RFC 2524
Neda's Efficient Mail Submission and Delivery (EMSD) Protocol Specification Version 1.3
RFC 2524: Neda's Efficient Mail Submission and Delivery (EMSD) Protocol Specification Version 1.3 💖
Okay bestie, so this one is RFC 2524 🎀, written by M. Banan of Neda Communications, Inc. ✨, and dated February 1999. It's marked Informational 🌸, so it's here to share info with the Internet community and doesn't set an Internet standard. It doesn't list anything it obsoletes or updates, so it's giving independent little side quest energy 🧚.
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 🚨
Okay, this part is important, so read it carefully 👀. The protocol 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. 🙈
- 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 will 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]. 🦋
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
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 831. PRELIMINARIES ✨
Okay so mail on the Internet was not a super well-planned thing 🌿. It kinda grew in a more "organic" way, you know? 🌱
This introductory section is not meant to be a reference model and concept vocabulary for mail in the Internet. Instead, it only gives 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). 📮
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, most mail submission and delivery is currently done through SMTP. 🌐
SMTP was defined as a message transfer protocol, which means a way 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 happened on the server. Now, a split-MUA (Mail User Agent) model is common, with MUA functionality happening on both the user's own system and the server. 🖥️✨
In the split-MUA model, getting messages to the user happens through access to a mail-box on the server, using protocols such as POP and IMAP. In that model, the user's access to their messages is a "Message Pull" paradigm, where the user is required to poll their mailbox. Proper message delivery based on a "Message Push" paradigm is not currently supported. The EMSD protocol addresses this shortcoming with an emphasis on efficiency. 🚀
In the split-MUA model, message submission often happens through SMTP. SMTP is widely used as a message submission protocol. Widespread use of SMTP for submission is a reality, regardless of whether that is good or bad. The EMSD protocol provides an alternative mechanism for message submission that emphasizes efficiency. 💖
1.2 Relationship Of EMSD To Other Mail Protocols ✨
Okay bestie, so there are a bunch of Internet mail protocols, and each one handles different jobs in mail processing 💌
Figure 1 sorts out what SMTP, IMAP, POP and EMSD are each good at, based on these 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 FunctionsThe functions in that chart are:
- Mail Submission
- Mail Delivery
- Mail Routing (Relay)
- Mail Retrieval
- Mail-box Access
- Mail-box Synchronization
In Figure 1, the more "X"es you see in a box, the more that protocol supports that function 💅
Figure 1 totally shows that these protocols can team up and complement each other to give the user a rich experience 🫶 For example, someone who's super mobile and wants messaging that's on the go can use EMSD for "submission and delivery of time critical and important messages" and then use IMAP for full access to their 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 the number of bytes transmitted 🔥 Even with PIPELINING and other possible optimizations of SMTP, EMSD is still up to 3 times more efficient than SMTP, both in terms of packets and bytes transmitted 🚀 There are various efficiency studies comparing EMSD with SMTP, POP and IMAP out there. See Section C.1.1 for more info about how SMTP and EMSD's efficiency compare 🦋
1.3 EMSD Requirements and Goals 🎯
These are the requirements and goals that drove the design of the EMSD protocol, bestie 💖
- Provide for submission of short mail messages with the same level of functionality (or higher) that the existing Internet mail protocols provide.
- Provide for delivery of short mail messages with the same level of functionality (or higher) that the existing Internet mail protocols provide.
- Function as an extension of the existing mainstream Internet mail.
- Minimize the number of transmissions.
- Minimize the number of bytes transmitted.
- Be quick: minimize latency of message submission and delivery.
- Provide the same level of reliability (or higher) that the existing email protocols provide.
- 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.
- 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). 🔋
- 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. 🌈
- 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. 🔐
- Easy to implement: Re-use existing technology as much as possible. 🧚
1.4 Anticipated Uses Of EMSD 🌸
Any network and network operator that has significant bandwidth and capacity limitations can benefit from EMSD. Any network user who has to bear high costs for measured network usage can benefit from it too ✨
The initial use 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 protocol addressing requirements specific to a particular user's environment is likely to be developed. That kind of diversity on the edges of the network is 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 meant to help you picture the 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].
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 is a point-of-record. It documents information exchanges and behaviors of existing implementations, and it is a basis for implementing efficient mail submission and delivery user agents and servers 🌟
This specification was developed entirely outside of the IETF. It had the benefit of review by many people outside of the IETF, and much has been learned from existing implementations of this protocol 🙈 A number of deficiencies and areas of improvement have been identified, and they 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 the IETF 🌈
2. EFFICIENT MAIL SUBMISSION AND DELIVERY OVERVIEW ✨
Okay, bestie, this section is the big-picture tour 🗺️🫶 It's the "here's how the whole EMSD thing fits together" moment before we get into the nitty-gritty.
The EMSD-P&FS (Efficient Mail Submission and Delivery Protocol and Format Standards 💅) are what move messages between the EMSD - Server Agent (think a Message Center 📟) and the EMSD - User Agent (think a Two-Way Pager 🧚). See Figure 2 below for the vibe.
This spec defines the protocols between an EMSD - User Agent (EMSD-UA) and an EMSD - Server Agent (EMSD-SA). The EMSD-P&FS is made of two independent components, and honestly they're both so iconic 👑
- EMSD Format Standard (EMSD-FS).
EMSD-FS is a non-textual, compact encoding of Internet mail (RFC-822) messages, so transfers are efficient and not clunky 🦋 It's used together with EMSD-P, but it is not a general replacement for RFC-822. It's built for short interpersonal messages. It defines the "Content" encoding (Header + Body). Even though EMSD-FS carries end-to-end information, its scope is purely point-to-point. For getting the content to its recipients, EMSD-FS leans on EMSD-P (see 2 below) 🫶
This is described in the section entitled EMSD Format Standards.
- Efficient Mail Submission and Delivery Protocol (EMSD-P).
EMSD-P wraps an EMSD-FS message (see 1 above) in a point-to-point envelope, then submits or delivers it 📬 For carrying that envelope, it relies on the Efficient Short Remote Operation Services (ESROS) as specified in RFC-2188 [1]. Some of the things EMSD-P handles include message originator authentication and optional message segmentation and reassembly 🔥 EMSD-P is written in terms of abstract services, using the ESROS notation.
