ISO 22645:2005
(Main)Space data and information transfer systems — TM (telemetry) space data link protocol
Space data and information transfer systems — TM (telemetry) space data link protocol
ISO 22645:2005 specifies the telemetry (TM) space data link protocol, a data link layer protocol as defined in ISO/IEC 7498-1, and is be used over space-to-ground or space-to-space communications links by space missions.
Systèmes de transfert des données et informations spatiales — Protocole pour liaison de données spatiales TM (télémesure)
General Information
Relations
Standards Content (Sample)
INTERNATIONAL ISO
STANDARD 22645
First edition
2005-07-15
Space data and information transfer
systems — TM (telemetry) space data link
protocol
Systèmes de transfert des données et informations spatiales —
Protocole pour liaison de données spatiales TM (télémesure)
Reference number
ISO 22645:2005(E)
©
ISO 2005
---------------------- Page: 1 ----------------------
ISO 22645:2005(E)
PDF disclaimer
This PDF file may contain embedded typefaces. In accordance with Adobe's licensing policy, this file may be printed or viewed but
shall not be edited unless the typefaces which are embedded are licensed to and installed on the computer performing the editing. In
downloading this file, parties accept therein the responsibility of not infringing Adobe's licensing policy. The ISO Central Secretariat
accepts no liability in this area.
Adobe is a trademark of Adobe Systems Incorporated.
Details of the software products used to create this PDF file can be found in the General Info relative to the file; the PDF-creation
parameters were optimized for printing. Every care has been taken to ensure that the file is suitable for use by ISO member bodies. In
the unlikely event that a problem relating to it is found, please inform the Central Secretariat at the address given below.
© ISO 2005
All rights reserved. Unless otherwise specified, no part of this publication may be reproduced or utilized in any form or by any means,
electronic or mechanical, including photocopying and microfilm, without permission in writing from either ISO at the address below or
ISO's member body in the country of the requester.
ISO copyright office
Case postale 56 • CH-1211 Geneva 20
Tel. + 41 22 749 01 11
Fax + 41 22 749 09 47
E-mail copyright@iso.org
Web www.iso.org
Published in Switzerland
ii © ISO 2005 – All rights reserved
---------------------- Page: 2 ----------------------
ISO 22645:2005(E)
Foreword
ISO (the International Organization for Standardization) is a worldwide federation of national standards bodies
(ISO member bodies). The work of preparing International Standards is normally carried out through ISO
technical committees. Each member body interested in a subject for which a technical committee has been
established has the right to be represented on that committee. International organizations, governmental and
non-governmental, in liaison with ISO, also take part in the work. ISO collaborates closely with the
International Electrotechnical Commission (IEC) on all matters of electrotechnical standardization.
International Standards are drafted in accordance with the rules given in the ISO/IEC Directives, Part 2.
The main task of technical committees is to prepare International Standards. Draft International Standards
adopted by the technical committees are circulated to the member bodies for voting. Publication as an
International Standard requires approval by at least 75 % of the member bodies casting a vote.
Attention is drawn to the possibility that some of the elements of this document may be the subject of patent
rights. ISO shall not be held responsible for identifying any or all such patent rights.
ISO 22645 was prepared by the Consultative Committee for Space Data Systems (CCSDS) (as
CCSDS 132.0-B-1, September 2003) and was adopted (without modifications except those stated in Clause 2
of this International Standard) by Technical Committee ISO/TC 20, Aircraft and space vehicles, Subcommittee
SC 13, Space data and information transfer systems.
© ISO 2005 – All rights reserved iii
---------------------- Page: 3 ----------------------
INTERNATIONAL STANDARD ISO 22645:2005(E)
Space data and information transfer systems — TM (telemetry)
space data link protocol
1 Scope
This International Standard specifies the telemetry (TM) space data link protocol, a data link layer protocol as
defined in ISO/IEC 7498-1, and is be used over space-to-ground or space-to-space communications links by
space missions.
The scope and field of application are furthermore detailed in subclauses 1.1 and 1.2 of the enclosed CCSDS
publication.
2 Requirements
Requirements are the technical recommendations made in the following publication (reproduced on the
following pages), which is adopted as an International Standard:
CCSDS 132.0-B-1, September 2003, TM space data link protocol.
For the purposes of international standardization, the modifications outlined below shall apply to the specific
clauses and paragraphs of publication CCSDS 132.0-B-1.
