Space data and information transfer systems -- TM (telemetry) space data link protocol

ISO 22645:2016 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.

Systèmes de transfert des données et informations spatiales -- Protocole de liaison de données spatiales TM (télémétrie)

General Information

Status
Published
Publication Date
02-Nov-2016
Current Stage
9020 - International Standard under periodical review
Start Date
15-Oct-2021
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INTERNATIONAL ISO
STANDARD 22645
Second edition
2016-11-15
Space data and information transfer
systems — TM (telemetry) space data link
protocol
Systèmes de transfert des données et informations spatiales — Protocole de
liaison de données spatiales TM (télémétrie)
Reference number
ISO 22645:2016(E)
ISO 2016
---------------------- Page: 1 ----------------------
ISO 22645:2016(E)
COPYRIGHT PROTECTED DOCUMENT
© ISO 2016

All rights reserved. Unless otherwise specified, no part of this publication may be reproduced or utilized otherwise in any form or by any

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Permission can be requested from either ISO at the address below or ISO’s member body in the country of the requester.

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Published in Switzerland
ii © ISO 2016 – All rights reserved
---------------------- Page: 2 ----------------------
ISO 22645:2016(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.

The procedures used to develop this document and those intended for its further maintenance are described

in the ISO/IEC Directives, Part 1. In particular the different approval criteria needed for the different types of

ISO documents should be noted. This document was drafted in accordance with the editorial rules of the

ISO/IEC Directives, Part 2. www.iso.org/directives

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. Details of any patent

rights identified during the development of the document will be in the Introduction and/or on the ISO list of

patent declarations received. www.iso.org/patents

Any trade name used in this document is information given for the convenience of users and does not

constitute an endorsement.

For an explanation on the meaning of ISO specific terms and expressions related to conformity assessment,

as well as information about ISO's adherence to the WTO principles in the Technical Barriers to Trade (TBT)

see the following URL: Foreword - Supplementary information

ISO 22645 was prepared by the Consultative Committee for Space Data Systems (CCSDS) (as

CCSDS 132.0-B-2, September 2015) 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.

This second edition cancels and replaces the first edition (ISO 22645:2005), which has been technically

revised. It also incorporates the amendment ISO 22645:2005/Amd.1:2015.
© ISO 2016 – All rights reserved iii
---------------------- Page: 3 ----------------------
ISO 22645:2016(E)
CCSDS RECOMMENDED STANDARD 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 its members. 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 Recommended Standards and are not
considered binding on any Agency.

This Recommended Standard is issued by, and represents the consensus of, the CCSDS

members. Endorsement of this Recommendation is entirely voluntary. Endorsement,
however, indicates the following understandings:

o Whenever a member establishes a CCSDS-related standard, this standard will be in

accord with the relevant Recommended Standard. Establishing such a standard
does not preclude other provisions which a member may develop.
o Whenever a member establishes a CCSDS-related standard, that member will
provide other CCSDS members with the following information:
-- The standard itself.
-- The anticipated date of initial operational capability.
-- The anticipated duration of operational service.

o Specific service arrangements shall be made via memoranda of agreement. Neither

this Recommended Standard nor any ensuing standard is a substitute for a
memorandum of agreement.

No later than five years from its date of issuance, this Recommended Standard 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 Recommended Standard is issued, existing

CCSDS-related member standards and implementations are not negated or deemed to be non-

CCSDS compatible. It is the responsibility of each member to determine when such

standards or implementations are to be modified. Each member is, however, strongly

encouraged to direct planning for its new standards and implementations towards the later

version of the Recommended Standard.
CCSDS 132.0-B-2 Page ii September 2015
© ISO 2016 – All rights reserved
---------------------- Page: 4 ----------------------
ISO 22645:2016(E)
CCSDS RECOMMENDED STANDARD 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.

Attention is drawn to the possibility that some of the elements of this document may be the

subject of patent rights. CCSDS has processes for identifying patent issues and for securing

from the patent holder agreement that all licensing policies are reasonable and non-

discriminatory. However, CCSDS does not have a patent law staff, and CCSDS shall not be

held responsible for identifying any or all such patent rights.

