ETSI ETS 300 554 ed.1 (1994-09)

European digital cellular telecommunications system (Phase 2); Data Link (DL) layer; General aspects (GSM 04.05)

DE/SMG-030405P

Evropski digitalni celični telekomunikacijski sistem (faza 2) – Plast podatkovnih povezav (DL) Splošni vidiki (GSM 04.05)

General Information

• Status: Published
• Publication Date: 12-Sep-1994
• Technical Committee: SMG 3 - Network Aspects
• Current Stage: 12 - Completion
• Due Date: 03-Oct-1994
• Completion Date: 13-Sep-1994
• Ref Project: SIST ETS 300 554 E1:2003 - European digital cellular telecommunications system (Phase 2); Data Link (DL) layer; General aspects (GSM 04.05)

Standards Content (Sample)

SLOVENSKI STANDARD
SIST ETS 300 554 E1:2003
01-december-2003
(YURSVNLGLJLWDOQLFHOLþQLWHOHNRPXQLNDFLMVNLVLVWHPID]D±3ODVWSRGDWNRYQLK
SRYH]DY'/6SORãQLYLGLNL*60
European digital cellular telecommunications system (Phase 2); Data Link (DL) layer;
General aspects (GSM 04.05)
Ta slovenski standard je istoveten z: ETS 300 554 Edition 1
ICS:
33.070.50 Globalni sistem za mobilno Global System for Mobile
telekomunikacijo (GSM) Communication (GSM)
SIST ETS 300 554 E1:2003 en
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

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SIST ETS 300 554 E1:2003
EUROPEAN ETS 300 554
TELECOMMUNICATION September 1994
STANDARD
Source: ETSI TC-SMG Reference: GSM 04.05
ICS: 33.060.30
European digital cellular telecommunications system, Global System for Mobile communications
Key words:
(GSM)
European digital cellular telecommunications system (Phase 2);
Data Link (DL) layer
General aspects
(GSM 04.05)
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 1994. All rights reserved.
New presentation - see History box

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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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Contents
Foreword.5
1 General .7
1.1 Scope .7
1.2 Normative references .8
1.3 Definitions and abbreviations.9
2 Concepts and terminology.10
3 Overview description of LAPDm functions and procedures.13
3.1 General.13
3.2 Unacknowledged operation .14
3.3 Acknowledged operation.14
3.4 Information transfer mode.14
3.4.1 Information transfer on the BCCH .14
3.4.2 Information transfer on the PCH + AGCH .14
3.4.3 Information transfer on the DCCHs .14
3.5 Release of data links. 14
4 Service characteristics.15
4.1 General.15
4.2 Services provided to layer 3.15
4.2.1 General . 15
4.2.2 Priority .15
4.2.3 Segmentation.15
4.2.4 Unacknowledged information transfer service .16
4.2.5 Acknowledged information transfer services .16
4.2.6 Random access procedure .18
4.3 Services required from the physical layer.18
4.4 Administrative services .19
4.4.1 General description of administrative services .19
4.4.2 Definition of primitives for administrative services.19
5 Overview of data link layer structure .20
5.1 Functional composition.20
5.2 Identification of data link end points .20
5.3 Data link procedure .20
5.4 Data link distribution procedure .21
5.5 Random access procedures.21
6 Specific requirements .23
6.1 Mode of operation and allowed SAPIs.23
6.2 Acknowledged mode of operation.23
6.2.1 Window size .23
6.2.2 Processing capacity .23
History.24

