1、INTERNATIONAL TELECOMMUNICATION UNION)45G134 - TELECOMMUNICATIONSTANDARDIZATION SECTOROF ITU-!).4%.!.#%G0 ).4%2.!4)/.!,G0G04%,%0(/.%G0#)2#5)433%44).G0G050G0G0!.$G0G0,).).G0G050!.G0G0).4%2.!4)/.!,G0G0#)2#5)4these circuit sectionsconsist of two telephony channels, one for each direction of transmissio
2、n, or a mixed analogue/digital terminal section ora digital terminal section. The types of circuits and circuit sections for public telephony are described inRecommendation M.562.2.2 At the terminal stations of the circuit, access points are provided in accordance with Recommendation M.110(see also
3、Recommendation M.565). At intermediate stations an access point is provided (see also Recommen-dation M.110 for transit circuits), its position in the circuit being so chosen that as much as possible of theaudio-frequency apparatus in the station is included in any measurement made at that station i
4、n the direction oftransmission concerned.2.3 In establishing an international circuit, the circuit, line and circuit section access points define the limits of thecircuit, line and circuit section, and these are used as the basic elements involved in setting-up, lining-up, and faultlocation.Note The
5、 line access point at the terminal station will also be used as the circuit section access point at thatstation.3 Limits for the overall loss of a circuit and circuit sections3.1 Limits for overall loss at 1020 HzThe objective is to make the value of overall loss at 1020 Hz as near as possible to it
6、s nominal value. Whenadjustment is provided in steps, these should enable the loss to be adjusted to within 0.3 dB of the nominal value.3.2 Limits for the overall loss/frequency characteristicNational telephone networks are planned and provided by Administrations to give satisfactory telephonetransm
7、ission on national calls in the most economical way and will, in consequence, have but little margin againstadditional transmission impairment in calls on the longest connections.International telephone calls require the two corresponding parts of the national networks in the terminalcountries to be
8、 interconnected by a switched chain of international circuits. The present CCITT plan for worldwidetelephone connections specifies a maximum of six international circuits in a connection. In some circumstances thenominal reference equivalent of the connection could be 3 dB greater than in the past.
9、This additional loss, incombination with increased line noise, makes it very desirable to minimize the transmission impairments introduced bythe international circuits.In order to have an objective for a circuit for maintenance purposes, the following principles should beapplied.2 Fascicle IV.1 - Re
10、c. M.5803.2.1 The overall loss/frequency distortion of a circuit depends on whether it is set up entirely on 4-kHz spacedchannels, or entirely on 3-kHz spaced channels or on combinations of such channels, even including small sections ofaudio cable. Three sets of limits are given in Tables 1/M.580,
11、2/M.580 and 3/M.580.The principles on which the tables are based are as follows:a) the maximum loss in the relevant frequency range should not be greater than 9.0 dB relative to the lossat 1020 Hz in order to avoid disturbing the noise power distribution in the circuit to any extent;b) the use of eq
12、ualizers at intermediate stations should be avoided as far as possible;c) where a mixed type of composition is used the arrangement of 3-kHz plus 4-kHz spaced channels in acircuit would cater for most of the cases of composition likely to be encountered in practice (for example,one 3-kHz channel in
13、series with two 4-kHz channels);d) Administrations should be allowed some flexibility to use a measure of pre-equalization if necessary inorder to avoid low-level signals entering a long section.TABLE 1/M.580Limits for the overall loss/frequency characteristic between circuit access points and the a
14、ccess pointsof circuit sections for circuits and circuit sections using 4 kHz spacingOverall loss relative to that at 1020 HzFrequency Hz Between circuit access pointsAt the access pointat intermediate stationsdB dBBelow 300not less than 0.0otherwise unspecifiednot less than 3.0otherwise unspecified
15、300 to 400 +3.5 to 1.0 +9.0 to 3.0400 to 600 +2.0 to 1.0 + 6,0 a 3,0600 to 2400 +1.0 to 1.0 + 6.0 to 3.02400 to 3000 +2.0 to 1.0 + 6.0 to 3.03000 to 3400 +3.5 to 1.0 +9.0 to 3.0Above 3400not less than 0.0otherwise unspecifiednot less than 3.0otherwise unspecifiedFascicle IV.1 - Rec. M.580 3TABLE 2/M
16、.580Limits for the overall loss/frequency characteristic between circuit access points and the access pointsof circuit sections for circuits and circuit sections using 3 kHz spacingTABLE 3/M.580Limits for the overall loss/frequency characteristic between circuit access points and the access pointsof
17、 circuit sections for circuits and circuit sections using 3 kHz and 4 kHz spacingOverall loss relative to that at 1020 HzFrequency Hz Between circuit access pointsAt the access pointat intermediate stationsdB dBBelow 200not less than 0.0otherwise unspecifiednot less than 1.5otherwise unspecified200
