RFC 1895

RFC 1895: The Application/CALS-1840 Content-type 💖

Okay bestie, header first 🎀 This is RFC 1895 from the Network Working Group, a Request for Comments written by E. Levinson of Accurate Info. Sys., Inc. 💼 It's Category: Informational and dated February 1996, so it's giving "here's useful info" 🌸, not "here's a standard you have to follow." There's no Obsoletes or Updates line in the header, so it isn't replacing or changing any other RFCs, at least according to this header ✨.

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Status of this Memo 📜

This memo is giving "info for the Internet community" 🦋. It does not specify an Internet standard of any kind, so don't treat it like one, bestie. Distribution of this memo is unlimited 🌈.

Abstract ✨

Okay so this memo gives guidelines for using the US Department of Defense military standard MIL-STD-1840, "Automated Interchange of Technical Information," with the internet email standards RFC 822 and RFC 1521 💌. Email is a more convenient mechanism than physical media for certain types and quantities of data 📬. Software that already supports MIL-STD-1840 exchanges can keep being used alongside the email exchanges defined here 💻. The memo defines a new media type and a MIME message structure for exchanging data that conforms to MIL-STD-1840 🎀.

1. Introduction 🦋

The US Department of Defense (DOD) has defined a standard, MIL-STD-1840 [1840], for exchanging digital data 💾. Most uses of it run on 9-track tape as the transport medium 📼, which is a lot. The Application/CALS-1840 media-type is proposed to make those exchanges work over MIME [MIME] and network-based transport, aka electronic mail [822] ✉️.

This memo has been reviewed and authorized by the Continuous Acquisition and Life-cycle Support (CALS) Industry Steering Group (ISG). CALS is a US DOD initiative for using and exchanging digital data 🧠. The Industry Steering Group is made up of members from government and industry, and it guides the development of CALS standards like [1840] 🫶.

2. Definition 💅

Here's the structure, bestie. An [1840] exchange is a set of files with well defined file names (more on that below) 📂. Each set has a declaration file and one or more data files. The data files are header records immediately followed by the data, and the data itself may be formatted in accordance with a published specification or a contractual agreement 📋.

MIL-STD-1840 encodes the file's data type in the file name 🏷️.

You might think it makes sense to turn the 1840 headers into MIME headers and use the appropriate media type, basically turning the 1840 files into MIME body parts 🤔. But nope, and there are three reasons why. First, not all of the "types" used in [1840] are registered MIME types. Second, there's an installed base of software that can already read 1840 formatted files and process the data appropriately. Finally, the three existing revisions of the standard kept the same file structure, so a processor for the data may be able to handle any one of the standard's revisions 🙌. So a single Application/CALS-1840 is being proposed, and its body part contains headers and data in the [1840] format 💖.

A set of related files is a "transfer unit" in 1840, and each transfer unit shall correspond to a Multipart/Mixed MIME entity 📦. Each transfer unit includes a declaration file, which shall be the first body part in the Multipart/Mixed entity. Several transfer units may be included in a single MIME message 🧚.

2.1 Registration Information 📝

The form below is copied from RFC 1590, Appendix A, so we can register this media-type 🫶.

To:  IANA@isi.edu
Subject:  Registration of new Media Type content-type/subtype

Media Type name:           Application
Media subtype name:        CALS-1840
Required parameters:       filename, version
Optional parameters:       None
Encoding considerations:   Any valid MIME encodings my be used
Security considerations:   Depends solely on the referenced type
Published specification:   This document
Person & email address
to contact for further
information:               Alan Peltzman <peltzmaa@ncr.disa.mil>
                           +1 (703) 735-3568
                           Defense Information Systems Agency
                           Center for Standards
                           Code JIEO/JEBEB
                           10701 Parkridge Blvd
                           Reston, VA 22091-4398

2.2. The Filename Parameter 🎀

The filename parameter gives the transfer unit filename as defined by [1840]. Its value, called <1840-name>, follows the grammar below 🔤.

1840-name  := "D" 1840-tuseq [ 1840-type 1840-dfseq ]
1840-type  := letter ; limited to the set defined in
                     ; the appropriate version of
                     ; [1840, Table III]
1840-tuseq := 1840-seq
1840-dfseq := 1840-seq
1840-seq   := alphnum alphnum alphnum
alphanum   := letter / digit
letter     := "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"
digit      := "0" / "1" / "2" / "3" / "4" / "5" /
              "6" / "7" / "8" / "9" /

All Application/CALS-1840 body parts in a single Multipart/Mixed MIME entity shall have the same <1840-tuseq>. Within a single message, all filename values shall be unique 🔒.

