1、i INTERNATIONAL TELECOMMUNICATION UNION ITU-T TELECOMMUNICATION STANDARDIZATION SECTOR OF ITU DIGITAL EXCHANGES Q.543 (03193) DIGITAL EXCHANGE PERFORMANCE DESIGN OBJECTIVES ITU=T Recommendation Q.543 (Previously “CCITT Recommendation“) ITU-T RECNNxQ.543 93 W 486259l 0589055 Tlb m FOREWORD The ITU Te
2、lecommunication Standardization Sector (ITU-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 worldwide basis
3、. 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. ITU-T Recommendation 4.543 was revised by the ITU-T Study Group XI (1988-1993) and
4、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 CCITT ceased to exist as of 28 February 1993. In its place, the ITU Telecommunication Standardization Sector (ITU-T) was created as of 1 Mar
5、ch 1993. Similarly, in this reform process, the CCIR and the IFRB have been replaced by the Radiocommunication Sector.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 “CCITT, CCIR or IFRB” or their associated entitie
6、s 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 for concise
7、ness 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 RECflN*Q.543 73 48b259L 0589056 952 CONTENT
8、S 1 General . 2 Performance design objectives . 2.1 Reference loads . 2.2 Inadequately handled call attempts . 2.3 Delay probability - non-ISDN or mixed (ISDN - non-ISDN) environment 2.4 Delay probability - ISDN environment 2.5 Call processing performance objectives . f 2.6 Transmission performance
9、1 2.7 Slip rate . 3 Exchange performance during overload conditions . 3.1 Explanation of terms used in definition of overload parameters 3.2 3.3 Engineered exchange capacity 3.4 Overload control strategy . 3.5 Detection of overload . 3.6 Overload protection Call processing performance during overloa
10、d I 3.7 Grade of service during overload . I 3.8 Performance monitoring during overload control activation Annex A - An example of methodology for computing the call processing capacity of a Digital Exchange, taking into account ISDN services, including packet data handling . A.l General A.2 Definit
11、ions A.3 Processing capacity computation (for a central processing unit) A.4 Processing capacity computation (for an interface unit) . AS Examples of processing capacity computations . A.7 Capacity computation for exchange architectures other than that assumed in Figure A.1 . A.8 Conclusion Annex B
12、- An example of a methodology for measuring exchange capacity . B.l General B.2 Theory behind the measurement method B.3 Capacity measurement methodology for exchanges . A.6 Packet handling . Page 1 1 1 4 4 14 18 20 20 20 20 21 21 21 22 22 23 23 24 24 26 27 28 28 31 33 33 34 34 34 36 Recommendation
13、Q.543 (03/93) 1 ITU-T RECMN*Q=543 93 4Bb2591 0589057 899 = Recornmendation Q.543 DIGITAL EXCHANGE PERFORMANCE DESIGN OBJECTIVES (Melbourne 1988, modified at Helsinki 1993) 1 General This Recommendation applies to digital local, combined, transit and international exchanges for telephony in Integrate
14、d Digital Networks (IDN) and mixed (analoguddigital) networks, and also to local, 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. As to the application in an
15、 ISDN, transit connections and exchange connection types I, II, III and IV as defined in Recommendation 4.522 are covered (see Notes 1 and 2 in 2.1). Other types of connection and variants of these connections may be feasible in ISDN and will be the subject of further study. These performance design
16、 objectives are applicable to all exchange implementations at all points in the growth cycIe up to the maximum size. These reference loads and performance objectives may be used by manufacturers in designing digital switching systems and by Administrations in evaluating a specific exchange design or
17、 for comparing different exchange designs for potential use in the Administrations intended implementation. These recommended performance design objectives relate to the technical capabilities of exchange design. They are intended to assure that exchanges operating in their intended implementation w
