ITU-T Q 33-1988 PROTECTION AGAINST THE EFFECTS OF FAULTY TRANSMISSION ON GROUPS OF CIRCUITS《自动传输和信令测试》.pdf

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1、INTERNATIONAL TELECOMMUNICATION UNION)45G134 1 TELECOMMUNICATIONSTANDARDIZATION SECTOROF ITU%.%2!,G0G02%#/-%.$!4)/.3G0G0/.G0G04%,%0(/.%37)4#().G0G0!.$G0G03).!,).).4%2.!4)/.!,G0G0!54/-!4)#G0G0!.$3%-)G13!54/-!4)#G0G07/2+).02/4%#4)/.G0G0!).34G0G04(%G0G0%b) provide appropriate failure indications on est

2、ablished calls;c) provide a means of releasing circuit connections beyond the point of transmission failure.Paragraph 4 below details the actions to be taken for circuits employing Signalling Systems Nos. 5, 6 and7 (TUP and ISUP). For circuits employing Signalling System R2, Recommendation Q.416 det

3、ails the actions to betaken.1.5 The recognition time used by the international exchange to validate the alarm ON/alarm OFF states shall be20 10 milliseconds. The recognition time is defined as the duration that signals representing the alarm ON/OFF statesmust be present at the input of the exchange

4、terminal equipment.Following recognition of the alarm ON or alarm OFF states the exchange shall carry out the actions detailed in 4.2 Mixed transmission systems2.1 Some transmission links comprise differing transmission systems which for maintenance purposes are treatedseparately (see Recommendation

5、 G.704). Examples of such transmission links are those with:2 Fascicle VI.1 - Rec. Q.33- analogue/digital conversion via transmultiplexers;- conversion between 24 and 30 channel PCM systems;- links via TDMA/DSI satellite systems.In these cases, failure indications from the local multiplex equipment

6、can be used, but alone these do notprovide an end-to-end indication of circuit availability. Since the multiplex systems use different standards, it is usuallyimpossible to provide a ready conversion of alarms from one system to another. In order to retain the benefits of thealarm indications for gr

7、oups of circuits it is necessary to carry the fault indications on a circuit basis. This may beinherent in the normal circuit signalling (as in the case of the digital version of Signalling System R2) but in the generalcase some form of individual circuit supervision is required.2.2 Circuit supervis

8、ion for digital systems2.2.1 2048 kbit/s systems (Recommendations G.732, G.734)8448 kbit/s systems (Recommendation G.744)In these systems there are two frame structure possibilities. One supports channel associated signalling, andthe other is intended for common channel signalling which allows extra

9、 time-slots to be used for speech circuits. Inorder to provide circuit supervision it is necessary to use the frame structure for channel associated signalling, even inthe case of voice frequency and common channel signalling systems. This implies a number of restrictions:- in the 2048 kbit/s system

10、 time slot 16 is not available for speech. Additionally, the common channelsignalling links of Systems No. 6 and No. 7 must use a time slot other than number 16;- similarly, in the 8448 kbit/s system time slots 67-70 are required for the circuit supervision and cannot beused for speech.Other systems

11、 of transmitting circuit supervision information (for example, using a common channel) are forfurther study.2.2.2 1544 kbit/s systems (Recommendations G.733, G.735)In this system the S bit is used for circuit supervision in a similar manner to its use for channel associatedsignalling.2.2.3 Non-stand

12、ard systemsIn non-standard transmission systems it will often be necessary to provide a discrete signalling path for thetransmission of circuit supervision indications. Annex A to this Recommendation describes the arrangements used forcircuit supervision on TDMA/DSI satellite systems together with t

13、he interfacing with the terrestrial channels.3 Signalling of circuit supervision indications3.1 In integrated digital transmission systems interfacing directly with exchanges (e.g. Recommendations G.734,G.744) and where systems connect to the other Administrations, it is recommended that a standard

14、form of circuitsupervision be used. This is detailed below for 2048 kbit/s PCM systems and 1544 kbit/s PCM systems.3.2 2048 kbit/s PCM systemsSignalling bits “a“ and “b“ of time slot 16 are used. Under abnormal (alarm) conditions both a and b bits areset to 1. The normal (no-alarm) condition is when

15、 “a“ and “b“ bits are not both equal to 1.Fascicle VI.1 - Rec. Q.33 33.3 1544 kbit/s PCM systemsIn this system the circuit supervision information is generated:- by forcing bit 2 in every channel time slot to the value 0, or- by modifying the S bit as described in 3.1.3.2.2 of Recommendation G.704 f

16、or the 12 framemultiframe, or- by sending a frame alignment alarm sequence (1111111100000000) as described in 3.1.1.3 ofRecommendation G.704 for the 24 frame multiframe1).4 Actions in Signalling Systems Nos. 5, 6 and 7 when a transmission alarm occursThis section details the actions which should be

