1、ITU-T RECMN*Q.705 93 48b259L 05849b8 256 H INTERNATIONAL TELECOMMUNICATION UN ION ITU-T TELECOMMUNICATION STAN DARD IZATION SECTOR OF ITU SPECIFICATIONS OF SIGNALLING SYSTEM No. 7 Q.705 (03/93) SIGNALLING SYSTEM NO. 7 - SIGNALLING NETWORK STRUCTURE ITU-T Recommendation Q.705 (Previously “CCITT Recom
2、mendation”) COPYRIGHT International Telecommunications Union/ITU TelecommunicationsLicensed by Information Handling ServicesITU-T RECMN*Q=705 93 4862591 0584969 192 FOREWORD The ITU Telecommunication Standardization Sector (ITU-T) is a permanent organ of the International Telecom- munication Union.
3、The ITU-T is responsible for studying technical, operating and tariff questions and issuing Recommendations on them with a view to standardizing telecommunications on a worldwide basis. The World Telecommunication Standardization Conference (WTSC), which meets every four years, established the topic
4、s for study by the ITU-T Study Groups which, in their turn, produce Recommendations on these topics. ITU-T Recommendation 4.705 was revised by the ITU-T Study Group XI (1988-1993) and was approved by the WTSC (Helsinki, March 1-12, 1993). NOTES 1 As a consequence of a reform process within the Inter
5、national Telecommunication Union (ITU), the CCITT ceased to exist as of 28 February 1993. In its place, the ITU 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 Similarly, in this reform process, the CCIR and the IFRB have been replaced by the Radiocommunication Secto
6、r. In order not to delay publication of this Recommendation, no change has been made in the text to references containing the acronyms “CCIT, CCIR or IFRB” or their associated entities such as Plenary Assembly, Secretariat, etc. Future editions of this Recommendation will contain the proper terminol
7、ogy related to the 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 IT 1994 All rights reserved. No part of this publication may be reproduced or utilized in a
8、ny form or by any means, electronic or mechanical, including photocopying and microfilm, without permission in writing from the ITU. COPYRIGHT International Telecommunications Union/ITU TelecommunicationsLicensed by Information Handling Services - ITU-T RECMN*Q.705 93 m 48b259L 058V970 904 1 2 3 4 5
9、 6 7 8 9 CONTENTS Introduction Network components . 2.1 Signalling links . 2.2 Signalling points . Structural independence of international and national signalling networks . Considerations common to both international and national signalling networks . 4.1 Availability of the network . 4.2 Message
10、transfer delay . 4.3 Message sequence control 4.4 4.5 Satellite working . 5.1 General 5.2 5.3 5.4 Routing rules . 5.5 Structures 5.6 Procedures Signalling network for cross-border traffic 6.1 General 6.2 Use of international hierarchical level 6.3 Integrated numbering of national signalling networks
11、 . 6.4 Interworking of national signalling networks . National signalling network . Procedures prevent unauthorized use of an STP (optional) . 8.1 General 8.2 Identifying unauthorized SS No . 7 messages . 8.3 Treatment of unauthorized SS No . 7 messages 8.4 Measurements . 8.5 Notification to unautho
12、rized user . SS No . 7 Planning Tools Number of signalling links used in load sharing International signalling network . Number of signalling transfer points in signalling relations . Numbering of signalling points Annex A . Mesh signalling network examples . A.l General A.2 A.3 Routing . A.4 Action
13、s relating to failure conditions AS Basic network structures (example) Explanatory note from the implementors forum for clarification of load sharing Recommendation Q.705 (03/93) Page 1 1 1 1 2 3 3 3 3 3 3 4 4 4 4 4 4 4 5 5 5 5 5 5 5 5 6 6 6 6 7 7 7 7 9 17 22 i COPYRIGHT International Telecommunicat
14、ions Union/ITU TelecommunicationsLicensed by Information Handling ServicesRecommendation Q.705 SIGNALLING SYSTEM NO. 7 - SIGNALLING NETWORK STRUCTURE (Geneva, 1980; modified at Helsinki, 1993) 1 Introduction This Recommendation describes aspects which are pertinent to and should be considered in the
15、 design of international Signalling System No. 7 (SS No. 7) signalling networks. Some or all of these aspects may also be relevant to the design of national networks. Some aspects are dealt with for both international and national networks (e.g. availability), others are discussed in the context of
16、the international network only (e.g. the number of signalling transfer points in a signalling relation). A number of aspects require furiher study for national networks. This Recommendation also gives in Annex A examples of how the signalling network procedures may be applied to the mesh network rep
17、resentation. The national and international networks are considered to be structurally independent and, although a particular signalling point may belong to both networks, signalling points are allocated signalling point codes according to the rules of each network. The signalling network procedures
