ISO 22664:2013

INTERNATIONAL ISO
STANDARD 22664
Second edition
2013-06-01
Space data and information transfer
systems — TC (telecommand) space data
link protocol
Systèmes de transfert des données et informations spatiales —
Protocole de liaison pour données spatiales TC (télécommande)

Reference number
©
ISO 2013
©  ISO 2013
All rights reserved. Unless otherwise specified, no part of this publication may be reproduced or utilized otherwise in any form or by any
means, electronic or mechanical, including photocopying, or posting on the internet or an intranet, without prior written permission.
Permission can be requested 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 2013 – All rights reserved

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 22664 was prepared by the Consultative Committee for Space Data Systems (CCSDS) (as
CCSDS 232.0-B-2, September 2010) 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 22664:2005), which has been technically
revised.
INTERNATIONAL STANDARD ISO 22664:2013(E)

Space data and information transfer systems — TC
(telecommand) space data link protocol
1 Scope
1.1 This International Standard specifies the telecommand (TC) space data link protocol. This protocol is a
data link layer protocol (as defined in ISO/IEC 7498-1) intended for use over ground-to-space or space-to-
space communications links by space missions.
1.2 This International Standard defines the TC 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.
1.3 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.
1.4 The scope and field of application are furthermore detailed in subclauses 1.1, 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 232.0-B-2, September 2010, TC 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 232.0-B-2.
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:
[4] Document CCSDS 232.1-B-2, September 2010, is equivalent to ISO 22667:2013.
Page B-1
Add the following information to the reference indicated:
[B4] Document CCSDS 910.4-B-2, October 2005, is equivalent to ISO 15396:2007.
[B5] Document CCSDS 132.0-B-1, September 2003, is equivalent to ISO 22645:2005.
[B6] Document CCSDS 732.0-B-2, July 2006, is equivalent to ISO 22666:2007.
3 Revision of publication CCSDS 232.0-B-2
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 232.0-
B-2. To this end, NASA will act as a liaison body between CCSDS and ISO.

2 © ISO 2013 – All rights reserved

Recommendation for Space Data System Standards
TC SPACE DATA
LINK PROTOCOL
RECOMMENDED STANDARD
CCSDS 232.0-B-2
BLUE BOOK
September 2010
(Blank page)
CCSDS RECOMMENDED STANDARD FOR TC SPACE DATA LINK PROTOCOL
AUTHORITY
Issue: Recommended Standard, Issue 2
Date: September 2010
Location: Washington, DC, USA
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 documents is detailed in the 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 document is published and maintained by:

CCSDS Secretariat
Space Communications and Navigation Office, 7L70
Space Operations Mission Directorate
NASA Headquarters
Washington, DC 20546-0001, USA
CCSDS 232.0-B-2 Page i September 2010
CCSDS RECOMMENDED STANDARD FOR TC 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 232.0-B-2 Page ii September 2010
CCSDS RECOMMENDED STANDARD FOR TC 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 TC 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 ground-to-space or space-to-space communications links.
This Recommendation is developed from the specifications of an older CCSDS
Recommendation (reference [B2]), which defines essentially the same protocol and services
but in a slightly different context.
This Recommendation does not change the major technical contents defined in reference [B2],
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 Open Systems Interconnection (OSI) Basic Reference
Model (references [1] and [2]).
Together with the change in presentation, a few technical descriptions in reference [B2] have
been changed to allow flexibility for future extensions of the CCSDS protocol suite. Also,
some technical terms in reference [B2] 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 232.0-B-2 Page iii September 2010
CCSDS RECOMMENDED STANDARD FOR TC 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 e.V. (DLR)/Germany.
– European Space Agency (ESA)/Europe.
– Instituto Nacional de Pesquisas Espaciais (INPE)/Brazil.
– Japan Aerospace Exploration Agency (JAXA)/Japan.
– National Aeronautics and Space Administration (NASA)/USA.
– Russian Federal Space Agency (RFSA)/Russian Federation.
– 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.
– CSIR Satellite Applications Centre (CSIR)/Republic of South Africa.
– Danish National Space Center (DNSC)/Denmark.
– Departamento de Ciência e Tecnologia Aeroespacial (DCTA)/Brazil.
– 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.
– Space and Upper Atmosphere Research Commission (SUPARCO)/Pakistan.
– Swedish Space Corporation (SSC)/Sweden.
– United States Geological Survey (USGS)/USA.
CCSDS 232.0-B-2 Page iv September 2010
CCSDS RECOMMENDED STANDARD FOR TC SPACE DATA LINK PROTOCOL
DOCUMENT CONTROL
Document Title Date Status
CCSDS TC Space Data Link Protocol, September Original Issue
232.0-B-1 Recommended Standard, Issue 1 2003
CCSDS TC Space Data Link Protocol, September Current issue:
- updates Frame Error
232.0-B-2 Recommended Standard, Issue 2 2010
Control Field Encoding
Procedure to be
consistent with other
CCSDS Space Data
Link Protocol
specifications;
- adds specifications and
parameters to support a
systematic
retransmission option
(note).
NOTE – Substantive changes from the previous issue are indicated by change bars in the
right margin.
CCSDS 232.0-B-2 Page v September 2010
CCSDS RECOMMENDED STANDARD FOR TC 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 NORMATIVE REFERENCES . 1-5

