SIST ETS 300 012-1 E2:2003
(Main)Integrated Services Digital Network (ISDN); Basic User-Network Interface (UNI); Part 1: Layer 1 specification
Integrated Services Digital Network (ISDN); Basic User-Network Interface (UNI); Part 1: Layer 1 specification
This second edition of ETS 300 012 will incorporate the test suite specification and referenced material from ITU-T I.430
Digitalno omrežje z integriranimi storitvami (ISDN) – Osnovni vmesnik uporabnik-omrežje (UNI) – 1. del: Specifikacija prve plasti
General Information
Standards Content (Sample)
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.Digitalno omrežje z integriranimi storitvami (ISDN) – Osnovni vmesnik uporabnik-omrežje (UNI) – 1. del: Specifikacija prve plastiIntegrated Services Digital Network (ISDN); Basic User-Network Interface (UNI); Part 1: Layer 1 specification33.080Digitalno omrežje z integriranimi storitvami (ISDN)Integrated Services Digital Network (ISDN)ICS:Ta slovenski standard je istoveten z:ETS 300 012-1 Edition 2SIST ETS 300 012-1 E2:2003en01-december-2003SIST ETS 300 012-1 E2:2003SLOVENSKI
STANDARD
EUROPEANETS 300 012-1TELECOMMUNICATIONOctober 1998STANDARDSecond EditionSource: TMReference: RE/TM-03038-1ICS:33.020Key words:Basic, ISDN, layer 1, transmission, UNI, rateIntegrated Services Digital Network (ISDN);Basic User Network Interface (UNI);Part 1: Layer 1 specificationETSIEuropean Telecommunications Standards InstituteETSI SecretariatPostal address: F-06921 Sophia Antipolis CEDEX - FRANCEOffice address: 650 Route des Lucioles - Sophia Antipolis - Valbonne - FRANCEInternet: secretariat@etsi.fr - http://www.etsi.fr - http://www.etsi.orgTel.: +33 4 92 94 42 00 - Fax: +33 4 93 65 47 16Copyright Notification: No part may be reproduced except as authorized by written permission. The copyright and theforegoing restriction extend to reproduction in all media.© European Telecommunications Standards Institute 1998. All rights reserved.SIST ETS 300 012-1 E2:2003
Page 2ETS 300 012-1: October 1998Whilst every care has been taken in the preparation and publication of this document, errors in content,typographical or otherwise, may occur. If you have comments concerning its accuracy, please write to"ETSI Standards Making Support Dept." at the address shown on the title page.SIST ETS 300 012-1 E2:2003
Page 3ETS 300 012-1: October 1998ContentsForeword.91Scope.112Normative references.113Definitions, symbols and abbreviations.123.1Definitions.123.1.1General definitions.123.1.2Definition of services.123.1.3Primitives between layer 1 and other entities.133.1.4Modes of operation.133.1.5Definition of states.133.1.5.1TE states.133.1.5.2NT States.143.2Symbols.143.3Abbreviations.144Primitives associated with layer 1.155Wiring configurations and location of interface points.155.1General.155.1.1Point-to-point configuration.155.1.2Point-to-multipoint configuration.155.1.3 Location of the interfaces.155.2Support of wiring configurations.165.2.1 Wiring polarity integrity.165.2.2NT and TE associated wiring.166Functional characteristics.176.1Interface functions.176.1.1B-channel.176.1.2Bit timing.176.1.3Octet timing.176.1.4Frame alignment.176.1.5D-channel.176.1.6D-channel access procedure.176.1.7Power feeding.176.1.8Deactivation.176.1.9Activation.176.2Interchange circuits.176.3Connected/disconnected indication.186.3.1TEs powered across the interface.186.3.2TEs not powered across the interface.186.3.3Indication of connection status.186.4Frame structure.196.4.1Bit rate.196.4.2Binary organization of the frame.196.4.2.1TE to NT.196.4.2.2NT to TE.206.4.2.3Relative bit positions.206.5Line code.206.6Timing considerations.217Interface procedures.217.1D-channel access procedure.217.1.1Interframe (layer 2) time fill.21SIST ETS 300 012-1 E2:2003
