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rfc:rfc2524

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:
  1. 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.
  1. 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.
  1. Lack of character set internationalization
    EMSD has no provision for representation of characters outside of
    the ASCII repertoire or for language tags.

Banan Informational [Page 1] RFC 2524 EMSD February 1999

  1. 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].

Banan Informational [Page 2] 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

Banan Informational [Page 3] 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).

Banan Informational [Page 4] 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.

Banan Informational [Page 5] 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

Banan Informational [Page 6] 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.

Banan Informational [Page 7] RFC 2524 EMSD February 1999

  11. Secure:  provide the same level of security (or higher) that the
      existing email protocols provide.  Content confidentiality,
      originator/recipient authentication and message integrity must
      be available options to users.
  12. Easy to implement:  Re-use existing technology as much as
      possible.

1.4 Anticipated Uses Of EMSD

 Any network and network operator which has significant bandwidth and
 capacity limitations can benefit from the use of EMSD. Any network
 user who must bear high costs for measured network usage can benefit
 from the use of EMSD.
 Initial uses of EMSD is anticipated to be primarily over IP-based
 wireless networks to provide two-way paging services.
 EMSD can also function as an adjunct to Mail Access Protocols for
 "Mail Notification Services".
 Considering:
    o that most wireless networks shall converge toward being IP-
      based;
    o that two-way paging is the main proven application in most
      wide-area wireless networks;
    o that two-way paging industry and the Internet Email industry can
      and should converge based on a set of open protocols that
      address the efficiency requirements adequately;
    o that existing Internet email protocols are not bandwidth
      efficient;
    o that existing Internet email protocols do not properly support
      the "push" model of delivery of urgent messages,
 the EMSD protocol is designed to facilitate the convergence of IP-
 based two-way paging and Internet email.
 Mail submission and delivery take place at the edges of the network.
 More than one mail submission and delivery protocols which address
 requirements specific to a particular user's environment are likely
 to be developed.  Such diversity on the edges of the network is

Banan Informational [Page 8] RFC 2524 EMSD February 1999

 desirable and with the right protocols, this diversity does not
 adversely impact the integrity of the mail transfer system.  EMSD is
 the initial basis for the mail submission and delivery protocol to be
 used when the user's environment demands efficiency.

1.5 Definitions of Terms Used in this Specification

 The following informal definitions and acronyms are intended to help
 describe EMSD model described in this specification.
 Efficient Mail Submission and Delivery Protocol (EMSD-P): The
     protocol used to transfer messages between the EMSD - Server
     Agent (e.g., a Message Center) and the EMSD - User Agent (e.g., a
     Two-Way Pager), see Figure 2.
 Message Transfer Agent (MTA)
 Message Transfer Service (MTS)
 Message Routing Service (MRS): Collection of MTAs responsible for
     mail routing.
 Message User Agent (MUA)
 Efficient Mail Submission Server Agent (EMS-SA): An Application
     Process which conforms to this protocol specification and accepts
     mail from an EMS-UA and transfers it towards its recipients.
 Efficient Mail Delivery Server Agent (EMD-SA): An Application Process
     which conforms to this protocol specification and delivers mail
     to an EMD-UA.
 Efficient Mail Submission and Delivery Server Agent (EMSD-SA): An
     Application Process which incorporates both EMS-SA and EMD-SA
     capabilities.
 Efficient Mail Submission User Agent (EMS-UA): An Application Process
     which conforms to this protocol specification and submits mail to
     EMS-SA.
 Efficient Mail Delivery User Agent (EMD-UA): An Application Process
     which conforms to this protocol specification and accepts
     delivery of mail from EMD-SA.
 Efficient Mail Submission and Delivery User Agent (EMSD-UA): An
     Application Process which incorporates both EMS-UA and EMD-UA
     capabilities.

1.6 Conventions Used In This Specification

 The key words "MUST", "MUST NOT", "SHOULD", "SHOULD NOT", and "MAY"
 in this specification are to be interpreted as defined in [2].

Banan Informational [Page 9] RFC 2524 EMSD February 1999

 This specification uses the ES-OPERATION notation defined in
 Efficient Short Remote Operations (ESRO) protocols as specified in
 RFC-2188 [1].
 Operations and information objects are typically described using the
 ES-OPERATION and ASN.1 notations in the relevant sections of the
 specification.
 The complete machine verifiable ASN.1 modules are also compiled in
 one place in Appendix A and Appendix B.

1.7 About This Specification

 This protocol specification constitutes a point-of-record.  It
 documents information exchanges and behaviors of existing
 implementations.  It is a basis for implementation of efficient mail
 submission and delivery user agents and servers.
 This specification has been developed entirely outside of IETF. It
 has had the benefit of review by many outside of IETF. Much has been
 learned from existing implementations of this protocol.  A number of
 deficiencies and areas of improvement have been identified and are
 documented in this specification.
 This protocol specification is being submitted on October 23, 1998
 for timely publication as an Informational RFC.
 Future development and enhancements to this protocol may take place
 inside of IETF.

2 EFFICIENT MAIL SUBMISSION AND DELIVERY OVERVIEW

 This section offers a high level view of the Efficient Mail
 Submission and Delivery Protocol and Format Standards (EMSD-P&FS).
 The EMSD-P&FS are used to transfer messages between the EMSD - Server
 Agent (e.g., a Message Center) and the EMSD - User Agent (e.g., a
 Two-Way Pager), see Figure 2.
 This specification defines the protocols between an EMSD - User Agent
 (EMSD-UA) and an EMSD - Server Agent (EMSD-SA). The EMSD - P&FS
 consist of two independent components:
  1. EMSD Format Standard (EMSD-FS).
     EMSD-FS is a non-textual form of compact encoding of Internet
     mail (RFC-822) messages which facilitates efficient transfer of
     messages.  EMSD-FS is used in conjunction with the EMSD-P but is

Banan Informational [Page 10] RFC 2524 EMSD February 1999

     not a general replacement for RFC-822.  EMSD-FS defines a method
     of representation of short interpersonal messages.  It defines
     the "Content" encoding (Header + Body).  Although EMSD-FS
     contains end-to-end information its scope is purely point-to-
     point.  EMSD-FS relies on EMSD-P (see 2 below) for the transfer
     of the content to its recipients.
     This is described in the section entitled EMSD Format Standards.
  2. Efficient Mail Submission and Delivery Protocol (EMSD-P).
     EMSD-P is responsible for wrapping an EMSD-FS message (see 1
     above) in a point-to-point envelope and submitting or delivering
     it.  EMSD-P relies on the services of Efficient Short Remote
     Operation Services (ESROS) as specified in RFC-2188 [1] for
     transporting the point-to-point envelope.  Some of the services
     of EMSD-P include:  message originator authentication and
     optional message segmentation and reassembly.  The EMSD-P is
     expressed in terms of abstract services using the ESROS notation.
     This is described in the section entitled Efficient Mail
     Submission and Delivery Protocol.
 It is important to recognize that EMSD-P and EMSD-FS are not end-to-
 end, but focus on the point-to-point transfer of messages.  The two
 points being EMSD-SA and EMSD-UA. EMSD-P function as elements of the
 Internet mail environment, which provide end-to-end (EMSD-User to any
 other Messaging Originator or Recipient) services.
 Figure 2 illustrates how the EMSD-P&FS defines the communication
 between a specific EMSD-UA and a specific EMSD-SA. The Message
 Transfer System may include a number of EMSD-SAs.  Each EMSD-SA may
 have any number of EMSD-UAs with which it communicates.
 The Efficient Mail Submission and Delivery Services use the Efficient
 Short Remote Operation Services (ESROS). They also use the Duplicate
 Operation Detection Support Functions as described in the section
 entitled Duplicate Operation Detection Support Functions.  These
 functions guarantee that an operation is performed no more than once.

3 EFFICIENT MAIL SUBMISSION AND DELIVERY PROTOCOL

 EM Submission is the process of transferring a message from EMSD-UA
 to EMSD-SA. EM Delivery is the process of transferring a message from
 EMSD-SA to EMSD-UA.

Banan Informational [Page 11] RFC 2524 EMSD February 1999

 The Message-submission service enables an EMSD-UA to submit a message
 to the EMSD-SA for transfer and delivery to one or more recipients.
 The Message-submission Service comprises of the submit operation --
 invoked by the EMSD-UA -- and possibly the submitVerify operation --
 invoked by the EMSD-SA.
 The Message-delivery service enables the EMSD-SA to deliver a message
 to an EMSD-UA. The Message-delivery Service comprises of the deliver
 operation -- invoked by the EMSD-SA -- and possibly the deliverVerify
 operation -- invoked by the EMSD-UA.
 EMSD-UA uses the following services:
      o Message-submission
 +---------------------------------------------+
 | MTS                                         |
 |                                             |
 |  +-------------------------+                |
 |  | MRS                     |                |
 |  |  +---+          +---+   |                |
 |  |  |   |          | M |   |         +---+  |
 |  |  |   |<-------->| T |<----------->|   |  |
 |  |  |   |          | A |   |         |   |  |               +---+
 |  |  |   |          +---+   |         | E |  |               | E |
 |  |  |   |                  |         | M |  |               | M |
 |  |  | M |                  |         | S |  |   EMSD-P&FS   | S |
 |  |  | T |<-------------------------->| D |<---------------->| D |
 |  |  | A |                  |         | - |  |               | - |
 |  |  |   |          +---+   |         | S |  |               | U |
 |  |  |   |          | M |   |         | A |  |               | A |
 |  |  |   |<-------->| T |<----------->|   |  |               +---+
 |  |  |   |          | A |   |         |   |  |
 |  |  +---+          +---+   |         +---+  |
 |  |                         |                |
 |  +-------------------------+                |
 |                                             |
 |                                             |
 +---------------------------------------------+
       Figure 2:  Efficient Mail Submission and Delivery Protocol
    o Delivery-control (the deliveryControl operation).
 EMSD-SA uses the following services:
    o Message-delivery

Banan Informational [Page 12] RFC 2524 EMSD February 1999

    o Submission-control (the submissionControl operation).
 This specification expresses information objects using ASN.1 [X.208].
 This specification expresses Remote Operations based on the model of
 ESROS as specified in Efficient Short Remote Operations (RFC-2188)
 [1].  The ES-OPERATION notation of (RFC-2188) is used throughout this
 specification to define specific operations.
 This specification uses the Duplicate Operation Detection Support
 functions as specified in Section 4.

3.1 Use Of Lower Layers

3.1.1 Use of ESROS

 ESRO protocol, as specified in (RFC-2188 [1]), provides reliable
 connectionless remote operation services on top of UDP [6] with
 minimum overhead.  ESRO protocol supports segmentation and
 reassembly, concatenation and separation.
 ESRO Services (2-Way and 3-Way handshake) shall be used by the EMSD-
 P.
 ESRO Service Access Point (SAP) selectors used by EMSD-P are
 enumerated in the protocol.

3.1.2 Use Of UDP

 EMSD-P through ESRO MUST use UDP [6] port number 642 (esro-emsdp).
 Note that specification of Service Access Points (SAP) for EMSD-P
 include the UDP Port Number specification in addition to ESRO SAP
 selector specifications.  In other words, EMSD-P's use of ESRO SAPs
 does not preclude use of the same SAP selectors by other protocols
 which use a UDP port other than port 642.  Such usage of ESRO is a
 design characteristic of ESRO which results into bandwidth efficiency
 and is not a scalability limitation.

3.1.3 Encoding Rules

 Use of Basic Encoding Rules (BER) [5] is mandatory for both EMSD
 Format Standards and EMSD Protocol.
 In order to minimize data transfer, the following restrictions shall
 be maintained in the formatting of EMSD PDUs:
    o Specifically, when ASN.1 Basic Encoding Rules are being used:

Banan Informational [Page 13] RFC 2524 EMSD February 1999

       A. Only the "Definite" form of Length encoding MUST be used,
       B. The "Short" form of Length encoding MUST be used whenever
          possible (i.e.  when the Length is less than 128), and
       C. OCTET STRING and BIT STRING values, and any other native
          ASN.1 types which may be encoded as either "Primitive" or
          "Constructed", MUST always be encoded as "Primitive" and
          MUST never be "Constructed".

3.1.4 Presentation Context

 Parameter Encoding Type of "0" MUST be used in ESRO Protocol to
 identify Basic Encoding Rules for operation arguments.

3.2 EMSD-UA Invoked Operations

 The following operations are invoked by EMSD-UA:
  a. submit
  b. deliveryControl
  c. deliveryVerify
 The submit operation uses the duplication detection functional unit
 while deliveryControl and deliveryVerify don't use the duplication
 detection.
 The complete definition of these operations follows.

3.2.1 submit

 The submit ES-OPERATION enables an EMSD-UA to submit a message to the
 EMSD-SA for transfer and delivery to one or more recipients.
 submit ES-OPERATION
     ARGUMENT SubmitArgument
     RESULT SubmitResult
     ERRORS
     {
         submissionControlViolated,
         securityError,
         resourceError,
         protocolViolation,
         messageError
     } ::= 33;

Banan Informational [Page 14] RFC 2524 EMSD February 1999

 Duplicate operation detection is necessary for this operation.
 The successful completion of the ES-OPERATION signifies that the
 EMSD-SA has accepted responsibility for the message (but not that it
 has delivered it to its intended recipients).
 The disruption of the ES-OPERATION by an error signifies that the
 EMSD-SA cannot assume responsibility for the message.
 Arguments
 This operation's arguments are:
 SubmitArgument ::= SEQUENCE
 {
   -- Security features
   security                [0]    IMPLICIT SecurityElement OPTIONAL,
  1. - Segmentation features for efficient transport

segment-info SegmentInfo OPTIONAL,

  1. - Content type of the message

content-type ContentType,

  1. -
  2. - THE CONTENT –
  3. -
  1. - The submission content

content ANY DEFINED BY content-type

 };
 The fields are:
 Security
 See Section 3.4.1, "SecurityElements".
 Segment-info
 See Section 3.4.2, "Message Segmentation and Reassembly".

