5i' FASCICLE VI.8 Recommendations Q.721 to Q.766 SPECIFICATIONS OF SIGNALLING SYSTEM No. 7 | fR Blanc MONTAGE: PAGE 2 = PAGE BLANCHE SECTION 1 TELEPHONE USER PART (TUP) Recommendation Q.721 FUNCTIONAL DESCRIPTION OF THE SIGNALLING SYSTEM No. 7 TELEPHONE USER PART (TUP) 1 General Use of Signalling System No. 7 for telephone call control sig- nalling requires: - application of Telephone User Part | (TUP) func- tions, in combination with - application of an appropriate set of Message Transfer Part | (MTP) functions. A general description of the signalling system and the divi- sion of functions between the Message Transfer Part and the Tele- phone User Part are presented in Recommendation Q.700 and the requirements of interaction between those two parts are contained in Recommendation Q.701. 2 Telephone User Part The Telephone User Part specified in these specifications defines the necessary telephone signalling functions for use of Signalling System No. 7 for international telephone call control signalling. It is specified with the aim of providing the same features for telephone signalling as other CCITT telephone signal- ling systems. Signalling System No. 7 can be used to control the switching of all types of international circuits to be used in a worldwide connection, including circuits with speech interpolation and satel- lite circuits. The system meets all requirements defined by the CCITT con- cerning the service features for worldwide international semiau- tomatic and automatic telephone traffic. It is designed for the bothway operation of speech circuits. When used with homogeneous digital telephone circuits the con- tinuity of these circuits is ensured by the means for transmission quality supervision and failure detection that are inherent in the digital systems providing these circuits. However, the system includes means for link-by-link assurance of continuity check of the speech path when used with analogue telephone circuits and/or digital circuits including certain types of equipment, where fault indications are lost, e.g., circuit multiplication equipment. The signalling system is suitable for national telephone applications. Most telephone signalling message types and signals specified for international use are also required in typical national applications. In addition to these, national applications typically require additional signalling message types and signals; the system provides ample spare capacity for such additions. The standard label structure specified for telephone signal- ling messages requires that all exchanges using the signalling sys- tem are allocated codes from code plans established for the purpose of unambiguous identification of signalling points. The principles to apply to the international signalling network are specified in Recommendation Q.708. 3 Message Transfer Part The Message Transfer Part of Signalling System No. 7 is speci- fied in Recommendations Q.701 to Q.709. An overview description of the Message Transfer Part is contained in Recommendation Q.701. The Message Transfer Part defines a range of functions by which different signalling modes and different signalling network configurations may be realized. Any application of Signalling Sys- tem No. 7 requires that an appropriate selection of these functions is applied depending on the intended use of the system and the characteristics of the telecommunications network concerned. Recommendation Q.722 GENERAL FUNCTION OF TELEPHONE MESSAGES AND SIGNALS This Recommendation describes the general function of tele- phone signalling messages and the telephone signals and other information components contained in those messages. The require- ments relating to the use of the signalling messages and their sig- nal content are specified in Recommendations Q.723 and Q.724. 1 Telephone signalling messages The definition of formats and codes for telephone messages is based on a functional grouping as indicated in the following. It is expected that national application of the signalling system typi- cally will require further message types in addition to the inter- nationally defined message types indicated in the following. As a result of the criteria on which the grouping of message types are based some groups as yet only contain one message type. 1.1 Forward address message group This message group includes messages sent in the forward direction containing address information. Signals from S 3.3 may be included. Messages so far specified are as follows. 1.1.1 Initial address message A type of message sent first in the forward direction at call set-up. It contains address information and other information relating to the routing and handling of the call. 1.1.2 Initial address message with additional information A type of message sent first in the forward direction at call set-up. It contains address, routing and handling information such as charging and supplementary services information to be used in the call set-up procedures. 1.1.3 Subsequent address message A type of message sent in the forward direction subsequent to the initial address message and containing further address informa- tion. 1.1.4 Subsequent address message with one signal A type of message sent in the forward direction subsequent to the initial address message or to the subsequent address message and containing only one address signal. 1.2 Forward set-up message group This message group includes messages sent in the forward direction, subsequent to address messages containing further infor- mation for call set-up. Signals from S 3.3 may be included. Mes- sages so far specified are as follows. 1.2.1 General forward set-up information message A type of message containing information relating to the cal- ling line or possibly other information required for call set-up. This message is sent in response to a general request message. 1.2.2 Continuity check message A type of message containing a continuity signal or a continuity-failure signal. 1.3 Backward set-up request message group This message group includes messages sent in the backward direction requesting further information for call set-up. Signals from S 3.4 may be included. Messages so far specified are as fol- lows. 1.3.1 General request message A type of message containing a signal requesting transfer of information relating to a call, e.g., the identity or the category of the calling party. 1.4 Successful backward set-up information message group This message group includes messages sent in the backward direction containing information relating to a successful call set-up. Signals from S 3.4 may be included. Messages so far speci- fied are as follows. 1.4.1 Address-complete message A type of message containing a signal indicating that all address signals required for routing the call to the called party have been received and giving additional information relating to this. 1.4.2 Charging message A type of message containing charging information. 1.5 Unsuccessful backward set-up information message group This message group includes messages sent in the backward direction containing information relating to an unsuccessful call set-up. Signals from S 3.4 may be included. Messages so far speci- fied are as follows. 1.5.1 Simple unsuccessful backward set-up information mes- sage A message containing a signal from S 3.4, relating to an unsuccessful call set up. 1.5.2 Extended unsuccessful backward set-up information message A message containing a signal from S 3.4, relating to an unsuccessful call set up, and additional information. 1.6 Call supervision message group This message group includes messages sent in the forward or backward direction, relating to the supervision of the call. Sig- nals from S 3.5 are included. 1.7 Circuit supervision message group This message group includes messages sent in the forward and backward direction, relating to the supervision of the circuit. Signals from S 3.6 are included. 1.8 Circuit group supervision message group This message group contains messages from S 3.7, relating to the supervision of circuit groups. 1.9 Circuit network management message group This message group includes network management messages sent in the backward direction, which are used to control traffic flow to reduce exchange switching congestion. Messages so far specified are as follows. 1.9.1 Automatic congestion control information message A type of message containing information relating to the congestion status of the exchange. Signals from S 3.8 are included. 2 Service information The service information provides the highest level of discrim- ination between different sets of signalling messages. It contains the following components. (See also Note.) 2.1 Service indicator Information used to identify the User Part to which the sig- nalling message belongs. 2.2 Network indicator Information used for discrimination between international and national messages. In case of national messages, it may for example also be used for discrimination between different label alternatives for national use. Note - The service information octet and the label are not included in messages transferred between the telephone user part and the signalling connection control part (e.g., node to node mes- sages). 3 Signalling information 3.1 Label components In the case of the telephone signalling messages, the label is used for message routing and, in general, identification of the concerned telephone circuit. The standard label structure consists of the following components. 3.1.1 Destination point code Information identifying the signalling point to which the mes- sage is to be routed. 3.1.2 Originating point code Information identifying the signalling point from which the message has been originated. 3.1.3 Circuit identification code Information identifying the telephone circuit among those interconnecting the destination point and originating point. 3.2 Message format identifiers 3.2.1 Heading Information discriminating, as applicable, between different groups or individual types of messages within the set of messages identified by the service information. The heading is split into two levels. The first level discriminates between different groups. The second level either discriminates between different message types or contains a signal. 3.2.2 Field length indicator Information associated with and indicating the length of a variable length field. 3.2.3 Field indicator Information associated with and indicating the presence or absence of an optional field. 