џWPCL ћџ2BJ|xа АH аа АА X агга ХА6p&А6p&Х аеGI а HH аСр8QСааУ У Ф Ф GееЮ† а Hр аааУ Уб cмˆ4 PŽТ б Fascicle VI.8 Р-Р Rec. Q.724 Ф ФPAGE1У Уб cмˆ4 PŽТ б ЮееЃ† а HH аааб cмˆ4 PŽТ бPAGE1У Уб cмˆ4 PŽТ б Fascicle VI.8 Р-Р Rec. Q.724 Ѓеа H№ ааЬџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџHpи P Ј XА`ИhР!(#џџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџЬаа X аб cмˆ4 PŽТ бAll drawings contained in this Recommendation have been done in Autocad. ‚У УRecommendation Q.724 аЬџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџH јP Ј XА`ИhР!(#џџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџЬаСр(MСб cмˆ4 PŽТ бSIGNALLING PROCEDURES аЬџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџH јP Ј XА`ИhР!(#џџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџЬаТX  ТТX јТС€  СС€ HСб cмˆ4 PŽТ б1С  Сб cмˆ4 PŽТ бNormal call setР-РupФ ФЦЦ а H ааЬџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџHpи P Ј XА`ИhР!(#џџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџЬаб cмˆ4 PŽТ бС СIn this Recommendation the signalling procedures are described for the normal call setР-Рup of an international call. The messages and signals are defined in Recommendation Q.722 and the format and content are given in Recommendation Q.723. аЬџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџH јP Ј XА`ИhР!(#џџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџЬаТX  ТТX јТС€  СС€ HС1.1С   Сб cмˆ4 PŽТ бУУInitial address messageЦЦ а H ааЬџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџHpи P Ј XА`ИhР!(#џџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџЬаб cмˆ4 PŽТ бФФС СAnУУ initial address messageФФ which is sent as the first message of a call setР-Рup generally includes all of the information required by the next international exchange to route the call. The seizing function is implicit in the reception of this initial address message. а H аС СThe sending sequence of address information will be the country code (not sent to an incoming international exchange) followed by the national (significant) number. For calls to operator positions (code 11 and code 12), refer to Recommendation Q.107 [1]. а H аС СAll digits required for routing the call through the international network will be sent in the initial address message. On calls with a country code in the address (except in the case of calls to special operators), the initial address message will contain a minimum of 4 digits and should contain as many digits as are available. All digits of the address may be included; however, the initial address message can contain one digit in specific circumstances, e.g. national applications. С СSelection of the outgoing national circuit normally can start at the incoming international exchange on receipt of the initial address message and signalling can proceed on the first national link. а H аС СWhen no echo suppressor or natureР-РofР-Рcircuit indication is received from a preceding circuit using a signalling system with fewer facilities, the indicators will be considered as receivedУУ noФФ, unless exchange data indicates otherwise. С СУУNoteФФ Р-Р When additional signalling information (e.g. related to supplementary services) is to be sent, an initial address message with additional information may be used. аЬџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџH јP Ј XА`ИhР!(#џџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџЬаТX  ТТX јТС€  СС€ HС1.2С   Сб cмˆ4 PŽТ бУУSubsequent address messageЦЦ а H ааЬџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџHpи P Ј XА`ИhР!(#џџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџЬаб cмˆ4 PŽТ бФФС СThe remaining digits, if any, of the address may be sent individually in oneР-Рdigit messages or in groups in multidigit messages. Efficiency can be gained by grouping together as many digits as possible. С СHowever, to prevent an increase in postР-Рdialling delay in those cases where overlap operation with subscribers' dialling is used, it may be desirable to send the last few digits individually. With reference to the withholding of digits, sufficient digits should be withheld to avoid the operation at subsequent exchanges of the short 4-6 second timeout which may be used in certain cases to determine the address complete condition. (See Recommendation Q.608, РSР 8.2.1). а H аС СУУSubsequent address messagesФФ can be sent on the national network as they are received. If a continuityР-Рcheck has to be performed on one or more of the international circuits involved in the connection, appropriate measures [e.g. by withholding the last digit(s) of the national number] must be taken at the last common channel exchange to prevent ringing the called subscriber or alerting the operator until the continuity of such speech circuits has been verified. С СУУNoteФФ Р-Р If in the international network the code 0000 in the number of address signals field is received the message is considered as faulty. Та Т1.3СpСб cмˆ4 PŽТ бУУEndР-РofР-Рpulsing (ST) signalЦЦ а H аФФб cмˆ4 PŽТ бС СThe endР-РofР-Рpulsing (ST) signal is always sent in the following situations: Та ТТ№ ТС€ Сa)СpСsemiautomatic calls,ЦЦ Та ТТ№ ТС€ Сb)СpСtest calls, andЦЦ а H аТа ТТ№ ТС€ Сc)СpСwhen the endР-РofР-Рpulsing signal is received from a preceding circuit.ЦЦ а H аС СIn automatic working, the endР-РofР-Рpulsing signal will be sent whenever the outgoing international exchange is in a position to know, by digit analysis, that the final digit has been sent. Digit analysis may consist of an examination of the country code and counting the maximum (or fixed) number of digits of the national number. In other cases, the endР-РofР-Рpulsing signal is not sent and the endР-РofР-Рaddress information is determined by the receipt of one of the addressР-Рcomplete signals from the incoming international exchange. аЬџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџH јP Ј XА`ИhР!(#џџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџЬаТX  ТТX јТС€  СС€ HС1.4С   Сб cмˆ4 PŽТ бУУContinuityР-Рcheck of the telephone circuitsЦЦ а H ааЬџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџHpи P Ј XА`ИhР!(#џџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџЬаФФб cмˆ4 PŽТ бС СBecause the signalling in Signalling System No. 7 does not pass over the speech path, facilities should be provided for making aУУ continuityР-РcheckФФ of the speech path in the circumstances described below. С СThe application of the continuityР-Рcheck depends on the type of the transmission system used for the telephone circuit. а H аС СFor transmission systems having some inherent fault indication features giving an indication to the switching system in case of fault, a continuity check is not required. This situation commonly occurs when fully digital circuits are used. However, a perР-Рcall continuity check may be needed on fully digital circuits when circuits or bundles of circuits in primary multiplex groups are dropped and inserted en route between switches and alarm indications carried on bits of the primary multiplex frame structure are lost in passing through an intermediate transmission facility that does not relay them transparently. Typically, perР-Рcall continuity checks may be needed when the transmission link between switches contains a TDMA satellite system, a digital circuit multiplication system or a digital access and crossconnection system, where fault indications are lost. С СWhen an initial address message is received with a request for a continuityР-Рcheck relating to a digital circuit having inherent fault indication, one of the following actions is taken: Та ТТ№ ТС€ Сa)СpСthe continuityР-Рcheck request is disregarded; orЦЦ а H аТа ТТ№ ТС€ Сb)СpСa continuityР-Рcheck loop is connected and the maintenance system is alerted. In this case the call may fail since no continuity signal may be received from the distant end.ЦЦ а H аС СУУNoteФФ Р-Р The reception of such a request could only be caused by an abnormal condition such as administrative errors or the occurrence of signalling errors. а H аС СWhen the circuit type is unknown to a Signalling System No. 7 exchange, or in an application where both analogue and digital circuits may be served, or when no inherent fault indication is available, a continuityР-Рcheck loop should always be connected in the following cases: а H аТа ТТ№ ТС€ Сi)СpСwhen the exchange has the capability to process initial address messages with continuityР-Рcheck request and such messages are received;ЦЦ Та ТТ№ ТС€ Сii)СpСwhen continuityР-Рcheck requests are received.ЦЦ а H аС СFor analogue circuits with pilot supervision it is sufficient to perform the continuityР-Рcheck on a statistical basis or by test calls (see РSР 7.5)УУб cмˆ4 PŽТ б1ж  а HH ааа1)б cмˆ4 PŽТ бФФThe application to the international circuits and the quantitative aspects (in particular, the frequency of performing the continuityР-Рcheck) are for further study. ж)ФФб cмˆ4 PŽТ б. For analogue circuits not using pilot supervision and for mixed circuits, i.e. analogue and digital circuits, the continuityР-Рcheck should be performed on a per call basis. Within mixed connections, i.e. connections composed of circuits with and without continuityР-Рcheck on a per call basis, it shall be ensured that the continuity signal be forwarded to the destination point although no continuityР-Рcheck may have been performed on one or more parts of the endР-РtoР-Рend connection. а H аС СThe continuityР-Рcheck is not intended to eliminate the need for routine testing of the transmission path. а H аС СThe continuityР-Рcheck of the speech circuit will be done, linkР-РbyР-Рlink, on a per call basis or by a statistical method prior to the commencement of conversation. Procedures and requirements are specified in РSР 7. а H аС СThe actions to be taken when pilot supervision is used are described in РSР 9. аЬџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџH јP Ј XА`ИhР!