1、INTERNATIONAL TELECOMMUNICATION UNION ITU=T TELECOMMUNICATION STANDARDIZATION SECTOR OF ITU BROADBAND ISDN Q.21 O0 ITU-T RECNN*Q=ZLOO 74 48b259L 0576103 725 (07/94) B-ISDN SIGNALLING ATM ADAPTATION LAYER (SAAL) OVERVIEW DESCRIPTION ITU-T Recommendation Q.21 O0 (Previously “CCIlT Recommendation“) COP
2、YRIGHT International Telecommunications Union/ITU TelecommunicationsLicensed by Information Handling ServicesFOREWORD The IT Telecommunication Standardization Sector is a permanent organ of the International Telecommunication Union (). The iT-T is responsible for studying technical, operating and ta
3、riff questions and issuing Recommendations on them with a view to standardizing telecommunications on a worldwide basis. The World Telecommunication Standardization Conference (WTSC), which meets every four years, establishes the topics for study by the ITU-T Study Groups which, in their turn, produ
4、ce Recommendations on these topics. The approval of Recommendations by the Members of the ITU-T is covered by the procedure laid down in WTSC Resolution No. 1 (Helsinki, March 1-12, 1993). IT-T Recommendation 4.210 was prepared by the -T Study Group 11 (1993-1996) and was approved under the WTSC Res
5、olution No. 1 procedure on the 29th of July 1994. NOTE In this Recommendation, the expression “Administration” is used for conciseness to indicate both a telecommunication administration and a recognized operating agency. O ITU 1995 All rights reserved. No part of this publication may be reproduced
6、or utilized in any form or by any means, electronic or mechanical, including photocopying and microfilm, without permission in writing from the ITU. COPYRIGHT International Telecommunications Union/ITU TelecommunicationsLicensed by Information Handling Services ITU-T RECMN*Q.2100 94 W 48b2591 059610
7、5 5TB = CONTENTS Page 1 Scope 2 Normative references . 3 Abbreviations . 4 General . 5 Description of SAAL . 5.1 SAAL-SAP . 5.2 SSCF-UNI 5.3 SSCF-“I 5.4 SSCOP 5.5 CPCS 5.6 SAR 5.7 ATM-SAP . Recommendation Q.2100 (07/94) 1 1 1 2 2 i COPYRIGHT International Telecommunications Union/ITU Telecommunicati
8、onsLicensed by Information Handling ServicesSUMMARY This Recommendation briefly describes the various components which make up the AAL functions necessary to support signalling (SAAL). It is intended to serve as a guide to all other Recommendations required by a user for the implementation of an AAL
9、 for the purpose of signalling. The ATM adaptation layer (AAL) is defined as enhancing the services provided by the ATM layer to support the functions required by the next higher layer. Different AALS support various protocols to suit the different needs of a range of AAL service users. One particul
10、ar type of AAL service user is the signalling entity wishing to communicate with a peer entity. The SAAL comprises AAL functions necessary to support such a signalling entity. KEYWORDS AAL ATM B-ISDN CPCS “I SAAL SAP SAR SSCF SSCOP sscs UNI ATM Adaptation Layer Asynchronous Transfer Mode Broadband I
11、ntegrated Services Digital Network Common Part Convergence Sublayer Network Node Interface Signalling AAL Service Access Point Segmentation and Reassembly Service Specific Coordination Function Service Specific Connection riented Protocol Service Specific Convergence Sublayer User-Network Interface
12、11 Recommendation Q.2100 (07/94) COPYRIGHT International Telecommunications Union/ITU TelecommunicationsLicensed by Information Handling ServicesRecommendation Q.2100 B-ISDN SIGNALLING ATM ADAPTATION LAYER (SAAL) OVERVIEW DESCRIPTION (Geneva, 1994) 1 Scope This Recommendation briefly describes the v
13、arious components which make up the AAL functions necessary to support signalling (SAAL). It is intended to serve as a guide to all other Recommendations required by a user who intends to construct an AAL for the purpose of signalling. 2 Normative references The following Recommendations and other r
14、eferences contain provisions which, through reference in this text, constitute provisions of this Recommendation. At the time of publication, the editions indicated were valid. All Recommendations and other references are subject to revision: all users of this Recommendation are therefore encouraged
15、 to investigate the possibility of applying the most recent edition of the Recommendations and other references listed below. A list of currently valid ITU-T Recommendations is regularly published. - Recommendation 1.361, ATM layer specification for B-ISDN. - Recommendation 1.362, B-ISDN ATM adaptat
16、ion layerfunctional description. - Recommendation 1.363, B-ISDN ATM adaptation layer specification. - ITU-T Recommendation 4.21 10, B-ISDN ATM Adaptation Layer Service Specific Connection Oriented Protocol (SSCOP). - ITU-T Recommendation 4.21 30, B-ISDN ATM Adaptation Layer Service Specific Coordina
