1、INTERNATIONAL TELECOMMUNICATION UNION ITU-T TELECOMMUNICATION STANDARDIZATION SECTOR OF ITU E.526 (03193) TELEPHONE NETWORK AND ISDN QUALITY OF SERVICE, NETWORK MANAGEMENT AND TRAFFIC ENGINEERING DIMENSIONING A CIRCUIT GROUP AND NO OVERFLOW INPUTS WITH MULTI-SLOT BEARER SERVICES ITU-T Recommendation
2、 ES26 (Previously “CCIlT Recommendation“) STD-ITU-T RECMN E-52b-ENGL 1773 LiBb2571 Ob17731 272 M FOREWORD The IT Telecommunication Standardization Sector (IW-T) is a permanent organ of the Intemational Telecom- munication Union. The ITU-T is responsible for studying technical, operating and tariff q
3、uestions and issuing Recommendations on them with a view to standardizing telecommunications on a 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 Rec
4、ommendations on these topics. ITU-T Recommendation ES26 was prepared by the IT-T Study Group II (1988-1993) 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 (), the KITT ceased to exist as of 28 F
5、ebruary 1993. In its place, the IT Telecommunication Standardization Sector (IT-T) was created as of 1 March 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 Similarly, in this reform process, the CCIR and the IFRB have been replaced by the Radiocommunication Sector.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 bee
6、n made in the text to references containing the acronyms “CCITT, CCIR or IFRB” or their associated entities such as Plenary Assembly, Secretariat, etc. Future editions of this Recommendation will contain the proper terminology related to the new IT stmcture. 2 telecommunication administration and a
7、recognized operating agency. In this Recommendation, the expression “Administration” is used 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
8、microfilm, without permission in writing from the ITU, CONTENTS Page 1 Introduction 1 2 Grade of Service objectives . 1 3 Dimensioning methods 1 3.1 Full availability group . 1 3.2 Trunk modularity 2 3.3 Service protection . 2 . Annex A - Blocking probabilities of a full availability group Annex B -
9、 Sample of the capacity table (full availability group) . 2 4 . 5 References Recommendation ES26 (03/93) I Recommendation ES26 DIMENSIONING A CIRCUIT GROUP WITH MULTI-SLOT BEARER SERVICES AND NO OVERFLOW INPUTS (Helsinki, 1993) 1 Introduction This Recommendation describes methods for calculating the
10、 number of circuits in a fia circuit group, which has no overflow inputs, carrying on demand circuit switched ISDN bearer services with differeia bit rates. Examples of channel classes and information transfer rates for the bearer services up to the primary rate interface are as follows (see Recomme
11、ndation 1.21 1). - B-channel: 64 kbit/s; - HO-channel: 384 kbit/s; - Hi I-channel: 1536 kbit/s; - H12-channel: i920 kbiVs. Different implementation providing these services is possik.3, such as dedicated circuit groups for each channel class or common circuit groups for two or more channel classes.
12、Choice of implementation depends on available switching architecture, network structure, operational simplicity and flexibility, required Grade of Service, traffic demand, accuracy of the demand forecasting and others. Recommendation ES20 provides a dimensioning method for a dedicated circuit group.
13、 This Recommendation deals with the dimensioning methods for a common circuit group that is shared by the bearer services at different bit rates. Definition A unit circuit is defined as a circuit with the lowest information transfer rate among the bearer service classes sharing a circuit group. A un
14、it circuit is the elementary unit for dimensioning a circuit group and, hereafter, it will simply be called “circuit”. A single call for a class i bearer service requires di circuits; di is called the bandwidth factor of this class i service. Example: If B, HO and HlZchannel rate bearer services sha
15、re a circuit group, the bandwidth factors are i, 6 and 30. If HO and Hi i -channel rate bearer services share a circuit group, the bandwidth factors are 1 and 4. 2 Grade of Service objectives The Grade of Service (GOS) objectives used in a first approach is that the individual blocking probability f
16、or each service class will not exceed 1% for a normal load and 7% for a high load. The normal and high load levels are defined in Recommendation ESO. It will be desirable to consider the differences of the busy-hour and day-to-day traffic variations for the service classes. A more complicated situat
17、ion with different GOS standards for each service class X,% and Yi%, respectively is for further study. 3 Dimensioning methods 3.1 Full availability group A full availability group is described as follows. If a class i call arrives when there are fewer than di circuits idle in the group, it is lost,
18、 otherwise it seizes di circuits, even if they are not adjacent. Recommendation ES26 (03/93) 1 STD-ITU-T RECMN E-52b-ENGL 1993 LiAb2591 Ob1993Li TA1 The number of circuits needed for the group may be calculated based on a product form solution (see Annex A). Annex B shows samples of the capacity tab
19、le. It is desirable to use a computer or a programmable calculator. Calculation algorithms for the blocking probabilities of a full availability group are presented in I, 2, 5 and 181. No comparative evaluation of different methods is currently available. , 3.2 Trunk modularity According to Recommen
20、dation 1.2 I 1, multi-slot bearer services with “unrestricted”, “8 kHz structured” attributes require Time Slot Sequence Integrity (TSSI). One technique for ensuring TSSI is to route all the time slots of a call over the same transmission systems. This introduces the restriction that all di circuits
