Information technology — Telecommunications and information exchange between systems — Data link service definition for Open Systems Interconnection

Traitement de l'information — Télécommunications et échange d'informations entre systèmes — Définition du service de liaison de données pour l'interconnexion de systèmes ouverts

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ISO/IEC 8886:1992 - Information technology -- Telecommunications and information exchange between systems -- Data link service definition for Open Systems Interconnection
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First edition
1992-06-1 5
Information technology - Telecommunications
and information exchange between systems -
üata link service definition for Open Systems
Traitement de l'information - Télécommunications et échange
d'informations enfre systèmes - Définition du service de liaison de
données pour l'interconnexion de systèmes ouverts
Reference number
ISO/IEC 8886:1992(E)
---------------------- Page: 1 ----------------------
ISOllEC 8886:1992(E)
Section 1 - General
O Introduction
1 1
2 Normative references 1
3 Definitions 2
3.1 Basic Reference Model definitions 2
3.2 Service conventions definitions 2
3.3 Reference Model connectionless-mode data transmission definitions 2
4 Abbreviations 2
5 Convent ions 3
5.1 General conventions
5.2 Parameters 3
Overview of the Data Link Service 3
7 Classes and types of Data Link Service 4
Section 2 - Definition of connection-mode service 4
Features of the connection-mode Data Link Service 4
9 Model of the connection-mode Data Link Service 5
9.1 DLC endpoint connection identification 5
9.2 Model of a Data-link-connection
9.2.1 Queue model concepts
9.2.2 DLC establishment
9.2.3 Data transfer
9.2.4 Reset
9.2.5 DLC release
O ISOllEC 1992

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permission in writing horn the publisher.
ISOllEC Copyright Office Case Postale 56 CH-I211 Genéve 70 Switzerland
Printed in Switzerland
---------------------- Page: 2 ----------------------
ISWIEC 8886:1992(E)
1 O Quality of connection-mode service
10.1 Determination of QûS for connection-mode service 9
10.2 Definition of QûS parameter 10
10.2.1 Throughput 10
10.2.2 Transit delay 11
10.2.3 Residual error rate 11
1 O. 2.4 Resilience 12
10.2.5 Protection 12
10.2.6 Priority 12
11 Sequence of primitives
1 1.1 Concepts used to define the connection-mode Data Link Service
1 1.2 Constraints on sequence of primitives
1 1.2.1 Relation of primitives at the two DLC endpoints
1 1.2.2 Sequence of primitives at one DLC endpoint
12 Connection establishment phase
12.1 Function 17
12.2 Types of primitives and parameters 17
12.2.1 Addresses 18
12.2.2 Called address 18
12.2.3 Calling address 18
12.2.4 Responding address 18
12.2.5 Quality of Service parameter set 18
12.3 Sequence of primitives
13 Connection release phase 19
13.1 Function 19
13.2 Types of primitives and parameters 19
13.2.1 Originator 20
13.2.2 Reason 20
13.3 Sequence of primitives when releasing an established DLC 20

