EN ISO/IEC 7498-1:1995

Information technology - Open Systems Interconnection - Basic Reference Model: The Basic Model (ISO/IEC 7498-1:1994)

Migrated from Progress Sheet (TC Comment) (2000-07-10): AWATING ISO.

Informationstechnik - Kommunikation Offener Systeme - Basis-Referenzmodell: Basismodell (ISO/IEC 7498-1:1994)

Technologies de l'information - Modèle de référence de base pour l'interconnexion de systèmes ouverts (OSI): Le modèle de base (ISO/IEC 7498-1:1994)

Information technology - Open Systems Interconnection - Basic Reference Model: The Basic Model (ISO/IEC 7498-1:1994)

General Information

• Status: Withdrawn
• Publication Date: 18-Jul-1995
• Withdrawal Date: 27-Oct-1998
• ICS: 35.100.01 - Open systems interconnection in general
• Technical Committee: CEN/SS F12 - Information processing systems
• Drafting Committee: CEN/SS F12 - Information processing systems
• Current Stage: 9960 - Withdrawal effective - Withdrawal
• Start Date: 28-Oct-1998
• Completion Date: 28-Oct-1998
• Ref Project: SIST EN ISO/IEC 7498-1:1997 - Information technology - Open Systems Interconnection - Basic Reference Model: The Basic Model (ISO/IEC 7498-1:1994)

Standards Content (Sample)

SLOVENSKI STANDARD
SIST EN ISO/IEC 7498-1:1997
01-december-1997
Information technology - Open Systems Interconnection - Basic Reference Model:
The Basic Model (ISO/IEC 7498-1:1994)
Information technology - Open Systems Interconnection - Basic Reference Model: The
Basic Model (ISO/IEC 7498-1:1994)
Informationstechnik - Kommunikation Offener Systeme - Basis-Referenzmodell:
Basismodell (ISO/IEC 7498-1:1994)
Technologies de l'information - Modele de référence de base pour l'interconnexion de
systemes ouverts (OSI): Le modele de base (ISO/IEC 7498-1:1994)
Ta slovenski standard je istoveten z: EN ISO/IEC 7498-1:1995
ICS:
35.100.01 Medsebojno povezovanje Open systems
odprtih sistemov na splošno interconnection in general
SIST EN ISO/IEC 7498-1:1997 en
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

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SIST EN ISO/IEC 7498-1:1997

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SIST EN ISO/IEC 7498-1:1997

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SIST EN ISO/IEC 7498-1:1997

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SIST EN ISO/IEC 7498-1:1997
INTERNATIONAL
ISO/IEC
STANDARD
7498-l
Second edition
1994-l l-l 5
Corrected and reprinted
1996-06-l 5
Information technology - Open Systems
Interconnection - Basic Reference Model:
The Basic Model
Technologies de I’informa tion - Mod&/e de rt? f&ence de base pour
/‘in terconnexjon de s ys tkmes ouverts (OS/): Le mod&/e de base
Reference number
ISO/l EC 7498-l : 1994(E)

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SIST EN ISO/IEC 7498-1:1997
ISO/IEC 7498=1:1994(E)
Contents
Page
1
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
1 Scope
2
Definitions .
2
2
..........................................................................................................................................................
3 Notation
2
....................................................................................
4 Introduction to Open Systems Interconnection (OSI)
2
4.1 Definitions .
3
Open System Interconnection Environment .
4.2
4
.........................................................................................................
4.3 Modelling the OS1 Environment
5
Concepts of a layered architecture .
5
5
Introduction .
51
6
..........................................................................................................................
512 Principles of layering
9
Communication between peer-entities .
53
13
514 Identifiers .
14
Properties of service-access-points .
55 .
15
56 Data-units .
16
The nature of the (N)-service .
517
16
5.8 Elements of layer operation .
27
Routing .
59
27
...................................................................................................................
5110 Quality Of Service (QOS)
28
Introduction to the specific OS1 layers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .-.
6
28
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
61 Specific layers
29
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
The principles used to determine the seven layers in the Reference Model
612
30
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
63 Layer descriptions
30
. . . . . . . . . .~.
614 Combinations of connection-mode and connectionless-mode
31
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
65 . Configurations of OS1 Open Systems
32
...................................................................................
7 Detailed description of the resulting OS1 architecture
32
...............................................................................................................................
7.1 Application Layer
33
7.2 Presentation Layer .
34
......................................................................................................................................
7.3 Session Layer
37
7.4 Transport Layer .
41
75 Network Layer .
46
7:6 Data Link Layer .
49
.....................................................................................................................................
7.7 Physical Layer
0 ISO/IEC 1994
All rights reserved. Unless otherwise specified, no part of this publication may be
reproduced or utilized in any form or by any means, electronic or mechanical, including
photocopying and microfilm, without permission in writing from the publisher.
ISO/IEC Copyright Office l Case postale 56 l CH-1211 Geneve 20 l Switzerland
Printed in Switzerland
ii

