1、INTERNATIONAL TELECOMMUNICATION UNION ITU=T TELECOMMUNICATION STANDARDIZATION SECTOR OF ITU 1.1 50 (02/99) SERIES I: INTEGRATED SERVICES DIGITAL NETWORK General structure - General description of asynchronous transfer mode B-ISDN asynchronous transfer mode functional characteristics ITU-T Recommenda
2、tion 1.150 (Previously CClTT Recommendation) STDmITU-T RECMN IeL5O-ENGL L999 m 4862593 ObbOb82 377 m ITU-T I-SERIES RECOMMENDATIONS INTEGRATED SERVICES DIGITAL NETWORK ;ENERAL STRUCTURE Terminology Description of ISDNs General modelling methods Telecommunication network and service attributes 1.110-
3、1.119 1.120-1.129 1.130-1.139 1.140-1.149 SERVICE CAPABILITIES Scope General aspects of services in ISDN Common aspects of services in the ISDN Bearer services supported by an ISDN Teleservices supported by an ISDN Supplementary services in ISDN 3VERALL NETWORK ASPECTS AND FUNCTIONS Network function
4、al principles Reference models Numbering, addressing and routing Connection types Performance objectives Protocol layer requirements General network requirements and functions ISDN USER-NETWORK INTERFACES Application of I-series Recommendations to ISDN user-network interfaces Layer 1 Recommendations
5、 Layer 2 Recommendations Layer 3 Recommendations Multiplexing, rate adaption and support of existing interfaces Aspects of ISDN affecting terminal requirements INTERNETWORK INTERFACES MAINTENANCE PRINCIPLES B-ISDN EQUIPMENT ASPECTS ATM equipment Transport functions Management of ATM equipment 1.200-
6、1.209 1.210-1.219 1.220-1.229 1.230-1.239 1.240-1.249 1.250-1.299 1.310-1.319 1.320-1.329 1.330-1.339 1.340-1.349 1.350-1.359 1.360-1.369 1.370-1.399 1.420-1.429 1.430-1.439 1.440-1.449 1.450-1.459 1.460-1.469 1.470-1.499 1.500-1.599 1.600-1.699 1.730-1.739 1.740-1.749 1.750-1.799 For further detail
7、s, please refer to ITU-T List of Recommendations. STDmITU-T RECMN I-150-ENGL 1999 4Bb259L Ob60683 203 9 ITU-T RECOMMENDATION 1.150 B-ISDN ASYNCHRONOUS TRANSFER MODE FUNCTIONAL CHARACTERISTICS Summary This Recommendation defines the functions of the Asynchronous Transfer Mode (ATM) layer. This ATM la
8、yer is common to all services including signalling and OAM. Source ITU-T Recommendation 1.1 50 was revised by ITU-T Study Group 13 (1997-2000) and was approved under the WTSC Resolution No. 1 procedure on the 26th of February 1999. Recommendation 1.150 (02/99) 1 - FOREWORD ITU (International Telecom
9、munication Union) is the United Nations Specialized Agency in the field of telecommunications. The ITU Telecommunication Standardization Sector (ITU-T) is a permanent organ of the ITU. The ITU-T is responsible for studying technical, operating and tariff questions and issuing Recommendations on them
10、 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, produce Recommendations on these topics. The approval o
11、f Recommendations by the Members of the ITU-T is covered by the procedure laid down in WTSC Resolution No. l. In some areas of information technology which fall within ITU-Ts purview, the necessary standards are prepared on a collaborative basis with IS0 and IEC. NOTE In this Recommendation the term
12、 recognized operating agency (ROA) includes any individual, company, corporation or governmental organization that operates a public correspondence service. The terms Administration, ROA and public correspondence are defined in the Constitution of the ITU (Geneva, 1992). INTELLECTUAL PROPERTY RIGHTS
13、 The ITU draws attention to the possibility that the practice or implementation of this Recommendation may involve the use of a claimed Intellectual Property Right. The ITU takes no position concerning the evidence, validity or applicability of claimed Intellectual Property Rights, whether asserted
14、by ITU members or others outside of the Recommendation development process. As of the date of approval of this Recommendation, the ITU had received notice of intellectual property, protected by patents, which may be required to implement this Recommendation. However, implementors are cautioned that
15、this may not represent the latest information and are therefore strongly urged to consult the TSB patent database. O ITU 1999 All rights reserved. No part of this publication may be reproduced or utilized in any form or by any means, electronic or mechanical, including photocopying and microfilm, wi
16、thout permission in writing from the ITU. 1 2 3 3.1 3.2 3.3 3.4 CONTENTS Introduction Basic principles of ATM ATM layer ATM connections . 3 . 1 . 1 Connection definition 3.1.2 Connection identifiers . 3.1.3 Aspects of Virtual Channel Connections (VCCs) . 3.1.4 Aspects of Virtual Path Connections (VP
17、Cs) . 3.1.5 Pre-assigned cell header values . Service characteristics 3.2.1 Services expected from the physical layer Management plane interactions Functions of the ATM layer . 3.4.1 Cell multiplexing and switching . 3.4.2 Quality Of Service provided by the ATM layer 3.4.3 Payload type functions 3.4
18、.4 Generic Flow Control (GFC) at the UNI 3.2.2 Services provided to the higher layer Annex A . Alphabetical list of abbreviations contained in this Recommendation . . Page 1 1 2 2 2 2 3 5 6 6 6 6 6 7 7 7 8 8 11 Recommendation 1.150 (02/99) . 111 Recommendation 1.150 B-ISDN ASYNCHRONOUS TRANSFER MODE
