1、ITU-T RECflN*U.L5 93 4862571 0590045 85T = INTERNATIONAL TELECOMMUNICATION UNION ITU-T TELECOMMUNICATION STAN DARD IZATION SECTOR OF ITU TELEGRAPH SWITCHING SPECIFIC SIGNALLING SCHEMES AND INTERWORKING BETWEEN SIGNALLING SYSTEMS U.15 (03/93) INTERWORKING RULES FOR INTERNATIONAL SIGNALLING SYSTEMS AC
2、CORDING TO RECOMMENDATIONS U.1, U.ll AND U.12 ITU-T Recommendation U.15 (Previously “CCIlT Recommendation”) ITU-T RECMN*U-L5 93 4862593 0590046 796 = FOREWORD The ITU Telecommunication Standardization Sector (ITU-T) is a permanent organ of the International Telecom- munication Union. The ITU-T is re
3、sponsible for studying technical, operating and tariff questions and issuing Recommendations on them with a view to standardizing telecommunications on a worldwide basis. The World Telecommunication Standardization Conference (WTSC), which meets every four years, established the topics for study by
4、the ITU-T Study Groups which, in their turn, produce Recommendations on these topics. ITU-T Recommendation U.15 was revised by the ITU-T Study Group IX (1988-1993) and was approved by the WTSC (Helsinki, March 1-12, 1993). NOTES 1 As a consequence of a reform process within the International Telecom
5、munication Union (ITU), the CCITT ceased to exist as of 28 February 1993. In its place, the IT Telecommunication Standardization Sector (ITU-T) was created as of 1 March 1993. Similarly, in this reform process, the CCIR and the IFRB have been replaced by the Radiocommunication Sector. In order not t
6、o delay publication of this Recommendation, no change has been made in the text to references containing the acronyms “CCITT, CCIR or IFRB” or their associated entities such as Plenary Assembly, Secretariat, etc. Future editions of this Recommendation will contain the proper terminology related to t
7、he new ITU structure. 2 telecommunication administration and a recognized operating agency. In this Recommendation, the expression “Administration” is used for conciseness to indicate both a O ITU 1994 All rights reserved. No part of this publication may be reproduced or utilized in any form or by a
8、ny means, electronic or mechanical, including photocopying and microfilm, without permission in writing from the ITU. ITU-T RECMN+U.Z5 73 H 4862593 O570047 622 H CONTENTS 1 General . 2 3 4 5 6 7 8 Rules for alternative routing . Rules for conversion of TCICs and NICs A third COT on type D to allow c
9、onversion of NIC to TCIC. and overcome possible call connected signal Rules for service signal conversion Rules for exchange of line identifications Rules for call connected signal conversion Rules for obtaining the called subscribers answerback when interworking type D with other signalling systems
10、 . and answerback timing problems . Recommendation U.15 (03/93) Page 1 2 2 3 1 ITU-T RECMN*U-L5 93 4862593 0590048 569 Recommendation U.15 INTERWORKING RULES FOR INTERNATIONAL SIGNALLING SYSTEMS ACCORDING TO RECOMMENDATIONS U.l, U.ll AND U.12 (Malaga-Torremolinos, 1984; revised at Helsinki, 1993) Th
11、e CCITT, considering (a) (b) covered by those Recommendations; (cl signalling and Recommendation U. 12 signalling; (4 that it is also useful to cover in the same Recommendation any interworking problems between Recommendations U. 1 and U. 1 1 signalling standards; (e that in international transit ca
12、lls, a number of different signalling standards may be involved; that interworking between signalling systems according to Recommendations U.l and U.ll is already mostly that it is necessary to define specifically the interworking rules between Recommendations U.l or U.ll that the originating Admini
13、stration is responsible for international telex accounting; (0 (g) the originating centre; (h) type C (see Recommendation U. 1 1) signalling for transit working; (i) alternative routings are allowed; that it is desirable for standard arrangements to apply for obtaining the called customers answerbac
14、k; that it is essential to prevent alternative routing in transit centres if network identities cannot be conveyed to that the use of type D signalling according to Recommendation U.12 should be considered in preference to that types A and B (see Recommendation U.1) signalling may only be used for t
15、ransit working where no (i) that there may be cases where conversion of Network Identification Code (NIC) to a Transit Centre Identification Code (TCIC) or vice versa cannot be implemented. In such cases the TCICs and NICs shall be absorbed and alternative routing shall not be allowed within that tr
16、ansit centre. Onward selection shall indicate this condition by using the appropriate COT, unanimously declares the view that 1 General The rules for interworking should cover the following areas: - alternative routing; - - service signai conversion; - exchange of line identifications; - call-connec
17、ted signal conversion; - conversion of TCIC (see Recommendation U.11) and NIC (see Recommendation U.12) signals; methods for obtaining the called subscribers answerback. For the purposes of this Recommendation it shall be assumed that a typical type D interworking connection comprises a first and a
