ISO/IEC 11575:1995
(Main)Information technology — Telecommunications and information exchange between systems — Protocol mappings for the OSI Data Link service
Information technology — Telecommunications and information exchange between systems — Protocol mappings for the OSI Data Link service
Specifies general principles for the mappings between the OSI Data Link service, both connection-mode (CO-DLS) and connectionless-mode (CL-DLS), and standard Data Link protocols. Specifies the detailed mappings M1, M2, M5 and M6; also specifies the main features of the mappings M3 and M4. Does not specify individual implementations or products, nor does it constrain the implementation of Data Link entities and interfaces within an information processing system.
Technologies de l'information — Télécommunications et échange d'information entre systèmes — Applications du protocole au service de liaison de données OSI
General Information
Standards Content (Sample)
INTERNATIONAL
ISOAEC
STANDARD
ii575
First edition
1995-07-01
Information technology -
Telecommunications and information
exchange between Systems - Protocol
mappings for the OSI Data Link Service
Technologies de I’informa tion - T6kcommunications et kchange
d ‘in forma tion en tre systemes
- Applications du protocole au Service de
liaison de donnees OSI
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ISO/IEC 11575:1995(E)
Page
Contents
. . .
111
Foreword .
1
1 Scope .
2 Normative References .
3 Definitions .
4 Abbreviations .
5 Conformance .
6 General principles of the protocol mappings .
............
7 Protocol mapping for ISO/IEC 7776 Single link procedures
Protocol mapping for HDLC Unbalanced Operation Normal response mode
8
8
Class(UNC) .
11
Protocol mappings for LLC Types 1 and 2 .
9
15
10 Protocol mappings for HDLC connectionless-mode classes of procedure .
o ISO/IEC 1995
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HSO/IEC Copyright Office l Case postale 56 l CI-YI- 1211 Geneve 20 0 Switzerland
Printed in S witzerland
ii
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o ISO/IEC
ISO/IEC 11575:1995(E)
Foreword
ISO (the International Organization for Standardization) and IEC (the
International Electrotechnical Commission) form the specialized System for
worldwide standardization. National bodies that are members of ISO 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. ISO and IEC technical committees collaborate in fields
of mutual interest. Other international organizations, governmental and non-
governmental, in liaison with ISO and IEC, also take part in the work.
In the field of information technology, ISO 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 11575 was prepared by Joint Technical
Committee ISO/IEC JTC 1, Information technology.
. . .
111
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INTERNATIONAL STANDARD @ ISOmC ISO/IEC 11575 : 1995 (E)
Information technology - Telecommunications and
information exchange between Systems - Protocol
mappings for the OSI Data Link Service
1 Scope
This International Standard specifies general principles for the mappings between the OS1 Data Link Service (ISO/IEC 8886), both
connection-mode (CO-DLS) and connectionless-mode (CL-DLS), and Standard Data Link protocols, as follows:
Ml: HDLC X.25 LAPB-compatible DTE procedures, Single link procedures (ISO/IEC 7776)
CO-DLS -
M2: CO-DLS - HDLC Unbalanced Operation Normal response mode Class, UNC (ISO/IEC 3309, ISO/IEC 4335 and ISO/IEC 7809)
Logical link control (LLC) Type 2 (ISO/IEC 8802-2)
M3: CO-DLS -
M4: LLC Type 1 (lSO/lEC 8802-2)
CL-DLS -
M5: CL-DLS - HDLC Balanced Operation ConnectionIess-nlode Class, BCC (lSO/lEC 3309, ISO/IEC 4335 and ISO/IEC 7809)
M6: CL-DLS - HDLC Unbalanced Operation Connectionless-mode Class, UCC (ISO/IEC 3309, ISO/IEC 4335 and ISO/IEC 7809)
This International Standard specifies the detailed mappings Ml, M2, M5 and MG; it also specifies the main features of the mappings M3 and
M4.
This International Standard does not specify individual implernentations or products, nor does it constrain the implementation of Data Link
entities and interfaces within an information processing System.
NOTES
1 The above designations Ml to M6 for the mappings arc used elsewhere in this International Standard.
2 The possibility of adding further mappings to the above list in the t‘uture is not preciuded (for exumple, to cover Frame Relay protocols).
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 IEC and ISO maintain registers of currently valid International Standards.
