C:\WINWORD\CCITTREC.DOT All drawings contained in this Recommendation have been done in Autocad. 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, § 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 § 2; the heading codes and detailed message formats are described in § 3. 1.2 The service information octet The service information octet comprises the service indicator and the subservice field. The service indicator is used to associate signalling information with a particular User Part and is only used with message signal units (see Rec- ommendation Q.704, § 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 - CCITT 35510 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 interna- tional 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 message type appear in all messages of that type. 1.3.2 Optional subfields Subfields which have been declared optional for a given message 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 preced- ing fixed length subfield in terms of a predefined 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 trans- mitted 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 sig- nificant 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 signal- ling message and is used by the message routing function at Message Trans- fer Part level 3 to select the appropriate signalling route and by the User Part function to identify the particular transaction (e.g. the call) to which the message pertains. In general, label information encompasses an explicit or implicit indi- cation of the message source and destination and, depending on the applica- tion, various forms of transaction identification. For messages which are related to circuits or calls, the transaction 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 messages between exchanges at a time when no circuit is associated with the call. Such messages could be carried using the services of the Sig- nalling 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 cir- cuit identification code are not included in the information transferred between the Telephone User Part and the Signalling Connection Control Part. One standard label format is specified (§ 2.2) for international use. The same standard label is applicable for national use; admitted deviations from the format of the standard label are described in § 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 begin- ning of the signalling information field. The label structure is as shown in Figure 2/Q.723. Figure 2/Q.723 - CCITT 35520 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 identifi- cation code (CIC) indicates one speech circuit among those directly inter- connecting the destination and the originating points. The portion of the label that consists of the destination point code and origi- nating 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, § 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 identification of signalling points. Separate code plans will be used for the international signalling net- work and for different national signalling networks. The principles of code allocation which apply to the international sig- nalling network should be in accordance with Recommendation Q.708. The destination point code will be the code applicable to the tele- phone exchange to which the message is sent. The originating point code will be the code applicable to the telephone exchange from which the mes- sage 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 (Rec- ommendations G.732 [1] andG.734[2]) the circuit identification 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 (Rec- ommendation G.744 [3] andG.746[4]) the circuit identification code contains in the 7 least significant bits an identification 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 destination 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 identification code contains in the 6 least significant bits the identification of a chan- nel 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. TABLE 1/Q.723 0000000 channel 1 0000001 channel 2 | | 0011111 channel 32 0100000 channel 33 | | 1111110 channel 1127 | | 1111111 channel 128 TABLE 2/Q.723 000000 unallocat ed 000001 channel 1 | | 1st basic (FDM) group 001100 channel 12 001101 channel 1 001110 channel 2 001111 channel 3 010000 unallocat ed 2nd basic (FDM) group 010001 channel 4 | | 011001 channel 12 011010 channel 1 | | 011111 channel 6 100000 unallocat ed 3rd basic (FDM) group 100001 channel 7 | | 100110 channel 12 100111 channel 1 | | 101111 channel 9 110000 unallocat ed 4th basic (FDM) group 110001 channel 10 110010 channel 11 110011 channel 12 110100 channel 1 | | 5th basic (FDM) group 111111 channel 12 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 identifies a specific message group (see Recommendation Q.722, § 3.2.1) while H1 either con- tains a signal code or in case of more complex messages, identifies the for- mat of these messages. The allocation of the H0 and H1 code is summarized in Table 3/Q.723. TABLE 3/Q.723 Heading code allocation Me s- sag e gro up H1 H0 00 00 00 01 00 10 00 11 01 00 01 01 01 10 01 11 10 00 10 01 10 10 10 11 11 00 11 01 11 10 11 11 00 00 Spare, reserved for national use FA M 00 01 IA M IAI SA M SA O FS M 00 10 GS M CO T CC F BS M 00 11 GR Q SB M 01 00 AC M CH G UB M 01 01 SE C CG C NN C AD I CF L SS B UN N LO S SS T AC B DP N MP R EU M CS M 01 10 AN U AN C AN N CB K CL F RA N FO T CC L CC M 01 11 RL G BL O BL A UB L UB A CC R RS C GR M 10 00 M GB M BA M GU M UA HG B HB A HG U HU A GR S GR A SG Ba) SB Aa ) SG Ua ) SU Aa ) 10 01 RESERVED CN M 10 10 AC C Spare reserved for international 10 11 and basic national use 11 00 11 01 11 10 Spare, reserved for national use 11 11 a) National option. 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 mes- sage HGB Hardware failure oriented group blocking message HGU Hardware failure oriented group unblocking message HUA Hardware failure oriented group unblocking—acknowledgement mes- sage IAI Initial address message with additional information IAM Initial address message LOS Line—out—of—service signal MBA Maintenance oriented group blocking—acknowledgement message MGB Maintenance oriented group blocking message MGU Maintenance oriented group unblocking message MPR Misdialled trunk prefix MUA Maintenance oriented group unblocking—acknowledgement message NNC National—network—congestion signal RAN Reanswer signal RLG Release—guard signal RSC Reset—circuit signal SAM Subsequent address message SAO Subsequent address message with one signal SBA Software generated group blocking—acknowledgement message SBM Successful backward set—up information message SEC Switching—equipment—congestion signal SGB Software generated group blocking message SGU Software generated group unblocking message SSB Subscriber—busy signal (electrical) SST Send—special—information tone signal SUA Software generated group unblocking—acknowledgement UBA Unblocking—acknowledgement signal UBL Unblocking signal UBM Unsuccessful backward set—up information message UNN Unallocated—number signal Note — Each address complete