17、taken on circuits using Signalling Systems No. 5, No. 6 andNo. 7 when a transmission alarm occurs concerning the speech path. This annex is intended to be applied to newexchange equipment only.It is split into two broad areas dealing firstly with Signalling System No. 5 and then with Signalling Syst

18、emsNo. 6 and No. 7. This split is required because the actions taken for inband signalling systems is slightly different tothat taken for common channel signalling systems.4.1 Signalling System No. 5The action taken if a transmission alarm occurs during the states shown below is as follows:4.1.1 Out

19、going circuit failure4.1.1.1 IDLE STATETake the circuit out of service to outgoing traffic. Return to service when transmission is restored.4.1.1.2 REGISTER STATEThe register state is assumed to start with sending of seizure signal and to end with sending of end of pulsingsignal (ST).- Send clear fo

20、rward.- Send a call unsuccessful indication on incoming circuit or possibly carry out a repeat attempt.- If clear forward release guard sequence fails, inhibit the repeat clear forward sequence. Resume therepeat clear forward sequence when the transmission is restored limiting the number of simultan

21、eoussignals to a value which will prevent overload of the transmission system.- If the clear forward release guard sequence is successful, take the circuit out of service to outgoingtraffic.4.1.1.3 SEIZED BUT AFTER REGISTER STATE- Wait for calling party to clear and send clear forward.- If answer si

22、gnal has not been returned from called party, send a call unsuccessful indication on incomingcircuit.- If clear forward release guard sequence fails, inhibit the repeat clear forward sequence. Resume therepeat clear forward sequence when the transmission is restored limiting the number of simultaneo

23、ussignals to a value which will not overload the transmission system.- If clear forward release guard sequence is successful take the circuit out of service to outgoing traffic.4.1.1.4 BLOCKED- No special action required._1)The third method proposed cannot ensure a proper end to end supervision if a

24、 TDMA system with multidestination ofmultiplexes or a CME is involved in the connection.4 Fascicle VI.1 - Rec. Q.334.1.2 Incoming circuit failure4.1.2.1 IDLE STATENo special action required, respond to incoming call as normal.4.1.2.2 ALL OTHER STATES- In answered state no special action to be taken,

25、 send all signals as normal.- If answer signal has not been returned from called party, start a time out device which after a certaininterval clears the chain beyond the faulty circuit.4.1.3 Bothway circuit4.1.3.1 IDLE STATE- Take the circuit out of service to outgoing traffic, respond normally to i

26、ncoming signals.- Return to outgoing service when transmission is restored.4.1.3.2 OUTGOING REGISTER STATE- See 4.1.1.2.4.1.3.3 OUTGOING AFTER REGISTER STATE- See 4.1.1.3.4.1.3.4 INCOMING ANY STATE- See 4.1.2.4.1.3.5 BLOCKED- See 4.1.1.4.4.2 Signalling System No. 6 or Signalling System No. 7The acti

27、on taken per speech circuit is as follows.4.2.1 Outgoing circuit failure4.2.1.1 IDLE STATE- Take the circuit out of service to outgoing traffic. Return to service when the transmission is restored.4.2.1.2 REGISTER STATEThe register state is assumed to start with sending of Initial Address Message an

28、d to end with the receipt of anaddress complete message.- Send clear forward.- Send a call unsuccessful indication on incoming circuit or possibly carry out a repeat attempt to set upthe call on another circuit.- Following receipt of release guard signal, take the circuit out of service to outgoing

29、traffic. Return toservice when transmission is restored.- Inhibit any repeat continuity check which may be taking place.Fascicle VI.1 - Rec. Q.33 54.2.1.3 SEIZED BUT AFTER REGISTER STATE- If answer signal has not been received from called party, send a call unsuccessful indication on incomingcircuit

30、.- If answer signal received, no special action required.- Take the circuit out of service when it becomes idle. Return to service when the transmission is restored.4.2.1.4 BLOCKED- No special action required.4.2.2 Incoming circuit failure4.2.2.1 CIRCUIT IN ANY STATE- If answer signal has not been r

31、eturned from called party, start a time out device which after a certaininterval clears the chain beyond the faulty circuit.- If answer has been received no special action is required, the transmission of blocking messages whenend to end alarm continuity is not provided should be for further study.4

32、.2.3 Bothway circuit failure4.2.3.1 IDLE STATE- Take the circuit out of service to outgoing traffic, the transmission of blocking messages when end to endalarm continuity is not provided should be for further study.- Return to outgoing service when transmission is restored.4.2.3.2 OUTGOING REGISTER

33、STATE- See 4.2.1.2 above.4.2.3.3 OUTGOING AFTER REGISTER STATE- See 4.2.1.3 above.4.2.3.4 INCOMING CIRCUIT IN ANY STATE- See 4.2.2 above.4.2.3.5 BLOCKED- No special action required.ANNEX A(to Recommendation Q.33)Circuit supervision via TDMA/DSI satellite systemsA.1 GeneralA.1.1 When satellite system