ISO/IEC 3309: 1993, hzfornzatiou technology -- Tclcco~~~~321~~~icatio~rs arzd infwmation exchange between systems - High-level data link
control (HDLC) procedures - Frame stwctur-e.
ISO/IEC 4335: 1993, Iuformatiou tcchuologv - T~~lcconli7lrrrliccrtiorls cwd i~lf0rmatiou e.\rchu~~ge bctwee~z svstems - High-level data link
d
d
Eleme~~ts of’prowdwes.
corrtrol (HDLC) procedrrres -
.
ITU-T Recommendation X.200 (1994) I ISO/IEC 7498- 1: 1994, I#wmtrtiorl tccluwlogv - Opcll Systems Iiltcrcoruzcctiou -Basic Rcference
d
Model: The basic model.
ISO/IEC 7776: 1995, Information technology - Telecommunications and information exchange between Systems - High-level data link
control procedures - Description of the X.25 LAPB-compatible DTE data link procedures.
Tclcconlnllrrliccrtiorls aud i@wnzutiorl exchuuge betweeu systems - High-level data link
ISO/IEC 7809: 1993, Il$0rmutiorl tcchrlology -
control (HDLC) procedures - Clusses of yrocedurxv.
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ISO/IEC 11575 : 1995 (E)
ISOIIEC 8802-2: 1994, Information technology - Telecommunications and information exchange between Systems - Local and
metropolitan area networks - Specific requirements - Part 2: Logical link control.
ISO/IEC 8886: 1992, Information techr?ology - Telecommurlicatioru arid ijlformatioll exchange between Systems - Data Link Service
definition for Open Systems Interconnection.
ITU-T Recommendation X.210 (1993) I ISO/IEC 1073 1: 1994, Information technology - Open Systems Interconnnection - Basic
Reference Model ~ Conventions for the definition of OSI Services.
3 Definitions
3.1 This International Standard uses the following temjs defined in ITU-T Rec. X.200 I ISO/IEC 7498-1:
DL-address
DL-connection
DL-connectionless-mode transmission
DL-entity
DL-group address
DL-layer
DL-protocol-data-unit
DL-Service access Point
DL-Service access point address
DL-service-data-unit
DL-Subsystem
3.2 This International Standard uses the following terms defined in ITU-T Rec. X.210 1 ISO/IEC 10731:
DLS provider
DLS user
primitive
request (primitive)
indication (primitive)
response (primitive)
tonfirm (primitive)
3.3 For the purposes of this International Standard, the following definitions apply:
3.3.1 frame: A DL-PDU.
3.3.2 instance of IX-conmwnication: A DL connection or a Single DL-connectionless-mode transmission.
4 Abbreviations
BCC balanced Operation connectionless-mode class
connectionless-mode
CL
CO connection-mode
DISC disconnect
DL Data Link
DLC Data Link connection
DLS Data Link Service
DLSAP Data Link Service access Point
DLSDU Data Link Service data unit
DM disconnected mode
FRMR frame reject
HDLC High-level data link control
1 information
LLC Logical Link Control
NRM nomlal response mode
PDU protocol data unit
quality of Service
QOS
SABM set asynchronous balanced mode
SABME set asynchronous balanced mode extended
SLP Single link procedure
SNRM set nomlal response mode
SNRME set normal response mode extended
unnumbered acknowledgment
UA
2
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ucc unbalanced Operation connectionless-mode class
UI unnumbered infomlation
unbalanced Operation nomlal response mode class
UNC
5 Conformance
There is no direct confomlance of equipment to this International Standard considered in isolation. The provisions of this International
Standard have normative application to equipment implementing Network-layer protocols that are specified in terms of their use of the OS1
Data Link Service. For such Network-layer protocols, this International Standard links the behaviour of the underlying Data Link protocols to
the relevant features of the Data Link Service, and thus provides the basis for establishing conformance of the Network-layer protocol
implernentations to the specified usage of the Data Link layer.
