ITU-T R 79-1988 AUTOMATIC TESTS OF TRANSMISSION QUALITY ON TELEGRAPH CIRCUITS BETWEEN SWITCHING CENTRES《交换中心之间电报电路传输质量的自动测试》.pdf

《ITU-T R 79-1988 AUTOMATIC TESTS OF TRANSMISSION QUALITY ON TELEGRAPH CIRCUITS BETWEEN SWITCHING CENTRES《交换中心之间电报电路传输质量的自动测试》.pdf》由会员分享，可在线阅读，更多相关《ITU-T R 79-1988 AUTOMATIC TESTS OF TRANSMISSION QUALITY ON TELEGRAPH CIRCUITS BETWEEN SWITCHING CENTRES《交换中心之间电报电路传输质量的自动测试》.pdf（10页珍藏版）》请在麦多课文档分享上搜索。

1、INTERNATIONAL TELECOMMUNICATION UNION)45G134 2 TELECOMMUNICATIONSTANDARDIZATION SECTOROF ITU4%,%2!0(94%,%2!0(G0G042!.3-)33)/.!54/-!4)#G0G04%343G0G0/ amended at Geneva, 1980 and Melbourne, 1988)The CCITT,considering(a) that maintenance measurement on a telegraph circuit made in the course of routine

2、maintenancemeasurements takes a relatively long time to carry out and occupies staff at both ends of the circuit. This applies asmuch to circuits in a satisfactory condition (the majority of cases) as to faulty circuit;(b) that automatic tests of the transmission quality on telegraph circuits betwee

3、n switching centres can beorganized without intervention of personal;(c) that transmission characteristics for international links are contained in Recommendation R.58;(d) that the specification of muldexes is given for MCVFT equipment in the R.30-Series ofRecommendations and for TDM equipment in th

4、e R.100-Series of Recommendations;(e) that tests of TDM telegraph channels are possible using maintenance loops according toRecommendation R.115;(f) that standardized texts for distortion testing are given in Recommendations R.51 and R.51 bis; and(g) that the signalling aspects are contained in the

5、U-Series of Recommendations,unanimously declares the view(1) that Administrations (or recognized private operating agencies) may organize between internationalswitching and testing centres (ISTCs) an automatic maintenance test service for testing the international trunk circuitsof telex and Gentex n

6、etworks with automatic switching consisting of one or two multi-channel code independenttransmission links connected in tandem;(2) that automatic maintenance tests of telegraph circuits should be based on the following principles:1 Purpose of automatic tests1.1 The purpose of automatic testing is to

7、 make it possible to perform rapid tests; circuits found to be “satisfactory”in the course of these will not be subjected to full maintenance tests and the maintenance staff can thus concentrate onmaking full tests of circuits identified as “doubtful” during the rapid tests.1.2 Automatic tests shoul

8、d be organized in such a way that at least at one end of the group of circuits under test, nostaff is required. This end of the circuit will then be said to be “in the passive position”, while the end initiating thetests will be said to be “in the active position”.For these tests it is necessary to

9、distinguish between trunks including regenerative equipment and thosewithout. Tests on trunks were no regeneration is involved are dealt with in 2. Tests on trunks where regeneration isinvolved are dealt with in 3.Note 1 Unless stated otherwise, the end of the circuit in the active position will be

10、denoted by the letter A andthe end of the circuit in the passive position by the letter B throughout this Recommendation.Note 2 Where regenerative and non-regenerative sections of the telegraph circuits are connected in tandem(e.g. national extension DT in Figure 3/R.79) the tests to be conducted sh

11、all be defined in the framework of bilateralagreements.2 Fascicle VII.1 - Rec. R.792 Test of transmission quality of non-regenerative telegraph circuits2.1 Introduction2.1.1 This test method is intended for trunks set up with code-independent transmission systems. Figure 1/R.79presents a typical blo

12、ck diagram for this case. Station A is in active position and station B in passive.2.1.2 The tests shall consist of measurements of the degree of gross start-stop distortion made independently in eachdirection of transmission of the trunk circuit with the test text chosen.2.1.3 The tests shall check

13、 that, on each transmission direction of the circuit, the degree of gross start-stop distortionmeasured does not exceed a level called the “decision level”, which is established at 10% if the circuit consists of asingle code independent transmission link or at 14% if the channel consists of two code

14、 independent transmission linksin tandem. The degree of gross start-stop distortion at the transmission end shall not exceed 0.5% and the tolerance forthe decision level at the receiving end shall not exceed 0.5%.2.2 Circuits tested2.2.1 It must be possible for the end of the circuit in the active p

