1、INTERNATIONAL TELECOMMUNICATION UNION)45G134 TELECOMMUNICATION (03/93)STANDARDIZATION SECTOROF ITU$)4!,G0G03%#4)/.3G0G0!.$G0G0$)4!,G0G0,).%G0G03934%-3$)4!,G0G042!.3-)33)/.G0G03934%-G0G0/.-%4!,)#G0G0,/#!,G0G0,).%3G0G0 bit sequence independenttransmission of two B-channels and one D-channel as defined
2、 in Recommendation I.412 and the supplementaryfunctions of the access digital section defined in Recommendation I.603 for operation and maintenance.This Recommendation describes 4 transmission systems using different line codes and transmission methods. They aregiven in Appendices I to IV as example
3、s following the understanding that only one system should be recommended andprovided in an annex to this Recommendation when this is achieved in future.NOTE The main aspects which have made it impossible to achieve this objective are for example: local line electrical conditions; maintenance require
4、ments and line testing; EMC requirements; safety and protection requirements; local network evolution aspects.The individual appendices to this Recommendation distinguish core specifications from extension specifications. Theextension specifications are given in an annex to the relevant appendix.The
5、 core specifications consist of those aspects which are expected to be common to all applications using a particulartype of transmission technique. They correspond to the functions usually provided within typical VLSI transceiverintegrated circuits or are associated with the transmission characteris
6、tics at the 2-wire port.The extension functions generally correspond to NT/LT functions which are in some cases provided external to thetransceiver integrated circuits. Where a definition of an extension function is provided and the application is specified inthe relevant annex it is strongly recomm
7、ended that the application is not changed unless there is a need to change thedefinition of the function itself.The terminology used in this Recommendation is contained in Recommendations I.112 and G.701.1.2 DefinitionFigure 1 shows the boundaries of the digital transmission system in relation to th
8、e access digital section.The concept of the access digital section is used in order to allow a functional and procedural description and a definitionof the network requirements. Note that the reference points T and V1are not identical and therefore the access digitalsection is not symmetric.The conc
9、ept of a digital transmission system is used in order to describe the characteristics of an implementation, using aspecific medium, in support of the access digital section.2 Recommendation G.961 (03/93)T1814280-92/d01Digital transmission system(Note)Reference point Reference pointAccess digital sec
10、tionTE NT1 LT ETNOTE In this Recommendation digital transmission system refers to a line system using metallic lines.The use of one intermediate regenerator may be required.FIGURE 1/G.961Access digital section and transmission system boundariesTV1FIGURE 1/G.961 D01 7.5 cm1.3 ObjectivesConsidering th
11、at the access digital section between the local exchange and the customer is one key element of thesuccessful introduction of ISDN into the network the following requirements for the specification have been taken intoaccount: to meet the error performance specified in Recommendation G.960; to operat
12、e on existing 2-wire unloaded lines, open wires being excluded; the objective is to achieve 100% cable fill for ISDN basic access without pair selection, cablerearrangements or removal of bridged taps (BT) which exist in many networks; the objective to be able to extend ISDN basic access provided se
13、rvices to the majority of customerswithout the use of regenerators. In the remaining few cases special arrangements may be required; coexistence in the same cable unit with most of the existing services like telephony and voice band datatransmission; various national regulations concerning EMI shoul
14、d be taken into account; power feeding from the network under normal or restricted conditions via the basic access shall beprovided where the Administration provides this facility; the capability to support maintenance functions shall be provided.1.4 AbbreviationsA number of abbreviations are used i
15、n this Recommendation. Some of them are commonly used in the ISDN referenceconfiguration while others are created only for this Recommendation. The latter are given below:BER bit error ratioBT bridged tapCISPR Comit international spcial de perturbation radiolectrique (now part of IEC)CLcontrol chann
16、el of the line systemECH echo cancellationEMI electro-magnetic interferenceDLL digital local lineRecommendation G.961 (03/93) 3DTS digital transmission systemNEXT near-end crosstalkPSL power sum lossTCM time compression multiplexUI unit interval2 FunctionsFigure 2 shows the functions of the DTS on m
17、etallic local lines.T1820120-93/d02NT1 LT2 B-channelsD channelBit timingOctet timingFrame alignmentActivationDeactivationPower feedingOperations and maintenance(Note 2)NOTES1 The optional use of one regenerator must be foreseen.2 This function is optional.FIGURE 2/G.961Functions of the digital trans