3.3 Forward set-up telephone signals 3.3.1 Address signal A call set-up signal sent in the forward direction containing one element of information (digit 0, 1, 2, . | | , 9, Code 11 or Code 12) about the called party's number or the end-of-pulsing (ST) signal. For each call, a succession of address signals is sent. 3.3.2 End-of-pulsing (ST) signal An address signal sent in the forward direction indicating that there are no more address signals to follow. 3.3.3 Nature-of-address indicator Information sent in the forward direction indicating whether the associated address or line identity is an international, national significant or subscriber number. 3.3.4 Nature-of-circuit indicator Information sent in the forward direction about the nature of the circuit or any preceding circuit(s) already engaged in the con- nection: - a satellite circuit, or - no satellite circuit. An international exchange receiving this information will use it (in combination with the appropriate part of the address information) to determine the nature of the outgoing circuit to be chosen. 3.3.5 Outgoing echo suppressor indicator Information sent in the forward direction indicating whether or not an outgoing half-echo suppressor is included in the connec- tion. 3.3.6 Incoming international call indicator Information sent in the forward direction indicating that the call is an incoming international call. 3.3.7 Calling-party's-category Information sent in the forward direction about the category of the calling party and, in case of semiautomatic calls, about the service language to be spoken by the incoming, delay and assistance operators. The following categories are provided: - operator, - ordinary calling subscriber, - calling subscriber with priority, - data call, - test call, - payphone. 3.3.8 Incomplete calling line identity indicator An indicator sent in the forward direction indicating that the calling line identity is incomplete. 3.3.9 Continuity-check indicator Information sent in the forward direction indicating whether or not a continuity check will be performed on the circuit con- cerned or is being (has been) performed on a previous circuit in the connection. 3.3.10 Calling line identity Information sent in the forward direction indicating the national significant number of the calling party. 3.3.11 Calling line identity presentation indicator Information indicating whether or not the calling line iden- tity presentation is restricted. 3.3.12 Calling-line-identity-unavailable indicator Information sent in the forward direction indicating that the identity of the calling line is not available. 3.3.13 Calling party's category unavailable indicator Information sent in the forward direction to indicate that the calling party's category is not available. 3.3.14 Original called address not available indicator Information sent in the forward direction indicating that the original called address is not available. 3.3.15 Continuity signal A signal sent in the forward direction indicating continuity of the preceding System No. 7 speech circuit(s) as well as of the selected speech circuit to the following international exchange, including verification of the speech path across the exchange with the specified degree of reliability. 3.3.16 Continuity-failure signal A signal sent in the forward direction indicating failure of continuity of the System No. 7 speech circuit. 3.3.17 Redirected call indicator Information sent in the forward direction indicating that the call is a forwarded call. 3.3.18 Original called address Information sent in the forward direction indicating the address towards which the call was previously routed (before the redirection occurred). 3.3.19 All digital path required indicator Information sent in the forward direction indicating the type path required (64 kbit/s circuit switched connection-transparent). 3.3.20 Signalling path indicator Information sent in the forward direction indicating that the signalling system used since the originating exchange is System No. 7. 3.3.21 Additional signals relating to the closed user group facilities 3.3.21.1 Closed user group call indicator Information sent in the forward direction indicating whether or not the call involves a closed user group and whether or not outgoing access is allowed for the calling user. 3.3.21.2 Interlock code Information sent in the forward direction identifying a closed user group to which the calling user belongs. 3.3.22 Malicious call identification indicator Information sent in the forward direction indicating that the malicious call identification has been provided or not. 3.3.23 Hold indicator Information sent in the forward direction indicating whether the requested holding of the connection is possible or not. 3.3.24 Transit exchange identity type indicator Information sent in the forward direction indicating the type of information included as transit exchange identity. 3.3.25 Transit exchange identity Information sent in the forward direction indicating the iden- tity of the transit exchange by which the call is established such as signalling point code or a part of the calling line identity. 3.3.26 Incoming trunk identity Information sent in the forward direction indicating the iden- tity of the incoming trunk on which the call is established. 3.3.27 Signals related to charging facilities For further study. 3.3.28 Charging information Information sent in the forward direction for charging and/or accounting purposes. 3.4 Backward set-up telephone signals 3.4.1 Calling-line-identity-request indicator Information sent in the backward direction requesting transfer of the calling line identity from the originating exchange. 3.4.2 Calling party's category request indicator Information sent in the backward direction requesting transfer of the calling party's category from the originating exchange. 3.4.3 Original called address information request indica- tors Information sent in the backward direction requesting transfer of the original called address from the originating exchange. 3.4.4 Address-complete signal A signal sent in the backward direction indicating that all the address signals required for routing the call to the called party have been received and that no called-party's-line-condition signals (electrical) will be sent. 3.4.5 Address-complete signal, charge A signal sent in the backward direction indicating that all the address signals required for routing the call to the called party have been received, that no called-party's-line-condition signals (electrical) will be sent and that the call should be charged on answer. 3.4.6 Address-complete signal, no-charge A signal sent in the backward direction indicating that all the address signals required for routing the call to the called party have been received, that no called-party's-line-condition (electrical) will be sent and that the call should not be charged on answer. 3.4.7 Address-complete signal, payphone A signal sent in the backward direction indicating that all the address signals required for routing the call to the called party have been received, that no called-party's-line-condition (electrical) will be sent, that the call should be charged on answer and that the called number is a payphone station. 3.4.8 Subscriber-free indicator Information sent in the backward direction indicating that the called party's line is free. 3.4.9 Incoming echo suppressor indicator Information sent in the backward direction indicating that an incoming half-echo suppressor has been inserted or not. 3.4.10 Call forwarding indicator Information sent in the backward direction indicating that the call has been forwarded to a different address. 3.4.11 Signalling path indicator Information sent in the backward direction indicating that the signalling system used since the terminating exchange is Signalling System No. 7. 3.4.12 Charging information signals Information sent in the backward direction for charging and/or accounting purposes. 3.4.13 Outgoing echo suppressor request indicator Information sent in the backward direction requesting for the insertion of an outgoing suppressor. 3.4.14 Hold request indicator Information sent in the backward direction indicating that the hold of the connection is requested. The release of the call will be controlled by the terminating exchange. 3.4.15 Malicious call identification indicator Information sent in the backward direction indicating that a malicious call identification facility has been encountered. 3.4.16 Switching-equipment-congestion signal A signal sent in the backward direction indicating the failure of the call set-up attempt due to congestion encountered at inter- national switching equipment. 3.4.17 Circuit-group-congestion signal A signal sent in the backward direction indicating the failure of the call set-up attempt due to congestion encountered on an international circuit group. 3.4.18 National-network-congestion signal A signal sent in the backward direction indicating the failure of the call set-up attempt due to congestion encountered in the national destination network [excluding the busy condition of the called party's line(s)]. 3.4.19 Digital path not provided signal Information sent in the backward direction indicating that a routing which allows the complete digital path requested does not exist. 3.4.20 Address-incomplete signal A signal sent in the backward direction indicating that the number of address signals received is not sufficient for setting up the call. This condition may be determined in the incoming interna- tional exchange (or in the national destination network): - immediately after the reception of an ST signal, or - on timeout after the latest digit received. 3.4.21 Call-failure signal A signal sent in the backward direction indicating the failure of a call set-up attempt due to the lapse of a timeout or a fault not covered by specific signals. 3.4.22 Called party's line condition signals 3.4.22.1 Unallocated-number signal A signal sent in the backward direction indicating that the received number is not in use (e.g., spare level, spare code, vacant subscriber's number). 3.4.22.2 Subscriber-busy signal (electrical) A signal sent in the backward direction indicating that the line(s) connecting the called party with the exchange is (are) engaged. The subscriber-busy signal will also be sent in case of complete uncertainty about the place where the busy or congestions are encountered and in the case where a discrimination between subscriber-busy and national-network congestion is not possible. 3.4.22.3 Line-out-of-service signal A signal sent in the backward direction indicating that the called party's line is out-of-service or faulty. 