(#џџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџЬаТX  ТТX јТС€  СС€ HС1.5С   Сб cмˆ4 PŽТ бУУCrossР-Рoffice checkЦЦ а H ааЬџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџHpи P Ј XА`ИhР!(#џџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџЬаФФб cмˆ4 PŽТ бС СFor digital exchanges the requirements mentioned in Recommendation Q.504 [2] shall be met. For other exchanges Administrations shall ensure the reliability of a connection through a switching machine (crossР-Рoffice check) either on a per call basis or by a statistical method. With either method, the probability of the connection being established with an unacceptable speech path transmission quality should not exceed 10УУб cмˆ4 PŽТ бР-Р5ФФб cмˆ4 PŽТ б as the longР-Рterm average. аЬџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџH јP Ј XА`ИhР!(#џџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџЬаТX  ТТX јТС€  СС€ HС1.6С   Сб cмˆ4 PŽТ бУУAddressР-Рcomplete signalsЦЦ а H ааЬџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџHpи P Ј XА`ИhР!(#џџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџЬаФФб cмˆ4 PŽТ бС СAnУУ addressР-РcompleteФФ signal will not be sent until the continuity signal has been received and the crossР-Рoffice check made, if they are applicable. С СIf the succeeding network does not provide electrical calledР-Рparty'sР-РlineР-Рcondition signals, the last Signalling System No.7 exchange shall originate and send an addressР-Рcomplete signal when the end of address signalling has been determined and a possible GRQ/GSM cycle has been completed: Та ТТ№ ТС€ Сa)СpСby receipt of an endР-РofР-Рpulsing signal;ЦЦ а H аТа ТТ№ ТС€ Сb)СpСby receipt of the maximum number of digits used in the national numbering plan;ЦЦ а H аТа ТТ№ ТС€ Сc)СpСby analysis of the national (significant) number to indicate that a sufficient number of digits has been received to route the call to the called party;ЦЦ а H аТа ТТ№ ТС€ Сd)СpСby receipt of an endР-РofР-Рselection signal from the succeeding network (e.g. number received signal in Signalling System No. 4); orЦЦ а H аТа ТТ№ ТС€ Сe)СpСexceptionally, if the succeeding network uses overlap signalling and number analysis is not possible, by observing that 4 to 6 seconds have elapsed since the last digit was received, and that no fresh information has been received; in such circumstances, transmission to the national network of the last digit received must be prevented until the end of the waiting period which causes an addressР-Рcomplete signal to be sent over the international circuit. In this way, it is ensured that no national answer signal can arrive before an addressР-Рcomplete signal has been sent.ЦЦ а H аС СSpecifically, in cases d) and e) above, the addressР-Рcomplete charge signal should be sent. С СУУNoteФФ Р-Р If the succeeding network provides electrical calledР-Рparty'sР-РlineР-Рcondition signals, the last Signalling System No. 7 exchange shall originate and send addressР-Рcomplet signal when that condition has been received from the succeeding network and a possible GRQ/GSM cycle has been completed. а H аС СIf in normal operation, delay in the receipt of an addressР-Рcomplete or equivalent signal from the succeeding network is expected, the last common channel signalling exchange will originate and send an addressР-Рcomplete signal 15 to 20 seconds after receiving the latest address message. This timeР-Рout condition is an upper limit considering the clauses of РSР 6.4.1 (20 to 30 seconds for outgoing international exchanges in abnormal release conditions). а H аС СOn receipt of an addressР-Рcomplete signal, the first Signalling System No. 7 exchange will throughР-Рconnect the speech path of the interconnected circuitУУб cмˆ4 PŽТ б2жWЯа H ааа2)б cмˆ4 PŽТ бФФIt is envisaged that in the future evolution of the Telephone User Part (e.g. in the context of an integrated services digital network) the throughР-Рconnection immediately after sending of the initial address message may become a mandatory requirement. Wж)ФФб cмˆ4 PŽТ б. а H аС СAfter an addressР-Рcomplete signal, only the following signals relating to the call setР-Рup may be sent in the backward direction: а H аТа ТТ№ ТС€ Сa)СpСin normal operation, one of the answer or releaseР-Рguard signals;ЦЦ Та ТТ№ ТС€ Сb)СpСcallР-Рfailure signal; orЦЦ Та ТТ№ ТС€ Сc)СpСthe national network congestion signal; orЦЦ Та ТТ№ ТС€ Сd)СpСthe circuit group congestion signal.ЦЦ а H аС СУУNoteФФ Р-Р Cases b), c) and d) can only occur after an address complete signal without subscriber free. а H аС СAny further information about the calledР-Рparty'sР-РlineР-Рcondition will be transmitted to the calling subscriber or operator as audible tones or announcements. а H аС СThe addressР-Рcomplete signal with the subscriberР-Рfree indication is sent when it is known that the called subscriber's line is free (not busy). It must be originated in the called subscriber's exchange, and therefore cannot be followed by one of the unsuccessful backward setР-Рup information signals. а H аС СIf an incoming international exchange has sent a general request message, then an address complete message must not be sent until a general forward setР-Рup information message has been received in response to that general forward setР-Рup information message. аЬџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџH јP Ј XА`ИhР!(#џџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџЬаТX  ТТX јТС€  СС€ HС1.7С   Сб cмˆ4 PŽТ бУУAddressР-Рincomplete signalЦЦ а H ааЬџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџHpи P Ј XА`ИhР!(#џџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџЬаФФб cмˆ4 PŽТ бС СThe determination that the proper number of digits has not been received can be made at once if the endР-РofР-Рpulsing signal is received or by receipt of anУУ addressР-РincompleteФФ signal (or equivalent) from the national network. When overlap working is used and the endР-РofР-Рpulsing signal has not been received, the addressР-Рincomplete signal will be sent by the last common channel Signalling exchange 15 to 20 seconds after receipt of the latest digit. а H аС СEach Signalling System No. 7 exchange on receipt of the addressР-Рincomplete signal will send the signal to the preceding Signalling System No. 7 exchange, if any, and clear forward the connection. The first Signalling System No. 7 exchange will send a suitable signal on the preceding circuit if the related signalling system permits to do so; otherwise the appropriate tone or announcement for the national network concerned will be sent to the calling party. аЬџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџH јP Ј XА`ИhР!(#џџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџЬаТX  ТТX јТС€  СС€ HС1.8С   Сб cмˆ4 PŽТ бУУCongestion signalsЦЦ аЬџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџHpи P Ј XА`ИhР!(#џџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџЬаб cмˆ4 PŽТ бФФС СAs soon as the congestion condition is detected one of theУУ congestionФФ signals (see Recommendation Q.722, РSР 3.4) is sent without waiting for the completion of a possible continuityР-Рcheck sequence. а H аС СReception of a congestion signal at any Signalling System No. 7 exchange will cause the clearР-Рforward signal to be sent and cause an appropriate signal to be sent to the preceding exchange if the signalling system allows this or an appropriate tone or announcement to be sent to the originating subscriber or operator. аЬџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџH јP Ј XА`ИhР!(#џџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџЬаТX  ТТX јТС€  СС€ HС1.9С   Сб cмˆ4 PŽТ бУУCalledР-Рparty'sР-РlineР-Рcondition signalsЦЦ а H ааЬџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџHpи P Ј XА`ИhР!(#џџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџЬаФФб cмˆ4 PŽТ бС СTheУУ calledР-Рparty'sР-РlineР-РconditionФФ signals (see Recommendation Q.722, РSР 3.4) will be sent when the appropriate electrical signals are received at the incoming international exchange from the national network. а H аС СTheУУ calledР-Рparty'sР-РlineР-РconditionФФ signals will be sent without waiting for the completion of a possible continuity check. On receipt of one of these signals, the first Signalling System No. 7 exchange (or the outgoing international exchange) will clear forward the connection and cause an appropriate signal to be sent to the preceding exchange if the signalling system allows this or an appropriate tone or announcement to be sent to the originating subscriber or operator. а H аС СEach Signalling System No. 7 exchange on receipt of one of these signals has to clear forward the connection. аЬџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџH јP Ј XА`ИhР!