18、last type D exchange and intermediate type D exchanges if any. These are defined below: A first type D exchange uses type D signalling on the outgoing side and any other trunk signalling standard or directly connected subscriber line standard on the incoming side. An intermediate type D exchange use
19、s type D signalling on both the incoming and outgoing sides. Recommendatiqn U.15 (03/93) 1 ITU-T RECHNUU.35 93 4862593 0590049 4T5 A last type D exchange uses type D signalling on the incoming side and any other trunk signalling standard or directly connected subscriber line standard on the outgoing
20、 side. 2 Rules for alternative routing In general, alternative routing should not be allowed when the incoming circuit uses an A or 3 signalling standard. Table 1 gives details of each case. 3 Rules for conversion of TCICs and NICs (see Table 1 for details) Rule 1 - The last type D exchange should c
21、onvert any TCIC received from outgoing type C circuits to the type D NIC format. Where a bilateral agreement exists between Administrations to use TCICs on a type A signalling route, then these may be converted by the last type D exchange to the NIC format at the discretion of the Administration of
22、that exchange. This requires that the TCIC must always use the standard Administrations identification letter(s) as recommended in clause 4/u. 11 and defined in the ITU publication List of Indicators for the Telegraph Retransmission System and Telex Network Identification Codes, Part A (see 3.4.2.4F
23、.60). Rufe 2 - Non-standard information, e.g. type A register codes, will be absorbed by the last type D exchange. Such codes may also be received on type C circuits. It is therefore recommended that Administrations should, in no circumstances. return from terminating or transit centres any Internat
24、ional Telegraph Alphabet No. 2 (ITA2) sequences which could be incorrectly interpreted as TCICs. Rule 3 - In the case of calls from type A or C circuits routed to type D circuits, the network identification codes (NICs) received from the type D network may be converted into the type C transit centre
25、 identification code (TCIC format) by the first type D exchange, see Table 1. The NICs received from the type D network will be translated into the TCIC format of ITA2 Combination No. 29, followed by the TNIC code (as recommended in Recommendation F.60) followed by number of Combinations No. 30 to c
26、omplete a sequence of seven combinations. Rule 4 - In the case of calls from type B circuit routing to a type D circuit, the first type D exchange shall absorb any NICs. 4 A third COT on type D to allow conversion of NIC to TCIC, and overcome possible call connected signal and answerback timing prob
27、lems The conversion from 3 or 4 character NICs to 7 character TCICs can result firstly in the call-connected signal arriving at the first type D centre before complete transmission of the last TCIC, and secondly, in some cases, the answerback arriving before complete transmission of the call-connect
28、ed signal to the incoming circuit. It is necessary to overcome this difficulty by delaying the forwarding of selection in relation to the activities on the backward path. The third COT character should be sent by the first type D exchange to indicate (by bit 4) to the following type D exchanges that
29、 a delay of forward selection is necessary, since the call has been received from a non-type D signalling standard for which conversion of NICs to TCICs is required. Figure 1 shows the timing diagram of this protocol. NOTES 1 TCICs received from distant type C links would pass through the type D lin
30、ks with the appropflate conversion. Where the third COT indicates that conversion of NIC to TCIC is necessary, onward seizure should not occur before the complete transmission of CSC No. 12 of the locally generated NIC. Where the conversion of NIC to TCIC is not necessary, onward seizure of the outg
31、oing circuit should not occur before the complete transmission of the reception-confirmation signal. 2 A problem may exist where the same Recommendation E69 code is allocated to more than one ROA. 2 Recommendation U.15 (03/93) ITU-T RECMN*U.L5 93 9 4862571 0590050 117 5 Rule 1 - The last type D exch
32、ange will convert all returned standard service signais into the appropriate type D numeric service codes. In the case of additional information included in the service text i.e. a, 6, y, 6 preceding a Recommendation U. 1 type A or B service code (see 10.1.2AJ. i), only the standard Recommendation U
33、. 1/U. 1 1 service text will be translated by the type D transit centre. Table 7bN. 12 gives details of service signal conversion. Rules for service signal conversion 6 Rule 1 - If the incoming circuit is not a subscriber line, then the first type D exchange shall not request a called line identific
