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2、ecommendationG0G06 (Extract from the “LUEG0“OOK)NOTES1 ITU-T Recommendation V.37 was published in Fascicle VIII.1 of the Blue Book. This file is an extract fromthe Blue Book. While the presentation and layout of the text might be slightly different from the Blue Book version, thecontents of the file
3、 are identical to the Blue Book version and copyright conditions remain unchanged (see below).2 In this Recommendation, the expression “Administration” is used for conciseness to indicate both atelecommunication administration and a recognized operating agency. ITU 1988, 1993All rights reserved. No
4、part of this publication may be reproduced or utilized in any form or by any means, electronic ormechanical, including photocopying and microfilm, without permission in writing from the ITU.Fascicle VIII.1 - Rec. V.37 1Recommendation V.37Fascicle VIII.1 - Rec. V.37SYNCHRONOUS DATA TRANSMISSION AT A
5、DATA SIGNALLING RATEHIGHER THAN 72 kbit/s USING 60-108 kHz GROUP BAND CIRCUITS(Geneva, 1980; amended at Malaga-Torremolinos, 1984 and at Melbourne, 1988)1 IntroductionOn leased circuits, considering that there exist and will come into being other modems with features designedto meet the requirements
6、 of Administrations and users, this Recommendation in no way restricts the use of any othermodems.The only group reference pilot frequency which can be used in conjunction with this modem is 104.08 kHz.The modem is intended to be used on group band circuits not necessarily conforming to 1.Principal
7、characteristics:a) transmission of any type of high-speed synchronous data in duplex constant carrier mode on 4-wire(60-108 kHz) group band circuits;b) primary data signalling rates up to 144 kbit/s;c) inclusion of an automatic adaptive equalizer;d) class IV partial response pulse amplitude single s
8、ideband signalling and modulation;e) optional inclusion of an overhead-free multiplexer combining existing data signalling rates;f) optional voice channel.2 Data signalling rates2.1 The recommended synchronous data signalling rates are 96 kbit/s, 112 kbit/s, 128 kbit/s and 144 kbit/s. Forsome applic
9、ations with agreement from the Administration, data signalling rates up to 168 kbit/s are applicable. (Seethe Note to 7.)2.2 The permitted tolerance for all data signalling rates is 5 10-5.3 Scrambler/descramblerIn order to be bit sequence independent, to avoid high amplitude spectral components on
10、the line, and to allowthe automatic equalizer to remain converged, the data should be scrambled and descrambled by means of the logicalarrangements described in Appendix I.4 Encoding methodThe binary bit stream A, delivered by the scrambler, to be transmitted is divided into consecutive groups of2 b
11、its Aland A2(dibits), Albeing the first in time delivered by the scrambler.An amplitude level B is assigned to each dibit (A) as shown in Table 1/V.37.2 Fascicle VIII.1 - Rec. V.37TABLE 1/V.37A1A2Equivalent B amplitude level001101100+1+2+3A pre-encoder circuit converts the stream B into another quat
12、ernary stream C which conforms to the relation:5 Baseband signal shapingThe equivalent baseband signal shaping process is based upon the binary coded partial response pulse, oftenreferred to as class IV, whose time and spectral function are defined by:andrespectively, where 1/T denotes the modulatio
13、n rate.The reference to equivalent baseband signals recognizes that the modem implementation may be such that thebinary signal at the input and output of the modem is converted to and from the line signal without appearing as anactual baseband signal.The baseband signal formed by the processes descr
14、ibed above will present 7 levels (see Table 2/V.37).The baseband signal shaping is performed in the transmitter,Fascicle VIII.1 - Rec. V.37 3TABLE 2/V.37LevelBit valueA1A2+3+2+10-1-2-3110011001100116 Line signal in the 60-108 kHz band (at the line output of the modem)6.1 In the 60-108 kHz band, the
15、line signal should correspond to a single sideband signal with its carrierfrequency pilot and timing pilot at frequencies as specified in Table 3/V.37.6.2 The amplitude of the theoretical line signal spectrum, corresponding to a quaternary symbol (+1) appearing atthe output of the encoder, is sinuso
16、idal. The zeros and maxima of the theoretical line spectrum are shown inTable 3/V.37.TABLE 3/V.37Data rate(kbit/s)Zeros at(kHz)Maxima at(KHz)Pilot carrier frequency Timing pilot frequency14412811296168(optional)64 and 10068 and 10072 and 10076 and 10062 and 1048284868883100 kHz100 kHz100 kHz100 kHz1
17、04 kHz64 kHz68 kHz72 kHz76 kHz62 kHz6.3 In the 60-108 kHz band, amplitude distortion of the real spectrum relative to the theoretical spectrum asdefined under 6.2 above is not to exceed 1 dB; the group-delay distortion is not to exceed 15 s. These tworequirements are to be met for each frequency ban
18、d centred on one of the maxima mentioned in 6.2 and whose widthis equal to 80% of the frequency band used.6.4 The nominal level of the line data signal should be -6 dBm0. The actual level should be within 1 dB of thenominal level.6.5 A pilot carrier at the same frequency as the modulated carrier (10
19、0 kHz 2 Hz) at the transmitter and with alevel of -9 0.5 dB relative to the actual level mentioned under 6.4 above, should be added to the line signal. Therelative phase between the modulated carrier and the pilot carrier at the transmitter should be time invariant.Note - For the optional data signa
