1、- 1 7- - = 3404583 00964l14 440 r ETSI . REPORT ETR 117 December 1993 Source: ETSI TC-SPS Reference: DTR/SPS-O3017 UDC: 621.395 Key words: B-ISDN, ATM Broadband Integrated Services Digital Network (B-ISDN); Asynchronous Transfer Mode (ATM) Signalling ATM Adaptation Layer (AAL) requirements ETSI Euro
2、pean Telecommunications Standards Institute ETSI Secretariat Postal address: 06921 Sophia Antipolis Cedex - FRANCE Office address: Route des Lucioles - Sophia Antipolis - Valbonne - FRANCE Tel.: + 33 92 94 42 O0 - Fax: + 33 93 65 47 16 European Telecommunications Standards Institute I 993. All right
3、s reserved. No part may be reproduced except as authorised by written permission. The copyright and the foregoing restriction on reproduction extend to all media in which the information may be embodied, Page 2 ETR 117:1993 I Whilst every care has been taken in the preparation and publication of thi
4、s document, errors in content, typographical or otherwise, may occur. If you have comments concerning its accuracy, please write to “ETSI Editing and Standards Approval Dept.“ at the address shown off the title page. . W 3404583 0096416 213 W Page 3 ETR 117:1993 Contents Foreword . 1 Scope . 2 Refer
5、ences 3 Definitions. symbols and abbreviations . 4 General . 4.1 Concept and terminology AAL structure for signaliing applications 4.2 5 Service specific part 5.1 SSP-AALservices . 5.2 Operational attributes 6 Commonpart 6.1 CP-AALservices 6.2 Operational attributes 6.3 Primitives . 7 Service specif
6、ic part functions . 8 Definition of the AAL boundary 8.1 Definition of the AAL boundary at the UNI 8.1.1 Primitives 8.1.2 State diagram . 8.2 Definition of the AAL boundary at the NNI 8.2.1 Primitives 8.2.2 State diagram . Annex A: Example flow diagrams Annex B: Bibliography History . 5 7 7 7 8 8 10
7、 11 11 12 13 13 13 14 14 15 15 15 16 17 17 19 20 26 27 Page 5 ETR 117:1993 Foreword This ETSI Technical Report (ETR) has been produced by the Signalling Protocols and Switching (SPS) Technical Committee of the European Telecommunications Standards Institute (ETSI). ETRs are informative documents res
8、ulting from ETSI studies which are not appropriate for European Telecommunication Standard (ETS) or Interim European Telecommunication Standard (I-ETS) status. An ETR may be used to publish material which is either of an informative nature, relating to the use or the application of ETSs or I-ETSs, o
9、r which is immature and not yet suitable for formal adoption as an ETS or an I-ETS. Previous page is blank 1 Scope Page 7 ETR 117:1993 This ETR describes the Broadband Integrated Services Digital Network (B-ISDN) Asynchronous Transfer Mode (ATM) ATM Adaptation Layer (AAL) requirements to support the
10、 transfer of signalling messages. The AAL operates over an ATM virtual channel connection to provide a signalling link for the transfer of messages between two signalling entities. This is applicable for both User Network Interfaces (UNIS) and Network Node Interfaces (NNls). As such, the Signalling
11、ATM Adaptation Layer (SAAL) shall be able to provide the services provided by both Link Access Procedure on the D-channel (LAPD) and Message Transfer Part (MTP) layer 2. This ETR specifies the SAAL requirements. It is designed to assist the protocol experts in the design of a service specific SAAL.
12、These are minimum requirements, .e. based on services provided by the existing link layers of the UNI (ITU-T Recommendation Q.921 t51) and NNI (ITU-T Recommendation Q.703 41). The requirements are not intended to limit the protocol definition to only these capabilities, but form a basis for starting
13、 the work. 2 References For the purposes of this ETR, the following references apply: 11 1 ITU-T Recommendation 1.361 (1 993): “B-ISDN ATM layer specification“. t21 31 ITU-T Recommendation 1.362 (1 993): “B-ISDN ATM Adaptation Layer (AAL) functional description“. ITU-T Recommendation 1.363 (1 993):
14、“B-ISDN ATM Adaptation Layer (AAL) specification“. NOTE: ITU-T Recommendation 1.363 131 includes the specification of the Common Part (CP) of the AAL types 3 and 4. i41 ITU-T Recommendation Q.703 (1 993): “Signalling link“. i51 ITU-T Recommendation 0.921 (1 993): “ISDN user-network interface - Data
15、link layer specification“. 3 Definitions, symbols and abbreviations For the purposes of this ETR, the following abbreviations apply: AAL ATM B-ISDN CP LA PD MTP NNI os1 SAAL SAP SDH SDU SSP UNI ATM Adaption Layer Asynchronous Transfer Mode Broadband Integrated Services Digital Network Common Part Li
16、nk Access Procedure on the D-channel Message Transfer Part Network Node Interface Open Systems Interconnection Signalling AAL Service Access Point Synchronous Digital Hierarchy Signalling Data Unit Service Specific Part User Network Interface Previous page is blank 3404583 0096439 T22 m 4 t w Page 8
17、 ETR 117:1993 LM 1 Highestlayer I I i 4 General 4 4-w +-+ 4 w 4 b 4.1 Concept and terminology LM I (N+I)layer LM I (N) layer LM I (N-i) layer I i LM 1 Lowestlayer The basic structuring technique in 1. .e Open Systems Interconnection (OSI) reference model is layering. According to this technique, com
18、munication among application processes is viewed as being logically partitioned into an ordered set of layers represented in a vertical sequence as shown in figure 1. System Management 2 Figure 1: Layering A SAAL Service Access Point (SAP) is the point at which the SAAL provides services to layer 3.