(#џџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџЬа1.10УУТ№  Тб cмˆ4 PŽТ бAnswer signalsЦЦ а H ааЬџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџHpи P Ј XА`ИhР!(#џџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџЬаб cмˆ4 PŽТ бФФС СThe signalsУУ answer, charge and answer, no chargeФФ are sent as received from the national network or from the succeeding international link. а H аС СThe signals answer, charge and answer, no charge are used only as a result of the first offР-Рhook signal from the called party. аЬџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџH јP Ј XА`ИhР!(#џџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџЬа1.11УУТ№  Тб cмˆ4 PŽТ бClearР-Рback signalЦЦ а H ааЬџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџHpи P Ј XА`ИhР!(#џџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџЬаФФб cмˆ4 PŽТ бС СAУУ clearР-РbackФФ signal must not disconnect the speech path at a Signalling System No. 7 exchange. The requirements for the release of a connection in the event that a clearР-Рforward signal is not received are given in Recommendation Q.118 [3]. аЬџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџH јP Ј XА`ИhР!(#џџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџЬа1.12УУТ№  Тб cмˆ4 PŽТ бReanswer and clearР-Рback signal sequencesЦЦ а H ааЬџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџHpи P Ј XА`ИhР!(#џџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџЬаФФб cмˆ4 PŽТ бС СSubsequent offР-Рhook, onР-Рhook signals from the called party, such as will result from switchР-Рhook flashing, will cause the following sequence of signals to be sent: Та ТР-РТ№ ТclearР-Рback,ЦЦ Та ТР-РТ№ Тreanswer,ЦЦ Та ТР-РТ№ ТclearР-Рback,ЦЦ Та ТР-РТ№ Тreanswer,ЦЦ Та ТР-РТ№ Тetc.ЦЦ а H аС СIt is necessary that a flashing sequence be retransmitted to the operator (or the preceding link) and that the final condition of the circuit represents the final position of the called party's switch hook. аЬџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџH јP Ј XА`ИhР!(#џџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџЬа1.13УУТ№  Тб cмˆ4 PŽТ бForwardР-Рtransfer signalЦЦ а H ааЬџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџHpи P Ј XА`ИhР!(#џџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџЬаФФб cмˆ4 PŽТ бС СTheУУ forwardР-РtransferФФ signal may be sent in semiautomatic working in either of the following two cases: а H аТа ТТ№ ТС€ Сa)СpСfollowing a call switched automatically to a subscriber, or following a call established via a special operator, the controlling operator wishes to call in an assistance operator. On receipt of the forwardР-Рtransfer signal at the incoming international exchange, an assistance operator is called in;ЦЦ а H аТа ТТ№ ТС€ Сb)СpСfollowing a call via code 11 and 12, the controlling operator wishes to recall the incoming operator at the incoming international exchange. Receipt of the forwardР-Рtransfer signal at the incoming international exchange recalls the incoming operator on calls completed via the operator positions at the exchange.ЦЦ а HH ааЬџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџH јP Ј XА`ИhР!(#џџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџЬа1.14УУТ№  Тб cмˆ4 PŽТ бClearР-Рforward and releaseР-Рguard sequencesЦЦ а H ааЬџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџHpи P Ј XА`ИhР!(#џџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџЬаФФб cмˆ4 PŽТ бС СTheУУ clearР-РforwardФФ signal is overriding and all exchanges must be in a position to respond by releasing the circuit and sending aУУ releaseР-РguardФФ signal at any time during the progress of a call and even if the circuit is in the idle condition. If sent while a circuit is blocked it will not result in unblocking the circuit concerned (see РSР 5). The fact that the circuit is blocked will not delay the transmission of the releaseР-Рguard signal. аЬџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџH јP Ј XА`ИhР!(#џџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџЬа1.15УУТ№  Тб cмˆ4 PŽТ бReset of circuits and circuit groupsЦЦ а H ааЬџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџHpи P Ј XА`ИhР!(#џџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџЬаб cмˆ4 PŽТ бФФС СIn systems which maintain circuit status in memory there may be occasions when the memory becomes mutilated. In such a case the circuits must be reset to the idle condition in both exchanges to make them available for new traffic. Since the exchange with the mutilated memory does not know whether the circuits are idle, busy outgoing, busy incoming, blocked, etc., resetР-Рcircuit signals or a circuit group reset message should be sent as appropriate for the affected circuits. The resetР-Рcircuit signal may also be sent, in certain cases, when a signalling fault occurs (see РSРS 6.2 and 6.5). аЬџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџH јP Ј XА`ИhР!(#џџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџЬаТX  ТТX јТС€  СС€ HС1.15.1С јСб cмˆ4 PŽТ бУУResetР-Рcircuit signalЦЦ а H ааЬџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџHpи P Ј XА`ИhР!(#џџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџЬаФФб cмˆ4 PŽТ бС СIf only a few circuits are concerned a resetР-Рcircuit signal should be sent for each affected circuit. С СOn receipt of a resetР-Рcircuit signal the unaffected exchange will: а H аТа ТТ№ ТС€ Сa)СpСaccept the signal as a clearР-Рforward signal and respond by sending a releaseР-Рguard signal, after the circuit has been made idle, if it is the incoming exchange on a connection in any state of call setР-Рup or during a call;ЦЦ а H аТа ТТ№ ТС€ Сb)СpСaccept the signal as a clearР-Рback or callР-Рfailure signal, whichever is appropriate, and respond by sending a clearР-Рforward signal immediately if it is the outgoing exchange on a connection;ЦЦ а H аТа ТТ№ ТС€ Сc)СpСaccept the signal as a clearР-Рforward signal and respond by sending a releaseР-Рguard signal if the circuit is in the idle condition;ЦЦ а H аТа ТТ№ ТС€ Сd)СpСif it has previously sent a blocking signal, or if it is unable toд ё,д release the circuit as described above, respond by the blocking signal. If an incoming or outgoing call is in progress, this call should be disconnected and the circuit returned to the idle (blocked) state. A clearР-Рforward or releaseР-Рguard signal may be sent. The blocking signal should be acknowledged by the affected exchange. If the acknowledgement is not received, the repetition procedure specified in РSР 6.4.4 should be followed;ЦЦ а Hx аТа ТТ№ ТС€ Сe)СpСif it had previously received the blocking signal, respond by disconnecting any connected call, remove the blocked condition and restore the circuit to the idle state. If an outgoing call had been in progress, respond with a clearР-Рforward or, in all other cases, a releaseР-Рguard signal;ЦЦ а H аТа ТТ№ ТС€ Сf)СpСif a resetР-Рcircuit signal is received after the sending of an initial address message but before receipt of a backward signal relating to that call, clear the circuit and make an automatic repeat attempt on another circuit if appropriate.ЦЦ а H аТа ТТ№ ТС€ Сg)СpСif a resetР-Рcircuit signal is received after having sent a resetР-Рcircuit signal, respond by a releaseР-Рguard signal. The circuit should be restored to traffic;ЦЦ а H аТа ТТ№ ТС€ Сh)СpСsend an appropriate clearing signal on an interconnected circuit (e.g., clearР-Рforward, or a suitable backward signal).ЦЦ а H аС СThe affected exchange will then reconstruct its memory according to the received acknowledgement to the resetР-Рcircuit signal, and respond to the signals received in the normal way, i.e. releaseР-Рguard in response to a clearР-Рforward, blockingР-Рacknowledgement in response to a blocking signal. а H аС СIn addition, an interconnected circuit may be cleared by the use of an appropriate signal. If no acknowledgement to the resetР-Рcircuit signal is received before 4Р-Р15 seconds, the resetР-Рcircuit signal should be repeated. If an acknowledgement for the signal is not received within 1 minute after the sending of the initial resetР-Рcircuit signal, maintenance personnel should be notified to permit manual restoration procedures. However, the sending of the resetР-Рcircuit signal should continue at 1Р-Рminute intervals until maintenance intervention occurs. Та ТС€ HС1.15.2С СУУCircuit group reset messageЦЦ а H аФФС СIf a considerable number of circuits or all circuits are affected by the memory mutilation, circuit group reset messages should be used to make these circuits available for new traffic. а H аС СSince the effect of erroneous circuit group reset messages generated by undetected errors may seriously affect the quality of service, each circuit group reset message has to be sent twice. а H аС СOn receipt of two circuit group reset messages with 5 seconds for the same group or parts thereof the unaffected exchange will: Та ТТ№ ТС€ Сi)СpСIf the range field is not coded all zero:ЦЦ Та ТТ№ ТТhpТС€Сa)Си Сrestore the circuits involved to the idle state;ЦЦ а H аТа ТТ№ ТТhpТС€Сb)Си Сsend the appropriate group blocking message(s) if it had previously sent a hardware failure oriented and/or software generated group blocking message;ЦЦ а H аТа ТТ№ ТТhpТС€Сc)Си Сrespond by a circuit group resetР-Рacknowledgement message in which the status indicator bits of the circuits available for service or blocked for reasons of hardware failure or a software generated alarm are coded 0 and the status indicator bit of all circuits blocked for maintenance reasons are set to 1.