rfc2524.txt

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    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.






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    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





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   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].



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   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



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       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.







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   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



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      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:



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         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.