NOTES
1 This International Standard therefore functions as “glue” between Network-layer protocol Standards, written in terms of their use of the OS1 Data Link
usually for historical reasons -
service, and Data Link protocol Standards written - without reference to the OS1 Data Link service. Conformance to such a
Data Link protocol Standard will be expressed entirely in terms of the procedures and PDUs, etc.,
specified in that Standard; conformance to such a Network-
layer Standard in respect of its use of the Data Link layer will be expressed in terms of, for example. the transfer of NPDUs as DLSDUs, and (for the CO-DLS)
of procedures that apply in the event of DL connection reset or DL connection release. This International Standard specifies precisely how the procedures, etc.,
of the Data Link protocol in question are to be interpreted in terms of the OS1 Data Link Service, and therefore establishes a precise relationship between the
specifications of the Network-layer protocol and of the Data Link protocol.
2 Use of the OS1 Data Link Service in Network-layer protocol specifications offers the benefits of layer-independence, in that such a Network-layer
specification is available, without Change, for use over new or alternative Data Link technotogies, provided only that the appropriate mapping is specified
between the OSI Data Link Service and the relevant Data Link technology.
6 General principles of the protocol mappings
6.1 Data Link architecture
The OS1 Data Link Service defines the properties of individual instances of DL-communication between pairs of DLS users.The definition is
abstractly expressed in terms of primitives and Parameters exchanged, at Data Link Service access Points (DLSAPs), between each DLS user
and a Single DLS provider: this is illustrated in figure 1.
DLS user
-
y DLS primitives f
D
\
LSAP -4
D LS provider _I~--~----~--~~~-
Figure 1 - Model of Data Link Service provision
Operation of the DLS provider is modelled in terms of the exchange of DL-PDUs, in accordance with DL-protocols, between DL-entities
(figure 2). Esch DLSAP is attached to a unique DL-entity; a given DL-entity tan have one or more DLSAPs attached to it, depending upon
System configuration and the nature of the underlying DL-protocols.
When real equipment is considered, a data link consists of two or more stations communicating according to a particular DL-protocol or set
of related DL-protocols, together with the interconnecting media supporting information exchange among the stations. Possible
configurations of a real data link (see figure 3) include:
Point-to-Point data links, with just two stations (rnappings M 1 and M5 are for protocols used in data links of this type);
4
centralized multipoint data links, with one Station controlling communication between itself and a number of subsidiary stations
b)
(mappings M2 and M6 arc for protocols used in data links of this type);
distributed multipoint data links, with a number of stations any of which tan communicate with any other (local area networks are of
4
this type, see mappings M3 and M4).
The definition of stations and data links has a logical dimension, deriving from the protocols used, in addition to the physical equipment used
in constructing particular real data links. A Single real System tan be attached to two or more data links, in which case it is considered to
contain the corresponding number of distinct stations; a Single real System tan contain two or more stations attached to the Same data link;
and it is possible for a Single set of communications equipment to support two or more distinct data links.
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The Data Link Service model deals primarily with the properties of individual instances of DL-communication, each occurring between a
pair of DL-entities OT, for multicast communication, between a Single originating Source DL-entity and a set of destination DL-entities. DL-
protocols have to deal with multiple instances of communication, both between a given pair of DL-entities and, certainly for data links of
types (b) and (c) above, between different pairs (or multicast Sets) of DL-entities: representing the protocol facilities that support this forms a
part of the specification of the mapping between the protocol and the DLS. Aspects to be considered include the number of DLSAPs
supported by a given Station, the number of DL connections that tan be active simultaneously at a DLSAP, and the DL addressing facilities
that support discrimination among multiple stations.
DLS primitives
4
t’
1 I
I
DL-protocol
4 v
DL-entity * * DL-entity
(DL-PDUs)
I
DLS provider
Ie
1,
I
- - - -~~~-~~ -l
Figure 2 - Structure of DLS provider
1
4 *
a) Point-to-Point data link, two stations
,
only (e.g. combined stations or peer
stations)
, c
Controlling
b) Centralized multi-point data link,
communication between controlling
1
1
, 4
Station (e.g., primary Station or
1
control Station) and subsidiary
stations (e.g., secondary stations or
tributary stations)
Su bsidiary Subsidiary Su bsidiary
1
c) Distributed multipoint data link, any
Station to any Station
Types of clata link configuration
Fgure 3 -
4
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6.2 Modelling of Service primitives
Primitives are abstractions of the behaviour of real Systems engaging in data communication: in specifying the mapping between these
abstract primitives and the activity of real implernentations of DL-protocol entities, this allows freedom in modelling the timing of when
primitives occur, so as to simplify the mapping specification.
explicitly allows this
NOTE 1 - ISO/IEC 8886 freedom; it defines the constraints on the sequence in which primitives tan occur, but that other
constraints affect the ability of a DLS user or DLS provider t
:o issue a primit ive at any particular time.
