generating a cover sheet. Using the ABNF notation of RFC 822, the syntax for this content is: <content> ::= <recipient-info> CRLF <originator-info> [CRLF <cover-info>] <recipient-info> ::= "Recipient" ":" <value> CRLF <address-info> <originator-info> ::= "Originator" ":" <value> CRLF <address-info> <address-info> ::= ["Title" ":" <value> CRLF] ["Department" ":" <value> CRLF] ["Organization" ":" <value> CRLF] ["Mailstop" ":" <value> CRLF] ["Address" ":" <value> CRLF] ["Telephone" ":" <value> CRLF] "Facsimile" ":" <value> CRLF ["Email" ":" <value> CRLF] <value> ::= *text [CRLF LWSP-char <value> ] <cover-info> ::= *(*text CRLF) Rose & Malamud [Page 4]
RFC 1486 An Experiment in Remote Printing July 1993 Note that the value of the "Email" field is an RFC 822 mailbox address. 2.3. Usage Example Suppose someone wished to send the author some comments on this memo using this facility. The message constructed might look like this: To: remote-printer@0.1.5.2.8.6.9.5.1.4.1.tpc.int From: "John Q. Public" <jpublic@tpd.org> Date: Sun, 11 Apr 1993 20:34:13 -0800 Subject: Comments on "An Experiment in Remote Printing" Message-ID: <19930411203413000.456@tpd.org> MIME-Version: 1.0 Content-Type: multipart/mixed; boundary="----- =_aaaaaaaaaa0" ------- =_aaaaaaaaaa0 Content-Type: application/remote-printing Recipient: Marshall Rose Title: Principal Organization: Dover Beach Consulting, Inc. Address: 420 Whisman Court Mountain View, CA 94043-2186 US Telephone: +1 415 968 1052 Facsimile: +1 415 968 2510 Originator: John Q. Public Organization: The Public Domain Telephone: +1 801 555 1234 Facsimile: +1 801 555 6789 EMail: "John Q. Public" <jpublic@tpd.org> Any text appearing here would go on the cover-sheet. ------- =_aaaaaaaaaa0 Content-Type: text/plain; charset="us-ascii" Here are my comments on your draft. ... ------- =_aaaaaaaaaa0-- Rose & Malamud [Page 5]
RFC 1486 An Experiment in Remote Printing July 1993 2.4. Remote Printing without MIME If the originator's user agent doesn't support MIME, (e.g., the originator accesses the Internet mail infrastructure via a gateway in another mail dominion), then it is still possible for remote printing to occur, albeit in a more limited fashion. Specifically, because a "application/remote-printing" content is not present, cover sheet information must be derived from some other source; and, the message body will be treated as a "text/plain" content. Typically, a cover sheet consists of three sections: o information identifying the originator; o information identifying the recipient; and, o additional information supplied by the remote printer server. To identify the originator, the remote printer server will use the message headers, usually by stripping any trace headers (i.e., "Received" and "Return-Path") and then re-ordering the remaining headers starting with the "From" header. To identify the recipient, an alternative syntax is used for recipient addressing, in which the local-part of the remote printer server's address consists of "remote-printer" followed by an RFC 822 atom, e.g., remote-printer.Arlington_Hewes/Room_403@0.1.5.2.8.6.9.5.1.4.1.tpc.int This mailbox syntax is purposefully restricted in the interests of pragmatism. The atom following "remote-printer" is considered an opaque string for use in recipient identification when generating a cover sheet. To paraphrase RFC 822, an atom is defined as: atom = 1*atomchar atomchar= <any upper or lowercase alphabetic character (A-Z a-z)> / <any digit (0-9)> / "!" / "#" / "$" / "%" / "&" / "'" / "*" / "+" / "-" / "/" / "=" / "?" / "^" / "_" / "`" / "{" / "|" / "}" / "~" When generating a cover sheet using this opaque string, the remote printer server will interpret an underscore character ("_") as a Rose & Malamud [Page 6]
RFC 1486 An Experiment in Remote Printing July 1993 space, and a solidus character ("/") as an end-of-line sequence. A remote printer server will interpret two consecutive underscore characters in the opaque string as a single underscore, and two consecutive solidus characters as a single solidus. So, the opaque string, Arlington_Hewes/Room_403 used in the example above might appear on the cover sheet as To: Arlington Hewes Room 403 Note that some Internet mail software (especially gateways from outside the Internet) impose stringent limitations on the size of a mailbox-string. Thus, originating user agents should take care in limiting the local-part to no more than 70 or so characters. Note that by using the alternative syntax for recipient addressing, it is completely legal to send non- textual messages in which the cover sheet information is automatically derived -- simply by including "MIME-Version:" and "Content-Type:" headers in the message, but omitting the initial "application/remote-printing" content, e.g., To: remote-printer.Arlington_Hewes/Room_403@0.1.5.2.8.6.9.5.1.4.1.tpc.int cc: Marshall Rose <mrose@dbc.mtview.ca.us> From: Carl Malamud <carl@malamud.com> Date: Sun, 18 Jul 1993 09:14:13 -0500 Subject: proposal for enhancement Message-ID: <19930718141413000.123@malamud.com> MIME-Version: 1.0 Content-Type: application/postcript %! Note that by using the alternative syntax for recipient addressing, remote printing and e-mail recipients can be identified in the same message. 3. The Experiment In order to gain experience with this style of remote printing, an experiment is underway. Rose & Malamud [Page 7]
