1、= 3404583 0070526 BT3 ETSI/TC SMG Released by : ETSI/PT 12 Release date: February 1992 RELEASE NOTE Recommendation GSM 04.05 MS - BSS Data Link Layer - General Aspects Previously distributed version : 3.1.4 (Updated Release 1/90 New Released version February 92 : 3.1.5 (Release 92, Phase 1) Only pag
2、enumbering/layout/etc. has been changed since the previously distributed version. = 3404583 0070527 73T ETS I -G S M Tech n ka I Specification GSM 04.05 Version 3.1.5 UDC: 62 1.396.21 Key words: European Digital Cellular Telecommunications System, Global System for Mobile Communications (GSM) MS - B
3、SS Data Link Layer General Aspects ETSI European Telecommunications Standards Institute ETSI Secretariat: B.P.152 . F - 06561 Valbonne Cedex . France TP. + 33 92 94 42 O0 TF. + 33 93 65 47 16 Tx. 47 O0 40 F Previous page is blank Copyright European Telecommunications Standards Institute 1992. All ri
4、ghts reserved. No part may be reproduced or used except as authorised by contract or other written permission. The copyright and the foregoing restriction on reproduction and use extend to all media in which the information may be embodied. m 3404583 0070528 b7b m I PREFATORY NOTE ETSI has constitut
5、ed stable and consistent documents which give specifications for the implementation of the European Cellular Telecornmunications System, Historically, these documents have been identified as “GSM recommendations“. L . Some of these recommendations may subsequently become Interim European Telecommuni
6、cations Standards (I-ETSs) or European Telecommunications Standards (ETSs), whilst some continue with the status of ETSI-GSM Technical Specifications. These ETSI-GSM Technical Specifications are for editorial reasons still referred to as GSM recommendations in some current GSM documents. The numberi
7、ng and version control system is the same for ETSI-GSM Technical Specifications as for “GSM recommendations“. m 3404583 0070529 502 ETSI/GSM Version 3.1.5 Recomnendation : GSM 04.05 Title : DATA LINK LAYER - GENERAL ASPECTS Date : February 1992 LIST OF CONTENTS 1. 2. 3. 4. 5. Scope Concepts and term
8、inology Overview description of LAFDm functions and procedures 3.1 General 3.2 Unacknowledged operation 3.3 Acknowledged operation 3.4 Information transfer mode 3.5 Release of data links Service characteristics 4.1 General 4.2 4.3 4.4 Administrative services Overview of data link layer structure 5.1
9、 Functional composition 5.2 Identification of data link end points 5.3 Data link procedures 5.4 Data link distribution procedure 5.5 Random access procedure Services provided to layer 3 Services required from the physical layer Number of pages : 24 Language of original : English 3404583 0070530 224
10、1. Recommendation GSM 04.05 - version 3.1.5 - page 2 SCOPE This Recommendation 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 Recommendation GSM 04.06. The purpose o
11、f LWDm is to convey information between layer 3 entities across the GSM PLMN radio interface (MS - BS 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 Recommendat
12、ion 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); - CCIT“ Recommendations 4.920 and 4.921 - the specification of WD for the user-network interface in ISDN; - CCIT
13、T Recommendation X.25 LAPB - user-network interface for packet mode terminals: and - IS0 3309 and IS0 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 OS1 architecture. The relationshi
14、p 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 series GSM 07 Recommendations. . Note 2: The physical layer on the radio interface is defined in Recommendation G
15、SM 04.04 and layer 3 is defined in Recommendation GSM 04.07. 04.08, 04.10 and 04.11. Reference should be made to these Recommendations for the complete definitions of the protocols and procedures across the GSM PLMN radio interface. m 3404583 0070533 3bO m 2. Recommendation GSM 04.05 - version 3.1.5
16、 - page 3 Note 3: The term “data link layer“ is used in the main text of this Recommendation. However, mainly in figures and tables, the terms “layer 2“ and “L2“ are used abbreviations. Furthermore, in accordance with Recommendations GSM 04.07 and 04.08 the term “layer 3“ is used to indicate the lay
17、er above the data link layer. LAPDm is independent of transmission bit rate. It requires physical channels with characteristics as defined in Recommendation GSM 04.03. Section 2 below describes basic concepts used in this Recommendation and Recommendation GSM 04.06. Section 3 gives an overview descr
18、iption 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. CONCEPTS AND TERMINOLOGY The general l
19、ayering principles used in this Recommendation and other Recommendations in he 04 series are given in Recommendation GSM 04.01. The data link layer is the next lowest layer of the OS1 reference model. The data link layer receives services from the physical layer and provides services to layer 3. 340
20、4583 0070532 OT7 Recommendation GSM 04.05 - version 3.1.5 - page 4 * The services provided by the data link layer are the combination of the services and functions provided by both the date link layer and the physical layer. , A data link layer Service Access Point (SAP) is the point at which the da
21、ta link layer provides services to layer 3. The Services Access Point is identified by a Service Access Point Identifier (SAP). Associated with each data link layer SAP is one or more data link connection endpoints. See Figure 1. A data link connection endpoint is identified by a data link connectio
22、n endpoint identifier as seen from layer 3 and by a Data Link Connection Identifier (DLCI); as seen from the data link layer. The SAPIs and Layer 3 the DLCIs for LAPDm are defined in R5. Layer 3 Datalink layer service access point I I) Datalink connection endpoint layer layer entity Figure 1. Entiti
