1、ITU-T RECflN+Q.52L 93 W 4862573 0584588 430 INTERNATIONAL TELECOMMUN KATION UNION ITU-T TELECOMMUNICATION STANDARDIZATION SECTOR OF ITU DIGITAL EXCHANGES Q.521 (03/93) DIGITAL EXCHANGE FUNCTIONS ITU-T Recommendation Q.694 (Previously “CCIlT Recommendation”) ITU-T RECMN*d.521 93 W 4862591 0584620 636
2、 FOREWORD The Telecommunication Standardization Sector (IT-T) is a permanent organ of the International Telecom- munication Union. 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
3、worldwide basis. The World Telecommunication Standardization Conference (WTSC), which meets every four years, established the topics for study by the ITU-T Study Groups which, in their turn, produce Recommendations on these topics. IT-T Recommendation Q.521 was revised by the IT-T Study Group XI (19
4、88-1993) and was approved by the WTSC (Helsinki, March 1-12, 1993). NOTES 1 As a consequence of a reform process within the International Telecommunication Union (ITU), the CCIT ceased to exist as of 28 February 1993. In its place, the ITU Telecommunication Standardization Sector (ITU-T) was created
5、 as of 1 March 1993. Similarly, in this reform process. the CCIR and the IFFU3 have been replaced by the Radiocommunication Sector. 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 associ
6、ated entities such as Plenary Assembly, Secretariat, etc. Future editions of this Recommendation will contain the proper terminology related to the new ITU structure. 2 telecommunication administration and a recognized operating agency. In this Recommendation, the expression “Administration” is used
7、 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 any means, electronic or mechanical, including photocopying and microfilm, without permission in writing from the ITU. ITU-T RECflNMQ.521 93 4862593 0584623
8、 572 CONTENTS 1 General . 2 Exchange functions -Introduction and framework . 2.1 General 2.2 Exchange model 2.3 Utilization of exchange functions for services General functions required in an exchange for operation in the IDN, ISDN or mixed analogue/digital environment 3.1 Timing and synchronization
9、 . 3.2 Signalling 3.3 Data Packet Handling . 3.4 Information retrieval and analysis 3 3.5 Resource management 3.6 Ongoing operations . 4.1 Process Service Request . 4 Functions used in processing bearer service call attempts . 4.2 Connect (through connect)/Disconnect 4.3 Perform originating screenin
10、g (in originating exchange) . 4.4 Perform terminating screening (in terminating exchange) . 4.5 Process Attempt Additional functions required to provide ISDN Supplementary Services . 5 Page 1 1 1 1 1 2 2 3 3 3 4 4 5 5 5 5 6 6 7 Recommendation Q.521 (03/93) i ITU-T RECMN*Q.52L 93 48b2591 0584622 409
11、Recommendation Q.521 DIGITAL EXCHANGE FUNCTIONS (Melbourne 1988, modified at Helsinki, 1993) 1 General This Recommendation applies to digital local, combined, transit and international exchanges for telephony in Integrated Digital Networks (IDN) and mixed (analogue/digital) networks and also to loca
12、l, combined, transit and international exchanges in an Integrated Services Digital Network (ISDN). The field of application of this Recommendation is more fully defined in Recommendation 4.500. Some text may only apply to a certain type (types) of exchange, e.g. digital transit, local or combined. W
13、here this occurs, the application is defined in the text. Not all the recommended functions will necessarily be provided in every exchange. 2 Exchange functions - Introduction and framework 2.1 General The purpose of this Recommendation is to specifically address those functions required to support
14、basic and supplementary services in performing this test, this Recommendation takes account of the principles set down in Recommendation 1.310 and draws a clear distinction between services and the exchange capabilities required to support them. It should be noted that the list of functions identifi
15、ed in this Recommendation is not necessarily extensive. 2.2 Exchange model The functions described in this and associated Recommendations can be considered within the framework of an exchange functional model. Such a model is shown in Figure 1. This divides the exchange into three functional areas a
16、s follows: a) control functions - Those functions required to control services and connections, e.g. signalling, routing and connectionhesources handling functions; connection functions - Those functions directly related to the connection path through an exchange, i.e. switching and transmission mec
17、hanism (including ET); operation and maintenance functions - Those functions of an operational, management and maintenance nature which are not employed for call establishment and supervisory purposes, e.g. test functions. b) c) The exchange functional model shown in Figure 1 is appropriate to excha