2 OVERVIEW . 2-1

2.1 CONCEPT OF TC SPACE DATA LINK PROTOCOL . 2-1
2.2 OVERVIEW OF SERVICES . 2-4
2.3 OVERVIEW OF FUNCTIONS. 2-11
2.4 SERVICES ASSUMED FROM LOWER LAYERS . 2-15

3 SERVICE DEFINITION. 3-1

3.1 OVERVIEW . 3-1
3.2 SOURCE DATA. 3-1
3.3 MAP PACKET SERVICE. 3-3
3.4 VIRTUAL CHANNEL PACKET SERVICE. 3-7
3.5 MAP ACCESS SERVICE . 3-11
3.6 VIRTUAL CHANNEL ACCESS SERVICE . 3-15
3.7 VIRTUAL CHANNEL FRAME SERVICE . 3-19
3.8 MASTER CHANNEL FRAME SERVICE . 3-21
3.9 COP MANAGEMENT SERVICE . 3-24

4 PROTOCOL SPECIFICATION . 4-1

4.1 PROTOCOL DATA UNIT (TC TRANSFER FRAME) . 4-1
4.2 PROTOCOL DATA UNIT (CLCW) . 4-12
4.3 PROTOCOL PROCEDURES AT THE SENDING END . 4-18
4.4 PROTOCOL PROCEDURES AT THE RECEIVING END . 4-28

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 A MAP CHANNEL . 5-4
CCSDS 232.0-B-2 Page vi September 2010
CCSDS RECOMMENDED STANDARD FOR TC SPACE DATA LINK PROTOCOL
CONTENTS (continued)
Section Page
5.5 MANAGED PARAMETERS FOR PACKET TRANSFER . 5-4

ANNEX A ACRONYMS . A-1
ANNEX B INFORMATIVE REFERENCES .B-1
ANNEX C CHANGES FROM REFERENCE [B2] . C-1
Figure
1-1 Bit Numbering Convention . 1-4
2-1 Relationship with OSI Layers . 2-1
2-2 Relationships Between Channels . 2-4
2-3 Internal Organization of Protocol Entity (Sending End) . 2-12
2-4 Internal Organization of Protocol Entity (Receiving End) . 2-13
2-5 TC Space Data Link Protocol Channel Tree . 2-14
4-1 TC Transfer Frame Structural Components. 4-1
4-2 Transfer Frame Primary Header . 4-2
4-3 Segment Header . 4-8
4-4 Logic Diagram of the Encoder. 4-11
4-5 Logic Diagram of the Decoder . 4-12
4-6 Communications Link Control Word . 4-13
4-7 Internal Organization of Protocol Entity (Sending End) . 4-19
4-8 Abstract Model of MAP Packet Processing Function . 4-20
4-9 Example of MAP Packet Processing Procedures . 4-21
4-10 Abstract Model of MAP Generation Function . 4-22
4-11 Example of MAP Generation Procedures . 4-22
4-12 Abstract Model of MAP Multiplexing Function . 4-23
4-13 Abstract Model of VC Packet Processing Function . 4-24
4-14 Example of VC Packet Processing Procedures. 4-24
4-15 Abstract Model of Virtual Channel Generation Function . 4-25
4-16 Abstract Model of Virtual Channel Multiplexing Function . 4-26
4-17 Abstract Model of Master Channel Multiplexing Function. 4-27
4-18 Abstract Model of All Frames Generation Function . 4-28
4-19 Internal Organization of Protocol Entity (Receiving End) . 4-29
4-20 Abstract Model of MAP Packet Extraction Function . 4-30
4-21 Abstract Model of MAP Reception Function . 4-31
4-22 Abstract Model of MAP Demultiplexing Function . 4-31
4-23 Abstract Model of VC Packet Extraction Function . 4-32
4-24 Abstract Model of Virtual Channel Reception Function . 4-33
4-25 Abstract Model of Virtual Channel Demultiplexing Function . 4-34
4-26 Abstract Model of Master Channel Demultiplexing Function . 4-35
4-27 Abstract Model of All Frames Reception Function . 4-36
CCSDS 232.0-B-2 Page vii September 2010
CCSDS RECOMMENDED STANDARD FOR TC SPACE DATA LINK PROTOCOL
CONTENTS (continued)
Table Page
2-1 Summary of Services Provided by TC Space Data Link Protocol . 2-7
4-1 Interpretation of the Bypass and Control Command Flags. 4-4
4-2 Interpretation of the Sequence Flags . 4-8
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 . 5-3
5-4 Managed Parameters for a MAP Channel . 5-4
5-5 Managed Parameters for Packet Transfer . 5-4
C-1 Mapping of Terms That Have Been Changed .C-2