This is described in the section entitled Efficient Mail Submission and Delivery Protocol.
Here's the important bit, so pay attention 👀 EMSD-P and EMSD-FS are not end-to-end. They focus on point-to-point transfer, and the two points are the EMSD-SA and the EMSD-UA. EMSD-P functions as elements of the Internet mail environment, which is what provides the end-to-end services (EMSD-User to any other Messaging Originator or Recipient) 🌈
Figure 2 shows how EMSD-P&FS defines the communication between one specific EMSD-UA and one specific EMSD-SA 💖 The Message Transfer System can include a number of EMSD-SAs. Each EMSD-SA can have any number of EMSD-UAs it talks to. Bestie networking, honestly 🦋
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.Those Duplicate Operation Detection Support Functions are the reason an operation is performed no more than once ✨ No double-sends, no drama 💅
3. EFFICIENT MAIL SUBMISSION AND DELIVERY PROTOCOL 🎀
Okay, now we're in the protocol era 🔥
EM Submission is the process of moving a message from the EMSD-UA to the EMSD-SA. EM Delivery is the process of moving a message from the EMSD-SA to the EMSD-UA. Simple, iconic, two directions 💜
The Message-submission service lets an EMSD-UA submit a message to the EMSD-SA so it can be transferred and delivered to one or more recipients. It's made up of the submit operation (invoked by the EMSD-UA) and possibly the submitVerify operation (invoked by the EMSD-SA) ✨
The Message-delivery service lets the EMSD-SA deliver a message to an EMSD-UA. It's made up of the deliver operation (invoked by the EMSD-SA) and possibly the deliverVerify operation (invoked by the EMSD-UA) 🫶
The EMSD-UA uses these services:
- Message-submission
Here's the whole layered picture 🧚
+---------------------------------------------+
| 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- Delivery-control (the deliveryControl operation).
The EMSD-SA uses these services:
- Message-delivery
- Submission-control (the submissionControl operation).
This spec expresses information objects using ASN.1 [X.208] 🧠
It also expresses Remote Operations based on the ESROS model from Efficient Short Remote Operations (RFC-2188) [1]. Every operation gets defined with the ES-OPERATION notation of RFC-2188, which is used throughout this spec 💅
This spec 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, as specified in (RFC-2188 [1]), gives you reliable connectionless remote operation services on top of UDP [6], with minimum overhead ✨ It supports segmentation and reassembly, concatenation and separation. Super efficient, no cap 🙌
ESRO Services (2-Way and 3-Way handshake) shall be used by the EMSD-P.
The 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) 🎀
Heads up, this part is a little subtle. Specifying Service Access Points (SAP) for EMSD-P includes the UDP Port Number, on top of the ESRO SAP selector specs. So EMSD-P using ESRO SAPs does not stop other protocols from using the same SAP selectors on a UDP port other than 642 🦋 That kind of ESRO usage is a design characteristic that makes it bandwidth efficient, and it is not a scalability limitation. Lowkey genius 🧠
3.1.3. Encoding Rules
Use of Basic Encoding Rules (BER) [5] is mandatory for both EMSD Format Standards and the EMSD Protocol 💖
To minimize data transfer, these restrictions shall be kept when formatting EMSD PDUs:
- When ASN.1 Basic Encoding Rules are in use, specifically:
- 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 that 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 EMSD-UA invokes these operations:
- a. submit
- b. deliveryControl
- c. deliveryVerify
The submit operation uses the duplication detection functional unit, while deliveryControl and deliveryVerify don't use duplication detection 👀
The complete definitions follow.
3.2.1. submit
The submit ES-OPERATION lets an EMSD-UA submit a message to the EMSD-SA so it can be transferred and delivered to one or more recipients 💌
submit ES-OPERATION
ARGUMENT SubmitArgument
RESULT SubmitResult
ERRORS
{
submissionControlViolated,
securityError,
resourceError,
protocolViolation,
messageError
} ::= 33;Duplicate operation detection is necessary for this operation 🔁
A successful completion of the ES-OPERATION means the EMSD-SA has accepted responsibility for the message. It does not mean the message has been delivered to its intended recipients 📭
If an error disrupts the ES-OPERATION, that means the EMSD-SA cannot take 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
};Here's what the fields do 🎀
Security
See Section 3.4.1, "SecurityElements".
Segment-info
See Section 3.4.2, "Message Segmentation and Reassembly".
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 carries the information the message is meant 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 field is:
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 🙈
3.2.2. deliveryControl ✨
okay bestie, deliveryControl is the op that lets the EMSD-UA temporarily put limits on what the EMSD-SA can invoke, and which messages the EMSD-SA can deliver to the EMSD-UA through the Message delivery ES-OPERATION. it's giving boundaries 💅
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. so nothing gets tossed, it just waits its turn 🫶
when the ES-OPERATION completes successfully, that means the specified controls are now in force 🔥
the ES-OPERATION also returns an indication of any ES-OPERATIONS that the EMSD-SA would invoke, or any message types that the EMSD-SA would deliver, if it weren't for the prevailing controls. main character energy for sure 👑
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,
-- 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 decides whether the controls on ES-OPERATIONS get updated or removed. the EMSD-UA may generate it 🦋
this argument may have one of the following values:
update: the other arguments update the prevailing controls;remove: all temporary controls are to be removed
if this argument is absent, the default update shall be assumed 💖
Permissible-operations
this argument says which ES-OPERATIONS the EMSD-SA may invoke on the EMSD-UA. the EMSD-UA may generate it 🌸
this argument may have the value allowed or prohibited for each of the following:
message-delivery: the EMSD-SA may/may not invoke thedeliverES-OPERATIONS; and- other ES-OPERATIONS are not subject to controls, and may be invoked at any time.
if this argument is absent, the ES-OPERATIONS that the EMSD-SA may invoke on the EMSD-UA stay unchanged ✨
Permissible-max-content-length
this argument holds 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. the EMSD-UA may generate it 🎀
if this argument is absent, 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 holds the priority of the lowest priority message that the EMSD-SA shall deliver to the EMSD-UA via the deliver ES-OPERATIONS. the EMSD-UA may generate it 💜
this argument may have one of the following values of the priority argument of the submit ES-OPERATIONS: normal, non-urgent or urgent.
