Space data and information transfer systems -- Space link extension (SLE) -- Forward communications link transmission unit (CLTU) service specification

This document defines the Communications Link Transmission Unit (CLTU) service in conformance with the transfer services specified in reference [1], Cross Support Reference Model—Part 1: SLE Services. The Forward CLTU service is a Space Link Extension (SLE) transfer service that enables a mission to send Communications Link Transmission Units (CLTUs) to a spacecraft. This document defines, in an abstract manner, the Forward CLTU service in terms of: the operations necessary to provide the transfer service; the parameter data associated with each operation; the behaviors that result from the invocation of each operation; and the relationship between, and the valid sequence of, the operations and resulting behaviors. It does not specify: individual implementations or products; the implementation of entities or interfaces within real systems; the methods or technologies required to radiate data to a spacecraft and to acquire telemetry frames from the signals received from that spacecraft for extraction of the Operational Control Field; the methods or technologies required for communications; or the management activities necessary to schedule, configure, and control the Forward CLTU service.

Systèmes de transfert des informations et données spatiales -- Extension de liaisons spatiales (SLE) -- Service de l'unité de transmission pour la liaison d'envoi de télécommande (CLTU)

General Information

Status
Published
Publication Date
29-Jun-2021
Current Stage
5060 - Close of voting Proof returned by Secretariat
Start Date
28-May-2021
Completion Date
28-May-2021
Ref Project

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INTERNATIONAL ISO
STANDARD 22671
Fourth edition
2021-06
Space data and information transfer
systems — Space link extension
(SLE) — Forward communications
link transmission unit (CLTU) service
specification
Systèmes de transfert des informations et données spatiales —
Extension de liaisons spatiales (SLE) — Service de l'unité de
transmission pour la liaison d'envoi de télécommande (CLTU)
Reference number
ISO 22671:2021(E)
ISO 2021
---------------------- Page: 1 ----------------------
ISO 22671:2021(E)
COPYRIGHT PROTECTED DOCUMENT
© ISO 2021

All rights reserved. Unless otherwise specified, or required in the context of its implementation, 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
CP 401 • Ch. de Blandonnet 8
CH-1214 Vernier, Geneva
Phone: +41 22 749 01 11
Email: copyright@iso.org
Website: www.iso.org
Published in Switzerland
ii © ISO 2021 – All rights reserved
---------------------- Page: 2 ----------------------
ISO 22671:2021(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 (see 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 (see 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.

For an explanation of the voluntary nature of standards, the meaning of ISO specific terms and

expressions related to conformity assessment, as well as information about ISO's adherence to the World

Trade Organization (WTO) principles in the Technical Barriers to Trade (TBT) see
www.iso.org/iso/foreword.html.

This document was prepared by the Consultative Committee for Space Data Systems (CCSDS) (as CCSDS

912.1-B-4, August 2016) and was adopted (without modifications) by Technical Committee ISO/TC 20,

Space vehicles, Subcommittee SC 13, Space data and information transfer systems.

This fourth edition cancels and replaces the third edition (ISO 22671:2011), which has been technically

revised.
The main changes compared to the previous edition are as follows:
— adds clarifications and corrections.

Any feedback or questions on this document should be directed to the user’s national standards body. A

complete listing of these bodies can be found at www.iso.org/members.html.
© ISO 2021 – All rights reserved iii
---------------------- Page: 3 ----------------------
ISO 22671:2021(E)
CCSDS RECOMMENDED STANDARD FOR SLE FCLTU SERVICE
CONTENTS
Section Page

1 INTRODUCTION .......................................................................................................... 1-1

1.1 PURPOSE OF THIS RECOMMENDED STANDARD ........................................ 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 DEFINITIONS, NOMENCLATURE, AND CONVENTIONS ............................ 1-5

1.7 REFERENCES ..................................................................................................... 1-12

2 DESCRIPTION OF THE FORWARD CLTU SERVICE ......................................... 2-1

2.1 OVERVIEW ........................................................................................................... 2-1

2.2 SPACE LINK EXTENSION REFERENCE MODEL ........................................... 2-2

2.3 SERVICE MANAGEMENT .................................................................................. 2-3

2.4 ARCHITECTURE MODEL – FUNCTIONAL VIEW .......................................... 2-3

2.5 ARCHITECTURE MODEL – CROSS-SUPPORT VIEW .................................... 2-6

2.6 FUNCTIONAL DESCRIPTION ............................................................................ 2-7

2.7 OPERATIONAL SCENARIO ............................................................................. 2-14

2.8 SECURITY ASPECTS OF THE SLE FORWARD CLTU

TRANSFER SERVICE ........................................................................................ 2-16

3 FORWARD CLTU SERVICE OPERATIONS .......................................................... 3-1

3.1 GENERAL CONSIDERATIONS .......................................................................... 3-1

3.2 CLTU-BIND ........................................................................................................... 3-8

3.3 CLTU-UNBIND ................................................................................................... 3-15

3.4 CLTU-START ...................................................................................................... 3-18

3.5 CLTU-STOP ......................................................................................................... 3-22

3.6 CLTU-TRANSFER-DATA .................................................................................. 3-25

3.7 CLTU-ASYNC-NOTIFY ..................................................................................... 3-33

3.8 CLTU-SCHEDULE-STATUS-REPORT ............................................................. 3-39

3.9 CLTU-STATUS-REPORT ................................................................................... 3-43

3.10 CLTU-GET-PARAMETER ................................................................................. 3-48

3.11 CLTU-THROW-EVENT ...................................................................................... 3-53

3.12 CLTU-PEER-ABORT .......................................................................................... 3-58

4 CLTU PROTOCOL ....................................................................................................... 4-1

