Network Working Group M. Banan
Request for Comments: 2524 Neda Communications, Inc.
Category: Informational February 1999
Neda's
Efficient Mail Submission and Delivery (EMSD)
Protocol Specification Version 1.3
Status of this Memo
This memo provides information for the Internet community. It does
not specify an Internet standard of any kind. Distribution of this
memo is unlimited.
Copyright Notice
Copyright (C) The Internet Society (1999). All Rights Reserved.
IESG Note
The protocol specified in this document may be satisfactory for
limited use in private wireless IP networks. However, it is
unsuitable for general-purpose message transfer or for transfer of
messages over the public Internet, because of limitations that
include the following:
- Lack of congestion control
EMSD is layered on ESRO [RFC 2188], which does not provide
congestion control. This makes EMSD completely unsuitable for
end-to-end use across the public Internet. EMSD should be
considered for use in a wireless network only if all EMSD email
exchanged between the wireless network and the public Internet
will transit an EMSD<->SMTP gateway between the two regions.
- Inadequate security
The document specifies only clear-text passwords for
authentication. EMSD should be used across a wireless network
only if sufficiently strong encryption is in use to protect the
clear-text password.
- Lack of character set internationalization
EMSD has no provision for representation of characters outside of
the ASCII repertoire or for language tags.
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- Poorly defined gatewaying to and from Internet Mail
Because Internet Mail and EMSD have somewhat different and
conflicting service models and different data models, mapping
between them may provide good service only in limited cases, and
this may cause operational problems.
The IESG therefore recommends that EMSD deployment be limited to
narrow circumstances, i.e., only to communicate with devices that
have inherent limitations on the length and format of a message (no
more than a few hundred bytes of ASCII text), using either:
a. wireless links with adequate link-layer encryption and gatewayed
to the public Internet, or
b. a private IP network that is either very over-provisioned or has
some means of congestion control.
In the near future, the IESG may charter a working group to define an
Internet standards-track protocol for efficient transmission of
electronic mail messages, which will be highly compatible with
existing Internet mail protocols, and which wil be suitable for
operation over the global Internet, including both wireless and wired
links.
ABSTRACT
This document specifies the protocol and format encodings for
Efficient Mail Submission and Delivery (EMSD). EMSD is a messaging
protocol that is highly optimized for submission and delivery of
short Internet mail messages. EMSD is designed to be a companion to
existing Internet mail protocols.
This specification narrowly focuses on submission and delivery of
short mail messages with a clear emphasis on efficiency. EMSD is
designed specifically with wireless network (e.g., CDPD, Wireless-IP,
Mobile-IP) usage in mind. EMSD is designed to be a natural
enhancement to the mainstream of Internet mail protocols when
efficiency in mail submission and mail delivery are important. As
such, EMSD is anticipated to become an initial basis for convergence
of Internet Mail and IP-based Two-Way Paging.
The reliability requirement for message submission and message
delivery in EMSD are the same as existing email protocols. EMSD
protocol accomplishes reliable connectionless mail submission and
delivery services on top of Efficient Short Remote Operations (ESRO)
protocols as specified in RFC-2188 [1].
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Most existing Internet mail protocols are not efficient. Most
existing Internet mail protocols are designed with simplicity and
continuity with SMTP traditions as two primary requirements. EMSD is
designed with efficiency as a primary requirement.
The early use of EMSD in the wireless environment is manifested as
IP-based Two-Way Paging services. The efficiency of this protocol
also presents significant benefits for large centrally operated
Internet mail service providers.