18、to 250 +10.5 to 0.5not less than 1.5otherwise unspecified250 to 300 + 6.5 to 0.5 +9.0 to 1.5300 to 2700 +1.0 to 0.5 +7.0 to 1.52700 to 2900 +2.5 to 0.5 +7.0 to 1.52900 to 3050 + 6.5 to 0.5 +9.0 to 1.5Above 3050not less than 0.0otherwise unspecifiednot less than 1.5otherwise unspecifiedOverall loss r
19、elative to that at 1020 HzFrequency Hz Between circuit access pointsAt the access pointat intermediate stationsdB dBBelow 300not less than 0.0otherwise unspecifiednot less than 3.0otherwise unspecified300 to 400 +3.5 to 1.0 +9.0 to 3.0400 to 600 +2.0 to 1.0 + 6.0 to 3.0600 to 2400 +1.0 to 1.0 + 6.0
20、to 3.02400 to 2700 +2.0 to 1.0 + 6.0 to 3.02700 to 2900 +2.5 to 1.0 +9.0 to 3.02900 to 3050 + 6.5 to 1.0 +9.0 to 3.0Above 3050not less than 0.0otherwise unspecifiednot less than 3.0otherwise unspecified4 Fascicle IV.1 - Rec. M.5803.2.2 Table 1/M.580 is based on the limits recommended for a pair of 4
21、-kHz channel equipments(Recommendation G.232 2), a small addition having been made to the recommended limits to allow for the additionaldistortions likely to be introduced by the group link and by the circuit and exchange apparatus. The equalization limitsare three times the circuit limits.Table 2/M
22、.580 is similarly based on the limits recommended for a pair of 3-kHz channel equipments(Recommendation G.235 3) with an allowance for the group link and for circuit and exchange apparatus.For international circuits composed of 4-kHz and 3-kHz sections, the limits given in Table 3/M.580 are acombina
23、tion of the limits given in Tables 1/M.580 and 2/M.580, taking into account the factors given in 3.2.1 a) to3.2.1 c) above.The limits to be imposed on the loss/frequency characteristic at intermediate stations are also shown inTables 1/M.580, 2/M.580 and 3/M.580.Where a circuit or circuit section co
24、ntains mixed analogue/digital channels, the table to be used should bebased on the channel spacing of the analogue carrier associated with the mixed circuit or circuit section.A circuit section or that portion of a circuit made up of wholly digital channels should be treated as ananalogue circuit se
25、ction or circuit having 4 kHz spaced channels.Circuit sections made up of digital or mixed analogue/digital terminals should follow the limits given formeasurements between circuit access points in Table 1/M.580.4 Setting up and lining up analogue and mixed circuit sections4.1 The circuit sub-contro
26、l stations responsible for the various national and international circuit sections shouldarrange to set up these sections.The circuit sections are lined up and the overall loss/frequency characteristic of each is recorded fromterminated-level measurements.This is done by sending at a level of 10 dBm
27、0 at the reference test frequency at the access point at theintermediate sub-control station or at the line access point at the control station or terminal sub-control station andadjusting the received level at the access point at the adjacent intermediate sub-control station as close as possible to
28、 itsnominal level in the direction of transmission concerned.4.2 The loss/frequency characteristic should then be measured at frequencies chosen from the following list,according to the characteristics of the circuit section to be set up:200, 250, 300, 400, 600, 800, 1000, 1400, 2000, 2400, 2700, 29
29、00, 3000, 3050 and 3400 Hz.Technical services may agree to make measurements at other frequencies if it is considered useful to do so.The test signals should be applied at a level of 10 dBm0.For circuit sections effectively transmitting up to only 3000 Hz (for example, circuits using 3 kHz spacedcha
30、nnels) the measurement at 3400 Hz is, of course, not applicable.The overall loss at 1020 Hz1)should be as near as possible to the nominal value.The overall loss at other frequencies should lie within the limits given in Tables 1/M.580, 2/M.580 and3/M.580 (see 3.2.1).For each circuit section the resu
31、lts for each direction of transmission are forwarded to the control and terminalsub-control stations.At terminal stations, during these measurements, the signalling connections to the automatic equipment shouldbe disconnected if the signalling units are incorporated in the carrier terminal equipment
32、. When the line-signalling relaysets are included in the lines and apparatus being measured, any voice-frequency signalling receiver must be madeinoperative._1)For further information about the choice of test signal frequency, refer to Recommendation O.6 4.Fascicle IV.1 - Rec. M.580 55 Setting up an
33、d lining up mixed analogue/digital and digital terminal circuit sections5.1 As shown in Figure 2/M.562, mixed analogue/digital and digital terminal circuit sections can occur at bothterminal and intermediate locations in a circuit. However, in both cases these terminal circuit sections fall wholly w
