T1E1.4/98-004R2DRAFT ANSI (cid:226)(cid:226)T1.601-1998Revision ofANSI T1.601-1992American National Standardfor Telecommunications –Integrated Services Digital Network (ISDN)Basic Access Interface for Use on Metallic Loopsfor Application on the Network Side of the NT(Layer 1 Specification)SecretariatAlliance for Telecommunications Industry SolutionsApprovedAmerican National Standards Institute, Inc.AbstractThis interface standard was written to provide the minimal set of requirements to provide for satisfactorytransmission between the network and the NT, while conforming, wherever possible, with the I-series ofInternational Telecommunications Union - Telecommunications Standardization Sector (ITU-T)Recommendations, and while not compromising the principles of evolution expressed therein. Equipmentmay be implemented with additional functions and procedures.This standard presents the electrical characteristics of the integrated services digital network (ISDN) basicaccess signals appearing at the network side of the NT. It also describes the physical interface between thenetwork and the NT. The transport medium of the signal is a single twisted-wire pair that supports full-duplex(i.e., simultaneous two-way) service.
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`iContentsPageForeword..................................................................................................iii1Scope, purpose, and structure..............................................................12Normative reference............................................................................23Definitions..........................................................................................24Physical characteristics.......................................................................45Transmission method...........................................................................46Functional characteristics....................................................................97Electrical characteristics....................................................................188M-channel bit functions......................................................................219Environmental conditions...................................................................26Tables1Pin assignments for 8-position jack and plug.......................................27226 AWG PIC cable at 70°F.................................................................27324 AWG PIC cable at 70°F.................................................................28422 AWG PIC cable at 70°F.................................................................295Definitions of signals during start-up...................................................306Characteristics of dc metallic termination in the NT..............................307Power status bit assignments and messages.......................................318Messages required for command/response eoc mode...........................31Figures1Echo canceler with hybrid principle.....................................................322Interface on the network side of the NT...............................................3232B1Q encoding of 2B+D bit fields.......................................................334DSL framer functional description.......................................................335Example of 2B1Q quaternary symbols.................................................346Normalized pulse from NT appearing at interface.................................357Upper bound of power spectral density of signal from NTat interface.......................................................................................368Loops for testing received signal performance......................................379Laboratory test set-up for measuring BER...........................................4010PSD for simulated near end crosstalk (NEXT) for testing2B1Q system....................................................................................4111Crosstalk calibration impedance, Zc....................................................42
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`ii12Waveform for longitudinal noise..........................................................4213ISDN basic access 2B1Q DSL 1.5-millisecond basic frame....................42142B1Q superframe technique and overhead bit assignments...................4315DSL framing and overhead function temporal relationships...................4416Scrambler and descrambler................................................................4517State sequence for DSL transceiver start-up........................................4618NT loop testing states........................................................................4619MInimum return loss..........................................................................4720Measurement method for longitudinal output voltage............................4721Minimum longitudinal balance requirement..........................................4822Measurement method for longitudinal balance......................................4823Range of permissible sinusoidal jitter, signaloriginating from network.....................................................................4924Illustration of dc characteristics of the NT(bilateral switch and holding current)...................................................5025CRC-12 generator..............................................................................51AnnexesATest loops and performance measurements.........................................52BOvervoltage, surge protection, and EMC..............................................54CDSL start-up and activation................................................................56DLinearity measurement.......................................................................76EDiscussion of eoc addressing.............................................................77FSupporting information relating to dc metallic termination.....................80GPrimary constants of typical telephone cable........................................82HOptional powering across the interface................................................92JQuiet mode, insertion loss measurement test, and NTmetallic termination considerations for other countries..........................94KThe digital section for ISDN basic rate................................................95LChanges from ANSI T1.601 - 1992....................................................107MBibliography....................................................................................109
