ΗΥ537: Έλεγχος Πόρων και Επίδοση σε Ευρυζωνικά Δίκτυα,

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1 ΗΥ537: Έλεγχος Πόρων και Επίδοση σε Ευρυζωνικά Δίκτυα Βασίλειος Σύρης Τμήμα Επιστήμης Υπολογιστών Πανεπιστήμιο Κρήτης Εαρινό εξάμηνο 2008 Prcng and network control Incentves Smple modelng

2 Network externaltes Network externaltes: acton by one user affects all other users Postve externaltes: value of a network ncreases as square of users (Metcalf s law) Negatve externaltes: when a user accesses a shared resource t ncreases congeston whch affects all users Postve externalty n peer-to-peer networks: all peers beneft when one peer shares ts resources Prcng & control - 3 Prcng Prces affect demand: e.g. lowerng prces ncreases demand Prces can be used to control congeston Competton can drve prces to margnal cost Large fxed cost of constructng a network If there s no congeston, margnal cost of provdng one addtonal unt of servce s almost zero Networks and nformaton goods: costly to produce but cheap to reproduce (sunk cost, zero margnal cost) But networks also have operatonal and mantenance costs (ncludng bllng) Another dfference: networks can get congested Prcng & control - 4

3 Features of communcatons market All data transport servces are smply means of transportng bts at a gven qualty Can use ths basc servce for provdng other value added servces Statstcal multplexng => overbookng Traffc s bursty Economy of scales: larger network => more effcent multplexng Flexble, multdmensonal SLAs Exchange of sgnals on fast tmescales => renegotaton Commodtzed wholesale market Internet s a stupd network, hence can be effcently engneered Also reason for ts success Intellgence at edges Prcng & control - 5 Role of economcs Decentralzed control mechansms Use prce and congeston sgnals to provde ncentves Engneerng performance: n terms of utlzaton, delay, blockng, etc Economc effcency: nclude the value that customers obtan from usng the network Enttes (users-customer, network) are ratonal, seekng to maxmze there own beneft Prcng & control - 6

4 Overprovson or control? Overprovsonng possble n the core May be more dffcult n metropoltan and even more so n access networks Used by fewer customers Much more costly than core May be mpossble n wreless networks Prcng & control - 7 Some thoughts on chargng There s no unque vew on chargng for network servces Dsparate models, contradctng proposals There s no need for prcng network servces! No congeston n the future prce only content There s nothng new! (Economsts dd everythng already) yes and no! economsts need smple models to work wth => abstracton what s really relevant? Network abstracton model Economc theory Prcng & control - 8

5 Our vew on chargng Chargng s not only for makng profts, but for mprovng network performance provdng stablty and robustness creatng revenue Chargng should provde ncentve compatblty to users mportant nformaton to network control Chargng should be smple but not smplstc understandable mplementable compettve network fc prcng Prcng & control - 9 Network control and prcng Set of feasble servces depends on network control mechansms Economc ncentves nfluence network control mechansms Communcaton servce contracts (Servce Level Agreements - SLAs) provde substantal flexblty, and ablty to exchange economc sgnals on fast tmescale Network control: controls cell flows to guarantee contracts Prcng: controls demand n order to ncrease effcency Prcng & control - 10

6 Why Charge for Telecommuncaton Servces? In order for the Network (or Servce) Provder to: Recover costs Make profts and save captal for future expanson Control the system: examples: chargng of applcatons for admsson to U.S. unverstes chargng for street-parkng n Athens Obtan nformaton from users: examples: specal long-dstance call packages n U.S.A. => ther adopton s ndcatve of user s future behavor Prcng & control - 11 Types of Charge There a four types of charge: Fxed charge Usage charge Congeston charge Qualty charge A charge of a telecommuncaton servce consttutes a combnaton of the above components, whch may overlap Prcng & control - 12

7 Coca Cola s dynamc prcng experment Added thermometer to vendng machne Automatcally rased prces when weather was hot Ratonal: a coke has more value to people durng hot weather hgher demand durng hot weather, hence hgher prces Prcng & control - 13 Back to Coca Cola s dynamc prcng experment... Was t successful? Prces ddn t track congeston well... What they dd: ncrease of temperature ncrease of prce What the could have done: decrease of buyer nter-arrval tme ncrease of prce, or decrease of supply ncrease of prce Method for detectng congeston Prcng & control - 14

8 Incentves A chargng scheme nfluences users demand and behavor, accordng to the ncentves t offers to the user, regardng how to maxmse hs own utlty (beneft from servce vs charge) Each ndvdual user s behavor nfluences the global well-beng (socal welfare) of the socety (users and network) A chargng scheme s ncentve compatble f ndvdual user utlty optmsaton also results n socal welfare optmsaton Prcng & control - 15 Incentves Flat rate versus usage chargng Example: all-you-can eat Tme of day chargng n telephony Dynamc prcng n an Internet Café Fxed prce per tcket Normal & peak perods: duraton depends on # of users Tax tarffs: a+b*t+c*x, where a,b,c: tarffs parameters T: duraton, X: dstance T,X mutually exclusve: f speed small then charge T, else X Large b: ncentve for drver to ncrease duraton (drve fast between lghts, and wat long tme at lghts) Durng day when demand s hgh: make trps short, accommodate more people, and take advantage of fxed charge a Prcng & control - 16

9 A proposal for prcng Common network servces qualty Qualty $ dfferentated servces Qualty dfferentaton: guaranteed, best-effort, demand - low-hgh delay, blockng, relablty, access Prces dfferentate qualty of servce, not content Prces depend on demand, drven towards cost by competton; Prce relaton defned by substtuton; proportonal to - effectve bandwdths for guaranteed servces - throughput for best effort servces Prcng & control - 17 Sngle resource model Sngle lnk wth capacty C, shared by N customers How should t be shared? Soluton 1: Each user can get C/N But what f some users have demand < C/N? Bandwdth s wasted Soluton 2: far sharng (allocate resources teratvely) At each step t, allocate to each user C t /N t Next step C t+1 =remanng bandwdth But all users do not value bandwdth equally Prcng & control - 18

10 Takng nto account user utlty User utlty: Global plannng problem: But, dffcult to know all utltes Under condtons (utlty s concave), the above can be solved dstrbuted usng prces and allowng each user to solve max{ u ( x ) px} x Prce p set such that x ( p) = C max { x } u ( x Demand functon ) u ( x ) x ( p ) s. t. x C Prcng & control - 19 Takng nto account user utlty User utlty: Global plannng problem: But, dffcult to know all utltes Under condtons (utlty s concave), the above can be solved dstrbuted usng prces and allowng each user to solve max{ u ( x ) px} x Prce p set such that x ( p) = C max { x } u ( x Demand functon ) u ( x ) x ( p ) s. t. x C Prcng & control - 20

11 Propertes of approach Network does not need to know utlty of all users Decentralzed soluton, each user acts to maxmze ther own beneft Sharng done by users, not nternal network mechansms Network only provdes prce (=congeston sgnal) Incentve compatblty: best soluton for each user maxmzes aggregate utlty (socal welfare) Effcent (economc) resource utlzaton: capacty s used n full, by those who value t most Prcng & control - 21 Network revenue and user surplus Network revenue User surplus: u ( x ) p x ( p) = px pc Under no competton or regulaton, provder mght want to obtan all surplus Take-t-or-leave-t offer: u ( x ) e Dfferent prce p to dfferent users Nonlnear prces (e.g. a+b*x) Prcng & control - 22