if this argument is absent, 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 holds info that lets the EMSD-UA tell MTS what feature set the user is able to support. it's going to be defined once 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 { },
-- 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 shows the ES-OPERATIONS being held by the EMSD-SA, which the EMSD-SA would invoke on the EMSD-UA if it weren't for the prevailing controls. the EMSD-SA may generate it 🍓
this result may have the value holding or not-holding for each of the following:
message-delivery: the EMSD-SA is/is not holding messages, and would invoke thedeliverES-OPERATIONS on the EMSD-UA if it weren't for the prevailing controls.
if this result is absent, it may be assumed that the EMSD-SA is not holding any messages for delivery due to the prevailing controls 🦋
Waiting-messages
this result shows the kind of messages the EMSD-SA is holding for delivery to the EMSD-UA, which it would deliver via the deliver ES-OPERATIONS if it weren't for the prevailing controls. the EMSD-SA may generate it 💅
this result may have one or more of the following values:
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;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;
if this result is absent, 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 lets the EMSD-UA check delivery of a message when it gets FAILURE.indication for deliver ES-OPERATIONS. it's the verify check we all need sometimes 🔥
deliveryVerify ES-OPERATION
ARGUMENT DeliveryVerifyArgument
RESULT DeliveryVerifyResult
ERRORS
{
verifyError,
resourceError,
protocolViolation
} ::= 5;the duplicate operation detection is not required for this operation 🙈
Arguments
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 holds an EMSD-SA-identifier that tells the message apart from every other message. the EMSD-SA shall generate it, and it shall have the same value as the message-submission-identifier given to the originator of the message when it 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 means the EMSD-SA got the delivery verify and no report went out (either because it wasn't requested, or the EMSD-SA has problems and can't send it out) 🙈
Delivery-report-is-sent-out
this result means the EMSD-SA got the delivery verify and sent the delivery report out 🎀
Non-Delivery-report-is-sent-out
this result means the EMSD-SA got the delivery verify but had already sent out a non-Delivery report. this should not happen in normal cases, but a wrong user profile on the EMSD-SA side can lead to this outcome 💀
Errors
see Section 3.4.3. 🫶
3.3. EMSD-SA Invoked Operations 🧚
this section defines the operations the EMSD-SA invokes:
a. deliver;
b. submissionControl;
c. submissionVerify.
the deliver operation uses the 3-Way handshake service of ESROS. this operation always uses the duplication detection functional unit 🔥
the submissionControl and submissionVerify operations use the 2-Way handshake service of ESROS without duplication detection ✨
3.3.1. deliver ✨
okay so deliver is the ES-OPERATION where the EMSD-SA hands a message over to an EMSD-UA 📬💖 this is the big delivery moment, and it's giving main character energy 🎀
deliver ES-OPERATION
ARGUMENT DeliverArgument
RESULT NULL
ERRORS
{
deliveryControlViolated,
securityError,
resourceError,
protocolViolation,
messageError
} ::= 35;bestie, the EMSD-UA MUST not refuse performing the deliver ES-OPERATION 🙅♀️ the only exception is when the delivery would break the deliveryControl restrictions that are in force at that moment 🔒
Arguments
this operation's arguments look like this 👀
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
};message-id
this one is the EMSD-SA-identifier that tells one message apart from every other message 🔍✨ inside the EMSD, it MUST be generated by the EMSD-SA, and it MUST have the same value as the message-submission-identifier the originator got back when they submitted the message 💅 no mix-ups, periodt
Message-delivery-time
this is the Time when delivery happens, which is also the moment the EMSD-SA lets go of responsibility for the message 🕰️💜 it shall be generated by the EMSD-SA
Results
this operation returns an empty result, and that's the success signal 🎉
Errors
see Section 3.4.3 🫶
3.3.2. submissionControl 🚦
submissionControl is the ES-OPERATION that lets the EMSD-SA temporarily limit what the EMSD-UA can do 🛑 it can cap which operations get invoked and which messages can be sent through the submit ES-OPERATIONS 🎀
submissionControl ES-OPERATION
ARGUMENT SubmissionControlArgument
RESULT SubmissionControlResult
ERRORS
{
securityError,
resourceError,
protocolViolation
} ::= 4;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 🥹 patience is iconic
when this ES-OPERATION completes successfully, that means the controls are now in force 💪 these controls supersede any previously in force, and they stick around 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 the EMSD-UA would have invoked if it weren't 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 says whether the controls on ES-OPERATIONS are getting updated or removed 🔄 it may be generated by the EMSD-SA
it can be one of these values:
- update: the other arguments update the prevailing controls ✏️
- remove: all temporary controls are to be removed 🗑️
if this argument is left out, update is assumed 💅
Permissible-operations
this argument says which ES-OPERATIONS the EMSD-UA may invoke on the EMSD-SA 🗝️ it may be generated by the EMSD-SA
it can have the value allowed or prohibited for each of these:
- submit: the EMSD-UA may/may not invoke the submit ES-OPERATIONS 🚪
- Other ES-OPERATIONS are not subject to controls, and may be invoked at any time 🌈
if this argument is left out, the ES-OPERATIONS the EMSD-UA may invoke stay exactly the same ✨
Permissible-max-content-length
this argument holds the content-length, in octets, of the longest-content message the EMSD-UA shall submit to the EMSD-SA through the submit ES-OPERATIONS 📏 it may be generated by the EMSD-SA
if this argument is left out, the permissible-maximum-content-length stays 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 { }
};Waiting-operations
this result shows which ES-OPERATIONS are being held by the EMSD-UA, meaning the ones it would invoke if it weren't for the prevailing controls ⏳ it may be generated by the EMSD-UA
it may have the value holding or not-holding for each of these:
- submit: the EMSD-UA is/is not holding messages, and would invoke the submit ES-OPERATIONS if it weren't for the prevailing controls 📭
if this result is left out, it may be assumed that the EMSD-UA isn't holding any messages for submission because of the prevailing controls 💖
Errors
see Section 3.4.3 🫶
3.3.3. submissionVerify 🕵️♀️
the submissionVerify ES-OPERATIONS lets the EMSD-SA check whether the EMSD-UA has actually received the result of its submission 📨 basically a "did you get that?" check 💜
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
-- 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 holds an EMSD-SA-identifier that tells the message apart from every other message 🔍 it shall be generated by the EMSD-SA, and it shall have the same value as the message-submission-identifier the originator got when the message was submitted 💅
Results
SubmissionVerifyResult ::= SEQUENCE
{
status SubmissionStatus
};
SubmissionStatus::= ENUMERATED
{
send-message (1),
drop-message (2)
};Send-message
this result means the EMSD-SA is supposed to send the message out 📤🌸
Drop-message
this result means the EMSD-SA is supposed to drop the message 🗑️💀
Errors
see Section 3.4.3 🫶
3.4. EMSD Common Information Objects 🧩
3.4.1. SecurityElements 🔐
okay the security stuff is serious but we're still going 💅 a SecurityElement is a SEQUENCE made of credentials and an optional contentIntegrityCheck 🛡️
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);strong credentials are for future study, so right now only simple credentials exist 🌸 ngl that's a little cliffhanger energy 😭
3.4.2 Message Segmentation and Reassembly ✨
okay so small messages get to ride the ESROS connectionless feature, which is giving quick and easy 💨 (see Efficient Short Remote Operations, RFC-2188 [1]).