3.4.22.4 Send-special-information-tone signal A signal sent in the backward direction indicating that the special information tone should be returned to the calling party. This tone indicates that the called number cannot be reached for reasons not covered by other specific signals and that the unavai- lability is of a long-term nature (see also Recommendation Q.35 [1]). 3.4.23 Access barred signal Information sent in the backward direction indicating that the call is rejected because a compatibility check failed. 3.4.24 Misdialled trunk prefix A signal sent in the backward direction indicating the errone- ous inclusion of a trunk prefix (for national use). 3.5 Call supervision signals 3.5.1 Forward-transfer signal A signal sent in the forward direction on semiautomatic calls when the outgoing international exchange operator wants the help of an operator at the incoming international exchange. The signal will normally serve to bring an assistance operator (see Recommendation Q.101 [2]) into the circuit if the call is automati- cally set up at the exchange. When a call is completed via an operator (incoming or delay operator) at the incoming international exchange, the signal should preferably cause this operator to be recalled. 3.5.2 Answer signal, charge A signal sent in the backward direction indicating that the call is answered and subject to charge. In semiautomatic working, this signal has a supervisory func- tion. In automatic working, the signal is used: - to start metering the charge to the calling sub- scriber (Recommendation Q.28 [3]), and - to start the measurement of call duration for international accounting purposes (Recommendation E.260 [4]). 3.5.3 Answer signal, no charge A signal sent in the backward direction indicating that the call is answered but is not subject to charge. It is used for calls to particular destinations only. In semiautomatic working, this signal has a supervisory func- tion. In automatic working, the reception of this signal shall not start the metering to the calling subscriber. 3.5.4 Answer signal, unqualified (basic national use) A signal sent in the backward direction to indicate that the call is answered. 3.5.5 Clear-back signal A signal sent in the backward direction indicating that the called party has cleared. In semiautomatic working, this signal has a supervisory func- tion. In automatic working, the arrangements specified in Recommendation Q.118 [5] apply. 3.5.6 Re-answer signal A signal sent in the backward direction indicating that the called party, after having cleared, again lifts his receiver or in some other way reproduces the answer condition, e.g., switch-hook flashing. 3.5.7 Clear-forward signal A signal sent in the forward direction to terminate the call or call attempt and release the circuit concerned. This signal is normally sent when the calling party clears but also may be a proper response in other situations as, for example, when reset circuit is received. 3.5.8 Calling party clear signal | national option) A signal sent in the forward direction, when the holding of the connection is provided, to indicate that the calling party has cleared. 3.6 Circuit supervision signals 3.6.1 Release-guard signal A signal sent in the backward direction in response to a clear-forward signal, or if appropriate to the reset-circuit sig- nal, when the circuit concerned has been brought into the idle con- dition. 3.6.2 Reset-circuit signal A signal that is sent to release a circuit when, due to memory mutilation or other causes, it is unknown whether, for example, a clear-forward or clear-back signal is appropriate. If at the receiving end the circuit is blocked, this signal should remove that condition. 3.6.3 Blocking signal A signal sent only for maintenance purposes to the exchange at the other end of a circuit to cause engaged conditions of that cir- cuit for subsequent calls outgoing from that exchange. When a cir- cuit is used in the bothway mode of operation, an exchange receiv- ing the blocking signal must be capable of accepting incoming calls on that circuit unless it also has sent a blocking signal. Under conditions covered later, a blocking signal is also a proper response to a reset circuit signal. 3.6.4 Unblocking signal A signal sent to the exchange at the other end of a circuit to cancel in that exchange the engaged conditions of that circuit caused by an earlier blocking signal or maintenance-oriented group blocking message. 3.6.5 Blocking-acknowledgement signal A signal sent in response to a blocking signal indicating that the speech circuit has been blocked. 3.6.6 Unblocking-acknowledgement signal A signal sent in response to an unblocking signal indicating that the speech circuit has been unblocked. 3.6.7 Continuity-check-request signal A signal sent requesting an independent circuit continuity test. 3.7 Circuit group supervision messages 3.7.1 Maintenance oriented group blocking message A message sent for maintenance purposes to the exchange at the other end of a circuit group to cause an engaged condition on that circuit group or parts thereof for subsequent calls outgoing from that exchange. An exchange receiving the maintenance oriented group blocking message must be capable of accepting incoming calls on the blocked circuits of that circuit group unless it also has sent a blocking message. 3.7.2 Maintenance oriented group unblocking message A message sent to the exchange at the other end of a circuit group to cancel in that exchange the engaged condition on that cir- cuit group or parts thereof caused by an earlier maintenance-oriented group blocking message or blocking signal. 3.7.3 Hardware failure oriented group blocking message A message sent for reason of a hardware failure to the exchange at the other end of a circuit group to cause an engaged condition on that circuit group or parts thereof. An exchange receiving the hardware failure oriented group blocking message must be capable of accepting incoming calls on the blocked circuits of that circuit group unless it also has sent a blocking message. 3.7.4 Hardware failure oriented group unblocking message A message sent to the exchange at the other end of a circuit group to cancel in that exchange the engaged condition on that cir- cuit group or parts thereof caused by an earlier hardware failure oriented group blocking message. 3.7.5 Software generated group blocking message (national option) A message sent for reason of a software generated alarm to the exchange at the other end of a circuit group to cause an engaged condition on that circuit group or parts thereof. An exchange receiving the software generated group blocking message must be capable of accepting incoming calls on the blocked circuits of that circuit group unless it also has sent a blocking message. 3.7.6 Software generated group unblocking message (national option) A message sent to the exchange at the other end of a circuit group to cancel in that exchange the engaged condition on that cir- cuit group or parts thereof caused by an earlier software generated group blocking message. 3.7.7 Circuit group reset message A message that is sent to release a circuit group or parts thereof when, due to memory mutilation or other causes, it is unk- nown which of the clearing signals is appropriate for the particu- lar circuits within that circuit group. If at the receiving end circuits are blocked, this message should remove that condition. 3.7.8 Maintenance oriented group blocking-acknowledgement message A message sent in response to a maintenance oriented group blocking message indicating that the circuit group or parts thereof has/have been blocked. 3.7.9 Maintenance oriented group unblocking-acknowledgement message A message sent in response to a maintenance oriented group unblocking message indicating that the circuit group or parts thereof has/have been unblocked. 3.7.10 Hardware failure oriented group blocking-acknowledgement message A message sent in response to a hardware failure oriented group blocking message indicating that the circuit group or parts thereof has/have been blocked. 3.7.11 Hardware failure oriented group unblocking-acknowledgement message A message sent in response to a hardware failure oriented group unblocking message indicating that the circuit group or parts thereof has/have been unblocked. 3.7.12 Software generated group blocking-acknowledgement message (national option) A message sent in response to a software generated group blocking message indicating that the circuit group or parts thereof has/have been blocked. 3.7.13 Software generated group unblocking-acknowledgement message (national option) A message sent in response to a software generated group unblocking message indicating that the circuit group or parts thereof has/have been unblocked. 3.7.14 Circuit group reset-acknowledgement message A message sent in response to a circuit group reset message indicating that: i) if the range field is not coded all zero, the circuits are reset; or ii) if the range field is coded all zero, the reset of the circuit group has been started and the reset state of each circuit concerned will be reported by the appropriate call, circuit or circuit group supervision signal/message. 3.8 Automatic congestion control signals Signals generated by the exchange to indicate that a conges- tion threshold has been exceeded (see Recommendation Q.542, S 5.4.5). 3.8.1 Congestion level 1 A signal indicating that the first (less severe) congestion threshold in an exchange has been exceeded. 3.8.2 Congestion level 2 A signal indicating that the second (more severe) congestion threshold in an exchange has been exceeded. References [1] CCITT Recommendation Characteristics of the dial tone, ringing tone, busy tone, congestion tone, special information tone and warning tone, Rec. Q.35. [2] CCITT Recommendation Facilities provided in interna- tional semiautomatic working , Rec. Q.101. [3] CCITT Recommendation Determination of the moment of the called subscriber's answer in the automatic service , Rec. Q.28. [4] CCITT Recommendation Basic technical problems concern- ing the measurement and recording of call durations , Rec. E.260. [5] CCITT Recommendation Special release arrangements and indication of congestion conditions at transit exchanges , Rec. Q.118. Recommendation Q.723 FORMATS AND CODES 1 Basic format characteristics 1.1 General The telephone user messages are carried on the signalling data link by means of signal units, the format of which is described in Recommendation Q.703, S 2.2. The signalling information of each message constitutes the signalling information field of the corresponding signal unit and consists of an integral number of octets. It basically contains the label , the heading code and one or more signals and/or indications . Structure and function of the label are described in S 2; the heading codes and detailed message formats are described in S 3. 