34、s employ Time Division Multiple Access (TDMA) transmission techniques with DigitalSpeech Interpolation (DSI) equipment at an earth station, the integrity of multiplex transmission systems, FDM as wellas PCM, used for terrestrial access to the satellite system cannot be maintained within the satellit

35、e system. For example,time slots 0 and 16 of a 2048 kbit/s PCM system of the group pilot of a FDM system may not be available betweenearth stations for the transfer of signalling or transmission alarm information. The provision of equivalent facilitiesover the satellite section therefore needs speci

36、al consideration.A.1.2 Although not necessarily a fault condition, an increase in circuit activity on a TDMA/DSI system may lead toan overload condition, e.g. “bit stealing“ in the DSI equipment. Conveyance of overload indicators to the associatedISC may be used to initiate appropriate network manag

37、ement actions to reduce or eliminate the overload conditions ongroups of circuits routed on the TDMA/DSI systems.6 Fascicle VI.1 - Rec. Q.33Implementation of this capability is at the discretion of individual Administrations.A.1.3 In accordance with Recommendation Q.7, specified signalling systems c

38、onsidered to be suitable forinternational application via TDMA/DSI satellite systems are:- System R2, provided that the satellite system is designed to be transparent to pulsed inter-register signals;- System No. 5,- Systems Nos. 6 and 7.A.2 Circuit supervisionPossible methods of passing circuit sup

39、ervision information for these signalling systems via a TDMA/DSIsatellite system are as follows:A.2.1 Signalling System R2A.2.1.1 In the case of System R2, only the digital version of line signalling (Recommendations Q.421 -Q.424) isspecified for use on international digital links.A.2.1.2 A satellit

40、e Line Signalling Channel (LSC) is required to convey the System R2 digital line signalling code.Two signalling bits, “a“ and “b“ are required in the LSC for each System R2 terrestrial circuit accessing the satellitesection. Under transmission failure conditions, bits “a“ and “b“ are set to State 1,

41、 so that the line signalling protocols ofdigital R2 will eventually block the circuit.Appendix I shows a typical format and organization of the LSC for System R2 line signalling.A.2.1.3 Fault conditions detected at the earth station and the consequent actions to be taken are given: inTables A-1/Q.33

42、 and A-2/Q.33 when terrestrial access is via a 2048 kbit/s PCM system or via an FDM system withsignalling conversion employed at the earth station, respectively.The application of actions given in these tables enables appropriate end-to-end supervision to be provided ona per-circuit basis.A.2.2 Sign

43、alling System No. 5A.2.2.1 It should be noted that on circuits employing System No. 5 signalling, some administrations utilize a repeatforward clear procedure as a means of achieving clear down under failure conditions. This procedure, which mayinvolve periodic sending of forward clear signals synch

44、ronously on a number of circuits, can result in severe periodicoverloading of DSI channels. In order to avoid this possible overloading of DSI channels it is preferable to limit thenumber of simultaneous forward clear signals on the circuits involved.A.2.2.2 In order to convey circuit supervision in

45、formation via the satellite system, it will be necessary to provide asatellite signalling channel.The preferred method of conveying circuit supervision information by use of a satellite digital non-interpolated (DNI) channel is described in A.2.2.3.If an LSC, as provided for in System R2, is availab

46、le, then a second method of passing circuit supervisioninformation is as described in A.2.2.4.A.2.2.3 Use of a DNI supervision channelWhen a DNI channel is utilized for circuit supervision purposes, detection by an earth station of circuitfailures on its terrestrial sector will result in the setting

47、 of bits in the DNI channel to “1“, in accordance with theinformation contained in Appendix II.Thus, if the failed circuits are digital, the detection of failure conditions, such as loss of frame alignment,described in Table A-3/Q.33 will result in the setting to “1“ of bits in the DNI channel assoc

48、iated with the affectedcircuits.Fascicle VI.1 - Rec. Q.33 7When the affected circuits are analogue, the failure will be detected at the earth station, e.g. by the loss ofpilot, or if appropriate, by receipt of a pulsed backward pilot. Fault conditions and consequent actions when analogueaccess links

49、 are employed are given in Table A-4/Q.33.The alarm information passed over the DNI channel can be forwarded by the receiving earth station to itsassociated ISC as described in Recommendation Q.33.An Administration may utilize the alarm information at its ISC to block or busy affected circuits, or, forexample, to inhibit the sending of repeat forward clear signals.Appendix II shows the format and organization of the DNI supervisory channel.A.2.2.4 Use of System R2 LSCIn this case the “a“ and “b“ signalling bits in the LSC corresponding to the Te