13.4 Sequence of primitives in a DLS user rejection of DLC establishment attempt 21

13.5 Sequence of primitives in a DLS provider rejection of DLC establishment

13.6 Sequence of primitives in a DLS user abort of a DLC establishment attempt 22

14 Data transfer phase 23
14.1 Data transfer 23
14.1.1 Function 23
14.1.2 Types of primitives and parameter 23
14.1.3 Sequence of primitives 24
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ISOllEC 8886:1992(E)
14.2 Reset service 24
14.2.1 Function 24
14.2.2 Types of primitives and parameters 24
14.2.3 Sequence of primitives 25
Section 3 - Definition of connectionless-mode service
Features of the connectionless-mode primitives 27
Model of the connectionless-mode data link service 27
16.1 Model of a Data-link-connectionless-m& data transmission
17 Quality of connectionless-mode service 29
17.1 Determination of QOS for connectionless-mode service
17.2 Definition of connectionless-mode QOS parameters 29
17.2.1 Transit delay 30
17.2.2 Residual error rate 30
17.2.3 Protection 31
17.2.4 Priority 31
Sequence of connectionless-mode primitives at one DLSAP.
18 31
19 Data transfer 32
19.1 Function
19.2 Types of primitives and parameters
19.2.1 Addresses
19.2.2 Quality of service
19.2.3 DLS user-data
19.3 Sequence of primitives
Annex A
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ISOllEC 88861 992(E)
IS0 (the International Organization for Standardization) and IEC (the
International Electrotechnical Commission) form the specialised 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 com-
mittees collaborate in fields of mutual interest. Other international or-
ganizations, governmental and non-governmental, in liaison with IS0
and IEC, also take part in the work.
IÇO and IEC have established a
In the field of information technology,
joint technical committee, ISOIIEC JTC 1. Draft International Standards
adopted by the joint technical committee are circulated to national bod-
ies for voting. Publication as an International Standard requires ap-
proval by at least 75 Oh of the national bodies casting a vote.
International Standard ISO/IEC 8886 was prepared by Joint Technical
Committee ISO/IEC JTC 1, lnformation technology.
Annex A of this International Standard is for information only.
---------------------- Page: 5 ----------------------
ISOliEC 8886:1992(E)

This International Standard is one of a set of International Standards produced to facilitate the

interconnection of information processing systems. It is related to other standards in the set as

defined by IS0 7498. The Reference Model (IS0 7498) subdivides the area of standardization

for Open Systems Interconnection(OS1) into a series of layers of specification, each of a

manageable size.
Standard defines the service provided by the Data Link Layer to the Network
between the Data Link and Network Layers of the OS1 Basic Reference

Model. It provides for the designers of network protocols a definition of the Data Link Service

@LS) existing to support the network protocol and for designers of Data Link Protocols a

defiriition of the services to be made available through the action of the Data Link Protocol over the

underlying service. The relationship is shown in figure 1.
- uses Data Link
Network L
Data Link Service
Data Link -
- provides Data Link
Figure 1 - Relationship of this International Standard to other OS1 Standards

Throughout the set of OS1 standards, the term “service” refers to the abstract capability provided

by one layer of the OS1 Basic Reference Model to the layer immediately above. Thus, the Data

Link Service defined in this document is a conceptual architectural service, in-dependent of

administrative divisions.
---------------------- Page: 6 ----------------------
Information technology - Telecommunications and
information exchange between systems - Data link service
definition for Open Systems Interconnection
Section 1 : General
1 Scope
This International Standard defines the OS1 Data Link Service in terms of
a) the primitive actions and events of the service;

b) the parameters associated with each primitive action and event, and the form which they

take; and

c) the inter-relationship between, and the valid sequences of, these actions and events.

The principle objective of this International Standard is to specify the characteristics of a

conceptual Data Link Service and thus, supplement the Basic Reference Model in guiding the

development of Data Link protocols.

This International Standard does not specify individual implementation or products, nor does it

constrain the implementation of Data Link entities and interfaces within an information processing


There is no conformance of equipment to this Data Link Service Definition Standard. Instead,

conformance is achieved through implementation of conforming Data Link Protocols that fulfill the

Data Link Service defined in this International Standard.
2 Normative references

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

provisions of this International Standard.

At the time of publication, the editions indicated were valid. All standards are subject to revision,

and parties to agreements based on this International Standard are encouraged to investigate the

possibility of applying the most recent editions of the standards listed below. Members of EC and

IS0 maintain registers of currently valid International Standards.

IS0 7498: 1984, Information processing systems - Open Systems Interconnection - Basic

Reference Model (see also CCIïT Recommendation X.200).

IS0 7498JAdd.l: 1984, Information processing systems - Open Systems Interconnection - Basic

Reference Model - Addendum I Connectionless-rnode data transmission.