21、 for class i call have to be allocated to the same trunk module (e.g. primary PCM multiplex). In the case of such a restriction, blocking performance is dependent on circuit hunting strategies. Examples of hunting strategies: - - random hunting strategy -Calls are placed on any available trunk modul
22、e in random order; sequential hunting strategy - Idle circuits are searched in the same fixed order and calls are placed on the first available trunk module found; - call packing strategy - Calls are placed on the most heavily loaded available trunk module. The random hunting strategy should not be
23、used because it has the worst traffic performance, especially for wideband calls. The cai1 packing strategy is theoretically superior, but does not show practically significant differences from the simple sequential hunting strategy 11. Approximation methods for blocking probabilities that use the s
24、equential hunting strategy are proposed for one-way I and both-way circuits 3. 3.3 Service protection In the full availability system, the individual blocking probabilities of each class increase with the bandwidth factor 4. To improve the performance of wideband calls, the service protection method
25、s in Recommendation E.525 are available. If all classes must meet the same blocking standards, the easiest method is to use trunk reservation with the same limit (maximum bandwidth factor -1) applied to all classes. This means that calls are lost if the number of idle circuits at the arrival epoch i
26、s fewer than the largest bandwidth factor of all the classes. The approximation methods for blocking probabilities that use trunk reservation are proposed in 51, 61, 71 and BI. Annex A presents some considerations about the calculation of individual blocking probabilities in case of trunk reservatio
27、n. Annex A Blocking probabilities of a full availability group (This annex forms an integral part of this Recommendation) List of symbols . N M ai is the number of circuits in a group; is the number of service classes; is the traffic offered of class i service measured by each bandwidth; 2 Recommend
28、ation ES26 (03B3) di is the bandwidth factor for a class i service; P(n1, ., nM) Bi is the probability distribution of the number of calls for each class in a circuit group; is the blocking probabilities for class i calls. A product form solution: M aini P(n1, ., nM) = - P(0, ., O) n ni! i= I f P(0,
29、 ., O) = I)$ An approximate algorithm for practical calculations: We consider now the case where the N slots of a trunk group share the various multi-slot traffic flows to be handled, the accessibilify being rota1 (without restriction) for each traffic flow. These traffic flows are poissonian and id
30、entified by an index i = 1, 2, ., x. Notations Traffic flow No. i Overall parameters ! Traffic intensity per each time slot: bi ! Number of simultaneous time slots: di ! Call congestion: Bi ! Time congestion: I7 X ! Total traffic flow offered (in calls): b = 2 bi =I ! X ! Total traffic flow offered
31、(in circuits): M = bidi i= I X V = C bidi2, Z = V/M. K = N/Ml/Z i= I Recommendation ES26 (03193) 3 STD-ITU-T RECMN E-52b-ENGL 1993 m 4b2571 Ob1993b 54 W In 5 we find an algorithm which allows an evaluation of the call congestion Bi. From 8 we can apply the “reduced network method and use the very si
32、mple approximated expression below: where i = 1 corresponds to the case of ordinary calls: dl = 1. Moreover, we have: BI = =(I/Z)EN/Z(MLZ) (-4-3) where E, (a) is the Erlang loss formula for m fractional. We have: With the “circuit reservation” method of Recommendation E.525, the evaluation of Hi, is
33、 much more complex and it depends on the mean seizure durations associated with each traffic flow. However, if these mean durations increase with the value given to (di) the corresponding Bi values decrease in relation to the case where all these mean durations would be equal. Moreover, the circuit
34、reservation method mentioned above aims at decreasing the difference between the Bi values. For the upper values of (di) the corresponding Bi values decrease slightly whereas BI increases significantly to approach the highest B, values. Finally, the formulas (A-2) and (A-3) mentioned above, for the
35、upper values of (di), give estimated excess values for Bi in the case of an approximate equalization of the Bi values. Annex B Sample of the capacity table (full availability group) (This annex forms an integral part of this Recommendation) Let p = blocking probability Yi = individual traffic offere
36、d = diai r = traffic mix ratio = (y1 :y2: :Yhd M y = total traffic offered = yi i= 1 N = number of unit circuits p=X% r=? 4 Recommendation ES26 (03/93) STD-ITU-T RECMN E-52b-ENGl 1993 M 48b2591 b17737 790 m References CONRADT (J.), BUCHHEISTER (A.): Considerations on loss probability of multi-slot c
37、onnections. Proc. I Irh ITC, paper, 4.4B-2, Kyoto, 1985. KAUFMAN (J.S.): Blocking in a shared resource environment, IEEE Trans. Comm. 29, pp. 1474-1481, 1981. MIYAKE (K.): Traffic study on different bit rate calls carried by a trunk group with trunk modularity, J. ofthe IEICE, 57 1 -B. pp. 473-482,
38、1988. GIMPELSON (L.A.): Analysis of mixtures of wide- and narrow-band traffic, IEEE Trans. Comm. 13, pp. 258-266, 1965. ROBERTS (J.W.): Teletraffic models for the Telecom 1 integrated services network. Proc. 10th ITC, paper 1.1.2, Montreal, 1983. LINDBERGER (K.): Blocking for multi-slot heterogeneou
39、s traffic streams offered to a trunk group with reservation, 5th ITC seminar, Lake Como, 1987. TAKAGI (K.), SAKITA (Y.): Analysis of loss probability equalized by trunk reservation for mixtures of several bandwidth traffic, Proc. 12th ITC, paper, 5.1A.5, Turin, 1988. FICHE (G.), LE GAL (P.), RICUPERO (S.): Study of blocking for multi-slot connections in digital link systems, Proc. ITC-II, paper, 5.4B-2, Kyoto, 1985. Recommendation ES26 (03/93) 5 Printed in Switzerland Geneva, 1994