Page 4ETS 300 012-1: October 19987.1.2D-echo channel.217.1.3D-channel monitoring.217.1.4Priority mechanism.217.1.5Collision detection.227.2Activation/deactivation.227.2.1Activate primitives.227.2.2Deactivate primitives.227.2.3Management primitives.227.2.4Valid primitive sequences.237.3Signals.257.4Activation/deactivation procedure for TEs.257.4.1General TE procedures.257.4.2Specification of the procedure.267.5Activation/deactivation for NTs.267.5ANon-activating/non-deactivating NTs.267.6Timer values.267.7Activation times.267.7.1TE activation times.267.7.2NT activation times.307.8Deactivation times.318Frame alignment procedures.318.1Frame alignment procedure in the direction NT to TE.318.1.1Loss of frame alignment.318.1.2Frame alignment.318.2Frame alignment in the direction TE to NT.318.2.1Loss of frame alignment.318.2.2Frame alignment.328.3Multiframing.328.4Idle channel code on the B channels.329Electrical characteristics.329.1Bit rate.329.1.1Nominal rate.329.1.2Tolerance.329.2Jitter and bit-phase relationship between TE input and output.329.2.1Test configurations.329.2.2Timing extraction jitter.339.2.3Total phase deviation input to output.349.3NT jitter characteristics.369.4Termination of the line.369.5Transmitter output characteristics.369.5.1Transmitter output impedance.369.5.1.1NT transmitter output impedance.369.5.1.2TE transmitter output impedance.379.5.2Test load impedance.379.5.3Pulse shape and amplitude (binary ZERO).379.5.3.1Pulse shape.379.5.3.2Nominal pulse amplitude.389.5.4Pulse unbalance.389.5.4.1Pulse amplitude when transmitting a high density pattern.389.5.4.2Pulse unbalance of an isolated couple of pulses.399.5.5Voltage on other test loads (TE only).399.5.5.1400 W load.399.5.5.25,6 W load.399.5.6Unbalance about earth.399.5.6.1Longitudinal conversion loss.399.5.6.2Output signal balance.429.6Receiver input characteristics.429.6.1Receiver input impedance.429.6.1.1TE receiver input impedance.429.6.1.2NT receiver input impedance.429.6.2Receiver sensitivity - Noise and distortion immunity.42SIST ETS 300 012-1 E2:2003
Page 5ETS 300 012-1: October 19989.6.2.1TEs.429.6.2.2NTs for short passive bus (fixed timing).439.6.2.3NTs for both point-to-point and short passive busconfigurations (adaptive timing).449.6.2.4NTs for extended passive bus wiring configurations.449.6.2.5NTs for point-to-point configurations only.449.6.3NT receiver input delay characteristics.459.6.3.1NT for short passive bus.459.6.3.2NT for both point-to-point and passive bus.459.6.3.3NT for extended passive bus.459.6.3.4NT for point-to-point only.459.6.4Unbalance about earth.459.7Isolation from external voltages.469.8Interconnecting media characteristics.469.9Standard ISDN basic access TE cord.4610Power Feeding.4610.1Reference configuration.4610.1.1Functions specified at the access leads.4810.1.2Provision of power sources and sinks.4810.2Power available from NT.4810.2.1Power source 1 normal and restricted mode.4810.2.2Minimum voltage at NT from power source 1.4910.2.2.1Normal power conditions.4910.2.2.2Restricted power conditions.4910.2.3Minimum voltage of power source 2.4910.3Power available at a TE.4910.3.1Power source 1 - phantom mode.4910.3.1.1Normal power conditions.4910.3.1.2Restricted power conditions.4910.3.2Power source 2 - optional third pair.4910.3.2.1Normal power conditions.4910.3.2.2Restricted power conditions.4910.4Power source 1 consumption.5010.4.1Normal power conditions.5010.4.2Restricted power conditions.5010.4.2.1Power Available to a TE "designated" for restricted poweroperation.5010.4.2.2Power available to "non-designated" TEs.5110.5Galvanic isolation.5110.6Current transient.5110.6.1Current/time limitations for TEs.5110.6.2TE designed to minimize power disturbance.5310.6.2.1Optimized current/time mask.5310.6.2.2Alternative current/time mask for optimized TEs.5510.6.3Power source switch-over.5510.6.3.1Power source switch-over time.5510.6.3.2Restricted mode power source requirements underoverload conditions.5510.6.4Other TE requirements.5510.6.4.1Minimum TE start-up current.5510.6.4.2Protection against short term interruptions.5610.6.4.3Behaviour at the switch-over.5610.6.5Other power source requirements.5710.6.5.1Power source 1 restricted.5710.6.5.2Power source 1 normal.5710.6.5.3Requirements for type (a) sources.5710.6.5.4Requirements for both types of sources.5710.6.5.4.1Switch-on surge capability.5710.6.5.4.2TE connection surge capability.5810.7Current unbalance.5810.7.1Direct current unbalance.5810.7.1.1dc unbalance of power source 1.58SIST ETS 300 012-1 E2:2003
