ETSI ETS 300 402-2 ed.1 (1995-11)

Integrated Services Digital Network (ISDN); Digital Subscriber Signalling System No. one (DSS1) protocol; Data link layer; Part 2: General protocol specification [ITU-T Recommendation Q.921 (1993), modified]

DE/SPS-05035-2

Digitalno omrežje z integriranimi storitvami (ISDN) - Protokol digitalne naročniške signalizacije št. 1 (DSS1) - Podatkovna povezovalna plast - 2. del: Splošna specifikacija protokola (prilagojeno priporočilo ITU-T Q.921 (1993))

General Information

• Status: Published
• Publication Date: 20-Nov-1995
• Technical Committee: SPS 5 - Digital access signalling
• Current Stage: 12 - Completion
• Due Date: 01-Dec-1995
• Completion Date: 21-Nov-1995
• Mandate: T-234B
• Ref Project: SIST ETS 300 402-2:1996 - Integrated Services Digital Network (ISDN); Digital Subscriber Signalling System No. one (DSS1) protocol; Data link layer; Part 2: General protocol specification [ITU-T Recommendation Q.921 (1993), modified]

Standards Content (Sample)

SLOVENSKI STANDARD
SIST ETS 300 402-2:1996
01-GHFHPEHU-1996
'LJLWDOQRRPUHåMH]LQWHJULUDQLPLVWRULWYDPL,6'13URWRNROGLJLWDOQHQDURþQLãNH
VLJQDOL]DFLMHãW'663RGDWNRYQDSRYH]RYDOQDSODVWGHO6SORãQD
VSHFLILNDFLMDSURWRNRODSULODJRMHQRSULSRURþLOR,7874
Integrated Services Digital Network (ISDN); Digital Subscriber Signalling System No. one
(DSS1) protocol; Data link layer; Part 2: General protocol specification [ITU-T
Recommendation Q.921 (1993), modified]
Ta slovenski standard je istoveten z: ETS 300 402-2 E1
ICS:
33.080 Digitalno omrežje z Integrated Services Digital
integriranimi storitvami Network (ISDN)
(ISDN)
35.100.20 Podatkovni povezovalni sloj Data link layer
SIST ETS 300 402-2:1996 en
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

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PSIST ETS 300 402-2:1996

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PSIST ETS 300 402-2:1996
EUROPEAN ETS 300 402-2
TELECOMMUNICATION November 1995
STANDARD
Source: ETSI TC-SPS Reference: DE/SPS-05035-2
ICS: 33.080, 35.100.20
ISDN, DSS1, layer 2, D-channel, LAPD, SSIG, QSIG
Key words:
Integrated Services Digital Network (ISDN);
Digital Subscriber Signalling System No. one (DSS1) protocol;
Data link layer;
Part 2: General protocol specification
[ITU-T Recommendation Q.921 (1993), modified]
ETSI
European Telecommunications Standards Institute
ETSI Secretariat
F-06921 Sophia Antipolis CEDEX - FRANCE
Postal address:
650 Route des Lucioles - Sophia Antipolis - Valbonne - FRANCE
Office address:
c=fr, a=atlas, p=etsi, s=secretariat - [e-mail]
X.400: Internet:
Tel.: [phone] - Fax: [phone]
*
Copyright Notification: No part may be reproduced except as authorized by written permission. The copyright and the
foregoing restriction extend to reproduction in all media.
© European Telecommunications Standards Institute 1995. All rights reserved.

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PSIST ETS 300 402-2:1996
Page 2
ETS 300 402-2: November 1995
Foreword
This European Telecommunication Standard (ETS) has been produced by the Signalling Protocols and
Switching (SPS) Technical Committee of the European Telecommunications Standards Institute (ETSI).
This ETS is an updated version of ETS 300 125 Part 2. In addition, it was enhanced to cover service
aspects of the data link layer protocol for inter-exchange signalling between Private Telecommunications
Network eXchanges (PTNXs) in Private Telecommunication Networks (PTNs). Annex ZC identifies the
technical differences between this ETS and ETS 300 125 Part 2.
This ETS is part 2 of a multi-part standard covering the Integrated Services Digital Network (ISDN) Digital
Subscriber Signalling System No. one (DSS1) data link layer specification as described below:
Part 1: "General aspects [ITU-T Recommendation Q.920 (1993), modified]";
Part 2: "General protocol specification [ITU-T Recommendation Q.921 (1993), modified]";
Part 3: "Frame relay protocol specification";
Part 4: "Protocol Implementation Conformance Statement (PICS) proforma specification for the
general protocol";
Part 5: "PICS proforma specification for the frame relay protocol";
Part 6: "Test Suite Structure and Test Purposes (TSS&TP) specification for the general protocol";
Part 7: "Abstract Test Suite (ATS) and partial Protocol Implementation eXtra Information for Testing
(PIXIT) proforma specification for the general protocol".
Transposition dates
Date of adoption of this ETS: 10 November 1995
Date of latest announcement of this ETS (doa): 28 February 1996
Date of latest publication of new National Standard
or endorsement of this ETS (dop/e): 31 August 1996
Date of withdrawal of any conflicting National Standard (dow): 31 August 1996
Endorsement notice
The text of ITU-T Recommendation Q.921 (1993) was approved by ETSI as an ETS with agreed
modifications as given below.
NOTE: New or modified text is indicated using sidebars. In addition, underlining and/or strike-
out are used to highlight detailed modifications where necessary.
Whilst every care has been taken in the preparation and publication of this document, errors in content,
typographical or otherwise, may occur. If you have comments concerning its accuracy, please write to
"ETSI Editing and Committee Support Dept." at the address shown on the title page.