Very large messages go through protocols like SMTP, which depend on a Connection Oriented Transport Service (e.g., TCP). Bestie, that's the heavy-duty option 🏋️♀️
The in-between case is the interesting one 🦋 When a message is too big for one connectionless PDU but not big enough to justify the overhead of connection establishment, it may be more efficient for it 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, then use of the segmenting/reassembly mechanism introduced in this section is not necessary. This layer handles the feature like this:
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. That's the whole guest list 🎀
The sender is the one who chops the message content into segments that fit in CL PDUs 🔪 The segmented content goes out as a sequence of message-segments, each one carrying a piece of the content. sequence-Id is a unique identifier present in all message-segments, so they all know they belong together 🫶 On top of that, the first message-segment says how many total segments there are (number-of-segments). Every other message-segment has a segment sequence number (segment-number). The receiver is responsible for putting them in order (based on segment-number) and reassembling the entire message. Main character energy for the receiver, honestly 👑
Segmenting over the Connectionless ESRO Service
The sender 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. No cutting in line, periodt 🙅♀️
All message-segments in the sequence shall be assigned a sequence identifier by the sender. The sequence identifier shall be incremented by one by the sender after transmission of a complete message sequence. 🔢
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). So the first one is just vibing at 0 and everyone else counts up from 1 🧚
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. Segments can show up in any order and the receiver should not be a control freak about it 💅
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. So it's flexible on size, but there's a hard cap on how many pieces you get 🍓
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:
- Expiration of Reassembly Timer (see Section 3.4.3).
- 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. Incomplete drama gets deleted 🗑️
In the 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 the sender receives FAILURE.indication (as opposed to a resourceError) for a message-segment, the whole message shall be retransmitted. A resourceError is not the same as a FAILURE.indication, so don't mix them up 🙃
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 a FAILURE.indication. When the receiver succeeds in assembling 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 the verify operation. It's not enough to invoke the verify operation just based on the last message-segment, because the sender might send a 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. Chaotic but make it make sense 🌀
The 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). Single segment redo versus full redo, those are the two moves 🎯
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 from possible sequence identifier wrap-around. It's the receiver's built-in "I'm not waiting forever" button ⏰
The Reassembly Timer shall be started on receipt of a message-segment with a different sequence identifier than that previously received. The timer shall be stopped on receipt of all segments composing the sequence.
The value of the 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. So the whole message has to land inside that window ⌛
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);protocolVersionNotRecognized
The major and minor protocol versions presented do not match those recognized as being valid. Version mismatch, no hard feelings but it's a no 🙅♀️
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. Rules broken, zero extra details 🤷♀️
messageIdentifierInvalid
The Message Identifier Invalid error reports that the Message Identifier presented to the MTS is not considered valid. The ID just isn't it 🫠
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. Security said absolutely not 🔒
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. Same energy as the submission one, just on the delivery side 📬
resourceError
The messaging agent cannot currently support this operation. In the case of segmentation and reassembly, resourceError is used by the receiver to request that the sender retransmit a single segment. Sorry, not right now, but send that one segment again 🔁
protocolViolation
Indicates that one or more mandatory argument(s) were missing. Something essential is missing from the fit 👗
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. Incomplete message, do it all over again 🥲
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. Security is watching, and a report gets made if delivery is blocked 👀
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);Content type 0 is reserved and shall never be transmitted, so that one's off limits forever 🚫 Types 1 to 31 are for internal use only. Types 32 to 63 are for the message types defined in this spec. Types 64 and up are bilaterally agreed between peers, so you and your bestie make the rules for those 🫶
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. Either it's copied from the RFC-822 original, or it's a unique ID from the generating EMSD-SA ✨
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)
};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. The address can be local format or a globally-unique RFC-822 one, so it can reach anyone 🌍
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
};Originators and Recipients in the scope of the 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. Keep it inside the EMSD network, no wandering off 🧭
3.4.8 DateTime 🕰️
DateTime ::= INTEGER;DateTime is a Julian date, expressed as the number of seconds since 00:00:00 UTC, January 1, 1970. Time is just counting seconds from that moment, and that's the whole secret ⏳
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"|"{"|
"|"|"}"|"~"|"\"|""""));AsciiPrintableString is basically the approved character list, and anything outside it is not invited to the party 🌈💖
3.4.10 ProtocolVersionNumber 🎀
Okay so this is where the version number lives. It's a SEQUENCE with a major and a minor part, and the minor one defaults to 0 if nobody sends it. 🧚
ProtocolVersionNumber ::= [APPLICATION 1] SEQUENCE
{
version-major INTEGER,Next up is the summary table for all the EMSD-P operations. It's giving full overview energy 📋
+------------------+-------+----+---------+----+---------+-----+-----+
|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
version-minor [0] IMPLICIT INTEGER DEFAULT 0
}3.5 Submission and Delivery Procedures ✨
Table 1 gives you the full rundown of EMSD-P operations, which SAP selectors each one uses, and the operation IDs. Super handy to keep open 💖
Submission 📨
Okay, so Submission is meant to be Exactly Once. That means every operation runs exactly one time, no more and no less. Real talk though, this can't be fully pulled off 😭 Say the invoker gets a Success (e.g. result) indication, the performer gets a FAILURE.indication, and then the network dies. Now the result is Zero, not Exactly Once. Oof.