Banan Informational [Page 15] RFC 2524 EMSD February 1999

 Content-type
 This argument identifies the type of the content of the message.  It
 identifies the abstract syntax and the encoding rules used.
 Content
 This argument contains the information the message is intended to
 convey to the recipient(s).  It shall be generated by the originator
 of the message.
 Results
 This operation's results are:
 SubmitResult ::= SEQUENCE
     {
         -- Permanent identifier for this message.
         -- Also contains the message submission time.
         -- See comment regarding assignment of message identifiers,
         -- at the definition of EMSDLocalMessageId.
         message-id                              EMSDLocalMessageId
     };
 The fields are:
 Message-id
 This result contains an EMSD-SA-identifier that uniquely and
 unambiguously identifies the message-submission.  It shall be
 generated by the EMSD-SA.
 Errors
 See Section 3.4.3.

Banan Informational [Page 16] RFC 2524 EMSD February 1999

3.2.2 deliveryControl

 The deliveryControl ES-OPERATION enables the EMSD-UA to temporarily
 limit the operations that the EMSD-SA may invoke, and the messages
 that the EMSD-SA may deliver to the EMSD-UA via the Message delivery
 ES-OPERATION.
 deliveryControl ES-OPERATION
     ARGUMENT DeliveryControlArgument
     RESULT DeliveryControlResult
     ERRORS
     {
         securityError,
         resourceError,
         protocolViolation
     } ::= 2;
 The duplicate operation detection is not required for this operation.
 The EMSD-SA shall hold until a later time, rather than abandon, ES-
 OPERATIONS and messages that are presently suspended.
 The successful completion of the ES-OPERATION signifies that the
 specified controls are now in force.
 The ES-OPERATION returns an indication of any ES-OPERATIONS that the
 EMSD-SA would invoke, or any message types that the EMSD-SA would
 deliver, were it not for the prevailing controls.
 Arguments
 This operation's arguments are:
 DeliveryControlArgument ::= SEQUENCE
 {
   -- Request an addition of or removal of a set of restrictions
   restrict                [0]     IMPLICIT Restrict DEFAULT update,
  1. - Which operations are to be placed in the restriction set

permissible-operations [1] IMPLICIT Operations OPTIONAL,

  1. - What maximum content length should be allowed

permissible-max-content-length

                                   [2]     IMPLICIT INTEGER
                                    (0..ub-content-length) OPTIONAL,

Banan Informational [Page 17] RFC 2524 EMSD February 1999

  1. - What is the lowest priority message which may be delivered

permissible-lowest-priority

                                   [3]     IMPLICIT ENUMERATED
                                            {
                                              non-urgent     (0),
                                              normal         (1),
                                              urgent         (2)
                                            } OPTIONAL,
  1. - Security features

security [4] IMPLICIT SecurityElement

                                           OPTIONAL,
  1. - User Feature selection

user-features [5] IMPLICIT OCTET STRING

                                           OPTIONAL
 };
 Restrict
 This argument indicates whether the controls on ES-OPERATIONS are to
 be updated or removed.  It may be generated by the EMSD-UA.
 This argument may have one of the following values:
    o update:  The other arguments update the prevailing controls;
    o remove:  All temporary controls are to be removed
 In the absence of this argument, the default update shall be assumed.
 Permissible-operations
 This argument indicates the ES-OPERATIONS that the EMSD-SA may invoke
 on the EMSD-UA. It may be generated by the EMSD-UA.
 This argument may have the value allowed or prohibited for each of
 the following:
    o message-delivery:  The EMSD-SA may/may not invoke the deliver
      ES-OPERATIONS; and
    o Other ES-OPERATIONS are not subject to controls, and may be
      invoked at any time.

Banan Informational [Page 18] RFC 2524 EMSD February 1999

 In the absence of this argument, the ES-OPERATIONS that the EMSD-SA
 may invoke on the EMSD-UA are unchanged.
 Permissible-max-content-length
 This argument contains the content-length, in octets, of the
 longest-content message that the EMSD-SA shall deliver to the EMSD-UA
 via the deliver ES-OPERATIONS. It may be generated by the EMSD-UA.
 In the absence of this argument, the permissible-maximum-content-
 length of a message that the EMSD-SA may deliver to the EMSD-UA is
 unchanged.
 Permissible-lowest-priority
 This argument contains the priority of the lowest priority message
 that the EMSD-SA shall deliver to the EMSD-UA via the deliver ES-
 OPERATIONS. It may be generated by the EMSD-UA.
 This argument may have one of the following values of the priority
 argument of the submit ES-OPERATIONS: normal, non-urgent or urgent.
 In the absence of this argument, the priority of the lowest priority
 message that the EMSD-SA shall deliver to the EMSD-UA is unchanged.
 Security
 See Section 3.4.1, "SecurityElements".
 User-features
 This argument contains information that allows the EMSD-UA to convey
 to MTS the feature set that the user is capable of supporting.  This
 argument will be defined when the setConfiguration and
 getConfiguration operations are defined.
 Results
 DeliveryControlResult ::= SEQUENCE
 {
   -- Operation types queued at the EMSD-SA due to existing
   -- restrictions.
   waiting-operations      [0]     IMPLICIT Operations DEFAULT { },

Banan Informational [Page 19] RFC 2524 EMSD February 1999

  1. - Types of messages queued at the EMSD-SA due to
  2. - existing restrictions

waiting-messages [1] IMPLICIT WaitingMessages

                                   DEFAULT { },
  1. - Content Types of messages queued at the EMSD-SA

waiting-content-types SEQUENCE SIZE (0..ub-content-types) OF

                                          ContentType DEFAULT { }
 };
 Restrict ::= ENUMERATED
 {
     update                                      (1),
     remove                                      (2)
 };
 Operations ::= BIT STRING
 {
     submission                                  (0),
     delivery                                    (1)
 };
 WaitingMessages ::= BIT STRING
 {
     long-content                                (0),
     low-priority                                (1)
 };
 Waiting-operations
 This result indicates the ES-OPERATIONS being held by the EMSD-SA,
 and that the EMSD-SA would invoke on the EMSD-UA if it were not for
 the prevailing controls.  It may be generated by the EMSD-SA.
 This result may have the value holding or not-holding for each of the
 following:
    o message-delivery:  The EMSD-SA is/is not holding messages, and
      would invoke the deliver ES-OPERATIONS on the EMSD-UA if it were
      not for the prevailing controls.
 In the absence of this result, it may be assumed that the EMSD-SA is
 not holding any messages for delivery due to the prevailing controls.

Banan Informational [Page 20] RFC 2524 EMSD February 1999

 Waiting-messages
 This result indicates the kind of messages the EMSD-SA is holding for
 delivery to the EMSD-UA, and would deliver via the deliver ES-
 OPERATIONS, if it were not for the prevailing controls.  It may be
 generated by the EMSD-SA.
 This result may have one or more of the following values:
    o long-content:  The EMSD-SA has messages held for delivery to the
      EMSD-UA which exceed the permissible maximum-content-length
      control currently in force;
    o low-priority:  The EMSD-SA has messages held for delivery to the
      EMSD-UA of a lower priority than the permissible-lowest-priority
      control currently in force;
 In the absence of this result, it may be assumed that the EMSD-SA is
 not holding any messages for delivery to the EMSD-UA due to the
 permissible-maximum-content-length, permissible-lowest-priority or
 permissible-security context controls currently in force.
 Errors
 See Section 3.4.3.

3.2.3 deliveryVerify

 The deliveryVerify ES-OPERATIONS enables the EMSD-UA to verify
 delivery of a message when it receives FAILURE.indication for deliver
 ES-OPERATIONS.
 deliveryVerify ES-OPERATION
     ARGUMENT DeliveryVerifyArgument
     RESULT DeliveryVerifyResult
     ERRORS
     {
         verifyError,
         resourceError,
         protocolViolation
     } ::= 5;
 The duplicate operation detection is not required for this operation.
 Arguments

Banan Informational [Page 21] RFC 2524 EMSD February 1999

 This operation's arguments are:
 DeliveryVerifyArgument ::= SEQUENCE
 {
   -- Identifier of this message. This is the same identifier that
   -- was provided to the originator in the Submission Result.
   -- See comment regarding assignment of message identifiers,
   -- at the definition of EMSDMessageId.
   message-id                                      EMSDMessageId
 };
 Message-id
 This argument contains an EMSD-SA-identifier that distinguishes the
 message from all other messages.  It shall be generated by the EMSD-
 SA, and shall have the same value as the message-submission-
 identifier supplied to the originator of the message when the message
 was submitted.
 Results
 DeliveryVerifyResult ::= SEQUENCE
 {
          status  DeliveryStatus
 };
  DeliveryStatus  ::= ENUMERATED
 {
         no-report-is-sent-out                   (1),
         delivery-report-is-sent-out             (2),
         non-delivery-report-is-sent-out         (3)
  };
 No-report-is-sent-out
 This result indicates that EMSD-SA has received the delivery verify
 and no report is sent out (either because it has not been requested
 or EMSD-SA has problems and can not send it out).
 Delivery-report-is-sent-out
 This result indicates that EMSD-SA has received the delivery verify

Banan Informational [Page 22] RFC 2524 EMSD February 1999

 and has sent the delivery report out.
 Non-Delivery-report-is-sent-out
 This result indicates that EMSD-SA has received the delivery verify
 but it has already sent out a non-Delivery report.  This should not
 happen in normal cases but a wrong user profile on EMSD-SA side can
 result in this outcome.
 Errors
 See Section 3.4.3.

3.3 EMSD-SA Invoked Operations

 This section defines the operations invoked by the EMSD-SA:
    a. deliver;
    b. submissionControl;
    c. submissionVerify.
 The deliver operation uses 3-Way handshake service of ESROS. This
 operation always uses the duplication detection functional unit.
 The submissionControl and submissionVerify operations use 2-Way
 handshake service of ESROS without duplication detection.

3.3.1 deliver

 The deliver ES-OPERATIONS enables the EMSD-SA to deliver a message to
 an EMSD-UA.
 deliver ES-OPERATION
     ARGUMENT DeliverArgument
     RESULT NULL
     ERRORS
     {
         deliveryControlViolated,
         securityError,
         resourceError,
         protocolViolation,
         messageError
     } ::= 35;

Banan Informational [Page 23] RFC 2524 EMSD February 1999

 The EMSD-UA MUST not refuse performing the deliver ES-OPERATION
 unless the delivery would violate the deliveryControl restrictions
 then in force.
 Arguments
 This operation's arguments are:
 DeliverArgument ::= SEQUENCE
 {
   -- Identifier of this message. This is the same identifier that
   -- was provided to the originator in the Submission Result.
   -- See comment regarding assignment of message identifiers,
   -- at the definition of EMSDMessageId.
   message-id                                      EMSDMessageId,
  1. - Time the message was delivered to the recipient by EMSD-SA

message-delivery-time DateTime,

  1. - Time EMSD-SA originally took responsibility for processing
  2. - of this message. This field shall be omitted if the message-id
  3. - contains an EMSDLocalMessageId, because that field contains
  4. - the submission time within it.

message-submission-time [0] IMPLICIT DateTime OPTIONAL,

  1. - Security features

security [1] IMPLICIT SecurityElement OPTIONAL,

  1. - SegContentTypementation features for efficient transport

segment-info SegmentInfo OPTIONAL,

  1. - The type of the content

content-type ContentType,

  1. -
  2. - THE CONTENT –
  3. -
  1. - The submitted (and now being delivered) content

content ANY DEFINED BY content-type

 };

Banan Informational [Page 24] RFC 2524 EMSD February 1999

 message-id
 This argument contains an EMSD-SA-identifier that distinguishes the
 message from all other messages.  When within the EMSD, it MUST be
 generated by the EMSD-SA, and MUST have the same value as the
 message-submission-identifier supplied to the originator of the
 message when the message was submitted.
 Message-delivery-time
 This argument contains the Time at which delivery occurs and at which
 the EMSD-SA is relinquishing responsibility for the message.  It
 shall be generated by the EMSD-SA.
 Results
 This operation returns an empty result as indication of success.
 Errors
 See Section 3.4.3.

3.3.2 submissionControl

 submissionControl ES-OPERATION
     ARGUMENT SubmissionControlArgument
     RESULT SubmissionControlResult
     ERRORS
     {
         securityError,
         resourceError,
         protocolViolation
     } ::= 4;
 The submissionControl ES-OPERATIONS enables the EMSD-SA to
 temporarily limit the operations that the EMSD-UA may invoke, and the
 messages that the EMSD-UA may submit to the EMSD-SA via the submit
 ES-OPERATIONS.
 The duplicate operation detection is not required for this operation.
 The EMSD-UA should hold until a later time, rather than abandon, ES-
 OPERATIONS and messages that are presently suspended.

Banan Informational [Page 25] RFC 2524 EMSD February 1999

 The successful completion of the ES-OPERATIONS signifies that the
 specified controls are now in force.  These controls supersede any
 previously in force, and remain in effect until the association is
 released or the EMSD-SA re-invokes the submissionControl ES-
 OPERATIONS.
 The ES-OPERATIONS returns an indication of any ES-OPERATIONS that the
 EMSD-UA would invoke were it not for the prevailing controls.
 Arguments
 This operation's arguments are:
 SubmissionControlArgument ::= SEQUENCE
 {
   -- Request an addition of or removal of a set of restrictions
   restrict               [0]     IMPLICIT Restrict DEFAULT update,
  1. - Which operations are to be placed in the restriction set

permissible-operations [1] IMPLICIT Operations OPTIONAL,

  1. - What maximum content length should be allowed

permissible-max-content-length

                           [2]     IMPLICIT INTEGER
                                   (0..ub-content-length) OPTIONAL,
  1. - Security features

security [3] IMPLICIT SecurityElement

                                                   OPTIONAL
 };
 Restrict
 This argument indicates whether the controls on ES-OPERATIONS are to
 be updated or removed.  It may be generated by the EMSD-SA.
 This argument may have one of the following values:
    o update:  The other arguments update the prevailing controls;
    o remove:  All temporary controls are to be removed
 In the absence of this argument, the default update shall be assumed.

