ITU-T Q 7-1988 Signalling systems to be used for international automatic and semi-automatic telephone working《国际电联CCITT No 7信令系统的介绍》.pdf

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!.$3%-)G13!54/-!4)#G0G07/2+).3).!,).G0G03934%-3G0G04/G0G0“%G0G053%$(b) that the following signalling systems

2、have been standardized and are applicable for general use ininternational automatic and semi-automatic working:- Signalling System No. 4, standardized by the CCIF in 1954;- Signalling System No. 5, standardized by the CCITT in 1964;- Signalling System No. 6, standardized by the CCITT in 1968;- Signa

3、lling System No. 7, standardized by the CCITT in 1980;(c) that the following signalling systems have been standardized and are applicable for regional use ininternational automatic and semi-automatic telephone working:- Signalling System R1 (Regional Signalling System No. 1, formerly called the Nort

4、h American System),standardized by the CCITT in 1968;- Signalling System R2 (Regional Signalling System No. 2, formerly called the MFC Bern System),standardized by the CCITT in 1968;(d) that, under the conditions and subject to the reservations stated below, these signalling systems may beexpected t

5、o give acceptable results for international automatic and semi-automatic telephone working;desiringthat the CCITT Recommendation concerning the signalling systems for international automatic and semi-automatic telephone working be generally applied by all Administrations;unanimously recommendsthat,

6、under the conditions and subject to the reservations stated below, Administrations should use, forinternational automatic and semi-automatic telephone working, one or more of the standard signalling systemsmentioned in (b) and (c) above.1 Criteria for selecting a signalling systemMany factors influe

7、nce the selection of a given signalling system for a particular application. Factors thatshould be considered include:1.1 Satellite systems because of long round-trip propagation delays (540 40 ms)The inclusion of one satellite link in a telephone connection requires subscribers to keep more discipl

8、ine thanusual during a conversation. If use is made of two satellite links in tandem, requirements are even more stringent. Inaddition, there is the question of what transmission objectives are attainable on such a connection.2 Fascicle VI.1 - Rec. Q.7According to Recommendation Q.13 the inclusion o

9、f two satellite links in a connection should be avoided inall but exceptional cases. To facilitate the observance of this Recommendation, it is advisable to inform the subsequenttransit centres by means of signalling that a satellite link is already included in the connection. During the followingro

10、uting process the transit centre(s) should select a terrestrial link.1.2 Echo suppressorsBoth long terrestrial telephone links and satellite links call for the insertion of echo suppressors.Recommendations G.131 1 and Q.115 include basic requirements for the insertion of echo suppressors.Therefore,

11、signalling systems should be arranged to act in cooperation with switching equipment to achievethe goals covered by Recommendations G.131 1 and Q.115. This would be facilitated where the signalling system tobe used provides the possibility of controlling the inclusion of echo suppressors.In the futu

12、re, the use of echo cancellers may need to be considered (see Recommendation G.165 2).1.3 Speech interpolation systems (e.g. TASI)In the case of a transmission system with speech interpolation, it must be ensured that the signalling system tobe used is compatible with speech interpolation.2 Further

13、criteria for selecting a signalling systemOnce Administrations decide to establish a route, they will have to specify the general requirements to be metby the signalling system.In the following, some questions are drawn up which may serve as a guideline:a) Does the transmission system provide for su

14、fficient bandwidth (e.g. for outband line signalling)?b) Is the signal capacity sufficient to allow the setting-up of an ordinary connection?c) Is an additional exchange of information required, e.g.:- for echo suppressor control,- to increase routing facilities,- to obtain or to offer detailed info

15、rmation on congestion,- to obtain or to offer information on the condition of the called subscriber line,- to obtain or to offer information on the nature of the call:i) for identification orii) for management purposes?d) What requirements have to be set for the speed of the signalling system? What

16、post-dialling andanswering delays are to be tolerated?e) Is there any interdependence between the minimum bundle size and signalling (e.g., as in the case ofpilot interruption control of Signalling System R2)?f) In the case of satellite systems, does the earth station require an extra interface betw

17、een the terrestrialaccess circuits and the satellite links?g) Is it necessary to introduce a new signalling system?h) Is the signalling system suitable for application to the particular exchange type, e.g., electromechanicalexchanges?3 Characteristics of the standard CCITT Signalling Systems for gen