Pages i to v
This part is information which is relevant to the CCSDS publication only.
Page 1-5
Add the following information to the references indicated:
[3] Document CCSDS 131.0-B-1, September 2003, is equivalent to ISO 22641:2005.
1)
[4] Document CCSDS 135.0-B-1, January 2002, is equivalent to ISO 22647:— .
[6] Document CCSDS 133.0-B-1, September 2003, is equivalent to ISO 22646:2005.
Page B-1
Add the following information to the references indicated:
[B2] Document CCSDS 102.0-B-5, November 2000, is equivalent to ISO 13419:2003.
[B3] Document CCSDS 103.0-B-2, June 2001, is equivalent to ISO 17433:2003.
[B5] Document CCSDS 910.4-B-1, May 1996, is equivalent to ISO 15396:1998.
1) To be published.
© ISO 2005 – All rights reserved 1
---------------------- Page: 4 ----------------------
ISO 22645:2005(E)
[B6] Document CCSDS 232.0-B-1, September 2003, is equivalent to ISO 22664:2005.
It has been agreed with the Consultative Committee for Space Data Systems that Subcommittee
ISO/TC 20/SC 13 will be consulted in the event of any revision or amendment of publication CCSDS 132.0-B-1.
To this end, NASA will act as a liaison body between CCSDS and ISO.
2 © ISO 2005 – All rights reserved
---------------------- Page: 5 ----------------------
ISO 22645:2005(E)
RECOMMENDATION FOR SPACE
DATA SYSTEM STANDARDS
TM SPACE DATA
LINK PROTOCOL
CCSDS 132.0-B-1
BLUE BOOK
September 2003
© ISO 2005 – All rights reserved 3
---------------------- Page: 6 ----------------------
ISO 22645:2005(E)
(blank page)
4 © ISO 2005 – All rights reserved
---------------------- Page: 7 ----------------------
ISO 22645:2005(E)
CCSDS RECOMMENDATION FOR TM SPACE DATA LINK PROTOCOL
AUTHORITY
Issue: Blue Book, Issue 1
Date: September 2003
Location: Not Applicable
This document has been approved for publication by the Management Council of the
Consultative Committee for Space Data Systems (CCSDS) and represents the consensus
technical agreement of the participating CCSDS Member Agencies. The procedure for
review and authorization of CCSDS Recommendations is detailed in reference [B1], and the
record of Agency participation in the authorization of this document can be obtained from the
CCSDS Secretariat at the address below.
This Recommendation is published and maintained by:
CCSDS Secretariat
Office of Space Communication (Code M-3)
National Aeronautics and Space Administration
Washington, DC 20546, USA
CCSDS 132.0-B-1 Page i September 2003
© ISO 2005 – All rights reserved 5
---------------------- Page: 8 ----------------------
ISO 22645:2005(E)
CCSDS RECOMMENDATION FOR TM SPACE DATA LINK PROTOCOL
STATEMENT OF INTENT
The Consultative Committee for Space Data Systems (CCSDS) is an organization officially
established by the management of member space Agencies. The Committee meets
periodically to address data systems problems that are common to all participants, and to
formulate sound technical solutions to these problems. Inasmuch as participation in the
CCSDS is completely voluntary, the results of Committee actions are termed
Recommendations and are not considered binding on any Agency.
This Recommendation is issued by, and represents the consensus of, the CCSDS Plenary
body. Agency endorsement of this Recommendation is entirely voluntary. Endorsement,
however, indicates the following understandings:
– Whenever an Agency establishes a CCSDS-related standard, this standard will be in
accord with the relevant Recommendation. Establishing such a standard does not
preclude other provisions which an Agency may develop.
– Whenever an Agency establishes a CCSDS-related standard, the Agency will provide
other CCSDS member Agencies with the following information:
• The standard itself.
• The anticipated date of initial operational capability.
• The anticipated duration of operational service.
– Specific service arrangements are made via memoranda of agreement. Neither this
Recommendation nor any ensuing standard is a substitute for a memorandum of
agreement.
No later than five years from its date of issuance, this Recommendation will be reviewed by
the CCSDS to determine whether it should: (1) remain in effect without change; (2) be
changed to reflect the impact of new technologies, new requirements, or new directions; or,
(3) be retired or canceled.