Banan Informational [Page 26] RFC 2524 EMSD February 1999

 Permissible-operations
 This argument indicates the ES-OPERATIONS that the EMSD-UA may invoke
 on the EMSD-SA. It may be generated by the EMSD-SA.
 This argument may have the value allowed or prohibited for each of
 the following:
    o submit:  The EMSD-UA may/may not invoke the submit ES-
      OPERATIONS; and
    o Other ES-OPERATIONS are not subject to controls, and may be
      invoked at any time.
 In the absence of this argument, the ES-OPERATIONS that the EMSD-UA
 may invoke on the EMSD-SA are unchanged.
 Permissible-max-content-length
 This argument contains the content-length, in octets, of the
 longest-content message that the EMSD-UA shall submit to the EMSD-SA
 via the submit ES-OPERATIONS. It may be generated by the EMSD-SA.
 In the absence of this argument, the permissible-maximum-content-
 length of a message that the EMSD-UA may submit to the EMSD-SA is
 unchanged.
 Security
 See Section 3.4.1, "SecurityElements".
 Results
 SubmissionControlResult ::= SEQUENCE
 {
   -- Operation types queued at the EMSD-SA due to existing
   -- restrictions.
   waiting-operations    [0]   IMPLICIT Operations DEFAULT { }
 };

Banan Informational [Page 27] RFC 2524 EMSD February 1999

 Waiting-operations
 This result indicates the ES-OPERATIONS being held by the EMSD-UA,
 and that the EMSD-UA would invoke if it were not for the prevailing
 controls.  It may be generated by the EMSD-UA.
 This result may have the value holding or not-holding for each of the
 following:
    o submit:  The EMSD-UA is/is not holding messages, and would
      invoke the submit ES-OPERATIONS if it were not for the
      prevailing controls.
 In the absence of this result, it may be assumed that the EMSD-UA is
 not holding any messages for submission due to the prevailing
 controls.
 Errors
 See Section 3.4.3.

3.3.3 submissionVerify

 The submissionVerify ES-OPERATIONS enables the EMSD-SA to verify if
 the EMSD-UA has received the result of its submission.
 submissionVerify  ES-OPERATION
     ARGUMENT SubmissionVerifyArgument
     RESULT SubmissionVerifyResult
     ERRORS
     {
         submissionVerifyError,
         resourceError,
         protocolViolation
     } ::= 6;
 The duplicate operation detection is not required for this operation.
 Arguments
 This operation's arguments are:
 SubmissionVerifyArgument ::= SEQUENCE

Banan Informational [Page 28] RFC 2524 EMSD February 1999

  1. - Identifier of this message. This is the same identifier that
  2. - was provided to the originator in the Submission Result.
  3. - See comment regarding assignment of message identifiers,
  4. - at the definition of EMSDMessageId.

{

      message-id                                  EMSDMessageId
   };
 Message-id
 This argument contains an EMSD-SA-identifier that distinguishes the
 message from all other messages.  It shall be generated by the EMSD-
 SA, and shall have the same value as the message-submission-
 identifier supplied to the originator of the message when the message
 was submitted.
 Results
 SubmissionVerifyResult ::= SEQUENCE
 {
         status  SubmissionStatus
 };
 SubmissionStatus::= ENUMERATED
 {
         send-message            (1),
         drop-message            (2)
 };
 Send-message
 This result indicates that EMSD-SA is supposed to send the message
 out.
 Drop-message
 This result indicates that EMSD-SA is supposed to drop the message.
 Errors
 See Section 3.4.3.

Banan Informational [Page 29] RFC 2524 EMSD February 1999

3.4 EMSD Common Information Objects

3.4.1 SecurityElements

 SecurityElement ::= SEQUENCE
 {
   credentials                          Credentials,
   contentIntegrityCheck                ContentIntegrityCheck OPTIONAL
 };
 Credentials ::= CHOICE
 {
   simple                          [0]     IMPLICIT SimpleCredentials
  1. - Strong Credentials are for future study
  2. - strong [1] IMPLICIT StrongCredentials
  3. - externalProcedure [2] EXTERNAL

};

 SimpleCredentials ::= SEQUENCE
 {
   eMSDAddress                     EMSDAddress OPTIONAL,
   password                [0]     IMPLICIT OCTET STRING
                           SIZE (0..ub-password-length)) OPTIONAL
 };
  1. - StrongCredentials ::= NULL
  2. - for now.
  3. - ContentIntegrityCheck is a 16-bit checksum of content

ContentIntegrityCheck ::= INTEGER (0..65535);

3.4.2 Message Segmentation and Reassembly

 Small messages can benefit from the efficiencies of connectionless
 feature of ESROS (See Efficient Short Remote Operations, RFC-2188
 [1]).
 Very large messages are transferred using protocols (e.g., SMTP) that
 rely on Connection Oriented Transport Service (e.g., TCP).
 When a message is too large to fit in a single connectionless PDU but
 is not large enough to justify the overhead of connection
 establishment, it may be more efficient for the message to be
 segmented and reassembled while the connectionless service of ESROS
 is used.  If the underlying Remote Operation Service is capable of
 efficient segmentation/reassembly over connectionless (CL) services,

Banan Informational [Page 30] RFC 2524 EMSD February 1999

 then use of the segmenting/reassembly mechanism introduced in this
 section is not necessary.  This feature is accommodated in this layer
 by:
 SegmentInfo ::= CHOICE
 {
   first           [APPLICATION 2]         IMPLICIT FirstSegment,
   other           [APPLICATION 3]         IMPLICIT OtherSegment
 };
 FirstSegment ::= SEQUENCE
 {
   sequence-id                             INTEGER,
   number-of-segments                      INTEGER
   -- number-of-segments must not exceed ub-total-number-of-segments
 };
 OtherSegment ::= SEQUENCE
 {
   sequence-id                             INTEGER,
   segment-number                          INTEGER
 };
 Segmentation and reassembly only applies to Message-submission and
 Message-delivery.
 The sender of the message is responsible for segmenting the message
 content into segments that fit in CL PDUs.  The segmented content is
 sent in a sequence of message-segments each carrying a segment of the
 content.  sequence-Id is a unique identifier that is present in all
 message-segments.  In addition to sequence identifier, the first
 message-segment specifies the total number of segments (number-of-
 segments).  Other message-segments have a segment sequence number
 (segment-number).  The receiver is responsible for sequencing (based
 on segment-number) and reassembling the entire message.
 Segmenting over the Connectionless ESRO Service
 The sender of the message maps the original message into an ordered
 sequence of message-segments.  This sequence shall not be interrupted
 by other messages over the same ESROS association.
 All message-segments in the sequence shall be assigned a sequence
 identifier by sender.  The sequence identifier shall be incremented
 by one by the sender after transmission of a complete message
 sequence.

Banan Informational [Page 31] RFC 2524 EMSD February 1999

 The first message-segment specifies the total number of segments.
 All message-segments in the sequence except the first one shall be
 sequentially numbered, starting at 1 (first message-segment has
 implicit segment number of 0).
 Each message-segment is transmitted by issuing a Message-submission
 or Message-delivery ES-OPERATIONS. All segments of a segmented
 message are identified by the same sequence-id.  For a given message,
 the receiver should not impose any restriction on the order of
 arrival of message-segments.
 There is no requirement that any message-segment content be of
 maximum length allowed by ESROS for connectionless transmission;
 however, no more than ub-total-number-of-segments segments can be
 derived from a single message.
 The receiver reassembles a sequence of message-segments into a single
 message.  A message shall not be further processed unless all
 segments of the message are received.  Failure to receive the message
 shall be determined by the following events:
    o Expiration of Reassembly Timer (see Section 3.4.3).
    o Receipt of a message-segment with different sequence identifier.
 In the event of the above mentioned failures, the receiver shall
 discard a partially assembled sequence.
 In Reassembly process, all arguments other than content are ignored
 in all segments except the first one.  The content parts of all
 segments are concatenated to compose the original message content.
 When sender receives FAILURE.indication (as opposed to a
 resourceError) for a message-segment, the whole message shall be
 retransmitted.
 In the case of submission and delivery operations, the verify
 function is used as described below:
 Receiver ignores FAILURE.indications received for message-segments,
 and just collects the message-segments to complete the message.
 However, it keeps a failure status for a segmented message which says
 if any segment of the message has received FAILURE.indication.  When
 receiver succeeds to assemble the whole segmented message, then if
 the status of the message shows there has been a FAILURE.indication
 for any of the message-segments, it verifies the message through
 verify operation.  It's not enough to invoke verify operation just
 based on the last message-segment because the sender might send a

Banan Informational [Page 32] RFC 2524 EMSD February 1999

 segment without waiting for the result of the previous segment.  In
 such cases, there might be any combination of success and failure for
 message-segments on the sender side.
 Receiver uses the error code ResourceError (see Section 3.4.3) to ask
 for retransmission of a single segment and uses the error code
 MessageError (see Section 3.4.3) to ask for retransmission of all
 segments (the whole message).
 Reassembly Timer
 The Reassembly Timer is a local timer maintained by the receiver of
 message-segments that assists in performing the reassembly function.
 This timer determines how long a receiver waits for all segments of a
 message-segment sequence to be received.  The timer protects the
 receiver from the loss of a series of segments and possible sequence
 identifier wrap-around.
 The Reassembly Timer shall be started on receipt of a message-segment
 with different sequence identifier than that previously received.
 The timer shall be stopped on receipt of all segments composing the
 sequence.
 The value of Reassembly Timer is defined based on the network
 characteristics and the number of segments.  This requires that the
 transmission of all segments of a single message must be completed
 within this time limit.

3.4.3 Common Errors

 protocolVersionNotRecognized  ERROR PARAMETER NULL ::= 1;
 submissionControlViolated  ERROR PARAMETER NULL ::= 2;
 messageIdentifierInvalid  ERROR PARAMETER NULL ::= 3;
 securityError ERROR PARAMETER security-problem SecurityProblem ::= 4;
 deliveryControlViolated   ERROR PARAMETER NULL ::= 5;
 resourceError  ERROR PARAMETER NULL ::= 6;
 protocolViolation  ERROR PARAMETER NULL ::= 7;
 messageError  ERROR PARAMETER NULL ::= 8;
 SecurityProblem ::= INTEGER (0..127);

Banan Informational [Page 33] RFC 2524 EMSD February 1999

 protocolVersionNotRecognized
 The major and minor protocol versions presented do not match those
 recognized as being valid.
 submissionControlViolated
 The Submission control violated error reports the violation by the
 MTS-user of a control on submission services imposed by the MTS via
 the Submission control service.  The Submission control violated
 abstract-error has no parameters.
 messageIdentifierInvalid
 The Message Identifier Invalid error reports that the Message
 Identifier presented to the MTS is not considered valid.
 securityError
 The Security error reports that the requested operation could not be
 provided by the MTS or MTS-user because it would violate the security
 policy in force.
 deliveryControlViolated
 The Delivery control violated error reports the violation by the MTS
 of a control on delivery operations imposed by the MTS-user via the
 Delivery-control operation.
 resourceError
 The messaging agent cannot currently support this operation.  In the
 case of segmentation and reassembly, resourceError is by the receiver
 used to request that the sender retransmit of a single segment.
 protocolViolation
 Indicates that one or more mandatory argument(s) were missing.

Banan Informational [Page 34] RFC 2524 EMSD February 1999

 messageError
 For a multi-segment message, this error indicates that the messaging
 agent has not received the message completely and that the message
 must be retransmitted.
 SecurityProblem
 To ensure the security-policy is not violated during delivery, the
 message-security-label is checked against the security-context.  If
 delivery is barred by the security-policy then, subject to the
 security policy, a report instruction for this is generated.

3.4.4 ContentType

 ContentType ::=  INTEGER
 {
   -- Content type 0 is reserved and shall never be transmitted.
   reserved                                 (0),
   -- Content types between 1 and 31 (inclusive) are for
   -- internal-use only
   probe                                    (1), -- reserved
   delivery-report                          (2), -- reserved
  1. - Content types between 32 and 63 (inclusive) are for
  2. - message types defined within this specifications.

emsd-interpersonal-messaging-1995 (32),

   voice-messaging                          (33) -- reserved
  1. - Content types beyond and including 64 are for
  2. - bilaterally-agreed use between peers.

} (0..127);

3.4.5 EMSDMessageId

 If this message was originated as an RFC-822 message, then this
 EMSDMessageId shall be the "Message-Id:" field from that message.  If
 this message was originated within the EMSD domain, then this
 identifier shall be unique for the EMSD-SA generating this id.
 EMSDMessageId ::= CHOICE
 {
   EMSDLocalMessageId  [APPLICATION 4]
                       IMPLICIT EMSDLocalMessageId,
   rfc822MessageId     [APPLICATION 5]
                       IMPLICIT AsciiPrintableString

Banan Informational [Page 35] RFC 2524 EMSD February 1999

                       (SIZE (0..ub-message-id-length))
 };
 EMSDLocalMessageId ::= SEQUENCE
 {
   submissionTime            DateTime,
   messageNumber             INTEGER (0..ub-local-message-nu)
 };

3.4.6 EMSDORAddress

 EMSDORAddress ::= CHOICE
 {
   -- This is the local-format address
   emsd-local-address-format            EMSDAddress,
  1. - This is a globally-unique RFC-822 Address

rfc822DomainAddress AsciiPrintableString

 };
 In the global sense Originators and Recipients are represented by
 EMSDORAddress.  The rfc822Domain may be used to address any
 recipient.

3.4.7 EMSDAddress

 EMSDAddress ::= SEQUENCE
 {
   emsd-address        OCTET STRING (SIZE
                       (1..ub-emsd-address-length)),
   -- emsd-address is a decimal integer in BCD
      (Binary Encoded Decimal) format.
   -- If it had an odd number of digits, it is
   -- padded with 0 on the left.
   emsd-name          [0]  IMPLICIT OCTET STRING
                           (SIZE (0..ub-emsd-name-length))
                           OPTIONAL
 };
 Originator and Recipients in the scope of EMSD network are identified
 by a digit based addressing scheme.  EMSDAddress can only be used
 where the scope of addressing has clearly been limited to the EMSD
 network.