23、es, service access points and endpoints. Co-operation between data link layer entities is governed by a peer-to-peer protocol specific to the layer. In order for information to be exchanged between two or more layer 3 entities, an association must be established between the layer 3 entities in the d
24、ata 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). 3404583 0070533 T33 Recommendation GSM 04.05 - version Layer 3 entity Datalink layer service access p
25、oint I * 3.1.5 - Page 5 Layer 3 entity 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 pr
26、imitives. The same applies for the interaction between the data link layer and the physical layer. The primitives represent, in the abstract way, the logical exchange of information and control between the data link layer and adjacent layers. They do not specify or constrain implementation. The prim
27、itives that are exchanged between the data link layer and adjacent layers are of the following four types (see also Figure 3) D 3i104583 0070534 97T Recommendation GSM 04.05 - version 3.1.5 - page 6 LI Loyer 3 I. I! Response f- Note: The same principle applies for data link layer- physical layer int
28、eractions. 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 RE
29、QUEST. 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. 3404583 0070535 806 = Recommendation
30、GSM 04.05 - version 3.1.5 - page 7 Layer-to-layer interactions are specified in Recommendation GSM 04.06. Information is transferred, in various types of message units, between peer entities and between entities in adjacent layers that are attached to a specific SAP. The message units are of two typ
31、es : - 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-laye
32、r information concerning status and specialised service requests are never conveyed over a data link or a physical connection. The Recommendation specifies (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 acces
33、s points: b) the interactions between the data link layer and layer 3, and between the data link layer and the physical layer. 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 inter
34、face using the Dm channel. Specifically LAPDm will support: m 3404583 007053b 742 m Datal ink layer entity Recommendation GSM 04.05 - version 3.1.5 - page, 8 Datalink layer Datalink layer . peer-to-peer protocol Layer 3 layer layer/layer 3 service access point primitives Datalink Physical layer enti
35、ty Layer 3 entity Physical layer entity - Datalink layer/ physical layer primitives Physical layer service access point Figure 4. Data link layer reference model. = 3404583 0070537 689 * Recommendation GSM 04.05 - version 3.1.5 - page 9 - multiple layer 3 entities: - multiple physical layer entities
36、; - broadcast control channel (BCCH) signalling; - paging channel (PCH) signalling; - access grant channel (AGCH) signalling; - dedicated control channel (DCCH) signalling. Note: The DCCH designates a number of control channels (SDCCH, FACCH and SACCH) as defined in Recommendation GSM 04.03. Note: T
37、he 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 Recommendation GSM 04.06. T
38、he Dm channel between a BS and a specific MS may be distorted on several physical channels, e.g. PCH, SDCCH and FACCH during a connection. See also Recommendation GSM 04.03. LWDm includes functions for: a) the provision of one or more data link connections on a Dm channel. Discrimination between the
39、 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 connection
40、s; e) detection of format and operational errors on a data link; f) notification to the layer 3 entity of unrecoverable errors. Note: it is the responsibility of layer 3 entity to recover from errors; g) flow control; and h) contention resolution when establishing a data link after an access request
41、 has been made on the RACH. 3404583 0070538 515 3.2 3.3 Recommendation GSM 04.05 - version 3.1.5 - page 10 Two types of operation of the data link layer are defined for , layer 3 information transfer: unacknowledged operation and multiple frame operation. They may Co-exist on a Dm channel. The BCCH
42、and the (PCH + AGCH) will only support unacknowledged operation which the SDCCH, SACCH and FACCH will support both types of operation. Unacknowledged operation With this type of operation layer 3 information is transmitted in Unnumbered Information (UI) frames. At the data link layer the U1 frames a
43、re not acknowledge. Flow control mechanisms and error recovery mechanisms are not defined. Unacknowledged operation is applicable to all types of control channel except the RACH. Acknowledged operation With this type of operation, layer 3 information is transmitted in frames that are acknowledged at
44、 the data link layer. Error recovery procedures based on retransmission of unacknowledged frames are specified. In the case of errors which cannot be corrected by the data link layer, a report to the mobile management entity is made. Flow control procedures are also defined . Acknowledged operation
45、is applicable to DCCHs. Recommendation GSM 04.05 - version 3.1.5 - page 11 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
46、be outstanding at the same time. However, for many applications (eg signalling) a window of 1 will be 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
47、 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 “he BCCH exists only in the BS to MS direction and is used for broadcasting radio sub-system information
48、 to MSs. Only U1 frames are sent on the BCCH. 3.4.2. Information transfer on the PCH + AGCH These channels exist only in the BS to MS direction. AGCH only unacknowledged operation is possible. On the PCH + 3.4.3. Information transfer on the DCCHs On the DCCHs both unacknowledge operation and multipl
49、e frame operation are possible. The type of operation required at any time is determined by layer 3. W 3404583 0070540 I173 3.5 4. 4.1 Recommendation GSM 04.05 - version 3.1.5 - page 12 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 and 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 indica