ЦЦ Та ТТ№ ТС€ Сii)СpСIf the range field is coded all zero (national option)ЦЦ а H аТа ТТ№ ТТhpТС€Сa)Си Сsend the appropriate group blocking message(s) if it had previously sent a hardware oriented and/or a software generated group blocking message;ЦЦ а H аТа ТТ№ ТТhpТС€Сb)Си Сstart the restoration of the circuits on a per circuit basis in the same way as after receipt of a reset circuit for each circuit within the group (see РSР 1.15.1);ЦЦ а H аТа ТТ№ ТТhpТС€Сc)Си Сrespond by a circuit group resetР-Рacknowledgement message indicating that the restoration of the circuits concerned was started.ЦЦ а H аТа ТТ№ Тiii)Си СIndependent from the coding of the range field the following actions should take place in the unaffected exchange after receipt of two circuit group reset signals within 5 seconds:ЦЦ а H аТа ТТ№ ТТhpТС€Сa)Си Сif it had previously received (a) blocking signal(s) or (a) blocking message(s) for one or more of the circuit(s) involved the blocked condition will be removed and the circuits will be made available for service;ЦЦ а H аТа ТТ№ ТТhpТС€Сb)Си Сif a circuit group reset message is received after having sent a circuit group reset message or (a) reset circuit signal(s) the circuits involved in both the sent and the received message/signal(s) are made available for service;ЦЦ а H аТа ТТ№ ТТhpТС€Сc)Си Сappropriate signals should be sent on interconnected circuits to release them.ЦЦ а H аС СThe affected exchange will then reconstruct its memory according to the possibly received blocking messages and the received circuit group resetР-Рacknowledgement message. It will respond to the possibly received group blocking messages in the normal way. а H аС СIf no acknowledgement to a circuit group reset message is received before 4Р-Р15 seconds the circuit group reset message should be repeated (twice). If acknowledgement for the message is not received within 1 minute after sending the initial circuit group reset message maintenance personnel should be notified to permit manual restoration procedures. However, the sending of the circuit group reset message should continue at 1 minute intervals until maintenance intervention occurs. 1.16УУТ№  ТAnalysis of digit information for routingЦЦ ФФС С(See Recommendation Q.107УУ bisФФ.) 1.17УУТ№  ТDiagrams showing signal sequenceЦЦ а H аФФС СSome examples of call setР-Рup sequences are shown diagrammatically (Tables 1/Q.724 and 2/Q.724). 1.18УУТ№  ТUse of the General Request Message and the General Forward SetР-Рup Information Message (GRQ/GSM)ЦЦ а H аФФС СThe following procedures shall be applicable to exchanges generating or receiving GRQ or GSM messages: а Hx аТа ТТ№ ТС€ Сa)СpСThe GRQ/GSM protocol can only be initiated during call setР-Рup.ЦЦ а H аТа ТТ№ ТС€ Сb)СpСA unique GSM must be sent in response to a GRQ and must only contain answers to all requests contained in the GRQ.ЦЦ а H№ аТа ТТ№ ТС€ Сc)СpСAt a transit exchange, once a GRQ has been sent, there is no requirement to wait for the resultant GSM before setting upЦЦ а H аТа ТТ№ Тa connection to a succeeding exchange, unless the information requested is necessary for routing/analysis functions for that call.ЦЦ а H аТа ТТ№ ТС€ Сd)СpСAn exchange having sent a GRQ should wait until the GSM is received before sending an Address Complete Message (ACM). However, in a whole Signalling System No. 7 international network there is no requirement in the international transit exchange to delay sending the ACM, even if the GRQ/GSM cycle is not completed (i.e. ignore GSM).ЦЦ а H аТа ТТ№ ТС€ Сe)СpСA subsequent GRQ must not be sent from the same exchange before a reply (GSM) has been received in response to the previous GRQ. Consequently any GRQ's received by an exchange subsequent to the first GRQ and prior to replying with a GSM shall be ignored.ЦЦ а H аТа ТТ№ ТС€ Сf)СpСThe GRQР-РGSM interchange shall always take place on a linkР-РbyР-Рlink basis. This means that an exchange receiving a GRQ for which it does not hold the information, must initiate a separate GRQ/GSM cycle on the preceding link.ЦЦ а H аТа ТТ№ ТС€ Сg)СpСInformation received in the GSM, other than that specifically requested in the associated GRQ, will be ignored.ЦЦ а H аТа ТТ№ ТС€ Сh)СpСAn exchange shall store any information gained on a call by using the GRQ/GSM interchange or receipt of an IAM/IAI, until the call is completed successfully or failed.ЦЦ а H аТа ТТ№ ТС€ Сi)СpСIf a call attempt fails (e.g., receipt of CGC, NCC, CFL, etc.) during the period when an exchange is waiting for a GSM, then the appropriate backward call failure shall be sent without waiting for the GSM.ЦЦ а H аТа ТТ№ ТС€ Сj)СpСFailure to receive a GSM in response to a GRQ will result in the preceding exchange failing the call due to nonР-Рreceipt of the ACM (T2 timer expires in 20Р-Р30 seconds).ЦЦ а HH а‚Ср8LСб cмˆ4 PŽТ бTABLE 1/Q.724 Ср88СУ УSemiautomatic (SA) and automatic (A) terminal trafficФ Ф Ср8CС(errorР-Рfree operation assumed) б cмˆ4 PŽТ бвЦ‚HаРH!Цв‡аЬџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџH јP Ј XаџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџЬаааб cмˆ4 PŽТ бOutgoing international exchange аЬџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџHpШ xа H!џџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџЬаIncoming international exchange а Р( ааЬџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџРpШ xа H!џџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџЬаб cмˆ4 PŽТ бˆа Р( аб cмˆ4 PŽТ ба Р8 ааЬџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџ јP Ј XРА`ИhH!џџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџЬаб cмˆ4 PŽТ бУУNormal call to a free subscriber (using continuityЉcheck)ФФ а H( ааЬџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџH јP Ј XА`ИhH!џџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџЬаб cмˆ4 PŽТ ба H( аб cмˆ4 PŽТ бвЦ„HxhаР( H!Цв‡аЬџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџHpи P Ј xџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџЬаб cмˆ4 PŽТ бAddress signals from the national network are analysed а  ( ааЬџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџpи P Ј x џџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџЬаб cмˆ4 PŽТ бˆа  ( аб cмˆ4 PŽТ бвЦ„HxhаР( H!Цв‡а  а аб cмˆ4 PŽТ бThe outgoing circuit is seized. а  ( аб cмˆ4 PŽТ бˆа  ( аб cмˆ4 PŽТ бвЦƒHxh( H!Цв‡а  а ааЬџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџ8pи P Ј x џџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџЬаб cмˆ4 PŽТ бThe initial address message is sent: а 8№ аСO ССO ССO ССO ССO ССO ССO СЉС-.Сall address signals including ST in "en bloc" operation, orЦЦ а 8№ аСO ССO ССO ССO ССO ССO ССO СЉС-.Сall available address signals in overlap operation (a minute of 4 digits)ЦЦа  № а аЬџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџР(  џџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџЬаInitial address message б cмˆ4 PŽТ бУУa)ФФб cмˆ4 PŽТ бЦЦ а  № ааЬџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџ  pиШ0ЈX H!џџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџЬаThe address message is analysed to determine:ЦЦ а  Р аЉС-p2Сthe circuit to be sizedЦЦ а  а аЉС-p2Сcountry code not includedЦЦ а   аЉС-p2СnatureЉofЉcircuit (satellite or terrestrial)ЦЦ а  Р аЉС-p2Сecho suppressor controlЦЦ а  H аЉС-p2СcallingЉparty'sЉcategoryЦЦ а  а аЉС-p2СcontinuityЉcheck control.ЦЦ а  ( ааЬџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџ pиШ0ЈX H!џџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџЬаб cмˆ4 PŽТ бˆа  ( аб cмˆ4 PŽТ бвЦ„HxhаР( H!Цв‡а  р ааЬџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџpи P Ј x џџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџЬаб cмˆ4 PŽТ бThe echo suppressor, if present, is disabled so that the speech path continuityЉcheck may be performed. The transceiver for the speech path continuityЉcheck is attached, and the checkЉtone is transmitted on the outgoing circuit The echo suppressor, if present, is disabled so that the speech path continuityЉcheck may be performed. The loop for the speech path continuityЉcheck is attached to the incoming circuit а  ( аб cмˆ4 PŽТ бˆа  ( аб cмˆ4 PŽТ бвЦƒHxh( H!Цв‡б cмˆ4 PŽТ б аЬџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџР( џџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџЬаCheckЉtone б cмˆ4 PŽТ бУУa)ФФб cмˆ4 PŽТ б а  ( аб cмˆ4 PŽТ бˆа  ( аб cмˆ4 PŽТ бвЦ„HxhаР( H!Цв‡а  X ааЬџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџpи P Ј x џџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџЬаб cмˆ4 PŽТ бWhen the speech path continuityЉcheck and crossЉoffice check have been completed, and if the incoming circuit is used with common, channel signalling, when the continuity signal has been аЬџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџР( €џџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџЬа аЬџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџ €шиџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџЬа SetЉup the call in the national network begins when enough address signals are received for routing (overlap operation). а  ( аб cмˆ4 PŽТ бˆа  ( аб cмˆ4 PŽТ бвЦƒHxh( H!