3.4.8 DateTime

 DateTime ::= INTEGER;

Banan Informational [Page 36] RFC 2524 EMSD February 1999

 DateTime is a Julian date, expressed as the number of seconds since
 00:00:00 UTC, January 1, 1970.

3.4.9 AsciiPrintableString

 Iso8859String ::=  GeneralString;
 AsciiPrintableString ::= [APPLICATION 0]
                          IMPLICIT Iso8859String (FROM
     (" "|"!"|"#"|"$"|"%"|"&"|"'"|"("|")"|"*"|"+"|","|"-"|"."|"/"|
      "0"|"1"|"2"|"3"|"4"|"5"|"6"|"7"|"8"|"9"|":"|";"|"<"|"="|">"|
      "?"|"@"|"A"|"B"|"C"|"D"|"E"|"F"|"G"|"H"|"I"|"J"|"K"|"L"|"M"|
      "N"|"O"|"P"|"Q"|"R"|"S"|"T"|"U"|"V"|"W"|"X"|"Y"|"Z"|"["|"]"|
      "^"|"_"|"`"|"a"|"b"|"c"|"d"|"e"|"f"|"g"|"h"|"i"|"j"|"k"|"l"|
      "m"|"n"|"o"|"p"|"q"|"r"|"s"|"t"|"u"|"v"|"w"|"x"|"y"|"z"|"{"|
      "|"|"}"|"~"|"\"|""""));

3.4.10 ProtocolVersionNumber

 ProtocolVersionNumber ::= [APPLICATION 1]    SEQUENCE
 {
   version-major                   INTEGER,
+------------------+-------+----+---------+----+---------+-----+-----+
|Operation         |Invoker|Sap |Performer|Sap |Duplicate|OpId |ESROS|
|                  |       |Sel |         |Sel |Detect   |     |Use  |
|__________________|_______|____|_________|____|_________|_____|_____|
|submit            |UA     |4   |MTS      |5   |Yes      |33   |3-Way|
|__________________|_______|____|_________|____|_________|_____|_____|
|deliver           |MTS    |2   |UA       |3   |Yes      |35   |3-Way|
|__________________|_______|____|_________|____|_________|_____|_____|
|deliveryControl   |UA     |8   |MTS      |9   |No       |2    |2-Way|
|__________________|_______|____|_________|____|_________|_____|_____|
|submissionControl |MTS    |6   |UA       |7   |No       |4    |2-Way|
|__________________|_______|____|_________|____|_________|_____|_____|
|submissionVerify  |MTS    |6   |UA       |7   |No       |6    |2-Way|
|__________________|_______|____|_________|____|_________|_____|_____|
|deliveryVerify    |UA     |8   |MTS      |9   |No       |5    |2-Way|
|__________________|_______|____|_________|____|_________|_____|_____|
|getConfiguration  |UA     |8   |MTS      |9   |No       |7    |2-Way|
|__________________|_______|____|_________|____|_________|_____|_____|
|setConfiguration  |MTS    |6   |UA       |7   |No       |8    |2-Way|
+------------------+-------+----+---------+----+---------+-----+-----+
                 Table 1:  EMSD-P Operations Summary

Banan Informational [Page 37] RFC 2524 EMSD February 1999

   version-minor           [0]     IMPLICIT INTEGER DEFAULT 0
 }

3.5 Submission and Delivery Procedures

 Table 1 provides a comprehensive summary of EMSD-P operations, the
 SAP selectors used and the operation IDs used.
 Submission
 The semantics of a submission operation is Exactly Once.  Exactly
 Once means that every operation is carried out exactly one time, no
 more and no less.  This semantic can not be fully implemented
 because, if after invoking the operation, an invoker has a Success
 (e.g.  result) indication and the performer has a FAILURE.indication,
 and the network goes down, the result of the operation will be Zero
 (and not Exactly Once).
 No more than one is controlled and guaranteed by the performer by
 using the Duplicate Operation Detection Support Functions (see the
 chapter entitled Duplicate Operation Detection Support).
 Not zero but one is realized by performer by using the
 SubmissionVerify operation.  When the performer receives
 FAILURE.indication, it's responsibility is to resolve the case by
 using SubmissionVerify resulting in Not zero but one.
 Submission procedure is as follows:
    o Submit operation with 3-Way handshake and Duplicate Operation
      Detection Support Function is invoked.
    o If performer at EMSD-SA receives FAILURE.indication, it invokes
      SubmissionVerify.
    o Message is sent out by EMSD-SA only if result operation is
      confirmed or the operation is verified (in the case of
      FAILURE.indication).
 The semantic of SubmissionVerify operation is At Least Once.  This
 type of semantics corresponds to the case that invoker keeps trying
 over and over until it gets a proper reply.  This operation can be
 performed more than once without any harm.

Banan Informational [Page 38] RFC 2524 EMSD February 1999

 Implications:
    o MTS sends out the message if and only if it's sure that UA knows
      about it.
 Delivery
 The semantics of Deliver operation is Exactly Once.  Exactly Once
 means that every operation is carried out exactly one time, no more
 and no less.  This semantic can not be fully implemented and if after
 invoking the operation, invoker has Success indication and performer
 has FAILURE.indication, and the network goes down, the result of the
 operation will be Zero (and not Exactly Once).
 No more than one is controlled and guaranteed by performer and by
 using the Duplicate Operation Detection Support Functions.
 Not zero but one is realized by performer by using the DeliveryVerify
 operation.  When performer receives FAILURE.indication, it's
 responsible to resolve the case by using DeliveryVerify resulting in
 Not zero but one.
 Delivery procedure is as follows:
    o Deliver operation with 3-Way handshake is invoked.
    o If performer at User Agent (device) receives FAILURE.indication,
      it invokes DeliveryVerify.
 The semantic of DeliveryVerify operation is At Least Once.  This type
 of semantics corresponds to the case that invoker keeps trying over
 and over until it gets a proper reply.  This operation can be
 performed more than once without any harm.
 Implications:
    o A non-delivery report is sent by MTS only if the message is not
      delivered.
    o The UA is responsible for notifying the MTS (through an explicit
      deliveryVerify) to make sure that a delivery report is sent out.

Banan Informational [Page 39] RFC 2524 EMSD February 1999

4 DUPLICATE OPERATION DETECTION SUPPORT

4.1 Duplicate Operation Detection Support Overview

 Some operations are idempotent in nature, i.e.  they can be performed
 more than once without any harm.  However, some other operations are
 non-idempotent in nature, i.e.  they should be performed only once.
 In the case of non-idempotent operations, performer should be able to
 detect duplicate operations and perform each non-idempotent operation
 only once.
 Examples of non-idempotent operations are Submission and Delivery of
 messages which shouldn't be performed more than once.  Examples of
 idempotent operations are Submission-control and Delivery-control
 which can be performed more than once with no harm.
 ESRO Services don't detect duplicate invocation of operations.  As a
 result, the Duplicate Operation Detection Support Functional Unit is
 used to detect duplication when the same operation instance is
 invoked more than once.  Invoker assigns an Operation Instance
 Identifier to an operation and this Operation Instance Identifier is
 used at the peer performer entity to detect the duplicate invocation
 of the same operation.
 Using this support, non-idempotent operations can be repeated over
 and over with no harm because the duplicate invocations are detected
 by this functional unit.  This support helps the performer not to
 perform an operation more than once.
 Support for duplication detection is realized through allocating
 Operation Instance Id (see Section 4.1.2, "Operation Instance
 Identifier") to an operation by invoker.  When an operation is
 invoked using duplication detection support, performer logs the
 Operation Instance Identifier and checks the next operations against
 duplication.
 Operation value identifies whether performer should detect duplicate
 operations (see Section 4.1.1, "Operation Value") and Operation
 Instance Id is assigned by invoker and sent as the first byte of
 operation's parameter.

4.1.1 Operation Value

 Operation Values are divided into two groups.  Operation values from
 0 to 31 do not have Duplicate Operation Detection Support (0 to 31)
 and operation values from 32 to 63 have Duplicate Operation Detection
 Support.

Banan Informational [Page 40] RFC 2524 EMSD February 1999

 Duplicate Operation Detection Functional Unit checks for duplication
 only if Operation Value is in the range of 32 to 63.
 When invoker user uses an Operation Value in the range of 32 to 63
 which means operation with support for duplication detection, the
 user should specify an Operation Instance ID for the operation (see
 next section).

4.1.2 Operation Instance Identifier

 To support duplication detection, an Operation Instance Identifier is
 assigned by invoker user and sent as the first byte of the
 operation's parameter.  This identifier is used on performer side to
 detect duplicate invocation of the same operation.  Characteristics
 of Operation Instance Identifier is as follows:
    o Operation Instance Identifier is one byte and can have values
      from 0 to 255.
    o Operation Instance Identifier is sent as the first byte of the
      operations parameter (without encoding).
    o The length of Operation Instance Identifier is 8-bit, but
      depending on the performer capabilities, it might keep 0 to 127
      Operation Instance Identifiers for duplication detection.  The
      performer profile defines the number of outstanding Operation
      Instance Identifiers that are checked against duplication.  When
      a performer profile indicates support for 0 outstanding
      Operation Instance Identifier, it means it does not have support
      for Duplicate Operation Detection.  In this case, there should
      be only one outstanding operation at any point of time.
    o Instance ID check is not part of ESROS, per se.  Use of
      Duplicate Detection is determined by EMSD-P. Operation Instance
      ID for operations 32-63 is the first byte of the argument.
      Duplicate Detection suuport strips that byte.
    o The Instance ID is not subject to Basic Encoding Rules (BER).
    o The invoker user assigns the Operation Instance Identifier to
      the operation at the time of requesting the invoke service.  The
      Operation Value should be in the range of operation values with
      duplication detection support, i.e.  32 to 63.
    o It's the responsibility of the user to choose Operation Instance
      Identifier in a way that uniqely and unambiguously identifies
      the operation.

Banan Informational [Page 41] RFC 2524 EMSD February 1999

    o From the invoker's perspective, assumption is that two
      operations with the same operation Instance Identifier are
      totally identical which means they produce exact same results.
    o Operation Instance Identifier uniqely specifies a non-idempotent
      operation and multiple invocations of such an operation will
      eventually result in the same outcome because the duplicate
      instances are identified and the operation is not performed more
      than once.
    o From the performer's perspective, assumption is that two
      operations with the same Operation Instance Identifier should be
      executed once and once only.
    o If requested, the degree of duplication checked by Duplicate
      Operation Detection Support Functional Unit on the performer's
      side (i.e.  the total number of outstanding Operation Instance
      Identifier kept) can be communicated with the invoker to
      synchronize the invocations.
    o User of Duplicate Operation Detection Support is responsible to
      behave based on the performer profile and its limitations in
      this regard.  This behavior is defined based on the desired
      semantic of the operation which is to be implemented.
    o On the performer side, when an Operation Instance Identifier is
      received, a previous Operation Instance Identifier whose
      distance to this latest one is greater than or equal to half of
      the wrap-around range of the Operation Instance Identifier
      number is expired, i.e.  for an 8-bit Operation Instance
      Identifier, the distance of 128 causes an old Operation Instance
      Identifier to expire.
    o It's the responsibility of the invoker user to use consecutive
      Operation Instance Identifier numbers, or when it skips some
      Operation Instance Identifiers, it should remember that if there
      is an smaller Operation Instance Identifier on performer side
      with the distance explained above, it will be expired.

5 EMSD PROCEDURE FOR OPERATIONS

 The following sections shows the general procedures to be used in the
 implementation of the EMSD Message Transfer Server (MTS) and the EMSD
 User Agent (UA), with the option for 3-Way or 2-Way handshakes on
 operations which support them.  These procedures do not constitute
 complete behavior specifications for implementations.  The following
 sections contain information helpful to implementors.

Banan Informational [Page 42] RFC 2524 EMSD February 1999

 The MTS and the UA are event-driven.  Each waits for any of the
 possible event types, and, upon receiving an event, processes it.
 After processing the event, the next event is waited upon.

5.1 MTS Behavior

 The MTS is event-driven.
 If it received an event from ESROS, then it could be any of the
 following types:
    o Message submit indication;
    o Message submit confirm and failure indication;
    o Result and Error indication for a deliver operation;
    o DeliveryVerify indication;
    o Result and Error indication for a submissionVerify operation;
    o Result and Error indication for a submissionControl operation;
    o DeliveryControl indication.
 For an ESROS event responsibility is passed to the MTS performer
 (Section 5.1.1).
 If the MTS received an event:
    o for message delivery, from the RFC-822 mailer;
    o requesting submission controls upon the UA, or;
    o indicating an elapsed timer (meaning that it's time to re-
      attempt a message delivery)
 then responsibility is passed to the MTS invoker (Section 5.1.5).

5.1.1 MTS Performer

 The MTS performer is responsible for processing the following
 operations, received from ESROS:
    o Message-submission
    o Delivery-control

Banan Informational [Page 43] RFC 2524 EMSD February 1999

    o Delivery-verify
 The MTS performer should first make sure that it has received an
 INVOKE.indication.  Any other type of primitive shouldn't be
 occurring at this point, and should be ignored.
 If there's something wrong with the PDU or operation data, the MTS
 performer should send back an error to the proper invoker:
  1. Send an ESROS Error Request, then go wait for a response (either
     a confirmation or a failure indication).  The response is sent
     back on the same SAP type on which the event occurred.
  2. Keep track of the type of request that was issued.
 If there isn't anything wrong with the PDU or operation data, then
 the MTS performer has received a valid event from ESROS. This could
 be any of the defined Submission and Delivery Protocol operations.