In those instances when a new version of a Recommendation is issued, existing
CCSDS-related Agency standards and implementations are not negated or deemed to be
non-CCSDS compatible. It is the responsibility of each Agency to determine when
such standards or implementations are to be modified. Each Agency is, however,
strongly encouraged to direct planning for its new standards and implementations
towards the later version of the Recommendation.
CCSDS 132.0-B-1 Page ii September 2003
6 © ISO 2005 – All rights reserved
---------------------- Page: 9 ----------------------
ISO 22645:2005(E)
CCSDS RECOMMENDATION FOR TM SPACE DATA LINK PROTOCOL
FOREWORD
This document is a technical Recommendation for use in developing flight and ground
systems for space missions and has been prepared by the Consultative Committee for Space
Data Systems (CCSDS). The TM Space Data Link Protocol described herein is intended for
missions that are cross-supported between Agencies of the CCSDS.
This Recommendation specifies a communications protocol to be used by space missions to
transfer space application data over space-to-ground or space-to-space communications links.
This Recommendation is developed from the specifications of the Data Link Layer portion of
older CCSDS Recommendations (references [B2] and [B3]), which define essentially the
same protocol and services but in a slightly different context.
This Recommendation does not change the major technical contents defined in references
[B2] and [B3], but the presentation of the specification has been changed so that:
a) this protocol can be used to transfer any data over any space link in either direction;
b) all CCSDS space link protocols are specified in a unified manner;
c) the specification matches the OSI Basic Reference Model (references [1] and [2]).
Together with the change in presentation, a few technical specifications in references [B2]
and [B3] have been changed in order to define all Space Data Link Protocols in a unified
way. Also, some technical terms in reference [B3] have been changed in order to unify the
terminology used in all the CCSDS Recommendations that define space link. These changes
are listed in annex C of this Recommendation.
Through the process of normal evolution, it is expected that expansion, deletion or
modification to this document may occur. This Recommendation is therefore subject to
CCSDS document management and change control procedures, as defined in reference [B1].
Current versions of CCSDS documents are maintained at the CCSDS Web site:
http://www.ccsds.org/
Questions relating to the contents or status of this document should be addressed to the
CCSDS Secretariat at the address indicated on page i.
CCSDS 132.0-B-1 Page iii September 2003
© ISO 2005 – All rights reserved 7
---------------------- Page: 10 ----------------------
ISO 22645:2005(E)
CCSDS RECOMMENDATION FOR TM SPACE DATA LINK PROTOCOL
At time of publication, the active Member and Observer Agencies of the CCSDS were:
Member Agencies
– Agenzia Spaziale Italiana (ASI)/Italy.
– British National Space Centre (BNSC)/United Kingdom.
– Canadian Space Agency (CSA)/Canada.
– Centre National d’Etudes Spatiales (CNES)/France.
– Deutsches Zentrum für Luft- und Raumfahrt e.V. (DLR)/Germany.
– European Space Agency (ESA)/Europe.
– Instituto Nacional de Pesquisas Espaciais (INPE)/Brazil.
– National Aeronautics and Space Administration (NASA)/USA.
– National Space Development Agency of Japan (NASDA)/Japan.
– Russian Space Agency (RSA)/Russian Federation.
Observer Agencies
– Austrian Space Agency (ASA)/Austria.
– Central Research Institute of Machine Building (TsNIIMash)/Russian Federation.
– Centro Tecnico Aeroespacial (CTA)/Brazil.
– Chinese Academy of Space Technology (CAST)/China.
– Commonwealth Scientific and Industrial Research Organization (CSIRO)/Australia.
– Communications Research Laboratory (CRL)/Japan.
– Danish Space Research Institute (DSRI)/Denmark.
– European Organization for the Exploitation of Meteorological Satellites
(EUMETSAT)/Europe.
– European Telecommunications Satellite Organization (EUTELSAT)/Europe.
– Federal Service of Scientific, Technical & Cultural Affairs (FSST&CA)/Belgium.
– Hellenic National Space Committee (HNSC)/Greece.
– Indian Space Research Organization (ISRO)/India.
– Institute of Space and Astronautical Science (ISAS)/Japan.
– Institute of Space Research (IKI)/Russian Federation.
– KFKI Research Institute for Particle & Nuclear Physics (KFKI)/Hungary.
