1、W 2326434 OOObObB B W 1 T/N 21-02 E Page 1 Recommendation T/N 21-02 (Edinburgh 1988) NUMBERING AND ADDRESSING FOR GAP PHASE II Recommendation proposed by Working Group T/WG 14 “Network Aspects” (NA) Text of the Recommendation adopted by the “Telecommunications” Commission: “The European Conference o
2、f Postal and Telecommunications Administrations, considering - the common CEPT approach to the ISDN and general CEPT assumptions and policies for the evolution towards ISDN, - the I. Series Recommendations of CCITT, as well as other CCITT Recommendations on ISDN, - CCITT Recommendations E.163, E.164
3、, E.166, X.121 and X.122 concerning numbering and numbering inter- - that there is a need to complement existing CEPT and CCITT texts on numbering and addressing, working, recommends to the member Administrations of the CEPT, that they implement their numbering plans for ISDNs according to the guide
4、lines given in the attached text.” Edition of February 28, 1989 F 2326434 0006069 T T/N 21-02 E Page 2 INTRODUCTION The GAP proposals for the co-ordinated introduction of ISDN in the EEC identified a requirement for numbering, addressing and signalling arrangements to be defined such that interworki
5、ng with the existing public telephone network is possible, including a means for identifying different teleservices and terminals. This document supersedes the numbering guidelines for GAP Phase I and is the considered position of CEPT on the topic, giving guidelines on the numbering aspects of ISDN
6、 for Phase II of the GAP programme in the context of the emerging CCITT Recommendations. Due recognition continues to be given to the need for European numbering arrangements for services offered on an international basis to be capable of evolution within the overall world plans. Where necessary, is
7、sues which are likely to develop further or require further study are also identified. 1. 2. 3. TOPICS AREAS CONSIDERED The following are the numbering topics considered in connection with the early co-ordinated implementation of ISDN throughout Europe: - Numbering Plan Evolution; - Direct Dialling-
8、In (DDI), Multiple Subscriber Number (MSN) and Sub-Addressing; - Terminal selection procedures; - Numbering Aspects of interworking; - Interlock codes for Closed User Group. 4, NUMBERING PLAN EVOLUTION CCITT Recommendation E.164 documents the numbering plan for the ISDN era. In evolving their PSTNs
9、to ISDN Administrations are expected to enhance the capability of their systems to accommodate the requirements for increased international number length from 12 to 15 digits. CCITT, recognising the potential difficulties for some Administrations in meeting these requirements, has proposed that exis
10、ting networks should not be required to interwork with ISDNs using the increased capacity before 31 December 1996, this being defined as Time-T. The concept and application for Time-T is described in CCITT Recommendation E.165. It is recommended that Administrations avail themselves of every opportu
11、nity for early compliance with the provisions of E.165. 5. 6. DIRECT DIALLING-IN (DDI) 7. DDI in the PSTN is a service capability whereby direct access to terminals within a customer?s installation is made possible by the allocation of numbers from the PSTN numbering plan to that installation. The u
12、se of this facility can create considerable demand for numbering capacity and is therefore not favoured where there is an risk from depletion of numbering resources. MULTIPLE SUBSCRIBER NUMBERS (MSN) MSN provide the possibility that calls can be dialled from a line connected to the public network di
13、rectly to terminals connected to the public network directly to terminals connected to the basic access in a passive bus configuration. MSN will be offered as a supplementary service at subscription time. The number of digits which are passed across the user network interface can range from one digi
14、t to the whole number and will be fixed by the network providing service. MSNs need not be sequential, and because of that it may be necessary to send the whole number on every call to avoid future duplication problems. 8. SUB-ADDRESSING 9. The first consideration of sub-addressing arose in connecti
15、on with the application of the Data Nework numbering plan, X.121, to PSPDNs in Recommendation X.25. For that application public data network numbers were restricted, for example, to the first 12 out of the 14 digits of the X.121 number. The remaiiiiiig 2 digits were then made available for selection
16、 procedures at the DTE/DCE on the customers? premises. Digits 13 and 14 were labelled the Sub-Address. In the more recent work on numbering for both Data Network and ISDNs it has been recognised that a greater capacity is required for the transport of user equipment selection information as a supple
17、ment to the main network address. In X.25 this additional address information has been called Network Address Extension (NAE). In considering the numbering requirements for ISDN the concept of DDI has been retained and the term ?Sub-Address? used for address information that can supplement the E. 16
