1、INTERNATIONAL TELECOMMUNICATION UNION)45G134 TELECOMMUNICATIONSTANDARDIZATION SECTOROF ITU).4%2.!4)/.!,G0G0!.!,/5%G0G0#!22)%2G0G03934%-3%.%2!,G0G0#(!2!#4%2)34)#3G0G0#/-/.G0G04/G0G0!,!.!,/5%G0G0#!22)%2G1342!.3-)33)/.G0G03934%-302/4%#4)/.G0G0/ further amended)1 Interconnection of telephone circuits at
2、 audio frequencyIt is necessary that the interconnection of telephone circuits at audio frequency may be made without restrictionand without causing interference between the sent and received group and supergroup pilots. It is thereforerecommended that Recommendations G.232, 13 and G.234 1 be met, w
3、hich specify an attenuation of at least 20 dBin both modulating and demodulating equipments for the leaks of group pilots (channels 6 and 7 or 1 and 2) andsupergroup pilots (channels 1 and 2 or 11 and 12).2 Through-group connection2.1 Group routed on a supergroup equipped with pilots 411.860 and 411
4、.920 kHzTo permit unrestricted through-group connection without causing interference between the sent and receivedsupergroup pilots Recommendation G.233, 9.1.2, has to be followed. Otherwise, it is necessary at least to followRecommendation G.233, 9.1.1 and, moreover, to avoid routing a through grou
5、p in position 3 in two successivesupergroup links.2.2 Group routed on a supergroup equipped with pilot 547.920 kHzThe same provisions as in 2.1 apply, but to the group in position 5 and not in position 3 (in accordance withRecommendation G.233, 9.1.2.3 Through-supergroup connection3.1 Protection of
6、a line-regulating pilot against additional measuring frequenciesTo prevent interference with a line-regulating pilot lying adjacent to a through-connected supergroup, arisingfrom an additional measuring frequency on an adjacent line link, it is recommended that the combined through-supergroup equipm
7、ent, plus any additional blocking filter (e.g. associated with the through-supergroup equipment orprovided as a pilot suppression filter immediately preceding the point on the line at which the line-regulating pilot isinjected) should provide the following discrimination (relative to 412 kHz):- over
8、 the range 308 kHz 8 Hz, not less than 40 dB;- over the range 308 kHz + 40 Hz and the range 556 kHz 40 Hz, not less than 20 dB.Note 1 - In making this recommendation, it has been assumed that the addition of the various frequencycomponents within pilot-operated line regulators will follow a square o
9、r average law of addition.Note 2 - If, by mutual agreement, Administrations use an auxiliary line-regulating pilot, an additionalattenuation giving a discrimination of at least 40 dB relative to the attenuation at 412 kHz should be provided over asuitable frequency range around 556 kHz and in partic
10、ular in the range 556 kHz 10 Hz in the case of a 2792-kHz pilot,for which the CCITT has recommended that the frequency variations should not exceed 5 Hz.2 Fascicle III.2 - Rec. G.243Note 3 - When the synchronizing or frequency-checking pilot is also a line-regulating pilot (multipurpose pilot),then
11、where it passes from one regulated-line section to another, the pilot should be blocked and reintroduced (afterfiltration) on the following regulated-line section after its amplitude has been corrected.3.2 Protection of additional measuring frequenciesTo minimize interference between additional meas
12、uring frequencies on adjacent line sections and to preventinterference between additional measuring frequencies on non-adjacent line sections, it is recommended that through-supergroup equipment should provide the following discrimination (relative to 412 kHz):- over the range 308 kHz 50 kHz and the
13、 range 556 kHz 50 Hz, not less than 15 dB;- over the range 308 kHz 20 Hz and the range 556 kHz 20 Hz, not less than 20 dB;- at frequencies of 308 kHz and 556 kHz, not less than 40 dB.3.3 Protection of the mastergroup or 15-supergroup pilot against additional measuring frequenciesTo prevent interfere
14、nce with the mastergroup or 15-supergroup pilot arising from additional measuringfrequencies, it is recommended that the through-supergroup equipment, plus any necessary additional blocking filter,should provide the following discrimination relative to 412 kHz:- over the range 308 kHz 7 Hz and the r
15、ange 556 kHz 7 Hz, 50 dB;- over the range 308 kHz 40 Hz and the range 556 kHz 40 Hz, 30 dB.Any necessary additional blocking filter should be provided in association with the equipment wherethe 1552 kHz pilot is injected, that is, in the supergroup translating equipment on the sending side where the
16、 mastergroupor 15-supergroup assembly is formed.Figure 1/G.243 recapitulates all the attenuations recommended over the range 308 kHz and 556 kHz.FIGURE 1/G.243Minimum recommended relative attenuation around 308 kHz and 556 kHz for various casesof through-supergroup connectionFascicle III.2 - Rec. G.