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`iiiForeword (This foreword is not part of American National Standard T1.601-1998.)This specification of the layer 1 characteristics of the ISDN basic access interfaceon the network side of the NT for use on metallic loops was initiated under theauspices of the Accredited Standards Committee on Telecommunications, T1.The link between the ISDN switch or remote digital terminal and the ISDN user forbasic access (up to two B-channels and a D-channel) is a critical component in theend-to-end digital path that is the basis of ISDN. Since a majority of users arepresently served by a single twisted pair of telephone wires, full-duplex (i.e.simultaneous two-way) service at rates sufficient to accommodate ISDN basicaccess must be provided over this single pair. The digital subscriber line thatprovides this link, using a single pair, is specified in this standard in terms of theinterface on the network side of the customer-end termination.This standard has been written to help ensure the proper interfacing of digitalsubscriber line units; i.e. customer-end terminating unit (ISDN NT1 or a unitincluding this function located at a customer premises) with a combination of theloop and network-end terminating unit (LT). It is expected that the customer-endterminating unit will normally be manufactured and provided independently of theloop and network-end termination.This specification is the second issue of the layer 1 characteristics of the ISDNbasic access interface on the network side for the NT for use on metallic loops, andsupersedes American National Standard for Telecommunications – Integratedservices digital network (ISDN) – Basic access interface for use on metallic loopsfor application on the network side of the NT (Layer 1 specification), ANSI T1.601-1992, in its entirety. The basic transmission format has not changed, andequipment designed to either issue of this standard should be interoperable. Theimplementation of the following technical enhancements requires a period of timewherein equipment that conforms to ANSI T1.601-1988 may continue to bedeployed. Many revisions were editorial in nature. These were made to improveclarity and consistency. No revisions of technical substance were made that wouldaffect interoperability of older and newer implementations. The more significantrevisions include:–provisions for more consistent application of the reference model, andterminology U reference point, network interface, etc.;–addition of an annex describing the “digital section”;–addition of material in annex C dealing with loopbacks;–addition of new information describing accidental ringing voltages in annexB;–revisions to conform to new terminology where appropriate;-revisions to the PSD mask to further restrict signal components above 300kHz.Though the extent of the revisions is small, this standard has been reissued in itsentirety to provide the reader with a single specification that is current andcomprehensive.There are 12 annexes in this standard. They are informative and are not consideredpart of this standard.Suggestions for improvement of this standard are welcome. They should be sent tothe Alliance for Telecommunications Industry Solutions, 1200 G Street, NW,Washington, DC 20005.This standard was processed and approved for submittal to ANSI by AccreditedStandards Committee on Telecommunications, T1. Committee approval of thestandard does not necessarily imply that all committee members voted for its
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`ivapproval. At the time it approved this standard, Accredited Standards Committee T1had the following members:
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`T1E1.4/98-004R2____________________________________________________________________________________AMERICAN NATIONAL STANDARDDRAFT ANSI T1.601-1998________________________________________________________________________________________________________________________1American National Standardfor Telecommunications –Integrated Services Digital Network (ISDN) –Basic Access Interface for Use on Metallic Loopsfor Application on the Network Side of the NT(Layer 1 Specification)1. Scope, purpose, and structure1.1 ScopeThe requirements of this standard apply to a single digital subscriber line (DSL) consisting of an LT, atwo-wire metallic cable pair, and an NT (see clause 3). The transmission system is designed to operateon two-wire twisted metallic cable pairs with mixed gauges.This standard is based on the use of cables without loading coils, but bridged taps are acceptable withthe exception of unusual situations. See 5.4 for a definition of cable plant over which the system shouldoperate.Specifically, the scope of this standard is as follows: - it describes the transmission technique used to support full-duplex service on a single twisted-wirepair;- it specifies both the input signal with which the NT must operate and the output signal that the NTmust produce across the U reference point;- it defines the line code to be used, and the spectral composition of the transmitted signal at the Ureference point;- it describes the electrical and mechanical specifications of the network interface at the U referencepoint;- it describes the organization of transmitted data into frames and superframes;- it defines the functions of the operations channel;- it describes the maintenance modes of the NT.Although this standard does not include, except for some aspects of the frame structure, any directrequirements concerning the network side of the interface, such requirements are implied. It shall beunderstood that the network side conforms to the standard if it interfaces appropriately with anyconforming NT or equivalent. Appropriate interfacing shall be understood to mean that the aspects of thenetwork service related to physical characteristics associated with the interface can be provided.1.2 PurposeThis interface standard was written to provide the minimal set of requirements to provide for satisfactorytransmission between the network and the NT, while conforming, wherever possible, with the I-Series ofthe International Telecommunications Union - Telecommunications Standardization Sector (ITU-T)Recommendations, and while not compromising the principles of evolution expressed therein. Equipmentmay be implemented with additional functions and procedures.