Through the process of normal evolution, it is expected that expansion, deletion, or

modification of this document may occur. This Recommended Standard is therefore subject

to CCSDS document management and change control procedures, which are defined in
Organization and Processes for the Consultative Committee for Space Data Systems

(CCSDS A02.1-Y-4). 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 sent to the CCSDS

Secretariat at the e-mail address indicated on page i.
CCSDS 132.0-B-2 Page iii September 2015
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---------------------- Page: 5 ----------------------
ISO 22645:2016(E)
CCSDS RECOMMENDED STANDARD 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.
– Canadian Space Agency (CSA)/Canada.
– Centre National d’Etudes Spatiales (CNES)/France.
– China National Space Administration (CNSA)/People’s Republic of China.
– Deutsches Zentrum für Luft- und Raumfahrt (DLR)/Germany.
– European Space Agency (ESA)/Europe.
– Federal Space Agency (FSA)/Russian Federation.
– Instituto Nacional de Pesquisas Espaciais (INPE)/Brazil.
– Japan Aerospace Exploration Agency (JAXA)/Japan.
– National Aeronautics and Space Administration (NASA)/USA.
– UK Space Agency/United Kingdom.
Observer Agencies
– Austrian Space Agency (ASA)/Austria.
– Belgian Federal Science Policy Office (BFSPO)/Belgium.
– Central Research Institute of Machine Building (TsNIIMash)/Russian Federation.

– China Satellite Launch and Tracking Control General, Beijing Institute of Tracking and

Telecommunications Technology (CLTC/BITTT)/China.
– Chinese Academy of Sciences (CAS)/China.
– Chinese Academy of Space Technology (CAST)/China.

– Commonwealth Scientific and Industrial Research Organization (CSIRO)/Australia.

– Danish National Space Center (DNSC)/Denmark.
– Departamento de Ciência e Tecnologia Aeroespacial (DCTA)/Brazil.
– Electronics and Telecommunications Research Institute (ETRI)/Korea.
– European Organization for the Exploitation of Meteorological Satellites
(EUMETSAT)/Europe.
– European Telecommunications Satellite Organization (EUTELSAT)/Europe.
– Geo-Informatics and Space Technology Development Agency (GISTDA)/Thailand.
– Hellenic National Space Committee (HNSC)/Greece.
– Indian Space Research Organization (ISRO)/India.
– Institute of Space Research (IKI)/Russian Federation.
– KFKI Research Institute for Particle & Nuclear Physics (KFKI)/Hungary.
– Korea Aerospace Research Institute (KARI)/Korea.
– Ministry of Communications (MOC)/Israel.
– National Institute of Information and Communications Technology (NICT)/Japan.
– National Oceanic and Atmospheric Administration (NOAA)/USA.
– National Space Agency of the Republic of Kazakhstan (NSARK)/Kazakhstan.
– National Space Organization (NSPO)/Chinese Taipei.
– Naval Center for Space Technology (NCST)/USA.
– Scientific and Technological Research Council of Turkey (TUBITAK)/Turkey.
– South African National Space Agency (SANSA)/Republic of South Africa.
– Space and Upper Atmosphere Research Commission (SUPARCO)/Pakistan.
– Swedish Space Corporation (SSC)/Sweden.
– Swiss Space Office (SSO)/Switzerland.
– United States Geological Survey (USGS)/USA.
CCSDS 132.0-B-2 Page iv September 2015
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---------------------- Page: 6 ----------------------
ISO 22645:2016(E)
CCSDS RECOMMENDED STANDARD FOR TM SPACE DATA LINK PROTOCOL
DOCUMENT CONTROL
Document Title Date Status
CCSDS TM Space Data Link Protocol, September Original issue, superseded
132.0-B-1 Recommended Standard, Issue 1 2003
CCSDS TM Space Data Link Protocol, September Current issue:
132.0-B-2 Recommended Standard, Issue 2 2015 – adds specifications to
support the Space
Data Link Security
Protocol;
– updates Frame Error
Control Field
Encoding Procedure to
be consistent with
other CCSDS Space
Data Link Protocol
specifications;
– changes all
occurrences of ‘Packet
Service’ and ‘Packet
Transfer Service’ to
‘Virtual Channel
Packet Service’;
– corrects/clarifies
Service Specification
‘.indication’ text;
– updates/clarifies text
relating to Idle Packet
generation;
– removes obsolete
informative annex
detailing changes from
Historical
Recommendations
CCSDS 102.0-B-5-S
(1984–2005) and
CCSDS 103.0-B-2-S
(1996–2005).