ISOfïR 8509: 1987, Information processing systems - Open Systems Interconnection - Service

Conventions (see also CCITT Recommendation X.210).
---------------------- Page: 7 ----------------------
ISO/IEC 8886:1992(E)
3 Definitions
3.1 Basic Reference Model definitions

This International Standard is based on the concepts developed in IS0 7498 and makes use of the

following terms defined in it:
a) Data link entity
b) DataLinkLayer
c) Data Link Service
d) Data-link-service-access-point
e) Data-link-service-access-point-address
f) Data-link-service-dunit
g) Reset
3.2 Service conventions definitions

This International Standard makes use of the following terms defined in ISO/TR 8509, as they

apply to the Data Link Layer:
a) Data Link Service User
b) Data Link Service Provider
c) Pnmitive
d) Request
e) Indication
f) Response
g) Confrm
3.3 Data Link Service definitions

This International Standard makes use of the following terms defined in IS0 7498 and

IS07498/Add. 1 , as they apply to the Data Link Layer:
a) Data-link-connection
b) Data-link-connection-mode data transmission
c) Data-link-connectionless-mode data transmission
4 Abbreviations
DL Data Link
DLC Data-link-connection
DU DataLinkLayer
DU Data Link Service
DLSAP Data-link-service-access-point
DLSDU Data-link-service-data-u~t
OS1 Open Systems Interconnection
QOS Quality of Service
---------------------- Page: 8 ----------------------
ISOItEC 88861 992(E)
5 Conventions
5.1 General conventions

This International Standard uses the descriptive conventions given in ISO/TR 8509.

The service model, service primitives, and time-sequence diagrams used are entirely abstract

descriptions; they do not represent a specification for implementation.
5.2 Parameters

Service primitives, used to represent service user/service provider interactions (1SOlï.R 8509),

convey parameters which indicate information available in the user/provider interaction.

The parameters which apply to each group of Data Link Service primitives are set out in tables in

clauses 12 to 14 and 19. Each “X’ in the tables indicates that the primitive labelling the column in

which it fails may carry the parameter labelling the row in which it fails.
Some entries are further qualified by items in brackets. These may be
a) A Parameter specific constraint:

(=) indicates that the value supplied in an indication or confirm primitive is always

identical to that supplied in a previous request or response primitive issued at the peer

b) Indication that some note applies to the entry:

(see note X) indicates that the referenced note contains additional information pertaining

to the parameter and its use.

In any particular interface, not all parameters need be explicitly stated. Some may be implicitly

associated with the DLSAP at which the primitive is issued.
6 Overview of the Data Link Service

The DLS provides for the transparent and reliable transfer of data between DLS users. It makes

invisible to these DLS users the way in which supporting communications resources are utilized to

achieve this transfer.
In particular, the DLS provides for the following:

a) Independence of underlying Physical Layer - the DLS relieves DLS users from all concerns

regarding which configuration is available (e.g., point-to-point connection) or which

physical facilities are used (e.g., half-dulpex transmission).

b) Transparency of transferred information - the DLS provides for the transparent transfer of

DLS user-data. It does not resmct the content, format or coding of the information, nor

does it ever need to interpret its structure or meaning.
- the DLS relieves the DLS user from loss, insertion, corruption
c) Reliable transfer of data

or, if requested, misordering of data which may occur. In some cases of unrecoverable

errors in the Data Link Layer, duplication or loss of DLSDUs may occur.
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ISOllEC 88861992(E)
Note - Detection of duplicate or lost DLSDUs may be performed by DU users.

d) Quality of Service (QOS) selection - the DLS makes available to DLS users a means to

request and to agree upon a quality of service for the transfer of data. QOS is specified by

means of QûS parameters representing characteristics such as; throughput, transit delay,

accuracy and reliability,

e) Addressing.- The DLS allows the DLS user to identify itself and to specify the DLSAP to

which a DLC is to be established whenever more than two DLSAPs are supported by the

DLS provider. Data link addresses have only local significance within a specific data link

configuration over a single transmission medium (point-to-point or multi-point physical

connection) or a group of parallel transmission media (multi-link or splitting function).

Therefore, it is not appropriate to defme a global addressing structure.

Note - The DLS is required to differentiate between the individual systems that are physically or logically

connected to a multi-point data link and to differentiate between connections when the Data Link Layer

includes a multiplexing function. For commonality with other service definitions, this mechanism is

referred to as addressing and the objects used to differentiate between systems are referred to as addresses.