4.1 GENERIC PROTOCOL CHARACTERISTICS .................................................... 4-1

4.2 CLTU SERVICE PROVIDER BEHAVIOR .......................................................... 4-4

CCSDS 912.1-B-4 Page vi August 2016
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ISO 22671:2021(E)
CCSDS RECOMMENDED STANDARD FOR SLE FCLTU SERVICE
CONTENTS (continued)
Section Page

ANNEX A DATA TYPE DEFINITIONS (NORMATIVE) ......................................... A-1

ANNEX B PRODUCTION STATUS (NORMATIVE) .................................................B-1

ANNEX C CONFORMANCE OPTIONS MATRIX (NORMATIVE) ...................... C-1

ANNEX D INDEX TO DEFINITIONS (INFORMATIVE) ........................................ D-1

ANNEX E ACRONYMS (INFORMATIVE) .................................................................E-1

ANNEX F THROW EVENT DEFINITIONS (INFORMATIVE) .............................. F-1

ANNEX G INFORMATIVE REFERENCES (INFORMATIVE) .............................. G-1
Figure

1-1 SLE Services Documentation ....................................................................................... 1-4

2-1 Forward TC Space Link Processing SLE-FG ............................................................... 2-4

2-2 Forward CLTU Service Production and Provision ....................................................... 2-5

2-3 Example of Management and Provision of Forward CLTU Service ............................ 2-6

2-4 Simplified Forward CLTU Service Provider State Transition Diagram ...................... 2-9

2-5 Communications Realization of Forward CLTU Service........................................... 2-12

B-1 CLTU Production Status Transitions ............................................................................B-1

Table

2-1 Forward CLTU Service Operations .............................................................................. 2-8

3-1 Setting of Forward CLTU Service Configuration Parameters ..................................... 3-6

3-2 CLTU-BIND Parameters .............................................................................................. 3-9

3-3 CLTU-UNBIND Parameters ...................................................................................... 3-16

3-4 CLTU-START Parameters ......................................................................................... 3-18

3-5 CLTU-STOP Parameters ............................................................................................ 3-22

3-6 CLTU-TRANSFER-DATA Parameters ..................................................................... 3-25

3-7 CLTU-ASYNC-NOTIFY Parameters ........................................................................ 3-33

3-8 CLTU-SCHEDULE-STATUS-REPORT Parameters ................................................ 3-39

3-9 CLTU-STATUS-REPORT Parameters ...................................................................... 3-43

3-10 CLTU-GET-PARAMETER Parameters ..................................................................... 3-48

3-11 Forward CLTU Parameters ......................................................................................... 3-50

3-12 CLTU-THROW-EVENT Parameters ......................................................................... 3-54

3-13 CLTU-PEER-ABORT Parameters ............................................................................. 3-58

4-1 Provider Behavior ......................................................................................................... 4-7

4-2 Event Description References ..................................................................................... 4-10

4-3 Predicate Definitions .................................................................................................. 4-10

4-4 Boolean Flags ............................................................................................................. 4-11

4-5 Compound Action Definitions .................................................................................... 4-11

CCSDS 912.1-B-4 Page vii August 2016
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ISO 22671:2021(E)
CCSDS RECOMMENDED STANDARD FOR SLE FCLTU SERVICE
CONTENTS (continued)
Table Page

B-1 Production Status Changes and Notifications ...............................................................B-2

B-2 Effect of Production Status on Operations ...................................................................B-5

C-1 Conformance Matrix for CLTU Service (Operations) .................................................C-1

C-2 Conformance Matrix for CLTU Service (Other Requirements) ...................................C-1

F-1 Throw Event Examples ................................................................................................. F-1

CCSDS 912.1-B-4 Page viii August 2016
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---------------------- Page: 6 ----------------------
ISO 22671:2021(E)
CCSDS RECOMMENDED STANDARD FOR SLE FCLTU SERVICE
1 INTRODUCTION
1.1 PURPOSE OF THIS RECOMMENDED STANDARD

This Recommended Standard defines the Communications Link Transmission Unit (CLTU)

service in conformance with the transfer services specified in reference [1], Cross Support

Reference Model—Part 1: SLE Services. The Forward CLTU service is a Space Link

Extension (SLE) transfer service that enables a mission to send Communications Link

Transmission Units (CLTUs) to a spacecraft.
1.2 SCOPE

This Recommended Standard defines, in an abstract manner, the Forward CLTU service in

terms of:
a) the operations necessary to provide the transfer service;
b) the parameter data associated with each operation;
c) the behaviors that result from the invocation of each operation; and

d) the relationship between, and the valid sequence of, the operations and resulting

behaviors.
It does not specify:
a) individual implementations or products;
b) the implementation of entities or interfaces within real systems;

c) the methods or technologies required to radiate data to a spacecraft and to acquire

telemetry frames from the signals received from that spacecraft for extraction of the

Operational Control Field;
d) the methods or technologies required for communications; or

e) the management activities necessary to schedule, configure, and control the Forward

CLTU service.
1.3 APPLICABILITY
1.3.1 APPLICABILITY OF THIS RECOMMENDED STANDARD

This Recommended Standard provides a basis for the development of real systems that

implement the Forward CLTU service. Implementation of the Forward CLTU service in a

real system additionally requires the availability of a communications service to convey

invocations and returns of Forward CLTU service operations between service users and

CCSDS 912.1-B-4 Page 1-1 August 2016
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ISO 22671:2021(E)
CCSDS RECOMMENDED STANDARD FOR SLE FCLTU SERVICE

providers. This Recommended Standard requires that such a communications service ensure

that invocations and returns of operations are transferred:
a) in sequence;
b) completely and with integrity;
c) without duplication;

d) with flow control that notifies backpressure to the application layer in the event of

congestion; and

e) with notification to the application layer in the event that communications between

the Forward CLTU service user and the Forward CLTU service provider are
disrupted, possibly resulting in a loss of data.

