ISO 12174:2003

INTERNATIONAL ISO
STANDARD 12174
Second edition
2003-02-15
Space data and information transfer
systems — Telecommand —
Architectural specification for the data
management service
Systèmes de transfert des informations et données spatiales —
Télécommande — Définition architecturale du service de gestion des
données
Reference number
©
ISO 2003
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 2003
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 2003 – 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.
International Standard ISO 12174 was prepared by the Consultative Committee for Space Data Systems
(CCSDS) (as CCSDS 203.0-B-2, June 2001) 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 12174:1998), which has been technically
revised.
INTERNATIONAL STANDARD ISO 12174:2003(E)

Space data and information transfer systems —
Telecommand — Architectural specification for the data
management service
1 Scope
This International Standard specifies the requirements which define the architecture of a spacecraft
telecommand data management service. This architecture is intended to provide a common framework within
which space agencies may implement compatible future spacecraft telecommanding systems.
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 203.0-B-2, June 2001, Recommendation for space data system standards — Telecommand —
Part 3: Data management service — Architectural specification.
For the purposes of international standardization, the modifications outlined below shall apply to the specific
clauses and paragraphs of publication CCSDS 203.0-B-2.
Pages i to v
This part is information which is relevant to the CCSDS publication only.
Page 1-3
Add the following information to the references indicated:
[1] Document CCSDS 202.0-B-3, June 2001, is equivalent to ISO 12172:2003.
[2] Document CCSDS 201.0-B-3, June 2000, is equivalent to ISO 12171:2003.
[3] Document CCSDS 102.0-B-5, November 2000, is equivalent to ISO 13419:2003.
[4] Document CCSDS 101.0-B-5, June 2001, is equivalent to ISO 11754:2003.
[5] Document CCSDS 713.0-B-1, May 1999, is equivalent to ISO 15891:2000.
3 Revision of publication CCSDS 203.0-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 203.0-B-2. To this end, NASA will act as a liaison body between CCSDS and ISO.

2 © ISO 2003 – All rights reserved

Consultative
Committeefor
SpaceDataSystems
RECOMMENDATION FOR SPACE
DATA SYSTEM STANDARDS
TELECOMMAND
PART 3
DATA MANAGEMENT SERVICE
ARCHITECTURAL SPECIFICATION
CCSDS 203.0-B-2
BLUE BOOK
June 2001
(Blank page)
CCSDS RECOMMENDATION FOR TELECOMMAND: DATA MANAGEMENT SERVICE
AUTHORITY
Issue: Blue Book, Issue 2
Date: June 2001
Location: Oxfordshire, UK
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 the Reference [C1], 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
Program Integration Division (Code MT)
National Aeronautics and Space Administration
Washington, DC 20546, USA
CCSDS 203.0-B-2 Page i June 2001
CCSDS RECOMMENDATION FOR TELECOMMAND: DATA MANAGEMENT SERVICE
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:

o 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.

o 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.

o Specific service arrangements shall be 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 cancelled.
CCSDS 203.0-B-2 Page ii June 2001
CCSDS RECOMMENDATION FOR TELECOMMAND: DATA MANAGEMENT SERVICE
FOREWORD
This document, which is a technical Recommendation prepared by the Consultative
Committee for Space Data Systems (CCSDS), is intended for use by participating space
Agencies in their development of space telecommand systems.
This Recommendation allows the implementing organizations within each Agency to
proceed coherently with the development of compatible Standards for the flight and ground
systems that are within their cognizance. Agency Standards derived from this
Recommendation may implement only a subset of the optional features allowed herein, or
may incorporate features not addressed by the Recommendation.
In order to establish a common framework within which the Agencies may develop
standardized telecommand services, the CCSDS advocates adoption of a layered systems
architecture. Within this approach, specific layers of service (including their operational
protocol and data structuring techniques) may be selected for implementation according to
mission requirements.
The current layered set of CCSDS telecommand Recommendations was developed to match
the conventional free-flying mission environment, as characterized by the transmission of
command data at relatively low uplink data rates to spacecraft of moderate complexity. The
CCSDS is currently examining the extension of these Recommendations (perhaps by
defining expanded protocols and data structures within some of the layers) to a more
complex mission environment, including the transmission of multiple data types at very high
data rates to space vehicles which include extensive onboard data networking capability.
This Recommendation for Telecommand Data Management Service was developed within
the layered architectural framework, and embraces the standard data structures and data
communication procedures which may be used by conventional missions within the highest
telecommand system layers.
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 defined in Reference [C1].
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 Report should be addressed to the CCSDS
Secretariat at the address on page i.
CCSDS 203.0-B-2 Page iii June 2001
CCSDS RECOMMENDATION FOR TELECOMMAND: DATA MANAGEMENT SERVICE
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 Centre (CRC)/Canada.
– 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.
– Swedish Space Corporation (SSC)/Sweden.
– United States Geological Survey (USGS)/USA.