Page 6ETS 300 012-1: October 199810.7.1.2dc unbalance of power sink 1.5810.7.1.3Differential resistance in a pair of the installation wiring.5910.7.2Current unbalance in a pair.5910.8Additional requirements for an APS.6010.8.1Power available for an APS.6010.8.2APS switch-on time.6010.8.3APS switch-off time.6010.8.4APS power consumption when off.6010.8.5Dynamic behaviour of an APS.6010.9Additional requirements for NT1 restricted mode source for compatibility with an APS.6010.9.1Power source 1 restricted mode back-off.6010.9.2Power source 1 restricted mode power up.6110.9.3NT1 power consumption from APS normal mode.6111Interface connector contact.61Annex A (informative):Wiring configurations and round trip delay considerations used as a basis forelectrical characteristics.62A.1Introduction.62A.2Wiring configurations.62A.2.1Point-to-multipoint.62A.2.1.1Short passive bus (Figure A.1).62A.2.1.2Extended passive bus (Figure A.2).63A.2.2Point-to-point (Figure A.3).63Annex B (normative):Test configurations.65Annex C (normative):Test loopbacks defined for the basic UNI.67C.1Introduction.67C.2Loopback mechanism definitions.67C.3Test loopback reference configuration.68C.4Test loopback characteristics.69Annex D (normative):Additional requirements applicable to the (explicit) S reference point.70D.1Introduction.70D.2References.70D.3Definitions.70D.3.1Private Network Termination (PNT).70D.3.2Terminal Equipment (TE).70D.4Conformance.70D.5Requirements.70D.6Provision of power.70Annex E (informative):SDL representation of a possible implementation of the D-channel access.71Annex F (informative):SDL representation of activation/deactivation procedures for TEs and NTs.72F.1SDL representation of activation/deactivation procedures for TEs.72F.2SDL representation of activation/deactivation procedures for NTs.72SIST ETS 300 012-1 E2:2003
Page 7ETS 300 012-1: October 1998Annex G (informative):Multiframing mechanism.80G.1Multiframing.80G.1.1General mechanism.80G.1.2Q-bit position identification algorithm.80G.1.3TE multiframe identification.81G.2S-channel structuring algorithm.81Bibliography.83History.84SIST ETS 300 012-1 E2:2003
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Page 9ETS 300 012-1: October 1998ForewordThis second edition European Telecommunication Standard (ETS) has been produced by the ETSITechnical Committee Transmission and Multiplexing (TM).This ETS concerns the basic User Network Interface (UNI) for the Integrated Services Digital Network(ISDN) and consists of 7 parts as follows:Part 1:"Layer 1 specification";Part 2:"Implementation Conformance Statement (ICS) and Implementation eXtra Information forTesting (IXIT) specification for interface IA";Part 3:"Implementation Conformance Statement (ICS) and Implementation eXtra Information forTesting (IXIT) specification for interface IB";Part 4:"Conformance test specification for interface IA";Part 5:"Conformance test specification for interface IB";Part 6:"Abstract Test Suite (ATS) specification for interface IA";Part 7:"Abstract Test Suite (ATS) specification for interface IB";and is based on ITU-T Recommendation I.430 [10].Transposition datesDate of adoption of this ETS:18 September 1998Date of latest announcement of this ETS (doa):31 January 1999Date of latest publication of new National Standardor endorsement of this ETS (dop/e):31 July 1999Date of withdrawal of any conflicting National Standard (dow):31 July 1999SIST ETS 300 012-1 E2:2003