19、 Associated with each SAAL SAP are one or more SAAL connection endpoints, see figure 2. I Layer3 entity Layer 3 -_- SAAL END POINT layer entit Figure 2: Entities, service access points and endpoints Entities exist in each layer. Entities in the same layer but in different systems which need to excha
20、nge information to achieve a common objective are called “peer entities“. Entities in adjacent layers interact through their common boundary, The services provided by the data link layer are the combination of the services and functions provided by the SAAL Service Specific Part (SSP), SAAL Common P
21、art (CP) and the ATM layer. Cooperation between SAAL entities is governed by a peer-to-peer protocol specific to the layer. 1-3404583 0096420 744 Page 9 ETR 117:1993 SAAL Signalling Data Units (SDUs) are conveyed between SAAL entities by means of a physical connection. Layer 3 requests services from
22、 the SAAL via service primitives. The same applies for the interaction between the SAAL and the ATM layer. The primitives represent, in an abstract way, the logical exchange of information and control between the SAAL and the adjacent layers and between the SAAL SSP and the SAAL CP. They do not spec
23、ify or constrain implementation. The primitives that are exchanged between the SAAL and adjacent layers are of the following four types (see also figure 3): a) request; b) indication; c) response; d) confirm. Layer 3 A REQUEST INDICATION - RESPONSE SAP YI I .-.- - -. SAAL w$r+=r SAAL NOTE: The same
24、principle applies for SAA-ATM 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 any specif
25、ic activity which is service related. The indication primitive may be the result of an activity of the lower layer related to the primitive type request at the peer entity. The response primitive type is used by a layer to acknowledge receipt from a lower layer of the primitive type indication. The
26、confirm primitive type is used by the layer providing the requested service to confirm that the activity has been completed. Information is transferred, in various types of SDUs, between peer entities and between entities in adjacent layers (and sublayers) that are attached to a specific SAP. The SD
27、Us are of two types: - SDUs of a peer-to-peer protocol; and - SDUs that contain layer-to-layer information concerning status and specialized service requests. 3404583 0096421 b8O Page 10 ETR 117:1993 The SDUs of the layer 3 peer-to-peer protocol are carried by the SAAL connection. The SDUs containin
28、g layer-to-layer information concerning status and specialized service requests are never conveyed over a SAAL connection or an ATM (physical) connection. 4.2 AAL structure for signalling applications The AAL is functionally divided into the CP and SSP as shown in figure 4. I 4 PRIMITIVES SERVICE SP
29、ECIFIC i?% AAL FUNCTION COMMON AAL FUNCTIONS SSP-AAL I I CP-AAL lt PEER-TO-PEER MESSAGES PEER-TO-PEER MESSAGES Figure 4: AAL structure for signalling applications The CP may be used by different SSPs; the SSP is specific to the needs of the service application. The requirements in this ETR address t
30、he SSP. The CP protocol is specified in ITU-T Recommendation 1.363 31; the SSP protocol is in the responsibility of ETSI STCs SPS3/SPS5. Figure 5 shows the application topology of the CP and the SSP of the AAL. The CP and SSP are both peer-to-peer protocols with as much commonality between them as p
31、ossible. Commonality between the UNI and NNI is desirable. NOTE 1: One of the overall objectives in B-ISDN studies has been to achieve as much commonality as possible between UNI and NNI. In view of this, ETSI STC SPS3 requests ETSI STCs SPS2 and SPS5 to consider a common protocol in their study of
32、the AAL to support signalling. Page 11 ETR 117:1993 NODE NETWORK CP-AAL x Figure 5: AAL signalling structure application example It is hoped that this commonality, without increasing the complexity at the UNI, will have the following benefits: - - - - - reduce operating costs; - reduce manufacturing
33、 costs. reduce complexity at network nodes; reduce time required for production of two protocols; allow for flexibility in network operation and configuration (due to a common signalling mechanism); make for more efficient operation and maintenance of the network; However, the above should be taken
34、into account with the need to have a SAAL available for release 1. NOTE 2: For the point-to-multipoint connection, a subset of the protocol used for point-to-point is used. 5 Service specific part 5.1 SSP-AAL services The following services are provided by the signalling adaptation layer: a) Indepen