20、lling rate of 168 kbit/s, the pilot carrier should be 104 kHz 2 Hz.6.6 A timing pilot at a frequency difference from the carrier equal to half the modulation rate at the transmitterwith a level of -12 0.5 dB relative to the actual level mentioned under 6.4 above, should be added to the line signal.T
21、he relationship between the timing pilot and the pilot carrier should remain time invariant at the transmitter.4 Fascicle VIII.1 - Rec. V.377 Group reference pilot7.1 Provision should be made for facilitating the injection of a group reference pilot of 104.08 kHz from anexternal source.7.2 The prote
22、ction of the group reference pilot should conform to Recommendation H.52 2.Note - Group reference pilot must be removed from the channel for operation at 168 kbit/s.8 Optional voice channelThe service speech channel may be an integral part of the application of this system and is used on an optional
23、basis. The channel corresponds to channel 1 of a 12 channel SSB-AM system in the 104-108 kHz band (virtual carrierat 108 kHz). It can transmit continuous voice at a mean level of maximum -15 dBm0 or pulsed signalling tonesaccording to the individual specifications.To avoid overloading of the system
24、by peak signals, a limiter shall be used with cut-off levels above +3 dBm0.To avoid stability problems, the channel shall be connected to 4-wire equipment only.The transmit filter shall be such that any frequency applied to the transmit input terminals at a level of-15 dBm0 will not cause a level ex
25、ceeding:a) -73 dBm0p in the adjacent group;b) -61 dBm0 in the vicinity ( 25 Hz) of the pilot 104.08 kHz;c) -55 dBm0 in the data band between 64 and 101 kHz. When the 168 kbit/s data signalling rate is used thisrequirement applies between 62 and 104 kHz.The voiceband is sufficiently protected if the
26、same filter is used in the receive direction of the channel. Theattenuation/frequency characteristic, measured between the voice-frequency input and the group band output or thegroup input and the voice-frequency output, with respect to the value at 800 Hz is limited by:-1 dB over the 300-3400 Hz ba
27、nd,+2 dB between 540 and 2280 Hz.Note - When the modem is installed at the repeater station, the voice channel should be extended to thecustomers premises.9 Adjacent channel interferenceIn the bands 36-60 kHz and 108-132 kHz the adjacent channel interference should conform toRecommendation H.52 2.10
28、 Line characteristicsThe modem will allow proper operation of data signalling rates up to 128 kbit/s over a circuit of similarconstruction as the Hypothetical Reference Circuit as specified in reference 3.Note 1 - Reference 3 specifies a maximum number of 8 through-group filters, but this figure is
29、subject tofurther study and possible amendment.Note 2 - The modem will allow operation over a circuit having a maximum number of 5 through-group filtersat 144 kbit/s.Note 3 - The line characteristics for operation at 168 kbit/s are not specified.Fascicle VIII.1 - Rec. V.37 511 Synchronizing signalsT
30、ransmission of synchronizing signals is initiated by the modem. When the receiving modem detects acondition which requires resynchronizing, it shall turn circuit 106 OFF and generate synchronizing signals.The synchronizing signals for all data signalling rates are divided into three segments as indi
31、cated inTable 4/V.37.TABLE 4/V.37Segment 1 Segment 2 Segment 3 Total of segments1, 2 and 3Type of linesignalsOnly carrier and timingpilotsCarrier and timing pilotsand alternation of levels( 2)Carrier and timing pilotsand scrambled all binaryONEsData signallingrates(kbit/s)Approximatetime (s)96 5.76N
32、umber of112 4.93symbolintervals10 240 4096 262 144 128 4.32144 3.84168 3.2911.1 Segment 1 transmits the carrier pilot, the timing pilot and data signal corresponding with the dibits (0, 0)applied at the input of the encoder.11.2 Segment 2 consists of the carrier pilot, the timing pilot and an altern
33、ation between two signal levels (+2) and(-2) corresponding with the dibits (1, 1) applied at the input of the encoder.11.3 Segment 3 consists of the carrier pilot, the timing pilot and scrambled all binary ONEs.At the beginning of this segment:- the scrambler shift register must be set to all 0s (se
34、e Appendix I);- the adverse state detector counter must be set to all 1s (see Appendix I);- the pre-encoder must be set to all 0s.The equivalent baseband signal processed at the beginning of Segment 3 consists of a succession of 15 levels(0) followed by levels ( + 1), (0), ( - 1), ( + 1), (0), ( - 1
35、), ( + 1), (0), ( - 1), ( + 1), ( + 1), ( - 1) . . . .11.4 Circuit 106 is turned ON at the end of segment 3 and the users data may appear at the input of the scrambler.12 Optional multiplexingMultiplexing options shall be separately available to combine nominally available group band data rates of 4
36、8,56, 64 or 72 kbit/s into a single aggregate bit stream for transmission as shown in Table 3/V.37. These multiplexersshould be of a synchronous, overhead-free, bit interleave design. Using modem internal processing signals,multiplexers shall require no framing, allowing each subchannel to be a full
37、 one-half of the composite bit rate.The two port multiplexer uses the bits from port A and B for bits A1and A2respectively of the dibits definedin 4.6 Fascicle VIII.1 - Rec. V.3712.1 Transmit buffersIn the transmitter of each multiplex port, there shall be a data buffer of suitable capacity. In this
38、 way, bothphase variations and, within certain limits, frequency deviations are absorbed. The buffer shall be initialized when anOFF to ON condition of circuit 105 occurs and may be repositioned in the event of a buffer overflow.Note - The buffer may reinitialize upon a DCE resynchronization signal.