1.2 The service information octet The service information octet | comprises the service indica- tor and the subservice field . The service indicator is used to associate signalling informa- tion with a particular User Part and is only used with message sig- nal units (see Recommendation Q.704, S 12.2). The information in the subservice field permits a distinction to be made between national and international signalling messages. In national applications when this discrimination is not required possibly for certain national User Parts only, the subservice field can be used independently for different User Parts. The format of the service information octet is shown in Figure 1/Q.723. Figure 1/Q.723, (M), p. The following codes are used in the fields of the service information octet: a) The service indicator is coded 0100. b) Subservice field. bits B A Spare (see Note) bits D C Network indicator 0 0 International network 0 1 Spare (for international use only) 1 0 National network 1 1 Reserved for national use Note - The two unused bits in the service information octet are spare for possible future needs that may require a common solution for all international User Parts and Message Transfer Part level 3. The bits are coded 00. 1.3 Format principles The user generated information in the signalling information field is, in general, divided into a number of subfields which may be either of fixed or variable length. For a given message type identified by a unique message heading, the presence of a given subfield may be either mandatory or optional. The various types of subfields are further defined below. 1.3.1 Mandatory subfields Subfields which have been declared mandatory for a given mes- sage type appear in all messages of that type. 1.3.2 Optional subfields Subfields which have been declared optional for a given mes- sage type only appear when required in messages of that type. The presence or absence of each optional field is indicated by the state of a field indicator located in an indicator field, which in this case is a mandatory subfield. 1.3.3 Fixed length subfields Subfields which have been declared fixed length for a given message type, contain the same number of bits in all messages of that type. 1.3.4 Variable length subfields For subfields which have been declared variable length for a given message type, the number of bits may vary between messages of that type. The size of a variable length subfield is indicated in an immediately preceding fixed length subfield in terms of a prede- fined unit such as bits, octets or half-octets. 1.3.5 Order of subfield transmission For a given type of message the various types of subfields are transmitted in the following order: a) mandatory subfields, b) optional subfields. Within each of these two classes, the order of subfield transmission is, in general, as follows: 1) fixed length subfields (with the exception of the indicator field and subfields indicating the size of a variable length subfield), 2) variable length subfields. 1.3.6 Order of bit transmission Within each defined subfield the information is transmitted least significant bit first. 1.3.7 Coding of spare bits Spare bits are coded 0 unless indicated otherwise. 2 Label 2.1 General The label | is an item of information which forms part of every signalling message and is used by the message routing func- tion at Message Transfer Part level 3 to select the appropriate signalling route and by the User Part function to identify the par- ticular transaction (e.g. the call) to which the message pertains. In general, label information encompasses an explicit or implicit indication of the message source and destination and, depending on the application, various forms of transaction identif- ication. For messages which are related to circuits or calls, the tran- saction is conveniently identified by including the corresponding circuit identity in the label. This technique applies to messages which pass between adjacent nodes, and to messages which pass between nodes which are not adjacent; in this case the technique is known as the pass-along method. In future, the introduction of new subscriber services may require the transfer of call related mes- sages between exchanges at a time when no circuit is associated with the call. Such messages could be carried using the services of the Signalling Connection Control Part SCCP [6]. In this case the standard access to the Signalling Connection Control Part is used. Note - The service information octet, the routing label and the circuit identification code are not included in the information transferred between the Telephone User Part and the Signalling Con- nection Control Part. One standard label format is specified (S 2.2) for interna- tional use. The same standard label is applicable for national use; admitted deviations from the format of the standard label are described in S 2.3. 2.2 Standard telephone label 2.2.1 Label format The standard label | has a length of 40 bits and is placed at the beginning of the signalling information field. The label struc- ture is as shown in Figure 2/Q.723. Figure 2/Q.723, (M), p. The destination point code | (DPC) indicates the signalling point for which the message is intended, while the originating point code (OPC) indicates the signalling point which is the source of the message. The circuit identification code (CIC) indicates one speech circuit among those directly interconnecting the destination and the originating points. The portion of the label that consists of the destination point code and originating point code fields and of the four least significant bits of the circuit identification code field corresponds to the standard routing label specified in Recommendation Q.704, S 13.2. 2.2.2 Destination and originating point codes The standard label structure requires that each telephone exchange in its role as signalling point is allocated a code from code plans established for the purpose of unambiguous identifica- tion of signalling points. Separate code plans will be used for the international signal- ling network and for different national signalling networks. The principles of code allocation which apply to the interna- tional signalling network should be in accordance with Recommendation Q.708. The destination point code will be the code applicable to the telephone exchange to which the message is sent. The originating point code will be the code applicable to the telephone exchange from which the message is sent. 2.2.3 Circuit identification code The allocation of circuit identification codes to individual telephone circuits is determined by bilateral agreement and/or in accordance with applicable predetermined rules. Allocation rules for certain applications are defined below: a) 2048 kbit/s digital path For circuits which are derived from a 2048-kbit/s digital path (Recommendations G.732 [1] and G.734 [2]) the circuit identif- ication code contains in the 5 least significant bits a binary representation of the actual number of the time slot which is assigned to the speech circuit. The remaining bits in the circuit identification code are used where necessary, to identify one among several systems interconnecting an originating and destination point. b) 8448 kbit/s digital path For circuits which are derived from a 8448-kbit/s digital path (Recommendation G.744 [3] and G.746 [4]) the circuit identifi- cation code contains in the 7 least significant bits an identifica- tion of the channel which is assigned to the speech circuit. The codes in Table 1/Q.723 are used. The remaining bits are used, where necessary, to identify one among several systems interconnecting an originating and desti- nation point. c) Frequency division multiplex (FDM) systems in networks using the 2048-kbit/s pulse code modulation standard For FDM systems existing in networks that also use the 2048-kbit/s pulse code modulation standard, the circuit identifica- tion code contains in the 6 least significant bits the identifica- tion of a channel within a group of 60 channels carried by 5 basic FDM groups which may or may not be part of the same supergroup. The codes in Table 2/Q.723 are used. H.T. [T1.723] TABLE 1/Q.723 ______________________________________________________ 0000000 channel 1 0000001 | 0011111 channel 2 | channel 32 0100000 | 1111110 channel 33 | channel 127 1111111 channel 128 ______________________________________________________ | | | | Tableau 1/Q.723, [T1.723], p. H.T. [T2.723] TABLE 2/Q.723 ______________________________________________________________________________ 000000 unallocated ______________________________________________________________________________ 000001 | 001100 channel 1 | channel 12 1st basic (FDM) group ______________________________________________________________________________ { 001101 001110 001111 010000 010001 | 011001 } { channel 1 channel 2 channel 3 unallocated channel 4 | channel 12 } 2nd basic (FDM) group ______________________________________________________________________________ { 011010 | 011111 100000 100001 | 100110 } { channel 1 | channel 6 unallocated channel 7 | channel 12 } 3rd basic (FDM) group ______________________________________________________________________________ { 100111 | 101111 110000 110001 110010 110011 } { channel 1 | channel 9 unallocated channel 10 channel 11 channel 12 } 4th basic (FDM) group ______________________________________________________________________________ 110100 | 111111 channel 1 | channel 12 5th basic (FDM) group ______________________________________________________________________________ | | | | | | | | | | | | | | | | | | | | | | | | Tableau 2/Q.723, [T2.723], p. 2.3 Optional national labels For the purpose of satisfying the requirements imposed by specific characteristics of some national signalling networks, field sizes different from those specified for the standard label are admitted for the destination point code, originating point code and circuit identification code fields in national labels. 