RFC 1486 An Experiment in Remote Printing July 1993 3.1. Infrastructure The domain "tpc.int." is being populated in order to provide the MX- based infrastructure for routing to a remote printer server. In order to facilitate distributed operations, this domain is divided into a zone for each IDDD country code. Sites participating in the experiment contact the appropriate zone administrator in order to be listed, by examining the SOA resource record associated with the zone. For example, a site in the Netherlands (IDDD country code 31) would contact the zone administrator for the domain "1.3.tpc.int." in order to be listed, e.g., % dig 1.3.tpc.int. soa Each zone administrator has a simple set of procedures for listing a participant. For example, in the US (IDDD country code 1), participating sites send an "exchange file" to the administrator, which indicates the prefixes that the site wishes to list. The zone administrator for the domain "1.tpc.int." merges the exchange files from all participating sites to create a zone for each area code. These zones are then replicated using the normal DNS zone transfer procedures. 3.1.1. Zones It should be noted that zones under "tpc.int" are created on the basis of IDDD country codes and area codes; they are not created for each subdomain. For example, in the US and Canada (IDDD country code 1), no more than one zone is allocated for each area code. In contrast, for countries with a smaller numbering plan, only a single zone, for the whole country would be allocated. For example, if Fiji (IDDD country code 679), were to join the experiment, then it is likely that a single zone would be added to the DNS, i.e., "9.7.6.tpc.int." 3.1.2. MX records The MX records present in a zone can have an arbitrary level of precision. For example, the North American Numbering Plan (IDDD country code 1) is structured by a 3-digit area code, followed by a 3-digit exchange prefix, followed by a 4-digit station number. As such, one might expect that MX records in this zone would be similar to *.5.1.4.1.tpc.int. IN MX 10 dbc.mtview.ca.us. Rose & Malamud [Page 8]
RFC 1486 An Experiment in Remote Printing July 1993 which accessed any printer with a telephone number prefix of +1 415 (i.e., allowing access to any printer in area code 415), or might be similar to *.8.6.9.5.1.4.1.tpc.int. IN MX 10 dbc.mtview.ca.us. (i.e., allowing access to any printer in area code 415, exchange prefix 968). However, the level of precision is arbitrary. For example, if all of the printers in an organization had a telephone number prefix of +1 415 96 then an MX record such as *.6.9.5.1.4.1.tpc.int. IN MX 10 dbc.mtview.ca.us. could be used. 3.2. Accounting and Privacy There is no accounting nor settlement in the experiment; however, participating sites may implement access control to prevent abuse. Records may be kept for auditing purposes; however, the privacy of a participant's printing should be honored. As such, any auditing should contain at most this information: o the date the message was received; o the "From" and "Message-ID" fields; o the size of the body; o the identity (telephone number) of the printer; o any telephony-related information, such as call duration; and, o any G3-related information, such recipient ID. 3.3. Mailing list There is a mailing list for the experiment. Interested readers should send a note to: Rose & Malamud [Page 9]
RFC 1486 An Experiment in Remote Printing July 1993 tpc-rp-request@aarnet.edu.au and ask to subscribe to the tpc-rp@aarnet.edu.au list. 3.4. Prototype Implementation A prototype implementation is openly available. The MIME instructions for retrieval are: MIME-Version: 1.0 Content-Type: multipart/alternative; boundary="----- =_aaaaaaaaaa0" Content-Description: pointers to ftp and e-mail access ------- =_aaaaaaaaaa0 Content-Type: message/external-body; access-type="mail-server"; server="archive-server@ftp.ics.uci.edu" Content-Type: application/octet-stream; type="tar"; x-conversions="x-compress" Content-ID: <4599.735726126.1@dbc.mtview.ca.us> mimesend mrose/tpc/rp.tar.Z ------- =_aaaaaaaaaa0 Content-Type: message/external-body; access-type="anon-ftp"; name="rp.tar.Z"; directory="mrose/tpc"; site="ftp.ics.uci.edu" Content-Type: application/octet-stream; type="tar"; x-conversions="x-compress" Content-ID: <4599.735726126.2@dbc.mtview.ca.us> ------- =_aaaaaaaaaa0-- This package contains software for UNIX-based systems, and was developed and tested under SunOS, with an openly-available facsimile package (Sam Leffler's FlexFAX package), and contains information for sites acting as either client or server participants, and zone administrators. Rose & Malamud [Page 10]
