1、CCITT RECNN*E.862 (REV*L) 92 4862593 0573759 696 INTERNATIONAL TELECOMMUNICATION UNION CCITT E.862 (rev, 1 ) THE INTERNATIONAL TELEGRAPH AND TELEPHONE CONSULTATIVE COMMITTEE TELEPHONE NETWORK AND ISDN QUALITY OF SERVICE, NETWORK MANAGEMENT AND TRAFFIC ENGINEERING DEPEN DAB1 LITY PLAN NI NG OF TELECO
2、MMUNICATION NETWORKS Recommendation E.862 (rev.1) Geneva, 1992 - CCITT RECMN*E*BbZ (REV*L) 92 = 4862593 O573760 308 INTERNATIONAL TELECOMMUNICATION UNION CCITT E.862 (rev.1) ME INTERNATIONAL TELEGRAPH AND TELEPHONE CONSULTATIVE COMMITTEE TELEPHONE NETWORK AND ISDN QUALITY OF SERVICE, NETWORK MANAGEM
3、ENT AND TRAFFIC ENGINEERING DEPENDABILITY PLANNING OF TELECOMMUNICATION NETWORKS Recommendation E.862 (rev.1) Geneva, 1992 - _- - - -._ a -_- - - CCITT RECMN*E.B62 (REV*3) 72 4862573 0573761 244 FOREWORD Th CCI“ (the International Telegraph and Telephone Consultative Committee) j the International T
4、elecommunication Union (ITU). CCm is responsible for studying technica questions and issuing Recommendations on them with a view to standardizing telecommunia basis. permanent organ of operating and tariff ins on a worldwide The Plenary Assembly of CCIIT which meets every four years, esablishes the
5、topics for study and approves Recommendations prepared by its Study Groups. The approval of Recommendations by the members of CCM between Plenary Assemblies is covered by the procedure laid down in CCI“ Resolution No. 2 (Melbourne, 1988). Recommendation E.862 was prepared by Study Group II and was a
6、pproved under the Resolution No. 2 procedure on the 16th of June 1992. CCIT NOTE In this Recommendation, the expression “Administration“ is used for conciseness to indicate both a telecommunication Administration and a recognized private operating agency. O ITU 1992 All rights reserved. No part of t
7、his 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. - CCITT RECIN*E.862 (REV*iL) 92 W 4862593 0573762 180 W Recommendation E.862 DEPENDABILITY PLANNING OF TELECOMMUNICAT
8、ION NETWORKS (revised 1992) Introduction This Recommendation is concerned with models and methods for dependability planning, operation and maintenance of telecommunication networks, and the application of these methods to the various services in the international network. The CC, considering (a) th
9、at economy is often an important aspect of dependability planning; (b) that the ability of achieving a certain level of dependability differs between network providers; (c) that network providers often operate in a competitive environment; (d) that Recommendations E.845, E.850 and E.855 establish ob
10、jectives for serveability performance; (e) that objectives for dependability performance are deducible from Recommendations Q.504, Q.514, andX.134 to X.140; (0 that these objectives have been established in an intuitive manner rather than based on analysis of user needs; (s) that there exists no una
11、mbiguous way of implementing these objectives in planning; (h) that there is a need of establishing a method for dimensioning and allocating dependability in the telecommunication network; (i) that terms and definitions relevant to concepts used for dependability may be found in Recommendation E.800
12、, recommends that the procedures defined in this Recommendation shall be used by Administrations to plan, design, operate and maintain their networks. 1 General Dependability planning may be accomplished by using essentially two different methods. Intuitive method The level of dependability is deter
13、mined by making a synthesis of objectives and procedures presently used. It is a pragmatic method in absence of an analytical method or in the case when necessary data for a thorough analysis is not available. This method reflects the present status, but is inconsistent in achieving what Administrat
14、ions actually want to attain: the most economic level of dependability taking into account customer needs and inconvenience. Recommendation E.862 1 Analytical method The analytical method is based on principles defining the object of dependability planning. The principles are realized through a quan
15、titative model. The level of dependability is deduced by applying the model, taking into account all relevant factors in each planning case. - Basic principle - The main object of dependability planning is to find a balance between the customers needs for dependability and their demand for low costs
16、. - Model - Fault consequences are expressed in terms of money and are included as additional cost factors in planning and cost-optimization. The cost factor reflects the customers experience of faults in the network, quanWied in terms of money, as well as the Administrations costs for lost traffic
17、revenue and corrective maintenance. - Application - The Administration is provided with a method to integrate dependability as a natural part of planning, taking local information from the actual planning case into account. This method enables the preparation of simplified planning rules. The applic