Цв‡аЬџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџpи P Ј x џџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџЬаб cмˆ4 PŽТ бreceived from the national network, the continuity аЬџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџР( џџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџЬаCheckЉtone а  ( аб cмˆ4 PŽТ бˆа  ( аб cмˆ4 PŽТ бвЦ„HxhаР( H!Цв‡аЬџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџpи P Ј x џџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџЬаб cмˆ4 PŽТ бsignal is sent, and the transceiver is removed. а  ( аб cмˆ4 PŽТ бˆа  ( аб cмˆ4 PŽТ бвЦƒHxh( H!Цв‡а  h аб cмˆ4 PŽТ б(When the continuityЉcheck fails, the continuityЉfailure signal is sent forward. An automatic repeat attempt is made.) The echo suppressor, if present, is enabled as appropriate. The remaining address signals are sent forward in overlap operation. аЬџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџР( џџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџЬаContinuity Subsequent address messages The checkЉloop is removed and the echo suppressor, if present, is enabled. Address signals are passed into the national network. The speech path is switched through. а  ( аб cмˆ4 PŽТ бˆа  ( аб cмˆ4 PŽТ бвЦƒHxh( H!Цв‡а  № ааЬџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџpи P Ј x џџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџЬаб cмˆ4 PŽТ бOn receipt of the addressЉcomplete signal, registers (if any) are released and the speech path throughЉconnected, the address signals are erased. Subsequent supervisory signals are handled by the processor as appropriate аЬџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџР( €џџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџЬаСр,tСAddress complete аЬџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџ pиШ0ЈX H!џџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџЬа а  h аThe address messages are analysed to determined that all the required address signals have been receive (where applicable)б cмˆ4 PŽТ бУУb)ФФб cмˆ4 PŽТ б. SetЉup of the speech path is completed. Subsequent supervisory signals are handled by the processor as appropriate.б cмˆ4 PŽТ бˆа  ( аб cмˆ4 PŽТ бвЦƒHxh( H!Цв‡а  h ааЬџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџpи P Ј x џџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџЬаб cмˆ4 PŽТ бThe operator (SA), or the calling subscriber (A) hears ringing tone. аЬџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџР( €џџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџЬаСр,˜rСAudible ringing tone аЬџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџ pиШ0ЈX H!џџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџЬа а  а аRinging tone of the country of destination is sent back.б cмˆ4 PŽТ бˆа  ( аб cмˆ4 PŽТ бвЦƒHxh( H!Цв‡а  р ааЬџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџpи P Ј x џџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџЬаб cмˆ4 PŽТ бOn receipt of the answer signal, charging б cмˆ4 PŽТ бУУa)ФФб cмˆ4 PŽТ б meaЉsurement of call duration and conversation begin. аЬџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџР( €џџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџЬаСр,˜wСAnswer аЬџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџ pиШ0ЈX H!џџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџЬа а  h аSignals from the national network are passed to the outgoing international exchange as followsб cмˆ4 PŽТ бˆа  ( аб cмˆ4 PŽТ бвЦ„HxhаР( H!Цв‡аЬџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџpи P Ј x џџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџЬаб cмˆ4 PŽТ б аЬџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџР( €џџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџЬа аЬџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџ €шиџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџЬа а  H аThe called subscriber answers (charge or not charge) а  ( аб cмˆ4 PŽТ бˆа  ( аб cмˆ4 PŽТ бвЦƒHxh( H!Цв‡аЬџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџpи P Ј x џџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџЬаб cмˆ4 PŽТ б"ClearЉback" is recognized аЬџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџР( џџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџЬаClearЉback а  а аThe called subscriber hangs up. а  ( аб cмˆ4 PŽТ бˆа  ( аб cмˆ4 PŽТ бвЦ„HxhаР( H!Цв‡а  h ааЬџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџАpи P Ј x џџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџЬаб cмˆ4 PŽТ бSA:С/€0СA clearing supervisory signal to given to the controlling operator аЬџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџР( €џџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџЬа аЬџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџ €шиџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџЬа а   ааЬџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџ ppиШ0ЈX H!џџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџЬаТа,p2ТSA and A: С<@СAfter 2Љ3 min., if there is no clearЉforward signal, the national part of the connection is released.ЦЦ а p( ааЬџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџppиШ0ЈX H!џџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџЬаб cмˆ4 PŽТ бˆа p( аб cмˆ4 PŽТ бвЦ„HxhаР( H!Цв‡а p ааЬџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџАpи P Ј xpџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџЬаб cмˆ4 PŽТ бA:С4и5СAfter 1Љ2 min., if there is no clearЉforward signal, the international connection is released and charging and measurement of the call duration are ceased. аЬџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџР(€pџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџЬа аЬџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџ€pшиџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџЬа а p( ааЬџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџppиШ0ЈX H!џџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџЬа а p( аб cмˆ4 PŽТ бˆа p( аб cмˆ4 PŽТ бвЦƒHxh( H!Цв‡а p ааЬџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџАpи P Ј xpџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџЬаб cмˆ4 PŽТ бThe outgoing operator (SA) or the calling subscriber (A) clears. When the outgoing equipЉment is released, the clearЉforward signal is sent. аЬџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџР(pџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџЬаClearЉforward а p ааЬџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџppиШ0ЈX H!џџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџЬа"ClearЉforward" is recognized. The connection is released, and "clearЉforward" is sent to the national network of destination а  ( ааЬџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџ ppиШ0ЈX H!џџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџЬаб cмˆ4 PŽТ бˆа  ( аб cмˆ4 PŽТ бвЦƒHxh( H!Цв‡а  № ааЬџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџАpи P Ј x џџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџЬаб cмˆ4 PŽТ б"ReleaseЉguard" is recognized, and the outgoing circuit is made available for new traffic аЬџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџР( џџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџЬаReleaseЉguard аЬџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџ ppиШ0ЈX H!џџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџЬаWhen the incoming equipment has released, a releaseЉguard signal is sent back. The circuit is made available for new traffic а  ( аб cмˆ4 PŽТ бˆа H ааЬџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџH8pи P Ј XА`ИhР!(#џџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџЬаб cмˆ4 PŽТ бa)С  СSolid arrows denote common channel signals; dotted arrows are tones sent via the speech path (checkЉtone and audible tones). b)С  СAddressЉcomplete signal may come from the national network. а H аc)С  СUnless a noЉcharge answer or addressЉcomplete signal has been received. аЬџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџHpи P Ј XА`ИhР!(#џџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџЬаСр KСTABLE 2/Q.724 (sheet 1 of 4) б cмˆ4 PŽТ бУ УSemiautomatic (SA) and automatic (A) transit trafficФ Ф (errorР-Рfree operation assumed) а H аУУб cмˆ4 PŽТ бa)б cмˆ4 PŽТ бФФС  СSolid arrows denote common channel signals; dotted arrows are tones sent via the speech path (checkР-Рtone and audible tones).‚б cмˆ4 PŽТ б Ср KСTABLE 2/Q.724 (sheet 2 of 4) б cмˆ4 PŽТ бTables are in file named "924T2ЉE.DOC" б cмˆ4 PŽТ бУУb)ФФб cмˆ4 PŽТ бС  СThe addressР-Рcomplete signal may come from the national network. а H аУУб cмˆ4 PŽТ бc)б cмˆ4 PŽТ бФФС  СUnless a noР-Рcharge answer or addressР-Рcomplete signal has been received.‚б cмˆ4 PŽТ б Ср KСTABLE 2/Q.724 (sheet 3 of 4) Ср KСTABLE 2/Q.724 (sheet 4 of 4)б cмˆ4 PŽТ бУ У Та Т2СpСб cмˆ4 PŽТ бDual seizure with bothР-Рway operationФ ФЦЦ а HH аб cмˆ4 PŽТ б2.1Тh  ТУУDual seizureЦЦ а H аФФС СSince Signalling System No. 7 circuits have the capability ofУУ bothР-РwayФФ operation, it is possible that the two exchanges will attempt to seize the same circuit at approximately the same time. 2.2Тh  ТУУUnguarded intervalЦЦ ФФС СConsidering that with Signalling System No. 7: а H№ аТа ТТ№ ТС€ Сa)СpСsignalling data link propagation time may be relatively long,ЦЦ Та ТТ№ ТС€ Сb)СpСthere may be significant delay due to retransmissions,ЦЦ а H аТа ТТ№ ТС€ Сc)СpСquasiР-Рassociated operation may add extra message transfer time(s) at signalling transfer points,ЦЦ а H аthe unguarded interval during whichУУ dual seizureФФ can occur may be relatively long in some instances. The exchange must therefore detect dual seizure and take action as defined in РSР 2.5. 