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SIST EN ISO/IEC 7498-1:1997
ISO/IEC 7498=1:1994(E)
0 ISO/lEC
52
8 Management aspects of OSI . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
52
81 . Definitions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
53
8.2 Introduction .
53
8.3 Categories of management activities .
54
...............................................................................
8.4 Principles for positioning management functions
54
9 Compliance and Consistency with this reference model .
54
91 Definitions .
.................................................................. 55
912 Application of consistency and compliance requirements
56
- Brief explanation of how the layers were chosen . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Annex A
57
Annex B - Alphabetical index to definitions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
. . .
111

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SIST EN ISO/IEC 7498-1:1997
ISO/IEC 7498=1:1994(E) 0 ISO/IEC
Foreword
IS0 (the International Organization for Standardization) and IEC (the Inter-
national Electrotechnical Commission) form the specialized system for worldwide
standardization. National bodies that are members of IS0 or IEC participate in the
development of International Standards through technical committees established
by the respective organization to deal with particular fields of technical activity.
IS0 and IEC technical committees collaborate in fields of mutual interest. Other
international organizations, governmental and non-governmental, in liaison with
IS0 and IEC, also take part in the work.
In the field of information technology, IS0 and IEC have established a joint
technical committee, ISO/IEC JTC 1. Draft International Standards adopted by the
joint technical committee are circulated to national bodies for voting. Publication
as an International Standard requires approval by at least 75 % of the national
bodies casting a vote.
International Standard ISO/IEC 7498-l was prepared by Joint Technical
Committee ISO/IEC JTC 1, Information technology, in collaboration with ITU-T.
The identical text is published as ITU-T Recommendation X.200.
This second edition, along with parts 2, 3 and 4, cancels and replaces the first
edition (IS0 7498: 1984), which has been technically revised.
ISO/IEC 7498 consists of the following parts, under the general title Information
technology - Open Systems Interconnection - Basic Reference Model:
- Part 1: The Basic Model
- Part 2: Security Architecture
Part 3: Naming and addressing
Part 4: Management framework
Annex B forms an integral part of this part of ISO/IEC 7498. Annex A is for
information only.
iv

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SIST EN ISO/IEC 7498-1:1997
ISO/IEC 7498=1:1994(E)
Introduction
This reference model provides a common basis for the coordination of standards development for the purpose of systems
interconnection, while allowing existing standards to be placed into perspective within the overall reference model. It also
identifies areas for developing and improving standards and provides a common reference for maintaining consistency among
all related standards. The text was developed jointly with ITU-T and the main intent of this revision is to introduce the joint text,
which incorporates inclusion of the concept of connectionless transmission, in addition to a number of technical and editorial
refinements.
V

