1、INTERNATIONAL TELECOMMUNICATION UNION CCITT TH E INTERNATIONAL TELEGRAPH AND TELEPHONE CON SU LTATIVE COM M ITTEE Guidelines for Implementing a Signalling System No. 7 Network Geneva 1991 - STDBITU-T HDBK GIS-ENGL 1991 = 4862592 Ob81852 195 o ITU 1991 Au rights resewed. No part of this publication m
2、ay be reproduced or utilized in any form or by any means, electronic or mechanical, including photocopying and microfilm, without permission in writing from the . STDSITU-T HDBK GIS-ENGL L99L 4Bb2CqL 0681853 O21 131 TABLE OF CONTENTS Preface CHAPTER I . INTRODUCTION 1 2 3 3.3 4 Purpose and scope of
3、Handbook . Advantages and objectives of a common channel signalling system . 2.1 Channel associated signalling systems . 2.2 Common channel signalling Overview of Signalling System No . 7 3.1 Objectives and fields of application . 3.2 Signalling System No . 7 network 3.2.1 Signalling System No . 7 n
4、etwork components and basic concepts 3.2.2 Signalling network structure . Signalling System No . 7 protocol architecture 3.3.1 MTP . 3.3.2 Users of the MP . 3.3.3 Transaction capabilities 3.4 Operation. Administration and Maintenance (OA - can meet present and future requirements for the exchange of
5、 signalling and other information within telecommunication networks (e.g. call control for telephone, ISDN calls, management and maintenance signals): - provides a reliable means of transfer of information in correct sequence and without loss or duplication (note that this is an idealistic objective
6、 not totally achievable in practice - see Q.706); - can be used in national and international networks. SS No. 7 can be used both for the exchange of circuit-related and non-circuit-related information in, e.g. the PSTN, the ISDN or the PLMN (Public Land Mobile Network). While it is optimized for op
7、eration over 64 kbit/s digitai channels and can be used via satellite channels, it can also operate via analogue channels. The definition of SS No. 7 Recommendations is an ongoing process within the CCITT. Some Recommendations have aiready reached a (relatively) stable state, e.g. those for the MTP
8、and TUP (see Q 3.3), while others in the meantime are of little or no practical consequence like 4.710 and Q.741 (see Annex A). Due to the complex nature of SS No. 7 it can also happen that, at the end of a study period, Recommendations are being published which are not necessarily in a state stable
9、 enough to be implemented. They are published nevertheless so as to document the status and direction of the work and to serve as the basis for further development. Where necessary, therefore, some Recommendations are referred to in the following Chapters as “implementable” to indicate that - while
10、perhaps not yet fully stable - they can aiready be applied in the field. 3.2 Signalling System No. 7 network 3.2.1 Signalling System No. 7 network components and basic concepts The nodes of a telecommunication network (exchanges, processing nodes, etc.) which communicate with each other using SS No.
11、 7 are called Signalling Points (SPs). Signalling points are interconnected by signalling links. Signalling links are the dedicated communication channels used to transfer the signalling information between the signalling points. One signalling link is able to transfer the signalling information for
12、 many speech circuits. A collection of signalling links directly connecting two signalling points is called a signalling link set. Chapter I 3 STD-ITU-T HDBK GIS-ENGL Two signalling points directly connected by a signalling link set are called adjacent. Two SPs not directly connected by a signalling
13、 link set are called non-adjacent signalling points. The collection of signalling links and signalling points is called the signalling network. Functions which utilize the signalling network for the transmission of messages are called user functions. If two signalling points have to communicate with
14、 each other (Le. they maintain a signalling relation) but are non-adjacent, they have to transmit the information via a sequence of successive signalling points adjacent to each other. If messages take such a path then the signalling is said to take place in the quasi-associated mode. When two signa
15、lling points maintain a signalling relation and the messages take a direct linkset between these two points then the signalling takes place in the associated mode. Signalling points which can receive messages on one signalling link and transfer it to another by only using the MTP (see 5 3.3.1) are c