CCSDS 203.0-B-2 Page iv June 2001
CCSDS RECOMMENDATION FOR TELECOMMAND: DATA MANAGEMENT SERVICE
DOCUMENT CONTROL
Document Title and Issue Date Status
CCSDS Telecommand Part 3— January 1987 Original Issue (superseded).
203.0-B-1 Data Management Service,
Issue 1
Current Issue:
CCSDS Telecommand Part 3— June 2001
adds specifications to
203.0-B-2 Data Management Service,
support use of TC
Issue 2
Transfer Frame to
transport various types of
packets, including TC
Packets, CCSDS Network
Protocol (NP) datagrams,
and Internet Protocol (IP)
datagrams.
NOTE:  Substantive changes from the previous issue are flagged with change bars in the
inside margin.
CCSDS 203.0-B-2 Page v June 2001
CCSDS RECOMMENDATION FOR TELECOMMAND: DATA MANAGEMENT SERVICE
CONTENTS
Sections Page
1 INTRODUCTION. 1-1

1.1 PURPOSE AND SCOPE. 1-1
1.2 APPLICABILITY.1-1
1.3 BIT NUMBERING CONVENTION AND NOMENCLATURE. 1-2
1.4 REFERENCES.1-3

2 TELECOMMAND DATA MANAGEMENT SERVICE OVERVIEW. 2-1
3 APPLICATION PROCESS LAYER: STANDARD DATA STRUCTURES AND
PROCEDURES . 3-1

3.1 OVERVIEW OF THE LAYER . 3-1
3.2 STANDARD DATA STRUCTURES WITHIN THE LAYER. 3-3
3.3 STANDARD PROCEDURES WITHIN THE LAYER . 3-3

4 SYSTEM MANAGEMENT LAYER: STANDARD DATA STRUCTURES AND
PROCEDURES . 4-1

4.1 OVERVIEW OF THE LAYER . 4-1
4.2 STANDARD DATA STRUCTURES WITHIN THE LAYER. 4-2
4.3 STANDARD PROCEDURES WITHIN THE LAYER . 4-2

5 PACKETIZATION LAYER: STANDARD DATA STRUCTURES AND
PROCEDURES . 5-1

5.1 OVERVIEW OF THE LAYER . 5-1
5.2 CCSDS TELECOMMAND PACKET . 5-1
5.3 OTHER TYPES OF PACKETS . 5-6
5.4 STANDARD PROCEDURES WITHIN THE LAYER . 5-9

ANNEX A DATA MANAGEMENT SERVICE  ACRONYMS AND
TERMINOLOGY . A-1
ANNEX B DATA MANAGEMENT SERVICE SPECIFICATION. B-1
ANNEX C INFORMATIVE REFERENCES. C-1
CCSDS 203.0-B-2 Page vi June 2001
CCSDS RECOMMENDATION FOR TELECOMMAND: DATA MANAGEMENT SERVICE
CONTENTS
Figure Page
2-1 Telecommand System .2-2
3-1 Application Process Layer Functional Overview.3-2
5-1 Telecommand Packet Format.5-2