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ETS 300 554: September 1994 (GSM 04.05 version 4.0.3)
Foreword
This European Telecommunication Standard (ETS) has been produced by the Special Mobile Group
(SMG) Technical Committee (TC) of the European Telecommunications Standards Institute (ETSI).
This ETS defines in general terms the data link layer (layer 2) of the Mobile Station (MS) - network
interface within the European digital cellular telecommunications system (Phase 2).
This ETS correspond to GSM technical specification, GSM 04.05 version 4.0.3.
The specification from which this ETS has been derived was originally based on CEPT documentation,
hence the presentation of this ETS may not be entirely in accordance with the ETSI/PNE rules.
Reference is made within this ETS to GSM Technical Specifications (GSM-TSs) (NOTE).
Reference is also made within this ETS to GSM 07.xx. series. The specifications in the series can be
identified, with their full title, within the normative reference Clause of this ETS by the first two digits of
their GSM reference number e.g. GSM 07.xx series, refers to GSM 07.01, GSM 07.02 etc.
NOTE: TC-SMG has produced documents which give the technical specifications for the
implementation of the European digital cellular telecommunications system. Historically,
these documents have been identified as GSM Technical Specifications (GSM-TS).
These TSs may have subsequently become I-ETSs (Phase 1), or ETSs (Phase 2),
whilst others may become ETSI Technical Reports (ETRs). GSM-TSs are, for editorial
reasons, still referred to in GSM ETSs.

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1 General
1.1 Scope
This Technical Specification describes in general terms the Link Access Procedures on the Dm channel,
LAPDm. The application of this protocol to other channel types is for further study. Details are provided in
TS GSM 04.06.
The purpose of LAPDm is to convey information between layer 3 entities across the GSM PLMN radio
interface (MS to network interface) using the Dm channel.
NOTE: The term Dm channel is used for convenience to designate the collection of all the
various signalling channels required in the GSM system. See also TS GSM 04.03.
The definition of LAPDm is based on the principles and terminology of:
- CCITT Recommendations X.200 and X.210 : the reference model for Open Systems
Interconnection (OSI);
- CCITT Recommendations Q.920 and Q.921 : the specification of LAPD for the user-network
interface in ISDN;
- CCITT Recommendation X.25 LAPB : user-network interface for packet mode terminals; and
- ISO 3309 and ISO 4335 : High-level Data Link Control (HDLC) standards for frame structure and
elements of procedures.
LAPDm is a protocol that operates at the data link layer of the OSI architecture. The relationship between
the data link layer and other protocol layers is defined below.
NOTE 1: The interface between the mobile station and external terminal equipment/terminal
adapters is defined in the Technical Specifications of the GSM 07-series.
NOTE 2: The physical layer on the radio interface is defined in TS GSM 04.04 and layer 3 is
defined in TS GSM 04.07, 04.08, 04.10 and 04.11. Reference should be made to
these Technical Specifications for the complete definitions of the protocols and
procedures across the GSM PLMN radio interface.
NOTE 3: The term "data link layer" is used in the main text of this Technical Specification.
However, mainly in figures and tables, the terms "layer 2" and "L2" are used
abbreviations. Furthermore, in accordance with TS GSM 04.07 and 04.08 the term
"layer 3" is used to indicate the layer above the data link layer.
LAPDm is independent of the transmission bit rate. It requires physical channels with characteristics as
defined in TS GSM 04.03.
Section 2 below describes basic concepts used in this Technical Specification and TS GSM 04.06.
Section 3 gives an overview description of LAPDm functions and procedures.
Section 4 summarises the services that the data link layer provides to layer 3 and the services that the
data link layer requires from the physical layer.
Section 5 provides an overview of the data link layer structure.