34、ithinan individual Administrations boundaries. Thus, they would normally be set up and lined up independently according tonational practices. However, Administrations may bilaterally choose to apply a single procedure for setting up and liningup a combination of a digital circuit section terminated
35、at each end by a mixed analogue/digital terminal section. In thiscase, the procedures and limits given in 4 above for analogue circuit sections should be applied to this combination ofcircuit sections.5.2 In order to provide some guidelines for the setting up and lining up of mixed analogue/digital
36、terminalsections, two suggested procedures are described in Annex A.6 Setting up and testing digital circuit sections6.1 As with digital channels, because the test procedures required for setting up and initially testing the digital pathalso set-up and test the digital circuit section, no additional
37、 tests on a circuit section are recommended.7 Setting up and lining up an international circuit2)7.1 Setting up the circuit7.1.1 The sub-control station responsible for the various circuit sections having completed the setting-up andlining-up of those sections should arrange to connect them together
38、 and advise the control station. In addition, thecontrol and terminal sub-control stations, in conjunction with their testing points, should ensure that all associatedsignalling, switching and other terminal equipment has been connected, is free from faults, and is operatingsatisfactorily.7.1.2 When
39、 the control station has been advised by all the sub-control stations that the sections constituting thecircuit have been connected together, the control station should agree with the sub-control stations upon a time at whichthe whole circuit may be lined up.7.2 Lining up the circuit7.2.1 Preliminar
40、y work7.2.1.1 The receiving terminal sub-control station studies the test results of the individual circuit sections, particularlyobserving the way in which the variations within the permissible tolerances will accumulate when the sections areinterconnected. The receiving terminal sub-control statio
41、n for each direction of transmission determines from thesestudies and observations the amount of gain and equalization adjustment which will be required at intermediate andterminal stations to obtain a satisfactory overall characteristic.7.2.1.2 From the test results the cumulative overall loss over
42、 the frequency band at intermediate sub-control stations iscalculated with respect to the overall loss at 1020 Hz. An equalizer should be fitted at the request of the receive terminalsub-control station at those stations at which the sum of the measured overall loss/frequency characteristics of thei
43、ndividual sections exceeds the provisional limits (see 3.2.2). In determining the limits, due account must be taken of thepresence of 3-kHz spaced channel translating equipment.The number of intermediate equalizers should be kept to a minimum. When the receiving terminal sub-controlstation has been
44、advised by all the other sub-control stations that the circuit sections and any prescribed equalizers havebeen connected together, a time at which the circuit can be lined up should be agreed upon.7.2.2 Adjustment of the overall loss at the reference test frequency7.2.2.1 At the appropriate time of
45、line-up, the control station, in cooperation with the various sub-control stations,proceeds with the overall line-up of the circuit, first at a frequency of 1020 Hz3).For this, the control station arranges to send an 1020 Hz test signal at a level of 10 dBm0, for example at thecircuit access point o
46、f the circuit. In addition, the level at the line access point at the terminal stations should be adjustedas close as possible to the nominal value._2)The procedure given in 15 may be followed as an alternative to those given in 7 to 14 if agreement has been reached with thedistant Administration to
47、 use ATME No. 2 for lining up, measurement of circuit noise and functional tests. It should be noted thatthis procedure does not include the tests in 12. The Administrations involved should consider scheduling such tests, ifapplicable, when cooperative effort can be arranged.3)For further informatio
48、n about the choice of test signal frequency, refer to Recommendation O.6 4.6 Fascicle IV.1 - Rec. M.5807.2.2.2 The intermediate sub-control stations will then arrange to measure the level of the 1020 Hz test signal and toadjust it to the nominal value at the access points of the circuit (as defined
49、in 2.2) in that direction of transmission.Measurements and adjustments should also be made at frontier stations where the circuit includes an audio-frequencysection crossing a frontier.7.2.2.3 At the distant terminal sub-control station the received level of the test signal should be adjusted until therequired overall loss is obtained at the circuit access point.The procedure is then repeated for the other direction of transmission of the circuit.In order to minimize cumulative gain or loss a