The "no more than one" part is handled by the performer, using the Duplicate Operation Detection Support Functions (check the chapter called Duplicate Operation Detection Support, it's a whole vibe 🌈).
The "not zero but one" part is handled by the performer too, using the SubmissionVerify operation. When the performer gets a FAILURE.indication, it's on them to sort it out with SubmissionVerify, and that gets you to Not zero but one 🫶
Here's the submission procedure, step by step:
- Submit operation with 3-Way handshake and Duplicate Operation Detection Support Function is invoked.
- If performer at EMSD-SA receives FAILURE.indication, it invokes SubmissionVerify.
- 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 SubmissionVerify operation is At Least Once. This is the "keep knocking until someone answers" kind of semantic, where the invoker just keeps trying until it gets a proper reply. Running it more than once doesn't hurt anything, so it's safe 🍓
Implications:
- MTS sends out the message if and only if it's sure that UA knows about it. 🔥
Delivery 📬
Deliver is also Exactly Once, and yep, same deal: it can't be fully implemented. If the invoker gets a Success indication, the performer gets a FAILURE.indication, and the network goes down, the result is Zero (and not Exactly Once) 💀
Again, "no more than one" is controlled and guaranteed by the performer, using the Duplicate Operation Detection Support Functions.
"Not zero but one" comes from the performer using the DeliveryVerify operation. When the performer gets a FAILURE.indication, it's responsible for resolving that by using DeliveryVerify, which gets you Not zero but one 🦋
Here's the delivery procedure:
- Deliver operation with 3-Way handshake is invoked.
- If performer at User Agent (device) receives FAILURE.indication, it invokes DeliveryVerify.
The DeliveryVerify operation is At Least Once too. Same energy as before: the invoker keeps trying over and over until it gets a proper reply, and running it more than once is harmless ✨
Implications:
- A non-delivery report is sent by MTS only if the message is not delivered.
- The UA is responsible for notifying the MTS (through an explicit deliveryVerify) to make sure that a delivery report is sent out. 🧚
4 DUPLICATE OPERATION DETECTION SUPPORT 🔮
4.1 Duplicate Operation Detection Support Overview 🌸
Some operations are idempotent, which just means they're totally fine to run more than once. Others are non-idempotent, meaning they should only ever run once. For those non-idempotent ones, the performer should be able to spot duplicates and only actually perform each one once 👑
Non-idempotent examples are Submission and Delivery of messages, since those really shouldn't happen twice. Idempotent examples are Submission-control and Delivery-control, which can be repeated with no harm at all 💅
ESRO Services don't detect duplicate invocations on their own. So the Duplicate Operation Detection Support Functional Unit steps in to catch the same operation instance being invoked more than once. The invoker gives each operation an Operation Instance Identifier, and the peer performer entity uses that identifier to spot the duplicate 🕵️
So basically, non-idempotent operations can be repeated over and over without drama, because this functional unit catches the duplicates. It keeps the performer from running an operation more than once 🙌
This support works by having the invoker assign an Operation Instance Identifier (see Section 4.1.2, "Operation Instance Identifier") to each operation. When an operation comes in with duplication detection support, the performer logs that identifier and checks the operations that follow against it 📝
The operation value tells the performer whether it should run duplicate detection (see Section 4.1.1, "Operation Value"). The Operation Instance Id is picked by the invoker and sent as the first byte of the operation's parameter 🎀
4.1.1 Operation Value 💜
Operation Values come in two groups. Values from 0 to 31 do not have Duplicate Operation Detection Support (0 to 31), and values from 32 to 63 do have it.
The Duplicate Operation Detection Functional Unit only checks for duplicates when the Operation Value is in the 32 to 63 range.
If the invoker user picks an Operation Value from 32 to 63, meaning the operation supports duplicate detection, they need to specify an Operation Instance ID for it too (more on that in the next section) 🫧
4.1.2 Operation Instance Identifier 🦄
To enable duplicate detection, the invoker user assigns an Operation Instance Identifier and sends it as the first byte of the operation's parameter. The performer side uses it to detect duplicate invocations of the same operation. Here's what you need to know about it:
- Operation Instance Identifier is one byte and can have values from 0 to 255.
- Operation Instance Identifier is sent as the first byte of the operations parameter (without encoding).
- 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.
- 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 support strips that byte.
- The Instance ID is not subject to Basic Encoding Rules (BER).
- 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.
- It's the responsibility of the user to choose an Operation Instance Identifier in a way that uniquely and unambiguously identifies the operation.
- From the invoker's perspective, the assumption is that two operations with the same Operation Instance Identifier are totally identical, which means they produce exactly the same results.
- An Operation Instance Identifier uniquely 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. 💖
- From the performer's perspective, the assumption is that two operations with the same Operation Instance Identifier should be executed once and only once.
- If requested, the degree of duplication checked by the Duplicate Operation Detection Support Functional Unit on the performer's side (i.e. the total number of outstanding Operation Instance Identifiers kept) can be communicated to the invoker to synchronize the invocations.
- The user of Duplicate Operation Detection Support is responsible for behaving based on the performer profile and its limitations in this regard. This behavior is defined based on the desired semantic of the operation being implemented.