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SIST EN ISO/IEC 7498-1:1997
ISO/IEC 7498-l : 1994(E)
INTERNATIONAL STANDARD
CCITT RECOMMENDATION
INFORMATION TECHNOLOGY - OPEN SYSTEMS INTERCONNECTION -
BASIC REFERENCE MODEL: THE BASIC MODEL
1
Scope
1.1 The purpose of this Reference Model of Open Systems Interconnection is to provide a common basis for the
coordination of standards development for the purpose of systems interconnection, while allowing existing standards to
be placed into perspective within the overall Reference Model.
1.2 The term Open Systems Interconnection (OSI) qualifies standards for the exchange of information among
one another for this purpose by virtue of their mutual use of
systems that are “open” to the applicable standards.
does not imply
1.3 The fact that a system is open any particular systems implementation, technology or means of
interconnection, but refers to the mutual recognition and support of the applicable standards.
1.4 It is also the purpose of this Reference Model to identify areas for developing or improving standards, and to
provide a common reference for maintaining consistency of all related standards. It is not the intent of this Reference
Model either to serve as an implementation specification, or to be a basis for appraising the conformance of actual
implementations, or to provide a sufficient level of detail to define precisely the services and protocols of the
interconnection architecture. Rather, this Reference Model provides a conceptual and functional framework which
allows international teams of experts to work productively and independently on the development of standards for each
layer of the Reference Model for OSI.
1.5 The Reference Model has sufficient flexibility to accommodate ad vances in technology and expansion in user
This flexibility is also intended to allow the ph
demands. ased transition from existin g implementati .ons to OS1 standards.
1.6 While the scope of the general architectural principles required for OS1 is very broad, this Reference Model is
primarily concerned with systems comprising terminals, computers, and associated devices and the means for
transferring information between such systems. Other aspects of OS1 requiring attention are described briefly (see 4.2).
1.7 The description of the Basic Reference Model of OS1 is developed in stages:
1.8 Clause 4 establishes the reasons for Open Systems Interconnection, defines what is being connected, the scope
of the interconnection, and describes the modelling principles used in OSI.
1.9 Clause 5 describes the general nature of the architecture of the Reference Model; namely that it is layered,
what layering means, and the principles used to describe layers.
1.10 Clause 6 names, and introduces the specific layers of the architecture.
1.11 Clause 7 provides the description of the specific layers.
1.12 Clause 8 provides the description of Management Aspects of OSI.
1.13 Clause 9 specifies compliance and consistency with the OS1 Reference Model.
An indication of how the layers were chosen is given in Annex A to this Basic Reference Model.
1.14
Additional aspects of this Reference Model beyond the basic aspects are described in several parts. The first
1.15
part describes the Basic Reference Model. The second part describes the architecture for OS1 Security. The third part
describes OS1 Naming and Addressing. The fourth describes OS1 System Management.
1.16 The Basic Reference Model serves as a framework for the definition of services and protocols which fit within
the boundaries established by the Reference Model.
1.17 In those few cases where a feature is explicitly marked (optional) in the Basic Reference Model it should
remain optional in the corresponding service or protocol (even if at a given instant the two cases of the option are not yet
documented).
ITU-T Rec. X.200 (1994 E) 1

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ISO/IEC 7498-1 : 1994(E)
1.18 This Reference Model does not specify services and protocols for OSI. It is neither an implementation
specification for systems, nor a basis for appraising the conformance of implementations.
1.19 For standards which meet the OS1 requirements, a small number of practical subsets are defined from optional
functions, to facilitate implementation and compatibility.
2 Definitions
Definitions of terms are included at the beginning of individual clauses and sub-clauses. An index of these terms is
provided in Annex B for easy reference.
3 Notation
3.1 Layers are introduced in clause 5. An (N)-, (N+l)- and (N-l)- notation is used to identify and relate adjacent
layers:
(N)-layer: any specific layer;
(N+l)-layer: the next higher layer;
(N-1)-layer: the next lower layer.
This notation is also used for other concepts in the model which are related to these layers, for example (N)-protocol,
(N+l)-service.
3.2 Clause 6 introduces names for individual layers. When referring to these layers by name, the (N)-, (N+l)-
and (N-l)- prefixes are replaced by the names of the layers, for example transport-protocol, session-entity, and
network-service.
4 Introduction to Open Systems Interconnection (OSI)
NOTE - The general principles described in clauses 4 and 5 hold for all layers of the Reference Model, unless layer
specific statements to the contrary are made in clauses 6 and 7.
41 . Definitions
the associated software, peripherals, terminals, human
4.1.1 real system: A set of one or more computers,
that forms an autonomous whole capable of performing
operators, physical processes, information transfer means, etc.,
information processing and/or information transfer.
standards in its
4.1.2 real open system: A real system which complies with the requirements of OS1
systems.
communication with other real
4.1.3 open system: The representation within the Reference Model of those aspects of a real open system that are
pertinent to OSI.
4.1.4 application process: An element within a real open system which performs the information processing for a
particular application.
4.1.5 Open System Interconnection Environment (OSIE): An abstract representation of the set of concepts,
elements, functions, services, protocols, etc., as defined by the OS1 Reference Model and the derived specific standards
which, when applied, enable communications among open systems.
4.1.6 Local System Environment (LSE): An abstract representation of that part of the real system that is not
pertinent to OSI.
NOTE - The LSE may include functions necessary for non-OS1 communication.
4.1.7 A specific utilization of part or all of the capabilities of a given application
application-process-invocation:
process in support of a specific occasion of information processing.
4.1.8 application-process-type: A description of a class of application processes in terms of a set of information
processing capabilities.
2 ITU-T Rec. X.200 (1994 E)

