1、INTERNATIONAL TELECOMMUNICATION UNIONITU-TI.432.1TELECOMMUNICATIONSTANDARDIZATION SECTOROF ITU(02/99)SERIES I: INTEGRATED SERVICES DIGITALNETWORKISDN user-network interfaces Layer 1RecommendationsB-ISDN user-network interface Physical layerspecification: General characteristicsITU-T Recommendation I
2、.432.1(Previously CCITT Recommendation)ITU-T I-SERIES RECOMMENDATIONSINTEGRATED SERVICES DIGITAL NETWORKFor further details, please refer to ITU-T List of Recommendations.GENERAL STRUCTURETerminology I.110I.119Description of ISDNs I.120I.129General modelling methods I.130I.139Telecommunication netwo
3、rk and service attributes I.140I.149General description of asynchronous transfer mode I.150I.199SERVICE CAPABILITIESScope I.200I.209General aspects of services in ISDN I.210I.219Common aspects of services in the ISDN I.220I.229Bearer services supported by an ISDN I.230I.239Teleservices supported by
4、an ISDN I.240I.249Supplementary services in ISDN I.250I.299OVERALL NETWORK ASPECTS AND FUNCTIONSNetwork functional principles I.310I.319Reference models I.320I.329Numbering, addressing and routing I.330I.339Connection types I.340I.349Performance objectives I.350I.359Protocol layer requirements I.360
5、I.369General network requirements and functions I.370I.399ISDN USER-NETWORK INTERFACESApplication of I-series Recommendations to ISDN user-network interfaces I.420I.429Layer 1 Recommendations I.430I.439Layer 2 Recommendations I.440I.449Layer 3 Recommendations I.450I.459Multiplexing, rate adaption an
6、d support of existing interfaces I.460I.469Aspects of ISDN affecting terminal requirements I.470I.499INTERNETWORK INTERFACES I.500I.599MAINTENANCE PRINCIPLES I.600I.699B-ISDN EQUIPMENT ASPECTSATM equipment I.730I.739Transport functions I.740I.749Management of ATM equipment I.750I.799Recommendation I
7、.432.1 (02/99) iITU-T RECOMMENDATION I.432.1B-ISDN USER-NETWORK INTERFACE PHYSICAL LAYERSPECIFICATION: GENERAL CHARACTERISTICSSummaryThis Recommendation covers Physical Layer general characteristics for transporting ATM cells atvarious bit rates, at the TBand SBreference points of the B-ISDN User-Ne
8、twork Interface (UNI).The I.432 series Recommendations are published as several Recommendations for different bit ratesand applications, some of which may be used to take advantage of existing building wiring andequipment. This Recommendation should be used with each of the other Recommendations.In
9、each Recommendation, functionality is presented in terms of Physical Media Dependent andTransmission Convergence sublayers, and both SDH-based and cell-based formats are included.SourceITU-T Recommendation I.432.1 was prepared by ITU-T Study Group 13 (1997-2000) and wasapproved under the WTSC Resolu
10、tion No. 1 procedure on the 15thof February 1999.KeywordsATM, B-ISDN, UNI, User Network Interface.Recommendation I.432.1 (02/99)iiFOREWORDITU (International Telecommunication Union) is the United Nations Specialized Agency in the field oftelecommunications. The ITU Telecommunication Standardization
11、Sector (ITU-T) is a permanent organ ofthe ITU. The ITU-T is responsible for studying technical, operating and tariff questions and issuingRecommendations on them with a view to standardizing telecommunications on a worldwide basis.The World Telecommunication Standardization Conference (WTSC), which
12、meets every four years,establishes the topics for study by the ITU-T Study Groups which, in their turn, produce Recommendationson these topics.The approval of Recommendations by the Members of the ITU-T is covered by the procedure laid down inWTSC Resolution No. 1.In some areas of information techno
13、logy which fall within ITU-Ts purview, the necessary standards areprepared on a collaborative basis with ISO and IEC.NOTEIn this Recommendation the term recognized operating agency (ROA) includes any individual, company,corporation or governmental organization that operates a public correspondence s
14、ervice. The termsAdministration, ROA and public correspondence are defined in the Constitution of the ITU (Geneva, 1992).INTELLECTUAL PROPERTY RIGHTSThe ITU draws attention to the possibility that the practice or implementation of this Recommendation mayinvolve the use of a claimed Intellectual Prop
15、erty Right. The ITU takes no position concerning the evidence,validity or applicability of claimed Intellectual Property Rights, whether asserted by ITU members or othersoutside of the Recommendation development process.As of the date of approval of this Recommendation, the ITU had received notice o
16、f intellectual property,protected by patents, which may be required to implement this Recommendation. However, implementors arecautioned that this may not represent the latest information and are therefore strongly urged to consult theTSB patent database. ITU 1999All rights reserved. No part of this
17、 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.Recommendation I.432.1 (02/99) iiiCONTENTSPage1 Scope 12 Background 13 References 14 Definitions and abbreviations. 14.1 D