18、 are provided in order to effectively operate a signalling network having different degrees of complexity. They provide for reliable message transfer across the network and for reconfiguration of the network in the case of failures. The most elementary signalling network consists of originating and
19、destination signalling points connected by a single signalling link. To meet availability requirements this may be supplemented by additional links in parallel which may share the signalling load between them. If, for all signalling relations, the originating and destination signalling points are di
20、rectly connected in this way in a network, then the network operates in the associated mode. For technical or economic reasons a simple associated network may not be suitable and a quasi-associated network may be implemented in which the information between originating and destination signalling poi
21、nts may be transferred via a number of signalling transfer points. Such a network may be represented by a mesh network such as that given in Annex A, as other networks are either a subset of the mesh network or are structured using this network or its subsets as components. 2 Network components 2.1
22、Signalling links Signalling links are basic components in a signalling network connecting together signalling points. The signalling links encompass the level 2 functions which provide for message error control (detection and subsequent correction). In addition, provision for maintaining the correct
23、 message sequence is provided (see Recommendation 4.703). 2.2 Signalling points Signalling links connect signalling points at which signalling network functions such as message routing are provided at level 3 and at which the user functions may be provided at level 4 if it is also an originating or
24、destination point (see 2.4/Q.704). A signalling point that only transfers messages from one signalling link to another at level 3 serves as a signalling transfer point (STP). The signalling links, signalling transfer points, and signalling (originating or destination) points may be combined in many
25、different ways to form a signalling network. Recommendation Q.705 (0393) 1 COPYRIGHT International Telecommunications Union/ITU TelecommunicationsLicensed by Information Handling ServicesITU-T RECMN*Q.705 93 m 48b259L 0584972 787 m 3 Structural independence of international and national signalling n
26、etworks The worldwide signalling network is structured into two functionally independent levels, namely the international and national levels, as illustrated in Figure 1. This structure makes possible a clear division of responsibility for signalling network management and allows numbering plans of
27、signalling points of the international network and the different national networks to be independent of one another. country1 I Intemational hierarchical led N Naiianai Memhical lemi intematlonal signalling point (ISP) 0 Narnal signalling point (NSP) CouitryP FIGURE 1lQ.705 uitemtidandnatidsignallin
28、gm A signalling point (SP), including a signalling transfer point (SW), may be assigned to one of three categories: - national signalling point (NSP) (signalling transfer point) which belongs to the national signalling network only (e.g. NSP1) and is identified by a signalling point code (OX or DPC)
29、 according to the national numbering plan of signalling points; - international signalling point (ISP) (signalling transfer point) which belongs to the international signalling network only (e.g. ISP,) and is identified by a signalling point code (OX or DPC) according to the international numbering
30、plan of signalling points; - a node that functions both as an international signalling point (signalling transfer point) and a national signalling point (signalling transfer point) and therefore belongs to both the intemational signalling network and a national signalling network and accordingly is
31、identified by a specific signalling point code (OX or DPC) in each of the signalling networks. If a discrimination between intemational and national signalling point codes is necessary at a signalling point, the network indicator is used (see 14.UQ.704). 2 Recommendation Q.705 (0393) COPYRIGHT Inter
32、national Telecommunications Union/ITU TelecommunicationsLicensed by Information Handling Services4 Considerations common to both international and national signalling networks 4.1 Availability of the network The signalling network structure must be selected to meet the most stringent availability re
33、quirements of any User Part served by a specific network. The availability of the individual components of the network signalling links (signalling points and signalling transfer points) must be considered in determining the network structure (see Recommendation 4.709). Considerable attention is req
34、uired to STP routing tables to ensure that circular routing does not occur. (See Annex NQ.780 - Testing and Planning Tools.) 4.2 Message transfer delay In order to take account of signalling message delay considerations, regard should be given, in the structuring of a particular signalling network,
