Multicriteria analysis in telecommunications

Transcription

1 Poceedings of the 37th Hawaii Intenational Confeence on System Sciences Multiciteia analysis in telecommunications Janusz Ganat and Andze P. Wiezbicki National Institute of Telecommunications Szachowa 1, Wasaw, Poland, {J.Ganat, A.Wiezbicki}@itl.waw.pl Abstact The pape pesents an oveview of multiciteia analysis techniques applied to the design of telecommunication netwoks. A special module called ISAAP fo inteactive multiciteia analysis is adapted fo this pupose. We will also pesent the use of multiciteia analysis fo suppoting stategic decisions elated to negotiating inteconnection ageements in telecommunications. 1. Intoduction The lage dynamics and impotance of telecommunication secto and teleinfomatic infastuctue development, the stong competition in this secto pevailing in most counties motivate telecommunication opeatos to use new computeised tools. Such tools might help in planning netwok development, in assessing financial and economic standing, in netwok design and management, in copoate management including stategic decisions and negotiations of inteconnection ageements. An intensive development and deceasing costs of infomation technology contibute to the gowing availability of such tools. Taditional applications of compute technology in telecommunications elate to the suppot of day to day opeations and business pocesses, such as: Billing systems; Custome sevice systems; Netwok esouces management systems; Finance and accounting systems; Pesonnel systems. The economic cisis in the yeas was also elated to telecommunications and motivated telecommunication opeatos to change thei stategy. Befoe the cisis, the stategy was usually an extensive one, concentating on netwok expansion. Afte the cisis, the stategy changed to intensive one, concentating on the best use of existing mateial esouces. Thus, decision suppot systems have today a special impotance fo telecommunication opeatos, because they help to gain competitive advantage eithe by suppoting stategic analysis o by impoving business pocesses. Seveal aeas of using DSS in telecommunications can be distinguished: Stategic analysis; Custome behaviou analysis; Quality management suppot; Netwok management o planning and design. 2. Netwok models and thei optimisation Divese types of models (maket models, management models) can be used fo decision suppot in telecommunications, but typically used in the analysis of telecommunication netwoks ae netwoktype models. They ae used eithe as detailed models in the simulation mode, o as moe aggegated models in the optimisation mode; the optimisation is usually single-citeia. Typical poblems that ae solved today see e.g. [7] - when using single-citeia optimisation ae as follows: Change fom coppe to optic fibe technology and the analysis of netwok development; Route selection and detemination of tansmission ates; Sevice availability; Futue netwok achitectues and thei implementation; Channel allocation; Satellite location. Anothe cuent topic is planning and designing local access netwoks; the use of optimization tools fo this pupose is pesented in [3], [4], [6], [11], [16], [18]. A fundamental poblem in such applications is the computational complexity of exact solutions of /04 $17.00 (C) 2004 IEEE 1