5.1.2 Message-submission

  1. The Message-submission operation first checks to see which SAP
     this Submit Request came in on.
  2. The request could have arrived as 2-Way SAP (see #3) or a 3-Way
     SAP (see #7).
  3. If the event arrived on the 2-Way SAP, consider this a protocol
     violation and ignore it.
  4. Wait for a response to the request.  The response could be either
     an ERROR.confirm (see #5) or a FAILURE.indication (see #6).
  5. The ERROR.request has been confirmed.  The UA knows that the
     submitted message wasn't sent.  Since there was an error, there
     is nothing more to do, so return.
   6. If the result to the ErrorRequest is a Failure.indication, it
     can be assumed that either the UA has received nothing (the
     ERROR.request PDU was lost), which means failure for the UA; or
     that the 3-Way acknowledgment was lost, which means that the UA
     has in fact received the ERROR.request PDU and knows about the
     delivery failure.  Either way, the message can be ignored.  There
     is nothing more to do, so return.
  7. If the event was received on the 3-Way SAP, then this is the
     correct SAP on which to receive a Submit Request.  Send back a
     Result Request and keep track of the primitive which was issued.

Banan Informational [Page 44] RFC 2524 EMSD February 1999

  8. Now wait for a response to our request.  The response will be
     either a Result.confirm (see #9) or a Failure.indication (see
     #13).
  9. The RESULT.request has been confirmed.
  10. Submit the message to the RFC-822 mailer.
  11. Attempt, a number of times, to send the submitted message via
      the RFC-822 mailer.  If the send was successful, then return.
  12. If, after the maximum number of retries, the message was not
      able to be sent, consider it a failure.  Since the UA assumption
      has been that submission was successful, but now it has not been
      sent, a brand new message, a Non-Delivery message, must be
      generated and delivered to the UA. When this is completed, then
      return.
  13. A FAILURE.indication has occurred due to the previously issued
      RESULT.request.
  14. A Submission Verification is issued to the UA to see if the
      RESULT.request was received.  There are three possible results
      from sending the submission verification to the UA: Fail (see
      #15), Send Message (see #16) or Drop Message (see #20).
  15. Fail -- The Submission-verify request didn't reach the UA, or
      the Submission Verify response didn't get back.  Ignore the
      message and return.
  16. The Submission Verify operation succeeded, meaning that the UA
      received the request, and responded with a message stating that
      it wants the message to be sent.
  17. Attempt, a number of times, to send the submitted message via
      the RFC-822 mailer.
  18. If the message was submitted to the RFC-822 mailer successfully,
      then return.  If, after the maximum number of retries, the
      message was not able to send the message, consider it a failure.
  19. The UA already assumes that the Message-submission was
      successful.  Now since the submitted message has not been sent,
      a brand new message, a Non-Delivery message, must be generated
      and delivered to the UA. After this is accomplished, then
      return.

Banan Informational [Page 45] RFC 2524 EMSD February 1999

  20. The UA responded with a message stating that the message should
      be dropped.  This may occur if the UA never received the result
      from the MTS, meaning that it never received the Message Id, and
      had to therefore inform the user that the message couldn't be
      submitted.  This may also occur if the UA doesn't have the
      record of the message being verified.  It can be because the
      message record has been aged and expired, or because the EMSD-UA
      has not been able to keep the record of the received message
      because of storage or memory limitations.  There is nothing to
      do, so return.

5.1.3 Delivery-control

 This operation can be processed immediately.  After it is processed,
 the appropriate result is returned.

5.1.4 Delivery-verify

 This operation occurs when the UA doesn't think that the MTS has
 received the RESULT.indication from a previously delivered message.
 The UA wants to make sure that the MTS knows it has been delivered.
 The MTS will determine what it knows of the specified message, and
 send back a result.  This can be processed immediately, as it doesn't
 need to deal with duplicate detection.

5.1.5 MTS Invoker

 The MTS invoker is responsible for processing the following
 operations, received from ESROS:
    o Message-delivery
    o Submission-control
    o Submission-verify
 Submission-control
 Process the Submission Control request.
 Message-delivery
  1. Check the User Agent's profile to determine the SAP.
  2. Set the SAP to 3-Way.

Banan Informational [Page 46] RFC 2524 EMSD February 1999

  3. Issue the INVOKE.request on the appropriate SAP, with duplication
     detection enabled.  Since a local error is possible on issuing
     the INVOKE.request, a retry counter is needed.
  4. There are three possible events possible in result to the
     INVOKE.request:  an ERROR.indication (see #5), a
     RESULT.indication (see #9) or a FAILURE.indication (see #10).
  5. An ERROR.indication was received, which means that the UA can't
     accept the message right now.
  6. If the reason was one of a transient nature, wait for a while and
     then send the Deliver Request again.
  7. If the reason was one of a permanent nature, send back a non-
     delivery report to the originator.
  8. Since the error was one of a permanent nature, then the MTS must
     send back a non-delivery report, then log the unsuccessful
     delivery with error from UA and return.
  9. A RESULT.Indication was returned, which means that the Delivery
     was successful.  Send a delivery report to the originator if one
     was requested and log successful delivery and return.
     If the UA profile indicated that Complete mode was to be used,
     keep track of the fact that this message has been successfully
     delivered (as far as the MTS is concerned), so that if the UA
     sends us a Delivery Verify operation, we know that we consider
     the message to be delivered.
  10. A FAILURE.indication was returned, which means there was a
      problem getting the Deliver Request to the UA, or in getting the
      response back from the UA. In any case, a response was never
      received, so the request timed out.  Wait for a while, and then
      send the Deliver Request again.
      As long as a FAILURE.indication is returned and the number of
      retries has not been exceeded, keep trying to verify the
      delivery.
 Submission-verify
 The Submission-verify operation is always issued on the 2-Way SAP.
 The response is awaited.  If a response doesn't come, the request is
 queued and attempted again later.

Banan Informational [Page 47] RFC 2524 EMSD February 1999

  1. Issue the INVOKE.request on the 2-Way SAP, with duplication
     detection disabled.  Since a local error on issuing the invoke
     request is possible, a retry counter is needed.
  2. An INVOKE.Request has been issued and a response has been
     received.  The response will be either a a RESULT.indication (see
     #3) or a FAILURE.indication (see #4).  There are no defined
     errors to a Submission Verify operation, so an ERROR.indication
     should not be occurring here.
  3. A RESULT.indication was received.  Either ResponseSendMessage or
     ResponseDropMessage, as specified in the PDU, will be returned.
  4. A FAILURE.indication was received, which means that there was a
     problem getting the Submission Verify Request to the UA, or in
     getting the response back from the UA. In any case, the response
     was never received, so the request timed out.  Wait for a while,
     and then another attempt to send the Submission Verify request is
     needed.
 Non-Delivery Report
 Issue an INVOKE.request containing a Submit operation with a content
 type of Non-Delivery Report, to the UA. This operation is always
 issued on the 2-Way SAP. The response is awaited.  If a response
 doesn't come, the request is queued and attempted again later.
  1. Create a Submit operation.
  2. Issue the INVOKE.request on the 2-Way SAP, with duplication
     detection enabled.  Since a local error on issuing the invoke
     request is possible, a retry counter for is needed.
  3. A response to the INVOKE.Request has been received.  The response
     will be either a RESULT.indication (see #5), ERROR.indication
     (see #4), or a FAILURE indication (see #7).
  4. An ERROR.indication was received, which means that the UA doesn't
     know what to do with our non-delivery report.  That's the UAs
     problem, so just do nothing and return.
  5. A RESULT.indication was received, which means we delivered a
     successful non-delivery report.
  6. The result is logged.  Nothing more is needed, so return.

Banan Informational [Page 48] RFC 2524 EMSD February 1999

  7. A FAILURE.indication was received, which means there was a
     problem getting the Submit Request to the UA, or in getting the
     response back from the UA. In any case, the response was never,
     so the request timed out.  Wait for a while, and then send the
     Submission Verify request again.

5.2 UA Behavior

 The User Agent is event-driven.
 If it received an event from ESROS, then it could be any of the
 following types:
    o Message deliver indication;
    o Message deliver confirm and failure indication;
    o Result and Error indication for a submit operation;
    o Submission verify indication;
    o Result and Error indication for a delivery verify operation;
    o Result and Error indication for a delivery control operation;
    o Submission control indication.
 For an ESROS event responsibility is passed to the UA performer
 (Section 5.2.1).
 IF the UA received an event indicating that there's a message from
 the user, for submission, then responsibility is passed to the UA
 invoker (Section 5.2.2).

5.2.1 UA Performer

 The performer on the UA side is responsible for processing the
 following operations:
    o Message Delivery
    o Submission Verification
    o Submission Control

Banan Informational [Page 49] RFC 2524 EMSD February 1999

 Message-delivery
  1. A Message-delivery request is received.
  2. Check for the correctness of the PDU. If the PDU is bad the see
     #3.  If the PDU is good then see #8.
  3. Send an ESROS ERROR.request.  If the request arrived on a 3-Way
     SAP, use a 3-Way SAP for the result.  If the request arrived on a
     2-Way SAP, use a 2-Way SAP for the result.  Keep track of the
     type of request that was issued.
  4. Wait for the ESROS event.  The result could be an ERROR.confirm
     (see #5) or a FAILURE.indication (see #7).
  5. The ESROS event was an ERROR.confirm
  6. Log the message as the Non-Delivery was confirmed by the MTS and
     return.
  7. If the ESROS event was a FAILURE.indication, that means one of
     two things has occurred:
     A. The MTS has received nothing (the ERROR.request PDU was lost),
        which means that the MTS doesn't know that the message
        delivery has been rejected.  In this case, the MTS will
        eventually time out, and retransmit the message delivery
        request.
     B. The 3-Way acknowledgment was lost, which means that the MTS
        has in fact received the ERROR.request PDU and knows about the
        delivery failure.
     Either way, the message can now be ignored.
  8. Send an ESROS RESULT.request.  If the request arrived on a 3-Way
     SAP, use a 3-Way SAP for the result.  If the request arrived on a
     2-Way SAP, use a 2-Way SAP for the result.  Keep track of the
     type of request that was issued.
  9. Wait for the ESROS event.  The result could be an RESULT.confirm
     (see #10) or a FAILURE.indication (see #13).
  10. If the event is a RESULT.confirm, then the delivered message can
      now be given to the user.
  11. Deliver the message to the user.

Banan Informational [Page 50] RFC 2524 EMSD February 1999

  12. Log the message as Message Delivery Known to MTS.
  13. If the event is a FAILURE.indication, then, if the delivery was
      on a 3-Way SAP, a Delivery Verification request to the MTS can
      be issued to see if the MTS actually got the RSULT.request.  If
      the delivery was on a 2-Way SAP, then the message will delivered
      to the user and if the MTS has not received the RESULT.request,
      it will retransmit it later and the duplicate will be ignored.
  14. Deliver the message to the user.  Since a FAILRUE.indication was
      received in response to a RESULT.requst, it means that possible,
      the MTS didn't receive the RESULT.request.  The MTS could now
      time out, and send another copy of the same message.  Save the
      message for duplication detection.
  15. Log the fact that the message was delivered, but that the MTS
      might not be aware of it.
  16. If the UA supports Delivery Verification, and the Delivery
      Request was sent on the 3-Way SAP, then see #17.  If either of
      these conditions are not true, then return.
  17. Send a Delivery-verify request to see if the MTS got the
      RESULT.request.
      There are three possible results from sending the delivery
      verification to the MTS: Fail (see #18), ResponseNonDelivery
      (see #20) or ResponseDelivery (see #23).
  18. Fail -- Delivery Verify request didn't reach the MTS, or the
      Delivery Verify response didn't get back to the UA.
  19. Log this as delivering the message to the user, but the MTS
      having possibly sent a Non-Delivery report to the originator
      even though the UA did actually deliver the message to the user.
      Then return.
  20. ResponseNonDelivery -- Verify Response indicates that the MTS
      now knows (because of the Delivery Verify operation that the
      message has been delivered to the user, but had not received our
      RESULT.request nor a Delivery Verify operation in a timely
      manner, and had already sent out a Non-Delivery report to the
      originator.
  21. The MTS had not received, from the UA, in a timely manner, a
      RESULT.indication indicating that the message had been delivered
      to the user.  The MTS has already sent a Non-Delivery report to

Banan Informational [Page 51] RFC 2524 EMSD February 1999

      the originator.  The UA must let the user know about this.  Log
      the message as delivered to the user, but a Non-Delivery sent to
      the originator.
  22. Since the UA received a response to the Verify operation, it
      knows that the MTS knows about this message delivery, so the UA
      also knows that it won't be receiving a duplicate of it.  The UA
      can now remove this message's Message Id from the list of
      possible duplicates.
  23. ResponseDelivery -- Verify Response received from MTS.
  24. This means that the MTS knows (either because the MTS had
      received the RESULT.request that was sent by the UA or because
      the MTS has now received the UAs Delivery-verification message,
      informing that the UA received the message for delivery to the
      user.  The MTS is (or was) able to send a Delivery report to the
      originator if one was requested.  Log it as such.
  25. Since the UA received a response to the Verify operation, it
      knows that the MTS knows about this message delivery, so the UA
      also knows that it won't be receiving a duplicate of it.  The UA
      can now remove this message's Message Id from the list of
      possible duplicates and return.
 Submission-verify
 Process the Submission-verify request and return.
 Submission-control
 This operation can be processed immediately.  After it is processed,
 the appropriate result is returned.

5.2.2 UA Invoker

 The invoker on the UA side is responsible for processing the
 following operations:
    o Message-submission
    o Delivery-control
    o Delivery-verify

Banan Informational [Page 52] RFC 2524 EMSD February 1999

 Message-submission
 General procedures for UA's Message-submission mirror that of MTS's
 Message-delivery.
 Delivery-control
  1. Issue the INVOKE.request on the 3-Way SAP, with duplication
     detection enabled.  Since the UA can get a local error on issuing
     the invoke request, a retry counter is needed.
     If we got a local failure in issuing the Invoke Request, wait a
     while and then try again (up to the limit of the maximum number
     of retries).
  2. The UA has issued an INVOKE.Request.  Wait for a response from
     ESROS. The response will be either a RESULT.indication (see #5),
     ERROR.indication (see #3), or FAILURE.indication (see #7).
  3. A ERROR.indicaiton was received, meaning that the MTS told says
     that it cannot accept the message.
  4. Log the MTS rejection and return
  5. A RESULT.indication was received, which means that the Submission
     was successful.
  6. Log successful submission and return.
  7. a FAILURE.indication was received, meaning that there was a
     problem getting the Submit Request to the MTS, or in getting the
     response back from the MTS. In any case, the UA never received
     the response, so the request timed out.  Wait for a while, and
     then send the Submit Request again.
  8. The UA has exceeded the maximum number of retries.  Let the user
     know, log the failure and return.
 Delivery-verify
 General procedures for UA's Delivery-verify mirror that of MTS's
 Submission-verify.