CCSDS 232.0-B-2 Page viii September 2010
CCSDS RECOMMENDED STANDARD FOR TC SPACE DATA LINK PROTOCOL
1 INTRODUCTION
1.1 PURPOSE
The purpose of this Recommendation is to specify the Telecommand (TC) Space Data Link
Protocol. This protocol is a Data Link Layer protocol (see reference [1]) to be used over
ground-to-space or space-to-space communications links by space missions.
1.2 SCOPE
This Recommendation defines the TC 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 232.0-B-2 Page 1-1 September 2010
CCSDS RECOMMENDED STANDARD FOR TC 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:
a) section 1 presents the purpose, scope, applicability and rationale of this
Recommendation and lists the conventions, definitions, and normative references
used throughout the Recommendation;
b) section 2 provides an overview of the TC Space Data Link Protocol;
c) section 3 defines the services provided by the protocol entity;
d) section 4 specifies the protocol data units and procedures employed by the protocol
entity;
e) section 5 specifies the managed parameters used by the protocol entity;
f) annex A lists all acronyms used within this document;
g) annex B provides a list of informative references;
h) annex C lists the changes from the older CCSDS Recommendation (reference [B2]).
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 232.0-B-2 Page 1-2 September 2010
CCSDS RECOMMENDED STANDARD FOR TC 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 [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) 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.
asynchronous: not synchronous (see below).
CCSDS 232.0-B-2 Page 1-3 September 2010
CCSDS RECOMMENDED STANDARD FOR TC 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.
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.
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) shall be the first transmitted bit of the field, i.e., ‘Bit 0’ (see figure 1-1).
BIT N-1
BIT 0
N-BIT DATA FIELD
FIRST BIT TRANSMITTED = MSB
Figure 1-1: Bit Numbering Convention
CCSDS 232.0-B-2 Page 1-4 September 2010
CCSDS RECOMMENDED STANDARD FOR TC SPACE DATA LINK PROTOCOL
In accordance with standard data-communications practice, data fields are often grouped into
eight-bit ‘words’ which conform to the above convention. Throughout this
Recommendation, 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’.
1.7 REFERENCES
The following documents contain provisions which, through reference in this text, constitute
provisions of this Recommended Standard. At the time of publication, the editions indicated
were valid. All documents are subject to revision, and users of this Recommended Standard
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 Recommended Standards.
[1] Information Technology—Open Systems Interconnection—Basic Reference Model:
The Basic Model. International Standard, ISO/IEC 7498-1. 2nd ed. Geneva: ISO,
1994.
[2] Information Technology—Open Systems Interconnection—Basic Reference Model—
Conventions for the Definition of OSI Services. International Standard, ISO/IEC
10731:1994. Geneva: ISO, 1994.
[3] TC Synchronization and Channel Coding. Recommendation for Space Data System
Standards, CCSDS 231.0-B-2. Blue Book. Issue 2. Washington, D.C.: CCSDS, July
2010.
[4] Communications Operation Procedure-1. Recommendation for Space Data System
Standards, CCSDS 232.1-B-2. Blue Book. Issue 2. Washington, D.C.: CCSDS, July
2010.
[5] Space Link Identifiers. Recommendation for Space Data System Standards, CCSDS
135.0-B-4. Blue Book. Issue 4. Washington, D.C.: CCSDS, October 2009.
[6] CCSDS Global Spacecraft Identification Field Code Assignment Control Procedures.
Recommendation for Space Data System Standards, CCSDS 320.0-B-5. Blue Book.
Issue 5. Washington, D.C.: CCSDS, September 2007.
NOTE – Informative references are listed in annex B.