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PSIST ETS 300 402-2:1996
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ETS 300 402-2: November 1995
Page 1
Add the following four clauses (Scope, Normative references, Definitions, Abbreviations) at the start of the
text:
Scope
This European Telecommunication Standard (ETS) describes in general terms the link access procedure
of the Digital Subscriber Signalling System No. one (DSS1) protocol when used in the pan-European
Integrated Services Digital Network (ISDN) as provided by European public telecommunications
operators, or in a Private Telecommunication Network (PTN), at the T reference point or the S reference
point or the coincident S and T reference point (as defined in ITU-T Recommendation I.411 [15]).
Annex ZA of this ETS describes in general terms the link access procedure for use in a symmetrical
application between two Private Telecommunication Network eXchanges (PTNXs) at the Q reference
point (see ETS 300 475-1 [14]).
Conformance to this ETS is met by conforming to the specific protocol standards for individual
applications. Therefore, no separate method of testing is provided for this ETS.
The field of application of this ETS is determined by specific protocol standards for individual applications.
Normative references
This ETS incorporates by dated and undated reference, provisions from other publications. These
normative references are cited at the appropriate places in the text and the publications are listed
hereafter. For dated references, subsequent amendments to or revisions of any of these publications
apply to this ETS only when incorporated in it by amendment or revision. For undated references the latest
edition of the publication referred to applies.
[9] ETS 300 011 (1990): "Integrated Services Digital Network (ISDN); Primary rate
user-network interface layer 1 specification and test principles".
[10] ETS 300 012 (1990): "Integrated Services Digital Network (ISDN); Basic user-
network interface layer 1 specification and test principles".
[11] ETS 300 402-1: "Integrated Services Digital Network (ISDN); Digital Subscriber
Signalling System No. one (DSS1) protocol; Data link layer; Part 1: General
aspects [ITU-T Recommendation Q.920 (1993), modified]".
[12] ETS 300 403-1: "Integrated Services Digital Network (ISDN); Digital Subscriber
Signalling System No. one (DSS1) protocol; Signalling network layer for circuit-
mode basic call control; Part 1: Protocol specification [ITU-T Recommendation
Q.931 (1993), modified]".
[13] ETS 300 415 (1995): "Private Telecommunication Network (PTN); Terms and
definitions".
[14] ETS 300 475-1: "Private Telecommunication Network (PTN); Reference
configuration; Part 1: Reference configuration for PTN eXchanges (PTNX)
[ISO/IEC 11579-1 (1994), modified]".
[15] ITU-T Recommendation I.411 (1993): "ISDN user network interfaces - reference
configurations".
NOTE: The references listed in this ETS are a continuation of publications referenced in ITU-T
Recommendation Q.921.

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PSIST ETS 300 402-2:1996
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ETS 300 402-2: November 1995
Definitions
For the purposes of this ETS, the following definitions apply, together with those given in the referenced
publications:
Assignment Source Point (ASP): Layer management entity at the network side performing TEI
management.
automatic TEI assignment: Layer management procedure between user side and network side (ASP)
which associates within one interface a unique numeric value for a layer 2 terminal identity (TEI value) to a
variable called TEI of a specific terminal equipment. The TEI, which is part of the DLCI, is selected by the
ASP.
broadcast data link connection; broadcast connection: A connection with the capability to support
more than two connection-endpoints (see [X.200 § 5.3.1.4] multi-endpoint-connection).
confirm (primitive): [X.210 § 3.2.7] A primitive issued by a service-provider to complete, at a particular
service-access-point, some procedure previously invoked by a request at that service-access-point.
confirmed service: [X.210 § 3.2.12] A service which results in an explicit confirmation from the service-
provider. There is not necessarily any relationship to a response from the peer service user.
connection: [X.200 § 5.3.1.2] An association established by the "service provider" layer between two or
more "service user" entities for the transfer of data.
connection-endpoint: [X.200 § 5.3.1.3] A terminator at one end of a connection within a service-access-
point.
Connection Endpoint Identifier (CEI): [X.200 § 5.4.1.5] An identifier of a connection-endpoint which can
be used to identify the corresponding connection at a service-access-point.
Connection Endpoint Suffix (CES): [X.200 § 5.4.1.6] A part of a connection-endpoint-identifier which is
unique within the scope of a service-access-point.
Connection Management Entity (CME): An entity for the purpose of management of resources that
have impact on an individual data link connection.
D-channel: [I.412] The D-channel represents the portion of the information-carrying capacity of the ISDN
user-network interface primarily intended to carry access signalling information. In addition, a D-channel
may also be used to carry other information such as packet-switched data, teleaction information, etc.
data link connection: [X.212] An association established by a data link layer between two or more data
link service users for the transfer of data, which provides explicit identification of a set of data link data
transmissions and agreement concerning the data link transmission services to be provided for the set.
NOTE: This definition clarifies the definition given in CCITT Recommendation X.200.
Data Link Connection Identifier (DLCI): An address conveyed in a PDU which indicates the source and
destination of an intended instance of communication at the data link layer.
function: [X.200 § 5.2.1.7] A part of the activity of entities.
indication (primitive): [X.210 § 3.2.5] A primitive issued by a service-provider either:
a) to invoke some procedure; or
b) to indicate that a procedure has been invoked by the service-user at the peer service-access-
point.

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PSIST ETS 300 402-2:1996
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ETS 300 402-2: November 1995
interface-control-information: [X.200] Information transferred between a "service user" entity and a
"service provider" entity to co-ordinate their joint operation.
interface-data: [X.200] Information transferred from a "service user" entity to a "service provider" entity
for transmission to a correspondent "service user" entity over a connection, or conversely, information
transferred from a "service provider" entity to a "service user" entity after being received over a connection
from a correspondent "service user" entity.
Interface Data Unit (IDU): [X.200] The unit of information transferred across a service-access-point
between a "service user" entity and a "service provider" entity in a single interaction. Each interface-data-
unit contains interface-control-information and may also contain the whole or part of a service-data-unit.
Integrated Services Digital Network (ISDN): [I.112 § 2.3 definition 308] A network that provides or
supports a range of different telecommunication services and provides digital connections between user-
network interfaces.
layer: [X.200 § 5.2.1.2] A subdivision of the system architecture, constituted by subsystems of the same
rank.
layer management: [X.200 § 8.1.6] Functions related to the management of the layer partly performed in
the layer itself according to the protocol of the layer (activities such as activation and error control) and
partly performed as a subset of systems management.
Layer Management Entity (LME): An entity for the purpose of management of resources that have layer-
wide impact.
Link Access Procedure (LAP): Class of a procedure based on HDLC elements of procedures for use on
the link layer.
(N)-entity: [X.200 § 5.2.1.11] An active element within a (N)-subsystem.
(N)-subsystem: [X.200 § 5.2.1.1] An element in a hierarchical division of an open system which interacts
directly only with elements in the next higher division or the next lower division of that open system.
network side: Location in relation to the user-network interface indicating that the context to which this
term refers is at the network side of the user-network interface.
network side system management entity: An entity for the purpose of management communications at
the network side of the user-network interface.
non-automatic TEI assignment: Layer management local interaction between layer management entity
and data link layer entity at the user side which associates within one interface a numeric value for a
layer 2 terminal identity (TEI value) to a variable called TEI of a specific terminal equipment. The TEI,
which is part of the DLCI, is selected by the user.
persistent deactivation: The term "persistent layer 1 deactivation" defines condition which shall be
satisfied before the data link layer assumes layer 1 deactivation and takes the actions according to the
protocol specification. Persistency is achieved if:
a) the deactivation is an intended action within layer 1 caused by the functional block
responsible for deactivation of the layer 1; or
b) layer 1 lost connectivity during a time interval, the value of which is outside the scope of this
ETS, but which should be defined for each specific transmission facility.
point-to-point data link connection; point-to-point connection: A connection with two connection-
endpoints.
Private Telecommunication Network (PTN); private network: [ETS 300 415 [13] subclause 4.3].

