1、GENERAL SECRETARIAT INTERNATIONAL TELECOMMUNICATION UNION Subject: ITU-T Q.724 Amendment 1 (03/93) Geneva, 5 November 2001 TELECOMMUNICATION STANDARDIZATION SECTOR OF ITU ITU-T Recommendation Q.724 (1988) Telep hone user part signalling procedures i) Clause 1.4/Q.724: Replace: “When an initial addre
2、ss message is received . U) when continuity-check requests are received“ by: “When an initial address message is received with a request for a continuity-check, a continuity check loop is connected.“ U) SDL Figure 8/Q.724, sheet 2: delete the output “stop T11“ following the expiration of T13. iii) E
3、nd of 1.15.1, item c): add the following text: “From the point of view of these procedures, circuits served by the Telephone User Part are always considered to be both-way. If a circuit is used one-way only, then this is for the purpose of traffic control and has no bearing on the operation of the p
4、rotocol.“ “To avoid difficulties on digital transmission links, the frequency of the equipment should not be tuned on 2000 Hz.“ . iv) Subclause 7.2.3 add the following note: Union internationale des tlcommunications Place des Nations 121 1 GENVE 20 Suisse - Switzerland - Suiza CCITT FASCICLE VI98 88
5、 = 48b2.593 0509239 2 SIGNALLING PROCEDURES References i CCIT Recommendation Characteristics of primary PCM multiplex equipment operating at 2048 kbit/s, Rec. (3.732. 2 CCITT Recommendation Characteristics of 2048-kbit/s frame structure for use with digital exchanges, Vol. III, Rec. (3.734. CCITT Re
6、commendation Second order PCM multiplex equipment operating at 8448 kbit/s, Rec. G.744. 3 4 CCITT Recommendation Characteristics of 8448-kbit/s fiame structure for use with digital exchanges, Rec. (3.746. CCITT Recommendation Language digit or discriminating digits, Rec. Q.104. CCITT Recommendation
7、Signalling Connection Control Part, Recs. 4.71 1-4.714. 5 6 Recommendation Q.724 1 Normal call set-up In this Recommendation the signalling procedures are described for the normal call set-up of an international call. The messages and signals are defined in Recommendation 4.722 and the format and co
8、ntent are given in Recommendation Q.723. I. I Initial address message An initial address message which is sent as the first message of a call set-up generally includes all of the information required by the next international exchange to route the call. The seizing function is implicit in the recept
9、ion of this initial address message. The 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 I?), refer to Recommendation Q.107 i. All digits
10、 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 digi
11、ts as are available. Ail digits of the address may be included; however, the initial address message can contain one digit in specific circumstances, e.g. national applications. Selection of the outgoing national circuit normally can start at the incoming international exchange on receipt of the ini
12、tial address message and signalling can proceed on the first national link. When no echo suppressor or nature-of-circuit indication is received from a preceding circuit using a signalling system with fewer facilities, the indicators will be considered as received no, unless exchange data i n d i ca
13、t es otherwise. Note - When additional signalling information (e.g. related to supplementary services) is to be sent, an initial address message with additional information may be used. 1.2 Subsequent address message The remaining digits, if any, of the address may be sent individually in one-digit
14、messages or in groups in multidigit messages. Efficiency can be gained by grouping together as many digits as possible. However, to prevent an increase in post-dialling delay in those cases where overlap operation with subscribers dialling is used, it may be desirable to send the last few digits ind
15、ividually. With reference to the hithholding 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, 5 8.2.1). - -. - - Fa
16、scicle VI.8 - Rec. Q.724 43 F CCITT FASCICLE VI-A 8 4862591 0509220 9 Subsequent address messages can be sent on the national network as they are received. If a continuity- check has to be performed on one or more of the international circuits involved in the connection, appropriate measures e.g. by
17、 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. Note - If in the international network the code O000 in the number
18、 of address signals field is received the message is considered as faulty. 1.3 End-ofpulsing (ST) signal The end-of-pulsing (ST) signal is always sent in the following situations: a) semiautomatic calls, b) test calls, and c) when the end-of-pulsing signal is received from a preceding circuit. In au
19、tomatic working, the end-of-pulsing 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
20、of the national number. In other cases, the end-of-pulsing signal is not sent and the end-of-address information is determined by the receipt of one of the address-complete signals from the incoming international exchange. 1.4 Continuily-check of the telephone circuits Because the signalling in Sign
21、alling System No. 7 does not pass over the speech path, facilities should be provided for making a continuity-check of the speech path in the circumstances described below. The application of the continuity-check depends on the type of the transmission system used for the telephone circuit. For tran
22、smission 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 per-call continuity check may be needed on fully digital
23、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 trans
24、parently. Typically, per-call 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. When an initial address message is rec
25、eived with a request for a continuity-check relating to a digital circuit having inherent fault indication, one of the following actions is taken: a) b) the continuity-check request is disregarded; or a continuity-check loop is connected and the maintenance system is alerted. In this case the call m
26、ay fail since no continuity signal may be received from the distant end. Noie - The reception of such a request could only be caused by an abnormal condition such as administrative errors or the occurrence of signalling errors. When the circuit type is unknown to a Signalling System No. 7 exchange,