35、to the overall number of signalling links (where there are a number of signalling relations in tandem) related to a particular user transaction (e.g. to a specific call in the telephone application) (see Recommendation 4.709). 4.3 Message sequence control For all messages for the same transaction (e
36、.g. a telephone call) the MTP will maintain the same routing provided that the same signalling link selection code is used in the absence of failure. However, a transaction does not necessarily have to use the same signalling route for both forward and backward messages. 4.4 Number of signalling lin
37、ks used in load sharing The number of signalling links used to share the load of a given flow of signalling traffic typically depends on - the total traffic load; - the availability of the links; - the required availability of the path between the two signalling points concerned; and - the bit rate
38、of the signalling links. Load sharing requires at least two signalling links for all bit rates, but more may be needed at lower bit rates. When two links are used, each of them should be able to carry the total signalling traffic in case of failure of the other link. When more than two links are use
39、d, sufficient reserve link capacity should exist to satisfy the availability requirements specified in Recommendation 4.706. 4.5 Satellite working The service performance criteria and network operation aspects require balanced consideration in structuring SS No. 7 networks. Despite the relatively lo
40、ng delay of satellite connections, these connections can also be suitable for providing signalling data links. Especially for long distance international operation, transmission diversity (including satellites) is an important criterion in structuriIig SS No. 7 networks from a network availability a
41、nd reliability point of view. Recommendation Q.705 (03/93) 3 COPYRIGHT International Telecommunications Union/ITU TelecommunicationsLicensed by Information Handling ServicesITU-T RECMN*Q.705 93 48b2592 0584974 55T m In international operation, a terrestial signalling data link using the basic error
42、correction method may be restored, in exceptional circumstances and with bilateral agreement, by using a satellite data link. If this is done, the following precautions should be taken into account: - in order to ensure in these circumstances the correct operation of the basic error correction metho
43、d over the satellite data link, timer “7 (12.3/Q.703), at both ends of the restored signalling link, should have a value of at least 800 ms; - in order to take into account the additional delay caused by the satellite data link, the minimum values of the timers Tl-T6, specified in 16.8/Q.704, should
44、 take the specified values for routes with long propagation delays; the bit error rate guaranteed by the satellite link used is of significant influence. If the bit error rate is worse than 10-7, the dimensioning of the link loads should consider from the beginning the possibly lower loading potenti
45、al of a satellite link (see YQ.706). - The calculation of the value N2 (the number of message signal unit octets available for retransmission in the PCR error correction method (see 6.424.703) should take a signalling loop delay To range, depending on the geographical conditions, between a minimum o
46、f 480 ms and a maximum of 600 ms. 5 International signalling network 5.1 General The international signalling network will use the procedures to be defined in the SS No. 7 Recommendations. The international network structure to be defined can also serve as a model for the structure of national netwo
47、rks. 5.2 Number of signailing transfer points in signalling relations In the international signalling network the number of signalling transfer points between an originating and a destination signalling point should not exceed two in a normal situation. In failure situations, this number may become
48、three or even four for a short period of time. This constraint is intended to limit the complexity of the administration of the international signalling network. 5.3 Numbering of signalling points A 14-bit code is used for the identification of signalling points. The allocation scheme of internation
49、al signalling point codes is defined in Recommendation 4.708. 5.4 Routing rules 5.4.1 In order to ensure full flexibility for the routing of signalling in the SS No. 7 international signalling network it appears desirable that at least one signalling point in each country should provide means for the international STP function. Such an approach should ease the use of SS No. 7 on small traffk routes. 5.4.2 Other routing niles For further study. 5.5 Structures Requires further study. 5.6 Procedures Requires further study. 4 Recommendation Q.705 (03/93) COPYRIGHT International Telecommunic