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PSIST ETS 300 402-2:1996
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ETS 300 402-2: November 1995
Private Telecommunication Network eXchange (PTNX): [ETS 300 415 [13] subclause 4.4].
protocol: [X.200 § 5.2.1.9] A set of rules and formats (semantic and syntactic) which determines the
communication behaviour of entities in the performance of functions.
Protocol Data Unit (PDU): [X.200 § 5.6.1.3] A unit of data specified in a protocol and consisting of
protocol-control-information and possibly user-data.
Protocol Control Information (PCI): [X.200 § 5.6.1.1] Information exchanged between entities using a
connection (provided by the next lower layer), to co-ordinate their joint operation.
reference point: [I.411 § 2.3] Conceptual point dividing set of functions which form functional groups. In a
specific access arrangement, a reference point may correspond to a physical interface between pieces of
equipment, or there may not be any physical interface corresponding to the reference point. Physical
interfaces which do not correspond to a reference point (e.g. transmission link interfaces) will not be the
subject of ISDN user-network interface Recommendations.
request (primitive): [X.210 § 3.2.4] A primitive issued by a service-user to invoke some procedure.
response (primitive): [X.210 § 3.2.6] A primitive issued by a service-user to complete, at a particular
service-access-point, some procedure previously invoked by an indication at that service-access-point.
service ("layer" service): [X.200 § 5.2.1.5] A capability of the providing layer and the layers beneath it,
which is provided to "service user" entities at the boundary between the "service provider" layer and the
"service user" layer.
Service Access Point (SAP): [X.200 § 5.2.1.8] The point at which services are provided by a "service
provider" entity to a "service user" entity.
Service Data Unit (SDU): [X.200 § 5.6.1.4] An amount of interface-data whose identity is preserved from
one end of a connection to the other.
service-primitive; primitive: [X.210 § 3.2.3] An abstract, implementation independent interaction
between a service-user and the service-provider.
service-provider: [X.210 § 3.2.2] An abstract machine which models the behaviour of the totality of the
entities providing the service, as viewed by the user.
service-user: [X.210 § 3.2.1] An abstract representation of the totality of those entities in a single system
that make use of a service through a single access point.
system management: [X.200 § 8.1.4] Function in the Application Layer related to the management of
various system resources and their status across all layers of the system architecture.
system management entity: [X.200 § 8.1.5] An entity for the purpose of systems-management
communications.
Terminal Endpoint Identifier (TEI): Portion of a DLCI associated with one (point-to-point data link) or
more than one (broadcast data link) terminal equipment.
unconfirmed service: [X.210 § 3.2.11] A service which does not result in an explicit confirmation from
the service-provider.
user-data: [X.200 § 5.6.1.2] The data transferred between "service provider" entities on behalf of the
"service user" entities for whom "service provider" entities are providing services.
user side: Location in relation to the user-network interface indicating that the context to which this term
refers is at the user side of the user-network interface.
user side system management entity: An entity for the purpose of management communications at the
user side of the user-network interface.

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PSIST ETS 300 402-2:1996
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ETS 300 402-2: November 1995
Abbreviations
For the purposes of this ETS, the following abbreviations apply:
ACK ACKnowledgement
Ai Action indicator
ASP Assignment Source Point
C/R Command/Response field bit
CEI Connection Endpoint Identifier
CES Connection Endpoint Suffix
CME Connection Management Entity
DISC DISConnect
DL- communication between layer 3 and Data Link layer
DLCI Data Link Connection Identifier
DM Disconnected Mode
EA Extended Address field bit
ERR ERRor
ET Exchange Termination
FCS Frame Check Sequence
FRMR FRaMe Reject
HDLC High-level Data Link Control procedures
I Information
ID IDentity
IDU Interface Data Unit
ISDN Integrated Services Digital Network
k Maximum number of outstanding frames (window size)
L1 Layer 1
L2 Layer 2
L3 Layer 3
LAP Link Access Procedure
LAPB Link Access Procedure - Balanced
LAPD Link Access Procedure on the D-channel
LME Layer Management Entity
M Modifier function bit
MDL- communication between layer Management and Data Link layer
MPH- communication between system Management and PHysical layer
NT2 Network Termination 2
OSI Open System Interconnection
PCI Protocol Control Information
PDU Protocol Data Unit
P/F Poll/Final bit
PI Parameter Identifier
PH- communication between data link layer and PHysical layer
PL Parameter Length
PTN Private Telecommunication Network
PTNX Private Telecommunication Network eXchange
PV Parameter Value
RC Retransmission Counter
REC RECeiver
REJ REJect
Ri Reference number
RNR Receive Not Ready
RR Receive Ready
RX Receive
S Supervisory
S Supervisory function bit
SABME Set Asynchronous Balanced Mode Extended
SAP Service Access Point
SAPI Service Access Point Identifier
SDL Specification and Description Language
SDU Service Data Unit
TE Terminal Equipment
TEI Terminal Endpoint Identifier

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PSIST ETS 300 402-2:1996
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ETS 300 402-2: November 1995
TX Transmit
U Unnumbered
UA Unnumbered Acknowledgement
UI Unnumbered Information
V(S) Send state Variable
V(A) Acknowledge state Variable
V(R) Receive state Variable
N(S) Send sequence Number
N(R) Receive sequence Number
XID eXchange IDentification
Throughout the text of ITU-T Recommendation Q.921
Replace references as shown in the following table.
Reference in ITU-T Modified reference
Recommendation Q.921
ITU-T Recommendation I.430 [5] ETS 300 012 [10]
ITU-T Recommendation I.431 [6] ETS 300 011 [9]
ITU-T Recommendation Q.920 [1] ITU-T Recommendation Q.920 as modified by ETS 300 402-1 [11]
ITU-T Recommendation Q.931 [3] ITU-T Recommendation Q.931 as modified by ETS 300 403-1 [12]
Page 5, clause 1, last paragraph
Delete the last paragraph referring to abstract test suites:
The abstract test suites for testing conformance to this Recommendation are contained in
Recommendation Q.921 bis [4].
Page 1, subclause 2.3, second paragraph
Insert after the second paragraph referring to the support of a LAPB data link connection within the
D-channel:
Networks conforming to this ETS do not support the LAPB data link connection within the D-channel.
Page 3, subclause 2.7, last two paragraphs
The last two paragraphs have the status of notes. As a consequence, replace the last two paragraphs by:
NOTE 1: As a typical implementation at the transmitter, the initial content of the register of the
device computing the remainder of the division is preset to all 1s and is then modified
by division by the generator polynomial (as described above) on the address, control
and information fields; the ones complement of the resulting remainder is transmitted
as the 16-bit FCS.
NOTE 2: As a typical implementation at the receiver, the initial content of the register of the
device computing the remainder is preset to all 1s. The final remainder, after
16
multiplication by x and then division (modulo 2) by the generator polynomial
16 12 5
x + x + x + 1 of the serial incoming protected bits and the FCS, will be
15 0
0001 1101 0000 1111 (x through x , respectively) in the absence of transmission
errors.