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Page 11ETS 300 012-1: October 19981ScopeThis part 1 of ETS 300 012 specifies requirements for the ISDN basic rate UNI including the physical,electrical and functional characteristics and the information exchange with higher layers. This ensures thatinterface implementations in an ISDN equipment for use with ISDN basic access is portable within Europewith regard to layer 1 interface aspects and that interworking with higher layer protocols for ISDN issupported.This ETS is applicable to equipment having interface IA or IB for the connection to the ISDN basic accessintended to be installed on customer premises according to ITU-T Recommendation I.411 [9], this ETS isfor application to interfaces at reference points S, T and S/T (coincident S and T) of the ISDN referenceconfiguration.For the case where this ETS is applied to the T and the S/T reference point, the main body of this part 1 ofthe ETS and the parts 6 and 7 are normative.For the case where this ETS is applied to the S reference point, annex A to this part 1 of the standard isalso normative.This ETS does not specify:-safety requirements;-interface or equipment overvoltage protection requirements;-immunity requirements against electromagnetic interference;-emission limitation requirements.2Normative referencesThis ETS incorporates by dated and undated reference, provisions from other publications. Thesenormative references are cited at the appropriate places in the text and the publications are listedhereafter. For dated references, subsequent amendments to or revisions of any of these publicationsapply to this ETS only when incorporated in it by amendment or revision. For undated references the latestedition of the publication referred to applies.[1]CCITT Recommendation G.117 (1988): "Transmission aspects of unbalanceabout earth".[2]CCITT Recommendation I.412 (1988): "ISDN user-network interfaces; interfacestructures and access capabilities".[3]CCITT Recommendation X.211 (1988): "Physical service definition of opensystems interconnection for CCITT applications".[4]EN 28877 (1993): "Information technology; Telecommunications and informationexchange between systems; Interface connector and contact assignment forISDN Basic Access Interface located at reference points S and T(ISO/IEC 8877:1992)".[5]EN 60603-7 (1993): "Connectors for frequencies below 3 MHz for use withprinted boards; Part 7: Detail specification for connectors, 8-way, including fixedand free connectors with common mating features; (IEC 603-7:1990) (S)".[6]ENV 41004: "Reference Configuration for Connectivity Relations of PrivateTelecommunication Network Exchanges".[7]ETS 300 047-3 (1992): "Integrated Services Digital Network (ISDN); Basicaccess - safety and protection; Part 3: Interface Ia - protection".[8]ISO/IEC 9646-1 (1994): "Information technology; Open SystemsInterconnection; Conformance Testing Methodology and Framework; Part 1:General concepts".SIST ETS 300 012-1 E2:2003
Page 12ETS 300 012-1: October 1998[9]ITU-T Recommendation I.411 (1993): "ISDN user-network interfaces; referenceconfigurations".[10]ITU-T Recommendation I.430 (1995): "Basic user-network interface; layer 1specification".[11]EN 50081: "Electromagnetic compatibility; Generic emission standard".3Definitions, symbols and abbreviations3.1DefinitionsFor the purposes of this ETS, the following definitions apply:3.1.1General definitionsbasic access: A user-network access arrangement that corresponds to the interface structure composedof two B-channels and one D-channel. The bit rate of the D-channel for this type of access is 16 kbit/s.Implementation Conformance Statement (ICS): See ISO/IEC 9646-1 [8], subclause 3.4.6.Integrated Services Digital Network (ISDN): An integrated services network that provides digitalconnections between UNIs.interface: This ETS defines the layer 1 characteristics of the UNI to be applied at the S or T referencepoints for the basic interface structure defined in CCITT Recommendation I.412 [2]. The referenceconfiguration for the interface is defined in ITU-T Recommendation I.411 [9] and is reproduced in figure 1.Reference pointFunctional groupTransmissionLineNT1TSSRa)b)NT2TE1TE2TAFigure 1: Definition of interface points according to the ISDN reference configurationNetwork Termination (NT): The term NT is used to indicate network terminating layer 1 aspects of NT1and NT2 functional groups unless otherwise indicated. However, in subclauses 3.1.5 and 7.2 the term NTis used to indicate the layer 1 network side of the basic access interface.Terminal Equipment (TE): The term TE is used to indicate terminal terminating layer 1 aspects of TE1,TA and NT2 functional groups, unless otherwise indicated. However, in subclauses 3.1.5 and 7.2, theterm TE is used to indicate the layer 1 terminal side of the basic access interface.3.1.2Definition of servicesservices required from the physical medium: Layer 1 of this interface requires a balanced metallictransmission medium, for each direction of transmission, capable of supporting 192 kbit/s.SIST ETS 300 012-1 E2:2003