2.3Тh  ТУУDetection of dual seizureЦЦ а H аФФС СA dual seizure is detected by an exchange from the fact that it receives an initial address message for a circuit for which it has sent an initial address message (see also РSР 7.5.1). 2.4Тh  ТУУPreventive actionЦЦ а H аФФС СDifferent methods for circuit selection can be envisaged to minimize the occurrence of dual seizure. In the following, two methods are described. Further study is required to determine the field of application of each method and to ensure that the two methods do interwork satisfactorily. а H аС СOther methods for circuit selection may also be used provided that they give the same degree of protection against dual seizure also when one of the methods specified is used at the other end. С СУУMethod 1ФФ С СAn opposite order of selection is used at each terminal exchange of a bothР-Рway circuit group. С СУУMethod 2ФФ а H аС СEach terminal exchange of a bothР-Рway circuit group has priority access to the group of circuits which it is controlling (see РSР 2.5). Of this group а H аthe circuit which has been released the longest is selectedУУ (firstР-РinФФ Р-РУУ firstР-Рout)ФФ. In addition each terminal exchange of a bothР-Рway circuit group has nonpriority access to the group of circuits which it is noncontrolling. Of this group the latest released circuit is selectedУУ (lastР-РinФФ Р-РУУ firstР-Рout)ФФ. а H аС СFor call control purposes a bothР-Рway circuit group can be subdivided into subgroups in an exchange. а H аС СIt is necessary to take preventive action in cases where Signalling System No. 7 uses a signalling data link with long propagation time. 2.5Тh  ТУУAction to be taken on detection of dual seizureЦЦ а H аФФС СEach exchange will control one half of the circuits in a bothР-Рway circuit group. On detection of a dual seizure, the call being processed by the control exchange for that circuit will be completed and the received initial address message will be disregarded. а H аС СUnder these conditions, the call being processed by the control exchange will be allowed to complete although, when continuityР-Рcheck has to be performed, the continuity of the circuit may have been checked in the direction from noncontrol to control only. The call being processed by the noncontrol exchange will be backed off, switches released, the continuityР-Рcheck transceiver removed, and the checkР-Рloop connected unless or until a continuity signal has been received from the control exchange. A clearР-Рforward signal will not be sent. The noncontrol exchange will make an automatic repeat attempt on the same or on an alternative route. а H аС СFor the purpose of resolution of dual seizure on bothР-Рway circuits, the exchange with the higher signalling point code will control all evenР-Рnumbered circuits (circuit identification code) and the other exchange the oddР-Рnumbered circuits. The designation of control may also be used for maintenance control purposes. аЬџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџH јP Ј XА`ИhР!(#џџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџЬаТX  ТТX јТС€  СС€ HС‚У У3С  Сб cмˆ4 PŽТ бAutomatic repeat attemptЦЦ аЬџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџHpи P Ј XА`ИhР!(#џџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџЬаб cмˆ4 PŽТ бФ ФС СAutomatic repeat attempt, as defined in Recommendation Q.12 [4], is provided in Signalling System No. 7. С СAn automatic repeat attempt will be made: Та ТР-РТ№ Тupon failure of the continuityР-Рcheck (see РSР 7.3);ЦЦ а H аТа ТР-РТ№ Тon detection of dual seizure (at the noncontrol exchange) (see РSР 2.5);ЦЦ а H аТа ТР-РТ№ Тon receipt of the blocking signal after sending an initial address message and before any backward signal has been received (see РSР 6);ЦЦ а H аТа ТР-РТ№ Тon receipt of a resetР-Рcircuit signal after sending an initial address message and before a backward signal has been received;ЦЦ а H аТа ТР-РТ№ Тon receipt of unreasonable signalling information after sending an initial address message and before one of the backward signals required for call setР-Рup has been received.ЦЦ а HH ааЬџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџH јP Ј XА`ИhР!(#џџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџЬаТX  ТТX јТС€  СС€ HС‚У У4С  Сб cмˆ4 PŽТ бSpeed of switching and signal transfer in international exchangesЦЦ аЬџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџHpи P Ј XА`ИhР!(#џџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџЬаб cмˆ4 PŽТ бФ Ф4.1Тh  ТУУOutgoing international exchangeЦЦ ФФС СAt the outgoing international exchange: а Hx аТа ТР-РТ№ Тif overlap operation is used, the sending of the initial address message shall take place as soon as sufficient digits are received and analyzed to permit the selection of an outgoing circuit;ЦЦ а H аТа ТР-РТ№ Тif Р"Рen blocР"Р operation is used, the initial address message should be sent as soon as all the digits of the address including the endР-РofР-Рpulsing signal are available and the outgoing circuit has been chosen.ЦЦ а HH а4.2Тh  ТУУInternational transit exchangeЦЦ а H аФФС СAt the international transit exchange, the selection of an outgoing circuit should begin as soon as the digits necessary to determine the routing have been received and analyzed. 4.3Тh  ТУУIncoming international exchangeЦЦ ФФС СAt the incoming international exchange: а H аТа ТР-РТ№ Тif overlap operation is used in the national network, the settingР-Рup of the national part of the connection should start as soon as a sufficient number of digits has been received for routing;ЦЦ а H аТа ТР-РТ№ Тif Р"Рen blocР"Р operation is used in the national network, the settingР-Рup of the national part of the connection should start as soon as all the digits of the address including the endР-РofР-Рpulsing signal have been received.ЦЦ а HH ааЬџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџH јP Ј XА`ИhР!(#џџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџЬаТX  ТТX јТС€  СС€ HС‚У У5С  Сб cмˆ4 PŽТ бBlocking and unblocking of circuits and circuit groupsЦЦ а Hр ааЬџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџHpи P Ј XА`ИhР!(#џџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџЬаб cмˆ4 PŽТ бФ ФС СThe circuit blocking (unblocking) signal and the group blocking (unblocking) message are provided to permit the switching equipment or maintenance personnel to remove from (and return to) traffic, the а H аdistant terminal(s) at a circuit or circuit group because of fault or to permit testing. Specific conditions for automatic sending of blocking and unblocking signals and messages by the switching equipment in case of use of the interruption control on interexchange circuits appear in РSР 9. а H аС СSince circuits served by Signalling System No. 7 have bothР-Рway capability, the blocking signal or a group blocking message can be originated by either exchange. The receipt of the blocking signal or a group blocking message а H аwill have the effect of prohibiting calls on the relevant circuit(s) outgoing from that exchange until an unblocking signal or the appropriate group а H аunblocking message is received, but will not in itself prohibit calls incoming to that exchange. Acknowledgement sequences are always required for the blocking and unblocking signals as well as for the group blocking and group unblocking messages, using the blockingР-Рacknowledgement signal, the unblockingР-Рacknowledgement signal, the appropriate group blockingР-Рacknowledgement message and the appropriate group unblockingР-Рacknowledgement message, respectively. The acknowledgement is not sent until the appropriate action, either blocking or unblocking, has been taken. The clear forward signal should not override a blocking condition and return circuits to service which might be faulty. (A) blocked circuit(s) will be returned to service on transmission of theд ё, д unblockingР-Рacknowledgement signal or the appropriate group unblockingР-Рacknowledgement message at one exchange and on receipt of the unblockingР-Рacknowledgement signal or the appropriate group unblockingР-Рacknowledgement message at the other exchange. а H аС СA circuit that has been maintenance blocked by a blocking signal can be unblocked by either an unblocking signal or a maintenance oriented group unblocking message. A circuit that has been maintenance blocked by a maintenance oriented group blocking message can be unblocked by either an unblocking signal or a maintenance oriented group unblocking message. 