Table of Contents
1 PRELIMINARIES 4
1.1 Internet Mail Submission and Delivery . . . . 4
1.2 Relationship Of EMSD To Other Mail Protocols . . . 5
1.3 EMSD Requirements and Goals . . . . . . . 7
1.4 Anticipated Uses Of EMSD . . . . . . . . 8
1.5 Definitions of Terms Used in this Specification . . 9
1.6 Conventions Used In This Specification . . . . 9
1.7 About This Specification . . . . . . . . 10
2 EFFICIENT MAIL SUBMISSION AND DELIVERY OVERVIEW 10
3 EFFICIENT MAIL SUBMISSION AND DELIVERY PROTOCOL 11
3.1 Use Of Lower Layers . . . . . . . . . 13
3.1.1 Use of ESROS . . . . . . . . . 13
3.1.2 Use Of UDP . . . . . . . . . . 13
3.1.3 Encoding Rules . . . . . . . . . 13
3.1.4 Presentation Context . . . . . . . 14
3.2 EMSD-UA Invoked Operations . . . . . . . 14
3.2.1 submit . . . . . . . . . . . 14
3.2.2 deliveryControl . . . . . . . . 17
3.2.3 deliveryVerify . . . . . . . . . 21
3.3 EMSD-SA Invoked Operations . . . . . . . 23
3.3.1 deliver . . . . . . . . . . 23
3.3.2 submissionControl . . . . . . . . 25
3.3.3 submissionVerify . . . . . . . . 28
3.4 EMSD Common Information Objects . . . . . . 30
3.4.1 SecurityElements . . . . . . . . 30
3.4.2 Message Segmentation and Reassembly . . . 30
3.4.3 Common Errors . . . . . . . . . 33
3.4.4 ContentType . . . . . . . . . 35
3.4.5 EMSDMessageId . . . . . . . . . 35
3.4.6 EMSDORAddress . . . . . . . . . 36
3.4.7 EMSDAddress . . . . . . . . . 36
3.4.8 DateTime . . . . . . . . . . 36
3.4.9 AsciiPrintableString . . . . . . . 37
3.4.10 ProtocolVersionNumber . . . . . . . 37
3.5 Submission and Delivery Procedures . . . . . 38
4 DUPLICATE OPERATION DETECTION SUPPORT 40
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4.1 Duplicate Operation Detection Support Overview . . 40
4.1.1 Operation Value . . . . . . . . 40
4.1.2 Operation Instance Identifier . . . . . 41
5 EMSD PROCEDURE FOR OPERATIONS 42
5.1 MTS Behavior . . . . . . . . . . . 43
5.1.1 MTS Performer . . . . . . . . . 43
5.1.2 Message-submission . . . . . . . . 44
5.1.3 Delivery-control . . . . . . . . 46
5.1.4 Delivery-verify . . . . . . . . 46
5.1.5 MTS Invoker . . . . . . . . . 46
5.2 UA Behavior . . . . . . . . . . . 49
5.2.1 UA Performer . . . . . . . . . 49
5.2.2 UA Invoker . . . . . . . . . . 52
6 EMSD FORMAT STANDARDS 54
6.1 Format Standard Overview . . . . . . . . 54
6.2 Interpersonal Messages . . . . . . . . 54
6.2.1 Heading fields . . . . . . . . . 55
6.2.2 Body part types . . . . . . . . 61
7 ACKNOWLEDGMENTS 62
8 SECURITY CONSIDERATIONS 62
9 AUTHOR'S ADDRESS 62
A EMSD-P ASN.1 MODULE 63
B EMSD-IPM ASN.1 MODULE 74
C RATIONALE FOR KEY DESIGN DECISIONS 78
C.1 Deviation From The SMTP Model . . . . . . 78
C.1.1 Comparison of SMTP and EMSD Efficiency . . . 78
C.2 Use of ESRO Instead of TCP . . . . . . . 79
C.3 Use Of Remote Procedure Call (RPC) Model . . . . 79
C.4 Use Of ASN.1 . . . . . . . . . . . 80
D FURTHER DEVELOPMENT 81
E REFERENCES 82
F FULL COPYRIGHT STATEMENT 83
1 PRELIMINARIES
Mail in the Internet was not a well-planned enterprise, but instead
arose in more of an "organic" way.
