1、 INTERNATIONAL TELECOMMUNICATION UNION ITU-T Q.120-Q.139TELECOMMUNICATION STANDARDIZATION SECTOR OF ITU (11/1988) SERIES Q: SWITCHING AND SIGNALLING Specifications of Signalling System No. 4 ITU-T Recommendations Q.120-Q.139 (Formerly CCITT Recommendations) ITU-T Q-SERIES RECOMMENDATIONS SWITCHING A
2、ND SIGNALLING SIGNALLING IN THE INTERNATIONAL MANUAL SERVICE Q.1Q.3 INTERNATIONAL AUTOMATIC AND SEMI-AUTOMATIC WORKING Q.4Q.59 FUNCTIONS AND INFORMATION FLOWS FOR SERVICES IN THE ISDN Q.60Q.99 CLAUSES APPLICABLE TO ITU-T STANDARD SYSTEMS Q.100Q.119 SPECIFICATIONS OF SIGNALLING SYSTEMS No. 4 AND No.
3、5 Q.120Q.249 Specifications of Signalling System No. 4 Q.120Q.139 Specifications of Signalling System No. 5 Q.140Q.179 Interworking of Signalling Systems No. 4 and No. 5 Q.180Q.249 SPECIFICATIONS OF SIGNALLING SYSTEM No. 6 Q.250Q.309 SPECIFICATIONS OF SIGNALLING SYSTEM R1 Q.310Q.399 SPECIFICATIONS O
4、F SIGNALLING SYSTEM R2 Q.400Q.499 DIGITAL EXCHANGES Q.500Q.599 INTERWORKING OF SIGNALLING SYSTEMS Q.600Q.699 SPECIFICATIONS OF SIGNALLING SYSTEM No. 7 Q.700Q.799 Q3 INTERFACE Q.800Q.849 DIGITAL SUBSCRIBER SIGNALLING SYSTEM No. 1 Q.850Q.999 PUBLIC LAND MOBILE NETWORK Q.1000Q.1099 INTERWORKING WITH SA
5、TELLITE MOBILE SYSTEMS Q.1100Q.1199 INTELLIGENT NETWORK Q.1200Q.1699 SIGNALLING REQUIREMENTS AND PROTOCOLS FOR IMT-2000 Q.1700Q.1799 SPECIFICATIONS OF SIGNALLING RELATED TO BEARER INDEPENDENT CALL CONTROL (BICC) Q.1900Q.1999 BROADBAND ISDN Q.2000Q.2999 For further details, please refer to the list o
6、f ITU-T Recommendations. Signalling System No. 4 (1988) i ITU-T Recommendations Q.120-Q.139 Specifications of Signalling System No. 4 Source ITU-T Recommendations Q.120-Q.139 were prepared by CCITT Study Group XI (1985-1988) and approved by WTSC in Melbourne on 25 November 1988. Those texts were ori
7、ginally published in Blue Book, Fascicle VI.2. ii Signalling System No. 4 (1988) FOREWORD The International Telecommunication Union (ITU) is the United Nations specialized agency in the field of telecommunications. The ITU Telecommunication Standardization Sector (ITU-T) is a permanent organ of ITU.
8、 ITU-T is responsible for studying technical, operating and tariff questions and issuing Recommendations on them with a view to standardizing telecommunications on a worldwide basis. The World Telecommunication Standardization Conference (WTSC), which meets every four years, establishes the topics f
9、or study by the ITU-T study groups which, in turn, produce Recommendations on these topics. The approval of ITU-T Recommendations is covered by the procedure laid down in WTSC Resolution 1. In some areas of information technology which fall within ITU-Ts purview, the necessary standards are prepared
10、 on a collaborative basis with ISO and IEC. NOTE In this Recommendation, the expression “Administration“ is used for conciseness to indicate both a telecommunication administration and a recognized operating agency. INTELLECTUAL PROPERTY RIGHTS ITU draws attention to the possibility that the practic
11、e or implementation of this Recommendation may involve the use of a claimed Intellectual Property Right. ITU takes no position concerning the evidence, validity or applicability of claimed Intellectual Property Rights, whether asserted by ITU members or others outside of the Recommendation developme
12、nt process. As of the date of approval of this Recommendation, ITU had not received notice of intellectual property, protected by patents, which may be required to implement this Recommendation. However, implementors are cautioned that this may not represent the latest information and are therefore
13、strongly urged to consult the TSB patent database. ITU 2002 All rights reserved. No part of this publication may be reproduced or utilized in any form or by any means, electronic or mechanical, including photocopying and microfilm, without permission in writing from ITU. Signalling System No. 4 (198
14、8) iii CONTENTS Specifications of Signalling System No. 4 Rec. No. Page Q.120 Definition and function of signals . 1 Q.121 Signal code 6 Q.122 Signal sender . 12 Q.123 Signal receiver 12 Q.124 Splitting arrangements. 15 Q.125 Speed of switching in international exchanges 16 Q.126 Analysis and transf
15、er of digital information 16 Q.127 Release of registers 16 Q.128 Switching to the speech position . 18 Q.129 Maximum duration of a blocking signal 19 Q.130 Special arrangements in case of failures in the sequence of signals 19 Q.131 Abnormal release conditions of the outgoing register causing releas
16、e of the international circuit 19 Q.133 Numbering for access to automatic measuring and testing devices. 20 Q.134 Routine testing of equipment (local maintenance) 20 Q.135 Principles of rapid transmission testing equipment . 21 Q.136 Loop transmission measurements 21 Q.137 Automatic testing equipmen
17、t. 22 Q.138 Instruments for checking equipment and measuring signals . 23 Q.139 Manual testing 24 Signalling System No. 4 (1988) 1 SPECIFICATIONS OF SIGNALLING SYSTEM No. 4 CHAPTER I DEFINITION AND FUNCTION OF SIGNALS Recommendation Q.120 1. DEFINITION AND FUNCTION OF SIGNALS 1.1 seizing signal (sen