5.1Тh  ТУУOther actions on receipt of a blocking signalЦЦ ФФС СIn the event of the receipt of a blocking signal: Та ТР-РТ№ Тafter an initial address message has been sent, andЦЦ а Hx аТа ТР-РТ№ Тbefore a backward signal relating to that call has been received,ЦЦ а H аan automatic repeat attempt will be made on another circuit. The exchange receiving the blocking signal should clear forward the original attempt in the normal manner after sending the blockingР-Рacknowledgement signal. С СIf the blocking signal for a circuit is received: а H аТа ТР-РТ№ Тin the outgoing exchange after at least one backward signal relating to a call has been received, orЦЦ а H аТа ТР-РТ№ Тin the incoming exchange after at least one backward signal relating to a call has been sent,ЦЦ а HH аthe exchange will not seize that circuit for subsequent calls. а H аС СThe fact that the circuit is engaged on a call will not delay transmission of the blocking (unblocking)Р-Рacknowledgement signal. а H аС СIf a blocking signal is sent and subsequently an initial address message is received in the opposite direction, the following action is taken: а H аТа ТР-РТ№ Тfor test calls, the call should be accepted, if possible. In the case where the test call cannot be accepted, the blocking signal must be returned;ЦЦ а H аТа ТР-РТ№ Тfor calls other than test calls, the blocking signal must be returned.ЦЦ а H аС СBlocking of a circuit that has not been withdrawn from service by use of the blocking signal should not exceed five minutes, after which an alarm should be given at each terminal of the circuit. Should a call be in progress on the circuit involved, the five minutes time will commence when that call is cleared. If the work on the circuit must exceed five minutes, the circuit should be withdrawn from service. 5.2Тh  ТУУGroup blocking and unblocking messagesЦЦ а H аФФС СThe following group blocking (unblocking) messages and the appropriate acknowledgement messages are provided: Та ТР-РТ№ Тmaintenance oriented group blocking (unblocking) message;ЦЦ а Hр аТа ТР-РТ№ Тhardware failure oriented group blocking (unblocking) message;ЦЦ а Hx аТа ТР-РТ№ Тsoftware generated group blocking (unblocking) message (national option).ЦЦ а H аС СThe range of circuits to be blocked (unblocked) is dependent on the coding of the range field: а H аТа ТР-РТ№ Тif the range field is not coded all zero, the circuits indicated in the status field have to be blocked (unblocked);ЦЦ а H аТа ТР-РТ№ Тif the range field is coded all zero all circuits of the predetermined circuit group have to be blocked (unblocked).ЦЦ а HH аС СThe same rule applies to the acknowledgements. а Hx аС СSince the effect of erroneous group blocking (unblocking) messages generated by undetected errors may seriously affect the quality of service, each group blocking (unblocking) message has to be sent twice. Therefore, at the receiving exchange actions only take place after a blocking (unblocking) message was received twice within 5 seconds. а H аС СFor the circuits blocked for maintenance reasons the same conditions apply and the same actions have to be taken as described in РSР 5.1. С СFor the circuits blocked for reasons of hardware failure or software generated alarm, the following actions will be taken: Та ТР-РТ№ Тthe maintenance personnel will be alerted;ЦЦ а H№ аТа ТР-РТ№ Тall interconnected circuits will be released by the appropriate signals;ЦЦ а H аТа ТР-РТ№ Тthe affected circuits will be set to the condition idle/hardware or software blocked without any exchange of clearing signals.ЦЦ а HH ааЬџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџH јP Ј XА`ИhР!(#џџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџЬаТX  ТТX јТС€  СС€ HС‚У У6С  Сб cмˆ4 PŽТ бRelease of international connections and associated equipmentЦЦ аЬџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџHpи P Ј XА`ИhР!(#џџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџЬаб cмˆ4 PŽТ бФ Ф6.1Тh  ТУУNormal release conditionsЦЦ а H аФФС СConnections are normally released in the forward direction as a result of the receipt of a clearР-Рforward signal from the preceding exchange. а H аС СIn addition, the normal release of connections (or circuits) occurs as follows: Та ТР-РТ№ Тon continuityР-Рcheck failure (see РSР 7.3);ЦЦ Та ТР-РТ№ Тon receipt of an addressР-Рincomplete signal (see РSР 1.7);ЦЦ Та ТР-РТ№ Тon receipt of one of the congestion signals (see РSР 1.8);ЦЦ а H аТа ТР-РТ№ Тon receipt of one of the calledР-Рparty'sР-РlineР-Рcondition signals (see РSР 1.9);ЦЦ а H аТа ТР-РТ№ Тon receipt of the blocking signal or the maintenance oriented group blocking message after sending an initial address message and before a backward signal relating to that call has been received (see РSР 5);ЦЦ а H аТа ТР-РТ№ Тon receipt of unreasonable signalling information after sending an initial address message and before one of the backward signals required for call setР-Рup has been received (see РSР 6.5).ЦЦ а H аС СIf the conditions for the normal release of connections as described above are not fulfilled, release is provided as follows: Та ТР-РТ№ Тin the release under abnormal conditions (see РSР 6.4);ЦЦ Та ТР-РТ№ Тon receipt of a callР-Рfailure signal (see РSР 6.3);ЦЦ а H аТа ТР-РТ№ Тon failure to receive a clearР-Рforward signal after sending a clearР-Рback signal (see РSР 6.4);ЦЦ Та ТР-РТ№ Тon failure to receive an answer signal (see РSР 6.4);ЦЦ а H аТа ТР-РТ№ Тon receipt of a resetР-Рcircuit signal or circuit group reset message (see РSР 1.15).ЦЦ а H аС СAddress and routing information are released from memory in each of the exchanges of a connection as described in the following subsections. Та ТС€ HС6.1.1С СУУOutgoing international exchangeЦЦ ФФС СAddress and routing information stored at the outgoing international exchanges can be erased on receipt of one of the following backward signals: Та ТТ№ ТС€ Сa)СpСone of the addressР-Рcomplete signals,ЦЦ Та ТТ№ ТС€ Сb)СpСthe addressР-Рincomplete signal,ЦЦ Та ТТ№ ТС€ Сc)СpСone of the congestion signals,ЦЦ Та ТТ№ ТС€ Сd)СpСone of the calledР-Рparty'sР-РlineР-Рcondition signals,ЦЦ Та ТТ№ ТС€ Сe)СpСthe callР-Рfailure signal,ЦЦ а H аor when the connection is cleared earlier and no automatic repeat attempt has to be made. Та ТС€ HС6.1.2С СУУIncoming international exchangeЦЦ ФФС СAddress and routing information stored at the incoming international exchange can be erased on receipt of one of the backward signals indicated in РSР 6.1.1 (or equivalent) from a national signalling system, or when one of the following signals has been originated and sent to the outgoing international exchange: Та ТТ№ ТС€ Сa)СpСone of the addressР-Рcomplete signals,ЦЦ Та ТТ№ ТС€ Сb)СpСthe addressР-Рincomplete signal,ЦЦ Та ТТ№ ТС€ Сc)СpСone of the congestion signals,ЦЦ Та ТТ№ ТС€ Сd)СpСthe callР-Рfailure signal,ЦЦ Та ТТ№ ТС€ Сe)СpСthe resetР-Рcircuit signal, or circuit group reset message,ЦЦ а HH аor on receipt of a clearР-Рforward signal. Та ТС€ HС6.1.3С СУУInternational transit exchangeЦЦ а Hx аФФС СAddress and routing information stored at an international transit exchange can be erased on receipt of one of the backward signals indicated in РSР 6.1.1, on receipt of a clearР-Рforward signal, or when one of the congestion signals is originated in that exchange. 6.2Тh  ТУУAbnormal release conditions Р-Р ClearР-Рforward, releaseР-Рguard sequencesд ё, дЦЦŒТа ТС€ HСФФ6.2.1С СУУInability to release in response to a clearР-Рforward signalЦЦ а H аФФС СIf an exchange is unable to return the circuit to the idle condition in response to a clearР-Рforward signal, it should remove the circuit from service and send the blocking signal. Upon receipt of the blockingР-Рacknowledgement signal, the releaseР-Рguard signal is sent in acknowledgement of the original clearР-Рforward signal. Та ТС€ HС6.2.2С СУУInability to release in response to a backward signalЦЦ ФФС СIf an exchange is unable to release a circuit in response to an addressР-Рincomplete, congestion, calledР-Рparty'sР-РlineР-Рcondition or callР-Рfailure signal, it should remove the circuit from service by sending the blocking signal. Upon receipt of the blockingР-Рacknowledgement signal, the clearР-Рforward signal should be sent in reply to the original backward signal. а H аТа ТС€ HС6.2.3С СУУFailure to receive a releaseР-Рguard signal in response to a clearР-Рforward signalЦЦ а H аФФС СIf a releaseР-Рguard signal is not received in response to a clearР-Рforward signal before 4Р-Р15 seconds, the clearР-Рforward signal will be repeated. а H аС СIf, after sending a clearР-Рforward signal, a releaseР-Рguard signal is not received within a period of one minute after the first clearР-Рforward signal, the maintenance personnel shall be alerted. The repetition of the clearР-Рforward signal is ceased, and circuit reset is initiated. аЬџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџH јP Ј XА`ИhР!(#џџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџЬаТX  ТТX јТС€  СС€ HС6.3С   Сб cмˆ4 PŽТ бУУCallР-Рfailure signalЦЦ аЬџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџHpи P Ј XА`ИhР!(#џџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџЬаФФб cмˆ4 PŽТ бС СTheУУ callР-РfailureФФ signal is sent as the result of timeР-Рout situations, described in РSР 6.4 and whenever a call attempt fails and other specific signals do not apply, viz: Та ТР-РТ№ Тthe addressР-Рincomplete signal,ЦЦ Та ТР-РТ№ Тthe congestion signals, orЦЦ Та ТР-РТ№ Тthe calledР-Рparty'sР-РlineР-Рcondition signals.ЦЦ а H аС СReception of the callР-Рfailure signal at any Signalling System No. 7 exchange will cause the clearР-Рforward signal to be sent and, if the signalling system permits to do so, the appropriate signal to be sent to the preceding exchange or the appropriate tone or announcement to be sent to the national network. а H аС СFailure to receive a clearР-Рforward signal within 4Р-Р15 seconds of sending a callР-Рfailure signal causes the latter to be repeated. If no clearР-Рforward signal is received within 1 minute of sending the callР-Рfailure signal, repetition of the callР-Рfailure signal is ceased, maintenance personnel is alerted and circuit reset initiated. 