16、alled Signalling Transfer Points (STPs). STPs may or may not include user functions (e.g. may serve as a telephone exchange). A signailing point with an integrated STP capability which also includes Tup or ISUP (see 5 3.3.2) is commonly called an integrated STP. STPs not including ISUP or TUP are co
17、mmonly called stand-alone STPs. Note - In this Handbook the term STP generally refers to stand-alone as well as integrated STPs if not explicitly mentioned otherwise. The predetermined path consisting of the signalling point where a message is generated (originating point), zero or more signalling t
18、ransfer points, and the signalling point to which the message is destined (destination point), is called a signalling route. The collection of possible routes towards a destination point in a signalling point is called a signalling route set. Traffic between two SPs will take the available route(s)
19、with the highest priority. Only if a route becomes unavailable will routes of the next lower priority be used for the communication between the two signalling points. 3.2.2 Signalling network structure The world-wide signalling network is structured into two functionally independent levels, the nati
20、onal and the international level. Further divisions are possible. There are many ways of structuring an individual SS No. 7 network. Consideration must be given to traffic volume, reliability, security, performance requirements, costs, etc. Actual signalling network structures range from (almost) fu
21、lly interconnected (fully meshed) networks over hierarchically structured networks to networks where nodes communicate mainly over a few central STPs. 3.3 Signalling System No. 7protocol architecture The SS No. 7 protocol architecture is divided into different functional blocks and protocol levels,
22、respectively. This structure makes the SS No. 7 architecture very flexible. New functional blocks can be added and existing ones changed with little or no affect on other blocks. The main division of SS No. 7 is into: - the Message Transfer Part (MTP) which provides the basic means of communications
23、; - task specific user parts, and - transaction capabilities. 4 Chapter I The overall structure of the SS No. 7 protocol architecture can be seen in Figure 1fl. Users of CCITT No. 7 Transaction capabilities L- II I I 1 Signalling connection control part (SCCP) I Other I ISDN user part (ISDN-UP) I I
24、Telephone user part (TUP) I Ti 109720-91 MTP FIGURE 1/I Architecture of CCIIT SS No. 7 3.3.1 MTP The MTF comprises levels 1 to 3 of SS No. 7. It provides the basic communication functions for SS No. 7. Its Recommendations have reached a fairly stable status. Level 1 (signalling data link) provides t
25、he physical, electrical, and functional characteristics of a signalling data link and the means to access it. Level 2 (signalling link) defines the functions and procedures required for the reliable transfer of signalling messages over one individual signalling data link. The level 2 functions toget
26、her with the signalling data link form the signalling link. Level 3 (signalling network) defines those transport functions and procedures which are common to - and independent of - the operation of individual signalling links, e.g. addressing and routing, flow control etc. Chapter I 5 Figure 2/r sho
27、ws the function levels of SS No. 7. ISDN-UP Level 4 SCCP TUP Level 4 Level 4 Signalling data link functions Level 1 Examples of user parts Level 4 Message transfer part Levels 1-3 I T T1109730-91 FIGURE 2/I CCITT No. 7 functional levels 3.3.2 Users of the MTP Level 4 consists of the different user p
28、arts, each of which defines the functions and procedures of the signalling system that are - with the exception of the SCCP -particular to a certain type of user of the system. The Signalling Connection Control Part (SCCP) provides further communication functions in addition to the MTP such as conne
29、ctionless and connection-oriented network services including extended addressing capabilities and management of the users of the SCCP (called sub-systems). One of the usages of the SCCP is for end-to-end signalling in the ISDN (see also Chapter VII). The Telephone User Part (TUP) defines the necessa
30、ry signalling functions for telephone call control signalling. Its Recommendations have reached a stable state. The ISDN User Part (ISUP) defines the signalling functions necessary for the ISDN. While ISUP has reached an implementable state it is currently being extended (see also Chapter VII). 3.3.