18、ation of the analytical method gives, economically, the best-balanced level of dependability, seen from the customers point of view. This reduces the risk of customers complaints and loss of business to competitors as well as the risk of unnecessary investments. It is, therefore, considered to be th
19、e best general way of planning dependability for the Administration, as well as for the customers. Recommendations for operational dependability objectives are needed in order to discover impairments and to check and compare dependability performance in the national and international network. Experi
20、ence from the application of the analytical method may give reason to revise existing Recommendations. 2 Generic measures for dependability planning The dependability is described by measures defining the availabdity performance, the reliability performance and the maintainability performance of the
21、 network and its constituent parts as weil as the maintenance support performance (for the maintenance of the network). The recommended measures are: a) Availability pegionnance - Mean accumulated down time b) Reliability petformance - Mean failure intensity c) Maintainability performance - Mean und
22、etected fault time - Mean time to restoration - Mean active repair time d) Maintenance support performance - Mean administrative delay - Mean logistic delay Note - The definitions of these measures are given in Recommendation E.800 and Supplement No. 6. 2 Recommendation E.862 CCITT RECmN*E.B62 (REV*
23、L) 92 4862591 0573764 T53 The annual traffic disturbance cost is given by the interruption costs of circuit and packet switched traffic (first and second terms) and interruption costs of leased lines (last term): Ct = z - T. E. a A - cs + z . T. h - p r cp + z T. n 9 cl 3 Planning for economic optim
24、um 3.1 Economic dimensioning and allocation method The main principle of dependability planning is to find actions (investments, increased maintenance, etc.) that maximise the tota profit of the network ma ER - LCC LCR - life cycle revenue LCC - life cycle cost The revenues and costs are judged eith
25、er by their effect on the operating companys (Administrations) ability to reach its goals (a commercial evaluation) or by their effect on the weifare of a the members of society (a social evaluation). The principles for evaluating dependability may change and are to be regarded as a national matter.
26、 An equivalent statement of the probeb is to find actions that minimise the present value of the total costs of the network: min Cz + act + C, + . . .) - di where: Cl C, are the investment costs to achieve a certain degree of dependability; are the expected maintenance costs of year i; Ct is the exp
27、ected traffic disturbance cost (loss of revenue) for year i; di is the discount factor for calculating present value of costs occuring year i; Ct reflects the annoyance caused by faults and should be regarded as the basic service parameter which dimensions dependability in the network. A decrease in
28、 traffic disturbance cost represents an increase in life cycle revenue (UR = -AC#). Unlike quantitative objectives for dependability performance (the intuitive method), this method is generally applicable and does not become out of date with technological advances, changes in cost structure, etc. De
29、pendability is converted into one clear-cut measure (money) which makes it easier to evaluate actions to promote dependability and to compare and choose between different alternatives. The method is applicable for planning all parts of the national and international network and for dimensioning the
30、dependabfity of network components and the level of maintenance support. It may be used in short and long term planning as well as to quantify scenarios in strategic planning. 3.2 A simpled model for quantijEting trafic disturbance costs where: z T A is the failure intensity (failures per year); is
31、the mean down time (hours); is the busy hour intensity of switched traffic (erlangs); Recommendation E.862 3 a E cs h r cp is the factor reflecting the fraction of busy hour traffic demanded during the fault; is the probability of congestion during the fault; is the economic valuation of switched tr
32、affk (monetary unit per erlang-hour); is the intensity of busy hour packet calls (packets per hour); is the factor reflecting the fraction of busy hour packet cas demanded during the fault; is the probability of packet loss or delay during the fault; is the economic valuation of a lost or delayed pa
33、cket (monetary unit per packet); n is the number of leased lines; cl is the economic valuation of interruption of a leased circuit (monetary unit per circuit-hour). The model assumes that the parameters are stochastically independent and do not vary in time. However, this is seldom the case. If fail