6.4Тh  ТУУAbnormal release condition Р-Р other sequencesЦЦ ФФС СIf the conditions for normal release as covered in РSР 6.1 are not fulfilled, release will take place under the following conditions: Та ТС€ HС6.4.1С СУУOutgoing international exchangeЦЦ ФФС СAn outgoing international exchange shall: а H аТа ТТ№ ТС€ Сa)СpСrelease all equipment and clear forward the connection on failure to meet the conditions for normal release of address andЦЦ а H аТа ТТ№ Тrouting information as covered in РSР 6.1.1 before 20Р-Р30 seconds after sending the latest address message;ЦЦ а H аТа ТТ№ ТС€ Сb)СpСrelease all equipment and clear forward the connection on failure to receive an answer signal within the interval specified in Recommendation Q.118 [3];ЦЦ а H аТа ТТ№ ТС€ Сc)СpСrelease all equipment and clear forward the connection on failure to receive a clearР-Рforward signal from the national network after having received a clearР-Рback signal within the interval specified in Recommendation Q.118 [3].ЦЦ а HH аТа ТС€ HС6.4.2С СУУIncoming international exchangeЦЦ ФФС СAn incoming international exchange shall: а H аТа ТТ№ ТС€ Сa)СpСrelease all equipment, clear forward the connection into the national network and send back a callР-Рfailure signal in the following cases:ЦЦ а H аТа ТТ№ ТР-РТhpТon failure to receive a continuity or continuityР-Рfailure signal if applicable (see Recommendation Q.723, РSР 3.3.1) before 10Р-Р15 seconds after receipt of the initial address message; orЦЦ а H аТа ТТ№ ТР-РТhpТon failure to receive one of the backward signals indicated in РSР 6.1.1 (or equivalent) from a national network (where expected) before 20Р-Р30 seconds after receipt of the latest address message, unless the timing for sending the addressР-Рincomplete signal (see РSР 1.7) is provided; orЦЦ Та ТТ№ ТР-РТhpТon receipt of an addressР-Рincomplete signal after an addressР-Рcomplete signal has been generated;ЦЦ а H аТа ТТ№ ТС€ Сb)СpСsend the callР-Рfailure signal on failure to receive a clearР-Рforward signal for the incoming circuit before 4Р-Р15 seconds after sending an addressР-Рincomplete, congestion, callР-Рfailure or a calledР-Рparty'sР-РlineР-Рcondition signal indicating inability to complete the call.ЦЦ а H аТа ТТ№ ТIf a clearР-Рforward signal is not received within a period of one minute after sending the callР-Рfailure signal, the repetition of the callР-Рfailure signal should be ceased, maintenance personnel should be alerted, and a resetР-Рcircuit signal should be sent for the concerned circuit.ЦЦ а H аТа ТТ№ ТС€ Сc)СpСrelease all equipment and clear forward the connection into the national network on failure to receive a clearР-Рforward signal after sending a clearР-Рback signal within the interval specified in Recommendation Q.118 [3].ЦЦ а HH аТа ТС€ HС6.4.3С СУУInternational transit exchangeЦЦ ФФС СAn international transit exchange shall: а H аТа ТТ№ ТС€ Сa)СpСrelease all equipment, clear forward the connection and send back the callР-Рfailure signal in the following cases:ЦЦ а H аТа ТТ№ ТР-РТhpТon failure to receive a continuity or continuityР-Рfailure signal if applicable (see Recommendation Q.723, РSР 3.3.1) before 10Р-Р15 seconds after receipt of the initial address message; orЦЦ а H аТа ТТ№ ТР-РТhpТon failure to meet the conditions for normal release as covered in РSР 6.1.3 before 20Р-Р30 seconds after sending the latest address message; orЦЦ а H аТа ТТ№ ТС€ Сb)СpСsend the callР-Рfailure signal on failure to receive a clearР-Рforward signal for the incoming circuit before 4Р-Р15 seconds after sending an addressР-Рincomplete, congestion, callР-Рfailure or a calledР-Рparty'sР-РlineР-Рcondition signal indicating inability to complete the call.ЦЦ а H аТа ТТ№ ТIf a clearР-Рforward signal is not received within a period of one minute after sending the callР-Рfailure signal, the repetition of the callР-Рfailure signal should be ceased, maintenance personnel should be alerted, and a resetР-Рcircuit signal should be sent for the concerned circuit.ЦЦ а HH аТа ТС€ HС6.4.4С СУУFailure in the blocking/unblocking sequenceЦЦ а H аФФС СAn exchange will repeat the blocking (unblocking) signal or the group blocking (unblocking) messages on failure to receive the appropriate acknowledgement in response to one of these signals/messages before 4Р-Р15 seconds (see РSР 5). а H аС СIf an acknowledgement is not received within a period of one minute after sending the initial blocking (unblocking) signal or group blocking (unblocking) messages, maintenance personnel should be alerted, the repetition of the blocking (unblocking) signal or group blocking (unblocking) messages should be continued at one minute intervals. 6.5Тh  ТУУReceipt of unreasonable signalling informationЦЦ ФФС СThe Message Transfer Part of the signalling system will avoid misР-Рsequencing, or double delivery, of messages with a high reliability (Recommendation Q. 706, РSР 2). However, undetected errors at the signalling link level and exchange malfunctions may produce signalling information in messages that is either ambiguous or inappropriate. а H аС СIn order to resolve some possible ambiguities in the state of a circuitд ё, д when unreasonable signals are received the following will apply: а H аТа ТТ№ ТС€ Сa)СpСif a clearР-Рforward signal is received relating to an idle circuit it will be acknowledged with a releaseР-Рguard signal;ЦЦ а H аТа ТТ№ ТС€ Сb)СpСif a releaseР-Рguard signal is received relating to a circuit for which a clearР-Рforward signal has not been sent, the following actions will be undertaken:ЦЦ а Hx аТа ТТ№ ТР-РТhpТif the circuit is idle, the releaseР-Рguard signal is discarded;ЦЦ а H аТа ТТ№ ТР-РТhpТif the circuit is seized by a call, the releaseР-Рguard signal is considered as an ordinary unreasonable information (see item g));ЦЦ Та ТТ№ ТС€ Сc)СpСif a blocking signal is received for a blocked circuit, a blockingР-Рacknowledgement signal will be sent;ЦЦ а H аТа ТТ№ ТС€ Сd)СpСif an unblocking signal is received for an unblocked circuit, an unblockingР-Рacknowledgement signal will be sent;ЦЦ а H аТа ТТ№ ТС€ Сe)СpСif a blockingР-Рacknowledgement signal for which no blocking signal has been sent is received:ЦЦ а H аТа ТТ№ ТР-РТhpТrelating to a circuit blocked by sending a blocking signal, the blockingР-Рacknowledgement signal will be discarded,ЦЦ а H аТа ТТ№ ТР-РТhpТrelating to a circuit which is not blocked by sending a blocking signal, an unblocking signal will be sent;ЦЦ а H аТа ТТ№ ТС€ Сf)СpСif an unblockingР-Рacknowledgement signal for which no unblocking signal has been sent, is received:ЦЦ а H аТа ТТ№ ТР-РТhpТrelating to a circuit blocked by sending a blocking signal, the blocking signal will be sent,ЦЦ а H аТа ТТ№ ТР-РТhpТrelating to a circuit which is not blocked by sending a blocking signal, the unblockingР-Рacknowledgement signal will be discarded;ЦЦ а H аТа ТТ№ ТС€ Сg)СpСif other unreasonable signalling information is received, the following actions will be undertaken:ЦЦ Та ТТ№ ТР-РТhpТif the circuit is idle, the resetР-Рcircuit signal is sent;ЦЦ а H аТа ТТ№ ТР-РТhpТif the circuit is seized by a call, after receipt of a backward signal required for the call setР-Рup, the unreasonable signalling information is discarded;ЦЦ а H аТа ТТ№ ТР-РТhpТif the circuit is seized by a call, before receipt of a backward signal required for the call setР-Рup, the resetР-Рcircuit signal is sent. If the circuit is seized by an incoming call, the call will be released. If the circuit is seized by an outgoing call, an automatic repeat attempt is provided on another circuit.ЦЦ а HH ааЬџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџH јP Ј XА`ИhР!(#џџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџЬаТX  ТТX јТС€  СС€ HС‚У У7С  Сб cмˆ4 PŽТ бContinuityР-Рcheck for 4Р-Рwire speech circuitsФ ФЦЦ аЬџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџHpи P Ј XА`ИhР!(#џџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџЬаб cмˆ4 PŽТ б7.1Тh  ТУУGeneralЦЦ а H аФФС СThis specification relates only to that part of a 4Р-Рwire connection served by Signalling System No. 7. The part of the speech path to be checked may include a circuit with speech interpolation. As the presence of active echo suppressors in the circuit would interfere with the continuityР-Рcheck, it is necessary to disable the suppressors during the check and to reР-Рenable them, if required, after the check has been completed. а H аС СTheУУ transceiverФФ (checkР-Рtone transmitter and receiver) is connected to theУУ goФФ andУУ returnФФ paths of the outgoing circuit at the first and each а H аsucceeding exchange, excluding the last exchange, in that part of the connection served by Signalling System No. 7. TheУУ checkР-РloopФФ should be connected to theУУ goФФ andУУ returnФФ paths of the incoming circuit at each exchange except the first in that part of the connection served by Signalling System No. 7. A continuityР-Рcheck is considered successful when a tone is sent on theУУ goФФ path and is received on theУУ returnФФ path within acceptable transmission and timing limits.