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1.2 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.
[1] GSM 01.04 (ETR 100): "European digital cellular telecommunications system
(Phase 2); Abbreviations and acronyms".
[2] GSM 04.01 (prETS 300 550): "European digital cellular telecommunications
system (Phase 2); Mobile Station - Base Station System (MS - BSS) interface
General aspects and principles".
[3] GSM 04.03 (prETS 300 552): "European digital cellular telecommunications
system (Phase 2); Mobile Station - Base Station System (MS - BSS) interface
Channel structures and access capabilities".
[4] GSM 04.04 (prETS 300 553): "European digital cellular telecommunications
system (Phase 2); Layer 1 General requirements".
[5] GSM 04.06 (prETS 300 555): "European digital cellular telecommunications
system (Phase 2); Mobile Station - Base Station System (MS - BSS) interface
Data Link (DL) layer specification".
[6] GSM 04.07 (prETS 300 556): "European digital cellular telecommunications
system (Phase 2); Mobile radio interface signalling layer 3 General aspects".
[7] GSM 04.08 (prETS 300 557): "European digital cellular telecommunications
system (Phase 2); Mobile radio interface layer 3 specification".
[8] GSM 04.10 (prETS 300 558): "European digital cellular telecommunications
system (Phase 2); Mobile radio interface layer 3 Supplementary services
specification General aspects".
[9] GSM 04.11 (prETS 300 559): "European digital cellular telecommunications
system (Phase 2); Point-to-Point (PP) Short Message Service (SMS) support on
mobile radio interface".
[10] GSM 07.01 (prETS 300 582): "European digital cellular telecommunications
system (Phase 2); General on Terminal Adaptation Functions (TAF) for Mobile
Stations (MS)".
[11] GSM 07.02 (prETS 300 583): "European digital cellular telecommunications
system (Phase 2); Terminal Adaptation Functions (TAF) for services using
asynchronous bearer capabilities".
[12] GSM 07.03 (prETS 300 584): "European digital cellular telecommunications
system (Phase 2); Terminal Adaptation Functions (TAF) for services using
synchronous bearer capabilities".
[13] GSM 07.05 (prETS 300 585): "European digital cellular telecommunications
system (Phase 2); Use of Data Terminal Equipment - Data Circuit terminating
Equipment (DTE - DCE) interface for Short Message Service (SMS) and Cell
Broadcast Service (CBS)".

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[14] GSM 07.06 (prETS 300 586): "European digital cellular telecommunications
system (Phase 2); Use of the V series Data Terminal Equipment - Data Circuit
terminating Equipment (DTE - DCE) interface at the Mobile Station (MS) for
Mobile Termination (MT) configuration".
[15] CCITT Recommendation X.25: "Interface between data terminal equipment
(DTE) and data circuit - terminating equipment (DCE) for terminals operating in
the packet mode and connected to public data networks by dedicated circuit".
[16] CCITT Recommendation X.200: "Reference Model of Open Systems
Interconnection for CCITT Applications".
[17] CCITT Recommendation X.210: "Open Systems Interconnection layer service
definition conventions".
[18] CCITT Recommendation Q.920: "Integrated services digital network (ISDN)
user-network interface - Data link layer General aspects".
[19] CCITT Recommendation Q.921: "Integrated services digital network (ISDN)
user-network interface - Data link layer specification".
[20] ISO 3309: "Information technology - Telecommunications and information
exchange between systems - High level data link control (HDLC) procedures -
Frame structure".
[21] ISO/IEC 4335: "Information technology - Telecommunications and information
exchange between systems - High level data link control (HDLC) procedures -
Elements of procedures".
1.3 Definitions and abbreviations
Abbreviations used in this specification are listed in GSM 01.04