39、12.2 Transmit port timing arrangementsTable 5/V.37 shows all possible combinations of port and main DCE transmit timing clock arrangements.TABLE 5/V.37Source of port transmitter signalelement timing (used to clock incircuit 103)Source of DCE internal transmitterelement timing (internal transmit cloc
40、k)Port transmit bufferInternal(Independent timing)Not required114(DCE source)External a)(Circuit 113 of selected port)Not requiredReceiver timing(Loopback timing)Not requiredInternal(Independent timing)Required113(DTE source) a)External a)(Circuit 113 of selected port)Required for all ports except p
41、ortsupplying circuit 113 to DCEReceived timing(Loopback timing)Requireda)In these applications a source could also be another DCE.13 Digital interface requirements13.1 List of interchange circuits (see Table 6/V.37)The interchange circuit table is valid for the main channel or the subchannel interfa
42、ces.Fascicle VIII.1 - Rec. V.37 7TABLE 6/V.37Interchange circuit (see Note 1) Remark102102a102bSignal ground or common returnDTE commun returnDCE common returnSee Note 2See Note 3See Note 3103104Transmitted dataReceived data105106107109Request to sendReady for sendingData set readyData channel recei
43、ved line signal detectorSee Note 4See Note 4 and 5113114115128Transmitter signal element timing (DTE source)Transmitter signal element timing (DCE source)Receiver signal element timing (DCE source)receiver signal element timing (DTE source)See Note 4140141142Loop-back/Maintenance testLocal loop-back
44、Test indicatorSee Note 4See Note 6Note 1 - When the modem is installed at the repeater station, this interface should appear at the customers premises withoutrestrictions regarding the data signalling rate and the provision of the voice channel. The method to achieve this is subject to nationalregul
45、ations.Note 2 - The provision of this conductor is optional.Note 3 - Interchange circuits 102a and 102b are required where the electrical characteristics defined in Recommendation V.10 areused.Note 4 - Not essential in subchannel.Note 5 - During the synchronisation process of the main modem, the OFF
46、 condition of circuit 106 is signalled at all port interface.Note 6 - Circuit 142 is present on all ports of the multiplexer, but may be activated on an individual port basis for individual porttests. All are activated simultaneously for entire modem test.8 Fascicle VIII.1 - Rec. V.3713.2 Electrical
47、 characteristicsUse of electrical characteristics conforming to Recommendation V.10 and/or V.11 is recommended togetherwith the use of the connector and pin assignment plan specified by ISO 4902.i) Concerning circuits 103, 104, 113, 114 and 115, both the generators and the receivers shall be inaccor
48、dance with Recommendation V.11.ii) In the case of circuits 105, 106, 107 and 109, generators shall comply with Recommendation V.10 oralternatively Recommendation V.11. The receivers shall comply with Recommendation V.10, category1, or V.11 without termination.iii) In the case of all other circuits,
49、Recommendation V.10 applies, with receivers configured as specified byRecommendation V.10 for category 2.Note - For an interim period the connector and contact-assignment plan specified in ISO 2593 and commonlyreferred to as the “V.35 interface“ may optionally be used. In this case electrical characteristics may be either V.11 forcircuits 103, 104, 113, 114 and 115 together with V.10 (receivers configured as specified in category 2) for all othercircuits, or V.35 Appendix II together with V.28 respectively.14 Optional PCM interface altern