It is the specific intent of this Recommended Standard to define the Forward CLTU service

in a manner that is independent of any particular communications services, protocols, or

technologies.
1.3.2 LIMITS OF APPLICABILITY

This Recommended Standard specifies the Forward CLTU service that may be provided by

an SLE System for inter-Agency cross support. It is neither a specification of, nor a design

for, real systems that may be implemented for the control and monitoring of existing or

future missions.
1.4 RATIONALE

The goal of this Recommended Standard is to create a standard for interoperability between

the tracking stations or ground data handling systems of various agencies and the users of

forward services.
1.5 DOCUMENT STRUCTURE
1.5.1 DOCUMENT ORGANIZATION
This Recommended Standard is organized as follows:

a) section 0 provides purpose, scope, applicability, and rationale of this Recommended

Standard and lists definitions, nomenclature, conventions, and references used
throughout the Recommended Standard;

b) section 2 presents an overview of the Forward CLTU service including a functional

description, the service management context, and protocol considerations;
c) section 3 specifies the operations of the Forward CLTU service;
CCSDS 912.1-B-4 Page 1-2 August 2016
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ISO 22671:2021(E)
CCSDS RECOMMENDED STANDARD FOR SLE FCLTU SERVICE

d) section 4 specifies the dynamic behavior of the Forward CLTU service in terms of the

state transitions of the Forward CLTU service provider;

e) annex A is a formal specification of Forward CLTU service data types, using the

Abstract Syntax Notation One (ASN.1);

f) annex B explains the relationship of the Forward CLTU service provisioning on the

production status and its dependency on the status of the forward space link channel.

g) annex C provides a conformance matrix that defines what capabilities must be
provided for an implementation to be considered compliant with this Recommended
Standard;

h) annex D lists all terms used in this document and identifies where they are defined;

i) annex E lists all acronyms used within this document;
j) annex F contains examples of usage of the CLTU-THROW-EVENT operation;
k) annex G contains a list of informative references.
1.5.2 SLE SERVICES DOCUMENTATION TREE

This Recommended Standard is based on the architectural model for cross support defined in

reference [1]. It expands upon the concept of an SLE transfer service as interactions between

SLE Mission User Entities (MUEs) and an SLE transfer service provider for the purpose of

providing the Forward CLTU transfer service.

This Recommended Standard is part of a suite of documents specifying the SLE Services.

The SLE Services constitute one of the three types of Cross Support Services:
a) Part 1: SLE Services;
b) Part 2: Ground Communications Services;
c) Part 3: Ground Domain Services.

The basic organization of the SLE services documentation is shown in figure 1-1. The

documents are described in the following paragraphs.
CCSDS 912.1-B-4 Page 1-3 August 2016
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---------------------- Page: 9 ----------------------
ISO 22671:2021(E)
CCSDS RECOMMENDED STANDARD FOR SLE FCLTU SERVICE
Space Link Extension
Cross Support
Cross Support Concept SLE Executive
Reference Model
Part 1: SLE Services Summary
Part 1: SLE Services
SLE Transfer Services
Forward SLE Service
Return SLE Service
Specifications Specifications
SLE Service
Management Suite
SLE API for Internet Protocol for
Transfer Services Transfer Services
Recommended Recommended Informational
Legend:
Record (Yellow)
Standard (Blue) Practice (Magenta) Report (Green)
Figure 1-1: SLE Services Documentation

a) Cross Support Concept – Part 1: Space Link Extension Services (reference [G3]): a

Report introducing the concepts of cross support and SLE services;
b) Cross Support Reference Model—Part 1: Space Link Extension Services
(reference [1]): a Recommended Standard that defines the framework and
terminology for the specification of SLE services;

c) Return SLE Transfer Service Specifications: a set of Recommended Standards that

will provide specification of all return link SLE transfer services.

d) Forward SLE Transfer Service Specifications: a set of Recommended Standards that

will provide specification of all forward link SLE transfer services (this
Recommended Standard is one of the specifications in that set);

e) SLE API for Transfer Services Specifications: a set of Recommended Practices that

provide specifications of an Application Program Interface; a set of Recommended
Standards that provide specifications of an Application Program Interface and a
mapping to TCP/IP as underlying communications service for SLE services;

f) Internet Protocol for Transfer Services: defines a protocol for transfer of SLE Protocol

Data Units using TCP/IP as underlying communications service for SLE services;

g) SLE Service Management Specification Suite: a set of Recommended Standards that

establish the basis for SLE service management.
CCSDS 912.1-B-4 Page 1-4 August 2016
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ISO 22671:2021(E)
CCSDS RECOMMENDED STANDARD FOR SLE FCLTU SERVICE
1.6 DEFINITIONS, NOMENCLATURE, AND CONVENTIONS
1.6.1 DEFINITIONS

1.6.1.1 Definitions from Open Systems Interconnection (OSI) Basic Reference Model

This Recommended Standard makes use of a number of terms defined in reference [7]. The

use of those terms in this Recommended Standard shall be understood in a generic sense, i.e.,

in the sense that those terms are generally applicable to technologies that provide for the

exchange of information between real systems. Those terms are:
a) abstract syntax;
b) application entity;
c) application layer;
d) flow control;
e) Open System Interconnection (OSI);
f) real system;
g) service access point (SAP).
1.6.1.2 Definitions from Abstract Syntax Notation One