For primitives issued by the DLS user - those of types request and response -
this Lntemational Standard uses a rendezvous model: that is,
a primitive tan only occur if both the DLS user and the local DLS provider are prepared for it to occur. This provides two valuable
simplifica tions:
occurrence of DLS-user issued primitives tan always be related to the extemally observable transmission of corresponding frames -
d
the ability to transmit the frames is considered to be an essential part of the DLS provider being prepared for the primitive to occur;
and
there is no need to complicate the mapping by, for example, introducing any queueing of primitives that have been by the DLS
b)
user but ha ve not yet resulted in any protocol activity.
Conversely, for primitives issued by the DLS provider - those of types indication and confirrn - it is convenient to simplify the model
by
DLS provider is ready.
considering primitives to occur as soon as the
NOTES
free to use an interfxe that
2 An implementation of a DL-protocol is queues requests, eg, for data tra nsmission; however, the issuing of corresponding DLS
requests are removed from
primitives is modelled as occurring after the such a queue, not when they are entered into the queue.
3 Any queueing mechanisms in real Systems are matters of i mplementa tion detail; as in the ca-x descri bed in Note 2, the boundary between DLS provider
and DLS user is modelled as being at the DLS provi der3 end of the queue.
4 This model does not impose a req uirement to su pport queues of unbounded size: interface by the DLS user will in
t1ow control general
behaviou r of the DL-protocol entit y and prevent e xcessi ve demands.
6.3 Relationships between Service features and protocol functions
All of the rnappings covered by this Internat ionrll Sta .ndar-d use natura1 relationships between functions of the various protocols and
correspondi ng abstractions as Data Link Service features.
The primary function in each mapping is that of transferring units of user data.
For each mapping, the correspondence is between the
DLSDU of a DL-DATA or DL-UNITDATA primitive (in connection-mode or connectionless-mode Operation, respectively) and the basic
delimited unit of data transfer in the protocol: that is, for the mappings Ml to M6, the contents of the Information field of a Single frame
conveying user data.
NOTE 1 - It is possible that future Data Link layer protocols could provide intrinsic support for segmentation and reassembly of user data across sequences
of frames; the absence of this feature from the protocols considered in Ml to Mb does not preclude the possibility of Single DLSDUs mapping to multiple
frames of such future DL-protocols.
The other functions of DL-protocols are defined to complement the prirnary data-transfer function, and the correspondences in the DLS
mappings are similarly direct.
For connectionless-mode Operation, only functions related to addressing and quality of Service apply.
For connection-mode Operation, protocol fu nctions for setting up, disconnecting, and resetting the connections used for data transfer are
mapped to DL connection establishment, DL connection release and DL connection reset.
NOTE2- ISO/IEC 8886 defines a somewhnt idealized connection-mode Service, which does not fully represent all the peer-to-peer interactions that tan
occur when real DL-protocols such as ISO/IEC 7776 SLP and LLC Type 2 arc used. The differentes affect only link Lwtup, disconnection and reset, and not
any successfully established period of data transfer. They occur typically when DL PDUs responding to link setup, disconnection or reset are lost, and are
more likely to occur if, at the same time, one of the DL-entities undergoes two or more changes in its readiness to participate in data transfer. In such
a Single successful DLC establishment, w hereas the ot her observes a rejected incoming DLC
circumstances, one DL-entity may observe, for example,
establishment attempt followed by a successful incoming DLC est;rblishmen~; or one DL-entity may observe a Single DLC reset where the other observes two
DLC resets, with no data received between the two. These do not represent rnalfunctions of the protocols, since they never affect the integrity of any successful
transfers of user data between the DL-entities.
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7 Protocol mapping for ISO/IEC 7776 Single link procedure
7.1 General protocol functions
ISO/IEC 7776 SLP applies to a Point-to-Point data link (as in figure 3a), connecting the Single Station for which the SLP is specified (the
DTE) with a Single remote Station (the DCE or remote DTE). The protocol for the SLP provides no facilities for addressing or multiplexing;
consequently, the data link supports a Single DLSAP in the DTE and a Single DLSAP in the DCE or remote DTE, and there tan be at most
one DL connection in existente between the two DLSAPs at any given time.