35、dence of underlying layers The AAL service relieves AAL service users from all concerns regarding which configuration is available (e.g. point-to-point connection) or which physical facilities are used. 3404583 0096423 453 Page 12 ETR 117:1993 Unacknowledged transfer of data The AAL service provides
36、 for the transfer of AAL service user-data on point-to-point and point-to- multipoint ATM connections. The AAL service does not relieve the user from loss, insertion and misordering of data which may occur. Assured transfer of data The AAL service provides for the transfer of AAL service user-data o
37、n point-to-point ATM connections. The AAL service relieves the user from loss, insertion, corruption and misordering of data which may occur. In some cases unrecoverable errors in the AAL, duplication or loss of SDUs may occur. Transparency of transferred information The AAL service provides for the
38、 transparent transfer of AAL service user-data. It does not restrict the content, format or coding of information, nor does it ever need to interpret its structure or meaning. Establishment and release of AAL connections for assured transfer of data The AAL service provides for a means to establish
39、and release AAL connections which operate in assured mode. Alternatively, the AAL service provider may release the AAL connection. Depending on the conditions, release of an AAL connection may result in loss of AAL user-data. SDU retrieval The AAL service makes available to the AAL service user the
40、means by which the sending AAL service user may retrieve SDUs already handed over to the AAL. Status reporting The AAL service provides for a means to inform the AAL service user of the status of the AAL, The signalling SSP-AAL may be operated in the following manner: - LAPD emulation: the LAPD (ITU
41、-T Recommendation (2.921 51) service can be emulated by means of services a) to e). - MTP level 2 emulation: MTP level 2 (ITU-T Recommendation Q.703 41) can be emulated by means of services a) and cl to 91. 5.2 Operational attributes The operational attributes of the SSP-AAL include: a) symmetry: op
42、eration is symmetric on point-to-point virtual channel connections. Operation on multipoint connections is asymmetric; b) SDU size: a maximum of 4 096 octets shall be conveyed. SDUs are octet aligned; c) operational speed: the minimum signalling rate is 16 kbit/s and the maximum signalling rate is p
43、rotocol and traffic load dependent. The desired signalling rate is in the range of megabits per second. = 3404583 OOb4Z4 39T i Page 13 ETR 117:1993 d) performance requirements: - undetected SDU loss rate - less than 1 in lo7; - undetected SDU error rate - less than 1 in 10”; - maximum establishment
44、time: the maximum allowable time for establishment of a connection upon request from the user is less than one second for non-satellite connections and less than two seconds for satellite connections. 6 Common part The requirements for the signalling SSP-AAL have been defined based on the definition
45、 of services, operational attributes and primitives and supported by the CP-AAL as contained in this Clause. 6.1 CP-AAL services a) Independence of underlying layers The CP-AAL service relieves CP-AAL service users from all concerns regarding which configuration is available (e.g. point-to-point con
46、nection) or which physical facilities are used. b) Transparency of transferred information The CP-AAL service provides for the transparent transfer of AAL-CP service user-data. It does not restrict the content, format or coding of information, nor does it ever need to interpret its structure or mean
47、ing. c) Transfer of data The CP-AAL service provides for the transfer of CP-AAL service user-data on point-to-point and point-to-multipoint ATM connections. The CP-AAL service provides for CP-AAL service user-data integrity, but does not relieve the CP-AAL service user from loss, insertion and misor
48、dering of data which may occur. d) Error reporting The CP-AAL service indicates to the CP-AAL service user whether the received user-data is corrupted (the need for this service is still under study). 6.2 Operational attributes The operational attributes of the CP-AAL include: a) SDU size: a maximum
49、 of 4 096 octets plus the service specific overhead shall be conveyed. SDUs are octet aligned; b) operational speed: the minimum signalling rate is 16 kbit/s modified appropriately to include the service specific overhead and the maximum signalling rate is protocol and traffic dependent. The desired signalling rate is in the order of Mbit/s; c) performance requirements: the requirements need to be provided by ITU-T Study Group 1 3 (formerly CCITT Study Group XVIII). 3404583 0096425 22b = Page 14 ETR 117:1993 6.3 Primitives The proposed primitives across the service spec