7 Classes and types of Data Link Service
There are no distinct classes of Data Link Service defined.
There are two types of DLS:
a) a connection-mode service (defined in section 2), and
b) a connectionless-mode service (defined in section 3).

When making reference to this International Standard, a user or provider of Data Link Service shall

state which types of service it expects to use or provide.
Section 2 : Definition connection-mode service
Features of the connection-mode Data Link Service
The DLS provides the following features to the DLS user:

a) The means to establish a DLC with another DLS user for the purpose of exchanging


b) The establishment of an agreement between the initiating DLS user and the DLS provider

for a certain Quality of Service (QOS) associated with each DLC.

c) The means of transferring DLSDUs of restricted length on a DLC. The transfer of

DLSDUs is transparent, in that the boundaries of DLSDUs and the content of DLSDUs are

preserved unchanged by the DLS, and there are no constraints on the DLSDU content

imposed by the DLS.
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ISO/IEC 8886:1992(E)

Note - The length of a DLSDU may be limited because of internal mechanisms employed by the Data

Link Protocol (see sub-clause of IS0 7498).

d) The means by which the receiving DLS user may flow control the rate at which the sending

DLS user may send DLSDUs.

e) The means by which a DLC can be returned to a defined state and the activities of the two

DLS users synchronized by use of a Reset service element.

f) The unconditional, and therefore possibly destructive, release of a DLC by either of the

DLS users or by the DLS provider.
9 Model of the connection-mode Data Link Service

This International Standard uses the abstract model for a layer service defined in clause 4 of

ISODR 8509. The model defines the interactions between the DLS users and the DLS provider

which take place at the two DLSAPs. Information is passed between the DLS user and the DLS

by service primitives, which may convey parameters.
9.1 DLC endpoint connection identification

If a DLS user needs to distinguish among several DLCs at the same DLSAP, then a local

connection endpoint identification mechanism shall be provided. All primitives issued at such a

DLSAP within the context of a DLC would be required to use this mechanism to identify this DLC.

an implicit identification is not described in this international Standard.
9.2 Model of a Data-link-connection

Between the two endpoints of a DLC, there exists a flow control function that relates the behaviour

of the DLS user receiving data to the ability of the other DLS user to send data. As a means of

specifying this flow control feature and its relationship with other capabilities provided by the

connection-mode DLS, the queue model of a DLC, which is described in the following clauses, is


This queue model of a DLC is discussed only to aid in the understanding of the end-to-end service

features perceived by DLS users. It is not intended to serve as a substitute for a precise, formal

description of the DLS, nor as a complete specification of all allowable sequences of DLS

also the note below.) In
primitives. (Allowable primitive sequences are specified in clause 11, see

addition, this model does not attempt to describe all the functions or operations of DL entitles that

used to provide the DLS. No attempt to specify or constrain DLS implementations is implied


Note - The internal mechanisms which support the operation of the DLS are not visible to the DLS user. In

addition to the interactions between service primitives described by this model (e.g., the issue of a DL-RESET

request primitive at a DLSAP may prevent the receipt of a DL-DATA indication primitive, corresponding to a

previously issued DL-DATA request primitive, by the peer DLS user) there may also be:

a) constraints applied locally on the ability to invoke primitives;

b) service procedures defining particular sequencing constraints on some primitives.

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I SO/ I EC 8886 1 992( E)
9.2.1 Queue model concepts

The queue model represents the operation of a DLC in the abstract by a pair of queues linking the

two DLSAPs. There is one queue for each direction of information flow (see figure 2).

DLS User E?
DLS User A
0 I
0 I
Queue from A to E?
Queue from E? to A
Figure 2 - Queue Model of a DLC

Each queue represents a flow control function in one direction of transfer. The ability of a DLS

user to add objects to a queue will be determined by the behaviour of the other DLS user in

removing objects from the queue and the state of the queue. Objects are entered or removed from

the queue as a result of interactions at the two DLSAPs.
The pair of queues is considered to be available for each potential DLC.