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`T1E1.4/98-004R2 DRAFT ANSI T1.601-19982This standard presents the electrical characteristics of the integrated services digital network (ISDN)basic access signal appearing at the network side of the NT. It also describes the physical interfacebetween the network and the NT. The transport medium of the signal is a single twisted-wire pair thatsupports full-duplex (i.e., simultaneous two-way) service.While this standard is written explicitly to describe the physical interface of the network and the NT, itsuse in other circumstances, such as equivalent use of NT1 functionalities behind an NT2 (e.g., a PBX) isnot prohibited.1.3 StructureClause 1 describes the scope, purpose, and structure of this document. Clause 2 lists referenceddocuments. Clause 3 lists definitions helpful in interpreting the specifications. Clause 4 describes thephysical characteristics of the interface over which the transmission method specified in the document inclause 5 is intended to operate. Clause 6 describes the functional characteristics of the transmissionmethod. Clause 7 describes the electrical characteristics of the interface. Clause 8 describes thefunctions and operating procedures associated with the overhead bits included with the transmitted data.Clause 9 describes the environmental conditions. Information on testing is given in annex A, whileinformation on surge protection and out-of-band energy is given in annex B. Annex C providesinformation on activation, annex D provides information on linearity measurements, annex E is adiscussion on embedded operations channel addressing, and annex F gives supporting informationrelating to dc metallic termination. Annex G contains tables of primary constants for telephone cable.Annex H gives a description of a method of NT powering using pins of the interface connector. Annex Jdiscusses options that may be appropriate if these requirements are adopted as national standards incountries that require NT powering over the loop. Annex K documents the changes in this revisedstandard from requirements given in ANSI T1.601-1992. Annex L consists of a bibliography forinformative purposes only of related standards and publications.2. Normative referenceThe following standard contains provisions which, through reference in this text, constitute provisions ofthis American National Standard. At the time of publication, the edition indicated was valid. All standardsare subject to revision, and parties to agreements based on this American National Standard areencouraged to investigate the possibility of applying the most recent edition of the standard indicatedbelow.ISO 8877:1987, Information processing systems – Interface connector and contact assignments for ISDNbasic access interface located at reference points S and T 1)3. Definitions3.1 basic access: A term used to describe a standardized combination of access channels thatconstitute the access arrangements for the majority of ISDN users; specifically, any of the followingcombinations of access channels: - one D-channel;- one B-channel plus one D-channel;- two B-channels plus one D-channel.3.2 B-channel: A 64-kbit/s channel that carries customer information, such as voice calls, circuit-switched data, or packet-switched data. 1) Available from the American National Standards Institute, 11 West 42nd Street, New York, NY 10036.
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`T1E1.4/98-004R2 DRAFT ANSI T1.601-199833.3 D-channel: An access channel carrying control or signaling information and, optionally,packetized information and telemetry. When a part of basic access, the D-channel has a capacity of 16kbit/s.3.4 digital subscriber line (DSL): A technology that provides full-duplex service on a single twistedmetallic pair at a rate sufficient to support ISDN basic access and additional framing, timing recovery,and operations functions. The physical termination of the DSL at the network end is the LT; the physicaltermination at the user end is the NT.3.5 echo cancellation: A technique used for implementing a DSL in which a replica of thetransmitted signal is used to remove echoes of this signal that may have mixed with and corrupted thereceived signal (see figure 1).3.6 integrated services digital network (ISDN): An ISDN provides a wide range of voice andnonvoice services within the same network using a limited set of connection types and multipurposeuser–network interface arrangements. A variety of implementation configurations is supported, includingcircuit-switched, packet-switched, and nonswitched connections and their concatenations. New servicesare arranged to be compatible with 64-kbit/s switched digital connections. Service features, maintenancecapabilities, and network management functions are provided through intelligence built into the networkand compatible