ISO 18425:2013

INTERNATIONAL ISO
STANDARD 18425
First edition
2013-06-01
Space data and information transfer
systems — Spacecraft Onboard Interface
Services — Subnetwork Packet Service
Systèmes de transfert des informations et données spatiales —
Services d'interfaces à bord des véhicules spatiaux — Service en
paquets par sous-réseau
Reference number
©
ISO 2013
©  ISO 2013
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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
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International Electrotechnical Commission (IEC) on all matters of electrotechnical standardization.
The procedures used to develop this document and those intended for its further maintenance are described
in the ISO/IEC Directives, Part 1. In particular the different approval criteria needed for the different types of
ISO documents should be noted. This document was drafted in accordance with the editorial rules of the
ISO/IEC Directives, Part 2. www.iso.org/directives
Attention is drawn to the possibility that some of the elements of this document may be the subject of patent
rights. ISO shall not be held responsible for identifying any or all such patent rights. Details of any patent
rights identified during the development of the document will be in the Introduction and/or on the ISO list of
patent declarations received. www.iso.org/patents
Any trade name used in this document is information given for the convenience of users and does not
constitute an endorsement.
ISO 18425 was prepared by the Consultative Committee for Space Data Systems (CCSDS) (as
CCSDS 851.0-M-1, December 2009) 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.

INTERNATIONAL STANDARD ISO 18425:2013(E)

Space data and information transfer systems — Spacecraft
Onboard Interface Services — Subnetwork Packet Service
1 Scope
This International Standard is one of a family of documents specifying the SOIS-compliant services to be
provided by onboard subnetworks.
This International Standard defines services and service interfaces provided by the SOIS Subnetwork Packet
Service. Its scope is to specify the service only and not to specify methods of providing the service over a
variety of onboard data links.
This International Standard conforms to the principles set out in the Spacecraft Onboard Interface Services
Green Book and is intended to be applied together with it. The protocols which provide this service are to be
documented for individual links, and this can be in the purview of individual missions, agencies, or CCSDS,
depending on future circumstances.
The scope and field of application are furthermore detailed in subclause 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 851.0-M-1, December 2009, Spacecraft Onboard Interface Services — Subnetwork Packet Service.
For the purposes of international standardization, the modifications outlined below shall apply to the specific
clauses and paragraphs of publication CCSDS 851.0-M-1.
Pages i to v
This part is information which is relevant to the CCSDS publication only.
3 Revision of publication CCSDS 851.0-M-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 851.0-
M-1. To this end, NASA will act as a liaison body between CCSDS and ISO.

(Blank page)
2 © ISO 2013 – All rights reserved

Recommendation for Space Data System Practices
SPACECRAFT ONBOARD
INTERFACE SERVICES—
SUBNETWORK PACKET
SERVICE
RECOMMENDED PRACTICE
CCSDS 851.0-M-1
MAGENTA BOOK
December 2009
CCSDS RECOMMENDED PRACTICE FOR SOIS SUBNETWORK PACKET SERVICE
AUTHORITY
Issue: Recommended Practice, Issue 1
Date: December 2009
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 851.0-M-1 Page i December 2009
CCSDS RECOMMENDED PRACTICE FOR SOIS SUBNETWORK PACKET SERVICE
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 Recommendations and are not in
themselves considered binding on any Agency.
CCSDS Recommendations take two forms: Recommended Standards that are prescriptive
and are the formal vehicles by which CCSDS Agencies create the standards that specify how
elements of their space mission support infrastructure shall operate and interoperate with
others; and Recommended Practices that are more descriptive in nature and are intended to
provide general guidance about how to approach a particular problem associated with space
mission support. This Recommended Practice is issued by, and represents the consensus of,
the CCSDS members. Endorsement of this Recommended Practice is entirely voluntary
and does not imply a commitment by any Agency or organization to implement its
recommendations in a prescriptive sense.
No later than five years from its date of issuance, this Recommended Practice 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.
In those instances when a new version of a Recommended Practice is issued, existing
CCSDS-related member Practices and implementations are not negated or deemed to be non-
CCSDS compatible. It is the responsibility of each member to determine when such Practices
or implementations are to be modified. Each member is, however, strongly encouraged to
direct planning for its new Practices and implementations towards the later version of the
Recommended Practice.
CCSDS 851.0-M-1 Page ii December 2009
CCSDS RECOMMENDED PRACTICE FOR SOIS SUBNETWORK PACKET SERVICE
FOREWORD
This document is a technical Recommended Practice 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 Subnetwork Packet Service described herein is
intended for missions that are cross-supported between Agencies of the CCSDS, in the
framework of the Spacecraft Onboard Interface Services (SOIS) CCSDS area.
This Recommended Practice specifies a set of related services to be used by space missions
to transfer data over an onboard subnetwork. The SOIS Subnetwork Packet Service can
support various transport and network protocols like TCP/IP and can directly support
applications that only need to use a single subnetwork. The SOIS Subnetwork Packet Service
provides quality of service features and also provides a common service interface regardless
of the particular type of data link being used for communication.
Through the process of normal evolution, it is expected that expansion, deletion, or
modification of this document may occur. This Recommended Practice 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 851.0-M-1 Page iii December 2009
CCSDS RECOMMENDED PRACTICE FOR SOIS SUBNETWORK PACKET 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.
– 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.
– Russian Federal Space Agency (RFSA)/Russian Federation.
– Instituto Nacional de Pesquisas Espaciais (INPE)/Brazil.
– Japan Aerospace Exploration Agency (JAXA)/Japan.
– National Aeronautics and Space Administration (NASA)/USA.