Table 1 specifies the mapping between the principal protocol functions of ISO/IEC 7776 SLP and the corresponding features of the OS1 CO-
DLS.
Table 1 - Mapping between principal ISO/IEC 7776 SLP protocol functions and CO-DLS features
Protocol function Data Link Service feature
Absence of a DL connection (Tdle state): see Note
Asynchronous disconnected mode
DL connection establishment Phase
Link set-up
DL connection release Phase and absence of a DLC: see Note
Link disconnection
Data transfer Phase, normal data transfer
Information transfer
Data transfer Phase, reset
Link reset, including frame rejection exception condition
NOTE - The DL connection release Phase at each DLSAP is instantaneous, since it contains only a Single DL-DISCONNECT primitive. However, the
corresponding protocol exchanges are extended in time, with a resulting transient period at each DLSAP during which the protocol’s link disconnection
corresponds to absence of a DLC, with DLC establishment Phase unable to be entered.
7.2 DL connection establishment
Table 2 specifies the mapping between DL-CONNECT primitives and the frames used for link setup according to ISO/lEC 7776.
The called address, calling address and responding address Parameters of the DL-CONNECT primitives are associated a priori with the DTE
and the DCE or remote DTE at the two ends of the Point-to-Point data link, and hence arc not mapped in the protocol.
Similarly, the Quality of Service Parameter set parameters are not mapped in the protocol, since only one level of QOS is available and is
assumed known a priori.
- Mapping between primitives and ISO/IEC 7776 frames at DLC establislment
Table 2
Primitive Frame
SABM or SABME commtind transmitted when in disconnected mode, together with any
DL-CONNECT request
retransmissions on timet expiry
SABM or SABME comm;uld received when in disconnected mode
DL-CONNECT indication
DL-CONNECT response UA response transmitted in response to SABM or SABME command received in disconnected
mode
UA response received for SABM or SABME command (re)transmitted in disconnected mode
DL-CONNECT tonfirm
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7.3 DL connection release
Table 3 specifies the mapping between DL-DISCONNECT primitives and the frames used for link disconnection according to ISO/IEC
7776.
The Originator Parameter in a DL-DISCONNECT indication primitive is “DLS provider” if the primitive corresponds to a DM frame
received in data transfer Phase, and otherwise is “unknown”.
The Reason Parameter in every DL-DISCONNECT request and indication primitive is “reason unspecified”.
Table 3 - Mapping between primitives and ISO/IEC 7776 frames, etc., at DLC release
Primitive Frame, etc.
DL-DISCONNECT request DISC command transmitted when in information transfer Phase, together with any retransmissions
on timer expiry
DM response transmitted in response to SABM or SABME command received in disconnected
n-rode (rejection of DLC establishrnent)
DISC cornmand or DM response received when in information tmnsfer Phase
DL-DTSCONNECT indicat ion
DM response received for SABM or SABME command (re)transmitted in disconnected mode
(rejection of DLC establishment)
DM response transmitted during information transfer Phase (in response to received FRMR or
unsolicited UA response, or to unsolicited response frame with F bit set to l), together with any
retransmissions on timer expiry
Entry to disconnected mode on retransmission-count expiry during information trünsfer Phase or
link set-up
Detection of loss of Physical layer communication
7.4 Data transfer
Esch DL-DATA request primitive maps to transmission of an 1 frame, together with any retransmissions required by the ISO/IEC 7776
procedures for information transfer. Esch transrnitted 1 frarne with an Inforn-mtion field having non-Zero length corresponds to a DL-DATA
request primitive in this way.
Esch new in-sequence 1 frame received and accepted with non-Zero Information field length maps to a DL-DATA indication primitive.
The DLS User-data Parameter of a DL-DATA primitive is the sequence of octets that forms the Infomlation field of the corresponding
transmitted or received 1 frame.
7.5 DL connection reset
Table 4 specifies the mapping between DL-RESET primitives and the frrunes used for link reset according to ISO/IEC 7776.