intelligence in the user terminals.ISDNs will evolve over one or more decades from the existing telephone network into comprehensiveISDNs by progressively incorporating additional functions to provide for both existing and new services.Until then, interworking arrangements will provide for the inclusion of other capabilities such as circuit-switching and packet-switching of data. During the transition, equipment such as digital transmissionsystems using techniques such as frequency-division multiplexing, time-division multiplexing, time-compression multiplexing, time-division multiplex switching, and space-division multiplex switchingequipment will provide for the digital end-to-end connectivity of ISDNs. In the early stages of theevolution of ISDNs, some interim user–network arrangements may be needed to facilitate earlypenetration of digital service capabilities.3.7 interface point: The reference configuration for ISDN is shown in figure 2. It shows functionalgroups separated by reference points U and S/T.The network interface (NI) is located at the U reference point and is the point of demarcation between thecustomer premises equipment and the network.The NI at the U reference point has previously been called the U-interface.3.8 International Telecommunication Union (ITU): The ITU (part of UN) is a world-wideorganization within which governments and private sector coordinate the establishment and operationof telecommunication networks and services; it is responsible for the regulation, standardization,coordination and development of international telecommunications as well as the harmonization ofnational policies. The ITU is a specialized agency (since 1948) of the United Nations and is aninternational treaty organization. It traces its formal beginnings to 1865.3.9 International Telecommunications Union - Telecommunications Standardization Sector(ITU-T): The ITU-T is one of several ITU organizations. The ITU-T has responsibility fortelecommunications standards work done in the ITU. The general purpose of the ITU-T is to promoteand ensure the operation of international telecommunications systems.3.10 line termination (LT): The equipment that terminates the access line at the network end.3.11 M-channel: The maintenance channel is a 4-kbit/s channel that exists between the LT and theNT. It carries information for maintenance and other purposes relating to operation of the access. See6.2.3 and clause 8.3.12 network termination (NT): In this standard the equipment that terminates the DSL on thecustomer side of the interface. The NT function may be in an NT1, an NT2, or a TE. An NT1 is a networktermination of an access line that provides only physical layer functionality. An NT2 is a network
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`T1E1.4/98-004R2 DRAFT ANSI T1.601-19984termination with functionality that can include interfacing higher layer protocols. A TE is customerterminal equipment (e.g., a computer terminal) that may include network termination functions.3.13 network or network side: In this standard these terms represent the network side of theinterface or the network functions as seen from the interface.3.14 premises wiring (PW): Wiring on the customer’s premises on the customer’s side of the NI.3.15 reference points: Figure 2 shows functional groups TE, NT and NE, separated by the S/Treference point and the U reference point. Functional groups are sets of functions which may be neededin ISDN user access arrangements. Reference points are defined as conceptual regions separatingfunctional groups. (These descriptions are from ITU-T Recommendations I.410 and I.411.) In somedocumentation, e.g., T1.605, the S and T reference points are separately defined and are separated byan additional functional group, NT2. Distinction between the S and T reference points is not necessary inthis standard.4. Physical characteristics4.1 Wiring polarity integrityThe NT shall not be dependent on a specific polarity for the two wires of the access line as the pair maybe reversed.4.2 ConnectorFor single mountings, the NT shall connect to the network through a miniature 8-position nonkeyed jack.The cord from the NT shall terminate in a miniature 8-position nonkeyed plug. For multiple mountings(and PBXs), other connection arrangements may be appropriate. Except for pin assignments,specifications for the 8-position plug and jack shall be as described in ISO 8877-1987. The jack isequipped with the center two contacts (pins), which are used for the cable pair, commonly called tip (T)and ring (R). The terms tip and ring will not be used in this standard where their use can be avoidedbecause of the requirements given in 4.1. Table 1 gives the pin assignments for the 8-position jack andthe 8-position plug.NOTE - Figure 2 and Figure H.1 show a typical NT wiring configuration. The location and