– MIKOMTEK: CSIR (CSIR)/Republic of South Africa.
– Korea Aerospace Research Institute (KARI)/Korea.
– Ministry of Communications (MOC)/Israel.
– National Oceanic & Atmospheric Administration (NOAA)/USA.
– National Space Program Office (NSPO)/Taipei.
– Space and Upper Atmosphere Research Commission (SUPARCO)/Pakistan.
– Swedish Space Corporation (SSC)/Sweden.
– United States Geological Survey (USGS)/USA.
CCSDS 132.0-B-1 Page iv September 2003
8 © ISO 2005 – All rights reserved
---------------------- Page: 11 ----------------------
ISO 22645:2005(E)
CCSDS RECOMMENDATION FOR TM SPACE DATA LINK PROTOCOL
DOCUMENT CONTROL
Document Title and Issue Date Status
CCSDS TM Space Data Link Protocol, September Original Issue
132.0-B-1 Issue 1 2003
CCSDS 132.0-B-1 Page v September 2003
© ISO 2005 – All rights reserved 9
---------------------- Page: 12 ----------------------
ISO 22645:2005(E)
CCSDS RECOMMENDATION FOR TM SPACE DATA LINK PROTOCOL
CONTENTS
Section Page
1 INTRODUCTION.1-1
1.1 PURPOSE.1-1
1.2 SCOPE.1-1
1.3 APPLICABILITY.1-1
1.4 RATIONALE.1-2
1.5 DOCUMENT STRUCTURE.1-2
1.6 CONVENTIONS AND DEFINITIONS .1-2
1.7 REFERENCES.1-5
2 OVERVIEW.2-1
2.1 CONCEPT OF TM SPACE DATA LINK PROTOCOL.2-1
2.2 OVERVIEW OF SERVICES.2-3
2.3 OVERVIEW OF FUNCTIONS.2-10
2.4 SERVICES ASSUMED FROM LOWER LAYERS .2-13
3 SERVICE DEFINITION.3-1
3.1 OVERVIEW.3-1
3.2 SOURCE DATA.3-1
3.3 PACKET SERVICE.3-3
3.4 VIRTUAL CHANNEL ACCESS (VCA) SERVICE.3-6
3.5 VIRTUAL CHANNEL FRAME SECONDARY HEADER (VC_FSH)
SERVICE.3-9
3.6 VIRTUAL CHANNEL OPERATIONAL CONTROL FIELD (VC_OCF)
SERVICE.3-12
3.7 VIRTUAL CHANNEL FRAME (VCF) SERVICE.3-15
3.8 MASTER CHANNEL FRAME SECONDARY HEADER (MC_FSH)
SERVICE.3-18
3.9 MASTER CHANNEL OPERATIONAL CONTROL FIELD (MC_OCF)
SERVICE.3-21
3.10 MASTER CHANNEL FRAME (MCF) SERVICE .3-23
4 PROTOCOL SPECIFICATION.4-1
4.1 PROTOCOL DATA UNIT.4-1
4.2 PROTOCOL PROCEDURES AT THE SENDING END .4-14
4.3 PROTOCOL PROCEDURES AT THE RECEIVING END .4-21
CCSDS 132.0-B-1 Page vi September 2003
10 © ISO 2005 – All rights reserved
---------------------- Page: 13 ----------------------
ISO 22645:2005(E)
CCSDS RECOMMENDATION FOR TM SPACE DATA LINK PROTOCOL
CONTENTS (continued)
Section Page
5 MANAGED PARAMETERS .5-1
5.1 MANAGED PARAMETERS FOR A PHYSICAL CHANNEL .5-1
5.2 MANAGED PARAMETERS FOR A MASTER CHANNEL.5-2
5.3 MANAGED PARAMETERS FOR A VIRTUAL CHANNEL .5-2
5.4 MANAGED PARAMETERS FOR PACKET TRANSFER.5-3
ANNEX A ACRONYMS. A-1
ANNEX B INFORMATIVE REFERENCES . B-1
ANNEX C CHANGES FROM REFERENCES [B2] and [B3] . C-1
Figure
1-1 Bit Numbering Convention. 1-5
2-1 Relationship with OSI Layers. 2-1
2-2 Relationships Between Channels. 2-3
2-3 Asynchronous Service Model.2-5
2-4 Synchronous Service Model.2-6
2-5 Internal Organization of Protocol Entity (Sending End) . 2-11
2-6 Internal Organization of Protocol Entity (Receiving End) . 2-12
2-7 TM Space Data Link Protocol Channel Tree. 2-13
4-1 TM Transfer Frame Structural Components. 4-2
4-2 Transfer Frame Primary Header . 4-3
4-3 Transfer Frame Data Field Status . 4-6
4-4 Transfer Frame Secondary Header . 4-9
4-5 Internal Organization of Protocol Entity (Sending End) . 4-15
4-6 Abstract Model of Packet Processing Function. 4-16
4-7 Abstract Model of Virtual Channel Generation Function . 4-17
4-8 Abstract Model of Virtual Channel Multiplexing Function . 4-18
4-9 Abstract Model of Master Channel Generation Function. 4-19
4-10 Abstract Model of Master Channel Multiplexing Function. 4-20
4-11 Abstract Model of All Frames Generation Function . 4-21