CCSDS 232.0-B-2 Page 1-5 September 2010
(Blank page)
CCSDS RECOMMENDED STANDARD FOR TC SPACE DATA LINK PROTOCOL
2 OVERVIEW
2.1 CONCEPT OF TC SPACE DATA LINK PROTOCOL
2.1.1 ARCHITECTURE
The TC Space Data Link Protocol is a Data Link Layer protocol (see reference [1]) to be
used by space missions. This protocol has been designed to meet the requirements of space
missions for efficient transfer of space application data of various types and characteristics
over ground-to-space or space-to-space communications links (hereafter called space links).
Figure 2-1 illustrates the relationship of this protocol to the Open Systems Interconnection
(OSI) reference model (reference [1]). Two sublayers of the Data Link Layer are defined for
CCSDS space link protocols as shown in reference [B]. The TC Space Data Link Protocol
corresponds to the Logical Link Sublayer and provides functions of transferring various data
using a variable-length protocol data unit called the Transfer Frame. The Channel Coding
Sublayer provides some additional functions necessary for transferring Transfer Frames over
a space link. These functions are the delimiting/synchronizing of Transfer Frames, error-
correction coding/decoding, and bit transition generation/removal (optional). For the
Channel Coding Sublayer, the Channel Coding and Synchronization Recommendation
(reference [3]) must be used with the TC Space Data Link Protocol. How the TC Space Data
Link Protocol is used in overall space data systems is shown in reference [B3].
OSI LAYERS CCSDS LAYERS
CCSDS
PROTOCOLS
NETWORK AND NETWORK AND
UPPER LAYERS UPPER LAYERS
DATA LINK
TC SPACE DATA LINK
PROTOCOL
PROTOCOL
SUBLAYER
DATA LINK LAYER
TC CHANNEL CODING
SYNCHRONIZATION
AND CHANNEL AND
CODING SUBLAYER
SYNCHRONIZATION
PHYSICAL LAYER PHYSICAL LAYER
Figure 2-1: Relationship with OSI Layers
2.1.2 PROTOCOL FEATURES
The TC Space Data Link Protocol provides the users with several services to transfer service
data units over a space link. The major functions performed by this protocol are (1)
segmentation and blocking of service data units and (2) transmission control of service data
units.
CCSDS 232.0-B-2 Page 2-1 September 2010
CCSDS RECOMMENDED STANDARD FOR TC SPACE DATA LINK PROTOCOL
Because the underlying space link inherently includes a noisy signal path, there is a finite
probability that it will introduce an error. It is desirable to break large service data units into
relatively small pieces so that each piece has a lower probability of being invalidated by
transmission error than if the entire service data unit were sent contiguously. System
throughput efficiency is improved because only small pieces have to be retransmitted when
errors are detected. However, there may also be situations in which the service data units are
very small. For efficient transfer of service data units, it is desirable to group these small
units into larger pieces. The TC Space Data Link Protocol provides the capability to break
large service data units into relatively small pieces (segmentation) and to group small service
data units into larger pieces (blocking).
The TC Space Data Link Protocol controls the transmission of service data units through the
space link performing retransmissions needed to ensure delivery of service data units in
sequence and without gaps or duplication. This function is provided by an automatic
retransmission control mechanism called the Communications Operation Procedure (COP).
The specification of the COP is given in reference [4]. In addition, a systematic
retransmission mechanism for use on deep space links can optionally be provided by the
Synchronization and Channel Coding Sublayer as specified in reference [3].
The protocol data units employed by this protocol are the TC Transfer Frame (unless
otherwise stated, the terms ‘Transfer Frame’ and ‘Frame’ in this document refer to the TC
Transfer Frame) and the Communications Link Control Word (CLCW). Each Transfer
Frame contains a header, which provides protocol control information, and a variable-length
data field, within which higher-layer service data units are carried. Transfer Frames are sent
in the direction of the flow of service data units. Each CLCW contains a report that describes
the status of acceptance of Transfer Frames. CLCWs are sent from the receiver to the sender
of Transfer Frames.
A key feature of the TC Space Data Link Protocol is the concept of ‘Virtual Channels’. The
Virtual Channel facility allows one Physical Channel to be shared among multiple higher-
layer data streams, each of which may have different service requirements. A single Physical
Channel may therefore be divided into several separate logical data channels, each known as
a ‘Virtual Channel’ (VC). Each Transfer Frame transferred over a Physical Channel belongs
to one of the Virtual Channels of the Physical Channel.
Optionally, this protocol enables service data units from different sources to be multiplexed
together in one Virtual Channel using ‘Multiplexer Access Points’ (MAPs). If MAPs are
used, service data units arriving at the service access point for a MAP at the sending end are
transferred to the corresponding MAP at the receiving end.