Observer Agencies
– Austrian Space Agency (ASA)/Austria.
– Belgian Federal Science Policy Office (BFSPO)/Belgium.
– Central Research Institute of Machine Building (TsNIIMash)/Russian Federation.
– Centro Tecnico Aeroespacial (CTA)/Brazil.
– 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.
– 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 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 851.0-M-1 Page iv December 2009
CCSDS RECOMMENDED PRACTICE FOR SOIS SUBNETWORK PACKET SERVICE
DOCUMENT CONTROL
Document Title Date Status
CCSDS Spacecraft Onboard Interface December Original issue
851.0-M-1 Services—Subnetwork Packet 2009
Service, Recommended Practice,
Issue 1
CCSDS 851.0-M-1 Page v December 2009
CCSDS RECOMMENDED PRACTICE FOR SOIS SUBNETWORK PACKET SERVICE
CONTENTS
Section Page
1  INTRODUCTION . 1-1

1.1  PURPOSE AND SCOPE OF THIS DOCUMENT . 1-1
1.2  APPLICABILITY . 1-1
1.3  RATIONALE . 1-1
1.4  DOCUMENT STRUCTURE . 1-1
1.5  CONVENTIONS AND DEFINITIONS. 1-2
1.6  DOCUMENT NOMENCLATURE . 1-5
1.7  REFERENCES . 1-5

2  OVERVIEW . 2-1

2.1  FUNCTION . 2-1
2.2  CONTEXT . 2-1
2.3  ASSUMPTIONS . 2-2
2.4  QUALITY OF SERVICE . 2-2
2.5  SECURITY . 2-2

3  SUBNETWORK PACKET SERVICE . 3-1

3.1  SERVICE PARAMETERS . 3-1
3.2  PACKET SERVICE PRIMITIVES . 3-4

4  MANAGEMENT INFORMATION BASE . 4-1

4.1  OVERVIEW . 4-1
4.2  SPECIFICATIONS . 4-1
4.3  MIB GUIDANCE . 4-1

5  SERVICE CONFORMANCE STATEMENT PROFORMA . 5-2

ANNEX A INFORMATIVE REFERENCES . A-1
Figure
1-1  Bit Numbering Convention . 1-2
1-2  Relationship between PDU, SDU and PCI . 1-3
2-1  Subnetwork Packet Service Context . 2-1

