rfc1528.txt

<VC++网络游戏建摸与实现>源代码

Network Working Group                                         C. Malamud
Request for Comments: 1528                 Internet Multicasting Service
Obsoletes: 1486                                                  M. Rose
Category: Experimental                      Dover Beach Consulting, Inc.
                                                            October 1993


           Principles of Operation for the TPC.INT Subdomain:
                Remote Printing -- Technical Procedures

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 "Internet Official Protocol Standards" for the
   standardization state and status of this protocol.  Distribution of
   this memo is unlimited.

Table of Contents

   1. Introduction ..........................................   2
   2. Naming, Addressing, and Routing .......................   2
   2.1 Addressing ...........................................   2
   2.2 Routing ..............................................   3
   3. Procedure .............................................   3
   3.1 Content-Types ........................................   4
   3.2 Generating a Cover-Sheet .............................   4
   3.3 Return Receipt .......................................   6
   4. Usage Examples ........................................   6
   4.1 Explicit Cover Sheet .................................   6
   4.2 Implicit Cover Sheet .................................   7
   4.3 Minimal, Text-only ...................................   7
   5. Prototype Implementation ..............................   7
   6. Future Issues .........................................   9
   7. Security Considerations ...............................   9
   8. Acknowledgements ......................................   9
   9. References ............................................   9
   10. Authors' Addresses ..................................   10
   A. The application/remote-printing Content-Type .........   11
   B. The image/tiff Content-Type ..........................   12

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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RFC 1528        Remote Printing -- Technical Procedures     October 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.

2. 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.,

      [phone]

   where "+1" indicates the IDDD country code, and the remaining string
   is a telephone number within that country.

2.1 Addressing

   This number is used to construct the address of a remote printer
   server, which forms the recipient address for the message, e.g.,
   either

      remote-printer@0.1.5.2.8.6.9.5.1.4.1.tpc.int

      or

      remote-printer.ATOM@0.1.5.2.8.6.9.5.1.4.1.tpc.int

   where "ATOM" is an (optional) RFC 822 atom [1], an opaque string for
   use in recipient identification when generating a cover-sheet, and
   the domain-part is constructed by reversing the telephone number,
   converting each digit to a domain-label, and being placed under
   "tpc.int."















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RFC 1528        Remote Printing -- Technical Procedures     October 1993


   Note that the mailbox syntax is purposefully restricted in the
   interests of pragmatism.  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)>
                / "!" / "#" / "$" / "%" / "&" / "'" / "*" / "+"
                / "-" / "/" / "=" / "?" / "^" / "_" / "`" / "{"
                / "|" / "}" / "~"

   Finally, 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.

2.2 Routing

   The message is routed in exactly the same fashion as all other
   electronic mail, i.e., using the MX algorithm [2].  Since a remote
   printer server might be able to access many printers, the wildcarding
   facilities of the DNS [3,4] 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.

   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.

3. Procedure

   When information is to be remotely printed, the user application
   constructs an RFC 822 message, containing a "Message-ID" field.





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RFC 1528        Remote Printing -- Technical Procedures     October 1993


   If the local-part of the address does not contain an opaque string
   for use in recipient identification, then the body must consist
   "multipart/mixed" content [5] having at two parts, the first being a
   "application/remote-printing" content-type (defined in Appendix A),
   which will be used to generate a cover-sheet, and the second being an
   arbitrary content-type corresponding to the information to be
   printed.  If the local-part of the address does contain an opaque
   string for use in recipient identification, then the body consists of
   an arbitrary content-type corresponding to the information to be
   printed.

   Regardless, the message is then sent to the remote printer server's
   electronic mail address.

3.1 Content-Types

   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 B), 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.

      (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.

3.2 Generating a Cover-Sheet

   If the "application/remote-printing" content-type is present,
   this contains all the information necessary to generate a



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RFC 1528        Remote Printing -- Technical Procedures     October 1993


   cover-sheet.  Otherwise, the cover-sheet must be generated
   based on other information available.

   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, the opaque string from the local- part of
   the remote printer server's address is consulted.  For example, if
   the remote printer server's address is

   remote-printer.Arlington_Hewes/Room_403@0.1.5.2.8.6.9.5.1.4.1.tpc.int

   then the opaque string

   Arlington_Hewes/Room_403

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

      might appear on the cover-sheet as

      To: Arlington Hewes
      Room 403










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RFC 1528        Remote Printing -- Technical Procedures     October 1993


3.3 Return Receipt

   When the remote printer server finishes its processing, a message is
   returned to the originator, indicating either success (i.e., the
   message was successfully sent to the facsimile device), or failure,
   with an explanation (e.g., after several repeated attempts, there was
   no answer).

4.  Usage Examples

4.1 Explicit Cover Sheet

   To: remote-printer@0.1.5.2.8.6.9.5.1.4.1.tpc.int
   From: Carl Malamud <[e-mail]>
   Date: Thu, 22 Jul 1993 08:38:00 -0800
   Subject: First example
   Message-ID: <[e-mail]>
   MIME-Version: 1.0
   Content-Type: multipart/mixed;
           boundary="----- =_aaaaaaaaaa0"

   ------- =_aaaaaaaaaa0
   Content-Type: application/remote-printing

   Recipient:    Arlington Hewes
   Telephone:    [phone]
   Facsimile:    [phone]

   Originator:   Carl Malamud
   Organization: Internet Multicasting Service
   Address:      Suite 1155, The National Press Building
                 Washington, DC 20045
                 US
   Telephone:    [phone]
   Facsimile:    [phone]
   EMail:        [e-mail]

   Any text appearing here would go on the cover-sheet.

   ------- =_aaaaaaaaaa0
   Content-Type: text/plain; charset="us-ascii"

    Here are my comments...

   ------- =_aaaaaaaaaa0--






Malamud & Rose                                                  [Page 6]