the connector at the network interface maydiffer, depending on the state and federal regulatory requirements, from the connector given in 4.2 for the NT.5. Transmission method5.1 GeneralThe transmission system uses the echo canceler with hybrid (ECH) principle to provide full duplexoperation over a two-wire subscriber loop. With the ECH method, as illustrated in figure 1, the echocanceler (EC) produces a replica of the echo of the near-end transmitted signal, which is then subtractedfrom the total received signal.The system is intended for service on twisted-pair cables, including about 99% coverage of the NorthAmerican nonloaded loop population. This equates to operation over cables up to the limits of 18-kilofoot(5.5-km) 1300-ohm resistance design, or about 42-dB loss at 40 kHz.The foregoing is a general description that is not a specific performance requirement. For laboratory testrequirements, see 5.4. Performance requirements for equipment and systems installed on actual loopsare beyond the scope of this standard.5.2 Line codeThe line code shall be 2B1Q (2 binary, 1 quaternary). The 2-bit binary pairs are converted intoquaternary symbols that are called “quats” in the following text. This is a 4-level pulse amplitudemodulation (PAM) code without redundancy.The user-data bit stream, comprised of two 64-kbit/s B-channels and a 16-kbit/s D-channel, entering theNT across the S/Treference point (i.e., crossing the S/T reference point toward the NT) and the
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`T1E1.4/98-004R2 DRAFT ANSI T1.601-19985equivalent bit stream entering the LT from the network side shall be grouped into pairs of digits (bitfields) for conversion to quats. In each pair of bits so formed, the first bit is called the sign bit and thesecond is called the magnitude bit. Figure 3 shows the relationship of the bits in the B- and D-channels toquats. The B- and D-channel bits are also scrambled before coding. M1 through M6 bits are also paired,scrambled, and coded in the same way. See 6.2, 6.3, and figure 4, for a functional description of thecoding, framing, and scrambling operations of the transceiver.Each pair of scrambled bits in either binary data stream that is converted to a quaternarysymbol shall be output from the transmitter at the interface, as specified in the following table:FirstSecondQuaternarybitbitsymbol(sign)(magnitude)(quat)10+311+101–100–3The four values listed under “Quaternary symbol” in the table should be understood as symbol names,not numerical values.At the receiver, each quaternary symbol is converted to a pair of bits by reversing the table,descrambled, and finally formed into a bit stream or bit streams representing B- and D-channels, and M-channel bits for maintenance and other purposes as described in clauses 6 and 8. The bits in the B- andD-channels are properly placed by reversing the relationship in figure 3.Figure 5 is an example of 2B1Q pulses over time. Square pulses are used only for convenience ofdisplay and do not in any way represent the specified shape of real 2B1Q pulses (see 5.3.1). Quatidentifications and bit representations, after scrambling (see 6.3), are given beneath the waveform. Timeflows from left to right.5.3 Pulses originating at the NTFor measurement reference purposes, the termination impedance shall be 135 ohms resistive over afrequency band of 0 Hz to 160 kHz for all the requirements of this clause.5.3.1 Pulse shapeThe transmitted pulse shall have the shape specified in figure 6.The pulse mask for the four quaternary symbols shall be obtained by multiplying the normalized pulsemask shown in figure 6 by 2.5 V, 5/6 V, –5/6 V, or –2.5 V. Compliance of transmitted pulses withboundaries of the pulse mask is not sufficient to ensure compliance with the power spectral densityrequirement and the absolute power requirement. Compliance with requirements in 5.3.2.1 and 5.3.2.2 isalso required.5.3.2 Signal power5.3.2.1 Power spectral densityThe upper bound of the power spectral density (PSD) of the signal transmitted by the NT shall be asshown in figure 7. Measurements to verify compliance with this requirement are to use a noise powerbandwidth of 10 kHz.Note: The PSD requirement in Figure 7 is changed in the 1998 edition, to restrict signal power at frequencies above 1.4 mHz.Implementations existing on the date of publication of the 1998 edition or that are new within a period of one year thereafter arespecifically exempt from this requirement. The requirement applies to all new implementations thereafter.5.3.2.1.1 Sliding window PSD requirementThe purpose of the sliding window is to perform a higher bandwidth measurement in order to make surethat different systems do not fill the entire allowable band with noise up to the limit shown in figure 7.above 300 kHz. The sliding window parameters are given in the following Table.