27、or in an application where both analogue and digital circuits may be served, or when no inherent fault indication is available, a continuity-check loop should always be connected in the following cases: when the exchange has the capability to process initial address messages with continuity-check re
28、quest and such messages are received; when continuity-check requests are received. i) i) - - Fascicle VI.8 - Rec. Q.724 CCITT FASCICLE VI-A 88 W 4862593 0509223 O For analogue circuits with pilot supervision it is sufficient to perform the continuity-check on a statistical basis or by test calls (se
29、e 5 7.5)”. For analogue circuits not using pilot supervision and for mixed circuits, .e. analogue and digital circuits, the continuity-check should be performed on a per call basis. Within mixed connections, i.e. connections composed of circuits with and without continuity-check on a per call basis,
30、 it shall be ensured that the continuity signal be forwarded to the destination point although no continuity-check may have been performed on one or more parts of the end-to-end connection. The continuity-check is not intended to eliminate the need for routine testing of the transmission path. The c
31、ontinuity-check of the speech circuit will be done, link-by-link, on a per call basis or by a statistical method prior to the commencement of conversation. Procedures and requirements are specified in 8 7. The actions to be taken when pilot supervision is used are described in 9. i .5 Cross-office c
32、heck For digital exchanges the requirements mentioned in Recommendation 4.504 2 shall be met. For other exchanges Administrations shall ensure the reliability of a connection through a switching machine (cross-office check) either on a per call basis or by a statistical method. With either method, t
33、he probability of the connection being established with an unacceptable speech path transmission quality should not exceed as the long-term average. 1.6 Address-complete signals An address-complete signal will not be sent until the continuity signal has been received and the cross-office check made,
34、 if they are applicable. If the succeeding network does not provide electrical called-partys-line-condition signals, the last Signalling System No.7 exchange shall originate and send an address-complete signal when the end of address signalling has been determined and a possible GRQIGSM cycle has be
35、en completed: a) b) c) d) e) by receipt of an end-of-pulsing signal; by receipt of the maximum number of digits used in the national numbering plan; by 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
36、; by receipt of an end-of-selection signal from the succeeding network (e.g. number received signal in Signalling System No. 4); or exceptionally, 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
37、 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 address-complete signal to be sent over the international circuit. In this way,
38、 it is ensured that no national answer signal can arrive before an address-complete signal has been sent. Specifically, in cases d) and e) above, the address-complete charge signal should be sent. Note - If the succeeding network provides electrical called-partys-line-condition signals, the last Sig
39、nalling System No. 7 exchange shall originate and send address-complet signal when that condition has been received from the succeeding network and a possible GRQIGSM cycle has been completed. If in normal operation, delay in the receipt of an address-complete or equivalent signal from the succeedin
40、g network is expected, the last common channel signalling exchange will originate and send an address-complete signal 15 to 20 seconds after receiving the latest address message. This time-out condition is an upper limit considering the clauses of 5 6.4.1 (20 to 30 seconds for outgoing international
41、 exchanges in abnormal release conditions). On receipt of an address-complete signal, the first Signalling System No. 7 exchange will through-connect the speech path of the interconnected circuit I). ” The application to the international circuits and :he quantitative aspects (in particular, the fre
42、quency of performing the continuity-check) are for further study. It is envisaged that in the future evolution of the Telephone User Part (e.g. in the context of an integrated services digital network) the through-connection immediately after sending of the initial address message may become a manda
43、tory requirement. - -_ Fascicle V1.8 - Rec. 4.724 45 - 7 After an address-complete signal, only the following signals relating to the call set-up may be sent in the a) b) call-failure signal; or c) d) .Vore - Cases b), c) and d) can only occur after an address complete signal without subscriber free
44、. Anq further information about the called-partys-line-condition will be transmitted to the calling subscriber backward direction: in normal operation, one of the answer or release-guard signals: the national network congestion signal; or the circuit group congestion signal. or operator as audible t
45、ones or announcements. The address-complete signal with the subscriber-free indication is sent when it is known that the called subscribers line is free (not busy). It must be originated in the called subscribers exchange, and therefore cannot be followed by one of the unsuccessful backward set-up i
46、nformation signals. If an incoming international exchange has sent a general request message, then an address complete message must not be sent until a general forward set-up information message has been received in response to that general forward Set-up information message. 1.7 A ddress-incornplei
47、e signal The determination that the proper number of digits has not been received can be made at once if the end-of-pulsing signal is received or by receipt of an address-incompkfe signai (or equivalent) from the national network. When overlap working is used and the end-of-pulsing signal has not be
48、en received, the address-incom- plete signal will be sent by the last common channel Signalling exchange 15 to 20 seconds after receipt of the latest digit. Each Signalling System No. 7 exchange on receipt of the address-incomplete signal will send the signal to the preceding Signalling System No. 7
49、 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. 1.8 Congestion signals As soon as the congestion condition is detected one of the congestion signals (see Recommendation 4.722, 5 3.4) is sent without waiting for the completion of a possible continuity-check sequence. Reception of a conges