3 Telephone signal message formats and codes 3.1 General All telephone signal messages contain a heading | consisting of two parts, heading code H0 and heading code H1. Code H0 identi- fies a specific message group (see Recommendation Q.722, S 3.2.1) while H1 either contains a signal code or in case of more complex messages, identifies the format of these messages. The allocation of the H0 and H1 code is summarized in Table 3/Q.723. H.T. [1T7.723] TABLE 3/Q.723 Heading code allocation _________________________________________________________________________________________________________________________________________________________________________________________________________________________________________ Message group H1 | 0 0000 0001 0010 0011 0100 0101 | 0110 | 0111 | 1000 | 1001 | 1010 1011 1100 1101 1110 1111 _________________________________________________________________________________________________________________________________________________________________________________________________________________________________________ { _________________________________________________________________________________________________________________________________________________________________________________________________________________________________________ FAM 0001 IAM IAI SAM SAO _________________________________________________________________________________________________________________________________________________________________________________________________________________________________________ FSM 0010 GSM COT CCF _________________________________________________________________________________________________________________________________________________________________________________________________________________________________________ BSM 0011 GRQ _________________________________________________________________________________________________________________________________________________________________________________________________________________________________________ SBM 0100 ACM CHG _________________________________________________________________________________________________________________________________________________________________________________________________________________________________________ UBM 0101 SEC CGC NNC ADI CFL SSB UNN LOS SST ACB DPN MPR EUM _________________________________________________________________________________________________________________________________________________________________________________________________________________________________________ CSM 0110 ANU ANC ANN CBK CLF RAN FOT CCL _________________________________________________________________________________________________________________________________________________________________________________________________________________________________________ CCM 0111 RLG BLO BLA UBL UBA CCR RSC _________________________________________________________________________________________________________________________________________________________________________________________________________________________________________ GRM 1000 MGB MBA MGU MUA HGB HBA HGU HUA GRS | | | | | | | | | | | | | | | | | | | | GRA | | | | | | | | | | | | | | | | | | | | SGBa) | | | | | | | | | | | | | | | | | | | | | | | SBAa) | | | | | | | | | | | | | | | | | | | | | | | SGUa) | | | | | | | | | | | | | | | | | | | | | | | SUAa) | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | _________________________________________________________________________________________________________________________________________________________________________________________________________________________________________ 1001 RESERVED | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | _________________________________________________________________________________________________________________________________________________________________________________________________________________________________________ CNM 1010 ACC { | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | 1011 Spare reserved for international and basic national use } | | | | | | | | | | _________________________________________________________________________________________________________________________________________________________________________________________________________________________________________ 1100 | | | | | | _________________________________________________________________________________________________________________________________________________________________________________________________________________________________________ 1101 { | | | | | | | | 1110 Spare, reserved for national use } | | | | | | | | _________________________________________________________________________________________________________________________________________________________________________________________________________________________________________ { 1111 a) National option. } _________________________________________________________________________________________________________________________________________________________________________________________________________________________________________ | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | Tableau 3/Q.723, [1T7.723], p.5 Blanc H.T. [2T7.723] TABLEAU AVEC (AR) Abbreviations used in Table 3/Q.723 __________________________________________________________ ACB Access barred signal { ACC Automatic congestion control information message } { ACM Address complete message (note) } ADI Address incomplete signal ANC Answer signal, charge ANN Answer signal, no charge { ANU Answer signal, unqualified } { BLA Blocking-acknowledgement signal } BLO Blocking signal { BSM Backward set-up message } CBK Clear-back signal { CCF Continuity-failure signal } { CCL Calling party clear signal } { CCM Circuit supervision message } { CCR Continuity-check-request signal } CFL Call-failure signal { CGC Circuit-group-congestion signal } CHG Charging message CLF Clear-forward signal { CNM Circuit network management message group } COT Continuity signal CSM Call supervision message { DPN Digital path not provided signal } { EUM Extended unsuccessful backward set-up information message } FAM Forward address message { FOT Forward-transfer signal } FSM Forward set-up message { GRA Circuit group reset-acknowledgement message } { GRM Circuit group supervision messages } GRQ General request message { GRS Circuit group reset message } { GSM General forward set-up information message } { HBA Hardware failure oriented group blocking-acknowledgement message } __________________________________________________________ | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | Tableau 3/Q.723, [2T7.723], p.6 3.2 Heading code H0 The heading code | H0 occupies the 4-bit field following the label and is coded as follows: 0000 spare, reserved for national use 0001 forward address messages 0010 forward set-up messages 0011 backward set-up request messages 0100 successful backward set-up information mes- sages 0101 unsuccessful backward set-up information mes- sages 0110 call supervision messages 0111 circuit supervision messages 1000 circuit group supervision messages 1001 reserved 1010 circuit network management messages 1011 reserved for international and basic national use 1100 to reserved for national use 1111 3.3 Forward address messages The following types of forward address messages | are speci- fied and are each identified by a different heading code H1: - Initial address message. - Initial address message with additional informa- tion. - Subsequent address message (with one or more address signals). - Subsequent address message with one (address) signal. 3.3.1 Initial address message The basic format of the initial address message | is shown on Figure 3/Q.723. Figure 3/Q.723, (M), p. The following codes are used in the fields of the initial address message. a) Label: see S 2 b) Heading code H0 is coded 0001 c) Heading code H1 is coded 0001 d) Calling party category bits F E D C B A 0 0 0 0 0 0 unknown source (Note 1) 0 0 0 0 0 1 operator, language French 0 0 0 0 1 0 operator, language English 0 0 0 0 1 1 operator, language German 0 0 0 1 0 0 operator, language Russian 0 0 0 1 0 1 operator, language Spanish 0 0 0 1 1 0 0 0 0 1 1 1 0 0 1 0 0 0 -v'2P' -v'1p' available to Administrations for selecting a particular language provided by mutual agreement 0 0 1 0 0 1 reserved (see Recommendation Q.104 [5]) (Note 2) 0 0 1 0 1 0 ordinary calling subscriber 0 0 1 0 1 1 calling subscriber with priority 0 0 1 1 0 0 data call 0 0 1 1 0 1 test call 0 0 1 1 1 0 spare 0 0 1 1 1 1 payphone 0 1 0 0 0 0 to spare 1 1 1 1 1 1 Note 1 - The calling party category "unknown source" is clas- sified, for the time being, for basic national use. The use of this category in the international network is for further study. Note 2 - In national networks, code 001001 may be used to indicate that the calling party is a national operator. e) Spare The bits in this field are spare for international alloca- tion. f ) Message indicators bits B A: nature of address indica- tor 0 0 subscriber number 0 1 spare, reserved for national use 1 0 national (significant) number 1 1 international number bits D C: nature-of-circuit indica- tor 0 0 no satellite circuit in the connection 0 1 one satellite circuit in the connection 1 0 spare 1 1 spare bits F E: continuity-check indica- tor 0 0 continuity-check not required 0 1 continuity-check required on this cir- cuit 1 0 continuity-check performed on a previ- ous circuit 1 1 spare bit G: echo-suppressor indicator 0 outgoing half echo suppressor not included 1 outgoing half echo suppressor included bit H: incoming international call indica- tor 0 call other than international incoming 1 incoming international call bit I: redirected call indicator 0 not a redirected call 1 redirected call bit J: all-digital-path-required indicator 0 ordinary call 1 digital path required bit K: signalling path indicator 0 any path 1 all signalling system No. 7 path bit L: spare Note - The spare indicator may be used, e.g., to provide the u/A law conversion control, pending further study. g) Number of address signals A code expressing in pure binary representation the number of address signals contained in the initial address message, except for the code 0000 to which the meaning 16 digits including ST sig- nal is assigned. h) Address signals 0000 digit 0 0001 digit 1 0010 digit 2 0011 digit 3 0100 digit 4 0101 digit 5 0110 digit 6 0111 digit 7 1000 digit 8 1001 digit 9 1010 spare 1011 code 11 1100 code 12 1101 spare 1110 spare 1111 ST The most significant address signal is sent first. Subse- quent address signals are sent in successive 4-bit fields. i) Filler In case of an odd number of address signals, the filler code 0000 is inserted after the last address signal. This ensures that the variable length field which contains the address signals consists of an integral number of octets. 