1、340Y583 0077863 854 Released: July 1, 1993 GSM 04.05 Version: 4.0.0 Date: 25 June, 1993 Work Item No: Key words: European digital cellular telecommunication system (phase 2); Data Link Layer - General Aspects ETSI European Telecommunications Standards institute ETSI Secretariat: Route des Lucioles,
2、F-O6921 Sophia Antipolis Cedex . France TP. + 33 92 94 42 O0 TF. + 33 93 65 47 16 Tx. 47 O0 40 F This is an unpublished work the copyright in which vests in the European Telecommunications Standards Institute. All rights reserved. The information contained herein is the property of ETSI and no pan m
3、ay 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. 1 . 2 . 3 . 4 . 5 . 6 . m 303 007qms TB m Page 3 GSM 04.05 . version 4.0.0 : June 1
4、993 Contents SCOPE 5 CONCEPTS AND TERMINOLOGY 6 OVERVIEW DESCRIPTION OF LAPDm FUNCTIONS AND PROCEDURES . 10 3.1 . General 10 3.2. Unacknowledged operation . 11 3.3. Acknowledged operation 11 3.4. Information transfer mode 11 . 3.4.1. Information transfer on the BCCH 11 3.4.2. Information transfer on
5、 the PCH + AGCH . 11 3.4.3. Information transfer on the DCCHs 11 3.5, Release of data links 12 SERVICE CHARACTERISTICS . 12 4.1 . General 12 4.2. Services provided to layer 3 . 12 4.2.1 . General 12 4.2.2. Priority . 13 4.2.3. Segmentation 13 4.2.4. Unacknowledged information transfer service 13 4.2
6、.5. Acknowledged information transfer services., 14 4.2.6. Random access proceduree . 15 4.3. Services required from the physical layer 16 4.4. Administrative services 17 4.4.1 General description of administrative services . 17 4.4.2. Definition of primitives for administrative services 17 OVERVIEW
7、 OF DATA LINK LAYER STRUCTURE . 18 5.1 . Functional composition 18 5.2. Identification of data link end points 18 5.3. Data link procedure . 19 5.4. Data link distribution procedure . 19 5.5. Random access procedures 19 SPECIFIC REQUIREMENTS . 21 6.1 . Mode of operation and allowed SAPls 21 6.2. Ack
8、nowledged mode of operation 22 6.2.1 . Window size . 22 6.2.2. Processing capacity . 22 W 3404583 0079336 234 Page 5 GSM 04.05 - version 4.0.0 : June 1993 1. SCOPE This Technical Specification describes in general terms the Link Access Procedures on the Dm channel, LAPDm. The application of this pro
9、tocol 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 des
10、ignate 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 (Osil; - CCITT Recomme
11、ndations 0.920 and Q.921 : the specification of LAPD for the user-network interface in ISDN; - CCIlT 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
12、. LAPDm is a protocol that operates at the data link layer of the OS1 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
13、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 04.1 1. Reference should be made to these Technical Specifications for the complete definitions of the protocols and procedures a
14、cross 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. Funhermore, in accordance with TS GSM 04.07 and 04.08 the term “layer 3“ is used
15、 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 overv
16、iew 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. rn 340453 007337 170 m Page 6
17、 GSM 04.05 - version 4.0.0: June 1993 Layer 3 2. CONCEPTS AND TERMINOLOGY Q I Layer 3 entity The general layering principles used in this Technical Specification and other specifications in the 04 series are given in TS GSM 04.01. Datalink layer The data link layer is the next to lowest layer of the
18、 OS1 reference model. The data link layer receives services from the physical layer and provides services to layer 3. Datalink layer entity 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 da
19、ta 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
20、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). SAPls and DLCls used bv MPDm are defined in section 5.2. I Datalink layer service access point * Dat
21、alink connection endpoint I 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 t
22、he 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 21. M 3404583 0079338 007 Page 7 GSM 04.05 - version 4.0.0 : June 1993 layer
23、service access point * * Datalink connection endpoint -r 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. T
24、he 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 ink layer and its adjacent layers. They do not specify or constrain implementations. The primitives t
25、hat are exchanged between the data link layer and adjacent layers are of the following four types (see also Figure 3). m 3404553 0079339 T43 m Page 8 GSM 04.05 - version 4.0.0: June 1993 Layer 3 n i Data rc Request f SAP II Response f I 1 . 7 0- . . u Layer 2 peer-to-peer protocol link layer Note: T
26、he 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
27、 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 act
28、ivity 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 pr
29、otocol; and - message units that contain layer-to-layer information concerning status and specialised service requests. m 3404583 0079340 7b5 Page 9 GSM 04.05 - version 4.0.0 : June 1993 The message units of the layer 3 peer-to-peer protocol are carried by the data link connection. The message units
30、 containing layer-to-layer information concerning status and specialised service requests are never conveyed over a data link connection or a physical connection. This Technical Specification introduces (see also Figure 4): a) the peer-to-peer protocol for the transfer of information and control bet
31、ween 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 1 entity I entity Datalink layer Layer/layer 3 service access point primitives Data I ink 1 I Datal ink Datalink layer
32、Datal ink entity peer-to-peer protocol entity Datalink layer service access point I 1 Physical layer service access point 1 ayer entity Datalink layer/ physical layer primitives Phyo i cal i ayer rl entity Physical connection Figure 4. Data link layer reference model. Page 10 GSM 04.05 - version 4.0
33、.0: June 1993 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 laye
34、r entities; - - paging channel (PCH) signalling; - - broadcast control channel (BCCH) signalling; access grant channel (AGCHI 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. N
35、ote: 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
36、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: the provision of one or more data link co
37、nnections on a Dm channel. Discrimination between the data link connections is by means of a data link connection identifier (DLCI); allowing recognition of frame types; allowing layer 3 message units to be passed transparently between layer 3 entities; sequence control, to maintain the sequential o
38、rder of frames across a data link connections; detection of format and operational errors on a data link; notification to the layer 3 entity of unrecoverable errors. Note: flow control; and contention resolution when establishing a data link after an access request has been made on the RACH. types o
39、f operation of the data link layer are defined for layer 3 information transfer: It is in the responsibility of layer 3 entity to recover from these errors; unacknowledged operation and acknowledged (multiple frame) operation. They may co-exist on a Dm channel. The BCCH and the (PCH + AGCH) will onl
40、y support unacknowledged operation. The SDCCH, SACCH and FACCH will support both types of operation. W 3Y04583 0079342 538 Page 11 GSM 04.05 - version 4.0.0 : June 1993 3.2. Unacknowledged operation In unacknowledged operation, layer 3 information is transmitted in Unnumbered Information (UI) frames
41、. 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, la
42、yer 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. F
43、low 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 i
44、n 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 site of 1 is required. Multiple frame operation is initiated by a multiple frame establishment procedure using a Set Asynchronous Balance
45、d 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
46、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. i
47、nformation transfer on the DCCHs On the DCCHs both unacknowledged operation and multiple frame operation are possible (see section 6.11. The type of operation required at any time is determined by layer 3. = 3404583 0079343 474 m Page 12 GSM 04.05 - version 4.0.0: June 1993 3.5. Release of data link
48、s 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 wi
49、thout 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. 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