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SIST EN ISO/IEC 7498-1:1997
ISO/IEC 7498-l : 1994(E)
42 . Open System Interconnection Environment
4.2.1 In the concept of OSI, a real system is a set of one or more computers, associated software, peripherals,
terminals, human operators, physical processes, information transfer means, etc., that forms an autonomous whole
capable of performing information processing and/or information transfer.
An application process is an element within a real open system which performs the information processing for
4.2.2
a particular application.
4.2.3 Application processes can represent manual processes, computerized processes or physical processes.
4.2.4 Some examples of application processes that are applicable to this open system definition are the following:
a person operating a banking terminal is a manual application-process;
a FORTRAN program executing in a computer center and accessing a computerized
a remote database is
b)
application-process; the remote database management systems server is also an application -process; and
program executing
a process control in a dedicated computer attached to some industrial equipment
C)
li .nked into a plan .t control system is a physical application-process.
4.2.5 An application process represents a set of resources, including processing resources, within a real open system
that may be used to perform a particular information processing activity. An application process may organize its
interactions with other application processes in whatever way is necessary to achieve a particular information processing
goal: no constraints are imposed by this Reference Model either on the form of these interactions or on the possible
relationships that may exist between them.
4.2.6 The activity of a given application process is represented by one or more application process invocations.
Cooperation between application processes takes place via relationships established among application process
invocations. At a particular time, an application, process may be represented by none, one or more application process
invocations. An application process invocation is responsible for coordinating its interactions with other application
process invocations. Such coordination is outside the scope of this Reference Model.
exchange functioning of
4.2.7 OS1 is concerned with the of information between open systems (and not the internal
each individual real open system).
4.2.8 As shown in Figure 1, the physical for Open Systems Interconnection provides the means for the
transfer of information between open systems.
Physical media
TlSO2830-94/dOl
Figure 1 - Open systems connected by physical media
4.2.9
OS1 is concerned only with the interconnection of systems. All other aspects of systems which are not related
to interconnection are outside the scope of OSI.
ITU-T Rec. X.200 (1994 E) 3