3.3.2 Initial address message with additional information The basic format of the initial address message with addi- tional information | is shown in Figure 4/Q.723. Figure 4/Q.723, (MC), p. The following codes are used in the initial address message with additional information: a) Label: see S 2 b) Heading code H0 is coded 0001 c) Heading code H1 is coded 0010 d) Calling party category: [see S 3.3.1 | )] e) Message indicators: [see S 3.3.1 | )] f ) Number of address signals: [see S 3.3.1 | )] g) Address signals: [see S 3.3.1 | )] h) First indicator octet bit A: network capability or user facility information indicator 0 network capability or user facility information not included 1 network capability or user facility information included bit B: closed user group information indi- cator 0 closed user group information not included 1 closed user group information included bit C: additional calling party information indicator 0 additional calling party information not included 1 additional calling party information included bit D: additional routing information indi- cator 0 additional routing information not included 1 additional routing information included bit E: calling line identity indicator 0 calling line identity not included 1 calling line identity included bit F: original called address indicator 0 original called address not included 1 original called address included bit G: charging information indicator 0 charging information not included 1 charging information included bit H: spare, reserved for indicating the presence or absence of a second indicator octet i) Network capability or user facility information: spare, reserved for national use. (This optional field may be used in national applications to indicate specific network capabilities and/or user facility information.) j ) Closed user group (CUG) information The basic format of the closed user group information field is shown in Figure 4a/Q.723. H.T. [T3.723] _____________________________________________________________ DCBA _____________________________________________________________ Interlock code Spare CUG indicator _____________________________________________________________ 32 4 { 4 FIGURE 4a/Q.723 Closed user group information field } _____________________________________________________________ | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | Figure 4a/Q.723 (comme tableau) [T3.723], p. The following codes are used in the subfields of the closed user group information field. - bits B A: CUG call indi- cator 0 0 ordinary call 0 1 successful check 1 0 outgoing access allowed 1 1 outgoing access not allowed - bits C D: spare - Interlock code A code identifying the closed user group involved in the call. The nature of this code is for further study. k) Additional calling party information: for further study. (This optional field is of fixed length and will indicate additional information concerning the calling party, which is not carried by the calling party's category indicator.) l) Additional routing information: for further study. (This optional field is of fixed length and will indicate that the call has to be routed in some particular way, due for example to additional customer services.) m) Calling line identity The basic format of the calling line identity field is shown in Figure 4b/Q.723. H.T. [T4.723] _______________________________________________________________________________ DCBA DCBA _______________________________________________________________________________ Calling line identity Number of address signals Address indicator _______________________________________________________________________________ n | (mu | 4 { 4 FIGURE 4b/Q.723 Calling line identity field } _______________________________________________________________________________ | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | Figure 4b/Q.723 (comme tableau) [T4.723], p. The following codes are used in the subfields of the cal- ling line identity field. - Address indicators: bits B A: nature of address indica- tor 0 0 subscriber number 0 1 spare, reserved for national use 1 0 national significant number 1 1 international number bit C: calling line identity presentation indicator 0 calling line identity presentation not restricted 1 calling line identity presentation restricted bit D: incomplete calling line identity indicator 0 no indication 1 incomplete calling line identity - Number of address signals bits D C B A 0 0 0 0 calling line iden- tity not available indicator 0 0 0 1 to 1 1 1 1 -v'2P' -v'1p' a code expressing in pure binary representa- tion the number of address signals. - Calling line address signals Each signal is coded as indicated in S 3.3.1 h) as applica- ble. n) Original called address The basic format of the original called address field is shown in Figure 4c/Q.723. H.T. [T5.723] __________________________________________________________________________________ DCBA DCBA __________________________________________________________________________________ Original called address Number of address signals Address indicators __________________________________________________________________________________ n | (mu | 4 { 4 FIGURE 4c/Q.723 Original called address field } __________________________________________________________________________________ | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | Figure 4c/Q.723 (comme tableau) [T5.723], p. The following codes are used in the subfields of the origi- nal address field: - Address indicator bits B A: nature of address indica- tor 0 0 subscriber number 0 1 spare, reserved for national use 1 0 national (significant) number 1 1 international number bits D C: spare - Number of address signals bits D C B A 0 0 0 0 original called address not available 0 0 0 1 to 1 1 1 1 -v'2P' -v'1p' a code expressing in pure binary representa- tion the number of address signals. - Original called address signals Each signal is coded as indicated in S 3.3.1 h) as applica- ble. o) Charging information: for further study. (This optional field will contain information to be sent to a successive exchange for charging and/or accounting purposes.) 3.3.3 Subsequent address message The basic format of the subsequent address | message (SAM) is shown in Figure 5/Q.723. Figure 5/Q.723, (M), p. The following codes are used in the fields of the subsequent address message: a) Label: see S 2 b) Heading code H0 is coded 0001 c) Heading code H1 is coded 0011 d) Address signal is coded as indicated in S 3.3.1 | ) as applicable e) Number of address signals: a code expressing in pure binary representation the number of address signals contained in the subsequent address message. 3.3.4 Subsequent address message with one signal The basic format of the subsequent address message with one signal | is shown in Figure 6/Q.723. Figure 6/Q.723, (M), p. The following codes are used in the fields of the subsequent address message with one signal: a) Label: see S 2 b) Heading code H0 is coded 0001 c) Heading code H1 is coded 0100 d) Address signal is coded as indicated in S 3.3.1 | ) as applicable. 3.4 Forward set-up messages The following types of forward set-up messages are specified and are each identified by a different heading code H1: - general forward set-up information message, - continuity-check message. Unallocated H1 codes in this message group are spare. 3.4.1 General forward set-up information message The basic format of the general forward set-up information message is shown in Figure 7/Q.723. Figure 7/Q.723, (M), p. The following codes are used in the fields of the general for- ward set-up information message: a) Label: see S 2 b) Heading code H0 is coded 0010 c) Heading code H1 is coded 0001 d) Response type indicator bit A: calling party category indicator 0 calling party category not included 1 calling party category included bit B: calling line identity indicator 0 calling line identity not included 1 calling line identity included bit C: incoming trunk and transit exchange: identity indicator 0 incoming trunk and transit exchange identity not included 1 incoming trunk and transit exchange identity included bit D: original called address indicator 0 original called address not included 1 original called address included bit E: outgoing echo suppressor indicator 0: outgoing half echo suppressor not included 1: outgoing half echo suppressor included bit F: malicious call identification indi- cator 0 malicious call identification not provided 1 malicious call identification provided bit G: hold indicator 0 hold not provided 1 hold provided bit H: spare e) Calling party category: bits F E D C B A 0 0 0 0 0 0 unknown source/calling party category unavailable indicator 0 0 0 0 0 1 to (see S 3.3.1 d)) 1 1 1 1 1 1 f ) Calling line identity: Format and codes are the same as used in the calling line identity contained in the initial address message with additional information (see S 3.3.2). g) Incoming trunk and transit exchange identity: The basic format of the incoming trunk and transit exchange identity field is shown in Figure 8/Q.723. H.T. [T6.723] ______________________________________________________________________________________________________________________________________ DCBA DCBA DCBA ______________________________________________________________________________________________________________________________________ Incoming trunk identity Field length indicator Spare Transit exchange identity { Exchange identity length indicator } Identity type indicator ______________________________________________________________________________________________________________________________________ n | (mu | 4 4 n | (mu | 4 { 4 FIGURE 8/Q.723 Incoming trunk and transit exchange identity field } ______________________________________________________________________________________________________________________________________ | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | Figure 8/Q.723 (comme tableau) [T6.723], p. The following codes are used in the subfields of the incoming trunk and transit exchange identity field: - Identity type indicator bits B A: 0 0 spare 0 1 signalling point code 1 0 available part of calling line identity 1 1 spare bits D C: spare - Exchange identity length indicator A code expressing in pure binary representation the number of address signals included in the transit exchange identity sub- field for the case when part of the calling line identity is used for this purpose. When the transit exchange is identified by the signalling point code, this subfield is coded 0000. - Transit exchange identity A code consisting of either: i) the signalling point code of the exchange, or ii) a part of the calling line identity, in which case each address digit contained in this identity is coded as indicated in S 3.3.1 h) where applicable. - Field length indicator A code indicating in pure binary representation the number of octets in the incoming trunk identity field. Code 0000 indicates that the incoming trunk identity is not provided. - Incoming trunk identity A code contained in a maximum of 15 octets, identifying the incoming trunk. The encoding of the incoming trunk identity is for further study. h) Original called address See S 3.3.2 n). 