18、t in the forward direction) This signal is transmitted at the beginning of a call to initiate circuit operation at the incoming end of an international circuit. The seizing signal can also perform switching functions and two different types of seizing signal are provided for this purpose, viz: a) th
19、e terminal seizing signal, which can be used at the incoming international exchange, to seize equipment used exclusively for switching the call to the national network of the incoming country; b) the transit seizing signal, which can be used in the exchange at the incoming end of the international c
20、ircuit to seize equipment used exclusively for switching the call to another international exchange. 1.2 proceed-to-send signal (sent in the backward direction) This signal is sent from the incoming end of an international circuit, following the receipt of a seizing signal, to indicate that the equi
21、pment is ready to receive the numerical signals. In System No. 4 two different proceed-to-send signals are provided: a) the terminal proceed-to-send signal, used to invite the sending of the language digit1)(or the discriminating digit1)plus the national (significant) number1); b) the transit procee
22、d-to-send signal, used to invite the sending of only those numerical signals (beginning with the first digit of the country code)1)necessary for routing the call through the international transit exchange towards the incoming international exchange or to another international transit exchange. 1.3 n
23、umerical signal (sent in the forward direction) This signal provides an clement of information necessary to effect the switching of the call in the desired direction. There is always a succession of numerical signals sent. _ 1)For definitions, see Recommendations Q.10/E.160 and Q.104. 2 Signalling S
24、ystem No. 4 (1988) 1.4 end-of-pulsing signal, also called for System No. 4 code 15 (sent in the forward direction) This numerical type signal is sent from the international outgoing exchange to show that there are no more numerical signals to follow. In semi-automatic working, this signal is always
25、sent. In automatic working, this signal may be sent, viz., when, in the outgoing international exchange, it is known that there are no more digits to follow. 1.5 number-received signal (sent in the backward direction) 1.5.1 This signal is sent from the incoming international exchange to the outgoing
26、 international exchange when the incoming register has recognized that all the digits required for routing the call to the called subscriber have been received. Purpose of the signal 1.5.2 In the semi-automatic working, the number-received signal may be used to inform the outgoing operator that the
27、international switching operations have been completed. 1.5.3 In automatic working, this signal is essential to show the outgoing register at the outgoing international exchange that it can release, and to set up speech conditions at this exchange. Hence, it is desirable that the signal be sent as s
28、oon as possible. Generation of the signal 1.5.4 In semi-automatic working, the incoming register (or associated equipment) after reception of the end-of-pulsing signal acknowledges this numerical signal with an x and then sends back the number-received signals. 1.5.5 In automatic working, the incomi
29、ng register (or associated equipment) recognizes that all the digits of a national (significant) number2)have been received3): 1.5.5.1 by the receipt of the end-of-pulsing signal; or 1.5.5.2 a) by checking the number of digits received, in countries where the national (significant) number2)is always
30、 made up of the same number of digits; or b) in countries where this is not so: i) by the receipt of the maximum number of digits, used in the numbering plan of the country; or ii) by analyzing the first digits in the national (significant) number to decide how many digits there are in the subscribe
31、rs numbers in the particular national numbering zone; or iii) by using a national end-of-selection or national “electrical“ ringing-tone signal; or iv) exceptionally, by observing that 4 to 10 (for new equipment 4 to 6) seconds have elapsed since the last digit was received, and that no fresh inform
32、ation has been received; in such circumstances, retransmission to the national network of the last digit received must be prevented until the end of the waiting period which causes the number-received signal to be sent over the international circuit. In this way, it is ensured that no national answe
33、r signal can arrive before the number-received signal has been sent. 1.6 busy-flash signal (sent in the backward direction) This signal is sent to the outgoing international exchange to show that either the route or the called subscriber is busy. The conditions of use of this signal are as follows:
34、a) An international transit exchange must send this signal to indicate that there is congestion at that exchange or on the appropriate outgoing routes. b) An incoming international exchange must send this signal if there is congestion at that exchange or on the outgoing routes directly connected to
35、it, but sending the signal is optional when there is congestion beyond that exchange (when there is congestion at a point in the national network of the incoming country or when the called subscribers line is busy). This signal is optional because there are several countries that do not send it from
36、 their national networks. _ 2)See definition in Recommendation Q.10/E.160. 3)See Recommendation Q.180 for interworking between Systems No. 4 and No.5, Q.232 for interworking between Systems No. 4 and No. 5 bis, Q.261 for interworking between Systems No. 4 and No. 6, Q.381 for interworking between Sy
37、stems No. 4 and R2, Q.382 for interworking between Systems No. 5 and R2, Q.383 for interworking between Systems No. 5 bis and R2 and Q.388 for interworking between Systems No. 6 and R2. Signalling System No. 4 (1988) 3 Note The receipt of the busy-flash signal at the outgoing exchange will cause: an
38、 appropriate indication to be given to the outgoing operator or to the calling subscriber; and in automatic working, the sending of the clear-forward by the outgoing exchange to release the international connection (except when otherwise arranged, for example, in the case of observations on circuits
39、). 1.7 answer signal (sent in the backward direction) This signal is sent to the outgoing international exchange to show that the called party has answered the call4). In semi-automatic working, the signal has a supervisory function. In automatic working, it is used: to start metering the charge to
40、the calling subscriber, to start the measurement of call duration for international accounting purposes. 1.8 clear-back signal (sent in the backward direction) This is sent to the outgoing international exchange to indicate that the called party has cleared. In the semi-automatic service, it perform
41、s a supervisory function. It must not permanently open the speech path at the outgoing international exchange. In automatic working, arrangements must be made to clear the international connection, stop the charging and stop the measurements of call duration if, between one and two minutes after rec
42、eipt of the clear-back signal, the calling subscriber has not cleared. Clearing of the international connection should preferably be controlled from the point where the charging of the calling subscriber is carried out. Notes on the answer and clear-back signals 1.8.1 Note 1 In general, the sequence
43、 of answer and clear-back signals that will be sent when the called subscriber depresses and releases the switch-hook of his telephone will not always be able to follow the frequency of this operation of the switch-hook, but correct indication of the final position of the switch-hook must always be
44、given: to the outgoing international operator in semi-automatic operation; to the outgoing international equipment in automatic operation. 1.8.2 Note 2 The “call party“ referred to in the definitions of the answer and clear-back signals may be: the called subscriber; in semi-automatic working, the o
45、perator who puts the call through in her own country and who sends an answer signal when she answers the call. 1.8.3 Note 3 The following is a detailed description of the various possible circumstances in which the answer and clear-back signals are sent. A. Called subscriber obtained automatically b
46、y the international outgoing operator The answer and clear-back signals are sent every time the called subscriber answer or clears. B. Called subscriber not obtained automatically by the international outgoing operator a) Only one operator involved in the incoming country, without through-supervisio
47、n via her position (This operator can be an incoming or a delay operator or a manual exchange operator obtained automatically from the outgoing international exchange.) The answer signal is sent when the operator enters the circuit. The clear-back signal is sent when the operator clears the connecti
48、on. _ 4)See Recommendation Q.27 for the action to be taken to ensure that answer signals both national and international, are transmitted as quickly as possible. 4 Signalling System No. 4 (1988) b) Only one operator involved in the incoming country, with through-supervision via her position (The ope
49、rator can be the same as for a) above.) Through-supervision can be effected: via the cord circuits, the incoming operator intervening to clear down the connection at the end of the call; via cordless positions, in which case the connection is released automatically without the intervention of an operator when the called subscriber clears and when the outgoing operator causes the clear-forward signal to be sent. The answer signal is sent when the operator enters the circuit. A clear-back sig