4-12 Internal Organization of Protocol Entity (Receiving End) . 4-22
4-13 Abstract Model of Packet Extraction Function. 4-23
4-14 Abstract Model of Virtual Channel Reception Function. 4-24
4-15 Abstract Model of Virtual Channel Demultiplexing Function . 4-25
4-16 Abstract Model of Master Channel Reception Function . 4-26
4-17 Abstract Model of Master Channel Demultiplexing Function . 4-27
4-18 Abstract Model of All Frames Reception Function. 4-28
CCSDS 132.0-B-1 Page vii September 2003
© ISO 2005 – All rights reserved 11
---------------------- Page: 14 ----------------------
ISO 22645:2005(E)
CCSDS RECOMMENDATION FOR TM SPACE DATA LINK PROTOCOL
CONTENTS (continued)
Table Page
2-1 Summary of Services Provided by TM Space Data Link Protocol . 2-7
5-1 Managed Parameters for a Physical Channel . 5-1
5-2 Managed Parameters for a Master Channel. 5-2
5-3 Managed Parameters for a Virtual Channel. 5-2
5-4 Managed Parameters for Packet Transfer. 5-3
C-1 Mapping of Terms of Reference [B3] That Have Been Redefined .C-2
CCSDS 132.0-B-1 Page viii September 2003
12 © ISO 2005 – All rights reserved
---------------------- Page: 15 ----------------------
ISO 22645:2005(E)
CCSDS RECOMMENDATION FOR TM SPACE DATA LINK PROTOCOL
1 INTRODUCTION
1.1 PURPOSE
The purpose of this Recommendation is to specify the Telemetry (TM) Space Data Link
Protocol. This protocol is a Data Link Layer protocol (see reference [1]) to be used over
space-to-ground or space-to-space communications links by space missions.
1.2 SCOPE
This Recommendation defines the TM Space Data Link Protocol in terms of:
a) the services provided to the users of this protocol;
b) the protocol data units employed by the protocol; and
c) the procedures performed by the protocol.
It does not specify:
a) individual implementations or products;
b) the implementation of service interfaces within real systems;
c) the methods or technologies required to perform the procedures; or
d) the management activities required to configure and control the protocol.
1.3 APPLICABILITY
This Recommendation applies to the creation of Agency standards and to future data
communications over space links between CCSDS Agencies in cross-support situations. The
Recommendation includes comprehensive specification of the services and protocol for inter-
Agency cross support. It is neither a specification of, nor a design for, real systems that may
be implemented for existing or future missions.
The Recommendation specified in this document is to be invoked through the normal
standards programs of each CCSDS Agency and is applicable to those missions for which
cross support based on capabilities described in this Recommendation is anticipated. Where
mandatory capabilities are clearly indicated in sections of the Recommendation, they must be
implemented when this document is used as a basis for cross support. Where options are
allowed or implied, implementation of these options is subject to specific bilateral cross
support agreements between the Agencies involved.
CCSDS 132.0-B-1 Page 1-1 September 2003
© ISO 2005 – All rights reserved 13
---------------------- Page: 16 ----------------------
ISO 22645:2005(E)
CCSDS RECOMMENDATION FOR TM SPACE DATA LINK PROTOCOL
1.4 RATIONALE
The CCSDS believes it is important to document the rationale underlying the
recommendations chosen, so that future evaluations of proposed changes or improvements
will not lose sight of previous decisions.
