rfc2524.txt

著名的RFC文档,其中有一些文档是已经翻译成中文的的.

Network Working Group                                         M. Banan
Request for Comments: 2524                   Neda Communications, Inc.
Category: Informational                                  February 1999


                                 Neda's
             Efficient Mail Submission and Delivery (EMSD)
                   Protocol Specification Version 1.3

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.

IESG Note

   The protocol specified in this document may be satisfactory for
   limited use in private wireless IP networks.  However, it is
   unsuitable for general-purpose message transfer or for transfer of
   messages over the public Internet, because of limitations that
   include the following:

   - Lack of congestion control

      EMSD is layered on ESRO [RFC 2188], which does not provide
      congestion control.  This makes EMSD completely unsuitable for
      end-to-end use across the public Internet.  EMSD should be
      considered for use in a wireless network only if all EMSD email
      exchanged between the wireless network and the public Internet
      will transit an EMSD<->SMTP gateway between the two regions.

   - Inadequate security

      The document specifies only clear-text passwords for
      authentication.  EMSD should be used across a wireless network
      only if sufficiently strong encryption is in use to protect the
      clear-text password.

   - Lack of character set internationalization

      EMSD has no provision for representation of characters outside of
      the ASCII repertoire or for language tags.




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RFC 2524                          EMSD                     February 1999


   - Poorly defined gatewaying to and from Internet Mail

      Because Internet Mail and EMSD have somewhat different and
      conflicting service models and different data models, mapping
      between them may provide good service only in limited cases, and
      this may cause operational problems.

   The IESG therefore recommends that EMSD deployment be limited to
   narrow circumstances, i.e., only to communicate with devices that
   have inherent limitations on the length and format of a message (no
   more than a few hundred bytes of ASCII text), using either:

   a. wireless links with adequate link-layer encryption and gatewayed
      to the public Internet, or

   b. a private IP network that is either very over-provisioned or has
      some means of congestion control.

   In the near future, the IESG may charter a working group to define an
   Internet standards-track protocol for efficient transmission of
   electronic mail messages, which will be highly compatible with
   existing Internet mail protocols, and which wil be suitable for
   operation over the global Internet, including both wireless and wired
   links.

ABSTRACT

   This document specifies the protocol and format encodings for
   Efficient Mail Submission and Delivery (EMSD). EMSD is a messaging
   protocol that is highly optimized for submission and delivery of
   short Internet mail messages.  EMSD is designed to be a companion to
   existing Internet mail protocols.

   This specification narrowly focuses on submission and delivery of
   short mail messages with a clear emphasis on efficiency.  EMSD is
   designed specifically with wireless network (e.g., CDPD, Wireless-IP,
   Mobile-IP) usage in mind.  EMSD is designed to be a natural
   enhancement to the mainstream of Internet mail protocols when
   efficiency in mail submission and mail delivery are important.  As
   such, EMSD is anticipated to become an initial basis for convergence
   of Internet Mail and IP-based Two-Way Paging.

   The reliability requirement for message submission and message
   delivery in EMSD are the same as existing email protocols.  EMSD
   protocol accomplishes reliable connectionless mail submission and
   delivery services on top of Efficient Short Remote Operations (ESRO)
   protocols as specified in RFC-2188 [1].




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RFC 2524                          EMSD                     February 1999


   Most existing Internet mail protocols are not efficient.  Most
   existing Internet mail protocols are designed with simplicity and
   continuity with SMTP traditions as two primary requirements.  EMSD is
   designed with efficiency as a primary requirement.

   The early use of EMSD in the wireless environment is manifested as
   IP-based Two-Way Paging services.  The efficiency of this protocol
   also presents significant benefits for large centrally operated
   Internet mail service providers.