CCSDS 203.0-B-2 Page vii June 2001
(Blank page)
CCSDS RECOMMENDATION FOR TELECOMMAND: DATA MANAGEMENT SERVICE
1 INTRODUCTION
1.1 PURPOSE AND SCOPE
The purpose of this document is to establish a common Recommendation which defines the
systems architecture of a spacecraft telecommand "Data Management Service". The intent of
this architecture is to provide a common framework within which the Agencies participating
in the Consultative Committee for Space Data Systems (CCSDS) may implement compatible
future spacecraft telecommanding systems. The operating principles and procedures for the
CCSDS are defined in Reference [C1]. The context of the Data Management Service within
the overall Telecommand System is described in Reference [C2].
This Recommendation primarily addresses the data unit formats and functions which are
implemented within the the Application Process layer, the System Management layer and the
Packetization layer of the CCSDS telecommand Data Management Service. Recognizing
that much future work remains to be done relative to these top layers, their specification has
been deliberately minimized by the CCSDS. IN PARTICULAR, THE DETAILED
OPERATIONAL PROTOCOLS WHICH OPERATE ACROSS THESE LAYERS,
AND THE FLOW OF CONTROL INFORMATION REQUIRED TO INITIALIZE
THE LAYERS AND DIRECT THE TRANSFER OF DATA BETWEEN THEM, ARE
NOT PRESENTLY ADDRESSED WITHIN THIS DOCUMENT: THESE REMAIN
ITEMS FOR POTENTIAL EXTENSION OF THIS RECOMMEN- DATION.
1.2 APPLICABILITY
This Recommendation serves as a guideline for the development of compatible internal
Agency standards in field of spacecraft commanding. This Recommendation is not
retroactive, nor does it commit any Agency to implement the recommended telecommand
concepts at any future time. Nevertheless, all CCSDS Agencies accept the principle that all
future implementations of telecommand which are used in cross-support situations will be
based on this Recommendation.
The CCSDS has developed a layered concept for future spacecraft telecommanding, which is
fully described in Reference [C2]. Standard services are defined within each layer, and
Agencies will be encouraged to develop corresponding facilities to provide these services in
support of Projects.  To be fully compatible with the CCSDS concept, a Project's
telecommanding architecture should follow this Recommendation for Data Management
Service, plus the Recommendations for telecommand "Data Routing Service" and
telecommand "Channel Service" which are described in References [1] and [2]. Projects
may also elect to be partially compatible with the concept by interfacing with the standard
systems at intermediate layers within any of the service specifications.
CCSDS 203.0-B-2 Page 1-1 June 2001
CCSDS RECOMMENDATION FOR TELECOMMAND: DATA MANAGEMENT SERVICE
Where preferred options or mandatory capabilities are clearly indicated herein, the indicated
sections of the specification must be implemented when this Recommendation is used as a
basis for cross-support. Where optional subsets or capabilities are allowed or implied in this
specification, implementation of these options or subsets is subject to specific bilateral cross-
support agreements between the Agencies involved.
The recommendations in this document are to be invoked through the normal standards
programs of each member Agency, and are applicable to those missions for which cross-
support based on capabilities described in these recommendations is anticipated.
No later than five years from its date of issue, this Recommendation should be reviewed by
the CCSDS Agencies 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.
1.3 BIT NUMBERING CONVENTION AND NOMENCLATURE
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".
BIT 0 BIT N-1
N-BIT DATA FIELD
FIRST BIT TRANSMITTED = MSB
In accordance with modern data communications practice, spacecraft data fields are often
grouped into 8-bit "words" which conform to the above convention. Throughout this
Recommendation, the following nomenclature is used to describe this grouping:

