1、INTERNATIONAL TELECOMMUNICATION UNION)45G134 % TELECOMMUNICATIONSTANDARDIZATION SECTOROF ITU4%,%0(/.%G0G0.%47/2+G0G0!.$G0G0)3$.15!,)49G0G0/&G0G03%26)#% G0G0.%47/2+G0G0-!.!%-%.4!.$G0G042!&)#G0G0%.).%2).2!$%3G0G0/&G0G03%26)#%G0G0).G0G0$)4!,).4%2.!4)/.!,G0G04%,%0(/.%G0G0%8#(!.%3)45G134G0G0Recommendatio
2、nG0G0% (Extract from the “LUEG0“OOK)NOTES1 ITU-T Recommendation E.543 was published in Fascicle II.3 of the Blue Book. This file is an extract from theBlue Book. While the presentation and layout of the text might be slightly different from the Blue Book version, thecontents of the file are identica
3、l to the Blue Book version and copyright conditions remain unchanged (see below).2 In this Recommendation, the expression “Administration” is used for conciseness to indicate both atelecommunication administration and a recognized operating agency. ITU 1988, 1993All rights reserved. No part of this
4、publication may be reproduced or utilized in any form or by any means, electronic ormechanical, including photocopying and microfilm, without permission in writing from the ITU.Fascicle II.3 - Rec. E.543 1Recommendation E.543Fascicle II.3 - Rec. E.543GRADES OF SERVICE IN DIGITALINTERNATIONAL TELEPHO
5、NE EXCHANGES1 Introduction1.1 The grade of service (GOS) parameters and values to be used as dimensioning standards and as performanceobjectives for international telephone exchanges are indicated below. Procedures to monitor the actual GOSperformance of the exchanges are also recommended.1.2 The GO
6、S standards for international telephone exchanges defined in this Recommendation assume “fullyoperative“ conditions for the exchange and they are based on the load levels specified in Recommendation E.500.2 Scope of the Recommendation2.1 The GOS standards are specified for an exchange as a whole, i.
7、e. neither the delay nor the loss parameters areassociated solely with the control area or with the connecting network, so that no particular system concept is favoured.2.2 Although the GOS parameters defined in this Recommendation apply to the digital as well as to the analogueexchanges, the numeri
8、cal values recommended for these parameters are primarily intended for digital exchanges. TheGOS may be too stringent for analogue exchanges and Administrations are advised to make suitable allowances whenapplying to the analogue exchanges.Administrations may also consider these GOS values for dimen
9、sioning the national transit exchanges so that theend-to-end GOS performance for international connections is maintained at a high level.3 Grade of service parametersThe loss and delay GOS standards are defined as follows:3.1 Loss grade of serviceinternal loss probability: for any call attempt, it i
10、s the probability that an overall connection cannot be set upbetween a given incoming circuit and any suitable free outgoing circuit within the switching network.The loss grade of service is to be met by every pair of incoming and outgoing trunk groups averaged over allinlets of the incoming group.T
11、his approach takes explicit account of the fact that the Administrations will take actions such as the favourableloading of switch blocks in order to balance access to all trunk groups. These actions will minimize the impact of theworst case upon the traffic flow capacity of the switch, by confining
12、 the necessary adjustments to localized regions ofthe switching network.These actions should ensure that the switching system operates as efficiently as possible within the constraintsimposed by this loss standard.3.2 Delay grade of service in case of channel-associated signallingincoming response d
13、elay: The interval from the instant when an incoming seizure signal has arrived at theincoming side of the exchange to the instant when a proceed-to-send signal is returned to the preceding exchange bythe receiving exchange.The incoming response delay may affect the holding time of the preceding tru
14、nks and of the common controlequipment in the preceding exchange(s). It may also be perceived by the subscriber as dial-tone delay, in case ofspecial dial tone for international calls in outgoing international exchanges, or may contribute to the post-dialling delayexperienced by the subscriber in al
15、l other cases. The contribution to post-dialling delay does not necessarily comprisethe whole of the incoming response delay.Note The above definition of incoming response delay does not explicitly mention that it includes receiverattachment delay. However, for the purpose of this Recommendation, it
16、 is assumed that receiver attachment delay is apart of the incoming response delay.2 Fascicle II.3 - Rec. E.5433.3 Delay grade of service in case of any combination of channel-associated and common channel signallingexchange call set-up delay: The interval from the instant when the address informati
17、on required for setting upa call is received at the incoming side of the exchange to the instant when the seizing signal or the correspondingaddress information is sent to the subsequent exchange.through-connection delay (end-to-end channel associated or common channel signalling): the intervalfrom
18、the instant when the information required for setting up a through-connection in an exchange is available forprocessing in the exchange to the instant when the switching network through-connection is established between theincoming and outgoing circuits.through-connection delay (link-by-link channel
19、 associated signalling): the interval from the completion ofoutpulsing to the establishment of a communication path through the exchange between the incoming and the outgoingcircuits.4 Grade of service standardsThe values shown in Table 1/E.543 are recommended for GOS standards of international digi
20、tal telephoneexchanges. The normal and high load levels are the ones defined in Recommendation E.500.TABLE 1/E.543Normal load High loadIncoming response delay a) b)Exchange call set-up delayb)Through-connection delayb)P ( 0.5 sec.) 5 %P ( 0.5 sec.) 5 %P ( 0.5 sec.) 5 %P ( 1 sec.) 5 %P ( 1 sec.) 5 %P
21、 ( 1 sec.) 5 %Internal loss probabilityc)0.002 0.01a)See Note in 3.2.b)The determination of the number of bids for the different devices or exchange modules at normal and high load levelsshould be made according to Rec. E.500. Circuit group or exchange load levels will be used according to the devic
22、es or exchangemodules affected.c)The values of traffic offered to the circuit group and to the switching network of the exchange, to be used for lossprobability evaluation, should correspond to the traffic flow levels defined for circuit groups and exchanges, respectively, inRec. E.500.In case of di
23、fferences between exchange and circuit group busy hours it is recommended to use models whichcan take account of the different traffic values in the different parts of the exchange. For example, models used fordimensioning the auxiliary equipment could take advantage of the differences of busy hour
24、of the different circuitgroups using the same auxiliary equipment.5 Measurements to monitor exchange GOS performanceIn the context of traffic Administration, monitoring the GOS performance in an exchange is a means ofdetecting potential problems which can affect the GOS performance of that exchange.