Table of Contents

   1  PRELIMINARIES                                                 4
      1.1 Internet Mail Submission and Delivery     .   .   .   .   4
      1.2 Relationship Of EMSD To Other Mail Protocols  .   .   .   5
      1.3 EMSD Requirements and Goals   .   .   .   .   .   .   .   7
      1.4 Anticipated Uses Of EMSD  .   .   .   .   .   .   .   .   8
      1.5 Definitions of Terms Used in this Specification   .   .   9
      1.6 Conventions Used In This Specification    .   .   .   .   9
      1.7 About This Specification  .   .   .   .   .   .   .   .  10
   2  EFFICIENT MAIL SUBMISSION AND DELIVERY OVERVIEW              10
   3  EFFICIENT MAIL SUBMISSION AND DELIVERY PROTOCOL              11
      3.1 Use Of Lower Layers   .   .   .   .   .   .   .   .   .  13
          3.1.1 Use of ESROS    .   .   .   .   .   .   .   .   .  13
          3.1.2 Use Of UDP  .   .   .   .   .   .   .   .   .   .  13
          3.1.3 Encoding Rules  .   .   .   .   .   .   .   .   .  13
          3.1.4 Presentation Context    .   .   .   .   .   .   .  14
      3.2 EMSD-UA Invoked Operations    .   .   .   .   .   .   .  14
          3.2.1 submit  .   .   .   .   .   .   .   .   .   .   .  14
          3.2.2 deliveryControl     .   .   .   .   .   .   .   .  17
          3.2.3 deliveryVerify  .   .   .   .   .   .   .   .   .  21
      3.3 EMSD-SA Invoked Operations    .   .   .   .   .   .   .  23
          3.3.1 deliver     .   .   .   .   .   .   .   .   .   .  23
          3.3.2 submissionControl   .   .   .   .   .   .   .   .  25
          3.3.3 submissionVerify    .   .   .   .   .   .   .   .  28
      3.4 EMSD Common Information Objects   .   .   .   .   .   .  30
          3.4.1 SecurityElements    .   .   .   .   .   .   .   .  30
          3.4.2 Message Segmentation and Reassembly     .   .   .  30
          3.4.3 Common Errors   .   .   .   .   .   .   .   .   .  33
          3.4.4 ContentType     .   .   .   .   .   .   .   .   .  35
          3.4.5 EMSDMessageId   .   .   .   .   .   .   .   .   .  35
          3.4.6 EMSDORAddress   .   .   .   .   .   .   .   .   .  36
          3.4.7 EMSDAddress     .   .   .   .   .   .   .   .   .  36
          3.4.8 DateTime    .   .   .   .   .   .   .   .   .   .  36
          3.4.9 AsciiPrintableString    .   .   .   .   .   .   .  37
          3.4.10 ProtocolVersionNumber  .   .   .   .   .   .   .  37
      3.5 Submission and Delivery Procedures    .   .   .   .   .  38
   4  DUPLICATE OPERATION DETECTION SUPPORT                        40



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RFC 2524                          EMSD                     February 1999


      4.1 Duplicate Operation Detection Support Overview    .   .  40
          4.1.1 Operation Value     .   .   .   .   .   .   .   .  40
          4.1.2 Operation Instance Identifier   .   .   .   .   .  41
   5  EMSD PROCEDURE FOR OPERATIONS                                42
      5.1 MTS Behavior  .   .   .   .   .   .   .   .   .   .   .  43
          5.1.1 MTS Performer   .   .   .   .   .   .   .   .   .  43
          5.1.2 Message-submission  .   .   .   .   .   .   .   .  44
          5.1.3 Delivery-control    .   .   .   .   .   .   .   .  46
          5.1.4 Delivery-verify     .   .   .   .   .   .   .   .  46
          5.1.5 MTS Invoker     .   .   .   .   .   .   .   .   .  46
      5.2 UA Behavior   .   .   .   .   .   .   .   .   .   .   .  49
          5.2.1 UA Performer    .   .   .   .   .   .   .   .   .  49
          5.2.2 UA Invoker  .   .   .   .   .   .   .   .   .   .  52
   6  EMSD FORMAT STANDARDS                                        54
      6.1 Format Standard Overview  .   .   .   .   .   .   .   .  54
      6.2 Interpersonal Messages    .   .   .   .   .   .   .   .  54
          6.2.1 Heading fields  .   .   .   .   .   .   .   .   .  55
          6.2.2 Body part types     .   .   .   .   .   .   .   .  61
   7  ACKNOWLEDGMENTS                                              62
   8  SECURITY CONSIDERATIONS                                      62
   9  AUTHOR'S ADDRESS                                             62
   A  EMSD-P ASN.1 MODULE                                          63
   B  EMSD-IPM ASN.1 MODULE                                        74
   C  RATIONALE FOR KEY DESIGN DECISIONS                           78
      C.1 Deviation From The SMTP Model     .   .   .   .   .   .  78
          C.1.1 Comparison of SMTP and EMSD Efficiency  .   .   .  78
      C.2 Use of ESRO Instead of TCP    .   .   .   .   .   .   .  79
      C.3 Use Of Remote Procedure Call (RPC) Model  .   .   .   .  79
      C.4 Use Of ASN.1  .   .   .   .   .   .   .   .   .   .   .  80
   D  FURTHER DEVELOPMENT                                          81
   E  REFERENCES                                                   82
   F  FULL COPYRIGHT STATEMENT                                     83

1  PRELIMINARIES

   Mail in the Internet was not a well-planned enterprise, but instead
   arose in more of an "organic" way.

   This introductory section is not intended to be a reference model and
   concept vocabulary for mail in the Internet.  Instead, it only
   provides the necessary preliminaries for the concepts and terms that
   are essential to this specification.

1.1  Internet Mail Submission and Delivery

   For the purposes of this specification, mail submission is the
   process of putting mail into the mail transfer system (MTS).