Page 13ETS 300 012-1: October 1998services provided to layer 2: Layer 1 provides the following services to layer 2 and the managemententity.transmission capability: Layer 1 provides the transmission capability, by means of appropriatelyencoded bit streams, for the B- and D-channels and the related timing and synchronization functions.activation/deactivation: Layer 1 provides the signalling capability and the necessary procedures toenable customer TEs and/or NTs to be deactivated when required and reactivated when required. Theactivation and deactivation procedures are defined in subclause 7.2.D-channel access: Layer 1 provides the signalling capability and the necessary procedures to allow TEsto gain access to the common resource of the D-channel in an orderly fashion while meeting theperformance requirements of the D-channel signalling system. These D-channel access controlprocedures are defined in subclause 7.1.maintenance: Layer 1 provides the signalling capability, procedures and necessary functions at layer 1 toenable maintenance functions to be performed.status indication: Layer 1 provides an indication to the higher layers of the status of layer 1.3.1.3Primitives between layer 1 and other entitiesPrimitives represent, in an abstract way, the logical exchange of information and control between layer 1and other entities. They neither specify nor constrain the implementation of entities or interfaces.3.1.4Modes of operationBoth point-to-point and point-to-multipoint modes of operation, as described below, are intended to beaccommodated by the layer 1 characteristics of the UNI. In this ETS, the modes of operation apply only tothe layer 1 procedural characteristics of the interface and do not imply any constraints on modes ofoperation at higher layers.Point-to-point operation: This mode of operation at layer 1 implies that only one source (transmitter) andone sink (receiver) are active at any one time in each direction of transmission at an S or T referencepoint. (Such operation is independent of the number of interfaces which may be provided on a particularwiring configurations - see clause 5).Point-to-multipoint operation: This mode of operation at layer 1 allows more than one TE (source andsink pair) to be simultaneously active at an S or T reference point. (The multipoint mode of operation maybe accommodated, as discussed in clause 5, with point-to-point or point-to-multipoint wiringconfigurations).3.1.5Definition of states3.1.5.1TE statesState F1 (INACTIVE): In this inactive (powered-off) state, the TE is not transmitting and cannot detect thepresence of any input signals. In the case of locally powered TEs which cannot detect theappearance/disappearance of power source 1 or 2, this state is entered when local power is not present.For TEs which can detect power source 1 or power source 2, this state is entered whenever loss of power(required to support all TEI functions) is detected, or when the absence of power from source 1 or 2,whichever power source is used for determining the connection status, is detected.State F2 (SENSING): This state is entered after the TE has been powered on but has not determined thetype of signal (if any) that the TE is receiving. When in this state, a TE may go to a low-powerconsumption mode as specified in subclause 6.1.8.State F3 (DEACTIVATED): This is the deactivated state of the physical protocol. Neither the NT nor theTE is transmitting. When in this state, a TE may go to a low-power consumption mode as specified insubclause 6.1.8.SIST ETS 300 012-1 E2:2003