8-BIT WORD = "OCTET"
By CCSDS convention, all "spare" bits shall be permanently set to value "zero". Note that
throughout this document, the word "Telecommand" may be abbreviated as "TC".
CCSDS 203.0-B-2 Page 1-2 June 2001
CCSDS RECOMMENDATION FOR TELECOMMAND: DATA MANAGEMENT SERVICE
1.4 REFERENCES
[1] Telecommand Part 2—Data Routing Service. Recommendation for Space Data System
Standards, CCSDS 202.0-B-3. Blue Book. Issue 3. Washington, D.C.: CCSDS, June
2001.
[2] Telecommand Part 1—Channel Service. Recommendation for Space Data System
Standards, CCSDS 201.0-B-3. Blue Book. Issue 3. Washington, D.C.: CCSDS, June
2000.
[3] Packet Telemetry. Recommendation for Space Data System Standards, CCSDS 102.0-
B-5. Blue Book. Issue 5. Washington, D.C.: CCSDS, November 2000.
[4] Telemetry Channel Coding. Recommendation for Space Data System Standards,
CCSDS 101.0-B-5. Blue Book. Issue 5. Washington, D.C.: CCSDS, June 2001.
[5] Space Communications Protocol Specification (SCPS)—Network Protocol (SCPS-NP).
Recommendation for Space Data System Standards, CCSDS 713.0-B-1. Blue Book.
Issue 1. Washington, D.C.: CCSDS, May 1999.
[6] J. Postel. Internet Protocol. STD 5, September 1981. [RFC 791, RFC 950, RFC 919,
†
RFC 922, RFC 792, RFC 1112]
[7] S. Deering and R. Hinden. Internet Protocol, Version 6 (IPv6) Specification. RFC 1883,
December 1995.
The latest issues of these documents may be obtained from the CCSDS Secretariat at the
address indicated on page i.
† Internet Request for Comments (RFC) texts are available on line in various locations (e.g.,
http://ietf.org/rfc/); Internet standards are made up of one or more RFCs, which are identified in
square brackets following the entry.
CCSDS 203.0-B-2 Page 1-3 June 2001
(Blank page)
CCSDS RECOMMENDATION FOR TELECOMMAND: DATA MANAGEMENT SERVICE
2 TELECOMMAND DATA MANAGEMENT SERVICE OVERVIEW
A complete summary of the acronyms and terminology used internal to this document is
presented in Annex A, and a detailed specification of the services provided by each layer is
presented in Annex B.  The first-time reader should digest these Annexes before proceeding
further in this document.
Figure 2-1 illustrates the significance of the TC Data Management Service within the overall
Telecommand System, which contains three principal elements of service: Telecommand
Data Management Service; Telecommand Data Routing Service; and Telecommand Channel
Service. Each of these services is documented in separate Recommendations. A more
thorough discussion of the layered services, including expansion of Figure 2-1 in greater
detail, is contained in Reference [C2]. The Telecommand System is related to the Telemetry
System as documented in Reference [3] and Reference [4].
The TC Data Management Service enables user requests for command activity to be
generated, integrated, aggregated, translated and scheduled for delivery to the spacecraft by
drawing upon the Data Routing and Channel Services. The Data Management Service
contains three distinct layers of data handling operations:
(1) An APPLICATION PROCESS layer, which allows human users to control a
space mission by generating commands and supervising their delivery and
execution.
(2) A SYSTEM MANAGEMENT layer, which translates user command directives
into detailed command application data and delivery instructions, and which
manages their end-to-end delivery to the proper Application Process on the
spacecraft.
(3) A PACKETIZATION layer, which formats the command application data into
transportable telecommand data units and moves them to the spacecraft.
CCSDS 203.0-B-2 Page 2-1 June 2001
CCSDS RECOMMENDATION FOR TELECOMMAND: DATA MANAGEMENT SERVICE