18、nges operating in an IDN and also those operating in an IDN which is evolving towards an ISDN. In terms of this Recommendation, most of the functions fall within the control functions area. Connection functions are primarily covered in Recommendation 4.522, These address the basic switch characteris
19、tics of different connection types. OA b) c) the appropriate type of connection is established by use of the ConnectiodResources Handling Functions; Supplementary Services which involve additional functions and information flows beyond those required for bearer services, are provided under the contr
20、ol of logic residing in the Service Processing Function. This logic is designed to provide specific services. Corresponding service/feature capabilities must also reside in the Signalling and ConnectiodResources Handling Functions. In addition to services provided by use of logiddata residing in the
21、 exchange, some services may be provided under the control of logic located at separate specialized nodes (Service Control Points). Also, data required or process certain service requests may be kept in a remote data base accessed by use of the Signalling Function. 3 General functions required in an
22、 exchange for operation in the IDN, ISDN or mixed analoguddigital environment 3.1 Timing and synchronization 3.1.1 Exchange timing Distribute timing within the exchange so that it will maintain synchronism on 64 kbith channel timeslots in a connection through the exchange. 3.1.2 Synchronization Oper
23、ate in the IDN or ISDN in synchronism with other digital entities and provide timing signals to other network entities as required. 3.1.3 Interval timing Measure time between events as required for call processing and/or signalling. 2 Recommendation Q.521 (03/93) ITU-T RECMN*Q*521 93 m 4862591 05846
24、24 28% m 3.1.4 Time of day clock Determine and indicate as required, time of day. NOTE - The level of accuracy of the time of day clock is for further study. 3.2 Signalling 3.2.1 User access signalling functions 3.2.1.1 In-band signalling Receivehansmit and interpret decadic or Dual Tone Multi-Frequ
25、ency (DTMF) signalling frondto users. 3.2.1.2 Digital subscriber signalling Support user access signalling layers 1 and 2 in accordance with Recommendations 1.430, 1.431 and 4.921. Communicate with user terminals using layer 3 signalling in accordance with Recommendation 4.93 1. - - 3.2.2 Network si
26、gnalling functions 3.2.2.1 CCITT Signalling systems - Support and use CCITT signalling systems included in Recommendation 4.7 as required, particularly CCIT Signalling System No. 7. Communicate with other network entities using the CCITT Signalling System No. 7, Q.700-Series of Recommendations User
27、Parts. - 3.3 Data Packet Handling 3.3.1 Handle Packets Transmit and receive data messages to/from users and data networks in accordance with Recommendation X.31. 3.3.2 Interwork with data network(s) Interface and interact with data networks in accordance with Recommendations X.31. 3.4 Information re
28、trieval and analysis 3.4.1 Access data bases Gain access to data bases internal or external to the exchange. 3.4.2 Retrieve information from: 3.4.2.1 Userhine data bases Retrieve information about access lines and/or users such as ?class of service?, priority level, parameters of basic bearer and te
29、leservices subscribed to, etc. 3.4.2.2 Interexchange circuit data bases Retrieve information about interexchange circuit groups, such as the identity of the entity to which it connects, the size of the circuit group and the location of its terminations, the type of circuits (incoming, outgoing or bo
30、th ways), type of transmission system (analogue, digital), signalling required, etc. 3.4.2.3 Retrieve information about other terminations on the exchange (tone circuits, announcements, bridge terminations, etc.). Data base relating to ?other terminations? Recommendation Q.521 (03/93) 3 ITU-T RECMN*
31、Q*521 93 H 4862591 0584625 118 H 3.4.24 Data base related to routing information Retrieve information needed to determine how to route a call attempt based on the called number, call history andor other pertinent information (e.g. network management information). 3.4.2.5 Data base of charging inform
32、ation Retrieve information needed to determine the charging functions and rates needed for a particular call attempt or service usage. 3.4.3 Analyze information Relate information pertaining to a call attempt or service request to information obtained from data base) to determine the appropriate cou
33、rse of action. 3.5 Resource management 3.5.1 Monitor the status of resources Detect changes in status (busy, idle, out of service, etc.) of resources (lines, interexchange circuits, other terminations, exchange components, etc.). 3.5.2 Maintain status information Determine in red time the availabili
34、ty of all resources for use in call attempt or service request processing and for other functions (e.g. network management). 3.5.3 Establish and maintain information relating to cai1 attempts Establish and maintain in registers for as long as necessary, information (service used, calling and called