This Recommended Standard makes use of the following terms defined in reference [6]:

a) Abstract Syntax Notation One (ASN.1);
b) object identifier;
c) (data) type;
d) (data) value.
NOTE − In annex A of this Recommended Standard, ASN.1 is used for specifying the
abstract syntax of the invocations and returns of the operations of the Forward
CLTU service. The use of ASN.1 as a descriptive language is intended to

support the specification of the abstract Forward CLTU service; it is not intended

to constrain implementations. In particular, there is no requirement for
implementations to employ ASN.1 encoding rules. ASN.1 is simply a

convenient tool for formally describing the abstract syntax of the invocations and

returns of the Forward CLTU service.
1.6.1.3 Definitions from TC Synchronization and Channel Coding

This Recommended Standard makes use of the following terms defined in reference [2]:

CCSDS 912.1-B-4 Page 1-5 August 2016
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ISO 22671:2021(E)
CCSDS RECOMMENDED STANDARD FOR SLE FCLTU SERVICE
a) acquisition sequence;
b) Communications Link Transmission Unit (CLTU);
c) Carrier Modulation Mode (CMM);
d) idle sequence;
e) Physical Layer operations procedure (PLOP).
1.6.1.4 Definitions from TC Space Data Link Protocol

This Recommended Standard makes use of the following term defined in reference [3]:

Communications Link Control Word (CLCW).
1.6.1.5 Definitions from SLE Reference Model

This Recommended Standard makes use of the following terms defined in reference [1]:

a) abstract binding;
b) abstract object;
c) abstract port;
d) abstract service;
e) CLTU channel;
f) Forward CLTU service;
g) invoker;
h) Mission Data Operation System (MDOS);
i) Mission User Entity (MUE);
j) offline delivery mode;
k) online delivery mode;
l) operation;
m) performer;
n) physical channel;
o) service agreement;
p) service provider (provider);
q) service user (user);
CCSDS 912.1-B-4 Page 1-6 August 2016
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ISO 22671:2021(E)
CCSDS RECOMMENDED STANDARD FOR SLE FCLTU SERVICE
r) SLE Complex;
s) SLE Complex Management;
t) SLE data channel;
u) SLE functional group (SLE-FG);
v) SLE protocol data unit (SLE-PDU);
w) SLE service data unit (SLE-SDU);
x) SLE service package;
y) SLE transfer service instance;
z) SLE transfer service production;
aa) SLE transfer service provision;
bb) SLE Utilization Management;
cc) space link;
dd) space link data channel;
ee) space link data unit (SL-DU);
ff) space link session.
1.6.1.6 Additional Definitions

For the purposes of this Recommended Standard, the following definitions also apply.

1.6.1.6.1 Association

An association is a cooperative relationship between an SLE service-providing application

entity and an SLE service-using application entity. An association is formed by the

exchange of SLE protocol data units through use of an underlying communications service.

1.6.1.6.2 Communications Service

A communications service is a capability that enables an SLE service-providing application

entity and an SLE service-using application entity to exchange information.
NOTE – If an SLE service user and an SLE service provider are implemented using

different communications services, then interoperability between them is possible

only by means of a suitable gateway. Adherence to this Recommended Standard
ensures, at least in principle, that it is possible to construct such a gateway.
CCSDS 912.1-B-4 Page 1-7 August 2016
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ISO 22671:2021(E)
CCSDS RECOMMENDED STANDARD FOR SLE FCLTU SERVICE
1.6.1.6.3 Confirmed Operation

A confirmed operation is an operation that requires the performer to return a report of its

outcome to the invoker.
1.6.1.6.4 Initiator

The initiator is the object that issues the request to bind to another object (the responder).

NOTE – In other words, the initiator is always the invoker of the request to bind to

another object. Therefore, in the context of the request to bind, the terms
‘initiator’ and ‘invoker’ refer to the same object and are synonyms.
1.6.1.6.5 Invocation

The invocation of an operation is the making of a request by an object (the invoker) to

another object (the performer) to carry out the operation.
1.6.1.6.6 Parameter

A parameter of an operation is data that may accompany the operation’s invocation or return.

NOTE – The term parameter is also used to refer to mission-dependent configuration

information used in production or provision of the service.
1.6.1.6.7 Performance

The performance of an operation is the carrying out of the operation by an object (the

performer).
1.6.1.6.8 Port Identifier

A port identifier identifies a source or a destination in a communications system.

NOTE – See 2.6.4.6 for more information.
1.6.1.6.9 Responder

The responder is the object that receives a request to bind and completes the binding (if

possible) with the initiator in order for a service association to exist between the two objects.

CCSDS 912.1-B-4 Page 1-8 August 2016
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ISO 22671:2021(E)
CCSDS RECOMMENDED STANDARD FOR SLE FCLTU SERVICE

NOTE – In other words, the responder is always the performer of the binding. Therefore,

in the context of binding, the terms ‘responder’ and ‘performer’ refer to the same

object and are synonyms.
1.6.1.6.10 Return

The return of an operation is a report, from the performer to the invoker, of the outcome of

the performance of the operation.
1.6.1.6.11 Service Instance Provision Period

A service instance provision period is the time during which a service instance (i.e., the

capability to transfer one or more SLE data channels of a given type) is scheduled to be

provided.
1.6.1.6.12 Unconfirmed Operation

An unconfirmed operation is an operation that does not require a report of its outcome to be

returned to the invoker by the performer.
1.6.2 NOMENCLATURE
The following conventions apply throughout this Recommended Standard:
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
1.6.3.1 Specification of Operations
1.6.3.1.1 General

Section 3 of this Recommended Standard specifies the operations that constitute the Forward

CLTU service. The specification of each operation is divided into subsections as follows:

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ISO 22671:2021(E)
CCSDS RECOMMENDED STANDARD FOR SLE FCLTU SERVICE
1.6.3.1.2 Purpose Subsection

The Purpose subsection briefly describes the purpose and functioning of the operation.