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PSIST ETS 300 402-2:1996
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ETS 300 402-2: November 1995
Page 5, subclause 2.9, item b)
Replace item b) and add a note:
b) has fewer than six octets between flags of frames that contain sequence numbers
(see note) and fewer than five octets between flags of frames that do not contain
sequence numbers, or
NOTE: The order of checking the content of the control field, and frame formats for
compliance with the specification, are an implementation matter. Therefore, a S-format
with two octet address field and modulo 8 sequence number format can be identified to
be an invalid frame according to subclause 2.9 item b), or to be an undefined control
field according to subclause 3.6.1. Either of these two verdicts is in compliance with
this ETS.
Page 9, table 2/Q.921
Replace table 2/Q.921 by:
SAPI value Related layer or layer management entity
0 Call control procedures
1-11 Reserved for future standardization
12 Connectionless network applications
13-15 Reserved for future standardization
16 Packet communication conforming to X.25 level 3 procedures
17-31 Reserved for future standardization
32-62 Not available for Q.921
63 Layer 2 management procedures
Page 10, table 5/Q.921, note
Replace the note in table 5/Q.921 by:
NOTE: According to subclause 5.4.2.2, European networks do not support automatic negotiation of
data link layer parameter values, thus XID is associated with an application not supported.
Consequently, the XID frame shall be discarded and no action shall be taken as a result of
that frame, according to subclause 3.6.1.
Page 11, subclause 3.6.7, second paragraph
Add after the second paragraph:
The optional procedure for the retransmission of an REJ response frame is not used by networks
conforming to this ETS.

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PSIST ETS 300 402-2:1996
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ETS 300 402-2: November 1995
Subclause 4.1.1, table 6/Q.921
Replace table 6/Q.921 by:
Type Parameters Parameter data
Generic name Request Indication Response Confirm Priority Parameter contents
indicator data
(note 1)
L3 <---> L2
DL-ESTABLISH u + n u + n - u + n - - -
DL-RELEASE u + n u + n - u + n - - -
DL-DATA u + n u + n - - - X Layer 3 PDU
(peer-to-peer message)
DL-UNIT DATA u + n u + n - - - X Layer 3 PDU
(peer-to-peer message)
M <---> L2
MDL-ASSIGN u + n u - - - X TEI value, CES
(note 2)
MDL-REMOVE u + n - - - - X TEI value, CES
MDL-ERROR - u + n u - - X Reason for error message
Layer management PDU
MDL-UNIT DATA u + n u + n - - - X (peer-to-peer message)
L2 <---> L1
PH-DATA u + n u + n - - X X Data link layer PDU
(note 3) (peer-to-peer frame)
PH-ACTIVATE u + n u + n - - - - -
(note 4)
PH-DEACTIVATE - u + n - - - - -
M <---> L1
MPH-ACTIVATE - u + n - - - - -
(note 5)
MPH-DEACTIVATE n u + n - - - - -
(note 5)
MPH-INFORMATION - u - - - X Connected/disconnected
(note 6)
L3 <---> L2 := Layer 3/data link layer boundary
L2 <---> L1 := Data link layer/physical layer boundary
M <---> L2 := Management entity/data link layer boundary
M <---> L1 := Management entity/physical layer boundary
u := Exists at user side
n := Exists at network side
u + n := Exists at both user and network side
X := Exists
- := Does not exist
NOTE 1: Although not shown below, the CES is implicitly associated with each L3-L2 primitive,
indicating the applicable connection endpoint.
NOTE 2: TEI value is included only in the MDL-ASSIGN.request.
NOTE 3: The parameter "Priority indicator" only relates to the request type.
NOTE 4: The PH-ACTIVATE.indication primitive is also used as confirm.
NOTE 5: The MPH-ACTIVATE and MPH-DEACTIVATE primitive are confined to the usage defined in
annex G/Appendix III. Other uses are outside the scope of this ETS.
NOTE 6: Only applies to the basic access.
Page 16, subclause 4.1.1.9
Delete subclause 4.1.1.9. The MDL-XID primitives are not applicable to networks conforming to this ETS.

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PSIST ETS 300 402-2:1996
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ETS 300 402-2: November 1995
Page 17, figure 7/Q.921
In figure 7/Q.921 there is an editorial error. The arrow for the response primitive points in the wrong
direction. The correct relationship of the primitive types to layer 3 and the data link layer is illustrated in
the figure below.
Layer 3
confirm request indication response
* *
SAP
Data link layer
Data link layer peer-to-peer protocol
Page 17, subclause 4.1.3.1
Replace the text of subclause 4.1.3.1 by:
Since several SAPs may exist on the network side or user side, SDUs sent across one SAP may concur
with those sent across other SAPs for the physical resources available for information transfer. Within the
data link layer, SDUs associated with SAPI = 0 shall have a high priority, and SDUs associated with other
SAPIs shall have a low priority. This priority shall be respected within the data link layer and shall be
indicated to the physical layer by means of the priority indicator.
The priority indicator shall take the value "1" for high priority and the value "2" for low priority.
NOTE: Within a user side in a point-to-multipoint configuration, this priority indicator is used at
the physical layer to the influence the contention resolution between different terminals.
In all other cases, the effect is local to any queues that may be provided.
Page 18, subclause 4.2.1, second paragraph
Replace the second paragraph:
In the scope of this ETS the interactions between layer 3 and the data link layer, and those between the
data link layer and the physical layer are specified.
Page 18
Add a new subclause 4.2.3:
4.2.3 Data link layer - physical layer interactions
The interactions across the boundary between the data link layer and the physical layer allow:
a) The data link layer at either side of the user-network interface to invoke the activation of the
physical layer connection making use of the PH-ACTIVATE.request primitive. At the user
side of the basic access, no PH-ACTIVATE.request primitive shall be issued, if the terminal is
not in the connected status as indicated by the MPH-INFORMATION.indication primitive with
the parameter "disconnected". In all other cases, the status is permanently connected. The
successful activation is confirmed by the PH-ACTIVATE.indication primitive. An unsuccessful
activation is indicated by the PH-DEACTIVATE.indication primitive.

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PSIST ETS 300 402-2:1996
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ETS 300 402-2: November 1995
b) The physical layer to indicate to the data link layer that the physical layer connection has
been activated, by means of the PH-ACTIVATE.indication primitive.
c) The physical layer to indicate to the data link layer that the physical layer connection has
been deactivated, by means of the PH-DEACTIVATE.indication primitive.
d) The data link layer at either side of the user-network interface to request the physical layer in
the activated state the transmission of the SDU passed from the data link layer to the
physical layer by means of a PH-DATA.request primitive. The PH-DATA.request primitive
includes a priority indicator with the values "high" or "low", representing two priority classes.
The two priority classes apply to the physical layer and allow the data link layer to control the
priority for the processing of SDUs within the physical layer. The priority mechanism makes
provision that no low priority SDU is transmitted on the D-channel as long as there are high
priority SDUs pending transmission within the physical layer.
e) The physical layer in the activated state to deliver to the data link layer a received SDU This
SDU is passed from the physical layer to the data link layer by means of a PH-
DATA.indication primitive.
The interactions described in a), b) and c) above are related to physical connection status control while d)
and e) refer to the information transfer on an activated physical connection i.e. on a activated D-channel.
The data link layer shall make provision that activation of the physical layer connection is invoked making
use of the PH-ACTIVATE.request primitive when a data link layer connection is to be establish
...