Page 14ETS 300 012-1: October 1998State F4 (AWAITING Signal): When the TE is requested to initiate activation by means of aPH-ACTIVATE REQUEST primitive, it transmits a signal (INFO 1) and waits for a response from the NT.State F5 (IDENTIFYING Input): At the first receipt of any signal from the NT, the TE ceases to transmitINFO 1 and awaits identification of signal INFO 2 or INFO 4.State F6 (SYNCHRONIZED): When the TE receives an activation signal (INFO 2) from the NT, itresponds with a signal (INFO 3) and waits for normal frames (INFO 4) from the NT.State F7 (ACTIVATED): State F7 is the only state where B and D channel contain operational data. Thisis the normal activate state with the protocol activated in both directions.State F8 (LOST Framing): This is the condition when the TE has lost frame synchronization and isawaiting re-synchronization by receipt of INFO 2 or INFO 4 or deactivation by receipt of INFO 0.3.1.5.2NT StatesState G1 (DEACTIVATED): In this deactivated state, the NT is not transmitting. When in this state, an NTmay go to a low-power consumption mode as specified in subclause 6.1.8.State G2 (PENDING Activation): In this partially active state the NT sends INFO 2 while waiting forINFO 3. This state will be entered on request by higher layers, by means of a PH-ACTIVATE REQUESTprimitive, or on the receipt of INFO 0 or lost framing while in the active state (G3). The choice to eventuallydeactivate is up to higher layers at the network side.State G3 (ACTIVE): This is the normal active state where the NT and TE are active with INFO 4 andINFO 3, respectively. A deactivation may be initiated by the NT system management, by means of anMPH-DEACTIVATE REQUEST primitive, or the NT may be the active state all the time, under non-faultconditions.State G4 (PENDING Deactivation): When the NT wishes to deactivate, it may wait for a timer to expirebefore returning to the deactive state.3.2SymbolsFor the purposes of this ETS, the following symbols apply:ONEBinary "1"ZEROBinary "0"3.3AbbreviationsFor the purposes of this ETS, the following abbreviations apply:APSAuxiliary Power Sourcedcdirect currentHDLCHigh level Data Link ControlICSImplementation Conformance StatementIUTImplementation Under TestIXITImplementation eXtra Information for TestingNTNetwork TerminationPBXPrivate Branch eXchangePTNXPrivate Telecommunication Network eXchangeTETerminal EquipmentTEITerminal Endpoint IdentifierSIST ETS 300 012-1 E2:2003
Page 15ETS 300 012-1: October 19984Primitives associated with layer 1The primitives to be passed across the layer 1/2 boundary or to the management entity and parametervalues associated with these primitives are defined and summarized in table 1. For description of thesyntax and use of the primitives, refer to CCITT Recommendation X.211 [3] and relevant detaileddescriptions in clause 7.Table 1: Primitives associated with layer 1GenericSpecific nameParameterMessage unit contentREQUESTINDICATIONPriorityindicatorMessageunitL1<->L2PH-DATAX(note 1)XX(note 2)XLayer 2 peer-to-peermessagePH-ACTIVATEXX--PH-DEACTIVATE-X--M<->L1MPH-ERROR-X-XType of error or recoveryfrom a previously reportederrorMPH-ACTIVATE-X--MPH-DEACTIVATEXX--MPH-INFORMATION-X-XConnected/disconnectedNOTE 1:PH-DATA REQUEST implies underlying negotiation between layer 1 and layer 2 for theacceptance of the data.NOTE 2:Priority indication applies only to the request type.5Wiring configurations and location of interface points5.1GeneralThe electrical characteristics of the UNI are determined on the basis of certain assumptions about thevarious wiring configurations which may exist in the user premises. These assumptions are identified intwo major configuration descriptions, subclauses 5.1.1 and 5.1.2, together with additional materialcontained in annex A. Figure 2 shows a general reference configuration for wiring in the user premises.5.1.1Point-to-point configurationA point-to-point wiring configuration implies that only one source (transmitter) and one sink (receiver) areinterconnected