1、INTERNATIONAL TELECOMMUNICATION UNION ITU-T TELECOMMUNICATION STANDARDIZATION SECTOR OF ITU 1.761 SERIES I: INTEGRATED SERVICES DIGITAL NETWORK B-ISDN equipment aspects - Multiplexing aspects (03/2 000) Inverse multiplexing for ATM (IMA) ITU-T Recommendation 1.761 (Formerly CCITT Recommendation) STD
2、.ITU-T RECMN 1-7bL-ENGL 2000 m 4b2593 0687045 T2b m ITU-T I-SERIES RECOMMENDATIONS INTEGRATED SERVICES DIGITAL NETWORK GENERAL STRUCTURE Terminology Description of ISDNs General modelling methods Telecommunication network and service attributes General description of asynchronous transfer mode Scope
3、 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 Network functional principles Reference models Numbering, addressing and routing Connection types Performance objectives P
4、rotocol layer requirements General network requirements and functions Application of I-series Recommendations to ISDN user-network interfaces Layer 1 Recommendations Layer 2 Recommendations Layer 3 Recommendations Multiplexing, rate adaption and support of existing interfaces Aspects of ISDN affecti
5、ng terminal requirements SERVICE CAPABILITIES OVERALL NETWORK ASPECTS AND FUNCTIONS ISDN USER-NETWORK INTERFACES INTERNETWORK INTERFACES MAINTENANCE PRINCIPLES B-ISDN EQUIPMENT ASPECTS ATM equipment Transport functions Management of ATM eaubment I. 1 1 0-1. 1 1 9 I. 120-1.129 I. 130-1.139 I. 140-1.1
6、49 1.150-1.199 1.200-1.209 1.2 10-1.2 19 1.220-1.229 1.230-1.239 1.240-1.249 1.250-1.299 1.3 10-1.319 1.320-1.329 1.330-1.339 1.34CI.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 I. 740-1.749 1.750-
7、1.759 For further details, please refer to ihe list of ITU-TRecommendations. STD*ITU-T RECMN 1.7blr-ENGL 2000 4Bb259L Ob8904b 962 ITU-T Recommendation 1.761 Inverse multiplexing for ATM (IMA) Summary This ITU-T Recommendation defines a protocol for inverse multiplexing of an ATM cell stream over mul
8、tiple physical links, and to retrieve the onginal stream at the far-end from these links. Multiplexing of the ATM cell stream is perfonned on a cell-by-cell basis across the multiple links Source ITU-T Recommendation 1.761 was prepared by ITU-T Study Group 13 (1997-2000) and approved under the WTSC
9、Resolution 1 procedure on 10 March 2000. FOREWORD The International Telecommunication Union (ITU) is the United Nations specialized agency in the field of telecommunications. The ITU Telecommunication Standardization Sector (ITU-T) is a permanent organ of IT. ITU-T is responsible for studying techni
10、cal, operating and tariff 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,
11、 in turn, produce Recommendations on these topics. The approval of ITU-T Recommendations is covered by the procedure laid down in WTSC Resolution 1. In some areas of information technology which fall within ITU-Ts purview, the necessary standards are prepared on a collaborative basis with IS0 and EC
12、. NOTE In this Recommendation, the expression “Administration” is used for conciseness to indicate both a telecommunication administration and a recognized operating agency. INTELLECTUAL PROPERTY RIGHTS ITU draws attention to the possibility that the practice or implementation of this Recommendation
13、 may involve the use of a claimed Intellectual Property Right. ITU takes no position concerning the evidence, validity or applicability of claimed Intellectual Property Rights, whether asserted by ITU members or others outside of the Recommendation development process. As of the date of approval of
14、this Recommendation, ITU had not received notice of intellectual property, protected by patents, which may be required to implement this Recommendation. However, implementors are cautioned that this may not represent the latest information and are therefore strongly urged to consult the TSB patent d
15、atabase. o ITU 2001 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, without permission in writing from the ITU. Scope ,. References . . . . . . . . . . . . . . . . . . . . . .