2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.Integrated Services Digital Network (ISDN); Digital Subscriber Signalling System No. one (DSS1) protocol; Data link layer; Part 2: General protocol specification [ITU-T Recommendation Q.921 (1993), modified]35.100.20Podatkovni povezovalni slojData link layer33.080Digitalno omrežje z integriranimi storitvami (ISDN)Integrated Services Digital Network (ISDN)ICS:Ta slovenski standard je istoveten z:ETS 300 402-2 Edition 1PSIST ETS 300 402-2:1996en01-oktober-1996PSIST ETS 300 402-2:1996SLOVENSKI
STANDARD



PSIST ETS 300 402-2:1996



EUROPEANETS 300 402-2TELECOMMUNICATIONNovember 1995STANDARDSource: ETSI TC-SPSReference: DE/SPS-05035-2ICS:33.080, 35.100.20Key words:ISDN, DSS1, layer 2, D-channel, LAPD, SSIG, QSIGIntegrated Services Digital Network (ISDN);Digital Subscriber Signalling System No. one (DSS1) protocol;Data link layer;Part 2: General protocol specification[ITU-T Recommendation Q.921 (1993), modified]ETSIEuropean Telecommunications Standards InstituteETSI SecretariatPostal address: F-06921 Sophia Antipolis CEDEX - FRANCEOffice address: 650 Route des Lucioles - Sophia Antipolis - Valbonne - FRANCEX.400: c=fr, a=atlas, p=etsi, s=secretariat - Internet: [e-mail].: [phone] - Fax: [phone]Copyright Notification: No part may be reproduced except as authorized by written permission. The copyright and theforegoing restriction extend to reproduction in all media.© European Telecommunications Standards Institute 1995. All rights reserved.PSIST ETS 300 402-2:1996



Page 2ETS 300 402-2: November 1995ForewordThis European Telecommunication Standard (ETS) has been produced by the Signalling Protocols andSwitching (SPS) Technical Committee of the European Telecommunications Standards Institute (ETSI).This ETS is an updated version of ETS 300 125 Part 2. In addition, it was enhanced to cover serviceaspects of the data link layer protocol for inter-exchange signalling between Private TelecommunicationsNetwork eXchanges (PTNXs) in Private Telecommunication Networks (PTNs). Annex ZC identifies thetechnical differences between this ETS and ETS 300 125 Part 2.This ETS is part 2 of a multi-part standard covering the Integrated Services Digital Network (ISDN) DigitalSubscriber Signalling System No. one (DSS1) data link layer specification as described below:Part 1:"General aspects [ITU-T Recommendation Q.920 (1993), modified]";Part 2:"General protocol specification [ITU-T Recommendation Q.921 (1993), modified]";Part 3:"Frame relay protocol specification";Part 4:"Protocol Implementation Conformance Statement (PICS) proforma specification for thegeneral protocol";Part 5:"PICS proforma specification for the frame relay protocol";Part 6:"Test Suite Structure and Test Purposes (TSS&TP) specification for the general protocol";Part 7:"Abstract Test Suite (ATS) and partial Protocol Implementation eXtra Information for Testing(PIXIT) proforma specification for the general protocol".Transposition datesDate of adoption of this ETS:10 November 1995Date of latest announcement of this ETS (doa):28 February 1996Date of latest publication of new National Standardor endorsement of this ETS (dop/e):31 August 1996Date of withdrawal of any conflicting National Standard (dow):31 August 1996Endorsement noticeThe text of ITU-T Recommendation Q.921 (1993) was approved by ETSI as an ETS with agreedmodifications as given below.NOTE:New or modified text is indicated using sidebars. In addition, underlining and/or strike-out are used to highlight detailed modifications where necessary.Whilst every care has been taken in the preparation and publication of this document, errors in content,typographical or otherwise, may occur. If you have comments concerning its accuracy, please write to"ETSI Editing and Committee Support Dept." at the address shown on the title page.PSIST ETS 300 402-2:1996



Page 3ETS 300 402-2: November 1995Page 1Add the following four clauses (Scope, Normative references, Definitions, Abbreviations) at the start of thetext:ScopeThis European Telecommunication Standard (ETS) describes in general terms the link access procedureof the Digital Subscriber Signalling System No. one (DSS1) protocol when used in the pan-EuropeanIntegrated Services Digital Network (ISDN) as provided by European public telecommunicationsoperators, or in a Private Telecommunication Network (PTN), at the T reference point or the S referencepoint or the coincident S and T reference point (as defined in ITU-T Recommendation I.411 [15]).Annex ZA of this ETS describes in general terms the link access procedure for use in a symmetricalapplication between two Private Telecommunication Network eXchanges (PTNXs) at the Q referencepoint (see ETS 300 475-1 [14]).Conformance to this ETS is met by conforming to the specific protocol standards for individualapplications. Therefore, no separate method of testing is provided for this ETS.The field of application of this ETS is determined by specific protocol standards for individual applications.Normative referencesThis ETS incorporates by dated and undated reference, provisions from other publications. Thesenormative references are cited at the appropriate places in the text and the publications are listedhereafter. For dated references, subsequent amendments to or revisions of any of these publicationsapply to this ETS only when incorporated in it by amendment or revision. For undated references the latestedition of the publication referred to applies.[9]ETS 300 011 (1990): "Integrated Services Digital Network (ISDN); Primary rateuser-network interface layer 1 specification and test principles".[10]ETS 300 012 (1990): "Integrated Services Digital Network (ISDN); Basic user-network interface layer 1 specification and test principles".[11]ETS 300 402-1: "Integrated Services Digital Network (ISDN); Digital SubscriberSignalling System No. one (DSS1) protocol; Data link layer; Part 1: Generalaspects [ITU-T Recommendation Q.920 (1993), modified]".[12]ETS 300 403-1: "Integrated Services Digital Network (ISDN); Digital SubscriberSignalling System No. one (DSS1) protocol; Signalling network layer for circuit-mode basic call control; Part 1: Protocol specification [ITU-T RecommendationQ.931 (1993), modified]".[13]ETS 300 415 (1995): "Private Telecommunication Network (PTN); Terms anddefinitions".[14]ETS 300 475-1: "Private Telecommunication Network (PTN); Referenceconfiguration; Part 1: Reference configuration for PTN eXchanges (PTNX)[ISO/IEC 11579-1 (1994), modified]".[15]ITU-T Recommendation I.411 (1993): "ISDN user network interfaces - referenceconfigurations".NOTE:The references listed in this ETS are a continuation of publications referenced in ITU-TRecommendation Q.921.PSIST ETS 300 402-2:1996