19、 FUNCTIONAL CHARACTERISTICS (revised in 1999) 1 Introduction This Recommendation addresses specifically the functions of the Asynchronous Transfer Mode (ATM) layer. This layer is common to all services including signalling and OAM. 2 Basic principles of ATM ATM is the transfer mode solution for impl
20、ementing a B-ISDN. It influences the standardization of digital hierarchies, multiplexing structures, switching and interfaces for broadband signals. ATM is used in this Recommendation for addressing a specific packet-oriented transfer mode which uses asynchronous time division multiplexing techniqu
21、es. The multiplexed information flow is organized into blocks of fixed size called cells. A cell consists of an information field and a header. The primary role of the header is to identify cells belonging to the same virtual channel within the asynchronous time division multiplex. Transfer capacity
22、 is assigned by negotiation and is based on the source requirements and the available capacity. Cell sequence integrity on a virtual channel connection is preserved by the ATM layer. ATM is a connection-oriented technique. Connection identifiers are assigned to each link of a connection when require
23、d and released when no longer needed. In general, signalling and user information are carried on separate ATM connections. ATM offers a flexible transfer capability common to all services, including connectionless services. Additional fimctionalities on top of the ATM layer e.g. in the ATM Adaptatio
24、n Layer (AAL) are provided to accommodate various services. The boundary between the ATM layer and the AAL corresponds to the boundary between functions supported by the contents of the cell header and functions supported by AAL-specific information. The AAL-specific information is contained in the
25、information field of the ATM cell. The information field is transported transparently by the ATM layer. No processing, e.g. error I control, is performed on the information field at the ATM layer. , The header and information field each consist of a fixed integer number of octets. The header size (5
26、 octets) and the information field size (48 octets) remain constant at all reference points, including the User-Network Interface (UNI) and the Network-Node Interface (NNI), where the ATM technique is applied. For a multipoint-to-point virtual channel connection, cell sequence integrity is preserved
27、 for cells from each VCC endpoint of the VCC. Recommendation 1.150 (02/99) 1 3 ATM layer 3.1 ATM connections 3.1.1 Connection definition An ATM connection consists of the concatenation of ATM layer links in order to provide an end-to- end transfer capability to access points. 3.1.2 Connection identi
28、fiers 3.1.2.1 Virtual Path Identifiers (VPIs) and Virtual Channel Identifiers (VCIs) At a given interface, in a given direction, the different Virtual Path (VP) links multiplexed at the ATM layer into the same physical layer connection are distinguished by the VPI. The different indicated in Figure
29、l. Virtual Channel (VC) links in a Virtual Path Connection (VPC) are distinguished by the VCI as I Physical layer connection . . u”.K L T1307470-96 NOTE - VCI, and VCI, represent two of the possible values of VCI within the VP link with the value VPI,. Similarly, VPI, and VPI, refer to two of the po
30、ssible values of VPI within the physical layer connection. Figure 14.150 - ATM connection identifiers 3.1.2.2 VPI-VCI relationships Two different VCs belonging to two different VPs at a given interface may have the same VCI value. Therefore, a VC is only fully identified at an interface by both VPI
31、and VCI values. A specific value of VCI has no end-to-end significance if the Virtual Channel Connection (VCC) is switched. VPIs may be changed wherever VP links are terminated (e.g. cross-connects, concentrators and switches). VCIs may only be changed where VC links are terminated. As a consequence
32、, VCI values are preserved within a VPC. 3.1.2.3 Number of active connections at the UNI At the UNI, 24 bits are available in the VPINCI field for connection identification. The actual number of routing bits in the VPI and VCI fields used for routing is negotiated between the user and the network, e
33、.g. on a subscription basis. This number is determined on the basis of the lower requirement of the user or the network. The rules to determine the position of the routing bits used within the VPINCI field are given in 2.2.3A.361. NOTE - The number of VCI field routing bits used in a user-to-user VP
34、 is negotiated between the users of the VP. STD-ITU-T RECMN ImLSO-ENGL L999 4Bh2591 OhhOb88 895 3.1.2.4 Number of active connections at the NNI At the NNI, 28 bits are available in the VPINCI field for connection identification. The actual number of routing bits in the VPI and VCI fields used for ro
35、uting across the interface is established at installation. This number is determined on the basis of the requirement of each entity. The rules to determine the position of the routing bits used within the VPINCI field are given in 2.2.3D.36 l. 3.1.3 Aspects of Virtual Channel Connections (VCCs) 3.1.