15、osition to be connected up automatically with theautomatic testing equipment at the passive end. Rapid automatic tests should therefore only be envisaged over circuitsconnected at the incoming end to an automatic circuit switching centre, i.e. on circuits of the telex and Gentexnetworks.2.2.2 For pr

16、actical reasons, which will be explained later, tests are limited to circuits connecting two internationalswitching centres. No tests are envisaged for the time being on chains of circuits set up through a transit switchingcentre.2.2.3 If a trunk circuit system between two centres A and B is divided

17、 into groups of circuits made up, say, of agroup of circuits confined to traffic from A to B, a group of circuits confined to traffic from B to A and a group ofboth-way circuits, station A can be in the active position only for the both-way circuits and the circuits confined totraffic from A to B; a

18、nd, vice versa, station B will be active for tests concerned with traffic from B to A and may alsobe active on both-way circuits.2.2.4 Separate tests must be made in each direction of transmission of the circuit being tested since, if tests are madein the two directions in tandem, an inadmissible bi

19、as distortion on the forward path can be masked by a bias distortionof opposite sense on the backward path.2.2.5 The test is carried out over only one circuit of a trunk group. The test of the next circuit begins when the lastcircuit tested can be used for traffic.2.2.6 The automatic tests should ta

20、ke place in a slack period. To prevent collision between two international centresA trying to seize the same passible station B at the same time, a timetable for the automatic tests should be establishedby the Administration concerned to enable Administrations to have access to a particular passive

21、station one after theother.2.2.7 To make sure that circuits that are busy when due to be tested, or on which busy conditions from the distantnetwork are encountered when testing, are not overlooked during automatic testing, the Administrations concernedshall agree on when new attempts should be carr

22、ied out on these circuits.2.3 Test station equipmentAn automatic measurement station will consist of two main groups of equipment (see Figure 1/R.79):2.3.1 A transmission unit consisting of a test transmitter TT and a test analyser TA. The test analyser will be adjustedto a particular degree of dist

23、ortion, called the decision level, in such a way that if the latter value is exceeded in thesignals received during the measurement, the transmission channel being tested will be classified as “doubtful”;otherwise it will be classified as “satisfactory”. (To allow for very occasional distortion of a

24、 fortuitous nature, it wouldbe useful to classify a channel as “doubtful” only if the decision level is exceeded twice during the measurement.)Fascicle VII.1 - Rec. R.79 32.3.2 A switching unit for access operations; selection and signalling on the A-to-B circuit to be operated inaccordance with the

25、 characteristics of switching centre B, checking at station A the call-connected signal originating atstation B; receiving the call, transmitting the call-connected signal and the identification signals when the station is inthe passive position.2.3.3 In an ISTC, a station is normally in the passive

26、 condition. In this condition it can be seized by an incoming callfor automatic tests and can participate in these tests without the intervention of an operator.2.4 Test text: decision levels and decision signals2.4.1 The texts chosen for the tests by bilateral agreement between Administrations are

27、given inRecommendations R.51 (Q9S) and R.51 bis (QKS).Note 1 For tests over circuits with regeneration of telegraph signals, the use of the test pattern ofRecommendation R.51 (Q9S) is only possible when the pattern is modified such that an average character length of atleast 150 ms is maintained.Not

28、e 2 It should be noted that there is equipment in use that applies the test text specified inRecommendation R.51 (the Q9S text) but with 1.5 units stop element length.Note 3 In some cases predistorted test signals may be used by Administrations for testing code independenttransmission systems.2.4.2

29、The choice of the decision level is complicated by the fact that, while most international telex or Gentex circuitsare made up of a single voice-frequency telegraph (VFT) channel, these are also links in which these circuits consist oftwo VFT channels in tandem. International circuits consisting of

30、three interconnected VFT channels in tandem are veryrare and can be ignored as far as the organization of automatic maintenance tests is concerned (which means that thesecircuits can only with difficulty be subjected to automatic maintenance tests).2.4.3 Recommendations R.57 and R.58 specify the fol

31、lowing values for the limit of inherent start-stop distortion onstandardized texts:a) 8% for a switched network circuit consisting of a single VFT channel;b) 13% for a switched network circuit consisting of two VFT channels.2.4.4 The following decision levels are recommended:a) 10% for a circuit con