25、 By analysing deviations frompreviously established GOS performance thresholds, problem areas can be detected. After having identified theproblems, actions such as load balancing, fault removal, extensions, etc., can be derived from GOS performancemonitoring. These actions are not taken on a real-ti
26、me basis, and consequently the data collection and analysis do nothave real-time constraints. The traffic measurements recommended below do not separate the causes of call attemptfailure or excessive delay.When the values of the GOS performance are consistently worse than the GOS standards specified
27、 in 4, itwill be necessary to identify the causes of such a situation through the analysis of ad-hoc measurement procedures.Considering the above framework, errors in GOS estimation are only important to the extent that they can generateover- or under-reactions to exchange situations.Fascicle II.3 -
28、 Rec. E.543 3For each of the GOS parameters a statistical estimator has been defined. The measurements must be made on aper circuit group and per exchange basis. Eventually, savings could be derived from delay measurements made on thebasis of signalling types when several circuit groups share the sa
29、me auxiliary devices. All measurements describedbelow refer to a specific measurement period.5.1 Delay measurements5.1.1 Incoming response delayThe exchange GOS performance with respect to this parameter can be estimated by means of the ratio:pBA= ,whereA is the number of call attempts accepted for
30、processing from a given incoming circuit groupB is the number of call attempts out of the set A, for which the incoming response delay exceeded thepredetermined value XNote In SPC exchanges a certain time may elapse from the moment that the incoming seizure signal appearsat the incoming circuit unti
31、l the moment that the processor accepts the call attempt for processing. Measuring this delaywould require external equipment to the call handling processors. The above measurement only provides an indicationof the incoming response delay after the call has been accepted for call processing. In the
32、case where this delay issignificant, it should be taken into account in dimensioning and should be subtracted from the total time allowed for theincoming response delay.5.1.2 Exchange call set-up delayThe exchange performance with respect to this parameter can be measured by means of the following r
33、atio:qDC= ,whereC is the number of call attempts for which sufficient address information has been received at the incomingside of the exchange, which are addressed to a certain outgoing circuit group and for which the seizingsignal or the corresponding address information is sent to the subsequent
34、exchange.D is the number of call attempts already counted in C for which the call set-up delay exceeds thepredetermined value, T.5.1.3 Through-connection delayThe exchange performance with respect to this parameter can be measured by means of the following ratio:rFE= ,whereE (for end-to-end channel
35、associated and common channel signalling) is the number of call attempts forwhich the required information for setting up a through-connection is available for processing in theexchange for a certain circuit group.E (for link-by-link channel associated signalling) is the number of call attempts whic
36、h have completedoutpulsing in a certain circuit group.4 Fascicle II.3 - Rec. E.543F is the number of call attempts already counted in E for which the through-connection delay has exceededthe predetermined value V.Note 1 The loss of call attempts caused by the exchange itself, premature subscriber re
37、lease or time-outexpiration in an upstream exchange may modify the outcome of the above delay measurements. However, the effectwill only be significant under abnormal conditions which should be investigated separately.Note 2 It is recommended that values for X, T, and V be either 0.5 s (normal load)
38、 or 1 s (high load).Note 3 Measuring delays on a per call basis could produce severe cost penalties to the exchange. Since theaccuracy requirements from the statistical viewpoint are not very high, call sampling procedures or test calls can besufficient for GOS monitoring purposes.5.2 Loss measureme
39、ntsOne estimator of this parameter per circuit group is:sHG= ,where:G is the number of call attempts which require a connection from an inlet to the desired outgoing circuitgroup having at least one free circuit and for which sufficient call handling information was made availableto the exchange.H is the number of those call attempts described by G which failed to build up the required connection.Note The loss of call attempts caused by premature subscriber release or time-out expiration in an upstreamexchange, may modify the outcome of the above measurement.