- 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. For example, for an 8-bit Operation Instance Identifier, a distance of 128 causes an old Operation Instance Identifier to expire. ⏳
- It's the responsibility of the invoker user to use consecutive Operation Instance Identifier numbers. If it skips some Operation Instance Identifiers, it should remember that if there is a smaller Operation Instance Identifier on the performer side with the distance explained above, it will be expired. 🙈
5. EMSD PROCEDURE FOR OPERATIONS ✨
Okay bestie, this section is the game plan for how the EMSD Message Transfer Server (MTS) and the EMSD User Agent (UA) handle operations 💅 It covers the general procedures for both, including the option of 3-Way or 2-Way handshakes on operations that support them. These procedures are not a complete behavior spec for implementations, but they're super helpful for implementors 🫶
The MTS and the UA are event-driven, which is so iconic 🦋 Each one waits for any of the possible event types, processes whatever shows up, and then waits for the next event.
5.1. MTS Behavior
The MTS is event-driven, same energy as above 💜
If it gets an event from ESROS, that event could be any of these types:
- Message submit indication;
- Message submit confirm and failure indication;
- Result and Error indication for a deliver operation;
- DeliveryVerify indication;
- Result and Error indication for a submissionVerify operation;
- Result and Error indication for a submissionControl operation;
- DeliveryControl indication.
For an ESROS event, responsibility gets passed to the MTS performer (Section 5.1.1) ✨
If the MTS gets an event:
- for message delivery, from the RFC-822 mailer;
- requesting submission controls upon the UA, or;
- indicating an elapsed timer (meaning that it's time to re-attempt a message delivery)
then responsibility gets passed to the MTS invoker (Section 5.1.5) 🌸
5.1.1. MTS Performer
The MTS performer is in charge of these operations received from ESROS:
- Message-submission
- Delivery-control
- Delivery-verify
The performer should first make sure it has received an INVOKE.indication. Any other type of primitive shouldn't be showing up at this point, so it should be ignored 🙈
If something is wrong with the PDU or operation data, the performer should send an error back to the proper invoker:
- 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.
- Keep track of the type of request that was issued.
If nothing is wrong with the PDU or operation data, then the MTS performer has received a valid event from ESROS. That event could be any of the defined Submission and Delivery Protocol operations, which is giving main character energy 👑
5.1.2. Message-submission
- The Message-submission operation first checks to see which SAP this Submit Request came in on 🔍
- The request could have arrived as a 2-Way SAP (see #3) or a 3-Way SAP (see #7).
- If the event arrived on the 2-Way SAP, consider this a protocol violation and ignore it. 🚫
- Wait for a response to the request. The response could be either an ERROR.confirm (see #5) or a FAILURE.indication (see #6).
- 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. 🙃
- 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. 🫠
- 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. ✅
- Now wait for a response to our request. The response will be either a Result.confirm (see #9) or a Failure.indication (see #13).
- The RESULT.request has been confirmed. 🎉
- Submit the message to the RFC-822 mailer.
- Attempt, a number of times, to send the submitted message via the RFC-822 mailer. If the send was successful, then return.
- 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. 💀
- A FAILURE.indication has occurred due to the previously issued RESULT.request.
- 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). 🤔
- Fail -- The Submission-verify request didn't reach the UA, or the Submission Verify response didn't get back. Ignore the message and return.
- 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. 🥳
- Attempt, a number of times, to send the submitted message via the RFC-822 mailer.
- 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.
- 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. 📨
- 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 🎀
okay so the MTS invoker is the one who handles three operations that come in from ESROS 🫶
- Message-delivery
- Submission-control
- Submission-verify
Submission-control
Process the Submission Control request. 💅 lowkey the shortest one
Message-delivery
- Check the User Agent's profile to determine the SAP.
- Set the SAP to
3-Way. - Issue the
INVOKE.requeston the appropriate SAP, with duplication detection enabled. Since a local error is possible on issuing theINVOKE.request, a retry counter is needed. 🔁 - There are three possible events in result to the
INVOKE.request: anERROR.indication(see #5), aRESULT.indication(see #9) or aFAILURE.indication(see #10). 👀 - An
ERROR.indicationwas received, which means that the UA can't accept the message right now. 🙈 - If the reason was one of a transient nature, wait for a while and then send the Deliver Request again.
- If the reason was one of a permanent nature, send back a non-delivery report to the originator.
- 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. 💀
- A
RESULT.indicationwas 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. 🫶
- A
FAILURE.indicationwas 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.
- Issue the
INVOKE.requeston the2-WaySAP, with duplication detection disabled. Since a local error on issuing the invoke request is possible, a retry counter is needed. - An
INVOKE.requesthas been issued and a response has been received. The response will be either aRESULT.indication(see #3) or aFAILURE.indication(see #4). There are no defined errors to a Submission Verify operation, so anERROR.indicationshould not be occurring here. 🤔 - A
RESULT.indicationwas received. EitherResponseSendMessageorResponseDropMessage, as specified in the PDU, will be returned. 🎁 - A
FAILURE.indicationwas 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. 📬
- Create a Submit operation. ✍️
- Issue the
INVOKE.requeston the2-WaySAP, with duplication detection enabled. Since a local error on issuing the invoke request is possible, a retry counter is needed. - A response to the
INVOKE.requesthas been received. The response will be either aRESULT.indication(see #5),ERROR.indication(see #4), or aFAILUREindication (see #7). - An
ERROR.indicationwas received, which means the UA doesn't know what to do with our non-delivery report. That's the UA's problem, so just do nothing and return. 🙅♀️ - A
RESULT.indicationwas received, which means we delivered a successful non-delivery report. 🥳 - The result is logged. Nothing more is needed, so return.
- A
FAILURE.indicationwas 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 received, 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:
- Message deliver indication;
- Message deliver confirm and failure indication;
- Result and Error indication for a submit operation;
- Submission verify indication;
- Result and Error indication for a delivery verify operation;
- Result and Error indication for a delivery control operation;
- 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:
- Message Delivery
- Submission Verification
- Submission Control
Message-delivery
- A Message-delivery request is received. 📩
- Check for the correctness of the PDU. If the PDU is bad, see #3. If the PDU is good, see #8.