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ISO/IEC 7498-l : 1994(E)
4.2.10 OSI is concerned not only with the transfer of information between systems, i.e. transmission, but also with
their capability to interwork to achieve a common (distributed) task. In other words, OS1 is concerned with the
interconnection aspects of cooperation l) between systems, which is implied by the expression “systems interconnection.”
4.2.11 The objective of OS1 is to define a set of standards to enable real open systems to cooperate. A system which
complies with the requirements of applicable OS1 standards in its cooperation with other systems is termed a real open
system.
4.2.12 The design intent of the OS1 standards is to specify a set of standards that make it possible for autonomous
systems to communicate. Any equipment which communicates in conformance with all applicable OS1 protocol
standards is a real world equivalent of the model concept “open system”. Equipment that is in the “terminal” category,
that is, one that requires human intervention for the dominant parts of information processing, may satisfy the conditions
of the previous sentences when the appropriate OS1 standards are employed in communication with other open systems.
43 . Modelling the OS1 Environment
4.3.1 The development of OS1 standards, i.e. standards for the interconnection of real open systems, is assisted by
the use of abstract models. To specify the external behavior of interconnected real open systems, each real open system
is replaced by a functionally equivalent abstract model of a real open system called an open system. Only the
interconnection aspects of these open systems would strictly need to be described. However to accomplish this, it is
necessary to describe both the internal and external behavior of these open systems. Only the external behavior of open
systems is retained for the definition of standards for real open systems. The description of the internal behavior of open
systems is provided in the Basic Reference Model only to support the definition of the interconnection aspects. Any real
system which behaves externally as an open system can be considered to be a real open system.
4.3.2 This abstract modelling is used in two steps.
4.3.3 First, basic elements of open systems and some key decisions concerning their organization and functioning,
are developed. This constitutes the Basic Reference Model of Open Systems Interconnection described in this
Recommendation I Part of this International Standard.
4.3.4 Then, the detailed and precise description of the functioning of the open system is developed in the framework
formed by the Basic Reference Model. This constitutes the services and protocols for OS1 which are the subject of other
Recommendations and/or International Standards.
4.3.5 It should be emphasized that the Basic Reference Model does not, by itself, specify the detailed and precise
functioning of the open system and, therefore, it does not specify the external behavior of real open systems and does not
imply the structure of the implementation of a real open system.
4.3.6 The reader not familiar with the technique of abstract modelling is cautioned that those concepts introduced in
the description of open systems constitute an abstraction despite a similiar appearance to concepts commonly found in
real systems. Therefore, real open systems need not be implemented as described by the Model.
l) Cooneration among open systems involves a broad range of activities of which the following have been identified:
A
interprocess communication, which concerns the exchange of information and the synchronization of activity
a)
between OS1 application processes;
data representation, which concerns all aspects of the creation and maintenance of data descriptions and data
b)
transformations for reformatting data exchanged between open systems;
data storage, which concerns storage media, and file and database systems for managing and providing access to data
d
stored on the media;
process and resource management, which concerns the means by which OS1 application processes are declared,
d)
initiated and controlled, and the means by which they acquire OS1 resources;
integrity and security, which concern information processing constraints that have to be preserved or assured during
d
the operation of the open systems; and
program support, which concerns the definition, compilation, linking, testing, storage, transfer, and access to the
f)
programs executed by OS1 application-processes.
Some of these activities may imply exchange of information between the interconnected open systems and their interconnection
aspects may, therefore, be of concern to 0%
This Basic Reference Model covers the elements of OS1 aspects of these activities which are essential for early development of OS1
standards.
4
ITU-T Rec. X.200 (1994 E)

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SIST EN ISO/IEC 7498-1:1997
ISO/IEC 7498-1: 1994(E)
4.3.7 Throughout the remainder of this Basic Reference Model, only the aspects of real systems and application-
processes which lie within the OS1 Environment (OSIE) are considered. Their interconnection is illustrated throughout
this Reference Model as depicted in Figure 2.
4.3.8 The extent of the application of the OSIE concept through the use of OS1 standards may result in subsets of the
OSIE which corresponds to partially disjoint sets of real open systems, which are not physically cauable of OS1
I
communication between them.
Aspects of application-processes of concern to OSI,
i.e. applications-entities (see 7.1)
open system s
Aspects of real
open systems of
concern to OSI
1
r
I
TlSO2840-94/dO2
Physical media for OSI
Associations
Figure 2 - Basic elements of OS1
Concepts of a layered architecture
5
51 . Introduction
5.1.1 Clause 5 sets forth the architectural concepts that are applied in the development of the Reference Model of
Open Systems Interconnection. Firstly, the concept of a layered architecture (with layers, entities, service-access-points,
protocols, connections, etc.) is described. Secondly, identifiers are introduced for entities, service-access-points, and
connections. Thirdly, service-access-points and data-units are described. Fourthly, elements of layer operation are
described including connections, transmission of data, and error functions. Then, routing aspects are introduced and
finally, management aspects are discussed.
51.2 The concepts described in clause 5 are those required to describe the Reference Model of Open Systems
Interconnection. However, not all of the concepts described are employed in each layer of the Reference Model.
5
ITU-T Rec. X.200 (1994 E)

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ISO/IEC 7498-l : 1994(E)
5.1.3 Four elements are basic to the Reference Model (see Figure 2):
open systems;
a)
b) the application-entities which exist within the OS1 Environment (see 7.1);
the associations (see 5.3) which join the application-entities and permit them to exchange information;
C)
and
d) the physical media for OSI.
NOTE - Security aspects which are also general architectural elements of protocols are discussed in CCITI’ Rec. X.800 I
IS0 7498-2.
. Principles of layering
52
5.2.1 Definitions
a hierarchical division of an open system which interacts only with
5.2.1.1 (N)-subsystem: An element in directly
in the next higher division or the next lower division of that open
...