18、mission systemFIGURE 2/G.961 D02 9.5 cm2.1 B-channelThis function provides, for each direction of transmission, two independent 64 kbit/s channels for use as B-channels(as defined in Recommendation I.412).2.2 D-channelThis function provides, for each direction of transmission, one D-channel at a bit
19、 rate of 16 kbit/s, (as defined inRecommendation I.412).2.3 Bit timingThis function provides bit (signal element) timing to enable the receiving equipment to recover information from theaggregate bit stream. Bit timing for the direction NT1 to LT shall be derived from the clock received by the NT1 f
20、romthe LT.2.4 Octet timingThis function provides 8 kHz octet timing for the B-channels. It shall be derived from frame alignment.4 Recommendation G.961 (03/93)2.5 Frame alignmentThis function enables the NT1 and the LT to recover the time division multiplexed channels.2.6 Activation from LT or NT1Th
21、is function restores the DTS between the LT and NT1 to its normal operational status. Procedures required toimplement this function are described in 6.Activation from the LT could apply to the access digital section only (partial activation) or to the access digital sectionplus the customer equipmen
22、t. In case the customer equipment is not connected, the access digital section can still beactivated.NOTE The functions required for operation and maintenance of the NT1 and one regenerator (if required) and for someactivation/deactivation procedures are combined in one transport capability to be tr
23、ansmitted along with the 2B + D-channels. Thistransport capability is named the CL-channel.2.7 DeactivationThis function is specified in order to permit the NT1 and the regenerator (if it exists) to be placed in a low powerconsumption mode or to reduce intrasystem crosstalk to other systems. The pro
24、cedures and exchange of information aredescribed in 6. This deactivation can only be initiated by the exchange (ET). See also note to 2.6.2.8 Power feedingThis optional function provides for remote power feeding of one regenerator (if required) and NT1. The provision ofwetting current is recommended
25、 (see 8.5).NOTE The provision of line feed power to the user-network interface, normal or restricted power feeding as defined inRecommendation I.430 is required by some Administrations.2.9 Operations and maintenanceThis function provides the recommended actions and information described in Recommend
26、ation I.603.The following categories of functions have been identified: maintenance command (e.g. loopback control in the regenerator or the NT1); maintenance information (e.g. line errors); indication of fault conditions; information regarding power feeding in NT1.See Note to 2.6.3 Transmission med
27、ium3.1 DescriptionThe transmission medium over which the DTS is expected to operate, is the local line distribution network.A local line distribution network employs cables of pairs to provide services to customers.In a local line distribution network, customers are connected to the local exchange v
28、ia local lines.A metallic local line is expected to be able to simultaneously carry bi-directional digital transmission providing ISDNbasic access between LT and NT1.To simplify the provision of ISDN basic access, a DTS must be capable of satisfactory operation over the majority ofmetallic local lin
29、es without requirement of any special conditioning. Maximum penetration of metallic local lines isobtained by keeping ISDN requirements at a minimum.In the following, the term Digital Local Line (DLL) is used to describe a metallic local line that meets minimum ISDNrequirements.Recommendation G.961
30、(03/93) 53.2 Minimum ISDN requirementsa) No loading coils.b) No open wires.c) When BTs are present, some restrictions may apply. Typical allowable BT configurations are discussed in4.2.1.3.3 DLL physical characteristicsIn addition to satisfying the minimum ISDN requirements, a DLL is typically const
31、ructed of one or more twisted-pairsegments that are spliced together. In a typical local line distribution network, these twisted-pair segments occur indifferent types of cables as described in Figure 3.T1820130-93/d03NT1 LTInstallationcableDistributioncableMaincableExchangecableCross-connectpointCr
32、oss-connectpointMaindistributionframeFIGURE 3/G.961DLL physical modelFIGURE 3/G.961 D03 5 cm3.4 DLL electrical characteristics3.4.1 Insertion lossThe DLL will have non-linear loss versus frequency characteristic. For any DLL of a particular gauge mix, with no BTsand with an insertion loss of x dB at
33、 80 kHz, the typical behaviour of its insertion loss versus frequency is depicted inFigure 4.3.4.2 Group delayTypical ranges of values of DLL group delay as a function of frequency are shown in Figure 5.3.4.3 Characteristic impedanceTypical ranges of values of the real and imaginary parts of the cha
