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!.$3%-)G13!54/-!4)#G0G07/2+).3).!,).G0G0G03934%-3G0G04/G0G0“%G0G053%$G0G0(b) that manual and automatic operat
2、ion of international leased circuits require different technicalarrangements;(c) that the standard signalling systems set out in Recommendation Q.7 are primarily intended for the publicservice;(d) that the national circuit sections of international leased circuits may need to conform to local regula
3、tionsof the Administration(s) concerned;(e) that the method of signalling will be affected by the type of transmission and vice versa;(f) that the method of signalling will be affected by the characteristics of the service(s) carried on thecircuit;recommendsthat Administrations should use for manual
4、 international analogue leased circuits the standard signallingsystem specified in 1 below;and draws the attention of Administrationsto the guidance clauses and related annexes concerning automatic signalling on international analogue leasedcircuits, as set out in 2 below.1 Signalling on manual inte
5、rnational analogue leased circuits1.1 Signalling shall take place by the transmission of a single frequency signalling current, analogous to thesignalling method used in the international manual service and specified in Recommendations Q.1 and Q.2.1.2 The signalling current shall have a nominal freq
6、uency of either 2280 Hz or 2600 Hz. One of thesefrequencies shall be chosen for both directions of transmission by bilateral agreement between the Administrationsconcerned. Failing such an agreement, each Administration shall determine which of the two frequencies it wishes toreceive.1.3 The duratio
7、n of the transmitted tone shall be between 300 ms and 2 seconds. The upper limit of 2 secondsallows the partial use of signalling equipment designed for 500/20 Hz working according to Recommendation Q.1.1.4 The signal recognition time shall be between 100 ms and 200 ms:- The minimum duration of 100
8、ms has been chosen so as to avoid the recognition of false signals due toimitation by speech currents;- The maximum duration of 200 ms has been chosen so as to allow a safe margin between this time and theminimum transmission time.2 Fascicle VI.1 - Rec. Q.8Exceptionally, a maximum signal recognition
9、 time of 1200 ms may be used where it is known that thetransmitted signal has a 2 second duration. Such arrangements allow the partial use of signalling equipment designedfor 500/20 Hz working according to Recommendation Q.1.1.5 Other technical clauses for 2280 Hz signalling are set out in Annex A t
10、o this Recommendation.1.6 Other technical clauses for 2600 Hz signalling are set out in Annex B to this Recommendation.2 Signalling on automatic international analogue leased circuits2.1 This section refers to international analogue leased circuits employing automatic signalling. Such circuits areco
11、nsidered to form part of a private network extending across international frontiers and linking exchanges carrying outthe switching function in a private network. The exchanges may be Private Automatic Branch Exchanges (PABXs).Private tandem exchanges, or switching equipments provided by the Adminis
12、tration to carry out switching functions ina private network. Where the exchanges are privately owned, part of the signalling function may be provided by theAdministration.This Recommendation does not cover the case of international leased circuits directly connecting subscriberlines to remote switc
13、hing equipment. However, most of the following text is equally applicable to this case. Annex D, D.3 and Annex E give further information on such signalling.2.2 Many Administrations have regulations concerning the use of signalling frequencies on leased circuits andthese may apply to international l
14、eased circuits also. These regulations are intended to ensure non-interference betweenparts of the voice spectrum used for signalling and those available for use by subscriber apparatus. This does not createexceptional difficulties for manual working since the frequencies used (2280 Hz, 2600 Hz) can
15、 be converted to otheracceptable frequencies at the Terminal International Centre. However, for automatic circuits it should be the aim toprovide an uninterrupted path between the ends of the leased circuit.Some World regions have existing or proposed signalling systems which meet the regulatory arr
16、angements inthose regions and a summary of two such systems are given in Annexes C and D to this Recommendation.Administrations are invited to note these existing systems that may meet their needs for automatic signalling onanalogue leased circuits.2.3 In order to reduce the cost of providing leased
17、 circuits some inter-regional leased circuits may be providedwith various forms of bandwidth economizing systems, such as speech interpolation systems and digital voicecompression. These systems usually have their own internal digital signalling capability and these are not covered bythis Recommenda