Page 4ETS 300 402-2: November 1995DefinitionsFor the purposes of this ETS, the following definitions apply, together with those given in the referencedpublications:Assignment Source Point (ASP): Layer management entity at the network side performing TEImanagement.automatic TEI assignment: Layer management procedure between user side and network side (ASP)which associates within one interface a unique numeric value for a layer 2 terminal identity (TEI value) to avariable called TEI of a specific terminal equipment. The TEI, which is part of the DLCI, is selected by theASP.broadcast data link connection; broadcast connection: A connection with the capability to supportmore than two connection-endpoints (see [X.200 § 5.3.1.4] multi-endpoint-connection).confirm (primitive): [X.210 § 3.2.7] A primitive issued by a service-provider to complete, at a particularservice-access-point, some procedure previously invoked by a request at that service-access-point.confirmed service: [X.210 § 3.2.12] A service which results in an explicit confirmation from the service-provider. There is not necessarily any relationship to a response from the peer service user.connection: [X.200 § 5.3.1.2] An association established by the "service provider" layer between two ormore "service user" entities for the transfer of data.connection-endpoint: [X.200 § 5.3.1.3] A terminator at one end of a connection within a service-access-point.Connection Endpoint Identifier (CEI): [X.200 § 5.4.1.5] An identifier of a connection-endpoint which canbe used to identify the corresponding connection at a service-access-point.Connection Endpoint Suffix (CES): [X.200 § 5.4.1.6] A part of a connection-endpoint-identifier which isunique within the scope of a service-access-point.Connection Management Entity (CME): An entity for the purpose of management of resources thathave impact on an individual data link connection.D-channel: [I.412] The D-channel represents the portion of the information-carrying capacity of the ISDNuser-network interface primarily intended to carry access signalling information. In addition, a D-channelmay also be used to carry other information such as packet-switched data, teleaction information, etc.data link connection: [X.212] An association established by a data link layer between two or more datalink service users for the transfer of data, which provides explicit identification of a set of data link datatransmissions and agreement concerning the data link transmission services to be provided for the set.NOTE:This definition clarifies the definition given in CCITT Recommendation X.200.Data Link Connection Identifier (DLCI): An address conveyed in a PDU which indicates the source anddestination of an intended instance of communication at the data link layer.function: [X.200 § 5.2.1.7] A part of the activity of entities.indication (primitive): [X.210 § 3.2.5] A primitive issued by a service-provider either:a)to invoke some procedure; orb)to indicate that a procedure has been invoked by the service-user at the peer service-access-point.PSIST ETS 300 402-2:1996



Page 5ETS 300 402-2: November 1995interface-control-information: [X.200] Information transferred between a "service user" entity and a"service provider" entity to co-ordinate their joint operation.interface-data: [X.200] Information transferred from a "service user" entity to a "service provider" entityfor transmission to a correspondent "service user" entity over a connection, or conversely, informationtransferred from a "service provider" entity to a "service user" entity after being received over a connectionfrom a correspondent "service user" entity.Interface Data Unit (IDU): [X.200] The unit of information transferred across a service-access-pointbetween a "service user" entity and a "service provider" entity in a single interaction. Each interface-data-unit contains interface-control-information and may also contain the whole or part of a service-data-unit.Integrated Services Digital Network (ISDN): [I.112 § 2.3 definition 308] A network that provides orsupports a range of different telecommunication services and provides digital connections between user-network interfaces.layer: [X.200 § 5.2.1.2] A subdivision of the system architecture, constituted by subsystems of the samerank.layer management: [X.200 § 8.1.6] Functions related to the management of the layer partly performed inthe layer itself according to the protocol of the layer (activities such as activation and error control) andpartly performed as a subset of systems management.Layer Management Entity (LME): An entity for the purpose of management of resources that have layer-wide impact.Link Access Procedure (LAP): Class of a procedure based on HDLC elements of procedures for use onthe link layer.(N)-entity: [X.200 § 5.2.1.11] An active element within a (N)-subsystem.(N)-subsystem: [X.200 § 5.2.1.1] An element in a hierarchical division of an open system which interactsdirectly only with elements in the next higher division or the next lower division of that open system.network side: Location in relation to the user-network interface indicating that the context to which thisterm refers is at the network side of the user-network interface.network side system management entity: An entity for the purpose of management communications atthe network side of the user-network interface.non-automatic TEI assignment: Layer management local interaction between layer management entityand data link layer entity at the user side which associates within one interface a numeric value for alayer 2 terminal identity (TEI value) to a variable called TEI of a specific terminal equipment. The TEI,which is part of the DLCI, is selected by the user.persistent deactivation: The term "persistent layer 1 deactivation" defines condition which shall besatisfied before the data link layer assumes layer 1 deactivation and takes the actions according to theprotocol specification. Persistency is achieved if:a)the deactivation is an intended action within layer 1 caused by the functional blockresponsible for deactivation of the layer 1; orb)layer 1 lost connectivity during a time interval, the value of which is outside the scope of thisETS, but which should be defined for each specific transmission facility.point-to-point data link connection; point-to-point connection: A connection with two connection-endpoints.Private Telecommunication Network (PTN); private network: [ETS 300 415 [13] subclause 4.3].PSIST ETS 300 402-2:1996



Page 6ETS 300 402-2: November 1995Private Telecommunication Network eXchange (PTNX): [ETS 300 415 [13] subclause 4.4].protocol: [X.200 § 5.2.1.9] A set of rules and formats (semantic and syntactic) which determines thecommunication behaviour of entities in the performance of functions.Protocol Data Unit (PDU): [X.200 § 5.6.1.3] A unit of data specified in a protocol and consisting ofprotocol-control-information and possibly user-data.Protocol Control Information (PCI): [X.200 § 5.6.1.1] Information exchanged between entities using aconnection (provided by the next lower layer), to co-ordinate their joint operation.reference point: [I.411 § 2.3] Conceptual point dividing set of functions which form functional groups. In aspecific access arrangement, a reference point may correspond to a physical interface between pieces ofequipment, or there may not be any physical interface corresponding to the reference point. Physicalinterfaces which do not correspond to a reference point (e.g. transmission link interfaces) will not be thesubject of ISDN user-network interface Recommendations.request (primitive): [X.210 § 3.2.4] A primitive issued by a service-user to invoke some procedure.response (primitive): [X.210 § 3.2.6] A primitive issued by a service-user to complete, at a particularservice-access-point, some procedure previously invoked by an indication at that service-access-point.service ("layer" service): [X.200 § 5.2.1.5] A capability of the providing layer and the layers beneath it,which is provided to "service user" entities at the boundary between the "service provider" layer and the"service user" layer.Service Access Point (SAP): [X.200 § 5.2.1.8] The point at which services are provided by a "serviceprovider" entity to a "service user" entity.Service Data Unit (SDU): [X.200 § 5.6.1.4] An amount of interface-data whose identity is preserved fromone end of a connection to the other.service-primitive; primitive: [X.210 § 3.2.3] An abstract, implementation independent interactionbetween a service-user and the service-provider.service-provider: [X.210 § 3.2.2] An abstract machine which models the behaviour of the totality of theentities providing the service, as viewed by the user.service-user: [X.210 § 3.2.1] An abstract representation of the totality of those entities in a single systemthat make use of a service through a single access point.system management: [X.200 § 8.1.4] Function in the Application Layer related to the management ofvarious system resources and their status across all layers of the system architecture.system management entity: [X.200 § 8.1.5] An entity for the purpose of systems-managementcommunications.Terminal Endpoint Identifier (TEI): Portion of a DLCI associated with one (point-to-point data link) ormore than one (broadcast data link) terminal equipment.unconfirmed service: [X.210 § 3.2.11] A service which does not result in an explicit confirmation fromthe service-provider.user-data: [X.200 § 5.6.1.2] The data transferred between "service provider" entities on behalf of the"service user" entities for whom "service provider" entities are providing services.user side: Location in relation to the user-network interface indicating that the context to which this termrefers is at the user side of the user-network interface.user side system management entity: An entity for the purpose of management communications at theuser side of the user-network interface.PSIST ETS 300 402-2:1996



