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
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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.
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(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.
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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:
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.,
When generating a cover sheet using this opaque string, the remote printer server will interpret an underscore character ("_") as a
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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