3.4.2 Continuity-check message The basic format of the continuity-check | message is shown in Figure 9/Q.723. Figure 9/Q.723, (M), p. The following codes are used in the fields of the continuity-check message: a) Label: see S 2 b) Heading code H0 is coded 0010 c) Heading code H1 contains signal codes as fol- lows: 0011 continuity signal 0100 continuity-failure signal 3.5 Backward set-up request message The following type of backward set-up request message is specified and is identified by one of the heading codes H1. The other H1 codes in this message group are spare. 3.5.1 General request message The basic format of the general request | message is shown in Figure 10/Q.723. Figure 10/Q.723, (M), p. The following codes are used in the fields of the general request message: a) Label: see S 2 b) Heading code H0 is coded 0011 c) Heading code H1 is coded 0001 d) Request type indicators bit A: calling party category request indi- cator 0 no calling party category request 1 calling party category request bit B: calling line identity request indi- cator 0 no calling line identity request 1 calling line identity request bit C: original called address request 0 no original called address request 1 original called address request bit D: malicious call identification indi- cator (national option) 0 no malicious call identification encountered 1 malicious call identification encountered bit E: hold request indicator 0 hold not requested 1 hold requested bit F: echo suppressor request indicator 0 no outgoing half echo suppressor requested 1 outgoing half echo suppressor requested bit GH: spare 3.6 Successful backward set-up information messages The following types of successful backward set-up information messages are specified and are each identified by a different head- ing code H1: - address-complete message - charging message. 3.6.1 Address-complete message The basic format of the address-complete | message is shown in Figure 11/Q.723. Figure 11/Q.723, (M), p. The following codes are used in the fields of the address-complete message: a) Label: see S 2 b) Heading code H0 is coded 0100 c) Heading code H1 is coded 0001 d) Message indicators bits B A: type of address-complete signal indicators 0 0 address-complete signal 0 1 address-complete signal, charge 1 0 address-complete signal, no charge 1 1 address-complete signal, payphone bit C: subscriber-free indicator 0 no indication 1 subscriber-free bit D: incoming echo suppressor indicator 0 no incoming half echo suppressor included 1 incoming half echo suppressor included bit E: call forwarding indicator 0 call not forwarded 1 call forwarded bit F: signalling path indicator 0 any path 1 all signalling system No. 7 path bits G H: spare, for national use (may be used to indicate call redirection, holding of the connec- tion or the end-to-end signalling method to be used). Note - The address-complete signal without qualification is classified for the time being in the basic national category of signals. The use of this signal in the international network is for further study. 3.6.2 Charging message | (see Note) The basic format of the charging | message is shown in Figure 12/Q.723. Figure 12/Q.723, (M), p. The following codes are used in the fields of the charging message: a) Label: see S 2 b) Heading code H0 is coded 0100 c) Heading code H1 is coded 0010 d) Charging information (Possible formats and codes of the charging information field are shown in Annex A.) Note - The charging message is classified, for the time being, in the basic national category of messages. The use of this message in the international network is for further study. 3.7 Unsuccessful backward set-up information messages 3.7.1 Simple unsuccessful backward set-up information mes- sage The basic format of the simple unsuccessful backward set-up information message is shown in Figure 13/Q.723. Figure 13/Q.723, (M), p. The following codes are used in the fields of the simple unsuccessful backward set-up information message. a) Label: see S 2 b) Heading code H0 is coded 0101 c) Heading code H1 contains signal codes as fol- lows: 0000 spare 0001 switching-equipment-congestion signal 0010 circuit-group-congestion signal 0011 national-network-congestion signal 0100 address-incomplete signal 0101 call-failure signal 0110 subscriber-busy signal (electrical) 0111 unallocated-number signal 1000 line-out-of-service signal 1001 send-special-information-tone signal 1010 access barred signal 1011 digital path not provided signal 1100 misdialled trunk prefix signal (for national use) 1101 to spare 1110 3.7.2 Extended unsuccessful backward set-up information message The basic format of the extended unsuccessful backward set-up information message is shown in Figure 13a/Q.723. Figure 13a/Q.723, (M), p. The following codes are used in the fields of the extended unsuccessful backward set-up information message: a) Label: see S 2 b) Heading code H0 is coded 0101 c) Heading code H1 contains signal code 1111 d) Octet indicator bits D C B A: unsuccessful indicator 0 0 0 0 spare 0 0 0 1 subscriber busy 0 0 1 0 to spare 1 1 1 1 bits H G F E: spare. e) Signalling point code The point code of the signalling point in which the message is originated. 3.8 Call supervision message The basic format of the call supervision | message is shown in Figure 14/Q.723. Figure 14/Q.723, (M), p. The following codes are used in the fields of the call super- vision message: a) Label: see S 2 b) Heading code H0 is coded 0110 c) Heading code H1 contains signal codes as fol- lows: 0000 answer signal, unqualified 0001 answer signal, charge 0010 answer signal, no charge 0011 clear-back signal 0100 clear-forward signal 0101 re-answer signal 0110 forward-transfer signal 0111 calling party clear signal (national option) 1000 to spare 1111 3.9 Circuit supervision message The basic format of the circuit supervision | message is shown in Figure 15/Q.723. Figure 15/Q.723, (M), p. The following codes are used in the fields of the circuit supervision message: a) Label: see S 2 b) Heading code H0 is coded 0111 c) Heading code H1 contains signal codes as fol- lows: 0000 spare 0001 release-guard signal 0010 blocking signal 0011 blocking-acknowledgement signal 0100 unblocking signal 0101 unblocking-acknowledgement signal 0110 continuity-check-request signal 0111 reset-circuit signal 1000 to spare 1111 3.10 Circuit group supervision message The basic format of the circuit group supervision message is shown in Figure 16/Q.723: Figure 16/Q.723, (M), p. The following codes are used in the fields of the circuit group supervision message: a) Label: see S 2 The following interpretations apply to the CIC given in the label: i) If the range field is not coded all zero the CIC given in the label is the first CIC within the circuit group or the first CIC within that part of the circuit group. ii) If the range field is coded all zero (national option) the CIC given in the label is a representative CIC within the circuit group. b) Heading code H0 is coded 1000 c) Heading code H1 contains message codes as fol- lows: 0000 spare 0001 Maintenance oriented group blocking message 0010 Maintenance oriented group blocking-acknowledging message 0011 Maintenance oriented group unblocking message 0100 Maintenance oriented group unblocking-acknowledgement message 0101 Hardware failure oriented group blocking mes- sage 0110 Hardware failure oriented group blocking-acknowledge message 0111 Hardware failure oriented group unblocking message 1000 Hardware failure oriented group unblocking-acknowledgement message 1001 Circuit group reset message 1010 Circuit group reset-acknowledgement message 1011 Software generated group blocking message (national option) 1100 Software generated group blocking-acknowledgement message (national option) 1101 Software generated group unblocking message (national option) 1110 Software generated group unblocking-acknowledgement message (national option) 1111 spare d) Range: in principle, two different codings are possible: i) not all zero: The message is related to a whole circuit group or a part thereof, and includes a status field unless the message is the circuit group reset message. The number of con- secutive circuits to be handled is indicated by the value contained in the range field increased by 1. The CIC of the first circuit to be handled is given in the label. The number of circuits to be indicated is 2 (range value 1) to 256 (range value 255). ii) all zero (national option): The message is related to a pre-determined circuit group. No status field is included. In this case the circuit group is addressed by means of a representative CIC within the circuit group. Note - In national networks, the range field may not be used if only the concept of pre-determined circuit group applies. e) Status field All circuit group supervision messages except the circuit group reset message include a status field containing status indi- cator bits when the range field is not coded all zero. The number of status indicator bits is indicated by the value given in the range field increased by one. The status field contains up to 256 one bit status indica- tors. The first status indicator bit is related to the circuit indicated by the CIC contained within the label, the second one is related to the circuit address by the CIC contained in the label increased by 1. figure 17/Q.723, (M), p. The CIC of the last circuit concerned is obtained by adding the value given in the range field to the CIC in the label. The status field consists of an integral number of octets. Bits within the last octet that are not used as status indicators are filled with zeros. The status indicator bits are coded as follows: - in all group blocking messages (MGB, HGB, SGB) 1 blocking 0 no blocking - in all group blocking-acknowledgement messages (MGB, HBA, SBA) 1 blocking acknowledgement 0 no blocking acknowledgement _________________________ Range value zero is only for national use. - in all unblocking messages (MGU, HGU, SGU) 1 unblocking 0 no unblocking - in all group unblocking-acknowledgement messages (MUA, HUA, SUA) 1 unblocking acknowledgement 0 no unblocking acknowledgement - in the circuit group reset-acknowledgement mes- sage (GRA) 1 blocking for maintenance reasons 0 no blocking for maintenance reasons 3.11 Circuit network management messages The following type of circuit network management message is specified and identified by one of the heading codes H1. Unallo- cated H1 codes in this message group are spare. 