34、ures are more likely to occur at certain hours of the day, there may be a correlation between traffk and failure intensity (time is a common parameter). Down time may be dependent on the time of day or week when the failure occurs. Correlations between parameters can be dealt with by assuming models
35、 of time variations of traffic, failure intensity, down time, etc. The problem is simplified if failures are assumed to uniformly distributed in time. The fiaction of busy hour r the market structure (degree of competition, etc.); - - - the category of customers and services affected; the degree of
36、congestion, delay or transmission disturbance; the duration of the fault; - - - the accessibility to alternative communication means for the affected customer; time of day, week or year when the fault is in effect; how often faults have occured in the past, etc. Administrations are recommended to ma
37、ke their own investigations among their customers in order to determine the values to be used in planning. Annex B gives an example of such an investigation. If this is not possible, rough estimates may be obtained from information about actions taken previously in the network, The cost of actions i
38、s compared to the amount of traffic saved. Actions that intuitively are regarded as reasonable, give a lower limit of c, actions that obviously are unreasonable give an upper limit. The values derived in this way are then used under the assumption that they are valid also for planning the future net
39、work. If c is not possible to estimate at all, the method may still be used to make priorities among competing alternatives and thus roughly finding an optimum allocation of a given amount of resources. 4 Recommendation E.862 CCITT RECMN*E.B62 (REV*I) 92 m LiBb2591 0573768 826 m 3.4 Planning procedu
40、re Traffic disturbance costs are included as additional cost-factors in economical calculations for planning, thus integrating dependabiity as a naturai part of planning. The procedure of dependability planning is performed in four steps: Step I - Plan a network attaining functional and capacity req
41、uirements. The starting point is a network planned and dimensioned in order to comply with the functional and capacity requirements, but without special consideration of dependability (zero-alternative). The second step is to identify what changes may be necessary to promote dependability. Step 2 -
42、Search for actions to promote dependability. There is a need for actions to promote dependability if traffic disturbance costs are high or if the actions can be taken at a low cost. A non-exhaustive list from which actions could be identuied is given below: - protection of equipment in order to prev
43、ent failures; choice of reliable and maintainable equipment; modernization and reinvestment of worn out equipment; - - - redundancy; - overdimensioning; - increase in maintenance support; - network management actions to reduce fault effects. Step 3 - Analyse the actions. Express improvements in term
44、s of changes in traffic disturbance and maintenance costs (Act + ACm) for each action. It is only necessary to calculate costs that differ between the alternatives. Annex A gives examples of dependability models for network design, maintenance support planning and for determining requirements for ne
45、twork components. Compare ACt + AC, to the increased investment cost (ACz) for each action, e.g. by the present value method. Choose the best set of actions, i.e. which gives the lowest total cost. Step 4 - Check that minimum requirements are complied with. A minimum service level may be stipulated
46、by governmental regulations, by CCITT Recommendations, for commercial or for other reasons. The establishment of any minimum requirements on the national level is a national matter. For planning of the international network the Administration is recommended to check if dependability objectives deduc
47、ible from existing CCIT Recommendations are met. If not, the reasons for non-compliance should be examined more closely. If it is justified, the level of dependability should be adjusted. Recommendation E.862 5 3.4.1 Numerical example based on the above Step i - Network planned without special consi
48、deration of dependability. The network studied is the trunk between two exchanges. Step 2 - Search for actions to promote dependability. The action considered is to introduce a physically redundant cable. It is assumed to be dimensioned to carry the whole traffic load, i.e. a single failure WU not d
49、isturb the traffic. 6 Z*T TO20149048 Step 3 -Analyse the action. Assumptions Failure intensity Mean down time Mean offered traffic Congestion z = 0.1 failwedyear T = 2Ah A = 100E P = 1 (without redundancy) P = O(withredundancy) Monetary valuation of disturbed traffic volume c = 400monetaryunitsEh Discount factor (iifetime 25 years, interest 5% per year) d = 14 Maintenance cost per failure Cm = loo0 monetary uniidfailure Cost of redundant cable CI = 400000monetaryuniis Calculations Traffic disturbance costs for network without redundancy: Ct = P A - z T