18、efinitions14.2 Abbreviations . 25 Reference configuration . 25.1 Interface location with respect to reference configuration . 25.2 Interface location with respect to the customer installation. 36 Characteristics of the Physical Media Dependent (PMD) sublayer. 37 Functions provided by the Transmissio
19、n Convergence (TC) sublayer 37.1 Transfer capability 37.1.1 SDH-based 37.1.2 Cell-based 37.2 Transport-specific TC functions. 37.3 ATM-specific TC functions . 47.3.1 ATM cell format . 47.3.2 Header Error Control (HEC). 47.3.3 Cell delineation . 67.3.4 Scrambler operation 87.3.5 Idle cells 127.4 OAM
20、Implementation 128 Operational functions . 129 Power feeding. 12Appendix I Impact of random bit errors on cell delineation performance . 13Appendix II Distributed sample scrambler implementation example 14Recommendation I.432.1 (02/99) 1Recommendation I.432.1B-ISDN USER-NETWORK INTERFACE PHYSICAL LA
21、YERSPECIFICATION: GENERAL CHARACTERISTICS(Geneva, 1999)1 ScopeThis Recommendation covers Physical Layer general characteristics for transporting ATM cells atvarious bit rates, at the TBand SBreference points of the B-ISDN User-Network Interface (UNI).The I.432 series Recommendations are published as
22、 several Recommendations for different bit ratesand applications, some of which may be used to take advantage of existing building wiring andequipment. This Recommendation should be used with each of the other Recommendations.In each Recommendation, functionality is presented in terms of physical me
23、dia dependent andtransmission convergence sublayers, and both SDH-based and cell-based formats are included.2 BackgroundThis Recommendation was previously contained in Recommendation I.432 (as published inMarch 1993) along with characteristics specific to 155 520 kbit/s and 622 080 kbit/s.This Recom
24、mendation contains those characteristics that are general to all B-ISDN systems at theUNI. Other Recommendations of the I.432 series give relevant characteristics for the specific bitrates.3 ReferencesThe following ITU-T Recommendations and other references contain provisions which, throughreference
25、 in this text, constitute provisions of this Recommendation. At the time of publication, theeditions indicated were valid. All Recommendations and other references are subject to revision; allusers of this Recommendation are therefore encouraged to investigate the possibility of applying themost rec
26、ent edition of the Recommendations and other references listed below. A list of the currentlyvalid ITU-T Recommendations is regularly published.1 ITU-T Recommendation I.113 (1997), Vocabulary of terms for broadband aspects of ISDN.2 ITU-T Recommendation I.361 (1995), B-ISDN ATM layer specification.3
27、 ITU-T Recommendation I.432.2 (1996), B-ISDN User-network interface Physical layerspecification: 155 520 kbit/s and 622 080 kbit/s operation.4 Definitions and abbreviations4.1 DefinitionsNone.Recommendation I.432.1 (02/99)24.2 AbbreviationsThis Recommendation uses the following abbreviations.ATM Asy
28、nchronous Transfer ModeB-ISDN Broadband Integrated Services Digital NetworkB-NT Broadband Network TerminationB-NT1 Broadband Network Termination 1B-NT2 Broadband Network Termination 2B-TA Broadband Terminal AdaptorB-TE Broadband Terminal EquipmentCLP Cell Loss PriorityCRC Cyclic Redundancy CheckHEC
29、Header Error ControlIEC International Electrotechnical CommissionOAM Operations Administration and MaintenancePMD Physical Medium DependentPRBS Pseudo-Random Binary SequenceSDH Synchronous Digital HierarchyTC Transmission ConvergenceTE Terminal EquipmentUNI User-Network InterfaceVCI Virtual Channel
30、IdentifierVPI Virtual Path Identifier5 Reference configuration5.1 Interface location with respect to reference configurationAn interface point Iais adjacent to the B-TE or the B-NT2 on their network side; interface point Ibisadjacent to the B-NT2 and to the B-NT1 on their user side (see Figure 1).T1
31、302050-93IaIbB-TE B-NT2 B-NT1IbIaSB TBFigure 1/I.432.1 Reference configuration at reference point SB/TBRecommendation I.432.1 (02/99) 35.2 Interface location with respect to the customer installationThe interface points are located between the socket and the plug of the connector attached to theB-TE
32、, B-NT2 or B-NT1. The location of the interface point is shown in Figure 2.In this Recommendation, the term “B-NT“ is used to indicate network terminating layer 1 aspects ofB-NT1 and B-NT2 functional groups, and the term “TE“ is used to indicate terminal terminatinglayer 1 aspects of B-TE1, B-TA and
33、 B-NT2 functional groups, unless otherwise indicated.T1302060-93IaIbB-TE B-NTConnecting cordsWiring at thecustomer premisesNOTE The length of the connecting cord can be zero.Figure 2/I.432.1 Wiring configuration6 Characteristics of the Physical Media Dependent (PMD) sublayerRefer to the appropriate