The following objects may be placed in a queue by a DLS user (see clauses 12 to 14):

a) a connect object, representing a DL-CONNECT primitive and its parameters;
b) a data object, representing a DL-DATA primitive and its parameters;
c) a reset object, representing a DL-RESET primitive and its parameters; and

d) a disconnect object, representing a DL-DISCONNECT primitive and its parameters.

The following objects may be placed in a queue by the DLS-provider (see clauses 12 to 14):

1) a reset object, representing a DL-RESET primitive and its parameters;
2) a synchronization mark object (see 9.2.4); and

3) a disconnect object, representing a DL-DISCONNECT primitive and its parameter.

are defined to have the following general properties:
The queues

i) a queue is empty before a connect object has been entered and can be returned to this state,

with loss of its contents, by the DLS provider;
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ISO/IEC 8886:1992(E)

ii) objects are entered into a queue by the sending DLS user, subject to control by the DLS

provider. Objects may also be entered by the DLS provider;

iii) objects are removed from the queue, under the control of the receiving DLS user;

iv) objects are normally removed in the same order that they were entered (however, see

9.2.3); and

v) a queue has a limited capacity, but this capacity is not necessarily either fixed or

9.2.2 DLC establishment

A pair of queues is associated with a DLC between two DLSAPs when the DLS provider receives

a DL-CONNECT request primitive at one of the DLSAPs, and a connect object is entered into one

From the standpoint of the DLS users of the DLC, the queues remain associated
of the queues.

with the DLC until a disconnect object representing a DL-DISCONNECT primitive is either entered

or removed from the queue.

DLS user A, who initiates a DLC establishment by entering a connect object representing a DL-

CONNECT request primitive into the queue from DLS user A to DLS user B, is not allowed to

enter any other object, other than a disconnect object, into the queue until after the connect object

representing the DL-CONNECT confirm primitive has been removed from the DLS user B to DLS

user A queue. In the queue from DLS user B to DLS user A, objects can be entered only after

DLS user B has entered a connect object representing a DL-CONNECT response primitive.

The properties exhibited by the queues while the DLC exists represent the agreements reached

among the DLS users and the DLS provider during this connection establishment procedure

concerning QOS.
9.2.3 Data transfer

Flow control on the DLC is represented in this queue model by the management of the queue

capacity, allowing objects to be added to the queues. The addition of a object may prevent the

a further object.
addition of

Once objects are in the queue, the DLS provider may manipulate pairs of adjacent objects, resulting

in deletion. An object may be deleted if, and only if, the object which follows it is defined to be

destructive with respect to the object. If necessary, the last object on the queue will be deleted to

allow a destructive object to be entered - they may therefore always be added to the queue.

Disconnect objects are defined to be destructive with respect to all other objects. Reset objects are

defined to be destructive with respect to all other objects except connect and disconnect objects.

The relationships between objects which may be manipulated in the above fashion are summarized

in table

Whether the DLS provider performs actions resulting in deletion or not will depend upon the

QOS for DLC. In general, if a DLS user does not
behaviour of the DLC users and the agreed

remove objects from a queue, the DLS provider shall, after some unspecified period of time,

perform all the permitted deletions.
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ISOllEC 88861992(E)
Table 1 - Relationships between Oueue Model ob-iects
The following
object Y Is
\ respect to defined
Reset ization
Connect Data
Mark nect
the preceding
obiect X..
NIA : X will not precede Y in a valid state of a queue
Key :
- : not to be destructive nor to be able to advance ahead
DES : to be destructive to the preceding object
9.2.4 Reset

In order to accurately model the reset service a synchronization mark object is required. The

synchronization mark object exhibits the following properties:
a) It cannot be removed from a queue by a DLS-user;

b) A queue appears empty to a DLS-user when a synchronization mark object is the next

object in the queue;
c) A synchronization mark can be destroyed by a Disconnect object (see table 1).

d) When a Reset object is immediately preceded by a synchronization mark object, both the

Reset object and the synchronization mark object are deleted from the queue.
The initiation of a reset procedure is represented in the two queues as follows:

i) initiation of a reset procedure by the DLS provider is represented by the introduction into

each queue of a reset object followed by a synchronization mark object;

ii) a reset procedure initiated by a DLS user is represented by the addition, by the DLS

provider, of a reset object into the queue from the Reset initiator to the peer DLS user and

the insertion of a reset object followed by a synchronization mark object into the other

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ISO/I€C 8886:1992(E)

Unless destroyed by a disconnect object, a synchronization mark object remains in the queue until

the next object following it in the queue is a reset object. Both the synchronization mark object and

the following reset object are then deleted by the DLS provider.