17、243 34 End of a supermastergroup linkThe supermastergroup pilot should be blocked at the end of a supermastergroup link, unless otherwise agreedbetween Administrations. The end of a supermastergroup link shall be considered as any point where basicsupermastergroup working is no longer used, even tho
18、ugh the supermastergroup may not be broken up into mastergroupsat that point.For example, in the case described in Figure 2/G.243, point M is the end of a supermastergroup link, at whichpoint the supermastergroup pilot should not be transmitted to country B (even though the supermastergroups continu
19、e tobe transmitted to line without demodulation), unless country B agrees to depart from this rule. Moreover, country B,which does not use the basic supermastergroup, is not required to transmit this supermastergroup pilot over the link PM.In any case, the supermastergroup pilot is considered as blo
20、cked when it undergoes an additional attenuationof 40 dB.Note - It is assumed that countries A and C use the basic supermastergroup and that country B does not.FIGURE 2/G.243Definition of a supermastergroup link5 Direct through-connectionLet B be a repeater station where one or several supergroups,
21、mastergroups, supermastergroups or 15-supergroup assemblies are through-connected by direct filtering1) from a line section AB on to another line section BC(see Figure 3/G.243). At point B special precautions should be taken with respect to pilots and additional measuringfrequencies, so that these s
22、ignals are transmitted to certain line sections where it is desired to route them but, on the otherhand, do not interfere with pilots of the same type transmitted on other sections.FIGURE 3/G.2431)If the supergroups are in the basic supergroup frequency band, this becomes the case dealt with in 3.4
23、Fascicle III.2 - Rec. G.2435.1 Precautions to be taken in the use of pilot signals and additional measuring frequencies where there is directthrough-connection within a regulated line section5.1.1 Line-regulating pilotsWhen the regulation of line section BD is to be performed together with the regul
24、ation of line section AB (andwith that section only), the regulated line section extends from A to D and point B is not the end of the regulated linesection AB. If one or two line-regulating pilots are outside the frequency band of the supergroups, mastergroups orsupermastergroups diverted over BD,
25、or lie at the edge of this frequency band, special arrangements must be made atpoint B for these pilots to be extended beyond B on to section BD (see Recommendation G.213, 1 General Remarks,2).In the direction of C, however, the line-regulating pilots of section AB should be stopped, in the samecond
26、itions as at the end of the regulated-line section, so as not to be transmitted on section BC.5.1.2 Additional measuring frequenciesAt a station where there is direct through-connection and which is within a regulated-line section (station B ofsection AD in the preceding example) the additional meas
27、uring frequencies within the frequency bands of thesupergroups, mastergroups or supermastergroups are diverted as a whole.It may not be possible to use additional measuring frequencies at the edges of a through-connected frequencyband because the amplitudes of these frequencies are affected by the d
28、irect through-connection filters. It might thereforebe desirable in certain cases to specify “measuring sections“ over which these additional measuring frequencies would beused. The choice of such measuring sections is left to the discretion of the Administrations concerned.5.1.3 Other pilot frequen
29、ciesIn each particular case, the Administrations concerned should decide on the points where the synchronizing orfrequency-checking pilot and any switching pilot should be blocked so as not to interfere with other parts of the link.However, should one of these pilots also be a line-regulating pilot
30、(multipurpose pilot) the rules defined above for line-regulating pilots should be applied.5.2 Precautions to be taken at a direct through-connection point at the end of a regulated-line section5.2.1 Line-regulating pilotsIf it is not desired to associate the line regulation of section AB with that o