18、eral use3.1 Signalling System No. 4Described and specified in Fascicle VI.2.Suitable for one-way operation.Suitable for terminal and transit working; in the latter case two or three circuits equipped with SignallingSystem No. 4 may be switched in tandem.Fascicle VI.1 - Rec. Q.7 3Signalling System No

19、. 4 is used in Europe and the Mediterranean Basin.It makes use of a two-frequency code within the speech band.A four-element binary code is employed for interregister signalling. Each of these elements consists of one ofthe two signal frequencies.Each digit is acknowledged. In the case of long propa

20、gation times, these acknowledgements have an adverseeffect because the propagation time is included twice in one signalling cycle. This disadvantage is more or lesscompensated for by the overlap mode of operation.Signalling System No. 4 has a signal capacity of 16 codes for forward interregister sig

21、nals and no registersignals in the backward direction other than the acknowledgement signals.One signal is provided for echo suppressor control on mutual agreement.A signal is not provided to indicate whether the connection already includes a satellite link.Not suitable for operation on transmission

22、 systems with speech interpolation.3.2 Signalling System No. 5Described and specified in Fascicle VI.2.Suitable for both-way operation.Suitable for terminal and transit working; in the latter case two or three circuits equipped with SignallingSystem No. 5 may be switched in tandem.A multifrequency c

23、ode (MFC: 2 out of 6) within the speech band is used for interregister signalling. The linesignals consist of 1 or 2 frequencies within the speech band.The entire address information is stored up to the last signal. It is then transmitted en bloc as a rapid sequenceof pulsed multifrequency code sign

24、als.The application of the en bloc mode of operation may result in an increased post-dialling delay, especially ifthe ST condition is determined by time out.Signalling System No. 5 has a signal capacity of 15 codes for forward interregister signals and no backwardinterregister signals.Signals are no

25、t provided either for echo suppressor control or for indicating whether the connection alreadyincludes a satellite link.Suitable for operation on transmission systems with speech interpolation and on satellite links.3.3 Signalling System R1Described and specified in Fascicle VI.4.Signalling System R

26、1 is mainly used in North America.Suitable for both-way operation.Specified for terminal working.A multifrequency code (MFC: 2 out of 6) within the speech band is used for interregister signalling.In the analogue version of the Signalling System R1 line signalling, one frequency within the speech ba

27、nd isused. In the digital version of the Signalling System R1 line signalling, the two resultant signalling channels per speechcircuit may be regarded as outband channels.4 Fascicle VI.1 - Rec. Q.7The following three modes of operation can be used to transmit the address information:- en bloc,- en b

28、loc/overlap, or- overlap.The mode of operation selected influences:- the seizing time of the next link, as well as- the post-dialling delay.The address information is transmitted as pulsed MFC signals.Signalling System R1 has a signal capacity of 15 codes for forward interregister signals but no bac

29、kwardinterregister signals.Signals are not provided either for echo suppressor control or for indicating whether the connection alreadyincludes a satellite link.Signalling System R1 can be used on satellite links. A variant of Signalling System R1 may be suitable foroperation on transmission systems

30、 with digital speech interpolation, provided that the systems are designed andengineered to be transparent to pulsed interregister signals.3.4 Signalling System R2Described and specified in Fascicle VI.4.Used for one-way operation on analogue transmission systems. Both-way operation is possible on d

31、igitaltransmission systems.Suitable for terminal and transit working.Signalling System R2 is used in both national and international telephone networks in several regions of theworld.A multifrequency code (MFC: 2 out of 6) within the speech band is used for interregister signalling. Since twodiffere

32、nt sets of six frequencies in separate bands are defined for forward and backward interregister signals, SignallingSystem R2 interregister signalling is suitable for use on 2-wire circuits as well as on 4-wire circuits.For the analogue version of the Signalling System R2 line signalling, use is made

33、 of a low-level tone-on-idlemethod out of band. In addition, pilot interruption control is used.The digital version of the line signalling uses two signalling channels to transmit the signalling informationand for circuit supervision. For 2048 kbit/s PCM systems, the signalling information of the 30