APPLICATION PROCESS LAYER
COMMAND DIRECTIVE
TELECOMMAND,
PART 3: DATA
SYSTEM MANAGEMENT LAYER
MANAGEMENT SERVICE
TC APPLICATION DATA
PACKETIZATION LAYER
PACKET
SEGMENTATION LAYER
TELECOMMAND,
PART 2: DATA
SEGMENT
ROUTING SERVICE
TRANSFER LAYER
TRANSFER FRAME
CODING LAYER
TELECOMMAND,
CLTU
PART 1: CHANNEL
SERVICE
PHYSICAL LAYER
PHYSICAL WAVEFORM
Figure 2-1: Telecommand System
CCSDS 203.0-B-2 Page 2-2 June 2001
CCSDS RECOMMENDATION FOR TELECOMMAND: DATA MANAGEMENT SERVICE
NOTE A: Figure 2-1 represents a logical view of the TC System and physical
implementations may not necessarily correspond to the sequential flow of
operations implied by the figure.
NOTE B: This Recommendation primarily specifies the data structures and procedures
flowing ACROSS the layers from the sending to the receiving end of the
TC system, since these have a direct impact on the long lead-time design of
future spacecraft hardware and software. Comprehensive definition of the
associated operational protocols within each layer and the control
instructions, which are required to initialize the layers and to direct the flow
of TC data units BETWEEN the layers, remain items for potential future
extension of this document.
NOTE C: Inter-Agency cross-support gateways for telecommand are discussed in
Reference [C2].
CCSDS 203.0-B-2 Page 2-3 June 2001
(Blank page)
CCSDS RECOMMENDATION FOR TELECOMMAND: DATA MANAGEMENT SERVICE
3 APPLICATION PROCESS LAYER: STANDARD DATA
STRUCTURES AND PROCEDURES
3.1 OVERVIEW OF THE LAYER
The service provided by the Application Process layer is to allow users to control remote
instruments or subsystems in space. The layer performs this service by providing its own
internal functions, and by drawing on services provided by the lower layers of the TC
System.  A functional overview of the Application Process layer is presented in Figure 3-1.
The sending end of the layer contains a large number of diverse Application Processes,
arranged to form a system which is used to supervise a particular space mission.  For the
purpose of illustration, a few representative clusters of application processes are shown in the
figure.  The Application Processes are supervised by an "Application Executive" which
controls the overall flow of activities within the layer. Within the system, clusters of
specialized application processes (e.g., flight path control, spacecraft and communication
network monitor and control) exist to support the users.
Users enter the Application Process layer via application processes in their workstations.
These application processes provide the man/machine interface which permit them to
communicate via the Application Executive with the other application processes within the
system.
One cluster of application processes provides the planning, scheduling and "mission
sequencing" function that integrates all user command requests into a workable flight profile.
The output of these application processes is an integrated, aggregated, validated, constraint-
checked set of "Command Directives" which specify (in a high-level language) the sets of
user commands that are to be delivered to the spacecraft for execution.  Some of these
Command Directives, which are addressed to the onboard sequence control process, define
the system conditions which must exist before the remaining sets of commands are released
for execution. The mission sequencing process provides control and coordination of the
assignment of names which identify the sets of commands throughout delivery and execution.
Command Directives, formatted in a logical notation known as an "abstract transfer syntax",
contain high-level expressions of the desired command activity.  They contain the commands
themselves, plus requirements for control of their delivery such as time windows,
interrelationship and interdependency information, user naming conventions, contingency
procedures, etc.
Management of the end-to-end delivery of commands is provided by another cluster of
specialized "delivery control" application processes, which interface the Application Process
layer with the supporting telecommand layers that interconnect its sending and receiving
ends.
CCSDS 203.0-B-2 Page 3-1 June 2001
CCSDS RECOMMENDATION FOR TELECOMMAND: DATA MANAGEMENT SERVICE
CCSDS 203.0-B-2 Page 3-2 June 2001
RECEIVING RECEIVING RECEIVING RECEIVING
ELEMENT ELEMENT ELEMENT ELEMENT
USER USER USER USER
APPLICATION APPLICATION APPLICATION
APPLICATION
APPLICATION APPLICATION APPLICATION APPLICATION
PROCESS: PROCESS: PROCESS:
PROCESS:
PROCESS: PROCESS: PROCESS: PROCESS:
Man/Machine Man/Machine Man/Machine
Man/Machine
Instrument Subsystem Instrument Subsystem
Interface Interface Interface
Interface
Interface Interface Interface Interface
APPLICATION APPLICATION
APPLICATION APPLICATION
PROCESSES: APPLICATION EXECUTIVE PROCESSES:
PROCESSES: APPLICATION EXECUTIVE PROCESSES:
Flight Path (Sending End) Mission
Attitude (Receiving End) Sequence
Control Sequencing
Control Control
APPLICATION APPLICATION APPLICATION APPLICATION
APPLICATION APPLICATION
PROCESSES: PROCESSES: PROCESSES: PROCESSES:
PROCESSES: PROCESSES:
Spacecraft TC Delivery Comm. Net. Maneuver
Spacecraft TC Delivery
Control Control Control Control
Management Control
SUPPORTING TELECOMMAND LAYERS
Figure 3-1: Application Process Layer Functional Overview