18、tion, except that the effect that speech interpolation equipment has on analogue signalling isdiscussed.2.4 In the most general case, the choice of signalling and transmission in a private network will be determined bythe availability of suitable equipment, and by the decisions of the network user a
19、nd the Administrations concerned. Thefollowing sections give guidance on transmission factors which affect signalling, the important characteristics ofsignalling systems which could affect the choice of transmission medium, and the interaction between signalling andnon-voice services.2.5 Transmissio
20、n factors2.5.1 Recommendations for the transmission characteristics of leased circuits forming part of a private telephonenetwork are given in Recommendation G.171.2.5.2 Where large groups of circuits are concerned and the transmission multiplex equipment is on the renterspremises, it is advisable t
21、o protect against the effects of faulty transmission on groups of circuits.Recommendation Q.33 gives details of such measures.2.5.3 Satellite systemsi) Some signalling systems will not function correctly over satellite links since the long propagation delay(270 20 ms one way) exceeds that assumed by
22、 the line signalling specification. Amongst the standardsystems for public telephony, Signalling System R2 incorporates special precautions because of thisdelay. In addition the speed of multi-frequency compelled interregister signalling is affected, which maycause undesirable post-dialling delay. I
23、f signalling systems based on R2 are used in private networks thenreference should be made to information contained in Recommendations Q.7 and Q.400 to Q.490.Fascicle VI.1 - Rec. Q.8 3ii) Consideration should be given to the possibility that two satellite links may, in some cases, need to beconnecte
24、d in tandem. Means to prevent this may also need to be considered. (Further information iscontained in Recommendations E.171, G.131, Q.14 and Q.115.)iii) If satellite links via Time Division Multiple Access Systems with Digital Speech Interpolation(TDMA/DSI) are used, then guidance on circuit superv
25、ision signalling arrangements can be found inRecommendation Q.33. However, Digital Non-Interpolated (DNI) channels are usually assigned forleased circuits and these exhibit fewer problems for signalling.iv) If satellite links via Single Channel Per Carrier (SCPC) systems are used, then it should be
26、noted thatthese systems employ voice activated carriers for telephony type circuits. On transmission systems of thistype, the use of tone-on-idle signalling systems should be avoided, since such signalling systems wouldoverride the voice activation feature of SCPC systems.2.5.4 Echo controlParagraph
27、 9 of Recommendation G.171 should be observed concerning the location of echo control deviceswhere these are required. All analogue channel associated signalling systems operate more effectively if the line signalreceiver, and often the line signal sender also, are located on the line side of any ec
28、ho control device. In addition, somesignalling systems require echo control devices to be locally disabled during interregister signalling. For these reasons,the echo control device should be located at the private renters premises and not the terminal international centre.2.5.5 Speech interpolation
29、Some signalling systems may not be compatible with speech interpolation systems for the followingreasons:i) Signalling systems employing continuous state tone signalling will cause permanent operation of thespeech detectors and thus permanent trunk to channel association. This prevents the correct o
30、peration ofthe interpolation process.ii) The speech interpolation equipment may not be transparent to out-band signalling.iii) The speech interpolation equipment may cause excessive clipping of pulse signals resulting in their non-recognition by the distant signalling equipment.iv) The speech interp
31、olation equipment may not provide sufficient speech detector hangover to allow thesuccessful transmission of some signals, e.g. en bloc multi-frequency signals.Information on the characteristics of some speech interpolation systems is given in Supplement No. 2 ofFascicle V1.1, though different syste
32、ms may also be used on leased circuits.In the case of continuous state tone signalling, compatibility with speech interpolation systems can beachieved by converting the tone signalling to interface with any in-built signalling capability the system may provide.If the transmission difficulty only exi
33、sts in the interregister signalling phase, then this can be obviated by thesimultaneous transmission of a speech interpolation locking tone, e.g. 2800 Hz.Note that fully compelled signalling techniques are compatible with speech interpolation systems.2.6 Characteristics of signalling systems2.6.1 Li