Additionally, it indicates whether the operation may be invoked by the user, provider, or

both; whether the operation is confirmed or unconfirmed; and whether there are any

constraints on when the operation may be invoked.
1.6.3.1.3 Invocation, Return, and Parameters Subsection

The Invocation, Return, and Parameters subsection describes the parameters associated with

each operation, including their semantics. A table accompanying the description of each

operation lists all parameters associated with the operation and, for both the invocation and

return, whether the parameter is always present, always absent, or conditionally present.

For parameters that are conditionally present, the parameter description specifies the

conditions for the presence or absence of the parameter. The condition is generally based on

the value of another parameter in the same invocation or return; for example, in return of an

operation, the diagnostic parameter is present if and only if the value of the result

parameter is ‘negative result’. For a conditional parameter in a return, the condition may be

based on the value of a parameter in the corresponding invocation.

In the table, the following convention is used to indicate whether a parameter is always

present, always absent, or conditionally present:
M always present (mandatory)
C conditionally present
Blank always absent

NOTE – Even though a parameter may be characterized as always present, its description

may specify that its value is permitted to be ‘null’ or ‘unused’ or the like.
1.6.3.1.4 Effects Subsection

The Effects subsection describes the effects an operation has on the invoker, the performer,

the association between them, or any combination thereof. The details of how those ef

...

INTERNATIONAL ISO
STANDARD 22671
Fourth edition
Space data and information transfer
systems — Space link extension
(SLE) — Forward communications
link transmission unit (CLTU) service
specification
Systèmes de transfert des informations et données spatiales —
Extension de liaisons spatiales (SLE) — Service de l'unité de
transmission pour la liaison d'envoi de télécommande (CLTU)
PROOF/ÉPREUVE
Reference number
ISO 22671:2021(E)
ISO 2021
---------------------- Page: 1 ----------------------
ISO 22671:2021(E)
COPYRIGHT PROTECTED DOCUMENT
© ISO 2021

All rights reserved. Unless otherwise specified, or required in the context of its implementation, 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
CP 401 • Ch. de Blandonnet 8
CH-1214 Vernier, Geneva
Phone: +41 22 749 01 11
Email: copyright@iso.org
Website: www.iso.org
Published in Switzerland
ii PROOF/ÉPREUVE © ISO 2021 – All rights reserved
---------------------- Page: 2 ----------------------
ISO 22671:2021(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 (see www.iso.org/directives).

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This document was prepared by the Consultative Committee for Space Data Systems (CCSDS) (as CCSDS

912.1-B-4, August 2016) and was adopted (without modifications) by Technical Committee ISO/TC 20,

Space vehicles, Subcommittee SC 13, Space data and information transfer systems.

This fourth edition cancels and replaces the third edition (ISO 22671:2011), which has been technically

revised.
The main changes compared to the previous edition are as follows:
— adds clarifications and corrections.

Any feedback or questions on this document should be directed to the user’s national standards body. A

complete listing of these bodies can be found at www.iso.org/members.html.
PROOF/ÉPREUVE
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CONTENTS
Section Page

1 INTRODUCTION .......................................................................................................... 1-1

1.1 PURPOSE OF THIS RECOMMENDED STANDARD ........................................ 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 DEFINITIONS, NOMENCLATURE, AND CONVENTIONS ............................ 1-5

1.7 REFERENCES ..................................................................................................... 1-12

2 DESCRIPTION OF THE FORWARD CLTU SERVICE ......................................... 2-1

2.1 OVERVIEW ........................................................................................................... 2-1

2.2 SPACE LINK EXTENSION REFERENCE MODEL ........................................... 2-2

2.3 SERVICE MANAGEMENT .................................................................................. 2-3

2.4 ARCHITECTURE MODEL – FUNCTIONAL VIEW .......................................... 2-3

2.5 ARCHITECTURE MODEL – CROSS-SUPPORT VIEW .................................... 2-6

2.6 FUNCTIONAL DESCRIPTION ............................................................................ 2-7

2.7 OPERATIONAL SCENARIO ............................................................................. 2-14

2.8 SECURITY ASPECTS OF THE SLE FORWARD CLTU

TRANSFER SERVICE ........................................................................................ 2-16

3 FORWARD CLTU SERVICE OPERATIONS .......................................................... 3-1

3.1 GENERAL CONSIDERATIONS .......................................................................... 3-1

3.2 CLTU-BIND ........................................................................................................... 3-8

3.3 CLTU-UNBIND ................................................................................................... 3-15

3.4 CLTU-START ...................................................................................................... 3-18

3.5 CLTU-STOP ......................................................................................................... 3-22