Banan Informational [Page 53] RFC 2524 EMSD February 1999

6 EMSD FORMAT STANDARDS

6.1 Format Standard Overview

 EMSD Format Standard (EMSD-FS) is a non-textual form of compact
 encoding of Internet mail (RFC-822) messages which facilitates
 efficient transfer of messages.  EMSD-FS is used in conjunction with
 the EMSD-P but is not a general replacement for RFC-822.  EMSD-FS
 defines a method of representation of short interpersonal message.
 It defines the "Content" encoding (Header + Body).  Although EMSD-FS
 contains end-to-end information its scope is purely point-to-point.
 The "Efficient InterPersonal Message Format Standard" is defined in
 this section.  This standard is primarily intended for communication
 among people.
 The EMSD Format Standard is designed to be fully consistent with
 RFC-822 [3].  In many ways EMSD-FS can be considered to be an
 efficiency oriented encoder and decoder.  Through use of EMSD-FS an
 RFC-822 message is converted to a more compact binary encoding.  This
 more compact message is then transfered between an EMSD-SA and EMSD-
 UA. The compact message (represented in EMSD-FS) may then be
 converted back to RFC-822 intact.
 For messages that are originated (submitted) with EMSD protocol,
 certain fields (e.g., addresses, message-id) can have special forms
 that are specialized and produce more compact EMSD-FS encoding.
 These special forms are legitimate values of RFC-822 messages.
 This specification expresses information objects using ASN.1 [X.208].
 Encoding of ASN.1 shall be based on Basic Encoding Rules (BER) [5].
 Future revisions of this specification will use Packed Encoding Rules
 (PER) [4].
 The convention of (O) "OPTIONAL", (D) "DEFAULT", (C) "CONDITIONAL"
 and (M) "MANDATORY" which express requirements for presence of
 information is used in this section.

6.2 Interpersonal Messages

 An interpersonal message (IPM) consists of a heading and a body.
 IPM ::=   SEQUENCE
 {
   heading       Heading,

Banan Informational [Page 54] RFC 2524 EMSD February 1999

   body          Body OPTIONAL
 };

6.2.1 Heading fields

 The fields that may appear in the Heading of an IPM are defined and
 described below.
 Heading ::= SEQUENCE
 {
   -- Address of the sending agent (person, program, machine) of
   -- this message. This field is mandatory if the sender
   -- is different than the originator.
   sender                      [0]     EMSDORAddress OPTIONAL,
  1. - Address of the originator of the message
  2. - (not necessarily the sender)

originator EMSDORAddress,

  1. - List of recipients and flags associated with each.

recipient-data SEQUENCE SIZE (1..ub-recipients)

                                       OF PerRecipientFields,
  1. - Flags applying to this entire message

per-message-flags [1] IMPLICIT BIT STRING

    {
    -- Priority values
    -- At most one of "non-urgent" and "urgent" may be specified
    -- concurrently.  If neither is specified, then a Priority
    -- level of "normal" is assumed.
    priority-non-urgent             (0),
    priority-urgent                 (1),
  1. - Importance values
  1. - At most one of "low" and "high" may be specified
  2. - concurrently. If neither is specified, then an
  3. - Importance level of "normal" is assumed.

importance-low (2),

    importance-high                 (3),
  1. - Indication of whether this message has been

automatically forwarded

    auto-forwarded                  (4)
    } OPTIONAL,

Banan Informational [Page 55] RFC 2524 EMSD February 1999

  1. - User-specified recipient who is to receive replies

to this message.

   reply-to                    [2]     IMPLICIT SEQUENCE SIZE
                                       (1..ub-reply-to)
                                      OF EMSDORAddress OPTIONAL,
  1. - Identifier of a previous message, for which this message
  2. - is a reply

replied-to-IPM EMSDMessageId OPTIONAL,

  1. - Subject of the message.

subject [3] IMPLICIT AsciiPrintableString

                                       (SIZE (0..ub-subject-field))
                                                 OPTIONAL,
  1. - RFC-822 header fields not explicitly provided for in
  2. - this Heading. For messages incoming from the external
  3. - world (i.e. in RFC-822 format), the Message-Id: field
  4. - need not go here, as it is placed in the
  5. - Envelope's EMSDMessageId (message-id) field.

extensions [4] IMPLICIT SEQUENCE

                          (SIZE (0..ub-header-extensions))
                          OF  IPMSExtension OPTIONAL,
  1. - MIME Version (if other than 1.0)

mime-version [5] IMPLICIT AsciiPrintableString

                                   (SIZE (0..ub-mime-version-length))
                                                OPTIONAL,
  1. - Top-level MIME Content Type

mime-content-type [6] IMPLICIT AsciiPrintableString

                                   (SIZE (0..
                                    ub-mime-content-type-length))
                                             OPTIONAL,
  1. - MIME Content Id

mime-content-id [7] IMPLICIT AsciiPrintableString

                                   (SIZE (0..
                                    ub-mime-content-id-length))
                                             OPTIONAL,
  1. - MIME Content Description

mime-content-description [8] IMPLICIT AsciiPrintableString

                                   (SIZE (0..ub-mime-content-
                                   description-length))
                                             OPTIONAL,
   -- Top-level MIME Content Type
   mime-content-transfer-encoding

Banan Informational [Page 56] RFC 2524 EMSD February 1999

                            [9]     IMPLICIT AsciiPrintableString
                                    (SIZE (0..ub-mime-content-
                                    transfer-encoding))
                                             OPTIONAL
 };
 Some fields have components and thus are composite, rather than
 indivisible.  A field component is called a sub-field.
 Sender
 This field is mandatory if the sender is different from the
 originator.
 Originator
 The Originator heading field (O) identifies the IPM's originator.
 Recipient-data
 PerRecipientFields ::= SEQUENCE
 {
   recipient-address                            EMSDORAddress,
   per-recipient-flags                          BIT STRING
   {
   -- Recipient Types.
   -- At most one of "copy" and "blind-copy" may be
   -- specified concurrently for a single recipient.  If
   -- neither is specified, than the recipient
   -- is assumed to be a "primary" recipient.
   recipient-type-copy                             (0),
   recipient-type-blind-copy                       (1),
  1. - Notification Request Types.
  2. - Only one of "rn" and "nrn" may be specified
  3. - concurrently, \x110011 for a single recipient.
  4. - "rn" implies "nrn" in addition.

notification-request-rn (2),

   notification-request-nrn                        (3),
   notification-request-ipm-return                 (4),
  1. - Report Request Types

Banan Informational [Page 57] RFC 2524 EMSD February 1999

  1. - At most one of these should be set for a
  2. - particular recipient. "delivery" implies "non-delivery"
  3. - in addition.

report-request-non-delivery (5),

   report-request-delivery                         (6),
  1. - Originator-to-Recipient request for a reply.

reply-requested (7)

   } DEFAULT { report-request-non-delivery }
 };
 recipient-address
 The Primary Recipients heading field identifies the zero or more
 users who are the "primary recipients" of the IPM. The primary
 recipients might be those users who are expected to act upon the IPM.
 per-recipient-flags
 The Copy Recipients heading field identifies the zero or more users
 who are the "copy recipients" of the IPM. The copy recipients might
 be those users to whom the IPM is conveyed for information.
 recipient-type-copy
 This field is set if the recipient is on the Carbon Copy (CC) list.
 recipient-type-blind-copy
 This field is set if the recipient is on the Blind Carbon Copy (BCC)
 list.
 The Blind Copy Recipients heading field (C) identifies zero or more
 users who are the intended blind copy recipients of the IPM.
 The phrase "copy recipients" above has the same meaning as in "Copy
 Recipients" from Section 6.2.1 .  A blind copy recipient is one whose
 role as such is disclosed to neither primary nor copy recipients.

Banan Informational [Page 58] RFC 2524 EMSD February 1999

 In the instance of an IPM intended for a blind copy recipient, this
 conditional field shall be present and identify that user.  Whether
 it shall also identify the other blind copy recipients is a local
 matter.  In the instance of the IPM intended for a primary or copy
 recipient, the field shall be absent.
 notification-request-rn
 A receipt notification (rn) reports its originator's receipt, or his
 expected and arranged future receipt, of an IPM.
 notification-request-nrn
 A non-receipt notification (nrn) reports its originator's failure to
 receive, to accept, or his delay in receiving, an IPM.
 notification-request-ipm-return
 When this field is set, the contents of the message are returned
 along with the notification.
 report-request-non-delivery
 The report request enables the MTS to acknowledge to the MTS-user one
 or more outcomes of a previous invocation of the message-submission
 or probe-submission abstract-operations.
 A report is returned only in case of non-delivery.
 report-request-delivery
 For the message-submission, report-delivery indicates the delivery or
 non-delivery of the submitted message to one or more recipients.  For
 the probe-submission, the report-delivery indicates whether or not a
 message could be delivered if the message were to be submitted.
 reply-requested
 When set this field indicates that the originator requests that a
 recipient send a message in reply to the message which carries the
 request.

Banan Informational [Page 59] RFC 2524 EMSD February 1999

 per-message-Flags
 Priority
 The Priority field (default is normal) identifies the priority that
 the authorizing users attach to the IPM. It may assume any one of the
 following values:  urgent, normal, or non-urgent.
 At most one of either "non-urgent" or "urgent" may be specified
 concurrently.  If neither is specified, then a Priority level of
 "normal" is assumed.
 Importance
 The Importance heading field (default normal) identifies the
 importance that the authorizing users attach to the IPM. It may
 assume any one of the following values:  low, normal, or high.
 At most one of either "low" or "high" may be specified concurrently.
 If neither is specified, then a Importance level of "normal" is
 assumed.
 The values above are not defined by this specification; they are
 given meaning by users.
 auto-forwarded
 The Auto-forwarded heading field (default is false) indicates whether
 the IPM is the result of auto-forwarding.  It is a Boolean value.
 reply-to
 User-specified recipient or recipients who are to receive replies to
 this message.
 replied-to IPM
 The Replied-to IPM heading field (C) identifies the IPM to which the
 present IPM is a reply.  It comprises an IPM identifier.
 This conditional field shall be present if, and only if, the IPM is a
 reply.

Banan Informational [Page 60] RFC 2524 EMSD February 1999

 Note - In the context of forwarding, care should be taken to
 distinguish between the forwarding IPM and the forwarded IPM. This
 field should identify whichever of these two IPMs to which the reply
 responds.
 subject
 The Subject heading field (O) identifies the subject of the IPM. It
 corresponds to the "Subject:" field of RFC-822.
 extensions
 The Extensions heading field [D no extensions (i.e.  members)]
 conveys information accommodated by no other heading field.  It
 comprises a Set of zero or more IPMS extensions, each conveying one
 such information item.
 IPMSExtension ::= SEQUENCE
 {
     x-header-label                      AsciiPrintableString,
     x-header-value                      AsciiPrintableString
 };

6.2.2 Body part types

 The types of body parts that may appear in the Body of an IPM are
 structured using the MIME specification.
 Body ::= SEQUENCE
 {
   compression-method          [0]     IMPLICIT CompressionMethod
                                                OPTIONAL,
   -- If compression method is not specified,
   -- "no-compression" is implied.
   message-body                        OCTET STRING
   -- See MIME for structure of the Body.
   -- If a compression method is specified, the entire text containing
   -- the Content-Type: element followed by the RFC-822 body are
   -- compressed using the specified method, and placed herein.
 };
 CompressionMethod ::= INTEGER
 {
   -- Compression Methods numbered 0 to 63 are reserved for
   -- assignment within this and associated specifications.

Banan Informational [Page 61] RFC 2524 EMSD February 1999

   no-compression                  (0),
   lempel-ziv                      (1)
  1. - Compression Methods numbered between 64 and 127 may be
  2. - used on a bilaterally-agreed basis between peers.

} (0..127)

7 ACKNOWLEDGMENTS

 In the context of Limited Size Messaging (LSM) over CDPD and pACT
 over Narrowband PCS, AT&T Wireless Services (AWS), funded work which
 was relevant to the development of the EMSD protocols.

8 SECURITY CONSIDERATIONS

 This protocol supports simple authentication of the originator's
 address by the EMSD-SA and simple authentication of EMSD-SA by EMSD-
 UA.
 Mainstream Internet mail security mechanisms can be used in
 conjunction with the EMSD protocol.