2 Poceedings of the 37th Hawaii Intenational Confeence on System Sciences such mixed (binay-continuous) optimisation poblems. Appoximate solutions ae thus needed and heuistic algoithms ae commonly used; the application of genetic and evolutionay algoithms is also suggested. Thee ae seveal examples of optimisation tools used fo telecommunication netwoks planning: SONET Toolkit [5] a decision suppot system fo designing cost-effective and esilient optical fibe netwoks. This system was developed by Bellcoe; its application can esult in cost savings fom 10 to 30%; NETCAP [12] an inteactive optimisation system fo telephone netwok planning, developed in the laboatoies of GTE. Estimated savings of GTE by using this system ae ca. 30 million dollas yealy; Achane [2] a decision suppot system in the development of connections between switching bases, developed by NYNEX Science and technology. 3. Multiciteia analysis in telecommunications Multiciteia analysis has seveal advantages ove single-citeia optimisation and is intensively developed with applications in divese technical fields see e.g. [10], [17]. Howeve, multiciteia analysis is not yet boadly used in telecommunications, because its methods ae not widely known by eseaches woking on telecommunication netwoks. Anothe eason is that eseaches did not yet fully ealise the impact of fast gowing capabilities of moden computes. Multiciteia analysis equies epetitive optimisation, hence could not be applied to bigge netwok models in the past, when a single optimisation un could equie hous of computations. Today, howeve, this constaint is no longe stict, and anyway it neve applied to simple models needed e.g. in stategic management. Thee ae only fist attempts to use multiciteia analysis in telecommunications, see e.g. [13], [14], [20], [21], [22]. Since the inclusion of new sevices in telecommunications inceases the numbe of aspects o citeia with which a moden telecommunication netwok should be assessed, the tend to use multiciteia analysis will cetainly become moe pevalent in the futue. We can list hee the examples of poblem classes that multiciteia analysis might be applied in telecommunications. These ae: Suppot fo stategic management; Netwok planning; Netwok design; Routing poblems. Stategic management of the netwok is one of the most impotant aeas. The complexity of the sevices and infastuctues moves the impotance of the decisions fom opeational to stategic decisions. Examples can be found in [15], [22], whee poblems of vendo selection of a telecommunication system o suppot fo inteconnection ageement ae pesented. All poblems of stategic management ae in thei essence elated to multiciteia analysis; e.g. long-tem costs and benefits vesus shot tem outlays ae to be consideed in most stategic decisions. Planing of the telecommunications netwoks is a highly complex pocess. Application of vaious analytical modelling and analysis techniques significantly impoves the eliability and quality of netwok plans. The use of multiciteia analysis in netwok planning can be illustated by a simple poblem taken fom [14]. With the development of infomation society, it is impotant to cove bette ual aeas with telecommunication netwoks. The poblem of location of infomation sevice centes can be fomulated as follows. Suppose n possible locations ae consideed, with the decision x = 1 if the location is selected and x = 0 othewise. Each infomation cente can supply l vaious sevices indexed by k = 1,...l, with value of k-th sevice in the - th location denoted by b k. Suppose we want to minimise the numbe of selected locations, but also maximise the value of sevices deliveed. Additionally, we might want to maximise the dispesion of selected centes; this can be done eithe by intoducing an additional citeion, o by adding additional constaints. Suppose we intoduce binay numbes a i = 1, if the distance between centes is lowe than a given distance D, a i = 0 othewise. Then we can fomulate the multiciteia poblem as follows: max with constaints: n = 1 a i x n = 1 1 b min x n = 1 x k = 1, l k, i = 1,, n; x 0 lub x = 1. = i We have in this poblem l+1 optimization citeia and can select efficient solutions fo this poblem which ae such locations that the numbe of them cannot be /04 $17.00 (C) 2004 IEEE 2

3 Poceedings of the 37th Hawaii Intenational Confeence on System Sciences deceased without wosening the value of a given sevice. The analysis of vaious solutions of this poblem by zeo-one compomise pogamming can be found in [21]. As anothe effective tool of solving such poblems inteactively with the use (analysts o decision make), system DINAS can be suggested, see [23]. This example only illustates the possibility and impotance of using seveal citeia in telecommunication poblems. Thee ae many othe examples of multiciteia poblems in netwok planning. E.g. when consideing the poblem of locations of intenet eplicating seves (caches) in a teleinfomatic netwok, a fai solution to this poblem equies a simila level of sevice quality fo all egisteed uses. Thus, thee ae at least as many citeia as thee ae egisteed uses and some oveall cost citeia (shot-tem and long-tem) additionally. Netwok design [13], [19] is consideed on moe detailed level then netwok planning. Hee, the designe must choose the technology and has to find vaious paametes of the netwok ealized in a specific technology. An example of a design poblem will be descibed in Section 4. Routing poblems becomes one of the most significant aeas of management of the netwoks (see [20]). It is impotant poblem because the telecommunications netwoks ae an infastuctue to povide vaious sevices on diffeent level of quality of sevice. In outing poblems we usually conside seveal citeia, like: Cost; Bandwidth; Delay; Jitte; Packet loss (cell loss); Eo ate. The existing outing potocols conside moe than one citeion. Howeve, the scalaizing function and paametes ae given apioi. Fo example IGRP-Cisco System s Inte-Gateway Routing Potocol uses the following metic (scalaizing function): K 1 m = [ + ( K 2 * d )] * b * (1 o ) whee d is the topological delay time, b is the bandwidth of the naowest bandwidth segment of the path, o is the channel occupancy of the path, is the eliability of the path (eo ate), K1,K2 ae the constants. Specific advantages of using diectly multiciteia methods fo outing poblems can be found in [20]. It is known that existing outing potocols use many citeia aggegated togethe into an ad hoc metic function; a geneal advantage of multiciteia analysis is that we can analyse the impact of selection of vaious types of such aggegated metic function and select best of them fo netwok functioning. 4. Refeence point methodology as a tool fo multiciteia analysis of design poblems Refeence point methodology is one of the appoaches to vecto optimisation and multiciteia analysis, especially useful in pactical applications see e.g. [23]. Geneally, efeence point appoaches can be consideed eithe as an extension of penalty appoaches in vecto optimisation, o a modification of goal pogamming. In the latte intepetation, efeence point methods use a special achievement scalaising function (a poxy value function) instead of the distance used in the goal pogamming, and use one o two efeence points (aspiation and/o esevation levels fo all citeia) instead of the goal point used in goal pogamming. The achievement scalaising function is monotone with espect to impoving citeia, hence all maxima of this function ae Paetooptimal o geneally efficient, which is not necessaily tue when using a distance function as in classical goal pogamming. In this section we will show advantages of using efeence point methodology in designing telecommunication netwoks. We have chosen the poblem of the designing of a ing netwok [13]. We assume that vaious design options ae assessed on the basis of two citeia: costs of netwok constuction and upkeep can be expessed as: min ( E i i ) a X + c ( D i i< while anothe citeion expesses a poxy fo netwok esilience taken as the aveage numbe of nodes in a ing included in the netwok: min ( i ) X i E / X f i ) /04 $17.00 (C) 2004 IEEE 3

