ISO 21459:2006

INTERNATIONAL ISO
STANDARD 21459
First edition
2006-07-01

Space data and information transfer
systems — Proximity-1 space link
protocol — Coding and synchronization
sublayer
Systèmes de transfert des informations et données spatiales —
Protocole pour liaisons spatiales de proximité 1 — Sous-couche de
codage et synchronisation



Reference number
ISO 21459:2006(E)
©
ISO 2006

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ISO 21459:2006(E)
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ISO 21459:2006(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 21459 was prepared by the Consultative Committee for Space Data Systems (CCSDS) (as
CCSDS 211.2-B-1, April 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.

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INTERNATIONAL STANDARD ISO 21459:2006(E)

Space data and information transfer systems — Proximity-1
space link protocol — Coding and synchronization sublayer
1 Scope
Proximity space links are defined to be short-range, bi-directional, fixed or mobile radio links, generally used to
communicate among probes, landers, rovers, orbiting constellations, and orbiting relays. These links are
characterized by short time delays, moderate (not weak) signals, and short, independent sessions.
This International Standard defines the coding and synchronization sublayer of the Proximity-1 space link
protocol. It defines the data unit of this sublayer, i.e. the PLTU. It defines the coding and synchronization
mechanisms required for cross support. It also specifies the send and receive side functionality of this
sublayer. This International Standard does not specify
⎯ individual implementations or products,
⎯ implementation of service interfaces within real systems,
⎯ methods or technologies required to perform the procedures, or
⎯ management activities required to configure and control the protocol.
The scope and field of application are furthermore detailed in subclauses 1.2 and 1.3 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 211.2-B-1, April 2003, Proximity-1 space link protocol — Coding and synchronization sublayer.
For the purposes of international standardization, the modifications outlined below shall apply to the specific
clauses and paragraphs of publication CCSDS 211.2-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 reference indicated:
[2] Document CCSDS 101.0-B-6, October 2002, is equivalent to ISO 22641:2005.
[4] Document CCSDS 211.1-B-1, April 2003, is equivalent to ISO 21460:2006.
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ISO 21459:2006(E)
3 Revision of publication CCSDS 211.2-B-1
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 211.2-B-1. To this end, NASA will act as a liaison body between CCSDS and ISO.
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ISO 21459:2006(E)
Consultative
Committeefor
SpaceDataSystems





RECOMMENDATION FOR SPACE
DATA SYSTEM STANDARDS


PROXIMITY-1 SPACE LINK PROTOCOL—
CODING AND
SYNCHRONIZATION
SUBLAYER



CCSDS 211.2-B-1

BLUE BOOK


April 2003

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ISO 21459:2006(E)
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ISO 21459:2006(E)
CCSDS RECOMMENDATION FOR PROXIMITY-1 SPACE LINK
PROTOCOL—CODING AND SYNCHRONIZATION SUBLAYER
AUTHORITY


Issue: Blue Book, Issue 1
Date: April 2003
Location: Matera, Italy




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 Procedures Manual for
the Consultative Committee for Space Data Systems, 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 211.2-B-1 Page i April 2003
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ISO 21459:2006(E)
CCSDS RECOMMENDATION FOR PROXIMITY-1 SPACE LINK
PROTOCOL—CODING AND SYNCHRONIZATION SUBLAYER
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 211.2-B-1 Page ii April 2003
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ISO 21459:2006(E)
CCSDS RECOMMENDATION FOR PROXIMITY-1 SPACE LINK
PROTOCOL—CODING AND SYNCHRONIZATION SUBLAYER
FOREWORD

Through the process of normal evolution, it is expected that expansion, deletion, or
modification of this document may occur. This Recommendation is therefore subject to
CCSDS document management and change control procedures which are defined in the
Procedures Manual for the Consultative Committee for Space Data Systems. 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 211.2-B-1 Page iii April 2003
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ISO 21459:2006(E)
CCSDS RECOMMENDATION FOR PROXIMITY-1 SPACE LINK
PROTOCOL—CODING AND SYNCHRONIZATION SUBLAYER
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 211.2-B-1 Page iv April 2003
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ISO 21459:2006(E)
CCSDS RECOMMENDATION FOR PROXIMITY-1 SPACE LINK
PROTOCOL—CODING AND SYNCHRONIZATION SUBLAYER
DOCUMENT CONTROL

Document Title and Issue Date Status

CCSDS Proximity-1 Space Link Protocol October Superseded
211.0-B-1 2002

CCSDS Proximity-1 Space Link Protocol— April Current issue (see note)
211.2-B-1 Coding and Synchronization 2003
Sublayer


Note
This document contains the Coding and Synchronization Sublayer specification originally
published as part of CCSDS 211.0-B-1, Proximity-1 Space Link Protocol.