36、3.1 General characteristics of VCCs The definition of a VCC is given in Recommendation 1.1 13. This subclause provides additional explanations to facilitate the understanding of the following topics: a) Quality Of Service - A user of a VCC is provided with a Quality Of Service specified by parameter
37、s such as cell loss ratio and cell delay variation. b) Switched and (semi-) permanent VCCs - VCCs can be provided on a switched or (semi-) permanent basis. c) CeU sequence integrity - Cell sequence integrity is preserved within a VCC. NOTE- Whether this applies to all resource management (RM) cells
38、is for further study (see Recommendation 1.371). network the establishment of a VCC, traffic parameters shall be negotiated between a user and a network for each VCC at VCC establishment and may be subsequently renegotiated. Input cells from the user to the network may be monitored to ensure that th
39、e negotiated traffic parameters are not violated. Traffic contracts and conformance to traffic contracts are specified in Recommendation 1.37 l. d) Trafic parameter negotiation and usage monitoring - When a user requests from the At a B-ISDN interface (e.g. UNI or NNI), there are two directions of t
40、ransmission. When a routing field value (Le. VPI plus VCI) is assigned for a VC link at an interface (e.g. UNI or NNI), the same value is assigned for both directions of transmission. The routing field value used in one direction is only to be used in the opposite direction to identify the VC link i
41、nvolved in the same communication. It should be noted that: - the bandwidth in both directions may be the same (symmetric communication); or - the bandwidth in both directions may be different (asymmetric communication); or - the bandwidth of the opposite direction may be equal to zero (unidirection
42、al communication - the bandwidth of the opposite direction could be large enough to carry ATM layer without any reverse information); or management information (unidirectional communication with reverse management information). Within a user-to-user VPC, the network passes the VCI field transparentl
43、y with the exception of some standardized VCI values (see Recommendation 1.361). The routing field assignment is under the control of the user (e.g. user-to-user signalling procedures, user-to-user management procedures, etc.). Recommendation 1.150 (02/99) 3 STD-ITU-T RECMN I-350-ENGL 1999 m 4862593
44、 ObbOb89 723 m 3.1.3.2 Establishment and release of a VCC 3.1.3.2.1 Establishmenthelease at the UNI VCCs may be establishedreleased using one or more of the following four methods: a) without using signalling procedures, e.g. by subscription (semi-) permanent connections; b) meta-signalling procedur
45、es (see Recommendation 1.31 l), e.g. by using a meta-signalling c) user-to-network signalling procedures, e.g. using a signalling VCC to establishhelease a d) user-to-user signalling procedures, e.g. using a signalling VCC to establishhelease a VCC VCC to establishhelease a VCC used for signalling;
46、VCC used for end-to-end communications; within a pre-established VPC between two UNIS. The value assigned to a VCI at a UNI using the methods listed above could be assigned by one of the following: a the network; b) the user; c) negotiation between the user and the network; d) standardization. The s
47、pecific value assigned to a VCI at a UNI is, in general, independent of the service provided over that VC. For terminal interchangeability and initialization, it is desirable to use the same value for certain functions on all UNIS. For example, the same VCI value for the meta-signalling VC will be u
48、sed on all UNIS in order to simplify initialization of the terminal equipment. 3.1.3.2.2 EstablishmentlRelease at the NNI ATM network elements (e.g. ATM switches, cross-connects and concentrators) process the ATM cell header and may provide VCI andor VPI translation. Thus, whenever a VCC is establis
49、hedreleased across the ATM network, VC links may need to be establishedreleased at one or more NNIs. VC links are establishedreleased between ATM network elements using inter- and intra-network signalling procedures; other methods are also possible. 3.1.3.3 Pre-assigned VCIs Information concerning the use of the following VCI values in combination with VPI values can be found in Tables lA.361,2/1.361 and 3A.361. Pre-assigned VCI values are used for: a) unassigned cell identification and physical layer cell identification; NOTE - For the unassigned cell identification and ce