34、ne signalling systemsAnalogue line signalling systems can be divided into in-band and out-band systems. In addition, twosignalling techniques may be employed: pulse signalling or continuous signalling.Information on the comparative advantages of in-band and out-band systems can be found inRecommenda
35、tion Q.20. General requirements for signalling equipment are contained in Recommendations Q.112 toQ.114.i) In-band systemsAccording to Recommendation Q.22, signalling frequencies above 2000 Hz should be used (but see also 2.7.1 and 2.7.2 below).4 Fascicle VI.1 - Rec. Q.8The preferred power level for
36、 in-band signalling is -9 dBm0 for pulsed signals and -20 dBm0 forcontinuous signals (also see Recommendation Q.16).In-band systems require the use of a guarding characteristic to prevent false operation of the signallingequipment by speech currents. Even so, occasional receiver misoperation by spee
37、ch can occur, and thusin the speech phase a suitable minimum signal recognition time should be chosen.In-band systems require the use of splitting techniques in order to confine the signalling frequencies tothe link concerned, and this has an impact on minimum signal recognition times. Further infor
38、mation canbe found in Recommendation Q.25.If the leased circuit contains a digital transmission system in the terminal national section and thisconnects directly to a renters digital PABX using a first order PCM system, then the detection of in-bandsignalling requires digital filtering techniques.ii
39、) Out-band systemsRecommendation G.171 does not provide for the use of out-band signalling on leased circuits. Becauseof the frequencies used, out-band signalling requires the use of a transparent 4 kHz bandwidth betweenthe two signalling equipments. Part of the signalling equipment is usually provi
40、ded within thetransmission equipment.Nevertheless, where the required transmission facilities can be assured, out-band signalling may providea useful alternative to in-band signalling. Preferred signalling frequencies and power levels for out-bandsignalling are set out in Recommendation Q.21.iii) Pu
41、lsed signallingPulsed signalling allows a greater signal repertoire than continuos signalling, but requires more complexsignal recognition arrangements. In general, the signalling tone is recognized by the signal receiver butrequires persistence checking and correlation with the circuit state before
42、 the signal is validated.iv) Continuous signallingUsually continuos signalling is arranged to operate with “tone-on-idle“. Such systems have the inherentadvantage of allowing immediate identification of circuit availability.Since only two signal states are available in each direction, the possible s
43、ignal repertoire is lower thanpulsed systems, but recognition arrangements are simpler. A single persistence timing is usually providedto validate changes of signalling state.Where continuous in-band signalling uses the “tone-on“ condition after the interregister signalling phase,means must be provi
44、ded to prevent the calling or called parties from hearing the signalling tone withoutundue interference to the transmission of speech currents and tones. A band stop filter as used inSignalling System R1 (see Recommendation Q.313, 2.3.4) may be suitable. Alternatively, to obviatethese difficulties,
45、pulsed signalling could be used in the speech phase.2.6.2 Interregister signallingThe following types of interregister signalling may be suitable for use on leased circuits:i) Decadic signallingSignalling takes place using the same frequency and sender/receiver equipment as the line signalling.Forwa
46、rd signals are composed of a sequence of tone pulses analogous to subscriber line signallingemploying rotary dials. Backward signals may not always be provided, but proceed-to-send and addresscomplete signals can be used to advantage.ii) Multi-frequency signallingMulti-frequency (MF) signalling has
47、the advantage of greater speed and signal repertoire than decadicsystems. To provide both an adequate repertoire and signalling reliability, signals are composed of twofrequencies from a set of 4, 5, 6 or 8 frequencies. Different frequencies may be used for signalling in thebackward direction. The f
48、requencies used for MF signalling should lie below 2000 Hz in order that theydo not interfere with in-band line signalling.Fascicle VI.1 - Rec. Q.8 5MF systems may transmit signals in pulse form, or in a compelled sequence with signals in the oppositedirection. The preferred signal power level is -9
49、 dBm0 for each constituent tone.Three existing MF systems may be suitable as the basis for signalling on leased circuits. These are:1) The dual tone multi-frequency system as specified in Recommendation Q.23 and modified to act asan interregister signalling system. (See also Recommendation Q.24.)2) Signalling System R1. See Recommendations Q.7 and Q.310 to Q.331.3) Signalling System R2. See Recommendations Q.7 and Q.400 to Q.490.2.6.3 Overall signalling repertoireConsideration should be given to providing a set of signals capable of being adapted for different situation