3.11.1 Automatic congestion control information message The basic format of the automatic congestion control (ACC) information message is shown in Figure 18/Q.723: Figure 18/Q.723, (N), p. The following codes are used in the fields of the automatic congestion control information message. a) Label: see S 2 b) Heading code H0 is coded 1001 c) Heading code H1 is coded 0001 d) Message indicators bits B A ACC information 0 0 spare 0 1 congestion level 1 1 0 congestion level 2 1 1 spare bits HGFEDC spare ANNEX A (to Recommendation Q.723) Charging messages A.1 Introduction The application of Signalling System No. 7 in national net- works was recognized from the beginning of the discussions about the signalling system. The result of this can be found throughout the specifications especially in those Recommendations dealing with the TUP. One of the points which is particularly of interest for an Administration is the possibility of transfer of charging informa- tion. Signalling System No. 7 allows for such a feature for charg- ing a calling subscriber by defining a specific charging message as indicated in S 3.6.2. However, the detailed format, coding and related procedures are not given, mostly because this matter is very dependent on the circumstances within a specific national net- work. The following examples illustrate a particular implementation in a national network for telephony without exclusion of other pos- sible solutions. A.2 Starting points Before describing in detail the messages involved, a number of starting points have to be adopted. a) The first No. 7 exchange performs metering according to all possible tariffs. b) The determination of a particular tariff is per- formed in a point somewhere in the network. c) The receipt of messages containing charging information should be acknowledged within the call control pro- cedures. d) At dedicated moments the actual charging should be adapted. e) A variety of charging possibilities should be available. The effect of these starting points is: a) the actual generation of charging units accord- ing to a particular tariff is always performed at the lowest level of the national public telephone network (local exchange); b) the determination of tariffs for local and trunk calls is carried out in the local exchange and for international calls in the international exchange; however, also the use of a centre for determination of all kinds of tariffs is possible; c) the transmission of charging information is assured at the highest level of the call control procedures and possibly inhibits call completion without receipt of charging information; d) calls of long duration can be subject to dif- ferent charging rates; e) the application of charge free calls, specific charge on answer, time dependent charging during a call, additional (specific) charge during a call and a combination of these. A.3 Messages and procedures To meet all the above mentioned requirements a number of mes- sages are defined. A.3.1 Charging message This message has to be sent for any call, charge free or not. In the procedure this is covered by the fact that the charging mes- sage has to be received during call set up before receipt of the address complete message. If not, then the call should be cleared immediately. The content of the message will vary depending on the actual tariff and this is indicated by a number of indicators indicating the presence of certain fields in the message. Possible contents: a) charge band The indication of a certain charge band should allow the receiving exchange to charge a call according to a certain tariff including possible switchover times to higher or lower rates. This method results in a simple message but requires the receiving exchange to have all the information available related to all pos- sible charge bands, national and international. b) explicit charging indication In this case the message contains explicit indications of details of the tariff viz. - number of charging units on answer (packet) - time dependent tariff(s) - possible switchover time. This method results in a more complex message but does not require the permanent storage of any charging information. A.3.2 Change message A consequence of the adoption of the method with explicit charging indication (S A.3.1 b)) is the necessity to allow for tar- iff switchover for calls of very long duration or for calls which are answered just after the switchover time given in the message described in S A.3.1 b). The content of such at message is rather simple because it only contains the new applicable tariff and the actual switch-over time. The procedure to acknowledge the receipt of the message cannot be found in the normal call control procedure, therefore an ack- nowledgement message (see S A.3.5) in the forward direction is used. If this acknowledgement message is not received within a cer- tain time, the change message has to be repeated. A.3.3 Collection charging For a variety of reasons it might be necessary to charge a subscriber during the call a certain amount. For this purpose a message is used indicating the number of charging units related to the amount for which the subscriber has to be charged. The procedure to assure the receipt of this message is the same as described in S A.3.2 above. A possible further collection charging message should not be sent before receipt of the ack- nowledgement message and the charging confirmation message (see S A.3.4 charging confirmation). A.3.4 Charging confirmation In relation with the message described in S A.3.3 a message in the forward direction is required indicating how many charging units actually are charged to the subscriber. This number should match to the number given in the collection charging message, oth- erwise it must be concluded that for some reason the order is not executed, e.g., a certain service should now be withheld to be fur- nished to the subscriber. Again the procedure is the one as described in S A.3.2 above but in the opposite direction. A.3.5 Acknowledgement To acknowledge the receipt of the messages described in SS A.3.2, A.3.3 and A.3.4, an acknowledgement message is used in both directions only indicating the receipt of the related message. A.4 Formats and codes A.4.1 Charging messages A.4.1.1 Charge band tableau ccitt 86010, (M), p. - Charge band A charge indicates the combination of tariffs including switch-over times which is applicable for a certain period (e.g., day or week). A.4.1.2 Explicit charging indication tableau ccitt 86020, (M), p. - Message indicators bit A: tariff indicator current tariff (A) 0 packet charging field and tariff indicators current tariff (A) not present 1 packet charging field and tariff indicators current tariff (A) present bit B: tariff factor current tariff (A) 0 tariff factor field current tariff (A) not present 1 tariff factor field current tariff (A) present bit C: tariff indicator next tariff (B) 0 packet charging field and tariff indicators next tariff (B) not present 1 packet charging field and tariff indicators next tariff (B) present bit D: tariff factor next tariff (B) 0 tariff factor field next tariff (B) not present 1 tariff factor field next tariff (B) present bit H-E spare - Packet charging field 0000 | number of charging units on answer 1111 - Tariff indicators 0000 tariff scale 0 (no time dependent tar- iff) 0001 tariff scale I | tariff scale | every scale indicates a certain step in seconds or parts thereof 1111 tariff scale XV - Tariff factors If a call is charge free (A = B = C = D = 0) only the mes- sage indicator octet is present. If a call is charge free from the start but may become chargeable (A = 1, B = 0, C = 1, D = 0/1), the packet charging field for the current tariff is 0000 and the tariff indicator for the current tariff indicates scale 0. If a call is chargeable from the start but may become charge free (A = 1, B = 0/1, C = 1, D = 0) the packet charging field for the next tariff is 0000 and the tariff indicator for the next tariff indicates scale 0. If a call is chargeable according to only one tariff (A = 1, B = 0/1, C = 0, D = 0), also the time indi- cator is not present in the message. The actual tariff is deter- mined by multiplication of the step indicated by the tariff indica- tor with the tariff factor which gives then a specific charging unit interval in seconds. - Time indicator 000000 spare 000001 00.30 h 000010 01.00 h | | | | 110000 24.00 h A.4.2 Tariff change message tableau ccitt 86030, (M), p. - Message indicator Bit A: tariff factor next tariff 0 tariff factor field next tariff not present 1 tariff factor field next tariff present Bits D-B: spare - Tariff indicator, tariff factor and time indica- tor: see S A.4.1.2 A.4.3 Collection charging message tableau ccitt 86040, (M), p. The collection field contains the number of charging units which are to be charged to the calling subscriber. The field has a length of 8 bits so a maximum of 256 units is possible. A.4.4 Charging confirmation message tableau ccitt 86040 (?), (M), p. - Heading code H1 H1 = 0101 confirmation of packet charging H1 = 0110 confirmation of collection charging - Charging unit field Number of charging units which actually are charged to the calling party A.4.5 Acknowledgement message tableau ccitt 86050, (M), p. - Heading code H1 H1 = 1000 acknowledgement receipt of tariff review, collection charging or charging confirmation message References [1] CCITT Recommendation Characteristics of primary PCM multiplex equipment operating at 2048 kbit/s , Rec. G.732. [2] CCITT Recommendation Characteristics of 2048-kbit/s frame structure for use with digital exchanges , Vol. III, Rec. G.734. [3] CCITT Recommendation Second order PCM multiplex equip- ment operating at 8448 kbit/s , Rec. G.744. [4] CCITT Recommendation Characteristics of 8448-kbit/s frame structure for use with digital exchanges , Rec. G.746. [5] CCITT Recommendation Language digit or discriminating digits , Rec. Q.104. [6] CCITT Recommendation Signalling Connection Control Part , Recs. Q.711-Q.714. MONTAGE: RECOMMANDATION Q.724 SUR LE RESTE DE CETTE PAGE