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RFC 2524                          EMSD                     February 1999


   For the purposes of this specification, mail delivery is the process
   of the MTS putting mail into a user's final mail-box.

   Throughout the Internet, presently most of mail submission and
   delivery is done through SMTP.

   SMTP was defined as a message *transfer* protocol, that is, a means
   to route (if needed) and deliver mail by putting finished (complete)
   messages in a mail-box.  Originally, users connected to servers from
   terminals, and all processing occurred on the server.  Now, a split-
   MUA (Mail User Agent) model is common, with MUA functionality
   occurring on both the user's own system and the server.

   In the split-MUA model, getting the messages to the user is
   accomplished through access to a mail-box on the server through such
   protocols as POP and IMAP. In the split-MUA model, user's access to
   its message is a "Message Pull" paradigm where the user is required
   to poll his mailbox.  Proper message delivery based on a "Message
   Push" paradigm is presently not supported.  The EMSD protocol
   addresses this shortcoming with an emphasis on efficiency.

   In the split-MUA model, message submission is often accomplished
   through SMTP. SMTP is widely used as a message *submission* protocol.
   Widespread use of SMTP for submission is a reality, regardless of
   whether this is good or bad.  EMSD protocol provides an alternative
   mechanism for message submission which emphasizes efficiency.

1.2  Relationship Of EMSD To Other Mail Protocols

   Various Internet mail protocols facilitate accomplishment of various
   functions in mail processing.




















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RFC 2524                          EMSD                     February 1999


   Figure 1, categorizes the capabilities of SMTP, IMAP, POP and EMSD
   based on the following functions:

   +------------------+------+-------+-----+------+
   |         Protocols| SMTP |  IMAP | POP | EMSD |
   |Functions         |      |       |     |      |
   |------------------|------|-------|-----|------|
   |Submission        | XX   |       |     | XXX  |
   |------------------|------|-------|-----|------|
   |Delivery          | XXX  |       |     | XXX  |
   |------------------|------|-------|-----|------|
   |Relay (Routing)   | XXX  |       |     |      |
   |------------------|------|-------|-----|------|
   |Retrieval         |      |  XXX  | XXX |  XX  |
   |------------------|------|-------|-----|------|
   |Mailbox Access    |      |  XXX  |  X  |      |
   |------------------|------|-------|-----|------|
   |Mailbox Synch.    |      |  XXX  |     |      |
   +------------------+------+-------+-----+------+

   Figure 1:  Messaging Protocols vs.  Supported Functions


     o Mail Submission

     o Mail Delivery

     o Mail Routing (Relay)

     o Mail Retrieval

     o Mail-box Access

     o Mail-box Synchronization

   In Figure 1, the number of "X"es in each box denotes the extent to
   which a particular function is supported by a particular protocol.

   Figure 1 clearly shows that combinations of these protocols can be
   used to complement each other in providing rich functionality to the
   user.  For example, a user interested in highly mobile messaging
   functionalities can use EMSD for "submission and delivery of time
   critical and important messages" and use IMAP for comprehensive
   access to his/her mail-box.

   For mail submission and delivery of short messages EMSD is up to 5
   times more efficient than SMTP both in terms of the number of packets
   transmitted and in terms of number of bytes transmitted.  Even with



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RFC 2524                          EMSD                     February 1999


   PIPELINING and other possible optimizations of SMTP, EMSD is up to 3
   times more efficient than SMTP both in terms of the number of packets
   transmitted and in terms of number of bytes transmitted.  Various
   efficiency studies comparing EMSD with SMTP, POP and IMAP are
   available.  See Section C.1.1 for more information about comparison
   of SMTP and EMSD's efficiency.

1.3  EMSD Requirements and Goals

   The requirements and goals driving design of EMSD protocol are
   enumerated below.

    1. Provide for submission of short mail messages with the same level
       of functionality (or higher) that the existing Internet mail
       protocols provide.

    2. Provide for delivery of short mail messages with the same level
       of functionality (or higher) that the existing Internet mail
       protocols provide.

    3. Function as an extension of the existing mainstream Internet
       mail.

    4. Minimize the number of transmissions.

    5. Minimize the number of bytes transmitted.

    6. Be quick:  minimize latency of message submission and delivery.

    7. Provide the same level of reliability (or higher) that the
       existing email protocols provide.

    8. Accommodate varying sizes of messages:  the size of a message may
       determine how the system deals with the message, but the system
       must accommodate it.

    9. Be power efficient and respect mobile platform resources:
       including memory and CPU levels, as well as battery power
       longevity (i.e.  client-light and server-heavy).

    10. Highly extendible:  different users will demand different
        options, so the solution cannot require every feature to be a
        part of every message.  Likewise, usage will emerge that is not
        currently recognized as a requirement.  The solution must be
        extendible enough to handle new, emerging requirements.