9 AUTHOR'S ADDRESS

 Mohsen Banan
 Neda Communications, Inc.
 17005 SE 31st Place
 Bellevue, WA 98008
 EMail: mohsen@neda.com

Banan Informational [Page 62] RFC 2524 EMSD February 1999

A EMSD-P ASN.1 MODULE

 This section compiles in one place the complete ASN.1 Module for EM
 Submission and Delivery Protocol.
 EMSD-SubmissionAndDeliveryProtocol DEFINITIONS ::=
 BEGIN
 EXPORTS EMSDORAddress, AsciiPrintableString, ContentType,
 DateTime, EMSDMessageId, EMSDORAddress, ProtocolVersionNumber;
  1. - Upper bounds
 ub-recipients  INTEGER ::= 256;
 -- also defined in EMSD-InterpersonalMessaging1995
 ub-reply-to INTEGER ::= 256;
 -- also defined in EMSD-InterpersonalMessaging1995
 ub-subject-field INTEGER ::= 128;
 -- also defined in EMSD-InterpersonalMessaging1995
 ub-password-length INTEGER ::= 16;
 ub-content-length INTEGER ::= 65535;
 -- also defined in EMSD-Probe
 ub-content-types INTEGER ::= 128;
 ub-message-id-length INTEGER ::= 127;
 ub-total-number-of-segments INTEGER ::= 32;
 ub-header-extensions INTEGER ::= 64;
 -- also defined in EMSD-InterpersonalMessaging1995
 ub-emsd-name-length INTEGER ::= 64;
 ub-emsd-address-length INTEGER ::= 20;
 ub-rfc822-name-length INTEGER ::= 127;
 ub-mime-version-length INTEGER ::= 8;
 -- also defined in EMSD-InterpersonalMessaging1995
 ub-mime-content-type-length INTEGER ::= 127;
 -- also defined in EMSD-InterpersonalMessaging1995
 ub-mime-content-id-length INTEGER ::= 127;
 -- also defined in EMSD-InterpersonalMessaging1995
 ub-mime-content-description-length INTEGER ::= 127;
 -- also defined in EMSD-InterpersonalMessaging1995
 ub-mime-content-transfer-encoding INTEGER ::= 127;
 -- also defined in EMSD-InterpersonalMessaging1995
 ub-local-message-nu INTEGER ::= 4096;
  1. ———————
  2. - SUBMIT Operation –
  3. ———————
 submit ES-OPERATION

Banan Informational [Page 63] RFC 2524 EMSD February 1999

     ARGUMENT SubmitArgument
     RESULT SubmitResult
     ERRORS
     {
         submissionControlViolated,
         securityError,
         resourceError,
         protocolViolation,
         messageError
     } ::= 33;
 SubmitArgument ::= SEQUENCE
 {
   -- Security features
   security           [0]    IMPLICIT SecurityElement
                             OPTIONAL,
  1. - Segmentation features for efficient transport

segment-info SegmentInfo OPTIONAL,

  1. - Content type of the message

content-type ContentType,

  1. -
  2. - THE CONTENT –
  3. -
  1. - The submission content

content ANY DEFINED BY content-type

 };
 SubmitResult ::= SEQUENCE
 {
  1. - Permanent identifier for this message.
  2. - Also contains the message submission time.
  3. - See comment regarding assignment of message
  4. - identifiers, at the definition of EMSDLocalMessageId.

message-id EMSDLocalMessageId

     };
  1. ——————————-
  2. - Delivery Control Operation –
  3. ——————————-
 deliveryControl ES-OPERATION

Banan Informational [Page 64] RFC 2524 EMSD February 1999

     ARGUMENT DeliveryControlArgument
     RESULT DeliveryControlResult
     ERRORS
     {
         securityError,
         resourceError,
         protocolViolation
     } ::= 2;
 DeliveryControlArgument ::= SEQUENCE
 {
   -- Request an addition of or removal of a set of restrictions
   restrict             [0]     IMPLICIT Restrict DEFAULT update,
  1. - Which operations are to be placed in the restriction set

permissible-operations [1] IMPLICIT Operations OPTIONAL,

  1. - What maximum content length should be allowed

permissible-max-content-length

                           [2]     IMPLICIT INTEGER
                                   (0..ub-content-length) OPTIONAL,
  1. - What is the lowest priority message which may be delivered

permissible-lowest-priority

                           [3]     IMPLICIT ENUMERATED
                                   {
                                      non-urgent     (0),
                                      normal         (1),
                                      urgent         (2)
                                   } OPTIONAL,
  1. - Security features

security [4] IMPLICIT SecurityElement

                                                   OPTIONAL,
  1. - User Feature selection

user-features [5] IMPLICIT OCTET STRING OPTIONAL

 };
 DeliveryControlResult ::= SEQUENCE
 {
   -- Operation types queued at the EMSD-SA due to existing
   -- restrictions.
   waiting-operations    [0]   IMPLICIT Operations DEFAULT { },
  1. - Types of messages queued at the EMSD-SA due to
  2. - existing restrictions

Banan Informational [Page 65] RFC 2524 EMSD February 1999

   waiting-messages      [1]   IMPLICIT WaitingMessages DEFAULT { },
  1. - Content Types of messages queued at the EMSD-SA

waiting-content-types SEQUENCE SIZE (0..ub-content-types) OF

                                         ContentType DEFAULT { }
 };
 Restrict ::= ENUMERATED
 {
     update                                      (1),
     remove                                      (2)
 };
 Operations ::= BIT STRING
 {
     submission                                  (0),
     delivery                                    (1)
 };
 WaitingMessages ::= BIT STRING
 {
     long-content                                (0),
     low-priority                                (1)
 };
  1. - Delivery Verify Operation
 deliveryVerify ES-OPERATION
     ARGUMENT DeliveryVerifyArgument
     RESULT DeliveryVerifyResult
     ERRORS
     {
         verifyError,
         resourceError,
         protocolViolation
     } ::= 5;
 DeliveryVerifyArgument ::= SEQUENCE
 {
   -- Identifier of this message. This is the same identifier that
   -- was provided to the originator in the Submission Result.
   -- See comment regarding assignment of message identifiers,
   -- at the definition of EMSDMessageId.
   message-id                                      EMSDMessageId
 };

Banan Informational [Page 66] RFC 2524 EMSD February 1999

 DeliveryVerifyResult ::= SEQUENCE
 {
                          status  DeliveryStatus
 };
  DeliveryStatus  ::= ENUMERATED
 {
         no-report-is-sent-out                   (1),
         delivery-report-is-sent-out             (2),
         non-delivery-report-is-sent-out         (3)
 };
  1. ———————-
  2. - DELIVER Operation –
  3. ———————-
 deliver ES-OPERATION
     ARGUMENT DeliverArgument
     RESULT NULL
     ERRORS
     {
         deliveryControlViolated,
         securityError,
         resourceError,
         protocolViolation,
         messageError
     } ::= 35;
 DeliverArgument ::= SEQUENCE
 {
   -- Identifier of this message. This is the same identifier that
   -- was provided to the originator in the Submission Result.
   -- See comment regarding assignment of message identifiers,
   -- at the definition of EMSDMessageId.
   message-id                                      EMSDMessageId,
  1. - Time the message was delivered to the recipient by EMSD-SA

message-delivery-time DateTime,

  1. - Time EMSD-SA originally took responsibility for processing
  2. - of this message. This field shall be omitted if the message-id
  3. - contains an EMSDLocalMessageId, because that field contains
  4. - the submission time within it.

message-submission-time [0] IMPLICIT DateTime OPTIONAL,

  1. - Security features

security [1] IMPLICIT SecurityElement OPTIONAL,

Banan Informational [Page 67] RFC 2524 EMSD February 1999

  1. - SegContentTypementation features for efficient transport

segment-info SegmentInfo OPTIONAL,

  1. - The type of the content

content-type ContentType,

  1. -
  2. - THE CONTENT –
  3. -
  1. - The submitted (and now being delivered) content

content ANY DEFINED BY content-type

 };
  1. - Submission Control Operation
 submissionControl ES-OPERATION
     ARGUMENT SubmissionControlArgument
     RESULT SubmissionControlResult
     ERRORS
     {
         securityError,
         resourceError,
         protocolViolation
     } ::= 4;
 SubmissionControlArgument ::= SEQUENCE
 {
   -- Request an addition of or removal of a set of restrictions
   restrict               [0]     IMPLICIT Restrict DEFAULT update,
  1. - Which operations are to be placed in the restriction set

permissible-operations [1] IMPLICIT Operations OPTIONAL,

  1. - What maximum content length should be allowed

permissible-max-content-length

                           [2]     IMPLICIT INTEGER
                                   (0..ub-content-length) OPTIONAL,
  1. - Security features

security [3] IMPLICIT SecurityElement

                                                   OPTIONAL
 };
 SubmissionControlResult ::= SEQUENCE
 {
   -- Operation types queued at the EMSD-SA due to existing

Banan Informational [Page 68] RFC 2524 EMSD February 1999

  1. - restrictions.

waiting-operations [0] IMPLICIT Operations DEFAULT { }

 };
  1. ———————————
  2. - Submission Verify Operation –
  3. ———————————
 submissionVerify  ES-OPERATION
     ARGUMENT SubmissionVerifyArgument
     RESULT SubmissionVerifyResult
     ERRORS
     {
         submissionVerifyError,
         resourceError,
         protocolViolation
     } ::= 6;
 SubmissionVerifyArgument ::= SEQUENCE
   -- Identifier of this message. This is the same identifier that
   -- was provided to the originator in the Submission Result.
   -- See comment regarding assignment of message identifiers,
   -- at the definition of EMSDMessageId.
   {
      message-id                       EMSDMessageId
   };
 SubmissionVerifyResult ::= SEQUENCE
     {
         status  SubmissionStatus
     };
 SubmissionStatus::= ENUMERATED
 {
         send-message            (1),
         drop-message            (2)
 };
  1. - GetConfiguration Operation
  2. - To be fully defined later. This will possibly include,
  3. - but not be limited to:
  4. - get-local-time-zone
  5. - get-protocol-version
  6. - etc.
 getConfiguration ES-OPERATION

Banan Informational [Page 69] RFC 2524 EMSD February 1999

         ARGUMENT NULL
         RESULT NULL
         ERRORS
         {
             resourceError,
             protocolViolation
         } ::= 7;
  1. - SetConfiguration Operation
  2. - To be fully defined later.
 setConfiguration ES-OPERATION
         ARGUMENT NULL
         RESULT NULL
         ERRORS
         {
             resourceError,
             protocolViolation
         } ::= 8;
  1. - Security –
 SecurityElement ::= SEQUENCE
 {
   credentials                   Credentials,
   contentIntegrityCheck         ContentIntegrityCheck OPTIONAL
 };
 Credentials ::= CHOICE
 {
   simple                          [0]   IMPLICIT SimpleCredentials
   -- Strong Credentials are for future study
   -- strong                       [1]   IMPLICIT StrongCredentials
   -- externalProcedure            [2]   EXTERNAL
 };
 SimpleCredentials ::= SEQUENCE
 {
   eMSDAddress                         EMSDAddress OPTIONAL,
   password                    [0]     IMPLICIT OCTET STRING
                               (SIZE (0..ub-password-length)) OPTIONAL
 };
  1. - StrongCredentials ::= NULL
  2. - for now.

Banan Informational [Page 70] RFC 2524 EMSD February 1999

  1. - ContentIntegrityCheck is a 16-bit checksum of content

ContentIntegrityCheck ::= INTEGER (0..65535);

 SegmentInfo ::= CHOICE
 {
   first           [APPLICATION 2]         IMPLICIT FirstSegment,
   other           [APPLICATION 3]         IMPLICIT OtherSegment
 };
 FirstSegment ::= SEQUENCE
 {
   sequence-id                             INTEGER,
   number-of-segments                      INTEGER
   -- number-of-segments must not exceed ub-total-number-of-segments
 };
 OtherSegment ::= SEQUENCE
 {
   sequence-id                             INTEGER,
   segment-number                          INTEGER
 };
  1. ———-
  2. - Errors –
  3. ———–
 protocolVersionNotRecognized  ERROR PARAMETER NULL ::= 1;
 submissionControlViolated  ERROR PARAMETER NULL ::= 2;
 messageIdentifierInvalid  ERROR PARAMETER NULL ::= 3;
 securityError ERROR PARAMETER security-problem SecurityProblem ::= 4;
 deliveryControlViolated   ERROR PARAMETER NULL ::= 5;
 resourceError  ERROR PARAMETER NULL ::= 6;
 protocolViolation  ERROR PARAMETER NULL ::= 7;
 messageError  ERROR PARAMETER NULL ::= 8;
 SecurityProblem ::= INTEGER (0..127);

Banan Informational [Page 71] RFC 2524 EMSD February 1999

  1. -
  2. - EXPORTED Definitions (for use by associated specifications) –
  3. -
 ContentType ::=  INTEGER
 {
   -- Content type 0 is reserved and shall never be transmitted.
   reserved                                 (0),
   -- Content types between 1 and 31 (inclusive) are for
   -- internal-use only
   probe                                    (1), -- reserved
   delivery-report                          (2), -- reserved
  1. - Content types between 32 and 63 (inclusive) are for
  2. - message types defined within this specifications.

emsd-interpersonal-messaging-1995 (32),

   voice-messaging                          (33) -- reserved
  1. - Content types beyond and including 64 are for
  2. - bilaterally-agreed use between peers.