34、racteristic impedance of twisted pairs in different typesof cables are shown in Figure 6.3.4.4 Near-end crosstalk (NEXT)The DLL will have finite crosstalk coupling loss to other pairs sharing the same cable. Worst-case NEXT power sumloss (PSL) varies from 44 to 57 dB at 80 kHz (refer to 4.2.2).The D
35、LL loss and PSL ranges have been independently specified. However, it is not required that all points in bothranges be satisfied simultaneously. A combined DLL loss/PSL representation is shown in Figure 7 to define thecombined range of operation.3.4.5 Unbalance about earthThe DLL will have finite ba
36、lance about earth. Unbalance about earth is described in terms of longitudinal conversionloss. Worst-case values are shown in Figure 8.6 Recommendation G.961 (03/93)1 2 3 4 5 8 10 20 30 40 50 80100 200 300 kHzdBT1820140-93/d04Frequency (log scale)DLLloss(linearscale)NOTE The maximum value of x range
37、s from 37 dB to 50 dB at 80 kHz. The minimum valuecould be close to zero.FIGURE 4/G.961Typical insertion loss characteristic without presence of BTs1.75x1.50x1.25xx0.75x0.50x0.25xFIGURE 4/G.961 D04 11 cm10 1 10 100 1000 kHz8010T1T10 T11T1820150-93sFrequency (log scale)DLL group delay(log scale)NOTE
38、The maximum value of one-way group delay (T) ranges from 30 to60 microseconds at 80 kHz.FIGURE 5/G.961Typical group delay characteristicFIGURE 5/G.961 D05 12 cmRecommendation G.961 (03/93) 750040030020010005004003002001001 10 100 400 kHzT1820160-93/d06Frequency (log scale)ImaginarypartRealpart(linea
39、rscale)FIGURE 6/G.961Typical ranges of values of real and imaginary partsof characteristic impedance0.1FIGURE 6/G.961 D06 10 cm5037dB04457dBT1820170-93/d07CombinedDLL loss/PSLrange ofoperationDLL lossat 80 kHz(linear scale)(linear scale)Power sum loss at 80 kHzFIGURE 7/G.961Combined representation o
40、f DLL loss/PSL range of operationFIGURE 7/G.961 D07 9.5 cm8 Recommendation G.961 (03/93)44dB88080kHzT1820180-93/d08Slope5 dB/decadeLongitudinalconversion loss(linear scale)Frequency (log scale)FIGURE 8/G.961Worst-case longitudinal conversion loss versus frequencyFIGURE 8/G.961 D08 7.5 cm3.4.6 Impuls
41、e noiseThe DLL will have impulse noise resulting from other systems sharing the same cable as well as from other sources.4 System performance4.1 Performance requirementsPerformance limits for the access digital section are specified in 4/G.960. The DTS performance must be such that theseperformance
42、limits are met. For that purpose, a DTS is required to pass specific laboratory performance tests that aredefined in the next subclauses.4.2 Performance measurementsLaboratory performance measurement of a particular DTS requires the following preparations:a) definition of a number of DLL models to r
43、epresent physical and electrical characteristics encountered inlocal line distribution networks;b) simulation of the electrical environment caused by finite crosstalk coupling loss to other pairs in the samecable;c) simulation of the electrical environment caused by impulse noise;d) specification of
44、 laboratory performance tests to verify that the performance limits referred to in 4.1 will bemet.4.2.1 DLL physical modelsFor the purposes of laboratory testing of performance of a DTS providing ISDN basic access, some modelsrepresentative of DLLs to be encountered in a particular local line distri
45、bution network are required. The maximum lossin each model is optionally set between 37 and 50 dB at 80 kHz to satisfy requirements of the particular network.Similarly, the lengths of BTs are optionally set within the range defined in Figure 9.Recommendation G.961 (03/93) 9T1820190-93/d09AG9BG9CG9DG
46、9EG9FG9BT1 = 0-0.5 km/0.4mmBT2 = 0-0.5 km/0.4mmBT3 = 0-0.5 km/0.4mmBT1 = 0-0.15 km/0.5mmBT2 = 0-0.3 km/0.5mmBT3 = 0-0.5 km/0.5mmBT4 = 0-0.3 km/0.5mmBT5 = 0-0.15 km/0.5mmNOTES1 The value of x varies from 37 to 50 dB at 80 kHz.2 Equivalent gauges can be used. For example 0.6 mm is equivalent to AWG 22
47、.AWG stands for American Wire Gauge.FIGURE 9/G.961DLL physical models for laboratory testingxdBmmdBmmdBmmdBmmdBmm0.0 dB0.25x 0.25x 0.25x 0.25x0.4 0.40.60.50.05x0.40.05x0.40.9xBT1 BT2 BT30.2x0.40.4x0.40.2x0.4BT1BT2BT5BT3BT40.5x0.40.2x0.50.1x0.60.4, 0.5 or 0.60.6 or 0.8FIGURE 9/G.961 D09 16 cm4.2.2 In
48、trasystem crosstalk modelling4.2.2.1 Definition of intrasystem crosstalkCrosstalk noise in general results due to finite coupling loss between pairs sharing the same cable, especially those pairsthat are physically adjacent. Finite coupling loss between pairs causes a vestige of the signal flowing o
49、n one DLL(disturber DLL) to be coupled into an adjacent DLL (disturbed DLL). This vestige is known as crosstalk noise. Near-endcrosstalk (NEXT) is assumed to be the dominant type of crosstalk. Intrasystem NEXT or self NEXT results when allpairs interfere with each other in a cable carrying the same DTS. Intersystem NEXT results when pairs carrying differentDTSs interfere with each other. Definition of intersystem NEXT is not part of this Recommendation.Intrasystem NEXT noise coupled into a disturbed