This introductory section is not intended to be a reference model and
concept vocabulary for mail in the Internet. Instead, it only
provides the necessary preliminaries for the concepts and terms that
are essential to this specification.
1.1 Internet Mail Submission and Delivery
For the purposes of this specification, mail submission is the
process of putting mail into the mail transfer system (MTS).
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For the purposes of this specification, mail delivery is the process
of the MTS putting mail into a user's final mail-box.
Throughout the Internet, presently most of mail submission and
delivery is done through SMTP.
SMTP was defined as a message *transfer* protocol, that is, a means
to route (if needed) and deliver mail by putting finished (complete)
messages in a mail-box. Originally, users connected to servers from
terminals, and all processing occurred on the server. Now, a split-
MUA (Mail User Agent) model is common, with MUA functionality
occurring on both the user's own system and the server.
In the split-MUA model, getting the messages to the user is
accomplished through access to a mail-box on the server through such
protocols as POP and IMAP. In the split-MUA model, user's access to
its message is a "Message Pull" paradigm where the user is required
to poll his mailbox. Proper message delivery based on a "Message
Push" paradigm is presently not supported. The EMSD protocol
addresses this shortcoming with an emphasis on efficiency.
In the split-MUA model, message submission is often accomplished
through SMTP. SMTP is widely used as a message *submission* protocol.
Widespread use of SMTP for submission is a reality, regardless of
whether this is good or bad. EMSD protocol provides an alternative
mechanism for message submission which emphasizes efficiency.
1.2 Relationship Of EMSD To Other Mail Protocols
Various Internet mail protocols facilitate accomplishment of various
functions in mail processing.
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Figure 1, categorizes the capabilities of SMTP, IMAP, POP and EMSD
based on the following functions:
+------------------+------+-------+-----+------+
| Protocols| SMTP | IMAP | POP | EMSD |
|Functions | | | | |
|------------------|------|-------|-----|------|
|Submission | XX | | | XXX |
|------------------|------|-------|-----|------|
|Delivery | XXX | | | XXX |
|------------------|------|-------|-----|------|
|Relay (Routing) | XXX | | | |
|------------------|------|-------|-----|------|
|Retrieval | | XXX | XXX | XX |
|------------------|------|-------|-----|------|
|Mailbox Access | | XXX | X | |
|------------------|------|-------|-----|------|
|Mailbox Synch. | | XXX | | |
+------------------+------+-------+-----+------+
Figure 1: Messaging Protocols vs. Supported Functions
o Mail Submission
o Mail Delivery
o Mail Routing (Relay)
o Mail Retrieval
o Mail-box Access
o Mail-box Synchronization
In Figure 1, the number of "X"es in each box denotes the extent to
which a particular function is supported by a particular protocol.
Figure 1 clearly shows that combinations of these protocols can be
used to complement each other in providing rich functionality to the
user. For example, a user interested in highly mobile messaging
functionalities can use EMSD for "submission and delivery of time
critical and important messages" and use IMAP for comprehensive
access to his/her mail-box.
For mail submission and delivery of short messages EMSD is up to 5
times more efficient than SMTP both in terms of the number of packets
transmitted and in terms of number of bytes transmitted. Even with
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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.
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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.
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;
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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,
-- Segmentation features for efficient transport
segment-info SegmentInfo OPTIONAL,
-- Content type of the message
content-type ContentType,
--
-- THE CONTENT --
--
-- 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".
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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.
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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,
-- Which operations are to be placed in the restriction set
permissible-operations [1] IMPLICIT Operations OPTIONAL,
-- What maximum content length should be allowed
permissible-max-content-length
[2] IMPLICIT INTEGER
(0..ub-content-length) OPTIONAL,
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-- What is the lowest priority message which may be delivered
permissible-lowest-priority
[3] IMPLICIT ENUMERATED
{
non-urgent (0),
normal (1),
urgent (2)
} OPTIONAL,
-- Security features
security [4] IMPLICIT SecurityElement
OPTIONAL,
-- 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.