34、 speech circuits istransmitted in the Time Slot 16 (see Recommendation G.732 3).It should be noted that the analogue version of the line signalling can be used on digital links; the signallingstates are sent coded on one signalling channel. This use of the analogue version on digital links is not re

35、commendedon international circuits.When a circuit is composed of both digital and analogue links, a conversion between the two versions of theline signalling can occur at the interface (see Recommendation Q.430).Compelled signalling is used to transmit the address information in the overlap mode as

36、multifrequency codesignals, i.e., each forward interregister signal is acknowledged by a backward interregister signal. Considering that fourtimes the propagation time is to be included in one signalling cycle, the exchange of signals is rather slow if thepropagation time is long. This disadvantage

37、is more or less compensated for by the overlap mode of operation.Fascicle VI.1 - Rec. Q.7 5Signalling System R2 has a higher signalling capacity than Signalling Systems No. 4, No. 5 and R1. Theinterregister signals allow, amongst others:- improved routing,- detailed information on congestion,- infor

38、mation on:i) the nature of call,ii) the condition of the called subscriber line,- no-charge calls, and- address-complete information.Signalling System R2 includes both forward and backward interregister signals for echo suppressor control.In Signalling System R2, two signals are specified which indi

39、cate whether or not the connection alreadyincludes a satellite link.Signalling System R2 may be suitable for use on satellite circuits, especially when it is already employed inthe national or regional telephone networks concerned.When Signalling System R2 is to be used on satellite links, the follo

40、wing must be borne in mind:- In the case of analogue line signalling, intervals T1 and T2 have to be adapted.- Pilot interruption control requires bundles comprising a multiple of 12 speech circuits.- The register at the incoming end of a satellite link using Signalling System R2 shall be operated a

41、s anoutgoing R2 register.- The guard time for blocking and recognition of forward signals when pulsed signals are transmittedshould be adapted to the propagation time on the satellite link.Signalling System R2 may be suitable for operation on transmission systems with digital speech interpolation,pr

42、ovided the systems are designed and engineered to be transparent to pulsed interregister signals.With 3 kHz spaced channels, the interregister signalling of Signalling System R2 may be used with the linesignalling of Signalling System No. 4.3.5 Signalling System No. 6Fully described and specified in

43、 Fascicle VI.3.Suitable for both-way operation.Suitable for terminal and transit working.During the period from 1970 to 1972 Signalling System No. 6 was tested internationally.Some Administrations have introduced it for international telephone traffic. A variant of Signalling SystemNo. 6 is employed

44、 in the national telephone network of the United States.A common signalling link is used for signalling.May be used in either an associated or quasi-associated mode of operation. Use in a quasi-associated modemay be more economic for small bundles of circuits.Signalling is performed by means of sign

45、al units. Each unit is 28 bits in length, including 8 check bits.Transmission is at a speed of 2400 bit/s for the analogue version and 4 kbit/s (optionally 56 kbit/s) for the digitalversion.Each signal unit within a block of 11 signal units is acknowledged and retransmitted in case of errors.6 Fasci

46、cle VI.1 - Rec. Q.7The address information can be transmitted en bloc and in the overlap mode. Because the transmission speedof Signalling System No. 6 is considerably higher than that of channel-associated signalling systems, the influence ofthe mode of operation on the post-dialling delay is reduc

47、ed substantially.The signal capacity (including the spare codes) of Signalling System No. 6 is much higher than that ofSignalling Systems No. 4, No. 5, R1 and R2.Signalling System No. 6 contains signals for echo suppressor control as well as signals indicating whether asatellite link is already incl

48、uded in the connection.Signalling System No. 6 can be used for all types of telephone circuits including those with speechinterpolation.Signalling System No. 6 can be used on satellite links.3.6 Signalling System No. 7Fully described and specified in Fascicles VI.7, VI.8 and VI.9.Suitable for both-w

49、ay operation.Suitable for terminal and transit working.A common signalling link is used for signalling.Signalling System No. 7 can be used in national and international telecommunication networks.Signalling System No. 7 can be used for dedicated networks (e.g. data transmission, telephone) and within anintegrated services digital network. It is the preferred signalling system between Integrated Digital Network (IDN)exchanges and within the Integrated Services Digital Network (ISDN).Signalling System No. 7 may be used in either an associated or quasi-associated mode of opera