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2 Concepts and terminology
The general layering principles used in this Technical Specification and other specifications in the 04 series
are given in TS GSM 04.01.
The data link layer is the next to lowest layer of the OSI reference model. The data link layer receives
services from the physical layer and provides services to layer 3.
The services provided by the data link layer are the combination of the services and functions provided by
both the data link layer and the physical layer.
A data link layer Service Access Point (SAP) is the point at which the data link layer provides services to
layer 3. The Service Access Point is identified by a Service Access Point Identifier (SAPI). One or more
data link connection endpoints can be associated with each data link layer SAP. See figure 1. A data link
connection endpoint is identified by a data link connection endpoint identifier (as seen from layer 3) and by
a Data Link Connection Identifier DLCI (as seen from the data link layer).
SAPIs and DLCIs used by LAPDm are defined in section 5.2.
          �˜˜˜˜˜˜˜˜˜¿
      Layer 3 ‡ Layer 3 ‡
          ‡ entity ‡
          �˜˜˜´˜˜˜˜˜�
            ‡   Datalink layer service access point
            ‡
          ˜˜˜˜`˜˜˜˜˜
        ˜˜˜˜˜˜˜ * ˜˜˜˜˜˜˜˜
          ˜˜˜˜´˜˜˜˜˜
            ‡
            ‡   Datalink connection endpoint
         �˜˜˜˜˜˜`˜˜˜˜˜˜˜¿
    Datalink ‡ Datalink   ‡
    layer  ‡ layer entity ‡
         �˜˜˜˜˜˜˜˜˜˜˜˜˜˜�
Figure 1: Entities, service access points and endpoints
Co-operation between data link layer entities is governed by a peer-to-peer protocol specific to the layer.
For information exchange between two or more layer 3 entities, an association must be established
between the layer 3 entities in the data link layer using a data link layer protocol. This association is called
a data link connection. Data link connections are provided by the data link layer between two or more
SAPs (see figure 2).
   �˜˜˜˜˜˜˜˜˜¿                 �˜˜˜˜˜˜˜˜˜¿
   ‡ Layer 3 ‡                 ‡ Layer 3 ‡
   ‡ entity ‡                 ‡ entity ‡
   �˜˜˜´˜˜˜˜˜�                 �˜˜˜˜´˜˜˜˜�
     ‡   Datalink layer             ‡
     ‡   service access point          ‡
     ‡                       ‡
   ˜˜˜˜`˜˜˜˜˜                  ˜˜˜˜˜`˜˜˜˜˜
˜˜˜˜˜˜˜ * ˜˜˜˜˜˜˜˜             ˜˜˜˜˜˜˜ * ˜˜˜˜˜˜˜
   ˜˜˜˜´˜˜˜˜˜                  ˜˜˜˜˜´˜˜˜˜˜
     ‡                       ‡
     ‡   Datalink connection endpoint      ‡
     ‡                       ‡
     ‡    Datalink relationship        ‡
     �˜˜˜˜˜˜˜˜˜˜˜˜˜˜˜˜˜˜˜˜˜˜˜˜˜˜˜˜˜˜˜˜˜˜˜˜˜˜˜˜˜˜˜˜˜�
Figure 2: Peer-to-peer relationship
Data link layer message units are conveyed between data link layer entities by means of physical
connection.
Layer 3 requests services from the data link layer via service primitives. The same applies for the
interaction between the data link layer and the physical layer. The primitives represent, in an abstract way,
the logical exchange of information and control between the data link layer and its adjacent layers. They do
not specify or constrain implementations.

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The primitives that are exchanged between the data link layer and adjacent layers are of the following four
types (see also figure 3).
Layer 3
Indication     Response
Confirm     Request
* *
SAP
Data
link
layer
Layer 2 peer-to-peer protocol
NOTE: The same principle applies for data link layer- physical layer interactions.
Figure 3: Primitive action sequence
The REQUEST primitive type is used when a higher layer is requesting a service from the next lower layer.
The INDICATION primitive type is used by a layer providing a service to notify the next higher layer of
activities related to the primitive type REQUEST.
The RESPONSE primitive type is used by a layer to acknowledge receipt, from a lower layer, of the
primitive type INDICATION.
The CONFIRM primitive type is used by the layer providing the requested service to confirm that the
activity has been completed.
The precise specification of Layer-to-layer interactions is given in TS GSM 04.06.
Information between peer entities and between entities in adjacent layers attached to the same SAP is
transferred in two different types of message units:
- message units of a peer-to-peer protocol; and
- message units that contain layer-to-layer information concerning status and specialised service
requests.
The message units of the layer 3 peer-to-peer protocol are carried by the data link connection. The
message units containing layer-to-layer information concerning status and specialised service requests are
never conveyed over a data link connection or a physical connection.