4 Poceedings of the 37th Hawaii Intenational Confeence on System Sciences whee: a is the ADM cost coefficient, c is the cost coefficient fo taffic between ings, f is is the intensity of taffic between node i and tansfeed fom ing to ing s, [D i ] is N x N symmetic matix epesenting the demand fo taffic between the nodes i and, [E i ] is N x R matix defining the membeship of nodes in ings, N is the set of node indicies, R is the set of indices of candidate ings, X is the multiplicity of the ing. This model was analysed using multiciteia model analysis modules developed togethe with Intenational Institute fo Applied Systems Analysis (IIASA) in Laxenbug n.vienna. The model was witten in the AMPL modelling language, then a standad linea pogamming fom in MPS fomat was geneated, foming so-called basic substantive model. This model in tun is analysed multiciteially with the help of a gaphic use inteface ISAAP fo the definition of use pefeences based on the specification of aspiation and esevation levels fo consecutive citeia, see [9]. The examples of model analysis ae pesented in Figues 1, 2, 3. Figue 1 pesents so-called neutal solution, coesponding to a unifom specification of aspiation and esevation levels at the best (so-called utopia) and wost between efficient (so-called nadi) outcomes fo each citeia; the neutal solution coesponds in a sense to the middle of the set of efficient outcomes. Figue 2 pesents a solution when the use say, the designe of the netwok wanted to decease the aveage numbe of nodes in a ing (which inceases the esilience of the netwok) as compaed to the neutal solution. Fo this pupose, the use deceased significantly the esevation level fo the aveage numbe of nodes. This esulted in the aveage numbe of nodes in a ing deceasing to thei minimal numbe, but the cost of netwok constuction inceased to its maximal efficient value (white points in Figue 2). Convesely, if the use wanted to decease stongly the cost as compaed to the neutal solution, he/she could decease stongly the esevation level fo cost which would esult in the minimal cost but the maximal between efficient aveage numbe of nodes in a ing (white points in Figue 3). By choosing a moe balanced esevation and aspiation levels, the use could find all efficient solution between these boundaies. The multiciteia appoach esults in choosing a design that is a compomise between the netwok cost and its esilience. An example of such possible compomises is the neutal solution shown in Figue 1; othe compomises ae also possible. Figue 1. Neutal solution Figue 2. Pefeences on obustness of the netwok Figue 3. Pefeences on minima cost 5. Multiciteia suppot fo stategic management Anothe inteesting application of muticiteia analysis in telecommunications was shown in [15]. The poblem concens pepaation fo negotiations on /04 $17.00 (C) 2004 IEEE 4