32、sisting of a single VFT channel or equivalent;b) 14% for a circuit consisting of 2 VFT channels or equivalent.4 Fascicle VII.1 - Rec. R.79These decision levels for automatic tests are slightly in excess of the limits given in 2.4.3 in order to give agreater assurance that the circuits identified are

33、 genuinely “doubtful” and also because automatic tests can be morestringent than manual tests which can give rise to optimistic results due to missed peaks.2.4.5 Distortion tests on the backward signalling path will commence as soon as possible after the start of the testsignals on the forward signa

34、lling path.2.4.6 The test check results made at the passive station will be sent to the active station by means of the followingdecision signals:a) combination No. 20 (letter T) of International Telegraph Alphabet No. 2 (ITA2) for an affirmative reply(satisfactory channel AB of the circuit);b) combi

35、nation No. 22 (letter V) for a negative reply (doubtful channel AB of the circuit).2.5 Method of access and identification signals2.5.1 The circuits to be tested will be seized at the output of the switching equipment of A. A seized circuit will bemarket “busy” for outgoing calls from switching unit

36、 A (and at switching equipment B in the case of a both-waycircuit). Station A will call test station B on the circuit seized for the test in accordance with the selection and signallingsystem applicable to calls from A to B.2.5.2 In choosing between measurements with a decision level of 10% or of 14

37、%, one of the following principles canbe selected by bilateral agreement.a) For automatic maintenance tests between SPC type switching systems the decision level is contained in thetrunk group description table of both stations; one access number to station B is sufficient.b) If station B is not of

38、SPC-type the receive decision level can be determined from the identificationsequence of station A, as explained in 2.5.8. There is only one access number to station B in this case.c) For other switching systems station B may be given two access numbers, one for access to the 10%decision level and a

39、nother one to access the 14% decision level.These call numbers must be as short as possible and they should if possible be chosen from among the serviceposition numbers. The call numbers for access to the test analyser should if possible be the same for both telex andGentex circuit tests.2.5.3 Safeg

40、uards against seizure of test stations by telex subscribers are strongly recommended. It is alsorecommended that calls made in connection with automatic tests should not be included in traffic accounting on theinternational circuits.2.5.4 It would be useful if the outgoing access could be so arrange

41、d as to include the supervisory and other elementsnormally associated with the trunk circuits used for calls to make sure that these elements are not subject to faults liableto have an adverse effect on transmission. It is considered that normal switching equipment should be used to permitaccess to

42、the testing equipment at the incoming end of the circuits. This will obviate the need for special accessequipment and enable normal signalling functions to be tested in addition to transmission performance.2.5.5 If station A wishes to initiate automatic tests on an AB circuit (i.e. one permitting a

43、call from centre A to centreB), station A:i) Goes into the active position.ii) Checks that the AB circuit to be tested is not being used by switching unit A for a call and, if it is free,seizes this circuit on the outgoing side of switching equipment A. This seizure of the AB circuit marks thelatter

44、 as busy for outgoing calls from switching unit A.iii) Calls the automatic testing station B in accordance with the selection and signalling system to be used oncircuit AB.2.5.6 As soon as station B, in the passive position, is seized by the call, it sends the call-connected signal. This willbe foll

45、owed by the identification sequence (either automatically returned or returned in response to the WRU sent bystation A) and then by the RFT signal consisting of 4 x combination No. 11 (K) of ITA2 with a delay not exceeding500 ms after the end of the preceding block.Fascicle VII.1 - Rec. R.79 52.5.7

46、The identification of the station obtained should be indicated by the return of an answerback consisting of: letter-shift, carriage-return, line-feed, one or two letters representing the telex network identification codeof the country of the station and space; the letters MAT; the figures 00 if stat

47、ion B is reached by one access number as outlined under item b) of 2.5.2 or thefigures 10 or 14 in the other cases depending whether equipment with 10% or a 14% decision leveladjustment is involved.For networks that have to send an answer-back in accordance with Recommendation S.6 1, the requisitead

48、ditional letter shifts will be added.2.5.8 If two access numbers are used to access the measuring equipment of station B, the characters indicating thedecision level in the answerback return by station A may be replaced by figure shifts.When only one access number is provided at station B and when t

49、he decision level can not be obtained fromtables related to the trunk circuits that are to be tested, then station B has to solicit the identification of station A,containing either figure 10 or 14 corresponding to the decision levels involved, after sending its own identificationcontaining the figures 00.The passive station, on receipt of identification, shall adapt itself to the required received decision level.2.5.9 Station A will receive the call-connected signal, the identification code and the RFT signal. It may be necessaryeither as part of the normal signa