Note - Associated with the initiation of a reset procedure are restrictions on the issuance of certain other types of

primitives. These restrictions will result in restrictions on the entry of certain object types into the queue until the

reset procedure is completed (see 14.2.3).
9.2.5 DLC release

The insertion into a queue of a disconnect object, which may occur at any time, represents the

initiation of a DLC release procedure. The release procedure may be destructive with respect to

other objects in the two queues and eventually results in the emptying of the queues and the

disassociation of the queues with the DLC.

The insertion of a disconnect object may -also represent the rejection of a DLC establishment

attempt or the failure to complete DLC establishment. In such cases, if a connect object

representing a DL-CONNECT request primitive is deleted by a disconnect object, then the

disconnect object is also deleted. The disconnect object is not deleted when it deletes any other

object, including the case where it deletes a connect object representing a DL-CONNECT

10 Quality of connection-mode Data Link Service

The term “Quality of Service” (QOS) refers to certain characteristics of a DLC as observed between

the connection end-points. QOS describes aspects of a DLC which are attributable solely to the

DLS provider.

Once a DLC is established, the DLS users at the two ends have the same knowledge and

QOS over the DLC is.
understanding of what the
1 O. 1 Determination of QOS for connection-mode service

QOS is described in terms of QOS parameters. These parameters give DLS users a method of

specifying their needs, and give the DLS provider a basis for protocol selection.

The QOS parameters can be divided into the following two types, based upon the way in which

their values are determined:

a) those QOS parameters which may be selected on a per-connection basis during the

establishment phase of a DLC.

b) those QOS parameters which are not selected during DLC establishment but whose values are

known by other methods.

There are three QOS parameters, through put, protection and priority (as defined in 10.2.1, 10.2.5

and 10.2.6 respectively), which are of the type actually selected during DLC establishment. The

selection procedures for these parameters are described in detail in 12.2.5. Once the DLC is

established, throughout the lifetime of the DLC, the agreed QOS values are not reselected at any

point in time and their is no guarantee that the original values will be maintained. The DLS users

should also be aware that changes in QOS on a DLC are not explicitly signalled by the DLS

---------------------- Page: 15 ----------------------
ISOllEC 88861992(E)

The remaining QOS characteristics that are identified as parameters, but for which there is no

selection during DLC establishment, are defined in 10.2.2 through 10.2.4 respectively. The

values of these parameters for a particular DLC are determined by other methods such as, a priori

knowledge and agreement.

If selection is allowed, certain measures of QOS are requested by the sending DLS user when the

DL-CON primitive action is initiated. The requested measures (or parameter value and options) are

based on a priori knowledge by the DLS user of the service(s) available to it by the DLS provider.

Knowledge of the characteristics and type of service provided (i.e., the parameter, formats, and

options that effect the transfer of data) is made available to a DLS user through some layer

management interaction prior to (any) invocation of the DL connection-mode service. Thus, the

of the service it can expect to be provided
DLS user has explicit knowledge of the characteristics
with for each invocation of the service.

The DLS provider may also provide information on the current QOS independently of access to the

service by a DLS user. This seemingly dynamic aspect of QOS determination is not a negotiation

but provided with knowledge of the characteristics of the service currently outside of any instance

of the invocation of the service.
1 O. 2 Definition of connection-mode QOS parameters
QûS parameters can be classified as:
a) parameters that express DLS performance, as shown in table 2.
~ RI
r A A
Throughput Residual Error Rate
Transit Delay (corruption, duplication / loss)
b) parameters that express other DLS characteristics, as shown in table 3.
Table 3 - performance

Note - Some QOS parameters are defined in terms of the issuance of DLS primitives. Reference to a DLS

primitive refers to the complete execution o

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