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This Technical Specification introduces (see also figure 4):
a) the peer-to-peer protocol for the transfer of information and control between any pair of data link
layer service access points;
b) the interactions between the data link layer and layer 3, and between the data link layer and the
physical layer.
     �˜˜˜˜˜˜˜˜˜¿                  �˜˜˜˜˜˜˜˜˜¿
     ‡ Layer 3 ‡                  ‡ Layer 3 ‡
     ‡ entity ‡                  ‡ entity ‡
     �˜˜˜´˜˜˜˜˜�                  �˜˜˜˜´˜˜˜˜�
Datalink   ‡   Datalink layer              ‡
layer/layer 3‡   service access point           ‡
primitives  ‡                       ‡
     ˜˜˜˜`˜˜˜˜˜                  ˜˜˜˜˜`˜˜˜˜˜
  ˜˜˜˜˜˜˜   ˜˜˜˜˜˜˜˜             ˜˜˜˜˜˜˜˜   ˜˜˜˜˜˜˜˜
     ˜˜˜˜´˜˜˜˜˜                  ˜˜˜˜˜´˜˜˜˜˜
       ‡                       ‡
    �˜˜˜˜`˜˜˜˜˜¿                  �˜˜˜˜`˜˜˜˜˜¿
    ‡ Datalink ‡     Datalink layer      ‡ Datalink ‡
    ‡ layer  ‡ --------------------------------- ‡ layer  ‡
    ‡ entity  ‡    peer-to-peer protocol   ‡ entity  ‡
    �˜˜˜˜´˜˜˜˜˜�                  �˜˜˜˜´˜˜˜˜˜�
       ‡   Datalink layer              ‡
       ‡   service access point           ‡
     ˜˜˜˜`˜˜˜˜˜                  ˜˜˜˜˜`˜˜˜˜˜
  ˜˜˜˜˜˜˜   ˜˜˜˜˜˜˜˜             ˜˜˜˜˜˜˜˜   ˜˜˜˜˜˜˜˜
     ˜˜˜˜´˜˜˜˜˜                  ˜˜˜˜˜´˜˜˜˜˜
       ‡                       ‡
Datalink   ‡   Physical layer service          ‡
layer/    ‡   access point               ‡
physical   ‡                       ‡
layer    ‡
primitives  ‡
    �˜˜˜˜`˜˜˜˜˜¿                 �˜˜˜˜˜˜˜˜˜˜¿
    ‡ Physical ‡                 ‡ Physical ‡
    ‡ layer  ‡                 ‡ layer  ‡
    ‡ entity  ‡                 ‡ entity  ‡
    �˜˜˜˜´˜˜˜˜˜�                 �˜˜˜˜˜´˜˜˜˜�
       ‡      Physical connection        ‡
       �˜˜˜˜˜˜˜˜˜˜˜˜˜˜˜˜˜˜˜˜˜˜˜˜˜˜˜˜˜˜˜˜˜˜˜˜˜˜˜˜˜˜˜˜˜˜�
Figure 4: Data link layer reference model