3.6 CLTU-TRANSFER-DATA .................................................................................. 3-25

3.7 CLTU-ASYNC-NOTIFY ..................................................................................... 3-33

3.8 CLTU-SCHEDULE-STATUS-REPORT ............................................................. 3-39

3.9 CLTU-STATUS-REPORT ................................................................................... 3-43

3.10 CLTU-GET-PARAMETER ................................................................................. 3-48

3.11 CLTU-THROW-EVENT ...................................................................................... 3-53

3.12 CLTU-PEER-ABORT .......................................................................................... 3-58

4 CLTU PROTOCOL ....................................................................................................... 4-1

4.1 GENERIC PROTOCOL CHARACTERISTICS .................................................... 4-1

4.2 CLTU SERVICE PROVIDER BEHAVIOR .......................................................... 4-4

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CONTENTS (continued)
Section Page

ANNEX A DATA TYPE DEFINITIONS (NORMATIVE) ......................................... A-1

ANNEX B PRODUCTION STATUS (NORMATIVE) .................................................B-1

ANNEX C CONFORMANCE OPTIONS MATRIX (NORMATIVE) ...................... C-1

ANNEX D INDEX TO DEFINITIONS (INFORMATIVE) ........................................ D-1

ANNEX E ACRONYMS (INFORMATIVE) .................................................................E-1

ANNEX F THROW EVENT DEFINITIONS (INFORMATIVE) .............................. F-1

ANNEX G INFORMATIVE REFERENCES (INFORMATIVE) .............................. G-1
Figure

1-1 SLE Services Documentation ....................................................................................... 1-4

2-1 Forward TC Space Link Processing SLE-FG ............................................................... 2-4

2-2 Forward CLTU Service Production and Provision ....................................................... 2-5

2-3 Example of Management and Provision of Forward CLTU Service ............................ 2-6

2-4 Simplified Forward CLTU Service Provider State Transition Diagram ...................... 2-9

2-5 Communications Realization of Forward CLTU Service........................................... 2-12

B-1 CLTU Production Status Transitions ............................................................................B-1

Table

2-1 Forward CLTU Service Operations .............................................................................. 2-8

3-1 Setting of Forward CLTU Service Configuration Parameters ..................................... 3-6

3-2 CLTU-BIND Parameters .............................................................................................. 3-9

3-3 CLTU-UNBIND Parameters ...................................................................................... 3-16

3-4 CLTU-START Parameters ......................................................................................... 3-18

3-5 CLTU-STOP Parameters ............................................................................................ 3-22

3-6 CLTU-TRANSFER-DATA Parameters ..................................................................... 3-25

3-7 CLTU-ASYNC-NOTIFY Parameters ........................................................................ 3-33

3-8 CLTU-SCHEDULE-STATUS-REPORT Parameters ................................................ 3-39

3-9 CLTU-STATUS-REPORT Parameters ...................................................................... 3-43

3-10 CLTU-GET-PARAMETER Parameters ..................................................................... 3-48

3-11 Forward CLTU Parameters ......................................................................................... 3-50

3-12 CLTU-THROW-EVENT Parameters ......................................................................... 3-54

3-13 CLTU-PEER-ABORT Parameters ............................................................................. 3-58

4-1 Provider Behavior ......................................................................................................... 4-7

4-2 Event Description References ..................................................................................... 4-10

4-3 Predicate Definitions .................................................................................................. 4-10

4-4 Boolean Flags ............................................................................................................. 4-11

4-5 Compound Action Definitions .................................................................................... 4-11

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CONTENTS (continued)
Table Page

B-1 Production Status Changes and Notifications ...............................................................B-2

B-2 Effect of Production Status on Operations ...................................................................B-5

C-1 Conformance Matrix for CLTU Service (Operations) .................................................C-1

C-2 Conformance Matrix for CLTU Service (Other Requirements) ...................................C-1

F-1 Throw Event Examples ................................................................................................. F-1

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1 INTRODUCTION
1.1 PURPOSE OF THIS RECOMMENDED STANDARD

This Recommended Standard defines the Communications Link Transmission Unit (CLTU)

service in conformance with the transfer services specified in reference [1], Cross Support

Reference Model—Part 1: SLE Services. The Forward CLTU service is a Space Link

Extension (SLE) transfer service that enables a mission to send Communications Link

Transmission Units (CLTUs) to a spacecraft.
1.2 SCOPE

This Recommended Standard defines, in an abstract manner, the Forward CLTU service in

terms of:
a) the operations necessary to provide the transfer service;
b) the parameter data associated with each operation;
c) the behaviors that result from the invocation of each operation; and

d) the relationship between, and the valid sequence of, the operations and resulting

behaviors.
It does not specify:
a) individual implementations or products;
b) the implementation of entities or interfaces within real systems;

c) the methods or technologies required to radiate data to a spacecraft and to acquire

telemetry frames from the signals received from that spacecraft for extraction of the

Operational Control Field;
d) the methods or technologies required for communications; or

e) the management activities necessary to schedule, configure, and control the Forward

CLTU service.
1.3 APPLICABILITY
1.3.1 APPLICABILITY OF THIS RECOMMENDED STANDARD

This Recommended Standard provides a basis for the development of real systems that

implement the Forward CLTU service. Implementation of the Forward CLTU service in a

real system additionally requires the availability of a communications service to convey

invocations and returns of Forward CLTU service operations between service users and

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providers. This Recommended Standard requires that such a communications service ensure

that invocations and returns of operations are transferred:
a) in sequence;
b) completely and with integrity;
c) without duplication;

d) with flow control that notifies backpressure to the application layer in the event of

congestion; and

e) with notification to the application layer in the event that communications between

the Forward CLTU service user and the Forward CLTU service provider are
disrupted, possibly resulting in a loss of data.