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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 { },
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-- Types of messages queued at the EMSD-SA due to
-- existing restrictions
waiting-messages [1] IMPLICIT WaitingMessages
DEFAULT { },
-- 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.
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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
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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
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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;
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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,
-- Time the message was delivered to the recipient by EMSD-SA
message-delivery-time DateTime,
-- Time EMSD-SA originally took responsibility for processing
-- of this message. This field shall be omitted if the message-id
-- contains an EMSDLocalMessageId, because that field contains
-- the submission time within it.
message-submission-time [0] IMPLICIT DateTime OPTIONAL,
-- Security features
security [1] IMPLICIT SecurityElement OPTIONAL,
-- SegContentTypementation features for efficient transport
segment-info SegmentInfo OPTIONAL,
-- The type of the content
content-type ContentType,
--
-- THE CONTENT --
--
-- The submitted (and now being delivered) content
content ANY DEFINED BY content-type
};
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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.
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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,
-- Which operations are to be placed in the restriction set
permissible-operations [1] IMPLICIT Operations OPTIONAL,
-- What maximum content length should be allowed
permissible-max-content-length
[2] IMPLICIT INTEGER
(0..ub-content-length) OPTIONAL,
-- 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.
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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 { }
};
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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
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-- 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
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.
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3.4 EMSD Common Information Objects
3.4.1 SecurityElements
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
};
-- StrongCredentials ::= NULL
-- for now.
-- 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,
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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.
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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
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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);
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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.
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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
-- Content types between 32 and 63 (inclusive) are for
-- message types defined within this specifications.
emsd-interpersonal-messaging-1995 (32),
voice-messaging (33) -- reserved
-- Content types beyond and including 64 are for
-- 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
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(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,
-- 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;
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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
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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.
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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.
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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.
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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.
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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.
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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
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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.
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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.
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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.
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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.
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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.
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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
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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.
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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
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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
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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.
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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,
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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,
-- Address of the originator of the message
-- (not necessarily the sender)
originator EMSDORAddress,
-- List of recipients and flags associated with each.
recipient-data SEQUENCE SIZE (1..ub-recipients)
OF PerRecipientFields,
-- 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),
-- Importance values
-- At most one of "low" and "high" may be specified
-- concurrently. If neither is specified, then an
-- Importance level of "normal" is assumed.
importance-low (2),
importance-high (3),
-- Indication of whether this message has been
automatically forwarded
auto-forwarded (4)
} OPTIONAL,
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-- User-specified recipient who is to receive replies
to this message.
reply-to [2] IMPLICIT SEQUENCE SIZE
(1..ub-reply-to)
OF EMSDORAddress OPTIONAL,
-- Identifier of a previous message, for which this message
-- is a reply
replied-to-IPM EMSDMessageId OPTIONAL,
-- Subject of the message.
subject [3] IMPLICIT AsciiPrintableString
(SIZE (0..ub-subject-field))
OPTIONAL,
-- RFC-822 header fields not explicitly provided for in
-- this Heading. For messages incoming from the external
-- world (i.e. in RFC-822 format), the Message-Id: field
-- need not go here, as it is placed in the
-- Envelope's EMSDMessageId (message-id) field.
extensions [4] IMPLICIT SEQUENCE
(SIZE (0..ub-header-extensions))
OF IPMSExtension OPTIONAL,
-- MIME Version (if other than 1.0)
mime-version [5] IMPLICIT AsciiPrintableString
(SIZE (0..ub-mime-version-length))
OPTIONAL,
-- Top-level MIME Content Type
mime-content-type [6] IMPLICIT AsciiPrintableString
(SIZE (0..
ub-mime-content-type-length))
OPTIONAL,
-- MIME Content Id
mime-content-id [7] IMPLICIT AsciiPrintableString
(SIZE (0..
ub-mime-content-id-length))
OPTIONAL,
-- 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
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[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),
-- Notification Request Types.