18、ill be capable of supporting the network grades of service recommended in the E.5-Series Recommendations and will offer a level of performance consistent with the overall network performance objectives given in the I-Series Recommendations. The recommended parameters are design objectives which shou
19、ld not be construed to be grade of service or operating requirements. In actual operation, exchanges will be engineered to provide adequate grades of service as economically as possible and the performance requirements (delays, blocking, etc.) of the exchange in operation will differ from the recomm
20、ended values for these performance design objectives. 2 Performance design objectives 2.1 Reference loads The given reference loads are traffic load conditions under which the performance design objectives stated in 2.2 to 2.7 are to be met. In order to have a comprehensive characterization of excha
21、nge reference loads, supplementary services and other types of services must be taken into account. Administrations may specify hypothetical models for use in computing exchange loading. These models should characterize the sets of traffic parameters and services that are considered to be typical in
22、 the intended application of the exchange, and should include the traffic mix (originating- internal, originating-outgoing, incoming-terminating, transit, abandoned, busy non-answer, etc.), the mix of service classes (residential, business, PABX, coin, etc.), the types and volume of supplementary se
23、rvices (call waiting, call forwarding, etc.) and any other pertinent characteristics. Using the above information, it should be possible to “engineer” the exchange to produce the model. It should also be possible to determine the maximum size of the exchange by the computations discussed in 2.1.4. R
24、eference load A is intended to represent the normal upper mean level of activity which Administrations would wish to provide for on customer lines and inter-exchange activities. Reference load B is intended to represent an increased level beyond normal planned activity levels. 1 NOTES i For the time
25、 being, the following definitions and corresponding values are only applicable to 64 kbis circuit switched connections, i.e., including transit connections and connection types I, 11 and III option a). Other rates and transfer modes require further study. 2 The applicability of this Recommendation t
26、o connections originating or terminating on PABXs is for further study. 1 Recommendation Q.543 (0-3) 2.1.1 Reference load on incoming interexchange circuits a) Reference load A - 0.7 erlangs average occupancy on ail incoming circuits Exchange type W X Y Z 0.7 x number of incoming circuits Average ho
27、lding time in hours attempts/h = Average traffic intensity Average BHCA 0.03 E 1.2 0.06 E 2.4 0.10 E 4 0.17 E 6.8 NOTE - Ineffective call attempts must be included in reference call attempts. b) Reference load B - 0.8 erlangs average occupancy on all incoming circuits with 1.2 times the call attempt
28、dh for reference load A. 2.1.2 Characteristics of traffic offered to local exchanges vary widely depending upon factors such as the proportions of residence and business lines that are served. Table 1 provides reference load characteristics for lines typical of four possible local exchange applicati
29、ons. Also provided are representative ISDN cases which are discussed below. Administrations may elect to use other models and/or loads that are more suitable for their intended application. In the following text, ISDN lines will be referred to as digital lines and non-ISDN lines as analogue lines. R
30、eference load on subscriber lines (originating traffic) 2.1.2.1 Reference load A TABLE ldQ.543 Subscriber line traffic model - Non-ISDN subscriber lines with or without supplementary services r I I 1 The following ISDN models and traffic parameters are provisional and may be revised in subsequent st
31、udy periods. TABLE 1 b/Q.543 Subscriber line traffic model - ISDN digital subscriber access 2B + D I Line type Y I l y” I I y” Average traffic intensity per B channel 0.05 E , O.1OE 0.55 E Average BHCA per B channel 2 4 2 Average packets per second per D channel 0.05 (signalling) + Data packets”) o.