It is the specific intent of this Recommended Standard to define the Forward CLTU service

in a manner that is independent of any particular communications services, protocols, or

technologies.
1.3.2 LIMITS OF APPLICABILITY

This Recommended Standard specifies the Forward CLTU service that may be provided by

an SLE System for inter-Agency cross support. It is neither a specification of, nor a design

for, real systems that may be implemented for the control and monitoring of existing or

future missions.
1.4 RATIONALE

The goal of this Recommended Standard is to create a standard for interoperability between

the tracking stations or ground data handling systems of various agencies and the users of

forward services.
1.5 DOCUMENT STRUCTURE
1.5.1 DOCUMENT ORGANIZATION
This Recommended Standard is organized as follows:

a) section 0 provides purpose, scope, applicability, and rationale of this Recommended

Standard and lists definitions, nomenclature, conventions, and references used
throughout the Recommended Standard;

b) section 2 presents an overview of the Forward CLTU service including a functional

description, the service management context, and protocol considerations;
c) section 3 specifies the operations of the Forward CLTU service;
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d) section 4 specifies the dynamic behavior of the Forward CLTU service in terms of the

state transitions of the Forward CLTU service provider;

e) annex A is a formal specification of Forward CLTU service data types, using the

Abstract Syntax Notation One (ASN.1);

f) annex B explains the relationship of the Forward CLTU service provisioning on the

production status and its dependency on the status of the forward space link channel.

g) annex C provides a conformance matrix that defines what capabilities must be
provided for an implementation to be considered compliant with this Recommended
Standard;

h) annex D lists all terms used in this document and identifies where they are defined;

i) annex E lists all acronyms used within this document;
j) annex F contains examples of usage of the CLTU-THROW-EVENT operation;
k) annex G contains a list of informative references.
1.5.2 SLE SERVICES DOCUMENTATION TREE

This Recommended Standard is based on the architectural model for cross support defined in

reference [1]. It expands upon the concept of an SLE transfer service as interactions between

SLE Mission User Entities (MUEs) and an SLE transfer service provider for the purpose of

providing the Forward CLTU transfer service.

This Recommended Standard is part of a suite of documents specifying the SLE Services.

The SLE Services constitute one of the three types of Cross Support Services:
a) Part 1: SLE Services;
b) Part 2: Ground Communications Services;
c) Part 3: Ground Domain Services.

The basic organization of the SLE services documentation is shown in figure 1-1. The

documents are described in the following paragraphs.
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CCSDS RECOMMENDED STANDARD FOR SLE FCLTU SERVICE
Space Link Extension
Cross Support
Cross Support Concept SLE Executive
Reference Model
Part 1: SLE Services Summary
Part 1: SLE Services
SLE Transfer Services
Forward SLE Service
Return SLE Service
Specifications Specifications
SLE Service
Management Suite
SLE API for Internet Protocol for
Transfer Services Transfer Services
Recommended Recommended Informational
Legend:
Record (Yellow)
Standard (Blue) Practice (Magenta) Report (Green)
Figure 1-1: SLE Services Documentation

a) Cross Support Concept – Part 1: Space Link Extension Services (reference [G3]): a

Report introducing the concepts of cross support and SLE services;
b) Cross Support Reference Model—Part 1: Space Link Extension Services
(reference [1]): a Recommended Standard that defines the framework and
terminology for the specification of SLE services;

c) Return SLE Transfer Service Specifications: a set of Recommended Standards that

will provide specification of all return link SLE transfer services.

d) Forward SLE Transfer Service Specifications: a set of Recommended Standards that

will provide specification of all forward link SLE transfer services (this
Recommended Standard is one of the specifications in that set);

e) SLE API for Transfer Services Specifications: a set of Recommended Practices that

provide specifications of an Application Program Interface; a set of Recommended
Standards that provide specifications of an Application Program Interface and a
mapping to TCP/IP as underlying communications service for SLE services;

f) Internet Protocol for Transfer Services: defines a protocol for transfer of SLE Protocol

Data Units using TCP/IP as underlying communications service for SLE services;

g) SLE Service Management Specification Suite: a set of Recommended Standards that

establish the basis for SLE service management.
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1.6 DEFINITIONS, NOMENCLATURE, AND CONVENTIONS
1.6.1 DEFINITIONS

1.6.1.1 Definitions from Open Systems Interconnection (OSI) Basic Reference Model

This Recommended Standard makes use of a number of terms defined in reference [7]. The

use of those terms in this Recommended Standard shall be understood in a generic sense, i.e.,

in the sense that those terms are generally applicable to technologies that provide for the

exchange of information between real systems. Those terms are:
a) abstract syntax;
b) application entity;
c) application layer;
d) flow control;
e) Open System Interconnection (OSI);
f) real system;
g) service access point (SAP).
1.6.1.2 Definitions from Abstract Syntax Notation One

This Recommended Standard makes use of the following terms defined in reference [6]:

a) Abstract Syntax Notation One (ASN.1);
b) object identifier;
c) (data) type;
d) (data) value.
NOTE − In annex A of this Recommended Standard, ASN.1 is used for specifying the
abstract syntax of the invocations and returns of the operations of the Forward
CLTU service. The use of ASN.1 as a descriptive language is intended to

support the specification of the abstract Forward CLTU service; it is not intended

to constrain implementations. In particular, there is no requirement for
implementations to employ ASN.1 encoding rules. ASN.1 is simply a

convenient tool for formally describing the abstract syntax of the invocations and

returns of the Forward CLTU service.
1.6.1.3 Definitions from TC Synchronization and Channel Coding

This Recommended Standard makes use of the following terms defined in reference [2]:

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a) acquisition sequence;
b) Communications Link Transmission Unit (CLTU);
c) Carrier Modulation Mode (CMM);
d) idle sequence;
e) Physical Layer operations procedure (PLOP).
1.6.1.4 Definitions from TC Space Data Link Protocol

This Recommended Standard makes use of the following term defined in reference [3]:

Communications Link Control Word (CLCW).
1.6.1.5 Definitions from SLE Reference Model

This Recommended Standard makes use of the following terms defined in reference [1]:

a) abstract binding;
b) abstract object;
c) abstract port;
d) abstract service;
e) CLTU channel;
f) Forward CLTU service;
g) invoker;
h) Mission Data Operation System (MDOS);
i) Mission User Entity (MUE);
j) offline delivery mode;
k) online delivery mode;
l) operation;
m) performer;
n) physical channel;
o) service agreement;
p) service provider (provider);
q) service user (user);
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r) SLE Complex;
s) SLE Complex Management;
t) SLE data channel;
u) SLE functional group (SLE-FG);
v) SLE protocol data unit (SLE-PDU);
w) SLE service data unit (SLE-SDU);
x) SLE service package;
y) SLE transfer service instance;
z) SLE transfer service production;
aa) SLE transfer service provision;
bb) SLE Utilization Management;
cc) space link;
dd) space link data channel;
ee) space link data unit (SL-DU);
ff) space link session.
1.6.1.6 Additional Definitions

For the purposes of this Recommended Standard, the following definitions also apply.

1.6.1.6.1 Association

An association is a cooperative relationship between an SLE service-providing application

entity and an SLE service-using application entity. An association is formed by the

exchange of SLE protocol data units through use of an underlying communications service.

1.6.1.6.2 Communications Service

A communications service is a capability that enables an SLE service-providing application

entity and an SLE service-using application entity to exchange information.
NOTE – If an SLE service user and an SLE service provider are implemented using

different communications services, then interoperability between them is possible

only by means of a suitable gateway. Adherence to this Recommended Standard
ensures, at least in principle, that it is possible to construct such a gateway.
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1.6.1.6.3 Confirmed Operation

A confirmed operation is an operation that requires the performer to return a report of its

outcome to the invoker.
1.6.1.6.4 Initiator

The initiator is the object that issues the request to bind to another object (the responder).

NOTE – In other words, the initiator is always the invoker of the request to bind to

another object. Therefore, in the context of the request to bind, the terms
‘initiator’ and ‘invoker’ refer to the same object and are synonyms.
1.6.1.6.5 Invocation

The invocation of an operation is the making of a request by an object (the invoker) to

another object (the performer) to carry out the operation.
1.6.1.6.6 Parameter

A parameter of an operation is data that may accompany the operation’s invocation or return.

NOTE – The term parameter is also used to refer to mission-dependent configuration

information used in production or provision of the service.
1.6.1.6.7 Performance

The performance of an operation is the carrying out of the operation by an object (the

performer).
1.6.1.6.8 Port Identifier

A port identifier identifies a source or a destination in a communications system.

NOTE – See 2.6.4.6 for more information.
1.6.1.6.9 Responder

The responder is the object that receives a request to bind and completes the binding (if

possible) with the initiator in order for a service association to exist between the two objects.

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NOTE – In other words, the responder is always the performer of the binding. Therefore,

in the context of binding, the terms ‘responder’ and ‘performer’ refer to the same

object and are synonyms.
1.6.1.6.10 Return

The return of an operation is a report, from the performer to the invoker, of the outcome of

the performance of the operation.
1.6.1.6.11 Service Instance Provision Period

A service instance provision period is the time during which a service instance (i.e., the

capability to transfer one or more SLE data channels of a given type) is scheduled to be

provided.
1.6.1.6.12 Unconfirmed Operation

An unconfirmed operation is an operation that does not require a report of its outcome to be

returned to the invoker by the performer.
1.6.2 NOMENCLATURE
The following conventions apply throughout this Recommended Standard:
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
1.6.3.1 Specification of Operations
1.6.3.1.1 General

Section 3 of this Recommended Standard specifies the operations that constitute the Forward

CLTU service. The specification of each operation is divided into subsections as follows:

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1.6.3.1.2 Purpose Subsection

The Purpose subsection briefly describes the purpose and functioning of the operation.

Additionally, it indicates whether the operation may be invoked by the user, provider, or

both; whether the operation is confirmed or unconfirmed; and whether there are any

constraints on when the operation may be invoked.
1.6.3.1.3 Invocation, Return, and Parameters Subsection

The Invocation, Return, and Parameters subsection describes the parameters associated with

each operation, including their semantics. A table accompanying the description of each

operation lists all parameters associated with the operation and, for both the invocation and

return, whether the parameter is always present, always absent, or conditionally present.

For parameters that are conditionally present, the parameter description specifies the

conditions for the presence or absence of the parameter. The condition is generally based on

the value of another parameter in the same invocation or return; for example, in return of an

operation, the diagnostic parameter is present if and only if the value of the result

parameter is ‘negative result’. For a conditional parameter in a return, the condition may be

based on the value of a parameter in the corresponding invocation.

In the table, the following convention is used to indicate whether a parameter is always

present, always absent, or conditionally present:
M always present (mandatory)
C conditionally present
Blank always absent

NOTE – Even though a parameter may be characterized as always present, its description

may specify that its value is permitted to be ‘null’ or ‘unused’ or the like.
1.6.3.1.4 Effects Subsection

The Effects subsection describes the effects an operation has on the invoker, the performer,

the association between them, or any combination ther
...

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