message contains one of the following sig- nals: — ADC Address—complete, charge — ADN Address—complete, no charge — ADX Address—complete, coin box — AFC Address—complete, charge subscriber free — AFN Address—complete, no charge, subscriber free — AFX Address—complete, coin box, subscriber free 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 messages 0101 unsuccessful backward set—up information messages 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 ü to ý reserved for national use 1111 þ 3.3 Forward address messages The following types of forward address messages are specified and are each identified by a different heading code H1: — Initial address message. — Initial address message with additional information. — 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 - CCITT 35530 The following codes are used in the fields of the initial address message. a) Label: see § 2 b) Heading code H0 is coded 0001 c) Heading code H1 is coded 0001 d) Calling party category bit s 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 ü 0 0 0 1 1 1 ý available to Administrations for select- ing a particular language 0 0 1 0 0 0 þ 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 ü t o ý spare 1 1 1 1 1 1 þ Note 1 — The calling party category “unknown source” is classified, 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 allocation. f) Message indicators bits B A: nature of address indicator 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 indicator 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 indicator 0 0 continuity—check not required 0 1 continuity—check required on this circuit 1 0 continuity—check performed on a previous 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 indicator 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 m/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 signal 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. Subsequent 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 inte- gral number of octets. 3.3.2 Initial address message with additional information The basic format of the initial address message with additional infor- mation is shown in Figure 4/Q.723. Figure 4/Q.723 - CCITT 35541 The following codes are used in the initial address message with additional information: a) Label: see § 2 b) Heading code H0 is coded 0001 c) Heading code H1 is coded 0010 d) Calling party category: [see § 3.3.1 d)] e) Message indicators: [see § 3.3.1 f)] f) Number of address signals: [see § 3.3.1 g)] g) Address signals: [see § 3.3.1 h)] 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 indicator 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 indicator 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 applica- tions 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 Fig- ure 4a/Q.723. DCBA Interlock code Spare CUG indicator 32 4 4 FIGURE 4a/Q.723 Closed user group information field The following codes are used in the subfields of the closed user group infor- mation field. — bits B A: CUG call indicator 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 infor- mation 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 cus- tomer services.) m) Calling line identity The basic format of the calling line identity field is shown in Figure 4b/ Q.723. DCBA DCBA Calling line iden- tity Number of address signals Address indicator n × 8 4 4 FIGURE 4b/Q.723 Calling line identity field The following codes are used in the subfields of the calling line identity field. — Address indicators: bits B A: nature of address indicator 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 identity not available indicator 0 0 0 1 ü to ý a code expressing in pure binary representation the num- ber of address 1 1 1 1 þ signals. — Calling line address signals Each signal is coded as indicated in § 3.3.1 h) as applicable. n) Original called address The basic format of the original called address field is shown in Figure 4c/Q.723. DCBA DCBA Original called address Number of address signals Address indicator s n × 8 4 4 FIGURE 4c/Q.723 Original called address field The following codes are used in the subfields of the original address field: — Address indicator bits B A: nature of address indicator 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 ü to ý a code expressing in pure binary representation the num- ber of address 1 1 1 1 þ signals. — Original called address signals Each signal is coded as indicated in § 3.3.1 h) as applicable. o) Charging information: for further study. (This optional field will contain information to be sent to a successive exchange for charg- ing 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 - CCITT 35550 The following codes are used in the fields of the subsequent address mes- sage: a) Label: see § 2 b) Heading code H0 is coded 0001 c) Heading code H1 is coded 0011 d) Address signal is coded as indicated in § 3.3.1 h) as applicable e) Number of address signals: a code expressing in pure binary repre- sentation the number of address signals contained in the subse- quent 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 - CCITT 35560 The following codes are used in the fields of the subsequent address mes- sage with one signal: a) Label: see § 2 b) Heading code H0 is coded 0001 c) Heading code H1 is coded 0100 d) Address signal is coded as indicated in § 3.3.1 h) 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 - CCITT 85940 The following codes are used in the fields of the general forward set—up information message: a) Label: see § 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 indicator 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: bit s 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 ü t o ý (see § 3.3.1 d)) 1 1 1 1 1 1 þ f) Calling line identity: Format and codes are the same as used in the calling line identity con- tained in the initial address message with additional information (see § 3.3.2). g) Incoming trunk and transit exchange identity: The basic format of the incoming trunk and transit exchange iden- tity field is shown in Figure 8/Q.723. DCBA DCBA DCBA Incomin g trunk identity Field length indicator Spare Transit exchange identity Exchang e iden- tity length indicator Identity type indicator n × 8 4 4 n × 8 4 4 FIGURE 8/Q.723 Incoming trunk and transit exchange identity field 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 subfield 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 § 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 pro- vided. — Incoming trunk identity A code contained in a maximum of 15 octets, identifying the incom- ing trunk. The encoding of the incoming trunk identity is for fur- ther study. h) Original called address See § 3.3.2 n). 3.4.2 Continuity—check message The basic format of the continuity—check message is shown in Fig- ure 9/Q.723. Figure 9/Q.723 - CCITT 35570 The following codes are used in the fields of the continuity—check mes- sage: a) Label: see § 2 b) Heading code H0 is coded 0010 c) Heading code H1 contains signal codes as follows: 0011 continuity signal 0100 continuity—failure signal