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17、. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Abbreviations . . . . . . . . . . . . , . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . , . . . . . . . . . . . . . . . . . . . . . . . . . . . .
18、. . . . . . . . . . . . . . . . . . . . . . . . . . . . Overview of Inverse Multiplexing for ATM (IMA) Detailed requirements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . , . . . . . . . . . . . . , . . . Page
19、1 1 1 2 2 4 ITU-I Recommendation 1.761 Inverse multiplexing for ATM (IMA) 1 Scope This ITU-T Recommendation defines a protocol for inverse multiplexing of an ATM cell stream over multiple physical links, and to retrieve the original stream at the far-end fiom these links. Multiplexing of the ATM cel
20、l stream is performed on a cell-by-cell basis across the multiple links. The Inverse Multiplexing for ATM (MA) protocol provides a modular bandwidth for user access to ATM networks at rates between those used for UNI as defined in ITU-T Recommendation 1.432 series i, and for connection between ATM n
21、etwork elements at rates other than those defined by existing digital hierarchies. The introduction of ATM Inverse Multiplexers provides an effective method of combining the transport bandwidths of multiple links grouped to collectively provide higher intermediate rates. This ITU-T Recommendation de
22、fines a new sublayer located between the Physical Layer Transmission Convergence (TC) sublayer and the ATM layer. This sublayer is called the IMA sublayer. This ITU-T Recommendation also defines modifications to the TC sublayer over which IMA is implemented. 2 References The following ITU-T Recommen
23、dations and other references 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 t
24、herefore encouraged to investigate the possibility of applying the most recent edition of the Recommendations and other references listed below. A list of the currently valid ITU-T Recommendations is regularly published. i ITU-T Recommendation 1.432-series (1 993), B-ISDN User-Network Inteflace - Ph
25、ysical Layer Specijcation. 2 ATM Forum af-phy-0086.001 (1999), Inverse Multiplexing for ATM MA) Specification 1.1. 3 ITU-T Recommendation 1.361 (1999), B-ISDN ATM layer speczfzcation. 3 Definitions This ITU-T Recommendation defines the following terms: 3.1 filler cell: This cell is used to fill in t
26、he IMA frame when no cells are available at the ATM layer. 3.2 ICP cell: This cell is used to carry information to establish the IMA protocol between two MA units. 3.3 IMA frame: The IMA frame is used as the unit of control in the IMA protocol. It is a logical frame defined as M consecutive cells, n
27、umbered O to M-1, transmitted on each of the N links in an IMA group. 3.4 IMA group: Group of links at one end used to establish an MA virtual link to other end. - STD.ITU-T RECMN 1-7hL-ENGL 2000 W 4862593 Ob89050 393 3.5 IMA sublayer: Sublayer part of the Physical layer and located between the inte
28、rface specific Transmission Convergence (TC) sublayer and the ATM layer. 3.6 IMA virtual link: Virtual link established between two MA units over a number of physical links (MA group). 4 Abbreviations This ITU-T Recommendation uses the following abbreviations: CDV HEC ICP cell IMA LCD LIF LODS OIF P
29、HY PMD RDI TC Cell Delay Variation Header Error Check IMA Control Protocol cell Inverse Multiplexing for ATM Loss of Cell Delineation Loss of MA Frame defect Link Out of Delay Synchronization defect Out of MA Frame anomaly Physical Layer Physical Medium Dependent Remote Defect Indication Transmissio
30、n Convergence 5 The ATM inverse multiplexing technique involves inverse multiplexing and de-multiplexing of ATM cells in a cyclical fashion among links grouped to form a higher bandwidth logical link whose rate is approximately the sum of the link rates. This is referred to as an IMA group. Figure 1
31、 provides an illustration of the ATM Inverse Multiplexing technique for unidirectional connection. For bidirectional connections, the same technique applies. Overview of Inverse Multiplexing for ATM (IMA) Original ATM to ATM Layer Cell Stream Cell Stream from ATM Layer IMA Virtual Link Tx direction:
32、 cells distributed across links in round robin sequence Rx direction: cells recombined into single ATM stream _. . T131623-99 Figure 1D.761 - Inverse multiplexing and de-multiplexing of ATM cells via IMA groups STD.ITU-T RECMN I.761-ENGL 2000 = 4862571 Ob7051i 22T IMA groups terminate at each end of
33、 the IMA virtual link. In the transmit direction, the ATM cell stream received from the ATM layer is distributed on a cell-by-cell basis, across the multiple links within the IMA group. At the far-end, the receiving side of the IMA virtual link recombines the cells from each physical link, on a cell
34、-by-cell basis, recreating the original ATM cell stream. The aggregate cell stream is then passed to the ATM layer. The transmitting side of the IMA virtual link periodically transmits special cells that contain information that permits reconstruction of the ATM cell stream at the receiving side of
35、the IMA virtual link after accounting for the link differential delays, smoothing Cell Delay Variation (CDV) introduced by the control cells, etc. These cells, defined as IMA Control Protocol (ICP) cells, provide the definition of an MA frame. The transmitter must align the transmission of IMA frame
36、s on all links (shown in Figure 2). This allows the receiver to adjust for differential link delays among the constituent physical links. Based on this required behaviour, the receiver can detect the differential delays by measuring the arrival times of the IMA frames on each link. . ATM ATM ICP2 F
37、ATM . F ATM ICPl ATMATM . F ATM ICPOATM Link2 T131624O-99 ICP Cell in Frame #I Filler Cell Figure 2D.761 - Illustration of IMA frames At the transmitting end, the cells are transmitted continuously. If there are no ATM layer cells to be sent between ICP cells within an IMA frame, then the transmitti
38、ng side of the IMA virtual link sends Filler cells to maintain a continuous stream of cells at the physical layer. The insertion of filler cells provide cell rate decoupling at the IMA sublayer. The filler cells should be discarded by the receiving side of the IMA virtual link. A new OAM cell is def
39、ined for use by the IMA protocol. This cell has codes in its payload that define it as an ICP or filler cell (refer to ITU-T Recommendation 1.361 3). The IMA sublayer is part of the physical layer. It is located between the Transmission Convergence sublayer and the ATM layer. Figure 3 shows the loca
40、tion of the IMA sublayer in the layer reference model and the main functions of the IMA sublayer. The shaded areas of Figure 3 represent an overview of the IMA functions within the scope of this ITU-T Recommendation. STD-ITU-T RECMN 1.7bI-ENGL ZOO0 4862573 0689052 Ibb ATM layer Physical layer MA- sp
41、ecific transmission ;onvergence sublayer Interface- specific transmission convergence sublayer Physical medium dependent sublayer User plane functions ATM cell stream splitting and reconstruction ICP cell insertionhemoval Cell rate decoupling IMAframe synchronization Stuffing Discarding of cells wit
42、h No cell discarding No cell rate decoupling bad HEC Cell delineation, cell scrambling and descrambling (if required) (if required) generatiodverification Header error correction HEC Bit timing Line coding Physical medium Layer management functions . IMA connectivity ICP cell errors (OW LIF/LODS/RDI
43、- IMA defect processing RDI-IMA alarm generation Tx/Rx IMA link state report HECerror indication LCD-RDIalam generation (if required) Local alarm processing RDI alarms generation Plane management functions MA group configuration Link additioddeletion ATM cell rate change IMA group failure notificati
44、on IMA statistics LCD failure notification TC statistics Link failure notification PMDstate Figure 3n.761 - IMA sublayer in layer reference model 6 Detailed requirements The detailed requirements and protocols for the MA sublayer shall be in accordance with ATM Fom af-phy-0086.001 “Inverse Multiplexing for ATM (MA) Specification Version 1.1 It7 March 1999 2.