2.1.3 ADDRESSING
There are three identifier fields in the header of Transfer Frames: Transfer Frame Version
Number (TFVN), Spacecraft Identifier (SCID), and Virtual Channel Identifier (VCID). The
concatenation of a TFVN and a SCID is known as a Master Channel Identifier (MCID), and
CCSDS 232.0-B-2 Page 2-2 September 2010
CCSDS RECOMMENDED STANDARD FOR TC SPACE DATA LINK PROTOCOL
the concatenation of an MCID and a VCID is called a Global Virtual Channel Identifier
(GVCID). Therefore,
MCID = TFVN + SCID;
GVCID = MCID + VCID
= TFVN + SCID + VCID.
Each Virtual Channel on a Physical Channel is identified by a GVCID. Therefore, a Virtual
Channel consists of Transfer Frames having the same GVCID.
All Transfer Frames with the same MCID on a Physical Channel constitute a Master Channel
(MC). A Master Channel consists of one or more Virtual Channels. In most cases, a
Physical Channel carries only Transfer Frames of a single MCID, and the Master Channel
will be identical with the Physical Channel. However, a Physical Channel may carry
Transfer Frames with multiple MCIDs (with the same TFVN). In such a case, the Physical
Channel consists of multiple Master Channels. A Physical Channel is identified with a
Physical Channel Name, which is set by management and not included in the header of
Transfer Frames.
In the optional Segment Header, there is a field called Multiplexer Access Point Identifier
(MAP ID). All Transfer Frames with the same GVCID and MAP ID constitute a MAP
Channel. If the Segment Header is used, a Virtual Channel consists of one or multiple MAP
Channels. The concatenation of a GVCID and a MAP ID is known as a Global MAP ID
(GMAP ID). Therefore,
GMAP ID = GVCID + MAP ID
= MCID + VCID + MAP ID
= TFVN + SCID + VCID + MAP ID.
The relationships between these Channels are shown in figure 2-2.
CCSDS 232.0-B-2 Page 2-3 September 2010
CCSDS RECOMMENDED STANDARD FOR TC SPACE DATA LINK PROTOCOL
MAP Channel (Optional):
Identified by GMAP ID
Virtual Channel:
Identified by GVCID
Master Channel:
Identified by MCID
Physical Channel:
Identified by Physical
Channel Name
Figure 2-2: Relationships Between Channels
2.1.4 PROTOCOL DESCRIPTION
The TC Space Data Link Protocol is described in terms of:
a) the services provided to the users;
b) the protocol data units; and
c) the procedures performed by the protocol.
The service definitions are given in the form of primitives, which present an abstract model
of the logical exchange of data and control information between the protocol entity and the
service user. The definitions of primitives are independent of specific implementation
approaches.
The procedure specifications define the procedures performed by protocol entities for the
transfer of information between peer entities. The definitions of procedures are independent
of specific implementation methods or technologies.
This protocol specification also specifies the requirements for the underlying services
provided by the Channel Coding Sublayer and the Physical Layer.
2.2 OVERVIEW OF SERVICES
2.2.1 COMMON FEATURES OF SERVICES
The TC Space Data Link Protocol provides users with data transfer services. The point at
which a service is provided by a protocol entity to a user is called a Service Access Point
(SAP) (see reference [1]). Each service user is identified by a SAP address. At a SAP, two
ports may be provided, each of which is for one of the service types described in 2.2.2.
CCSDS 232.0-B-2 Page 2-4 September 2010
CCSDS RECOMMENDED STANDARD FOR TC SPACE DATA LINK PROTOCOL
Service data units of the same type submitted to a SAP (or a port if implemented) are
processed in the order of submission. No processing order is maintained for service data
units submitted to different SAPs (or ports).
NOTE – Implementations may be required to perform flow control at a SAP (or a port if
present) between the service user and the service provider. However, CCSDS
does not make any recommendations for a scheme for flow control between the
user and the provider.
The followings features are common to all the services defined by this Recommendation:
a) Unidirectional (one way) services: one end of a connection can send, but not receive,
data through the space link, while the other end can receive, but not send.
b) Asynchronous services: there are no predefined timing rules for the transfer of
service data units supplied by the service user or for the transmission of Transfer
Frames generated by the service provider. The user may request data transfer at any
time, but there may be restrictions imposed by the service provider on the data
generation rate. The timing of data transfer is determined by the provider in
accordance with mission-specific rules and may depend on the traffic at the time of
transfer.
c) Sequence preserving services: the sequence of service data units supplied by the
sending user is preserved through the transfer over the space link, although for the
Expedited Service, described below, there may be gaps in the sequence of service
data units delivered to the receiving user.
NOTE – This Recommendation assumes that these services are provided at the end points
...