Page 7ETS 300 402-2: November 1995AbbreviationsFor the purposes of this ETS, the following abbreviations apply:ACKACKnowledgementAiAction indicatorASPAssignment Source PointC/RCommand/Response field bitCEIConnection Endpoint IdentifierCESConnection Endpoint SuffixCMEConnection Management EntityDISCDISConnectDL-communication between layer 3 and Data Link layerDLCIData Link Connection IdentifierDMDisconnected ModeEAExtended Address field bitERRERRorETExchange TerminationFCSFrame Check SequenceFRMRFRaMe RejectHDLCHigh-level Data Link Control proceduresIInformationIDIDentityIDUInterface Data UnitISDNIntegrated Services Digital NetworkkMaximum number of outstanding frames (window size)L1Layer 1L2Layer 2L3Layer 3LAPLink Access ProcedureLAPBLink Access Procedure - BalancedLAPDLink Access Procedure on the D-channelLMELayer Management EntityMModifier function bitMDL-communication between layer Management and Data Link layerMPH-communication between system Management and PHysical layerNT2Network Termination 2OSIOpen System InterconnectionPCIProtocol Control InformationPDUProtocol Data UnitP/FPoll/Final bitPIParameter IdentifierPH-communication between data link layer and PHysical layerPLParameter LengthPTNPrivate Telecommunication NetworkPTNXPrivate Telecommunication Network eXchangePVParameter ValueRCRetransmission CounterRECRECeiverREJREJectRiReference numberRNRReceive Not ReadyRRReceive ReadyRXReceiveSSupervisorySSupervisory function bitSABMESet Asynchronous Balanced Mode ExtendedSAPService Access PointSAPIService Access Point IdentifierSDLSpecification and Description LanguageSDUService Data UnitTETerminal EquipmentTEITerminal Endpoint IdentifierPSIST ETS 300 402-2:1996



Page 8ETS 300 402-2: November 1995TXTransmitUUnnumberedUAUnnumbered AcknowledgementUIUnnumbered InformationV(S)Send state VariableV(A)Acknowledge state VariableV(R)Receive state VariableN(S)Send sequence NumberN(R)Receive sequence NumberXIDeXchange IDentificationThroughout the text of ITU-T Recommendation Q.921Replace references as shown in the following table.Reference in ITU-TRecommendation Q.921Modified referenceITU-T Recommendation I.430 [5]ETS 300 012 [10]ITU-T Recommendation I.431 [6]ETS 300 011 [9]ITU-T Recommendation Q.920 [1]ITU-T Recommendation Q.920 as modified by ETS 300 402-1 [11]ITU-T Recommendation Q.931 [3]ITU-T Recommendation Q.931 as modified by ETS 300 403-1 [12]Page 5, clause 1, last paragraphDelete the last paragraph referring to abstract test suites:The abstract test suites for testing conformance to this Recommendation are contained inRecommendation Q.921 bis [4].Page 1, subclause 2.3, second paragraphInsert after the second paragraph referring to the support of a LAPB data link connection within theD-channel:Networks conforming to this ETS do not support the LAPB data link connection within the D-channel.Page 3, subclause 2.7, last two paragraphsThe last two paragraphs have the status of notes. As a consequence, replace the last two paragraphs by:NOTE 1:As a typical implementation at the transmitter, the initial content of the register of thedevice computing the remainder of the division is preset to all 1s and is then modifiedby division by the generator polynomial (as described above) on the address, controland information fields; the ones complement of the resulting remainder is transmittedas the 16-bit FCS.NOTE 2:As a typical implementation at the receiver, the initial content of the register of thedevice computing the remainder is preset to all 1s. The final remainder, aftermultiplication by x16 and then division (modulo 2) by the generator polynomialx16 + x12 + x5 + 1 of the serial incoming protected bits and the FCS, will be0001 1101 0000 1111 (x15 through x0, respectively) in the absence of transmissionerrors.PSIST ETS 300 402-2:1996



Page 9ETS 300 402-2: November 1995Page 5, subclause 2.9, item b)Replace item b) and add a note:b)has fewer than six octets between flags of frames that contain sequence numbers(see note) and fewer than five octets between flags of frames that do not containsequence numbers, orNOTE:The order of checking the content of the control field, and frame formats forcompliance with the specification, are an implementation matter. Therefore, a S-formatwith two octet address field and modulo 8 sequence number format can be identified tobe an invalid frame according to subclause 2.9 item b), or to be an undefined controlfield according to subclause 3.6.1. Either of these two verdicts is in compliance withthis ETS.Page 9, table 2/Q.921Replace table 2/Q.921 by:SAPI valueRelated layer or layer management entity01-111213-151617-3132-6263Call control proceduresReserved for future standardizationConnectionless network applicationsReserved for future standardizationPacket communication conforming to X.25 level 3 proceduresReserved for future standardizationNot available for Q.921Layer 2 management proceduresPage 10, table 5/Q.921, noteReplace the note in table 5/Q.921 by:NOTE:According to subclause 5.4.2.2, European networks do not support automatic negotiation ofdata link layer parameter values, thus XID is associated with an application not supported.Consequently, the XID frame shall be discarded and no action shall be taken as a result ofthat frame, according to subclause 3.6.1.Page 11, subclause 3.6.7, second paragraphAdd after the second paragraph:The optional procedure for the retransmission of an REJ response frame is not used by networksconforming to this ETS.PSIST ETS 300 402-2:1996