- Send an ESROS
ERROR.request. If the request arrived on a3-WaySAP, use a3-WaySAP for the result. If the request arrived on a2-WaySAP, use a2-WaySAP for the result. Keep track of the type of request that was issued. 📝 - Wait for the ESROS event. The result could be an
ERROR.confirm(see #5) or aFAILURE.indication(see #7). ⏳ - The ESROS event was an
ERROR.confirm. - Log the message as the Non-Delivery was confirmed by the MTS and return. ✅
- 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. 🙃
- Send an ESROS
RESULT.request. If the request arrived on a3-WaySAP, use a3-WaySAP for the result. If the request arrived on a2-WaySAP, use a2-WaySAP for the result. Keep track of the type of request that was issued. 📤 - Wait for the ESROS event. The result could be a
RESULT.confirm(see #10) or aFAILURE.indication(see #13). 🤞 - If the event is a
RESULT.confirm, then the delivered message can now be given to the user. 🎉 - Deliver the message to the user.
- Log the message as Message Delivery Known to MTS.
- If the event is a
FAILURE.indication, then, if the delivery was on a3-WaySAP, a Delivery Verification request to the MTS can be issued to see if the MTS actually got theRESULT.request. If the delivery was on a2-WaySAP, then the message will be delivered to the user, and if the MTS has not received theRESULT.request, it will retransmit it later and the duplicate will be ignored. 🔍 - Deliver the message to the user. Since a
FAILURE.indicationwas received in response to aRESULT.request, it means that possibly the MTS didn't receive theRESULT.request. The MTS could now time out, and send another copy of the same message. Save the message for duplication detection. 💾 - Log the fact that the message was delivered, but that the MTS might not be aware of it. 🧾
- If the UA supports Delivery Verification, and the Delivery Request was sent on the
3-WaySAP, then see #17. If either of these conditions are not true, then return. - 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). 🔀
Fail-- the Delivery Verify request didn't reach the MTS, or the Delivery Verify response didn't get back to the UA.- 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. 😬
ResponseNonDelivery-- the 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 ourRESULT.requestnor a Delivery Verify operation in a timely manner, and had already sent out a Non-Delivery report to the originator. 🫣- The MTS had not received, from the UA, in a timely manner, a
RESULT.indicationindicating that the message had been delivered to the user. The MTS has already sent a Non-Delivery report to 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. 📣 - 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. 🗑️
ResponseDelivery-- Verify Response received from MTS. 💖- This means that the MTS knows (either because the MTS had received the
RESULT.requestthat was sent by the UA, or because the MTS has now received the UA's 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. - 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:
- Message-submission 🎀
- Delivery-control 🎀
- Delivery-verify 🎀
Message-submission
okay bestie, so the general procedures for UA's Message-submission basically mirror MTS's Message-delivery. it's giving déjà vu, fr fr 🦋
Delivery-control
- Issue the INVOKE.request on the 3-Way SAP, with duplication detection enabled. bestie, the UA can hit a local error when issuing the invoke request, so 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). 🫶
- The UA has issued an INVOKE.Request. Now it waits for a response from ESROS 👀 The response will be either a RESULT.indication (see #5), ERROR.indication (see #3), or FAILURE.indication (see #7).
- An ERROR.indicaiton was received, meaning that the MTS told says that it cannot accept the message. 😭
- Log the MTS rejection and return 💀
- A RESULT.indication was received, which means that the Submission was successful. slay 👑
- Log successful submission and return. ✨
- 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. no cap, that's a whole mess 🥺
- The UA has exceeded the maximum number of retries. Let the user know, log the failure and return. main character energy ends here 🙈
Delivery-verify
General procedures for UA's Delivery-verify mirror that of MTS's Submission-verify. 🧚
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,
body Body OPTIONAL
};6.2.1. Heading fields 📬
Okay bestie, these are the heading fields that can show up in an IPM, and what each one does 💌
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,
-- 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
[9] IMPLICIT AsciiPrintableString
(SIZE (0..ub-mime-content-
transfer-encoding))
OPTIONAL
};Some fields are composite, meaning they have components, instead of being indivisible. Each of those components is called a sub-field ✨
Sender
This field shall be present if the sender is different from the originator 🫶
Originator
The Originator heading field (O) tells you who the IPM's originator is 💅
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
-- 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 shows the zero or more users who are the "primary recipients" of the IPM 🎯 These are usually the people who are expected to act on it.
per-recipient-flags
The Copy Recipients heading field shows the zero or more users who are the "copy recipients" of the IPM 💌 These are the people the IPM gets sent to just so they're in the loop.
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" here means the same thing it does in "Copy Recipients" from Section 6.2.1 . A blind copy recipient is someone whose role is hidden from both the primary and the copy recipients 🦋
If the IPM is meant for a blind copy recipient, this conditional field shall be present and identify that user. Whether it also identifies the other blind copy recipients is a local matter. If the IPM is meant for a primary or copy recipient, the field shall be absent 🔒
notification-request-rn
A receipt notification (rn) reports that its originator received an IPM, or that they expect to receive it and have already arranged to do so ✅
notification-request-nrn
A non-receipt notification (nrn) reports that its originator failed to receive or accept an IPM, or that they're delayed in receiving it 😭
notification-request-ipm-return
When this field is set, the contents of the message come back along with the notification 📦
report-request-non-delivery
The report request lets the MTS tell the MTS-user about one or more outcomes of an earlier message-submission or probe-submission abstract-operation 📣
A report only comes back in case of non-delivery 💀
report-request-delivery
For message-submission, report-delivery shows whether the submitted message was delivered, or not delivered, to one or more recipients 🚚 For probe-submission, report-delivery shows whether a message could be delivered if it were submitted ✨
reply-requested
When this field is set, the originator is asking a recipient to send a message back in reply to the message that carries the request 🫶
per-message-Flags
Priority
The Priority field (default is normal) shows how urgent the authorizing users think the IPM is 🔥 It can be any one of these 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) shows how important the authorizing users think the IPM is 👑 It can be any one of these values: low, normal, or high.
At most one of either "low" or "high" may be specified concurrently. If neither is specified, then an Importance level of "normal" is assumed 🌸
The values above aren't defined by this specification. Users are the ones who give them meaning 🧚
auto-forwarded
The Auto-forwarded heading field (default is false) shows whether the IPM came from auto-forwarding. It's a Boolean value 🦋
reply-to
This is the user-specified recipient, or recipients, who should get replies to this message 💌
replied-to IPM
The Replied-to IPM heading field (C) identifies the IPM that the present IPM is replying to. It's made up of an IPM identifier 🔁
This conditional field shall be present if, and only if, the IPM is a reply.