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`T1E1.4/98-004R2 DRAFT ANSI T1.601-19986PARAMETERVALUEBandwidth of sliding window1 MHzReference frequencyLower edgeStep Size10 kHzStart Frequency300 kHzStop Frequency29 MHzThe sliding window PSD shall be measured as the total average power within a 1 MHz sliding window (1MHz bandwidth). The result shall be less than -120 dBm/Hz or more than 10 dB below the PSD limitshown in figure 7. See the dashed line in figure 7. The requirement is applicable between 300 kHz and30 MHz.Note: The sliding window PSD requirement in Figure 7 is added in the 1998 edition, to further restrict signal power at frequenciesbetween 300 kHz and 30 MHz. Implementations existing on the date of publication of the 1998 edition or that are new within a periodof one year thereafter are specifically exempt from this requirement. The requirement applies to all new implementations thereafter.5.3.2.2 Total powerThe average power over multiple frames of a signal consisting of a framed sequence of symbols with asynchronization word and equiprobable symbols at all other positions shall be between 13.0 dBm and14.0 dBm (nominally 13.5 dBm) over the frequency band from 0 Hz to 80 kHz. The nominal peak of thelargest pulse shall be 2.5 V (see 5.3.1).5.3.3 Transmitter linearityThe pulses at the interface from the NT toward the network, corresponding to the symbol names +3, +1,–1, and –3 shall nominally all have the same shape and have the ratio 3:1:–1:–3. The pulses at theinterface received from the network, though distorted by the transmission medium, shall have the sameproperty, though this property is best checked at the source. Impairment resulting from deviations fromthis ratio is called nonlinearity. This nonlinearity is defined as the residual after subtracting a perfectlylinear signal (a linearity standard) from the transmitter output line signal. The linear signal is constructedfrom the same random data as is input to the transmitter and processed through a linear filter. Theparameters of the linear filter are first optimized to reduce the residual to a minimum. The test principles,hardware, and procedures are described further in annex D.The transmitted and received signals shall have sufficient linearity so that the residual rms signal is atleast 36 dB below the rms signal at the interface. This requirement applies under all normal transceiverconditions and over the prescribed range of sealing current (see 7.5.1).5.4 Received line signal characteristicsWhen the pulses described above are transmitted over the loop plant, as defined in 5.4.1, the NT shallreceive any random sequences of these pulses with a bit error ratio (BER) of less than 10 -7, as describedin the remainder of clause 5.5.4.1 Definition of loop plantFor the purpose of 5.4, the loop plant is defined as a set of 16 loops, one being a null (zero length) loop,and crosstalk and other impairments as specified in this clause and in 5.4.4. The make-ups of the 15non-null loops are presented in figure 8.The characteristics of the loops in figure 8 are precisely defined over a broad frequency range by meansof the primary constants listed in tables 2, 3, and 4. The tables give values of resistance per mile (R),inductance per mile (L), conductance per mile (G), and capacitance per mile (C) based on a commonly
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`T1E1.4/98-004R2 DRAFT ANSI T1.601-19987used model of polyethylene insulated cable (PIC) at approximately room temperature (70°F). Obviously,actual cable deviates from the precise model, depending on such factors as temperature, insulation type,manufacturer, and detailed manufacturing conditions. Further information on the test loops and on thecharacteristics of cable are given in annexes A and G.5.4.2 Performance test requirementSatisfactory performance (BER < 10 -7) with sufficient margin (see 5.4.3) is required when the NT isreceiving a pseudorandom sequence of pulses attenuated and distorted as would result fromtransmission over each loop from a nominal source and with simulated crosstalk, and other impairmentssuperimposed, and while transmitting a pseudorandom sequence. The added impairments are describedspecifically in 5.4.4 and 7.4.1. The following detailed description of the performance requirement in thepresence of simulated crosstalk and other impairments is in terms of a laboratory test, though the testdescription is intended only to clarify the interface requirement.5.4.3 MarginSatisfactory performance shall be obtained, as described in 5.4.4, with a margin of at least 6 dB with thenull loop and with test loops 4–15, listed in figure 8. It is desirable to obtain satisfactory performance witha margin of at least 0 dB with test loops 1–3.5.4.4 Test procedureTo perform the test, two transceivers are required, one for each end of the test loop, as shown in figure9. A pseudorandom binary source (PRBS) test signal (binary sequence) shall be applied at point A andreceived at point B. Another PRBS shall be applied at point C to create realistic echo conditions for thereceiver at that end. No pattern receiver is required at point D because only one direction is under test atone time.Point F shall be on a transceiver controlled by an independent external clock signal; point E shall be on atransceiver that derives timing from the received signal. When these tests are performed in a laboratory,the test loops are likely to be assembled from pairs on cable reels with both ends of the pair appearing inthe same laboratory. The tests shall be