CCSDS 211.2-B-1 Page v April 2003
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ISO 21459:2006(E)
CCSDS RECOMMENDATION FOR PROXIMITY-1 SPACE LINK
PROTOCOL—CODING AND SYNCHRONIZATION SUBLAYER
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 CONVENTIONS AND DEFINITIONS.1-2
1.6 REFERENCES.1-4

2 OVERVIEW. 2-1

3 CODING AND SYNCHRONIZATION (C&S) SUBLAYER . 3-1

3.1 FUNCTIONS.3-1
3.2 PROXIMITY LINK TRANSMISSION UNIT (PLTU). 3-1
3.3 CODING.3-2
3.4 ATTACHED SYNCHRONIZATION MARKER . 3-3
3.5 C&S SUBLAYER SEND SIDE SIGNAL .3-3
3.6 IDLE PATTERN GENERATOR . 3-3
3.7 C&S SUBLAYER RECEIVE SIDE SIGNAL. 3-4
3.8 C&S SUBLAYER BUFFERS.3-4

ANNEX A CRC-32 CODING PROCEDURES . A-1
ANNEX B PROXIMITY-1 DIRECTIVES AFFECTING THE C&S SUBLAYER . B-3

Figure
1-1 Bit Numbering Convention. 1-4
2-2 Proximity-1 Layered Protocol Model. 2-4
3-3 Proximity-1 Link Transmission Unit (PLTU) . 3-2
A-1 A Possible Implementation of the Encoder . A-1
A-2 A Possible Implementation of the Decoder . A-2


CCSDS 211.2-B-1 Page vi April 2003
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ISO 21459:2006(E)
CCSDS RECOMMENDATION FOR PROXIMITY-1 SPACE LINK
PROTOCOL—CODING AND SYNCHRONIZATION SUBLAYER
1 INTRODUCTION
1.1 PURPOSE
The purpose of this document is to provide a Recommendation for Space Data System
Standards in the area of Proximity space links. Proximity space links are defined to be short-
range, bi-directional, fixed or mobile radio links, generally used to communicate among
probes, landers, rovers, orbiting constellations, and orbiting relays. These links are
characterized by short time delays, moderate (not weak) signals, and short, independent
sessions.
1.2 SCOPE
This Recommendation defines the coding and synchronization sublayer of the Proximity-1
Space Link Protocol. It defines the data unit of this sublayer, i.e., the PLTU. It defines the
coding and synchronization mechanisms required for cross support. It also specifies the send
and receive side functionality of this sublayer. This Recommendation does not specify a)
individual implementations or products, b) 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. The Data Link layer is
defined in the separate CCSDS recommendation entitled, Proximity-1 Space Link Protocol—
Data Link Layer; see reference [3]. The Physical layer is defined in the separate CCSDS
recommendation entitled, Proximity-1 Space Link Protocol—Physical Layer; see reference
[4].
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. It
applies also to internal Agency links where no cross-support is required. It includes
specification of the services and protocols for inter-Agency cross support. It is neither a
specification of, nor a design for, 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 211.2-B-1 Page 1-1 April 2003
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ISO 21459:2006(E)
CCSDS RECOMMENDATION FOR PROXIMITY-1 SPACE LINK
PROTOCOL—CODING AND SYNCHRONIZATION SUBLAYER
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. Concept and rationale behind the decisions that
formed the basis for Proximity-1 will be documented in the CCSDS Proximity-1 Space Link
Green Book, which is under development.
1.5 CONVENTIONS AND DEFINITIONS
1.5.1 DEFINITIONS
1.5.1.1 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 as follows:
a) connection;
b) Data Link layer;
c) entity;
d) physical layer;
e) protocol control information;
f) Protocol Data Unit (PDU);
g) real system;
h) segmenting;
i) service;
j) Service Access Point (SAP);
k) SAP address;
l) Service Data Unit (SDU).
1.5.1.2 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.
CCSDS 211.2-B-1 Page 1-2 April 2003
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ISO 21459:2006(E)
CCSDS RECOMMENDATION FOR PROXIMITY-1 SPACE LINK
PROTOCOL—CODING AND SYNCHRONIZATION SUBLAYER
asynchronous channel: a data channel where the symbol data are modulated onto the
channel only for the period of the message. The message must be preceded by an
acquisition sequence to achieve symbol synchronization. Bit synchronization must be
reacquired on every message. A hailing channel is an example of an asynchronous
channel.
asynchronous data link: a data link consisting of a sequence of variable-length Proximity
Link Transmission Units (PLTUs), which are not necessarily concatenated. Two
types of asynchronous data links are:
1) Asynchronous Data Link over an Asynchronous Channel
Hailing provides an example of an asynchronous data link over an asynchronous
channel. An important issue is resynchronization between successive hails. Idle
is provided for the reacquisition process.
2) Asynchronous Data Link over a Synchronous Channel
Data service provides an example of an asynchronous data link over a
synchronous channel. Once the link is established via hailing, communication
transitions to a synchronous channel and maintains the link in this configuration
until the session is interrupted or ends. If the physical layer does not receive data
from the data link layer, it provides idle to maintain a synchronous channel.
forward link: that portion of a Proximity space link in which the caller transmits and the
responder receives (typically a command link).
physical channel: The RF channel upon which the stream of bits is transferred over a space
link in a single direction.
PLTU: The Proximity Link Transmission Unit is the data unit composed of the Attached
Synchronization Marker, the Version-3 Transfer Frame, and the attached Cyclic
Redundancy Check (CRC)-32.
Proximity link: short-range, bi-directional, fixed or mobile radio links, generally used to
communicate among probes, landers, rovers, orbiting constellations, and orbiting
relays. These links are characterized by short time delays, moderate (not weak)
signals, and short, independent sessions.
return link: that portion of a Proximity space link in which the responder transmits and the
caller receives (typically a telemetry link).
space link: a communications link between transmitting and receiving entities, at least one of
which is in space.
synchronous channel: a continuous stream of bits at a fixed data rate. If the data link fails
to provide frames (data or fill), it is the responsibility of the physical layer to provide
the continuous bit stream.
CCSDS 211.2-B-1 Page 1-3 April 2003
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ISO 21459:2006(E)
CCSDS RECOMMENDATION FOR PROXIMITY-1 SPACE LINK
PROTOCOL—CODING AND SYNCHRONIZATION SUBLAYER
1.5.2 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.
1.5.3 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’, as shown in figure 1-1.
BIT 0 BIT N-1
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
8-bit ‘words’ that conform to the above convention. Throughout this Recommendation, such
an 8-bit word is called an ‘octet’.
The numbering for octets within a data structure begins with zero. Octet zero is the first octet
to be transmitted.
By CCSDS convention, all ‘spare’ bits shall be permanently set to value ‘zero’.
Throughout this Recommendation, directive, parameter, variable, and signal names are
presented with all upper-case characters; data-field and MIB-parameter names are presented
with initial capitalization; values and state names are presented with predominantly lower-
case characters, and are italicized.
1.6 REFERENCES
The following documents contain provisions which, through reference in this text, constitute
provisions of this Recommendation. At the time of publication, the editions indicated were
CCSDS 211.2-B-1 Page 1-4 April 2003
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CCSDS RECOMMENDATION FOR PROXIMITY-1 SPACE LINK
PROTOCOL—CODING AND SYNCHRONIZATION SUBLAYER
valid. All documents are subject to revision, and users of this Recommendation are
encouraged to investigate the possibility of applying the most recent editions of the
documents indicated below. The CCSDS Secretariat maintains a register of currently valid
CCSDS Recommendations.
[1] Information Technology—Open Systems Interconnection—Basic Reference Model:
The Basic Model. International Standard, ISO/IEC 7498-1. 2nd ed. Geneva: ISO,
1994.
[2] Telemetry Channel Coding. Recommendation for Space Data System Standards,
CCSDS 101.0-B-6. Blue Book. Issue 6. Washington, D.C.: CCSDS, October 2002.
[3] Proximity-1 Space Link Protocol—Data Link Layer. Recommendation for Space Data
System Standards, CCSDS 211.0-B-2. Blue Book. Issue 2. Washington, D.C.:
CCSDS, April 2003.
[4] Proximity-1 Space Link Protocol—Physical Layer. Recommendation for Space Data
System Standards, CCSDS 211.1-B-1. Blue Book. Issue 1. Washington, D.C.:
CCSDS, April 2003.