CCSDS RECOMMENDATION FOR TELECOMMAND: DATA MANAGEMENT SERVICE
The highest of the supporting telecommand layers is the System Management layer.
Downwards across the sending-end interface with the System Management layer flow named
sets of Command Directives containing abstract-syntax commands and delivery instructions,
while upwards flow reports describing the status of their delivery.  The System Management
layer provides the service of translating between the abstract transfer syntax of the
Application Process layer and the "concrete transfer syntax" used by the lower layers of the
data communication part of the Telecommand System.
The receiving end of the Application Process layer mirrors the sending end, i.e., an
Application Executive which orchestrates clusters of onboard application processes. Sets of
commands are received from the onboard System Management layer by a group of delivery
control processes, which report status back to the sending end. The sets of commands are
forwarded to a spacecraft sequence control function (e.g., a central onboard computer) or
directly to the addressed spacecraft instrument or subsystem. The receiving elements
themselves are supported by specialized application processes that convert command
directives into desired actions, and report their execution.
3.2 STANDARD DATA STRUCTURES WITHIN THE LAYER
The CCSDS is developing standard data interchange structures for the exchange of data
between application processes.
Although it is assumed that CCSDS standard data interchange structures will be used
extensively within the layer, particularly at the sending end of the TC System, the only formal
requirement in this issue of the Recommendation is that standard data interchange structures
must be used to carry information bidirectionally across the interface at the sending end of the
system between the Application Process layer and the System Management layer. The
concrete formats of the standard data interchange structures which pass information
"downwards" and "upwards" across this interface are presently unspecified.  The standard
data interchange structures shall contain the Telecommand data themselves, plus the control
instructions which must be passed to lower layers in order to specify the services required
during the delivery process. The use of CCSDS standard data interchange structures is
discussed in Reference [C2].
3.3 STANDARD PROCEDURES WITHIN THE LAYER
In the future, it is possible that a standardized core of mission independent services and
procedures may be provided within both ends of this layer. Projects will then be able to
augment this core with their own unique application processes.
However, in this issue of the Recommendation the procedures internal to this layer are left
unspecified by the CCSDS. This reflects an evolutionary philosophy whereby it is recognized
that many of these functions will continue to be developed on a mission-by-mission basis in the
near or medium term, or perhaps will be standardized within one Agency or one Center. The
CCSDS 203.0-B-2 Page 3-3 June 2001
CCSDS RECOMMENDATION FOR TELECOMMAND: DATA MANAGEMENT SERVICE
approach of the CCSDS is therefore to first agree on standardization of the lower layers of the
Telecommand System (i.e., the Packetization, Segmentation, Transfer, Coding and Physical
layers), and then to gradually migrate upwards into standardization of the higher layers as
experience is gained with actual operational use of the automated system.
Potential items for future standardization include:
(1) Selection of a standard language and procedures to be used at the interface
between the human user and sending end of the layer.
(2) Selection of a standard abstract transfer syntax for Command Directives.