-- Only one of "rn" and "nrn" may be specified
-- concurrently, \x110011 for a single recipient.
-- "rn" implies "nrn" in addition.
notification-request-rn (2),
notification-request-nrn (3),
notification-request-ipm-return (4),
-- Report Request Types
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-- At most one of these should be set for a
-- particular recipient. "delivery" implies "non-delivery"
-- in addition.
report-request-non-delivery (5),
report-request-delivery (6),
-- 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.
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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.
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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.
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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.
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no-compression (0),
lempel-ziv (1)
-- Compression Methods numbered between 64 and 127 may be
-- 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
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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;
-- 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;
----------------------
-- SUBMIT Operation --
----------------------
submit ES-OPERATION
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ARGUMENT SubmitArgument
RESULT SubmitResult
ERRORS
{
submissionControlViolated,
securityError,
resourceError,
protocolViolation,
messageError
} ::= 33;
SubmitArgument ::= SEQUENCE
{
-- Security features
security [0] IMPLICIT SecurityElement
OPTIONAL,
-- Segmentation features for efficient transport
segment-info SegmentInfo OPTIONAL,
-- Content type of the message
content-type ContentType,
--
-- THE CONTENT --
--
-- The submission content
content ANY DEFINED BY content-type
};
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
};
--------------------------------
-- Delivery Control Operation --
--------------------------------
deliveryControl ES-OPERATION
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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,
-- Which operations are to be placed in the restriction set
permissible-operations [1] IMPLICIT Operations OPTIONAL,
-- What maximum content length should be allowed
permissible-max-content-length
[2] IMPLICIT INTEGER
(0..ub-content-length) OPTIONAL,
-- What is the lowest priority message which may be delivered
permissible-lowest-priority
[3] IMPLICIT ENUMERATED
{
non-urgent (0),
normal (1),
urgent (2)
} OPTIONAL,
-- Security features
security [4] IMPLICIT SecurityElement
OPTIONAL,
-- 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 { },
-- Types of messages queued at the EMSD-SA due to
-- existing restrictions
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waiting-messages [1] IMPLICIT WaitingMessages DEFAULT { },
-- 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)
};
-- 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
};
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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)
};
-----------------------
-- DELIVER Operation --
-----------------------
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,
-- Time the message was delivered to the recipient by EMSD-SA
message-delivery-time DateTime,
-- Time EMSD-SA originally took responsibility for processing
-- of this message. This field shall be omitted if the message-id
-- contains an EMSDLocalMessageId, because that field contains
-- the submission time within it.
message-submission-time [0] IMPLICIT DateTime OPTIONAL,
-- Security features
security [1] IMPLICIT SecurityElement OPTIONAL,
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-- SegContentTypementation features for efficient transport
segment-info SegmentInfo OPTIONAL,
-- The type of the content
content-type ContentType,
--
-- THE CONTENT --
--
-- The submitted (and now being delivered) content
content ANY DEFINED BY content-type
};
-- 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,
-- Which operations are to be placed in the restriction set
permissible-operations [1] IMPLICIT Operations OPTIONAL,
-- What maximum content length should be allowed
permissible-max-content-length
[2] IMPLICIT INTEGER
(0..ub-content-length) OPTIONAL,
-- Security features
security [3] IMPLICIT SecurityElement
OPTIONAL
};
SubmissionControlResult ::= SEQUENCE
{
-- Operation types queued at the EMSD-SA due to existing
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-- restrictions.
waiting-operations [0] IMPLICIT Operations DEFAULT { }
};
----------------------------------
-- Submission Verify Operation --
----------------------------------
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)
};
-- GetConfiguration Operation
-- To be fully defined later. This will possibly include,
-- but not be limited to:
-- get-local-time-zone
-- get-protocol-version
-- etc.
getConfiguration ES-OPERATION
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ARGUMENT NULL
RESULT NULL
ERRORS
{
resourceError,
protocolViolation
} ::= 7;
-- SetConfiguration Operation
-- To be fully defined later.
setConfiguration ES-OPERATION
ARGUMENT NULL
RESULT NULL
ERRORS
{
resourceError,
protocolViolation
} ::= 8;
-- 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
};
-- StrongCredentials ::= NULL
-- for now.