1.5 DOCUMENT STRUCTURE
This document is divided into five numbered sections and three annexes:
– section 1 presents the purpose, scope, applicability and rationale of this
Recommendation and lists the conventions, definitions, and references used
throughout the Recommendation.
– section 2 provides an overview of the TM Space Data Link Protocol.
– section 3 defines the services provided by the protocol entity.
– section 4 specifies the protocol data units and procedures employed by the protocol
entity.
– section 5 specifies the managed parameters used by the protocol entity.
– annex A lists all acronyms used within this document.
– annex B provides a list of informative references.
– annex C lists the changes from the older CCSDS Recommendation (reference [B3]).
1.6 CONVENTIONS AND DEFINITIONS
1.6.1 DEFINITIONS
1.6.1.1 Definitions from the Open Systems Interconnection (OSI) Basic Reference
Model
This Recommendation makes use of a number of terms defined in reference [1]. The use of
those terms in this Recommendation shall be understood in a generic sense; i.e., in the sense
that those terms are generally applicable to any of a variety of technologies that provide for
the exchange of information between real systems. Those terms are:
a) blocking;
b) connection;
c) Data Link Layer;
d) entity;
e) flow control;
CCSDS 132.0-B-1 Page 1-2 September 2003
14 © ISO 2005 – All rights reserved
---------------------- Page: 17 ----------------------
ISO 22645:2005(E)
CCSDS RECOMMENDATION FOR TM SPACE DATA LINK PROTOCOL
f) Network Layer;
g) peer entities;
h) Physical Layer;
i) protocol control information;
j) protocol data unit;
k) real system;
l) segmenting;
m) service;
n) Service Access Point (SAP);
o) SAP address;
p) service data unit.
1.6.1.2 Definitions from OSI Service Definition Conventions
This Recommendation makes use of a number of terms defined in reference [2]. The use of
those terms in this Recommendation shall be understood in a generic sense; i.e., in the sense
that those terms are generally applicable to any of a variety of technologies that provide for
the exchange of information between real systems. Those terms are:
a) confirmation;
b) indication;
c) primitive;
d) request;
e) response;
f) service provider;
g) service user.
1.6.1.3 Terms Defined in This Recommendation
For the purposes of this Recommendation, the following definitions also apply. Many other
terms that pertain to specific items are defined in the appropriate sections.
aperiodic: not periodic (see below).
asynchronous: not synchronous (see below).
CCSDS 132.0-B-1 Page 1-3 September 2003
© ISO 2005 – All rights reserved 15
---------------------- Page: 18 ----------------------
ISO 22645:2005(E)
CCSDS RECOMMENDATION FOR TM SPACE DATA LINK PROTOCOL
delimited: having a known (and finite) length; applies to data in the context of data
handling.
Mission Phase: a period of a mission during which specified communications
characteristics are fixed. The transition between two consecutive Mission Phases may cause
an interruption of the communications services.
periodic: of or pertaining to a sequence of events in which each event occurs at a fixed time
interval (within specified tolerance) after the previous event in the sequence.
Physical Channel: a stream of bits transferred over a space link in a single direction.
space link: a communications link between a spacecraft and its associated ground system or
between two spacecraft. A space link consists of one or more Physical Channels in one or
both directions.
synchronous: of or pertaining to a sequence of events occurring in a fixed time relationship
(within specified tolerance) to another sequence of events. Note that ‘synchronous’ does not
necessarily imply ‘periodic’ or ‘constant rate’.
1.6.2 NOMENCLATURE
The following conventions apply throughout this Recommendation:
a) the words ‘shall’ and ‘must’ imply a binding and verifiable specification;
b) the word ‘should’ implies an optional, but desirable, specification;
c) the word ‘may’ implies an optional specification;
d) the words ‘is’, ‘are’, and ‘will’ imply statements of fact.
1.6.3 CONVENTIONS
In this document, the following convention is used to identify each bit in an N-bit field. The
first bit in the field to be transmitted (i.e., the most left justified when drawing a figure) is
defined to be ‘Bit 0’; the following bit is defined to be ‘Bit 1’ and so on up to ‘Bit N–1’.
When the field is used to express a binary value (such as a counter), the Most Significant Bit
(MSB
...
Questions, Comments and Discussion
Ask us and Technical Secretary will try to provide an answer. You can facilitate discussion about the standard in here.