1、INTERNATIONAL TELECOMMUNICATION UNION)45G134 - TELECOMMUNICATIONSTANDARDIZATION SECTOROF ITU-!).4%.!.#%G0 ).42/$5#4)/.G0G0!.$G0G0%.%2!,G0G002).#)0,%334!“),)49G0G0/b) the design of carrier generators with a view to great reliability;c) the design of power supplies; attention is particularly drawn to
2、the importance of the judicious choice andgrading of protective devices (fuses, circuit-breakers) in the power feeds to repeater station racks.Note See in this connection Recommendation G.231 2.5.3 Care in the organization of work in international exchanges, repeater stations, and on the transmissio
3、n lines,cables and systems used in the international networkExperience has shown that operations carried out on exchange and repeater station equipment and on theexternal plants (underground cables, etc.) are a major cause of attenuation and phase variations and of interruptions toservice in the int
4、ernational network.All work liable to cause interference should therefore be carried out, when possible, at times of light traffic. Itmust be recognized that for very long routes it will become increasingly difficult to find suitable periods of light traffic,bearing in mind the time differences whic
5、h will exist between the terminal countries on such routes. This will requiregood coordination and cooperation between Administrations. In particular, the control stations should be consulted wellin advance (see Recommendation M.490).5.4 Care in the organization of maintenanceThe same reasons for tr
6、ansferring working operations to times of light traffic apply to maintenance operations.It is desirable to avoid all equipment changeovers which are not absolutely necessary.It is also desirable to guard against maintenance operations which appear harmless but which may, however,result in short inte
7、rruptions and which are all the more dangerous if they affect common units (e.g. changeover of masteroscillators).5.5 Power supplies5.5.1 Too frequent changeover of power supplies for routine maintenance must be avoided. It should be possible tomake partial tests to check that the standby motor-gene
8、rator starts, without changing over the power supplies.5.5.2 The instruction or training of staff during the day on working power supplies should be forbidden.5.5.3 Changeover of power supplies should be carried out at times of light traffic and as far as possible at night.Fascicle IV.1 - Rec. M.160
9、 35.5.4 To ensure that circuits in the international network are not interrupted owing to the failure of public powersupplies, repeater stations in the international network should have power-continuity arrangements which ensure that thetransmission equipment continues to operate, without any interr
10、uption, in the event of a failure of the public powersupply.5.6 Care in the testing of new equipmentEquipment should not be put into service until after the most thorough inspection. It is necessary to ensure thatthe pressing needs of the operating services do not result in these tests being omitted
11、 or hastily done.Where the urgent requirements of the operating services resulted in equipment being put into service before ithad been sufficiently tested, the equipment should be temporarily taken out of service and a thorough inspection made assoon as possible.5.7 Vibration testingVibration tests
12、 using the principles described in 3, help in improving transmission stability and in ensuringsatisfactory operation of transmission equipment. They should be made, wherever applicable, when new equipment isput into service, under special circumstances for fault locating purposes or even as a routi
13、ne measure for preventivemaintenance, if the Administration concerned deems it necessary.5.8 Automatic regulation by pilots (group pilots, supergroup pilots, etc.)In carrier systems, the presence of pilots (line pilots, group pilots, supergroup pilots, etc.) makes it possible tosupervise transmissio
14、n, to keep track of short-duration phenomena where necessary and to give the alarm if there arelarge variations in level.Regulation by pilots and the way such regulation (manual or automatic) is carried out has a decisive effect ontransmission stability. In addition to regulation by line pilots, wit
15、h which wideband transmission systems are normallyequipped, it may be necessary to regulate the group links themselves (group links, supergroup links, etc.), both toachieve adequate stability for the circuits formed from the groups and to reduce system overloading risks due to theexistence of unduly
16、 high line levels.Automatic regulation of links is a convenient means to meet the requirements for the values of M and S of thepilot levels as stated under 2 above. Therefore, automatic regulators should be fitted into a link when these limitscannot be achieved by other means.However, when setting u
17、p a link the need for fitting automatic regulators cannot be determined solely by theserequirements. It is also necessary to take practical considerations into account such as those given in the Annex to thisRecommendation.In the case of through-connection points of group, supergroup, etc. links, th
18、e insertion of automatic regulatorsprevents overloading of sections further down the line. If a link is through-connected several times and several regulatorshave to be inserted for the same direction of transmission to meet the conditions of 2.2 above, the first insertion shouldbe made at the first
19、 through-connection point requiring regulation in that direction of transmission. A regulator should beinserted at the through-connection point nearest the frontier (in the outgoing direction) when there are one or more otherthrough-connection points before this point on the same link. This is to en
20、sure that the level of the signals entering thenext country is kept within the prescribed limits.4 Fascicle IV.1 - Rec. M.160ANNEX A(to Recommendation M.160)Practical aspects to be consideredwhen determining the need for regulatorsWhen setting up a link the need for fitting regulators cannot be dete
21、rmined solely by the requirements of 2above of this Recommendation. It is necessary to take the following practical considerations into account.A.1 In order to establish that a link meets the stability requirements of this Recommendation it is either necessaryto conduct long-term tests at the time o
22、f setting up the link or to accept measurements made on similar links, that is, topredict the performance.If the former method is adopted, then, in the case of a link passing in transit through the territory of a thirdAdministration it is probable that transit charges will apply from the date the li
23、nk is set up. In any event, the cooperationof the distant terminal Administration will be required and this may not be readily forthcoming.If the latter method is adopted and the stability requirements are not met, then the problem will arise of takingthe link out of service to fit a regulator and t
24、o reline the link. This could entail a substantial loss of revenue and willrequire distant end cooperation.A.2 It is unusual for a supergroup to be provided with all five groups allocated from the outset and it cannot beassumed that these groups will end at the same point as the supergroup. In any c
25、ase, if a group that ends at the samepoint is changed to a through-group, then, unless a supergroup regulator has already been fitted, it may be necessary tointerrupt service to fit a regulator and reline the supergroup link.A.3 Consideration also has to be given to the restoration requirements when
26、 deciding to fit regulators tosupergroup links. Lack of such regulators may seriously hamper restoration arrangements.A.4 Frequent rearrangements occur on international routes and are outside the control of the distantAdministration.References1 CCITT Supplement Statistical theory requirements, Green
27、 Book, Vol. IV.2, Supplement No. 1.6, ITU,Geneva, 1973.2 CCITT Recommendation Arrangement of carrier equipment, Vol. III, Rec. G.231.3 CCITT Supplement Vibration testing, Green Book, Vol. IV.2, Supplement No. 2.9, ITU, Geneva, 1973.4 CCITT Recommendation Line stability of cable systems, Vol. III, Rec. G.214.