Page 10ETS 300 402-2: November 1995Subclause 4.1.1, table 6/Q.921Replace table 6/Q.921 by:TypeParametersParameter dataGeneric nameRequestIndicationResponseConfirmPriorityindicatorParameterdatacontents(note 1)L3 <---> L2DL-ESTABLISHu + nu + n-u + n---DL-RELEASEu + nu + n-u + n---DL-DATAu + nu + n---XLayer 3 PDU(peer-to-peer message)DL-UNIT DATAu + nu + n---XLayer 3 PDU(peer-to-peer message)M <---> L2MDL-ASSIGNu + nu---XTEI value, CES(note 2)MDL-REMOVEu + n----XTEI value, CESMDL-ERROR-u + nu--XReason for error messageMDL-UNIT DATAu + nu + n---XLayer management PDU(peer-to-peer message)L2 <---> L1PH-DATAu + nu + n--X(note 3)XData link layer PDU(peer-to-peer frame)PH-ACTIVATEu + nu + n---(note 4)--PH-DEACTIVATE-u + n-----M <---> L1MPH-ACTIVATE(note 5)-u + n-----MPH-DEACTIVATE(note 5)nu + n-----MPH-INFORMATION-u(note 6)---XConnected/disconnectedL3 <---> L2L2 <---> L1M <---> L2M <---> L1unu + nX-:= Layer 3/data link layer boundary:= Data link layer/physical layer boundary:= Management entity/data link layer boundary:= Management entity/physical layer boundary:= Exists at user side:= Exists at network side:= Exists at both user and network side:= Exists:= Does not existNOTE 1:Although not shown below, the CES is implicitly associated with each L3-L2 primitive,indicating the applicable connection endpoint.NOTE 2:TEI value is included only in the MDL-ASSIGN.request.NOTE 3:The parameter "Priority indicator" only relates to the request type.NOTE 4:The PH-ACTIVATE.indication primitive is also used as confirm.NOTE 5:The MPH-ACTIVATE and MPH-DEACTIVATE primitive are confined to the usage defined inannex G/Appendix III. Other uses are outside the scope of this ETS.NOTE 6:Only applies to the basic access.Page 16, subclause 4.1.1.9Delete subclause 4.1.1.9. The MDL-XID primitives are not applicable to networks conforming to this ETS.PSIST ETS 300 402-2:1996



Page 11ETS 300 402-2: November 1995Page 17, figure 7/Q.921In figure 7/Q.921 there is an editorial error. The arrow for the response primitive points in the wrongdirection. The correct relationship of the primitive types to layer 3 and the data link layer is illustrated inthe figure below.* * Layer 3confirmData link layerrequest indicationresponseData link layer peer-to-peer protocolSAPPage 17, subclause 4.1.3.1Replace the text of subclause 4.1.3.1 by:Since several SAPs may exist on the network side or user side, SDUs sent across one SAP may concurwith those sent across other SAPs for the physical resources available for information transfer. Within thedata link layer, SDUs associated with SAPI = 0 shall have a high priority, and SDUs associated with otherSAPIs shall have a low priority. This priority shall be respected within the data link layer and shall beindicated to the physical layer by means of the priority indicator.The priority indicator shall take the value "1" for high priority and the value "2" for low priority.NOTE:Within a user side in a point-to-multipoint configuration, this priority indicator is used atthe physical layer to the influence the contention resolution between different terminals.In all other cases, the effect is local to any queues that may be provided.Page 18, subclause 4.2.1, second paragraphReplace the second paragraph:In the scope of this ETS the interactions between layer 3 and the data link layer, and those between thedata link layer and the physical layer are specified.Page 18Add a new subclause 4.2.3:4.2.3Data link layer - physical layer interactionsThe interactions across the boundary between the data link layer and the physical layer allow:a)The data link layer at either side of the user-network interface to invoke the activation of thephysical layer connection making use of the PH-ACTIVATE.request primitive. At the userside of the basic access, no PH-ACTIVATE.request primitive shall be issued, if the terminal isnot in the connected status as indicated by the MPH-INFORMATION.indication primitive withthe parameter "disconnected". In all other cases, the status is permanently connected. Thesuccessful activation is confirmed by the PH-ACTIVATE.indication primitive. An unsuccessfulactivation is indicated by the PH-DEACTIVATE.indication primitive.PSIST ETS 300 402-2:1996



Page 12ETS 300 402-2: November 1995b)The physical layer to indicate to the data link layer that the physical layer connection hasbeen activated, by means of the PH-ACTIVATE.indication primitive.c)The physical layer to indicate to the data link layer that the physical layer connection hasbeen deactivated, by means of the PH-DEACTIVATE.indication primitive.d)The data link layer at either side of the user-network interface to request the physical layer inthe activated state the transmission of the SDU passed from the data link layer to thephysical layer by means of a PH-DATA.request primitive. The PH-DATA.request primitiveincludes a priority indicator with the values "high" or "low", representing two priority classes.The two priority classes apply to the physical layer and allow the data link layer to control thepriority for the processing of SDUs within the physical layer. The priority mechanism makesprovision that no low priority SDU is transmitted on the D-channel as long as there are highpriority SDUs pending transmission within the physical layer.e)The physical layer in the activated state to deliver to the data link layer a received SDU ThisSDU is passed from the physical layer to the data link layer by means of a PH-DATA.indication primitive.The interactions described in a), b) and c) above are related to physical connection status control while d)and e) refer to the information transfer on an activated physical connection i.e. on a activated D-channel.The data link layer shall make provision that activation of the physical layer connection is invoked makinguse of the PH-ACTIVATE.request primitive when a data link layer connection is to be established and thephysical layer is in the deactivated state, otherwise no PH-ACTIVATE.request primitive shall be issued.The data link layer shall not issue a PH-DATA.request primitive, if the physical layer connection is not inthe activated state.Page 22, clause 5, noteThe note contains a mandatory requirement of this ETS. As a consequence, replace the note by:A FRMR-response shall not be generated by a data link layer entity; however, on receipt of this frameactions according to subclause 5.8.6 of this ETS shall be taken.Page 22, table 7/Q.921, noteDelete the note.Page 22, subclause 5.2.1Replace the complete text of subclause 5.2.1 by:The procedures which apply to the transmission of information in unacknowledged operation are definedin subclauses 5.2.2 and 5.2.3.No data link layer error recovery procedures are defined for unacknowledged operation.If an implementation conforming to this ETS is used only in conjunction with a defined set of applicationswhich do not use the unacknowledged information transfer service, and an open interface is not providedto user applications, e.g. for later inclusion of a new application, then, as an implementation option:a)the layer 2 protocol entity supporting any particular user application which does not useunacknowledged information transfer service, does not need to implement the generation ofthe UI frame, and may treat received UI frames as frames associated with an application notimplemented according to subclause 3.6.1;b)the layer 2 protocol entity supporting layer 2 management (broadcast data link procedures)does not need to be implemented, if no peer-to-peer layer management is provided (seeannex A).PSIST ETS 300 402-2:1996



Page 13ETS 300 402-2: November 1995Page 23, subclause 5.2.2, sixth
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