CCSDS 851.0-M-1 Page vi December 2009
CCSDS RECOMMENDED PRACTICE FOR SOIS SUBNETWORK PACKET SERVICE
1 INTRODUCTION
1.1 PURPOSE AND SCOPE OF THIS DOCUMENT
This document is one of a family of documents specifying the SOIS-compliant services to be
provided by onboard subnetworks.
The purpose of this document is to define services and service interfaces provided by the
SOIS Subnetwork Packet Service. Its scope is to specify the service only and not to specify
methods of providing the service over a variety of onboard data links.
This document conforms to the principles set out in the Spacecraft Onboard Interface
Services Green Book (reference [A1]) and is intended to be applied together with it. The
protocols which provide this service are to be documented for individual links, and this can
be in the purview of individual missions, agencies, or CCSDS, depending on future
circumstance.
1.2 APPLICABILITY
This document applies to any mission or equipment claiming to provide a CCSDS SOIS-
compliant Packet Service.
1.3 RATIONALE
SOIS provide service interface specifications in order to promote interoperability and
development reuse via peer-to-peer and vertical standardisation.
1.4 DOCUMENT STRUCTURE
The document has five major sections:
– this section, containing administrative information, definitions, and references;
– section 2, describing general concepts and assumptions;
– section 3, containing the Subnetwork Packet Service specification;
– section 4, containing the Management Information Base (MIB) for the service;
– section 5, comprising a Service Conformance Statement Proforma.
In addition, annex A contains informative references.
CCSDS 851.0-M-1 Page 1-1 December 2009
CCSDS RECOMMENDED PRACTICE FOR SOIS SUBNETWORK PACKET SERVICE
1.5 CONVENTIONS AND DEFINITIONS
1.5.1 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’ (see figure 1-1).
BIT 0 BITN–1
N-BIT DATA FIELD
FIRST BIT TRANSFERRED = MSB
Figure 1-1: Bit Numbering Convention
In accordance with modern data communications practice, spacecraft data fields are often
grouped into eight-bit ‘words’ widely known as bytes. Throughout this Recommended
Practice, such an eight-bit word is called an ‘octet’.
The numbering for octets within a data structure starts with zero. By CCSDS convention, any
‘spare’ bits are permanently set to ‘0’.
1.5.2 DEFINITIONS
1.5.2.1 General
For the purpose of this document the following definitions apply.
1.5.2.2 Definitions from the Open Systems Interconnection (OSI) Basic Reference
Model
This document is defined using the style established by the Open Systems Interconnection
(OSI) Basic Reference Model (reference [A3]). This model provides a common framework
for the development of standards in the field of systems interconnection.
The following terms, used in this Recommended Practice, are adapted from definitions given
in reference [A3]:
layer: subdivision of the architecture, constituted by subsystems of the same rank.
packet service access point (PSAP): the point at which SOIS Packet service is provided by a
Packet service entity to a Packet service user entity.
CCSDS 851.0-M-1 Page 1-2 December 2009
CCSDS RECOMMENDED PRACTICE FOR SOIS SUBNETWORK PACKET SERVICE
packet service access point address (PSAP Address): a Packet service address that is used to
identify a single PSAP. The PSAP Address may be a Packet Source SAP Address (PSSAP) or
Packet Destination SAP Address (PDSAP).
protocol data unit (PDU): unit of data specified in a protocol and consisting of Protocol
Control Information (PCI) and possibly user data.
protocol ID: identifier which uniquely identifies a SOIS Subnetwork user within a data
system.
service: capability of a layer (service provider) together with the layers beneath it, which is
provided to the service users.
service data unit (SDU): an amount of data whose identity is preserved when transferred
between peer packet service user entities and which is not interpreted by the SOIS
Subnetwork service provider entities.
NOTE – The relationship between PDU, SDU and PCI is shown in figure 1-2.

Figure 1-2: Relationship between PDU, SDU and PCI
subnetwork: an abstraction of a collection of equipment and physical media, such as a local
area network or a data bus, which forms and autonomous whole and can be used to interconnect
real systems for the purpose of data transfer.
user data: the data transferred between Packet service entities on the behalf of the Packet
service user entities for whom the Packet service entities are providing a service.
1.5.2.3 Terms Defined in this Recommended Practice
For the purposes of this Recommended Practice, the following definitions also apply. Many
other terms that pertain to specific items are defined in the appropriate sections.
channel: identifier for subnetwork resources associated with a resource reservation.
CCSDS 851.0-M-1 Page 1-3 December 2009
CCSDS RECOMMENDED PRACTICE FOR SOIS SUBNETWORK PACKET SERVICE
NOTE – A channel can be a list of time slots in a time division multiplexed system or a
bandwidth limit in a bandwidth division multiplexed system. The subnetwork
resources required for the communication can also be defined to allow
simultaneous use of non-conflicting resources on subnetworks that support this
feature.
data system: addressable entity, situated in a subnet, which hosts an instance of the
subnetwork protocols, subnetwork services, and subnetwork users.
NOTE – The subnetwork users are uniquely identifiable in a subnetwork by a combination
of data system address and a protocol ID. A data system is typically a computer
or a device.
data system address: identifier which uniquely identifies a data system in a subnetwork.
NOTE – The data system address can be referred to as a destination address or a source
address depending on the context of its invocation at the subnetwork service
interface.
error: data bit received with the inverse value from that with which it was sent.
maximum transmission unit (MTU): maximum size of data that a data link can transmit as
a single PDU.
NOTE – The MTU is required to ensure that different sources of data get fair access to the
transmission
...