Notes, because they matter 🧐:

1. Tuseq and dfseq correspond to transfer unit sequence number and data file sequence number respectively.
2. The filename for a declaration file has the form "D" 1840-tuseq, and for data files, the form "D" 1840-tuseq <letter> 1840-dfseq.

2.3. The Version Parameter 🧾

The specversion parameter's value shall indicate the particular version of MIL-STD-1840 that the data conforms to. Valid values are:

MIL-STD-1840C, 0, 199XXXXX
MIL-STD-1840B, 0, 19921103
MIL-STD-1840A, 0, 19871222

Notes:

1. The value "199XXXXX" is to be replaced with the actual issue date for MIL-STD-1840C.
2. The embedded blanks in the above strings are required, hence the value must be enclosed in quote marks (").

3. Example 🎬

In the example below, a single transfer unit is provided. It consists of three data files: the declaration, a contract defined file and an IGES file. The headers and data are in accordance with MIL-STD-1840B. The content-transfer-encoding preserves the data file's fixed record length 💫.

To:   you@some.org
From: me@here.com
Date: Fri, 03 Nov 1995 18:23:10 -0500
MIME-Version: 1.0
Content-Type: Multipart/Mixed;
    Boundary="DISA CFS - SFC ASID"

--DISA CFS - SFC ASID
Content-Type: Application/CALS-1840; filename=D001;
    version="MIL-STD-1840B, 0, 19921103"
Content-Transfer-Encoding: Base64

[Declaration File]
--DISA CFS - SFC ASID
Content-Type: Application/CALS-1840; filename=D001A001;
    version="MIL-STD-1840B, 0, 19921103"

Content-Transfer-Encoding: Base64

[Data File -- Contract Defined including headers]
--DISA CFS - SFC ASID
Content-Type: Application/CALS-1840; filename=D001Q001;
    version="MIL-STD-1840B, 0, 19921103"
Content-Transfer-Encoding: Base64

[Data File -- Raster including 1840 headers]
--DISA CFS - SFC ASID--

4. Security Considerations 🔐

None of the body parts, as constituted, represent executable data. When the 1840 file format is processed, the resultant data may be executable. Processing will be under the control of the process associated with Application/CALS-1840 🛡️.

Okay bestie, this is the serious part 💀. Classified information, or other information that cannot be disclosed except to authorized personnel, should not be sent via the Internet without using appropriate privacy enhancements, [PEM], [MOSS], or other privacy mechanism 🚨.

5. Acknowledgments 🫶

The author acknowledges the encouragement of Alan Peltzman, US DOD, DISA, and the suggestions of Richard Klobuchar, SAIC 💕.

This work was supported under U.S. Dept. of the Army, Contract DAAB07-93-D-T001, and prepared under the direction of the MIL-STD-1840 Revision C Review Team 🌟.

6. References 📚

• [1840] MIL-STD-1840B, "Automated Interchange of Technical Information", US Department of Defense, 3 November 1992.
• [822] Crocker, D., "Standard for the Format of ARPA Internet Text Messages", STD 11, RFC 822, UDEL, August 1982.
• [MIME] Borenstein, N. and N. Freed, "MIME (Multipurpose Internet Mail Extensions): Mechanisms for Specifying and Describing the Format of Internet Message Bodies", RFC 1521, Bellcore and Innosoft, September 1993.
• [MOSS] Crocker, S., Freed, N., Galvin, J., and S. Murphy, "MIME Object Security Services", RFC 1848, Cybercash, Innosoft, TIS, October 1995.
• [PEM] Linn, J., "Privacy Enhancement for Internet Electronic Mail: Part I: Message Encryption and Authentication Procedures", RFC 1421, IAB IRTF PSRG, IETF PEM WG, February 1993.

9. Author's Address 📮

Edward Levinson
Accurate Information Systems, Inc.
2 Industrial Way
Eatontown, NJ  07724-2265
USA

Phone: +1 908 389 5550
EMail: ELevinson@Accurate.com