The Originator and Reason Parameters in a DL-RESET indication primitive are respectively:
“DLS provider” and “Data Link error” if the primitive corr-esponds to a FRMR response transtnitted or received, or to a SABM or
a)
SABME command transmitted by the DL-entity in response to an error; or
“unknown” and “reason unspecified” when the primitive corresponds to a SABM or SABME command received.
b)
The Reason Parameter in a DL-RESET request primitive is “User resynchronization”.
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Table 4 - Mapping between primitives and ISO/IEC 7776 frames for DLC reset
Frame
Primitive
DL-RESET request SABM or SABME con~n~nd transmitted: see Note 1
DL-RESET indication SABM or SABME commund received: see Note 1
SABM or SABME command transmitted on receiving unsolicited UA response or unsolicited
response frame with F bit set to 1: see Note 1
FRMR response received: see Note 1
FRMR response transmitted on entry to frame rejection exception condition: see Note 1
Following a DL-RESET indication:
DL-RESET response (see Note 2)
UA response transmitted or received, as appropriate, to complete a link reset
Time-out waiting for UA response, after sending UA response to a colliding SABM or SABME
command received
Following a DL-RESET request: Stirne mapping as for DL-RESET response
DL-RESET tonfirm (see Note 2)
NC’TES
1 The first occurrence of one of these frames during normal data transfer, together with any retransmissions required by the ISO/IEC 7776 procedures,
maps to the DL-RESET request or indication primitive. Subsequent occurrences of other frames from this set before either the link reset is completed or
the link is disconnected do not map to any DLS primitive.
2 The correspondence between these primitives, marking completion of DLC resetting, and the protocol frames or time-outs uses the earliest externally
observable real-world events with which the abstract primitves tan be associated. The significance of the primitives in the CO-DLS is that they separate a
period when DL-DATA primitives cannot occur frorn the following period when DL-DATA primitives are again possible: the mapping specified simply
relates this to the equivalent Separation between the lSO/lEC 7776 link resetting procedure. during which no information transfer occurs, and the
resumption of the capability for normal information transfer 011 completion of the link reset. Within an in~~~lementation, it may be convenient to consider
representations of the primitives as occurring either earlier or later. lt’ earlier, there will be ;1 period during which DL-DATA request primitives cannot be
issued at the DLSAP, since the lSO/IEC 7776 procedures prevent transmission of 1 frarnes; if later, there will be a period following completion of the ISO/
IEC 7776 link reset during which 1 frames are not transmitted, because the local implementation is not ready. Such an implementation-related view is not
precluded, since it is outside the scope of OST standardization.
8 Protocol mapping for HDLC Unbalanced Operation Normal response mode Class (UNC)
8.1 General protocol functions
The HDLC unbalanced classes of procedure apply in general to a centralized multipoint data link configuration (as in figure 3b), containing a
Single primary Station that is responsible for controlling conmunication between itself and a number of secondary stations. (Point-to-Point
configurations containing only a Single secondary Station arc here considered to be only degenerate cases of the general configuration, and no
separate mapping or special considerations apply.)
Individual HDLC data Station addresses are used to identify each of the secondary stations in a given data link, and hence to identify the
DLSAPs in the secondary stations, one DLSAP per secondary Station. Except in a SNRM or SNRME command sent to set up a data link (see
8.2), these HDLC address field values function as DL-protocol-connection-identifiers, discriminating among the various DL connections that
tan be active on the multipoint data link.
The primary Station is also considered to contain a Single DLSAP. For each secondary Station in the data link, there tan be at most one DL
connection in existente at any given time, between the primary station’s DLSAP and the secondary station’s DLSAP. No DL connection tan
exist between two secondary stations.
Table 5 specifies the mapping between the principal protocol functions of HDLC UNC and the corresponding features of the OS1 CO-DLS.
8
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- Mapping between principal HDLC UNC protocol functions and CO-DLS features
Table 5
Protocol function Data Link Service feature
Ideritification of secondary Station DLSAPs
HDLC addressing
Normal disconnected mode Absence of a DL connection: see Note
Link set-up DL connection establishment Phase
Link disconnection DL connection release Phase and absence of a DLC: see Note
Exchange of 1 frames in normal response mode Data transfer Phase, normal data transfer
Data transfer Phase, reset
Link reset, including frame rejection exception condition
NOTE - The DL connection release Phase at each DLSAP is instantaneous, since it contains only a Single DL-DISCONNECT primitive. However, the
corr
...
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