34、ation. Rules for exchange of line identifications Rule 2 - When the incoming circuit is not a subscriber line and a request for calling line identification is received, the first type D exchange shall send CSC No. i2 only, to indicate that no identification is available as per Table 1AJ.12. Rule 3 -
35、 If the incoming circuit is a subscriber line and the called line identification is required, then the first type D exchange shall recognize receipt of the call-connected signai not preceded by an STTC and a TTC signal as an indication that a called line identification is not available. Rule 4 - If
36、the outgoing circuit is not a subscriber line, then the last type D exchange shall not request a calling line identification. Rule 5 - When the outgoing circuit is not a subscriber line and a request for called line identification is received, the last type D exchange shall indicate that the identif
37、ication is not available, as described in 3.13N.12. 7 Rule 1 - The last type D exchange shall convert ali variations of received call connected signals as defined in Recommendations U.l and U.11 to the type D call connected signal, indicating that call metering is required (CSC No. 13). Rule 2 - The
38、 first type D exchange shall convert CSC No. 13 to the call connected signal according to Recommendations U. I or U.11. Rules for call connected signal conversion Rule 3 - CSC No. 14 (call connected without metering) received at the first type D exchange may or may not be converted to a call connect
39、ed on type A, B or C circuits. The use of CSC No. 14 is left for further study. 8 Rules for obtaining the called subscribers answerback when interworking type D with other signalling systems Rules 2 to 4 apply to the first type D exchange and Rules 5 to 7 to the last type D exchange. A compilation o
40、f the rules is shown in Tables 2 and 3. Rule I - As a general rule, the first and the last type D exchanges should behave independently of each others interworking requirements with regard to controlling the answerback tripping, and intermediate exchanges will be transparent to this control. Rule 2
41、- For locally connected subscribers, the first type D exchange will generate the WRU signal on receipt of the call connected signal as per Appendix IIW. 12. Rule 3 - If the incoming circuit uses an automatic return of answerback trunk signalling standard, then the first type D exchange will generate
42、 a WRU signai two seconds after receipt of the call connected signal. Rule 4 - If the incoming circuit uses a non-automatic return of answerback trunk signalling standard, then the first type D exchange will through-connect on receipt of the call connected signai without generating a WRU signal. Rul
43、e 5 - For locally connected subscribers, the last type D exchange will through-connect after the call connected signai has been transmitted on the incoming type D trunk. Recommendation U.15 (03/93) 3 ITU-T RECUN*U.LS 93 Yb2591 0590053 053 Type B Type A with register codes Rule 6 - If the outgoing ci
44、rcuit uses an automatic return of answerback trunk signalling standard, then the last type D exchange will absorb any incoming characters on the forward path until two seconds from the commencement of the first backward path character. If no characters have been received on the backward path within
45、8-9 seconds following the start of the received call connected signal, then through-connection shall occur. The alternative of clearing the call is for further study. - No register des will be received. Alternative routing is not allowed (Note). Absorb register codes. Alternative routing is not allo
46、wed (Note). Rule 7 - If the outgoing circuit uses a non-automatic return of answerback trunk signalling standard, then the last type D exchange shall delay any received WRU signal until two seconds from the start of the received call connected signai. Through-connection shall occur following the ret
47、ransmission of the WRU signal or after two seconds from the start of the received call connected signal if no WRU signal has been received. Type D Type C with register codes or TCICs TABLE 1AJ.15 Any received NICs shall be absorbed. Alternative routing is not allowed (Note). Any received register co
48、des or TCICs shall be absorbed. Alternative routing is not allowed (Note). Rules for conversion of network identification codes (NICs) and transit centre identification codes (TCICs) and alternative routing Type A with register codes or TCICs Outgoing signalling Type D Any received register codes or
49、 TCICs shall be absorbed. Alternative routing is not allowed (Note). Action to be taken by the transit exchange The NIC shall be retransmitted as received. Alternative routing is allowed. TCICs shall be converted into NICs. Any type A register codes shall be absorbed. Alternative routing is allowed. - Type A with TCICs TCICs may be absorbed or converted to NICs at the discretion of individual Administrations. Alternative routing is not allowed (Note). Type C with register codes or TCICs NICs shall be converted into TCICs. Alternative routing is allowed. TCICs shall be retransmi