35、numbers, resources used, etc.) and events (connect time, disconnect time, etc.) related to individual calls, attempts or services used. 3.5.4 Check continuity Verify that proper transmission capability is available on a connection or resource when such a check is required and take appropriate action
36、 when the check fails. 3.5.5 Check proper operation of resources Verify the proper operation of user access and exchange or transit resources, as required, and to take appropriate action when verification fails. 3.5.6 Handle queues Establish and manage queues, as required, when the number of bids ex
37、ceeds the available resources required to handle them. 3.6 Ongoing operations 3.6.1 Make measurements Make and record counts of attempts and events, measurements of usage and occupancy of resources, as required. 3.6.2 Calculate percentages Calculate in real time the ratio or percent of total volumes
38、 attempts, events, etc., as required. 3.6.3 Detect and react to congestion Detect when specified congestion thresholds are reached and to take appropriate action. 4 Recommendation Q.521 (03/93) ITU-T RECMNUQ.521 93 4862591 0584626 O54 3.6.4 Generate and respond as required to network management cont
39、rols, signals and/or messages. Generatelrespond to network management controls 3.6.5 Interact with TMN operations systemdcentres Communicate and interact with Operations Systems (Network Management, Accounting, Maintenance, etc.) via the Telecommunications Management Network (TMN). 3.6.6 Report faul
40、ts/failure events Detect and report faults and their cause, if known, to the appropriate system(s) or centre(s). 3.6.7 Perform charging functions: 3.6.7.1 Accumulate and store call or service information required for proper billing. 3.6.7.2 Format charging data Assemble call or service charging deta
41、ils into the proper format for transfer as required for billing computation. Accumulate and store charging data 3.6.7.3 Transfer charging data Send charging details as required (batch or per call), to accounting centre or billing system or function. 3.6.7.4 Send charging information to user Indicate
42、 to the user, as required, the amount of charging involved in the use of the service. NOTE- This function may be a service feature provided on a national basis. 4 Functions used in processing bearer service call attempts 4.1 Process Service Request Recognize and respond to service request. Recognize
43、 and interpret signals or messages from users that indicate the initiation of a call (or a request for service), acknowledge the receipt of the signal or message as required and take action to process the call or initiate the service. 4.2 Connect (through connect)/Disconnect Establish, as required,
44、a path or virtual path through exchange (one-way or two-way)/ take down connection through exchange and make resources available for other call attempts. 4.3 4.3.1 Identify the calling user Determine the ISDN number of the user based on line or channel class and information sent by the user. 4.3.2 D
45、etermine the characteristics of the user terminal based on its ISDN number. Perform originating screening (in originating exchange) Determine the user terminal characteristics 4.3.3 Examine service request Determine the required service charcteristics by examining information sent by the calling ter
46、minal. Recommendation Q.521 (03/93) 5 ITU-T RECMN*Q.521 93 = 4862591 0584b27 T90 H 4.3.4 Examine users service authorization Determine whether or not the user is authorized to use the requested service. 43.5 Determine priority Determine the priority level assigned to a user line or terminal andfor p
47、riority level of a particular calllmessage based on priority information associated with the calllmessage. 4.3.6 Establish call reference Assign and retain for the duration of a call (or service usage), internal reference(s) for associating the resources used with the call (or service usage) and for
48、 keeping status information. 4.4 Perform terminating screening (in terminating exchange) 4.4.1 Identify called user (in exchange serving the called user) Identify the called user line(s)/channel(s) and their characteristics based on the called subscriber number. 4.4.2 Determine the user terminal cha
49、racteristics based on its ISDN number. 4.4.3 Verify that the called user is authorized and/or capable of receiving the call/service request. 4.4.4 Establish cai1 reference Assign and retain for the duration of the call (or service usage), internal reference(s) for associating the resources used with the call (or service usage) and for keeping status information. 4.5 Process Attempt 4.5.1 Analyze called number Examine the called number and determine routing and other required treatment (e.g. special handling and/or treatment). 4.5.2 Analyze routing information Analyze routing inform