CCSDS 211.2-B-1 Page 1-5 April 2003
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ISO 21459:2006(E)
CCSDS RECOMMENDATION FOR PROXIMITY-1 SPACE LINK
PROTOCOL—CODING AND SYNCHRONIZATION SUBLAYER
2 OVERVIEW
Proximity-1 is a bi-directional Space Link layer protocol to be used by space missions. It
consists of a Physical Layer (reference [4]) a Coding and Synchronization (C&S) sublayer
(of the data link layer) and a Data Link Layer (reference [3]). This protocol has been
designed to meet the requirements of space missions for efficient transfer of space data over
various types and characteristics of Proximity space links. On the send side, the Data Link
layer is responsible for providing data to be transmitted by the Coding and Synchronization
sublayer and Physical layer. The operation of the transmitter is state-driven. On the receive
side, the Data Link layer accepts the serial data output from the receiver and processes the
protocol data units received. It accepts directives both from the local vehicle controller and
across the Proximity link to control its operations. Once the receiver is turned on, its
operation is modeless. It accepts and processes all valid local and remote directives and
received service data units.
The layered model consists of two layers (Physical and Data Link) and has five component
sublayers within the Data Link layer:
a) Physical Layer
1) On the send side:
i) provides an Output Bit Clock to the Coding & Synchronization sublayer in
order to receive the Output Bitstream.
ii) provides status i.e., Carrier_Acquired and Bit_In_Lock_Status signals to the
Media Access Control sublayer.
2) On the receive side: Provides the Received Bit Clock/Data to the Coding &
Synchronization sublayer.
b) Coding and Synchronization Sublayer. The C&S sublayer includes PLTU delimiting
and verification procedures. In addition this sublayer performs as follows:
1) On the send side:
i) includes pre-pending Version-3 frames with the required Attached
Synchronization Marker (ASM);
ii) includes addition of CRC-32 to PLTUs.
2) On both the send and receive sides: Captures the value of the clock used for time
correlation process.
c) Frame Sublayer. The Frame sublayer includes frame validation procedures, such as
transfer frame header checks, and supervisory data processing for supervisory frames.
In addition, this sublayer performs as follows:
1) On the send side:
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