CCSDS 203.0-B-2 Page 3-4 June 2001
CCSDS RECOMMENDATION FOR TELECOMMAND: DATA MANAGEMENT SERVICE
4 SYSTEM MANAGEMENT LAYER: STANDARD DATA
STRUCTURES AND PROCEDURES
4.1 OVERVIEW OF THE LAYER
The service provided by the System Management layer is to translate between the high-level
commanding language used within the layer above and the detailed communications and
control language used by the layers below, and to manage the overall operation of the lower
layers so that reliable and error-free delivery of commands may be assured. The System
Management layer therefore performs the interface transformations between the output of the
Application Process layer, and the lower layer bit-level data communication systems which
move these commands to the spacecraft.
To provide this service, the System Management layer parses the Command Directives and
prepares them for transport. The user-named sets of commands and their execution
conditions are translated between the abstract transfer syntax used within the Application
Process layer and the concrete telecommand transfer syntax which is used by lower layers
during communication. At the sending end, this involves formatting the actual command
application data into a presentation syntax which is compatible with direct insertion into the
data units of the layer below (e.g., the data field of Telecommand Packets) for delivery to the
spacecraft. The System Management layer instructs lower layers whether the user application
data are to be handled as individual command messages, sequences of messages, or as an
integrated file.
The delivery instructions from the layer above are translated into TC Session control
instructions by the System Management layer by:
(1) Specifying the class of transport service required from lower layers (single
messages, or files of messages) and requesting any related lower-layer services
such as the attachment of telecommands to particular data routing paths, the
selection of retransmission protocols to be used during transfer to the spacecraft,
communications security procedures, etc.
(2) Managing the traceability of sets of telecommands by translating the user names
into identifiers which can be inserted into the transportable data units of the layer
below.
(3) Calling the appropriate lower-layer services required during the session, including
selection of operational procedures and time windows.
(4) Specifying the recovery procedures to be used in the event of service interruption
during a session.
The System Management layer provides management of interrelated sets of commands
during delivery. Local names are assigned to the sets of commands in order to trace and
supervise their transport: the local names are correlated with user names by the layer, so that
user visibility into the delivery process is provided.
CCSDS 203.0-B-2 Page 4-1 June 2001
CCSDS RECOMMENDATION FOR TELECOMMAND: DATA MANAGEMENT SERVICE
4.2 STANDARD DATA STRUCTURES WITHIN THE LAYER
Although it is assumed that standard data interchange structures will be used extensively
within the sending end of the layer, the only formal requirement in this issue of the
Recommendation is that these data structures must be used to carry information
bidirectionally across the interface between the sending end of the System Management layer
and lower layers. The concrete formats of the standard data interchange structures which
pass information "downwards" and "upwards" across this interface are presently unspecified.
4.3 STANDARD PROCEDURES WITHIN THE LAYER
In this issue of the Recommendation, operational procedures within the System Management
layer are unspecified by the CCSDS.
CCSDS 203.0-B-2 Page 4-2 June 2001
CCSDS RECOMMENDATION FOR TELECOMMAND: DATA MANAGEMENT SERVICE
5 PACKETIZATION LAYER: STANDARD DATA STRUCTURES
AND PROCEDURES
5.1 OVERVIEW OF THE LAYER
The service provided by the Packetization layer is to provide end-to-end transport of user
application data between the sending and receiving ends of the TC System. At the sending
end, user application data are given to the Packetization layer in concrete transfer syntax by
the layer above (i.e., the System Management layer): these data are encapsulated within
standard data interchange structures containing transport control instructions. The
Packetization layer draws upon the lower-layer capabilities of the Telecommand Data
Routing Service (Segmentation and Transfer layers) and the TC Channel Service (Coding and
Physical layers) in order to establish a transport path in response to a call for connection by
the System Management layer.
A packet is a standard data structure which encapsulates the user application data that are to
be transported from the output of the sending end to the input of the receiving end of the
System Management layer. Packets may exist as standalone entities, or may be batched
together into interdependent "TC Files". At the sending end TC Packets or Files are passed
to the layer below (e.g., the Data Routing Service) for transfer to the spacecraft by
encapsulating them within CCSDS standard data interchange structures which also contain
their routing control instructions.
The abstract content and concrete format of the CCSDS standard data interchange structures
which are used at the sending end of the TC System to pass data between the Packetization
layer and lower layers is presently unspecified.
5.2 CCSDS TELECOMMAND PACKET
The TC Packet is one of the standard transport data structure of the TC System. The CCSDS
TC Packet data structure is shown in Figure 5-1. It consists of the following major fields:
Major Field Length (Octets)
Primary Header 6
Secondary Header Variable (optional)
Application Data Variable, up to 65,536
It should be noted that the format of the TC Packet is virtually identical to that of the
Telemetry Packet (Reference [3]). The maximum end-to-end length of the current version of
the TC Packet is constrained by the implementation to be no more than 65,542 octets.

CCSDS 203.0-B-2 Page 5-1 June 2001
CCSDS RECOMMENDATION FOR TELECOMMAND: DATA MANAGEMENT SERVICE

PRIMARY HEADER
PACKET SECONDARY
PACKET PACKET APPLICATION
SEQUENCE HEADER
IDENTIFICATION LENGTH DATA
CONTROL (OPTIONAL)
VERSION TYPE SEC. APPLIC. SEQUENCE PACKET (MAY CONTAIN:
# HDR. PROCESS FLAGS NAME OR * S/C TIME
FLAG ID SEQUENCE * PACKET
COUNT  FORMAT
* ANCILLARY
DATA)
1 11
3 1 2 14
000 1
2 2 2
OCTETS OCTETS OCTETS (VARIABLE) (VARIABLE)
Figure 5-1: Telecommand Packet Format
5.2.1 PRIMARY HEADER
The Primary Header consists of 6 octets subdivided into the following fields:

Field Length (Bits)
PACKET IDENTIFICATION 16
- Version Number (3)
- Type (1)
- Secondary Header Flag (1)
- Application Process ID (11)
PACKET SEQUENCE CONTROL 16
- Sequence Flags (2)
- Packet Na
...