31、f the other sections, point B is, bydefinition, the end of a regulated line in section AB and the line-regulating pilots of this section AB should be stopped insuch a way that, on all the interconnected sections (in this case, BC and BD), they are at least 40 dB below the pilotsused on these section
32、s.When some (or all) of the pilots used on line-regulating section AB are not on the same frequency as those usedon a line-regulating section connected to it, suppression of these pilots by 20 dB only (which implies a residue of notmore than -30 dBm0 on the connected line-regulating section) may be
33、tolerated at direct through-connection point B, ifthis residue is further suppressed by 20 dB before reaching the injection point of a line-regulating pilot with the samefrequency on another line-regulating section connected at a distant point (for example, at D). However, the line-regulating pilot
34、should be suppressed by 40 dB whenever it is applied to an international line-regulated section crossingat least one frontier. It therefore follows that the line-regulating pilot should be suppressed by 40 dB if the followingsection is an international section, even with a line-pilot at a different
35、frequency. Similarly, if a line-regulating pilot issuppressed by 20 dB only, a supplementary attenuation of 20 dB must be introduced on the line frequency at the end ofthe corresponding line-regulating section before this pilot residue reaches a distant international section.With reference to the ex
36、ample in Figure 1/G.213, the sum of the suppression of (2) and (5) (see legend ofFigure 1/G.213) at the frequency of any received line-regulating pilot should therefore be at least 40 dB when thefrequencies of these pilots are the same on both interconnected regulated-line sections. Division of this
37、 suppressionbetween filters (2) and (5) may be made in different ways. As the two filters are in the same station this is not anFascicle III.2 - Rec. G.243 5international interconnection problem, but one of industrial standardization for countries which order systems fromseveral manufacturers.If it
38、is considered necessary always to have a filter (5) before the point of injection of an outgoing line-regulating pilot, for the suppression of unwanted signals from other equipments, and if the line-regulating pilots of thetwo interconnected regulated-line sections are on the same frequency, the div
39、ision may be made in the following way:filter (2) = 20 dB filter (5) = 20 dB.Thus, if the frequencies of the pilots do not coincide and there is no interconnection with an internationalsection, the 20 dB suppression recommended above will remain. Nevertheless, this provision may necessitate theaddit
40、ion of a further suppression at the adequate frequency at some point before reaching an international section.To avoid the latter difficulty, it may be considered preferable, in order to facilitate network arrangements, toadopt the value of 40 dB for (2). If the frequencies of the pilots are the sam
41、e on both interconnected regulated-linesections and if it has been considered desirable always to have a filter (5) before the point of injection of an outgoingline-regulating pilot, the suppression of the received line-regulating pilot will be very much greater than therecommended value of 40 dB. T
42、here is no technical objection to this.5.2.2 Additional measuring frequenciesThe additional measuring frequencies within the frequency band occupied by all the through-connectedsupergroups, etc., are normally transmitted without special blocking2). The level of the additional measuring frequenciesat
43、 the edges of this band may be affected by the sections of the through-connection filters.There is no need in such cases for equipments to include methodical provision of blocking filters for protectingline-regulating pilots against additional measuring frequencies sent over a preceding section. The
44、 arrangements to bemade by the maintenance staff when such blocking filters are not provided are shown in Recommendation M.500 2.References1 CCITT Recommendation 8-channel terminal equipments, Orange Book, Vol. III-1, Rec. G.234, ITU, Geneva,1977.2 CCITT Recommendation Routine maintenance measurements to be made on regulated line sections, Vol. IV,Rec. M.500.2)Such special blocking attenuation would in any case be both expensive and technically difficult to achieve.