} (0..127);

  1. - If this message was originated as an RFC-822 message, then this
  2. - EMSDMessageId shall be the "Message-Id:" field from that message.
  3. - If this message was originated within the EMSD domain,
  4. - then this identifier shall be unique for the Message Center
  5. - generating this id.
 EMSDMessageId ::= CHOICE
 {
   emsdLocalMessageId     [APPLICATION 4]  IMPLICIT
                          EMSDLocalMessageId,
   rfc822MessageId        [APPLICATION 5]  IMPLICIT
                          AsciiPrintableString
                          (SIZE (0..ub-message-id-length))
 };
 EMSDLocalMessageId ::= SEQUENCE
 {
   submissionTime                  DateTime,
   messageNumber                   INTEGER (0..ub-local-message-nu)
 };
  1. - An Originator/Recipient Address in EMSD Environment
 EMSDORAddress ::= CHOICE
 {

Banan Informational [Page 72] RFC 2524 EMSD February 1999

  1. - This is the local-format address

emsd-local-address-format EMSDAddress,

  1. - This is a globally-unique RFC-822 Address

rfc822DomainAddress AsciiPrintableString

 };
 EMSDAddress ::= SEQUENCE
 {
   emsd-address         OCTET STRING
                                  (SIZE (1..ub-emsd-address-length)),
  1. - emsd-address is a decimal integer in BCD (Binary Encoded Decimal)
  2. - format.
  3. - If it had an odd number of digits, it is padded with 0 on
  4. - the left.
   emsd-name                [0]     IMPLICIT OCTET STRING
                                    (SIZE (0..ub-emsd-name-length))
                                    OPTIONAL
 };
 DateTime ::= INTEGER;
 Iso8859String ::=  GeneralString;
 AsciiPrintableString ::= [ APPLICATION 0 ]
                          IMPLICIT Iso8859String (FROM
     (" "|"!"|"#"|"$"|"%"|"&"|"'"|"("|")"|"*"|"+"|","|"-"|"."|"/"|
      "0"|"1"|"2"|"3"|"4"|"5"|"6"|"7"|"8"|"9"|":"|";"|"<"|"="|">"|
      "?"|"@"|"A"|"B"|"C"|"D"|"E"|"F"|"G"|"H"|"I"|"J"|"K"|"L"|"M"|
      "N"|"O"|"P"|"Q"|"R"|"S"|"T"|"U"|"V"|"W"|"X"|"Y"|"Z"|"["|"]"|
      "^"|"_"|"`"|"a"|"b"|"c"|"d"|"e"|"f"|"g"|"h"|"i"|"j"|"k"|"l"|
      "m"|"n"|"o"|"p"|"q"|"r"|"s"|"t"|"u"|"v"|"w"|"x"|"y"|"z"|"{"|
      "|"|"}"|"~"|"\"|""""));
 ProtocolVersionNumber ::= [APPLICATION 1]    SEQUENCE
 {
   version-major                   INTEGER,
   version-minor           [0]     IMPLICIT INTEGER DEFAULT 0
 }
 END  -- end of EMSD-SubmissionAndDeliveryProtocol

Banan Informational [Page 73] RFC 2524 EMSD February 1999

B EMSD-IPM ASN.1 MODULE

 This section compiles in one place the complete ASN.1 Module for
 EMSD-IPM.
 EMSD-InterpersonalMessaging1995 DEFINITIONS ::=
 BEGIN
 IMPORTS EMSDORAddress, EMSDMessageId, AsciiPrintableString
   FROM EMSD-SubmissionAndDeliveryProtocol;
 ub-recipients  INTEGER ::= 256;
 ub-reply-to INTEGER ::= 256;
 ub-subject-field INTEGER ::= 128;
 ub-header-extensions INTEGER ::= 64;
 ub-emsd-name-length INTEGER ::= 64;
 ub-mime-version-length INTEGER ::= 8;
 ub-mime-content-type-length INTEGER ::= 127;
 ub-mime-content-id-length INTEGER ::= 127;
 ub-mime-content-description-length INTEGER ::= 127;
 ub-mime-content-transfer-encoding INTEGER ::= 127;
 IPM ::=   SEQUENCE
 {
   heading                              Heading,
   body                                 Body OPTIONAL
 };
 Heading ::= SEQUENCE
 {
   -- Address of the sending agent (person, program, machine) of
   -- this message. This field is mandatory if the sender
   -- is different than the originator.
   sender                      [0]     EMSDORAddress OPTIONAL,
  1. - Address of the originator of the message
  2. - (not necessarily the sender)

originator EMSDORAddress,

  1. - List of recipients and flags associated with each.

recipient-data SEQUENCE SIZE (1..ub-recipients)

                                       OF PerRecipientFields,
  1. - Flags applying to this entire message

per-message-flags [1] IMPLICIT BIT STRING

Banan Informational [Page 74] RFC 2524 EMSD February 1999

   {
      -- Priority values
      -- At most one of "non-urgent" and "urgent" may be specified
      -- concurrently.  If neither is specified, then a Priority
      -- level of "normal" is assumed.
      priority-non-urgent             (0),
      priority-urgent                 (1),
  1. - Importance values
  2. - At most one of "low" and "high" may be specified
  3. - concurrently. If neither is specified, then an
  4. - Importance level of "normal" is assumed.

importance-low (2),

      importance-high                 (3),
  1. - Indication of whether this message has been automatically
  2. - forwarded

auto-forwarded (4)

    }  OPTIONAL,
  1. - User-specified recipient who is to receive replies to this
  2. - message.

reply-to [2] IMPLICIT SEQUENCE SIZE

                                       (1..ub-reply-to)
                                       OF EMSDORAddress OPTIONAL,
  1. - Identifier of a previous message, for which this message
  2. - is a reply

replied-to-IPM EMSDMessageId OPTIONAL,

  1. - Subject of the message.

subject [3] IMPLICIT AsciiPrintableString

                                       (SIZE (0..ub-subject-field))
                                                 OPTIONAL,
  1. - RFC-822 header fields not explicitly provided for in
  2. - this Heading. For messages incoming from the external
  3. - world (i.e. in RFC-822 format), the Message-Id: field
  4. - need not go here, as it is placed in the
  5. - Envelope's EMSDMessageId (message-id) field.

extensions [4] IMPLICIT SEQUENCE

                             (SIZE (0..ub-header-extensions))
                                   OF  IPMSExtension OPTIONAL,
  1. - MIME Version (if other than 1.0)

mime-version [5] IMPLICIT AsciiPrintableString

                                   (SIZE
                                   (0..ub-mime-version-length))

Banan Informational [Page 75] RFC 2524 EMSD February 1999

                                           OPTIONAL,
  1. - Top-level MIME Content Type

mime-content-type [6] IMPLICIT AsciiPrintableString

                                   (SIZE (0..
                                    ub-mime-content-type-length))
                                              OPTIONAL,
  1. - MIME Content Id

mime-content-id [7] IMPLICIT AsciiPrintableString

                                   (SIZE (0..
                                    ub-mime-content-id-length))
                                             OPTIONAL,
  1. - MIME Content Description

mime-content-description [8] IMPLICIT AsciiPrintableString

                                   (SIZE (0..
                                ub-mime-content-description-length))
                                             OPTIONAL,
  1. - Top-level MIME Content Type

mime-content-transfer-encoding

                            [9]     IMPLICIT AsciiPrintableString
                      (SIZE (0..ub-mime-content-transfer-encoding))
                                                OPTIONAL
 };
 PerRecipientFields ::= SEQUENCE
 {
   recipient-address                            EMSDORAddress,
   per-recipient-flags                          BIT STRING
    {
       -- Recipient Types.
       -- At most one of "copy" and "blind-copy" may be
       -- specified concurrently for a single recipient.  If
       -- neither is specified, than the recipient
       -- is assumed to be a "primary" recipient.
       recipient-type-copy                             (0),
       recipient-type-blind-copy                       (1),
  1. - Notification Request Types.
  2. - Only one of "rn" and "nrn" may be specified
  3. - concurrently, \x110011 for a single recipient.
  4. - "rn" implies "nrn" in addition.

notification-request-rn (2),

       notification-request-nrn                        (3),
       notification-request-ipm-return                 (4),

Banan Informational [Page 76] RFC 2524 EMSD February 1999

  1. - Report Request Types
  2. - At most one of these should be set for a
  3. - particular recipient. "delivery" implies "non-delivery"
  4. - in addition.

report-request-non-delivery (5),

       report-request-delivery                         (6),
  1. - Originator-to-Recipient request for a reply.

reply-requested (7)

    }  DEFAULT { report-request-non-delivery }
 };
 IPMSExtension ::= SEQUENCE
 {
   x-header-label                      AsciiPrintableString,
   x-header-value                      AsciiPrintableString
 };
 Body ::= SEQUENCE
 {
   compression-method          [0]     IMPLICIT CompressionMethod
                                                  OPTIONAL,
   -- If compression method is not specified,
   -- "no-compression" is implied.
   message-body                        OCTET STRING
   -- See MIME for structure of the Body.
   -- If a compression method is specified, the entire text containing
   -- the Content-Type: element followed by the RFC-822 body are
   -- compressed using the specified method, and placed herein.
 };
 CompressionMethod ::= INTEGER
 {
   -- Compression Methods numbered 0 to 63 are reserved for
   -- assignment within this and associated specifications.
   no-compression                  (0),
   lempel-ziv                      (1)
  1. - Compression Methods numbered between 64 and 127 may be
  2. - used on a bilaterally-agreed basis between peers.

} (0..127)

 END  -- end of EMSD-InterpersonalMessaging1995

Banan Informational [Page 77] RFC 2524 EMSD February 1999

C RATIONALE FOR KEY DESIGN DECISIONS

 This section summarizes the rationale behind key design decisions
 that were made while developing the EMSD Protocols.

C.1 Deviation From The SMTP Model

 SMTP is the main mail transport mechanism throughout the Internet.
 SMTP is widely deployed and well understood by many engineers who
 specialize in Internet email.  Because of these reasons, works based
 on SMTP or derived from it have a higher likelyhood of being widely
 deployed throughout the Internet.
 However, SMTP is highly inefficient for transfer of short messages.
 SMTP's inefficiency applies to both the number of transmissions and
 also to the number of bytes transmitted.
 Even when fully optimized with PIPELINING, SMTP is still quite
 inefficient.
 Submission of a short message with SMTP involves 15 transmissions.
 Submission of a short message with SMTP and PIPELINING involves 9
 transmissions.  Submission of a short message with EMSD (EMSD-P and
 ESRO) involves 3 transmissions (in typical cases).
 The key requirement driving the design of EMSD is efficiency.  It was
 determined that the at least 3 fold gains in efficiency justifies the
 deviation from the SMTP model.

C.1.1 Comparison of SMTP and EMSD Efficiency

 The table below illustrates the number of N-PDUs exchanged for
 transfer of a short Internet email when using SMTP, SMTP and
 PIPELINING, QMTP and EMSD. The names used for identifying the PDUs
 are informal names.
         SMTP      SMTP + pipelining   QMTP, QMQP,   EMSD
         -------   -----------------   ------------  -----------
 client: SYN       SYN                 SYN           Submit.Req
 server: SYN ok    SYN ok              SYN           Submit.Resp
 client: HELO      EHLO                message       ack
 server: ok        PIPELINING          accept close
 client: MAIL      MAIL RCPT DATA      close
 server: ok        ok
 client: RCPT      message QUIT
 server: ok        accept ok close
 client: DATA      close
 server: ok

Banan Informational [Page 78] RFC 2524 EMSD February 1999

 client: message
 server: accept
 client: QUIT
 server: ok close
 client: close

C.2 Use of ESRO Instead of TCP

 In order to provide the same level of reliability that the existing
 email protocols provide for short messages, it is clear that a
 reliable underlying service is needed.  UDP [6], by itself, is
 clearly not adequate.
 Use of TCP however, involves three phases:
    1. Connection Establishment
    2. Data Transfer
    3. Disconnect
 Reliable transfer of a short message using TCP at a minimum involves
 5 transmissions as it is the case with QMTP.
 The key requirement driving the design of EMSD is Efficiency.  It was
 determined that elimination of the extra 2 transmissions that are an
 inherent characteristic of TCP, justifies deviation from it.
 ESRO protocol, as specified in (RFC-2188 [1]), provides reliable
 connectionless remote operation services on top of UDP [6] with
 minimum overhead.  ESRO protocol supports segmentation and
 reassembly, concatenation and separation.
 Reliable transfer of a short message using ESRO involves 3
 transmissions as it is the case with EMSD-P.

C.3 Use Of Remote Procedure Call (RPC) Model

 Many Internet protocols are "text-based".  Few Internet protocols are
 RPC based.  Protocols designed around the "text-based" approach have
 a better track record of acceptance throughout the Internet.
 Considering that message submission and delivery in EMSD involve no
 more than two data exchanges, the text-based model becomes the same
 as an operation.  Furthermore, the RPC model is the natural way of
 using ESRO.

Banan Informational [Page 79] RFC 2524 EMSD February 1999

C.4 Use Of ASN.1

 In order to minimize the number of bytes transferred, efficient
 encoding mechanisms are needed.
 Amongst today's encoding mechanisms, ASN.1 has the unique feature of
 separating the abstract syntax from the encoding rules.  By selecting
 ASN.1 as the notation used for expressing EMSD's information objects,
 EMSD has the flexibility of using the most efficient encoding rules
 such as Packed Encoding Rules (PER) when they are available.
 Efficient encoding can always be better performed when the syntax of
 the information is known.  In general, encoding and compression
 techniques which use the knowledge of the syntax of the information
 produce better results than those compression techniques that work on
 arbitrary text.

Banan Informational [Page 80] RFC 2524 EMSD February 1999

D FURTHER DEVELOPMENT

 Beyond this documentation of existing implementations, further
 development of EMSD protocol is anticipated.
 The following deficiencies and areas of improvement are identified.
    o Mapping of RFC-822 to EMSD-FS needs to be more explicit.
    o Mapping of EMSD-FS to RFC-822 needs to be more explicit.
    o Text of duplicate detection section needs more structure.
    o SubmissionControl operation needs more informative description.
    o Based on implementor's feedback the "EMSD PROCEDURE FOR
      OPERATIONS" section needs to be adjusted or re-done.
    o The EMSD protocol can be extended to also support transfer of
      raw RFC-822 text-based messages in addition to EMSD-FS. This
      would be a trade-off in favor of "ease of implementation"
      against "efficiency of bytes transfered".
    o Provide mechanisms to support fully automated initial
      provisioning of mail-boxes.
 Future development of the EMSD Protocol is anticipated to take place
 at http://www.emsd.org/.  Those interested in further development and
 maintenance of this protocol are invited to join the various mailing
 lists hosted at http://www.emsd.org/.

Banan Informational [Page 81] RFC 2524 EMSD February 1999

E. References

 [1] Banan, M., Cheng, J. and M. Taylor, "At&t/neda's efficient short
     remote operations (ESRO) protocol specification version 1.2.",
     RFC 2188, September 1997.
 [2] Bradner, S., "Key words for use in RFCs to indicate requirement
     levels", BCP 14, RFC 2119, March 1997.
 [3] Crocker, D., "Standard for the format of ARPA internet text
     messages", STD 11, RFC 822, August 1982.
 [4] Information Processing --- Open Systems Interconnection ---
     Specification of Packed Encoding Rules for Abstract Syntax
     Notation One (ASN.1). International Organization for
     Standardization and International Electrotechnical Committee.
     International Standard 8825-2.
 [5] Information Processing --- Open Systems Interconnection ---
     Specification of Basic Encoding Rules for Abstract Syntax
     Notation One (ASN.1). International Organization for
     Standardization and International Electrotechnical Committee,
     1987. International Standard 8825.
 [6] Postel, J., "User Datagram Protocol", STD 6, RFC 768, August
     1980.

Banan Informational [Page 82] RFC 2524 EMSD February 1999

F. 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.

Banan Informational [Page 83]

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