18、4 number. The term Sub-Address is defined in CCITT Recommendation E.164. 10. 11. 12. Edition of February 28, 1- 7 = 2326434 0006070 6 i! TIN 21-02 E Page 3 CURRENT STATUS OF STUDIES ON SUB-ADDRESSING FOR ISDN 13. CCITT Recommendation E.164 describes the relationship between a Sub-Address and an ISDN
19、 number. The significant concepts in the application of sub-addressing in ISDN are: - the functions related to the setting up of a cail between two customer/network interfaces on a public ISDN are determined and performed solely on the basis of analysis of the ISDN number, - public networks are not
20、required to analyse the content of a sub-address in any way either for the purpose of setting up a connection to a subscriberlnetwork interface or for establishing special call parameters related to charging, quality of service, etc., - sub-address information within ISDN must be conveyed transparen
21、tly between the originating and ter- minating users without alteration to the structure or content, except where the sub-address exceeds the maximum authorised length for any ked subscriber or network capability. In these cases none of the sub-address will be sent to the called terminal, - in cases
22、where interworking between different types of network is required, some mapping of the sub-address information may be necessary, - in the context of OSI, sub-addressing is a network layer function. In the more recent consideration of sub-addressing in CCIIT two areas of application have been identif
23、ied: - the conveyance of OS1 NSAP addressing of up to 40 digits120 octets (formerly 32 digits) between OS1 end systems, - the conveyance of non-OS1 supplementary address information of up to 40 digits120 octets. It is recom- mended that where this application is used as an alternative to DDI, the nu
24、mber of digits should be restricted to less than 10, - in the sub-address or Network Address Extension (NAE) field the two applications described above are mutually exclusive. Other applications are under study. 14. O USER PROCEDURES CCITT have not yet completed their studies on user procedures. The
25、 proposal being considered is the use of the symbol # to indicate end of address and the symbol * as the Sub-Address identifier. It should be noted that the use of * and # are relevant only at the man-machine interface and are not seen by the network. Example: 15. I I I I # Note. Where # is not used
26、 a time-out may be required. Figure 1 (T/N 21-02). 16. There is a clear need for a separator to be defined to indicate the start of a sub-address at the manIrnachine interface. It is recommended that European Administrations consider the adoption of the symbols * and # for user procedures at the man
27、/machine interface in anticipation of agreement to this aspect of the draft CCITT Recommendation. This matter must be subject to further study. MESSAGE CONTENT The CCITT agreed maximum length for a sub-address is 40 digits/20 octets. 17. USE OF SUB-ADDRESSING FOR GAP PHASE 2 18. 19. For GAP Phase II
28、, the use of sub-addressing and the adoption of the user procedure symbols * and # is a national matter. For GAP Phase II the international provision for the conveyance of a sub-address of up to 40 digits/20 octets is agreed. Edition of February 28, 1989 I_ n 232434 000073 A n T/N 21-02 E Page 4 TER
29、MINAL SELECTION PROCEDURES In an ISDN a terminal selection function may be required where multi-terminal installations are accessed via a user/network interface. The particular consideration for GAP Phase II is that concerning terminals connected in a Passive Bus configuration. Within an ISDN enviro
30、nment, the comparison techniques of Lower Layer Compatibility (LLC), Bearer Capability (BC) and Higher Layer Compatibility (HLC) will be available to identify and select a terminal according to service type. These comparison techniques are insufficient where : - 2 or more terminals of the same servi
31、ce type are connected to a passive bus, and where individual - a call to an ISDN passive bus configuration originating from a network which does not support the transfer Alternative selection procedures are required where either of both conditions apply. Three possibilities to supplement or substitu
32、te the HLC/service identification capability have been identified. These are: - Direct Dialling-In, - Multiple Subscriber Number, - Sub-Addressing. A national network may adopt one or more of these procedures. 20. 21. 22, identification is required, of the LLC, BC and HLC information, e.g. PSTN. 23,
33、 USE OF DDI OR MSN FOR TERMINAL SELECTION The allocation of ISDN numbers to each terminal that requires to be identified in a multi-terminal installation is recognised as the most practical method of terminal selection. DDI, as described in paragraph 7., is recommended as the method for accessing te