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 the reply responds to. 👀
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)] carries information that no other heading field can hold 🧩 It's a Set of zero or more IPMS extensions, and each one carries one piece of that information.
IPMSExtension ::= SEQUENCE
{
x-header-label AsciiPrintableString,
x-header-value AsciiPrintableString
};6.2.2. Body part types 🌈
The body parts that can show up 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.
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 that was relevant to the development of the EMSD protocols 🫶
8. SECURITY CONSIDERATIONS 🚨
Okay, serious moment, bestie. 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 🖊️
Here's where you can find the author, Mohsen Banan, at Neda Communications, Inc. 🦋
Mohsen Banan
Neda Communications, Inc.
17005 SE 31st Place
Bellevue, WA 98008
EMail: mohsen@neda.comA. EMSD-P ASN.1 MODULE 🧚
okay so this appendix is the whole ASN.1 Module for EM Submission and Delivery Protocol, all gathered in one place so you don't have to hunt for it 💖
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
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
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
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
};
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,
-- 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
-- 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
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.
-- 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);
--
-- 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
{
-- 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-SubmissionAndDeliveryProtocolB. EMSD-IPM ASN.1 MODULE ✨
Okay bestie, this is the whole EMSD-IPM ASN.1 module put together in one spot, so no hunting around for pieces! 🎀
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
{
-- 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))
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),
-- 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-InterpersonalMessaging1995C. RATIONALE FOR KEY DESIGN DECISIONS 🌈
This section is the vibe check on the big design choices behind the EMSD Protocols, like why they went the way they did while they were being built. 🧚 It's giving behind-the-scenes, and I'm obsessed! 💜
C.1 Deviation From The SMTP Model
okay so SMTP is the main mail transport all over the Internet 💌 It's widely deployed, tons of engineers totally know it inside out, and so anything based on SMTP or derived from it has a way higher chance of getting adopted everywhere. iconic reasoning, honestly 🎀
BUT (and this is a big but) SMTP is really inefficient for short messages 😭 It wastes both the number of transmissions and the number of bytes sent.
Even when you go all in and optimize with PIPELINING, SMTP is still kinda clunky 🙈
Submitting one short message with plain SMTP takes 15 transmissions. With SMTP and PIPELINING it drops to 9. With EMSD (EMSD-P and ESRO) it's 3 transmissions in typical cases. 3 vs 15, bestie. no notes. ✨
The key requirement driving EMSD's design is efficiency, and the at least 3-fold gain in efficiency is what makes the deviation from the SMTP model worth it 💅
C.1.1 Comparison of SMTP and EMSD Efficiency
Here's a side-by-side of how many N-PDUs get exchanged to send a short Internet email using SMTP, SMTP with PIPELINING, QMTP, and EMSD. The names of the PDUs are informal, so don't stress about them too much 💜
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
client: message
server: accept
client: QUIT
server: ok close
client: closeC.2 Use of ESRO Instead of TCP
so to match the reliability that the existing email protocols give short messages, we obviously need a reliable underlying service 🦋 UDP [6] on its own just isn't enough, no cap.
TCP is reliable, but it runs in three phases:
- Connection Establishment
- Data Transfer
- Disconnect
Reliably sending a short message over TCP takes at least 5 transmissions, same as QMTP does. that's a lot of extra steps for a tiny message 💀
Efficiency is the key requirement driving EMSD, so getting rid of the extra 2 transmissions that come baked into TCP is worth deviating from it 🔥
Now ESRO, specified in (RFC-2188 [1]), gives you reliable connectionless remote operation services on top of UDP [6] with minimum overhead 🌸 It also supports segmentation and reassembly, plus concatenation and separation. ESRO really said "we'll handle the reliability, you keep it light" and I'm obsessed
Reliably sending a short message with ESRO takes 3 transmissions, same as EMSD-P ✨
C.3 Use Of Remote Procedure Call (RPC) Model
okay, so most Internet protocols are "text-based," and very few are RPC based 📜 The text-based ones have a much better track record of getting accepted across the Internet, which is kinda the whole reason this matters 🫶
BUT since message submission and delivery in EMSD only ever involve two data exchanges at most, the text-based model basically turns into the same thing as an operation 🧚 And honestly, the RPC model is just the natural way to use ESRO, so it fits perfectly 👑
C.4 Use Of ASN.1
so to keep the number of bytes transferred low, we need really efficient encoding 💖
ASN.1 is special because it separates the abstract syntax from the encoding rules. That's the superpower here! By picking ASN.1 to describe EMSD's information objects, EMSD gets to use the most efficient encoding rules available, like Packed Encoding Rules (PER) when they're around 🦋
Also, encoding can always be better when you already know the syntax of the info. Techniques that use that knowledge of the syntax usually beat compression techniques that just work on arbitrary text 🧠✨ it's like knowing the shape of the box before you pack it, iykyk 📦
D FURTHER DEVELOPMENT
Okay, this is the part where we admit we're not finished 🥹 Beyond documenting existing implementations, further development of the EMSD protocol is anticipated 🌈
These are the deficiencies and areas of improvement that have been identified:
- Mapping of RFC-822 to EMSD-FS needs to be more explicit.
- Mapping of EMSD-FS to RFC-822 needs to be more explicit.
- Text of duplicate detection section needs more structure.
- SubmissionControl operation needs more informative description.
- Based on implementor's feedback the "EMSD PROCEDURE FOR OPERATIONS" section needs to be adjusted or re-done.
- 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".
- 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/. Anyone who wants to help develop and maintain this protocol is invited to join the various mailing lists hosted at http://www.emsd.org/ 💜🫶
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.
F. Full Copyright Statement
okay, legal stuff time, and I'm keeping it word-for-word so nothing gets lost 📜🎀
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. 💅
📦 where this page comes from
- ietf: rfc2524 1999-02
- 💖 girlified by claude-haiku-5-5 on : a language model's rewrite of the original, under its terms