on an interchange circuit.5.1.2Point-to-multipoint configurationA point-to-multipoint wiring configuration allows more than one source to be connected to the same sink ormore than one sink to be connected to the same source on an interchange circuit. Such distributionsystems are characterized by the fact that they contain no active logic elements performing functions(other than possibly amplification or regeneration of the signal).5.1.3 Location of the interfacesThe wiring in the user premises is considered to be one continuous cable run with jacks for the TEs andNT attached directly to the cable or using stubs less than one metre in length. The jacks are located atinterface points IA and IB (see figure 2). One interface point, IA, is adjacent to each TE. The other interfacepoint IB, is adjacent to the NT. However, in some applications, the NT may be connected to the wiringwithout the use of a jack or with a jack which accommodates multiple interfaces (e.g., when the NT is aport on a PBX). The required electrical characteristics (described in clause 9) for IA and IB are different insome aspects.SIST ETS 300 012-1 E2:2003
Page 16ETS 300 012-1: October 1998TE0BNTTE1TEnIIIIA0AnBTRTRA1ATR Terminating ResistorIElectrical InterfaceALocation of IA when the terminating resistor (TR) is included in the TEBLocation of IB when the terminating resistor (TR) is included in the NTFigure 2: Reference configuration for wiring in the user premises location5.2Support of wiring configurations5.2.1 Wiring polarity integrityFor a point-to-point wiring configuration, the two wires of the interchange circuit pair may be reversed.However, for point-to-multipoint wiring configuration, the wiring polarity integrity of the interchange circuit(TE-to-NT direction) shall be maintained between TEs (see the reference configuration given insubclause 10.1, figure 19).In addition, the wires of the optional pairs, which may be provided for powering, may not be reversed ineither configuration.5.2.2NT and TE associated wiringThe wiring from the TE or the NT to its appropriate jack affects the interface electrical characteristics. ATE, or an NT that is not permanently connected to the interface wiring, shall be equipped with either of thefollowing for connection to the interface point (IA and IB, respectively):-a hard wired connecting cord (of not more than ten metres in the case of a TE, and not more thanthree metres in the case of an NT) and a suitable plug, or;-a jack with a connecting cord (of not more than ten metres in the case of a TE, and not more thanthree metres in the case of an NT) which has a suitable plug at each end.Normally, these requirements apply to the interface point (IA and IB, respectively), and the cord forms partof the associated TE or NT. However, as a national option, where the terminating resistors are connectedinternally to the NT, the connecting cord shall be considered as an integral part of the interface wiring. Inthis case, the requirements of this ETS shall be applied to the NT at the connection of the connecting cordto the NT. Note that the NT shall attach directly to the interface wiring without a detachable cord. Also notethat the connector, plug and jack used for the connection of the detachable cord to the NT is subject tostandardization. Refer also to clause 11.Although a TE may be provided with a cord of less than five metres in length, it shall meet therequirements of this ETS with a cord having a minimum length of five metres. As specified above, the TEcord may be detachable. Such a cord may be provided as a part of the TE, or the TE may be designed toconform to the electrical characteristics specified in clause 9 with a standard ISDN basic access TE cordconforming to the requirements specified in subclause 9.9 of this ETS and having the maximum permittedcapacitance.The use of an extension cord, of up to 25 metres in length, with a TE is permitted but only onpoint-to-point wiring configurations. (The total attenuation of the wiring and of th
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