34、bit rate specific Recommendation of the I.432 series.7 Functions provided by the Transmission Convergence (TC) sublayer7.1 Transfer capability7.1.1 SDH-basedThe transfer capability for ATM cells includes user information cells, signalling cells, OAM cells,unassigned cells and cells used for cell rat
35、e decoupling. It excludes physical layer overhead cells.7.1.2 Cell-basedFor cell-based systems, Physical Layer overhead cells include Physical Layer OAM cells and idlecells.7.2 Transport-specific TC functionsRefer to the appropriate bit rate specific Recommendation of the I.432 series for both SDH-b
36、asedand cell-based systems.Recommendation I.432.1 (02/99)47.3 ATM-specific TC functions7.3.1 ATM cell formatThe ATM cell is defined in Recommendation I.361 2. ATM cells may be carried in one of twoformats; as cells carried into an SDH-based frame structure, or as a continuous stream of cells in acel
37、l-based format.7.3.2 Header Error Control (HEC)7.3.2.1 Header Error Control functionsThe Header Error Control (HEC) covers the entire cell header. The code used for this function iscapable of either: single bit error correction; or multiple bit error detection.The detailed description of the HEC pro
38、cedure is given in 7.3.2.2. Briefly, the transmitting sidecomputes the HEC field value. The receiver has two modes of operation as shown in Figure 3. Thedefault mode provides for single-bit error correction but should only be applied while the celldelineation mechanism is in the SYNC state, and for
39、a cell-based Physical Layer while thedescrambler is in the steady state. Each cell header is examined and, if an error is detected, one oftwo actions takes place. The action taken depends on the state of the receiver. In “correction mode“only single bit errors can be corrected and the receiver switc
40、hes to “detection mode“. In “detectionmode“, all cells with detected header errors are discarded. When a header is examined and found notto be in error, the receiver switches to “correction mode“. The term “no action“ in Figure 3 means nocorrection is performed and no cell is discarded.T1811410-90No
41、 error detected(No action)CorrectionmodeDetectionmodeSingle-bit error detected(Correction)Error detected(Cell discarded)No errordetected(No action)Multibit errordetected(Cell discarded)Figure 3/I.432.1 HEC: Receiver mode of operationThe flow chart in Figure 4 shows the consequence of errors in the A
42、TM cell header. The errorprotection function provided by HEC provides both recovery from single-bit header errors, and a lowprobability of the delivery of cells with errored headers under bursty error conditions. The errorcharacteristics of fibre-based transmission systems appear to be a mix of sing
43、le-bit errors andrelatively large burst errors. For some transmission systems the error correction capability might notbe invoked.Recommendation I.432.1 (02/99) 5T1302150-93Incoming cellwith uncorruptedheaderIncoming cellwith corruptedheaderYes Noerrordetected?correctionmode?detectionYes NoNopermiss
44、ibleheader(Note 2)correctionappear possible?YesNo YesYesNovalid cell (Note 1)correct header(intended service)discarded cell(Note 3)valid cell (Note 1)errored header(unintended service)Function usuallyperformed by the ATM layerpermissibleheader(Note 2)intendedheaderreconstructed?(Note 4)NOTE 1 Defini
45、tion of “valid cell“: a cell where the header is declared by the Header Error Control process to be free of errors (see Recommendation I.113 1).NOTE 2 An example of an impermissible header is a header whose VPI/VCI is neither allocated to a connection nor pre-assigned to a particular function (idle
46、cell, OAM cell, etc.) in many instances, the ATM layer will decide if the cell header is permissible.NOTE 3 A cell is discarded if its header is declared to be invalid; or if the header is declared to be valid and the resulting header is impermissible.NOTE 4 Definition of “intended“ header: the head
47、er generated by the transmitting device, as it was before being corrupted by one or more errors.Figure 4/I.432.1 Consequence of errors in ATM cell headerAppendix I gives information on how random bit errors impact the probability of occurrence ofdiscarded cells and valid cells with errored headers.7
48、.3.2.2 Header error control sequence generationThe transmitter calculates the HEC value across the entire ATM cell header and inserts the result inthe appropriate header field.The notation used to describe the header error control is based on the property of cyclic codes.(For example code vectors su
49、ch as 1000000100001 can be represented by a polynomialP(x) = x12+ x5+ 1). The elements of an n-element code word are thus the coefficients of apolynomial of order n1. In this application, these coefficients can have the value 0 or 1 and theRecommendation I.432.1 (02/99)6polynomial operations are performed using modulo 2 operations. The polynomial representing thecontent of a header excluding the HEC field is generated using the first bit of a header as thecoefficient of the highest order term.The HEC field sha