31、3 Transaction capabilities Transaction Capabilities (TC), currently consisting only of the Transaction Capabilities Application Part (TCAP), provide further communication functions for the exchange of non-circuit related information, e.g. data base enquiries. For further information see Chapter VII,
32、 0 1.3. 6 Chapter I STD-ITU-T HDBK GIS-ENGL 1991 4Bb259L ObBLBbb 78T = 3.4 Operation, Administration and Maintenance (OA - the SCCP see 4.711 to 4.714, Q.716; - the TUP see Q.721 to 4.725; - the ISDN supplementary services see Q.730; - the ISUP see Q.761 to 4.764, Q.766 (see also Chapter VII, 0 1.1)
33、; - the TCAP see 4.771 to 4.775; - testing see Q.780 to 4.783; - monitoring, measurements and OMAP see 4.791 and Q.795. The application of the ISUP for international ISDN connections is being defined in Recommendation Q.767 which is expected to be passed by accelerated procedure in 1991. In addition
34、, Fascicle VI.6 contains Recommendations (the Q.600-Series) regarding the interworking of different signalling systems. These include Recommendations for the interworking of Tup with the other CCITT signalling systems including the interworking between the Digital Subscriber Signalling System No. 1
35、(DSS 1) and SS No. 7. Furthermore, in the E.700-Series of Recommendations various Recommendations regarding grade of service parameters and methods for dimensioning resources for SS No. 7 networks are being developed. Note - Standards produced by other standard setting bodies regarding (aspects of)
36、SS No. 7 may exist currently or in the future. These are not CCIlT Recommendations and are not endorsed by the CCITT. They are not referred to in this Handbook. Chapter I 7 CHAPTER II EVALUATION CRITERIA FOR THE DECISION TO INTRODUCE SIGNALLING SYSTEM No. 7 The purpose of this Chapter is to provide
37、an understanding of the necessary considerations involved in the decision to implement Signalling System No. 7. As with any network implementation, and this is especially true for SS No. 7, careful consideration must be given to: - - - the required performance; and, - the economic factors involved.
38、the nature and amount of traffic that will be supported by the network; the type of services that could and will be offered; This Chapter also provides a brief historical perspective on switching, starting with the step-by-step and progressing to the fully SS No. 7 supported digitai switch. The func
39、tions and characteristics of various transmission methods and propagation techniques are also discussed. 1 Overall network evolution It is important to appreciate that, if modem signalling systems such as SS No. 7 are to be used successfully in networks, then they must be used in conjunction with mo
40、dem switching and transmission systems as well. This section outlines some of the recent developments in the technologies and systems used in telecommunications networks. 1.1 Switching systems As this is a Handbook on when and where to use SS No. 7, it is not appropriate to include here a comprehens
41、ive survey of switching systems used in exchanges. However, certain key points on switching systems must be included as SS No. 7 is not suitable for use with many of the earlier exchange designs. For example, a necessary prerequisite is that the exchanges must use Stored Programme Control (SPC) tech
42、niques before the use of SS No. 7 can even be considered - see 1.2.2. In the past most switching systems were electromechanical. Some were local switching systems which were directly connected to customer lines while others were used for switching long distance and tandem traffic. Increasingly multi
43、-purpose switches are coming into use. 1.1.1 Developments in switching systems The first electromechanical switching systems were step-by-step switches using a system invented by Mr. A.B. Strowger in 1889. Many networks still use step-by-step switches. In some of these switches calls are established
44、 through the switch by means of vertical and horizontai stepping motions caused by the pulses generated from dialling. These switching systems are never suitable for use with SS No. 7. After step-by-step switches, a generation of switching equipment used registered controlled switches, e.g. Crossbar
45、. A Crossbar switch interconnects “hunks” or “lines” through the use of a mamx of vertical and horizontai bars. Some Crossbar switches have been enhanced to include Stored Programme Control (SPC). However, some SPC implementations may not use the SPC for controlling all necessary exchange functions
46、which are required if SS No. 7 is to be implemented on that exchange. For example, the SPC may only be used to enable more flexible translation arrangements to be used for the routing of long distance and tandem calls, and the SPC may not control the switch itself. Previous page is blank. Chapter II
47、 9 Some exchanges have been called “electronic” which are still not SPC exchanges - for example, some of the earlier designs were based on Reed Relay technology and still use register controlled switches. As with the Crossbar switches, some of these designs were enhanced to include SPC. However, som
48、e of these enhanced designs still did not lend themselves readily for modification so as to make the implementation of SS No. 7 straightforward. Before deciding to use SS No. 7 on either crossbar or electronic switches, independent expert opinion should be obtained. Further information on “Economic
49、and technical aspects of the choice of telephone switching systems” can be found in the CCITT GAS 6 Handbook. 1.1.2 . Digital switching systems Most, but not all, digital switching systems are suitable for use with SS No. 7. If in doubt about a particular digital switch, independent expert opinion should be obtained. One characteristic of digital switching is that there is no individual electrical path switched through the exchange, but bit streams are exchanged instead. Digital switching design became widespread amongst major telecommunications manufacturers about the time thinki