5 Poceedings of the 37th Hawaii Intenational Confeence on System Sciences inteconnection ageement by one telecommunication opeato with anothe, o fo mediation of such ageements between telecommunication opeatos by a egulatoy agency. Fo this pupose, a model of the dependence of the demand fo telecommunication sevices on the pice of such sevices (at least fo a given aea o city) is needed. This model must be augmented with a model of the costs of supplying such sevices, eithe accoding to Fully Allocated Costs fomula, o to Long Range Incemental Costs fomula, fo both opeatos. If the model is used by one of the opeatos, it is supplemented with a postulated model fo the opposite opeato; if used by the egulatoy agency, the model is based on data supplied by both opeatos accoding to laws govening inteconnection issues. Such composite model can be analysed fom vaious points of view: 1) The point of view of a telecommunication opeato. An opeato could assume the pices demanded fo sevices by the opposite opeato and pefom a multiciteia analysis of the following poblem: what pices to chage in ode to incease its own shae of the maket but without loosing too much pofits. This is a bi-citeia poblem that can be analysed similaly as in the example above. Afte such analysis, an opeato could play the ole of its opponent and analyse the opponent esponses on the same model, given his own pices. A consecutive analysis of such esponse upon a esponse can lead to a Paeto-Nash equilibium of the game, see [15]. This can be seen as an initial pat of pepaation fo actual negotiations on inteconnection taiffs. By combining the obectives of both sides its own and those of the opposite side an opeato could analyse a multiciteia model (in this example, fou citeia ae needed - maket shaes and pofits fo both sides) in ode to obtain the chaacteisation of possible compomises in negotiations. If a status-quo solution is eithe given extenally o assumed (e.g. using the Paeto-Nash equilibium mentioned above), then the neutal solution with espect to the status-quo data is a genealisation of the Raiffa-Kalai-Smoodinsky coopeative equilibium of the game. 2) The point of view of a egulatoy agency The egulatoy agency can use such model to define and compute a neutal solution as in the example above, taking into account seveal citeia (say, not only fou citeia listed above, but also a citeion epesenting the inteests of pomoting univesal sevice). The status-quo point in such computations might epesent the data obtained by the egulatoy agency fom both opeatos and fom geneal monitoing of the telecommunication sevice maket. The egulatoy agency can use the neutal solution in possible abitation of disputes on inteconnection ageements. 3) The point of view of a dominating opeato The dominating opeato could use such models not only to pepae fo inteconnection ageements, but also to check whethe the inteconnection pices demanded would be fa away fom a possible neutal solution defined by the egulatoy agency. If the pices would diffe too much fom the expectations of the egulatoy agency, the dominant opeato uns the isk of an intevention by the agency. Thus, we conclude that multiciteia analysis of telecommunication maket models might be used by divese playes on the maket. The negotiation of inteconnection ageements is, moeove, only an example of vaious stategic poblems in telecommunications. Simila methods can be used fo othe stategic poblems, such as pepaing a local netwok investment as a oint ventue o public-pivate patneship of seveal actos. 6. Conclusions Decision suppot in telecommunications inceases the ange of its applications. In this pape, we have shown only some examples and some pespectives of the development of this field. Thee is no doubt that, with the inceasing complexity of telecommunication netwoks and sevices, the demand fo decision suppot in this field will also gow. 7. Refeences [1] Analysys Ltd. An Intoduction to the Analysys STEM Modelling System. Intenal Pape [2] T. Baena, et al. Achane: Planning the Inteoffice Facilities at NYNEX, Intefaces, Vol. 26, No. 1, 1996, pp [3] D. Bienstock, O. Gunluk, Capacited Netwok Design Polyhedal Stuctue and Computation, ORSA Juonal on Computing. Vol. 8, 1996, pp [4] S-G. Chang, B. Gavish, Lowe Bounding Pocedues fo Multipeiod Telecommunications Netwok Expansion Poblems, Opeations Reseach. Vol. 43, No. 1, 1995, pp [5] S. Cosaes, D.N. Deutch, I. Saniee, O.J. Wasem, S. Cosaes, SONET Toolkit: A Decision Suppot System fo /04 $17.00 (C) 2004 IEEE 5

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