NOTE – Substantive changes from the previous issue are marked by change bars in the

inside margin. For terminology changes affecting the entire document, only the first

instances are marked.
CCSDS 132.0-B-2 Page v September 2015
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ISO 22645:2016(E)
CCSDS RECOMMENDED STANDARD 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 ....................................................................................................... 1-6

2 OVERVIEW ................................................................................................................... 2-1

2.1 CONCEPT OF TM SPACE DATA LINK PROTOCOL ....................................... 2-1

2.2 OVERVIEW OF SERVICES ................................................................................. 2-4

2.3 OVERVIEW OF FUNCTIONS ............................................................................ 2-12

2.4 SERVICES ASSUMED FROM LOWER LAYERS ........................................... 2-14

3 SERVICE DEFINITION............................................................................................... 3-1

3.1 OVERVIEW ........................................................................................................... 3-1

3.2 SOURCE DATA..................................................................................................... 3-1

3.3 VIRTUAL CHANNEL PACKET (VCP) SERVICE ............................................. 3-4

3.4 VIRTUAL CHANNEL ACCESS (VCA) SERVICE ............................................. 3-8

3.5 VIRTUAL CHANNEL FRAME SECONDARY HEADER (VC_FSH)

SERVICE .............................................................................................................. 3-12

3.6 VIRTUAL CHANNEL OPERATIONAL CONTROL FIELD (VC_OCF) SERVICE3-15

3.7 VIRTUAL CHANNEL FRAME (VCF) SERVICE ............................................. 3-18

3.8 MASTER CHANNEL FRAME SECONDARY HEADER (MC_FSH)

SERVICE .............................................................................................................. 3-21

3.9 MASTER CHANNEL OPERATIONAL CONTROL FIELD (MC_OCF)

SERVICE .............................................................................................................. 3-24

3.10 MASTER CHANNEL FRAME (MCF) SERVICE .............................................. 3-27

4 PROTOCOL SPECIFICATION WITHOUT SDLS OPTION ................................. 4-1

4.1 PROTOCOL DATA UNIT ..................................................................................... 4-1

4.2 PROTOCOL PROCEDURES AT THE SENDING END .................................... 4-15

4.3 PROTOCOL PROCEDURES AT THE RECEIVING END ................................ 4-22

CCSDS 132.0-B-2 Page vi September 2015
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ISO 22645:2016(E)
CCSDS RECOMMENDED STANDARD FOR TM SPACE DATA LINK PROTOCOL
CONTENTS (continued)
Section Page

5 MANAGED PARAMETERS WITHOUT SDLS OPTION ....................................... 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

6 PROTOCOL SPECIFICATION WITH SDLS OPTION .......................................... 6-1

6.1 OVERVIEW ........................................................................................................... 6-1

6.2 USE OF SDLS PROTOCOL .................................................................................. 6-1

6.3 TM TRANSFER FRAME WITH SDLS ................................................................ 6-1

6.4 SENDING END PROTOCOL PROCEDURES WITH SDLS ............................... 6-4

6.5 RECEIVING END PROTOCOL PROCEDURES WITH SDLS ........................... 6-7

6.6 MANAGED PARAMETERS WITH SDLS .......................................................... 6-9

ANNEX A ACRONYMS (INFORMATIVE) ................................................................ A-1

ANNEX B INFORMATIVE REFERENCES (INFORMATIVE) ...............................B-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)............................................. 2-13

2-6 Internal Organization of Protocol Entity (Receiving End) ......................................... 2-13

2-7 TM Space Data Link Protocol Channel Tree .............................................................. 2-14

4-1 TM Transfer Frame Structural Components ................................................................. 4-2

4-2 Transfer Frame Primary Header.................................................................................... 4-2

4-3 Transfer Frame Data Field Status ................................................................................. 4-5

4-4 Transfer Frame Secondary Header ................................................................................ 4-8

4-5 Logic Diagram of the Encoder .................................................................................... 4-13

4-6 Logic Diagram of the Decoder .................................................................................... 4-14

4-7 Internal Organization of Protocol Entity (Sending End)............................................. 4-15

4-8 Abstract Model of Packet Processing Function .......................................................... 4-16

4-9 Abstract Model of Virtual Channel Generation Function ........................................... 4-18

4-10 Abstract Model of Virtual Channel Multiplexing Function ....................................... 4-19

4-11 Abstract Model of Master Channel Generation Function ........................................... 4-20

CCSDS 132.0-B-2 Page vii September 2015
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ISO 22645:2016(E)
CCSDS RECOMMENDED STANDARD FOR TM SPACE DATA LINK PROTOCOL
CONTENTS (continued)
Figure Page

4-12 Abstract Model of Master Channel Multiplexing Function ........................................ 4-21

4-13 Abstract Model of All Frames Generation Function .................................................. 4-22

4-14 Internal Organization of Protocol Entity (Receiving End) ......................................... 4-22

4-15 Abstract Model of Packet Extraction Function ........................................................... 4-24

4-16 Abstract Model of Virtual Channel Reception Function ............................................ 4-25

4-17 Abstract Model of Virtual Channel Demultiplexing Function ................................... 4-26

4-18 Abstract Model of Master Channel Reception Function ............................................ 4-27

4-19 Abstract Model of Master Channel Demultiplexing Function ................................... 4-28