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-- 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
};
-----------
-- 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);
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RFC 2524 EMSD February 1999
--
-- EXPORTED Definitions (for use by associated specifications) --
--
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
-- Content types between 32 and 63 (inclusive) are for
-- message types defined within this specifications.
emsd-interpersonal-messaging-1995 (32),
voice-messaging (33) -- reserved
-- Content types beyond and including 64 are for
-- bilaterally-agreed use between peers.
} (0..127);
-- 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 Message Center
-- 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)
};
-- An Originator/Recipient Address in EMSD Environment
EMSDORAddress ::= CHOICE
{
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-- This is the local-format address
emsd-local-address-format EMSDAddress,
-- This is a globally-unique RFC-822 Address
rfc822DomainAddress AsciiPrintableString
};
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
};
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
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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,
-- Address of the originator of the message
-- (not necessarily the sender)
originator EMSDORAddress,
-- List of recipients and flags associated with each.
recipient-data SEQUENCE SIZE (1..ub-recipients)
OF PerRecipientFields,
-- Flags applying to this entire message
per-message-flags [1] IMPLICIT BIT STRING
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{
-- 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),
-- Importance values
-- At most one of "low" and "high" may be specified
-- concurrently. If neither is specified, then an
-- Importance level of "normal" is assumed.
importance-low (2),
importance-high (3),
-- Indication of whether this message has been automatically
-- forwarded
auto-forwarded (4)
} OPTIONAL,
-- User-specified recipient who is to receive replies to this
-- message.
reply-to [2] IMPLICIT SEQUENCE SIZE
(1..ub-reply-to)
OF EMSDORAddress OPTIONAL,
-- Identifier of a previous message, for which this message
-- is a reply
replied-to-IPM EMSDMessageId OPTIONAL,
-- Subject of the message.
subject [3] IMPLICIT AsciiPrintableString
(SIZE (0..ub-subject-field))
OPTIONAL,
-- RFC-822 header fields not explicitly provided for in
-- this Heading. For messages incoming from the external
-- world (i.e. in RFC-822 format), the Message-Id: field
-- need not go here, as it is placed in the
-- Envelope's EMSDMessageId (message-id) field.
extensions [4] IMPLICIT SEQUENCE
(SIZE (0..ub-header-extensions))
OF IPMSExtension OPTIONAL,
-- MIME Version (if other than 1.0)
mime-version [5] IMPLICIT AsciiPrintableString
(SIZE
(0..ub-mime-version-length))
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OPTIONAL,
-- Top-level MIME Content Type
mime-content-type [6] IMPLICIT AsciiPrintableString
(SIZE (0..
ub-mime-content-type-length))
OPTIONAL,
-- MIME Content Id
mime-content-id [7] IMPLICIT AsciiPrintableString
(SIZE (0..
ub-mime-content-id-length))
OPTIONAL,
-- 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
[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),
-- Notification Request Types.
-- Only one of "rn" and "nrn" may be specified
-- concurrently, \x110011 for a single recipient.
-- "rn" implies "nrn" in addition.
notification-request-rn (2),
notification-request-nrn (3),
notification-request-ipm-return (4),
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RFC 2524 EMSD February 1999
-- Report Request Types
-- At most one of these should be set for a
-- particular recipient. "delivery" implies "non-delivery"
-- in addition.
report-request-non-delivery (5),
report-request-delivery (6),
-- 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)
-- Compression Methods numbered between 64 and 127 may be
-- used on a bilaterally-agreed basis between peers.
} (0..127)
END -- end of EMSD-InterpersonalMessaging1995
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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
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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.
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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.
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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/.
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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.
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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.
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