17、tion Function (SSCF) for signalling at the User Network Inteace (UNI), - ITU-T Recommendation 4.2140, B-ISDN ATM Adaptation Layer Service Specific Coordination Function (SSCF) for signalling at the Network Node Inteace (“1). 3 Abbreviations For the purposes of this Recommendation, the following abbr
18、eviations apply: AAL ATM Adaptation Layer ATM Asynchronous Transfer Mode CPCS Common Pari Convergence Sublayer “I Network Node Interface SAAL Signalling AAL SAP Service Access Point SAR Segmentation And Reassembly Recommendation Q.2100 (07/94) 1 COPYRIGHT International Telecommunications Union/ITU T
19、elecommunicationsLicensed by Information Handling ServicesITU-T RECMN*Q*ZLOO 94 48b259L 059b108 207 SSCF Service Specific coordination Function SSCOP SSCS Service Specific Convergence Sublayer UNI User-Network Interface Service Specific Connection Oriented Protocol 4 General The ATM adaptation layer
20、 (AAL) is defined as enhancing the services provided by the ATM layer to support the functions required by the next higher layer. Different AALS support various protocols to suit the different needs of a range of AAL service users. Recommendation 1.362 gives an overview of the basic structure of an
21、AAL and the manner in which it aligns with the service class. One particular type of AAL service user is the signalling entity wishing to communicate with a peer entity. Any such entity would require that functions are provided above the common part of the AAL specifically designed to facilitate thi
22、s task. The information transfer between the SAAL user and the SAAL is performed in Message Mode. Two peer-to-peer operational procedures may be offered: Unassured or Assured operation. 5 Description of SAAL The complete specification of the SAAL is indicated in Figure 1. The SAAL makes use of the s
23、ervice provided by the Common Part Convergence Sublayer (CPCS) and Segmentation and Re-assembly (SAR) which form the common part of AAL type 5. The Service Specific Convergence Sublayer (SSCS) part of AAL type 5 is performed by a combination of the Service Specific Connection Oriented Protocol (SSCO
24、P) and one of several types of Service Specific Coordination Function (SSCF), two of which are currently defined and shown in the figure. The function of the SSCOP is such as to make it equally well suited for use by the user plane. A description of each SAAL component follows. 5.1 SAAL-SAP This is
25、the Service Access Point (SAP) through which all SAAL functions are accessed by the next higher layer. It provides bi-directional flow of information. Further information regarding this component is found in Recommendations 4.2130 and Q.2140. 5.2 SSCF-UNI This is the Service Specific Coordination Fu
26、nction which maps the particular requirements of the UNI layer 3 protocol to the SSCOP services. Further information regarding this component is found in Recommendation Q.2130. 5.3 SSCF-NNI This is the Service Specific Coordination Function which maps the particular requirements of the “i layer 3 pr
27、otocol to the SSCOP services. Further information regarding this component is found in Recommendation Q.2140. 5.4 SSCOP This is the Service Specific Connection Oriented Protocol function which provides mechanisms for the establishment and release of connections and the reliable exchange of informati
28、on between peer entities. Further information regarding this component is found in Recommendation Q.2110. 2 Recommendation Q.2100 (07194) COPYRIGHT International Telecommunications Union/ITU TelecommunicationsLicensed by Information Handling Services - ITU-T RECMN*Q=23OO 94 W 4862593 0596309 143 Pla
29、ne Management I SAAL SAP I L-4 SSCF I t r SSCOP I u (2.21 1 O L-l + See chuse 6il.363 I / .i - Y ATM SAP 11153040-93/601 NOTE - SSCF-UNI (see Recommendation 4.2130) cr SSCF-”I (see Recommendation Q.2140). FIGURE 1/Q.2100 Complete AAL structure for signalling applications 5.5 CPCS This is the Common
30、Part Convergence Sublayer which provides transparent transport of Service Data Units produced by the next higher layer. Further information regarding this component is found in clause 6A.363. 5.6 SAR This is the Segmentation and Re-assembly function. It provides the services whereby SAR service data
31、 units (SDUs) are segmented to fit into outgoing ATM cells, while incoming cells are reassembled into SAR SDUs and data are passed up to the CPCS. Further information regarding this component is found in clause 6A.363. 5.7 ATM-SAP This is the point through which ail ATM functions are accessed by the ATM adaptation layer. It provides bidirectional now of information. Further information regarding this component is found in Recommendation 1.361. Recommendation Q.2100 (07/94) 3 COPYRIGHT International Telecommunications Union/ITU TelecommunicationsLicensed by Information Handling Services
