1、)45G134 8 TELECOMMUNICATIONSTANDARDIZATION SECTOROF ITU05“,)#G0G0$!4!G0G0.%47/2+3.%47/2+G0G0!30%#43#!,G0G0“,/#+).G0G0).G0G005“,)#G0G0$!4!.%47/2+3G0G07(%.G0G002/6)$).).4%2.!4)/.!,G0G039.#(2/./53#)2#5)4G1337)4#(%$G0G0$!4!G0G03%26)#%3)45G134G0G0RecommendationG0G08 (Extract from the “LUEG0“OOK)INTERNATI
2、ONAL TELECOMMUNICATION UNIONNOTES1 ITU-T Recommendation X.131 was published in Fascicle VIII.3 of the Blue Book. This file is an extract fromthe Blue Book. While the presentation and layout of the text might be slightly different from the Blue Book version, thecontents of the file are identical to t
3、he 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 public
4、ation 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 VIII.3 - Rec. X.131 1Recommendation X.131Fascicle VIII.3 - Rec. X.131CALL BLOCKING IN PUBLIC DATA NETWORKS WHEN PROVIDIN
5、GINTERNATIONAL SYNCHRONOUS CIRCUIT-SWITCHED DATA SERVICES(Former X.132, Geneva, 1980; amended at Malaga-Torremolinos, 1984)The CCITT,considering(a) that Recommendation X.1 specifies the user classes of service applicable to networks offering public dataservices;(b) that Recommendation X.2 specifies
6、the international user services and facilities to be offered by publicdata networks;(c) that Recommendations X.21 and X.21 bis define the DTE/DCE interface for circuit switched services;(d) that Recommendation X.60 specifies the common channel signalling for synchronous data networks;(e) that Recomm
7、endation X.71 specifies the channel associated signalling for synchronous data networks;(f) that Recommendation X.92 specifies the hypothetical reference connections for public data networks;(g) that Recommendation X.110 specifies the routing plan to be applied in the international portions of publi
8、cdata networks;(h) that Recommendation X.213 specifies the OSI Network Layer service;(i) that Recommendation X.140 specifies the user-oriented quality of service parameters applicable to dataservices,unanimously declaresthat when public data networks provide international synchronous circuit-switche
9、d data services, according toRecommendations X.21 and X.21 bis, the values of call blocking probability specified in this Recommendation shall betaken as provisional, worst-case values that should not be exceeded under the conditions specified therein.Introductory note - Design objectives that take
10、into account both user needs and network costs are for furtherstudy.1 Introduction1.1 Quality of service in circuit-switched public data networks has been considered in five basic areas as follows:i) call processing delays (Recommendation X.130);ii) failures due to congestion (blocking) (Recommendat
11、ion X.131);iii) failures due to malfunction;iv) loss of service; andv) transmission performance (including throughput).2 Fascicle VIII.3 - Rec. X.131This Recommendation specifies the objectives for ii) above. Each of the other areas of circuit-switchingquality of service identified above will be the
12、 subject of a separate Recommendation in the X-series.1.2 In telecommunication networks it is necessary, for economic reasons, to limit the resources provided forcarrying the offered traffic. This limitation may affect the quality of service to the user of circuit-switched services intwo different w
13、ays: by call processing delays and by blocking. Both of these aspects, that are consequences of the finitetraffic handling capacity of the network, constitute the grade of service. Grade of service together with malfunction, lossof service and transmission performance constitute the quality of servi
14、ce.1.3 In this Recommendation the values for the network blocking are quoted for two types of connection accordingto Recommendation X.92 as follows:Type 1: Typical terrestrial interconnection of moderate length with no satellite circuits either in the national orinternational portions. (Internationa
15、l portion: 1000 km.)Type 2: Long distance international connection with a satellite circuit in one national portion and two satellitecircuits in the international portion. (International portion: 160 000 km.)Where appropriate, values are also specified separately for the following network portions:-
16、 originating national network,- international portion,- destination national network.The boundaries for these portions are shown in Figure 1 /X.131.FIGURE 1/X.131National/international boundaries for call set-upand clear-down functionsFor the present, the values apply also to other normal routing op
17、tions within the international portion.Following the allocation of a blocking allowance to the international portion of an international transitconnection, it will be necessary to further apportion the allowance to individual transit networks and/or their componentparts within the international port
18、ion. The means by which useful and realistic constraints can be applied, consistent withmaintaining the maximum possible freedom for each involved Administration in the design and implementation of itsown network, is for further study.1.4 The values for blocking probability established in this Recom
19、mendation are to be considered as designobjectives in network planning together with the forecast traffic for the planned period. The actual blocking performancethat will be obtained will depend on the accuracy of the traffic estimations. Normally the actual blocking performancewill not coincide wit
20、h the one used as a basis for planning. Furthermore, if the network is planned for the traffic forecastFascicle VIII.3 - Rec. X.131 3at the end of the period considered, the actual blocking performance of the network may be better than the design value,worsening gradually to the end of the planning
21、period as traffic increases.The non-coincidence of busy hours in originating and destination national networks as well as in theinternational network will improve the overall blocking performance with respect to the sum of the nominal blockingprobabilities of the constituent parts of the connection.
22、1.5 The blocking probabilities are specified under conditions of normal busy hour load. Blocking probabilities forhigher loadings are for further study.1.6 Blocking probabilities are defined for a basic call which does not include any optional user facilities, e.g. thosedefined in Recommendation X.2
23、1.1.7 Recommendation X.21 permits the following blocking situations:i) non-reception of proceed to select;ii) non-connection of call.Item i) is considered to be a national matter and consequently the specification of its value is not appropriate tothis Recommendation. Objectives for item ii) are con
24、tained in 2 of this Recommendation.1.8 The quality of service implications of regional or national satellite systems using demand assignment forresource allocation require further study.2 Probability of non-connection due to congestion (blocking probability)Probability of non-connection due to conge
25、stion is the probability that a calling DTE does not receive theready for data signal but does receive a network congestion signal within 20 seconds after transmission of the end ofselection signal (or within 60 seconds when manual answering is permitted at the called DTE).2.1 Overall probability of
26、 non-connection due to congestionThe overall probability of non-connection due to congestion for an end-to-end connection seen from thecustomer point of view should not exceed the following values:Connection type 1: 13%Connection type 2: 15%See Introductory note to this Recommendation.2.2 Network po
27、rtion probability of non-connection due to congestionThe contribution of each network portion to overall probability of non-connection due to congestion shouldnot exceed the values shown in Table 1/X.131.TABLE 1/X.131Contributions to network probability of non-connectiondue to congestionNote - See introductory note to this Recommendation.International portionOriginal nationalportionDestinationnational portionConnection type125% 5% 3% 5%