RFC 1486 An Experiment in Remote Printing July 1993 4. Future Issues The experiment in remote printing described herein does not address several issues, e.g., o determining which content-types and character sets are supported by a remote printer server; o introduction of authentication, integrity, privacy, authorization, and accounting services; o preferential selection of a remote printer server; and, o aggregation of multiple print recipients in a single message. Initially, the experiment will not address these issues. However, subsequent work might consider these issues in detail. 5. Security Considerations Internet mail may be subject to monitoring by third parties, and in particular, message relays. 6. Acknowledgements Carl Malamud of the Internet Multicasting Service provided substantive comments on the design of the experiment. Douglas Comer of Purdue, Daniel Karrenberg of RIPE, Sam Leffler of SGI, Paul Mockapetris of ARPA, also provided comments. 7. References [1] Crocker, D., "Standard for the Format of ARPA Internet Text Messages", STD 11, RFC 822, UDEL, August, 1982. [2] Borenstein, N., and N. Freed, "MIME: Mechanisms for Specifying and Describing the Format of Internet Message Bodies", RFC 1341, Bellcore, Innosoft, June 1992. [3] Partridge, C., "Mail Routing and the Domain System", RFC 974, CSNET CIC BBN, August 1982. [4] Mockapetris, P., "Domain Names -- Concepts and Facilities", STD 13, RFC 1034, USC/Information Sciences Institute, November 1987. Rose & Malamud [Page 11]
RFC 1486 An Experiment in Remote Printing July 1993 [5] Mockapetris, P., "Domain Names -- Implementation and Specification", STD 13, RFC 1035, USC/Information Sciences Institute, November 1987. 8. Authors' Addresses Marshall T. Rose Dover Beach Consulting, Inc. 420 Whisman Court Mountain View, CA 94043-2186 US Phone: +1 415 968 1052 Fax: +1 415 968 2510 EMail: mrose@dbc.mtview.ca.us Carl Malamud Internet Multicasting Service Suite 1155, The National Press Building Washington, DC 20045 US Phone: +1 202 628-2044 Fax: +1 202 628 2042 EMail: carl@malamud.com Rose & Malamud [Page 12]
RFC 1486 An Experiment in Remote Printing July 1993 Appendix A. The image/tiff Content-Type (1) MIME type name: image (2) MIME subtype name: tiff (3) Required parameters: none (4) Optional parameters: none (5) Encoding considerations: base64 (6) Security considerations: none (7) Published specification: TIFF class F, as defined in: Tag Image File Format (TIFF) revision 6.0 Developer's Desk Aldus Corporation 411 First Ave. South Suite 200 Seattle, WA 98104 206-622-5500 Appendix B. Uniform Addressing A user may choose to include several recipients in a message, one or more of which may be recipients reached via remote printing. However, the message format accepted by a remote printer server contains only a single recipient. There are three solutions to this problem: first, during composition, a "smart" user agent can determine that one or more remote printing recipients are present, and submit the appropriate messages. This has the disadvantage that the submission for the e-mail recipients does not contain any information about the remote-printing recipients. A second solution is to use the alternative syntax for recipient addressing described in Section 2.4 -- however, this minimizes useful information available when constructing the cover sheet. A third solution is for a site participating as a client to offer a remote printing recipient exploder server to its users. Each remote printing recipient is assigned a mailbox relative to the exploder, and, as such, appears as an "ordinary" e-mail address. Using this strategy, the user agent has no knowledge of which recipients are accessible via e-mail or remote-printing -- the user simply specifies a collection of mailbox recipients. Those recipients which are accessible via remote-printing are automatically routed to the exploder. For each recipient in the envelope, a local database is Rose & Malamud [Page 13]
RFC 1486 An Experiment in Remote Printing July 1993 consulted to retrieve addressing information for the recipient, and a message is submitted to the appropriate remote printer server. For example, if the original message submitted was: To: mrose@rpexplode.tpd.org cc: Arlington Hewes <tpcadmin@dbc.mtview.ca.us> From: "John Q. Public" <jpublic@tpd.org> Date: Sun, 11 Apr 1993 20:34:12 -0800 Subject: Comments on "An Experiment in Remote Printing" Message-ID: <19930411203412000.123@tpd.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Here are my comments on your draft. ... then the first recipient, "mrose@rpexplode.tpd.org", would be routed to an remote printing exploder, which would submit the message shown in the example in Section 2.3. The second recipient, "tpcadmin@dbc.mtview.ca.us", would receive the message shown here. Note that a reply by this recipient could include the remote printing recipient. Rose & Malamud [Page 14]