32、 1 (signalling) + Data packetsa) 0.05 (signalling) + Data packetsa) BHCA Busy hour call attempts. a) Data packet rates are for further study. These include teleaction and packet services data. 2 Recommendation Q.543 (03/93) ITU-T RECMNmQ.543 93 48b2591 0589059 bbli Even though only limited ISDN traf
33、fic data is available, the specification of the corresponding reference load remains an important factor in exchange evaluation. For the case of digital subscriber lines in Table lb), access is assumed to utilize the Basic Access with 2B + D channels. The B channels are available for circuit-switche
34、d calls, while the D channel is used to carry signalling information or may be used to carry teleaction data and packet switched data. It is assumed that digital lines typically carry traffic comparable with the heavy-traffic analogue lines designated as case Y in Table la). Three cases representing
35、 likely ISDN applications are included in the table. Case Y? traffic per pair of B channels comparable to 1 Case Y line. Case Y? traffic per pair of B channels comparable to 2 Case Y lines. Case Y? traffic per pair of B channels comparable 1 Case Y line plus some very high traffic (e.g. circuit swit
36、ched data traffic at 1 erlang). Each of these digital lines also carries the associated ISDN signalling and data services on the D channel. For the circuit switched calling rates specified in Table lb), ISDN signalling is expected to contribute less than 0.05 packet per second per digital subscriber
37、 line. The packet rates for D channel ISDN data services can be much larger than this; however, these are left for further study. x 2.1.2.2 Reference load B Reference load B is defined as a traffic increase over reference load A of +25% in erlangs, with +35% in BHCA. Reference load B levels for D ch
38、annel activity are for further study. 2.1.3 Impact of supplementary services If the reference model exchange assumes that significant use is made of supplementary services, the performance of the exchange can be strongly affected, especially in exchange designs where processor capacity can become a
39、limiting item. The performance delays recommended in 2.3 and 2.4 can be significantly lengthened at a given call load under such circumstances. The Administration or Operating Agency defining the reference model should estimate the fractions of calls which use various supplementary services so that
40、an average processor impact relative to a basic telephone call can be calculated (e.g. possibly by a methodology similar to that of Annex A). I 2.1.4 Exchange capacity In order to evaluate and compare exchange designs, an Administration will usually want to know the maximum possible size of the exch
41、ange for the intended implementation. While several factors may limit exchange capacity, processing capacity will frequently be the limiting factor. The maximum possible number of lines and circuits served by an exchange, while meeting performance objectives, will depend on the mix, volumes and type
42、s of traffic and the services expected in the particular implementation. Two methods of determining exchange processing capacity are provided in the annexes to this Recommendation: - Annex A provides an example of methodology for computing processing capacity of an exchange using information provide
43、d by the manufacturer and estimates of traffic mix and load provided by the Administration. - Annex B provides an example of methodology for estimating the capacity of an exchange by making projections from measurements made on a functioning exchange in the laboratory or in the field. The test excha
44、nge must be representative of mix and load of traffic and services expected at maximum size. 2.1.5 Reference loads on other accesses and interfaces At this time, other applications, such as n x 64 kbit/s on the Primary Rate Interface, are left for further study Recommendation Q.543 (03/93) 3 ITU-T R
45、ECMNJQ-5q3 93 9 48b259i 05890b0 383 9 Internal Originating Terminating 2.2 inadequately handled call attempts 10-2 4x 1W2 5x 1W3 3 x 1t2 5x 1W3 3 x 1W2 2.2.1 Definition Inadequately handled call attempts are attempts which are blocked (as defined in the E.6WSeries Recommendations) or are excessively
46、 delayed within the exchange. “Excessive delays” are those that are greater than three times the “0.95 probability of not exceeding” values recommended in the tables in 2.3 and 2.4. (See Note.) For originating and transit calls, this inadequately handled call attempt parameter applies only when ther
47、e is at least one appropriate outlet available. NOTE - Provisionally, call request delay is not included in this parameter. Further study is required. 2.2.2 Probability of inadequately handled cai1 attempts occurring The values in Table 2 are recommended. TABLE 214.543 I Type of connection I Referen
48、ce load A 1 Reference load B I I Transit 2.3 Delay probability - non-ISDN or mixed (ISDN - non-ISDN) environment The non-ISDN environment is composed of analogue subscriber lines and/or circuits that use either channel associated or common channel signalling. The ISDN environment is composed of digi
49、tal (ISDN) subscriber lines andor circuits that use common channel signalling. This subclause defines delay parameters related to non-ISDN environment and mixed (ISDN - non-ISDN) environment. When a delay parameter in this subclause is also applicable to the pure ISDN environment, a reference to the appropriate part of 2.4 (delay probability - ISDN environment) is provided. In the following delay parameters, it is understood that delay timing begins when the signal is “recognizable”, that is, after the completion of signal verification, where applicable. It does not inc