4-20 Abstract Model of All Frames Reception Function .................................................... 4-28

6-1 Frame without SDLS Compared to Frame with SDLS................................................. 6-2

Table

2-1 Summary of Services Provided by TM Space Data Link Protocol ............................... 2-7

2-2 Summary of TM Services Supported by the Space Data Link Security Protocol ......... 2-8

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

6-1 Additional Managed Parameters for a Virtual Channel when

TM Space Data Link Protocol Supports SDLS ............................................................ 6-9

CCSDS 132.0-B-2 Page viii September 2015
© ISO 2016 – All rights reserved
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ISO 22645:2016(E)
CCSDS RECOMMENDED STANDARD FOR TM SPACE DATA LINK PROTOCOL
1 INTRODUCTION
1.1 PURPOSE

The purpose of this Recommended Standard 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 Recommended Standard 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 Recommended Standard applies to the creation of Agency standards and to future data

communications over space links between CCSDS Agencies in cross-support situations. The

Recommended Standard 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 Recommended Standard 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 Recommended Standard is anticipated.

Where mandatory capabilities are clearly indicated in sections of the Recommended

Standard, 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-2 Page 1-1 September 2015
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ISO 22645:2016(E)
CCSDS RECOMMENDED STANDARD 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 six numbered sections and two annexes:
– Section 1 presents the purpose, scope, applicability and rationale of this
Recommended Standard and lists the conventions, definitions, and references used
throughout the Recommended Standard.
– 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.

– Section 6 specifies the protocol entity with support for the Space Data Link Security

Protocol.
– Annex A lists all acronyms used within this document.
– Annex B provides a list of informative references.
1.6 CONVENTIONS AND DEFINITIONS
1.6.1 DEFINITIONS
1.6.1.1 Definitions from the Open Systems Interconnection (OSI) Basic Reference
Model

This Recommended Standard makes use of a number of terms defined in reference [1]. The

use of those terms in this Recommended Standard is to 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;
CCSDS 132.0-B-2 Page 1-2 September 2015
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ISO 22645:2016(E)
CCSDS RECOMMENDED STANDARD FOR TM SPACE DATA LINK PROTOCOL
e) flow control;
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 Recommended Standard makes use of a number of terms defined in reference [2]. The

use of those terms in this Recommended Standard is to 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 Recommended Standard

For the purposes of this Recommended Standard, the following definitions also apply. Many

other terms that pertain to specific items are defined in the appropriate sections.

aperiodic: not periodic (see below).
CCSDS 132.0-B-2 Page 1-3 September 2015
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ISO 22645:2016(E)
CCSDS RECOMMENDED STANDARD FOR TM SPACE DATA LINK PROTOCOL
asynchronous: not synchronous (see below).

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. It should be noted that

‘synchronous’ does not necessarily imply ‘periodic’ or ‘constant rate’.

(TM) Transfer Frame: The protocol data unit of the Telemetry (TM) Space Data Link

Protocol.
1.6.2 NOMENCLATURE
1.6.2.1 Normative Text

The following conventions apply for the normative specifications in this Recommended

Standard:
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.

NOTE – These conventions do not imply constraints on diction in text that is clearly

informative in nature.
1.6.2.2 Informative Text

In the normative sections of this document, informative text is set off from the normative

specifications either in notes or under one of the following subsection headings:

CCSDS 132.0-B-2 Page 1-4 September 2015
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ISO 22645:2016(E)
CCSDS RECOMMENDED STANDARD FOR TM SPACE DATA LINK PROTOCOL
– Overview;
– Background;
– Rationale;
– Discussion.
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) shall be the first transmitted bit of the field, i.e., ‘Bit 0’ (see figure 1-1).

BITN-1
BIT 0
N-BIT DATA FIELD
FIRST BIT TRANSMITTED = MSB
Figure 1-1: Bit Numbering Convention

In accordance with standard data-communications practice, data fields are often grouped into

eight-bit ‘words’ which conform to the above convention. Throughout this Recommended

Standard, such an eight-bit word is called an ‘octet’.

The numbering for octets within a data structure starts with zero. By CCSDS convention, all

‘spare’ bits shall be permanently set to ‘0’.
CCSDS 132.0-B-2 Page 1-5 September 2015
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ISO 22645:2016(E)
CCSDS RECOMMENDED STANDARD FOR TM SPACE DATA LINK PROTOCOL
1.7 REFERENCES

The following publications contain provisions which, through reference in this text,

constitute provisions of this document. At the time of publication, the editions indicated

were valid. All publications are subject to revision, and users of this document are

encouraged to investigate the possibility of applying the most recent editions of the

...

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