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3 Overview description of LAPDm functions and procedures
3.1 General
The purpose of LAPDm is to convey information between layer 3 entities across the GSM PLMN radio
interface using the Dm channel. Specifically LAPDm will support:
- multiple layer 3 entities;
- multiple physical layer entities;
- broadcast control channel (BCCH) signalling;
- paging channel (PCH) signalling;
- access grant channel (AGCH) signalling;
- dedicated control channel (DCCH) signalling.
NOTE: The term "DCCH" designates a number of control channels (SDCCH, FACCH and
SACCH) as defined in TS GSM 04.03.
NOTE: The random access channel (RACH) does not utilise LAPDm. However, for the purpose
of specification, the data link layer acts as a protocol interface between layer 3 and the
physical layer also for random access.
The frame structure of data link layer messages is defined in TS GSM 04.06.
The Dm channel between a network and a specific MS may be distorted on several control channels, e.g.
PCH, SDCCH and FACCH during a connection (See also TS GSM 04.03). Selection and activation of
these channels is performed by layer 3.
LAPDm includes functions for:
a) the provision of one or more data link connections on a Dm channel. Discrimination between the data
link connections is by means of a data link connection identifier (DLCI);
b) allowing recognition of frame types;
c) allowing layer 3 message units to be passed transparently between layer 3 entities;
d) sequence control, to maintain the sequential order of frames across a data link connections;
e) detection of format and operational errors on a data link;
f) notification to the layer 3 entity of unrecoverable errors.
NOTE: It is in the responsibility of layer 3 entity to recover from these errors;
g) flow control; and
h) contention resolution when establishing a data link after an access request has been made on the
RACH.
Two types of operation of the data link layer are defined for layer 3 information transfer: unacknowledged
operation and acknowledged (multiple frame) operation. They may co-exist on a Dm channel.
The BCCH and the (PCH + AGCH) will only support unacknowledged operation. The SDCCH, SACCH and
FACCH will support both types of operation.

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3.2 Unacknowledged operation
In unacknowledged operation, layer 3 information is transmitted in Unnumbered Information (UI) frames.
At the data link layer, the UI frames are not acknowledged. Flow control mechanisms and error recovery
mechanisms are not defined.
Applicability of unacknowledged operation to different types of control channels is specified in section 6.1.
3.3 Acknowledged operation
In acknowledged operation, layer 3 information is transmitted in frames that are acknowledged by the
receiving data link layer.
Error recovery procedures based on retransmission of unacknowledged frames are specified. In case of
errors which cannot be corrected by the data link layer, a report is issued to the layer 3 entity. Flow
control procedures are also defined.
Applicability of acknowledged operation to different types of control channels is specified in section 6.1.
Only one form of acknowledged information transfer is defined, ie multiple frame operation.
For multiple frame operation, layer 3 information is sent in numbered Information (I) frames. In principle, a
number of I frames may be outstanding at the same time. However, for many applications (eg signalling) a
window size of 1 is required. Multiple frame operation is initiated by a multiple frame establishment
procedure using a Set Asynchronous Balanced Mode (SABM) command.
If an access request has been made on the RACH, the establishment procedure also contains functions for
resolving any ambiguity that may arise as a result of this access method.
3.4 Information transfer mode
3.4.1 Information transfer on the BCCH
The BCCH exists only in the network to MS direction and is used for broadcasting radio sub-system
information to MSs. Only UI frames are sent on the BCCH.
3.4.2 Information transfer on the PCH + AGCH
These channels exist only in the network to MS direction. On the PCH + AGCH only unacknowledged
operation is possible.
3.4.3 Information transfer on the DCCHs
On the DCCHs both unacknowledged operation and multiple frame operation are possible (see section
6.1). The type of operation required at any time is determined by layer 3.
3.5 Release of data links
Multiple frame operation may be released in the following ways:
- normal release by exchange of commands/responses. This type of release is initiated by layer 3;
- local end release, ie without exchange of commands/responses, initiated and controlled by layer 3;
- abnormal local end release, ie without exchange of commands/responses, commanded by layer 3.
The release mode is indicated by layer 3.
No release mechanism using exchange of commands/responses is defined for unacknowledged operation.

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4 Service characteristics
4.1 General
The data link layer provides services to layer 3 and utilises the services provided by the physical layer.
In this Technical Specification and TS GSM 04.06 the following general syntax is used for describing
primitives.
XX - Generic Name - Type (Parameters).
where XX designates the layer providing the services. In this Technical Specification XX is DL and MDL for
the data link layer and PH for the physical layer.
4.2 Services provided to layer 3
4.2.1 General
The specific
...