34、rminals on ISPBXs, and MSNs, as described in paragraph 8., for accessing terminals on a passive bus. The use of MSN or DDI will enable ISDN terminals to be selected by users: i) on aISDN ii) on a PSTN iii) on a dedicated Data network Full international access will also be possible. 24. USE OF SUB-AD
35、DRESSING FOR TERMINAL SELECTION 25, Sub-Addressing is described in paragraphs 9.- 14. Sub-Addressing is recognised as the preferred long-term alternative to the use of DDI or MSN for terminal selection on multi-terminal installation. While Sub-Addres- sing may be used for this purpose for GAP Phase
36、II it will not provide universal accessibility to terminals. The following limitations should be noted. i) Sub-Addressing will not be available from PSTNs and ISDNs which do not provide it. ii) Full international use of Sub-Addressing in ISDN may not be possible due to limitations in some early nati
37、onal implementations of ISDN signalling protocols. 26. NUMBERING ASPECTS OF INTERWORKING For GAP Phase II ISDN the interworking situations on an international basis are considered to be restricted to: - ISDN to and from PSTN, - ISDN to and from PSPDN. Interworking arrangements involving CSPDNs have
38、not been considered. 27, ISDN/PSTN INTERWORKING ISDNs and PSTNs use the E. 164 numbering arrangements. For many Administrations there will be no easy distinction between PSTN and ISDN numbers. With the exception of the requirements for terminal selection, special numbering requirements for ISDN/PSTN
39、 interworking have not been identified. 28. Edition of February 28, .I 2326414 000b072 T i - A T/N 21-02 E Page 5 B ISDN/PSPDN INTERWORKING It is assumed that at 1988 most Administrations will operate X.25 based services on ISDN using the access method arrangements described in CCITT Recommendation
40、X.31. International interworking between an ISDN in one country and PSPDN in another country may be most effectively provided via the international PSPDN. Further details on numbering interworking are contained within CCITT Recommendation E. 166 and X. 122. E. 166 details the numbering interworking
41、scenarios from ISDN to other networks and X. 122 details the numbering interworking scenarios from PSPDNs to other networks. Members of CEPT are urged to ensure that they can conform with these Recommendations. It should be noted that CCITT may produce a single interworking Recommendation in the nex
42、t plenary period. It is further recommended that the foliowing should be the general rule: ISDN to PSPDN PSPDN to ISDN This approach permits number flow across the international interface to comply with agreed CCITT formats. Numbering arrangements including the use of escape codes and prefixes for a
43、ccess in an ISDN to interworking units can remain a national matter. It should be noted that where more than one interworking unit is used between a PSPDN and an ISDN to access different types of terminal, or similar terminals which are geographically distant, and where the terminals have E. 164 num
44、bers, the identification of the required interworking unit cannot be made on examination of the escape code alone. In such cases it will be necessary for PSPDN also to examine some digits of the E. 164 number. CCITT Recommendation X.121 recommends that up to 5 digits of the number should be examined
45、 for this purpose. Interworking facilities to be provided in country of origin. Interworking to be provided in country of destination. 29. 30. 31. 32. 33. 34. 35. CLOSED USER GROUP INTERLOCK CODE The supplementary service Closed User Group (CUG) when implemented in co-operation with other networks r
46、equires the provision of an interlock code structure by which validation of call requests within the CUG can be achieved. The CUG interlock code (international CUG Number ICN) structure used by dedicated data networks is dehed in CCITT Recommendation X. 180. The interlock code comprises two parts. T
47、he first part (A) identifies the coordinating Administration for the CUG; the second part (B) gives the unique identity of the CUG. In dedicated data networks the X.121 DNIC assigned to the network for numbering purposes offes a convenient basis for CUG Administration identifica- tion. There is no d
48、irect relationship between X.121 numbers for DTE/DCE interface numbering and CUG interlock codes. For ISDN based CUGs it is inappropriate to use DNICs for the part A function of the interlock code. The ideal, but impractical, approach would be the definition of a network independent interlock code s
49、eries to replace that in X. 180 which could be used by all networks to ensure securitya on CUG interworking calls. CCITT are currently considering the structure of CUG codes for ISDN. An interim arrangement, pending the full definition of the ISDN CUG interlock code structure is required for CUG services commencing in GAP Phase II ISDN. It is therefore proposed that an expedient interlock code series based on CCIT Draft Recommendation E.nic should be adopted for GAP Phase II. The part A of the code should comprise a pseudo DNIC formed by preceding the TCC by the digit 9 or O. I 9/0 TC
