ISO 18425:2013

Space data and information transfer systems — Spacecraft Onboard Interface Services — Subnetwork Packet Service

ISO 18425:2013 is one of a family of documents specifying the SOIS-compliant services to be provided by onboard subnetworks. ISO 18425:2013 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. ISO 18425:2013 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.

Systèmes de transfert des informations et données spatiales — Services d'interfaces à bord des véhicules spatiaux — Service en paquets par sous-réseau

General Information

• Status: Published
• Publication Date: 28-May-2013
• ICS: 49.140 - Space systems and operations
• Technical Committee: ISO/TC 20/SC 13 - Space data and information transfer systems
• Drafting Committee: ISO/TC 20/SC 13 - Space data and information transfer systems
• Current Stage: 9093 - International Standard confirmed
• Completion Date: 12-Sep-2018

Relations

• Consolidated By: ISO 7494-1:2018 - Dentistry — Stationary dental units and dental patient chairs — Part 1: General requirements
• Effective Date: 06-Jun-2022

Standards Content (Sample)

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 18425:2013(E)
ISO 2013
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ISO 18425:2013(E)
COPYRIGHT PROTECTED DOCUMENT
© 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

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

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Published in Switzerland
ii © ISO 2013 – All rights reserved
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ISO 18425:2013(E)
Foreword

ISO (the International Organization for Standardization) is a worldwide federation of national standards bodies

(ISO member bodies). The work of preparing International Standards is normally carried out through ISO

technical committees. Each member body interested in a subject for which a technical committee has been

established has the right to be represented on that committee. International organizations, governmental and

non-governmental, in liaison with ISO, also take part in the work. ISO collaborates closely with the

International Electrotechnical Commission (IEC) on all matters of electrotechnical standardization.

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

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

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

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

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

rights. ISO shall not be held responsible for identifying any or all such patent rights. Details of any patent

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

patent declarations received. www.iso.org/patents

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

constitute an endorsement.

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.
© ISO 2013 – All rights reserved iii
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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.
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ISO 18425:2013(E)
(Blank page)
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ISO 18425:2013(E)
Recommendation for Space Data System Practices
SPACECRAFT ONBOARD
INTERFACE SERVICES—
SUBNETWORK PACKET
SERVICE
RECOMMENDED PRACTICE
CCSDS 851.0-M-1
MAGENTA BOOK
December 2009
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ISO 18425:2013(E)
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
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ISO 18425:2013(E)
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
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ISO 18425:2013(E)
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
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ISO 18425:2013(E)
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
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ISO 18425:2013(E)
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
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ISO 18425:2013(E)
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
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ISO 18425:2013(E)
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
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ISO 18425:2013(E)
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
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ISO 18425:2013(E)
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
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ISO 18425:2013(E)
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 medium, by multiplexing traffic on a packet-by-packet basis. SDUs
larger than the MTU will be segmented into smaller PDUs.
octet: eight-bit word.
NOTE – An eight-bit word is commonly referred to as a byte.
packet: an arbitrary integer number of octets.
NOTE – The SDU for the packet service takes the form of a packet.
priority: transmit precedence of an SDU relative to other SDUs.

quality of service (QoS): ability of a communication system to provide predictable and

differentiated services.

NOTE – Quality of service for a communication service can be characterised in terms of

important features relevant to that communications service, for example:
reliability, transmission rate, effective bandwidth and latency, error rate.

segmentation: division of subnetwork service data units by the subnetwork into shorter

sections (segments) that are short enough to be sent over the data link.
CCSDS 851.0-M-1 Page 1-4 December 2009
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ISO 18425:2013(E)
CCSDS RECOMMENDED PRACTICE FOR SOIS SUBNETWORK PACKET SERVICE
NOTE – The subnetwork is responsible for reassembling the segments back into
subnetwork service data units when delivering to the subnetwork user entity.

service class: quality of service indicating whether resource reservation or reliability is

required.
1.6 DOCUMENT NOMENCLATURE
The following conventions apply throughout this Recommended Practice:
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.
1.7 REFERENCES

The following documents contain provisions which, through reference in this text, constitute

provisions of this Recommended Practice. At the time of publication, the editions indicated

were valid. All documents are subject to revision, and users of this Recommended Practice

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 Documents.
None.
NOTE – Informative references are contained in annex A.
CCSDS 851.0-M-1 Page 1-5 December 2009
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Communication Management
ISO 18425:2013(E)
CCSDS RECOMMENDED PRACTICE FOR SOIS SUBNETWORK PACKET SERVICE
2 OVERVIEW
2.1 FUNCTION

The SOIS Subnetwork Packet Service transfers Service Data Units, which comprise variable

length, delimited octet strings, from one endpoint on a data link/subnetwork to another

endpoint on the same data link/subnetwork, using the SOIS data link functions to move the

information across the data link/subnetwork.
2.2 CONTEXT

The SOIS Subnetwork layer provides for the movement of an SDU over a subnetwork to a

variety of user applications, Space Internet Services (SIS), and others. The service may be

provided over a variety of data links, and the method of such provision is not in the scope of

this document.

Data to be transported is passed to the Subnetwork Packet Service via the Subnetwork Packet

Service interface with a requested QoS. As shown in figure 2-1, the service is one of a

number of services which may be provided by the SOIS Subnetwork.
Mission
Application
Specific
Layer
Applications
Application
CMD & Data Time File & Message Device
Support Layer
Acquisition Access Packet Store Transfer Enumeration
Services Service Services Service Service
Transfer
Transport Protocol
Layer
Network Protocol
Subnetwork
Memory Device
Layer Packet Synchronisation Test
Access Discovery
Service Service Service
Service Service
Datalink Convergence Protocols
Milbus SpaceWire CAN Wireless
Figure 2-1: Subnetwork Packet Service Context

The Subnetwork Packet Service makes use of the data link to transfer data and control

information. A variety of data links may be suited to provision of the service, and the

strategy for such service provision is outlined in reference [A1].
A Subnetwork Management function is also provided for configuring, managing, and
collecting status information from the Subnetwork Packet Services.
CCSDS 851.0-M-1 Page 2-1 December 2009
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ISO 18425:2013(E)
CCSDS RECOMMENDED PRACTICE FOR SOIS SUBNETWORK PACKET SERVICE
2.3 ASSUMPTIONS
The following assumptions have been made in designing the SOIS Subnetwork Packet
Services:
– SOIS Subnetwork Packet Services are provided across single subnetworks.
– SOIS Subnetwork Packet Services are made available to protocol entities in the
Transfer, Application Support, and User Application Layers.
2.4 QUALITY OF SERVICE

The requested QoS is the concatenation of service class (Best-effort, Assured, Reserved, or

Guaranteed), priority, and, where appropriate, a channel identifier. Semantics and use of the

priority parameter are dependent on which service class is being invoked.

There are four communication service classes provided by the SOIS Subnetwork Packet

Service:
– Best-effort service class, as specified in 3.1.5.2 a);
– Assured service class, as specified in 3.1.5.2 b);
– Reserved service class, as specified in 3.1.5.2 c);
– Guaranteed service class, as specified in 3.1.5.2 d).

All service classes are sequence preserving within a channel or at a priority level. There is no

service-wide sequence preservation unless all users operate with no channelisation and at a

single priority.

The Best-effort and Reserved service classes deliver data in sequence and without errors; the

implication of these qualities is that PDUs that are received out of sequence or with errors

will not be delivered to the user. The user (sending or receiving) is not informed of such non-

delivery. It is therefore recommended that underlying data links be themselves inherently

...