H Χρέωση ως Μηχανισμός Ελέγχου Δικτύων. Κωνσταντίνος Κουρκουμπέτης, Βασίλειος Σύρης και Γεώργιος Δ. Σταμούλης

Transcription

1 H Χρέωση ως Μηχανισμός Ελέγχου Δικτύων Κωνσταντίνος Κουρκουμπέτης, Βασίλειος Σύρης και Γεώργιος Δ. Σταμούλης

2 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. unversty chargng for street-parkng n a cty Obtan nformaton from users examples: specal call packages for long-dstance fxed telephony or for moble telephony ther adopton s ndcatve of user s type and future behavor Δίκτυα Υπολογιστών Εισαγωγή - 2

3 Termnology prce: correlated wth servce unt E.g. /Mbyte of /callmnute tarff: charge structure more general form of chargng (.e., a+px) control mechansm charge: total amount that must be pad Δίκτυα Υπολογιστών Εισαγωγή - 3

4 Utlty functon Each consumer s characterzed by a utlty functon u(x) Translates nto monetary unts the beneft/satsfacton of the consumer from the use of the partcular network resource or servce Expresses consumer s wllngness-to-pay Can also have the meanng of beneft from tradng, resellng u A (x) u A ( 10) 5, ub(10) 2 u B (x) u C (x) x Δίκτυα Υπολογιστών Εισαγωγή - 4

5 Chargng Components 1. Fxed charge e.g.: monthly flat rate chargng of Internet access 2. Usage charge e.g.: fxed telephony s charged on tme and dstance may be hard to quantfy the unt of usage E.g. bursty traffc should not be charged on volume only, because t s harder to multplex than a constant-rate traffc stream (generatng the same volume), and thus consumes more resources. Δίκτυα Υπολογιστών Εισαγωγή - 5

6 Chargng Components 3. Congeston charge ts level depends on the congeston encountered or caused, smlarly to hghway tolls 4. Qualty charge οften combned wth usage or flat charges A charge of a telecommuncaton servce consttutes a combnaton of the above components Examples: a) monthly flat charge of Internet access depends on access rate,.e. on a qualty factor. b) Often, the followng combnaton apples: Usage + Congeston + Qualty Varable charge Δίκτυα Υπολογιστών Εισαγωγή - 6

7 Congeston Charge Depends on congeston durng servce Apples to cases where: everyone can be served, but congeston results n servce qualty degradaton E.g. hghways, Internet Example: Chargng access to hghways, accordng to the a pror set congeston charge Δίκτυα Υπολογιστών Εισαγωγή - 7

8 Congeston Charge (contnued) Free access traffc n hghway s heavy Pad Access traffc n hghway s lghter Worth? TOLL $5 Δίκτυα Υπολογιστών Εισαγωγή - 8

9 Capacty Expanson A network provder should expand capacty upon congeston socal welfare can be further ncreased, despte the cost for addtonal capacty Economc theory suggests that expanson can be funded by re-nvestng the revenue from congeston charges example: hghways wth tolls TOLL $5 $$$ TOLL $5 Δίκτυα Υπολογιστών Εισαγωγή - 9

10 Fxed and Varable charges Fxed charge: related to connecton cost Varable charge: related wth the sze of consumpton Recovery of usage cost, Control mechansm (of prorty) of consumer u A ( x) 2x C max 10 C max 10 Cost = 1 /unt Connecton Cost = 5 u B ( x) 10x C max 10 5 Cost based chargng: Every user receves x C max / 2 5 Is t economcally optmal? x Δίκτυα Υπολογιστών Εισαγωγή - 10

11 Prcng as a control mechansm (I) Servce provder does not know the utlty functon of the consumers Consumers are pursung ther own beneft The quantty of the avalable servce s fnte How can the total beneft of the consumers be maxmzed? The network proft? Prcng Mechansm! How much should I ask f the prce s p? C p x A How s the problem specalzed for networks? x B Δίκτυα Υπολογιστών Εισαγωγή - 11

12 Chargng as Control Mechansm Charges can be used as an nternal control mechansm of the system provder & users to reach the socal optmum Example: Socally Optmal Bandwdth Allocaton Network Provder sells bandwdth at a prce p per kbps, Gven ths prce, each user selects amount x (p) of kbps purchased Provder pays for capacty wth the revenue collected There exsts an equlbum prce p that leads to socal optmum,.e. maxmzes the sum of user utltes (= socal welfare) prce p socety user n... user 1 Network x 1 (p),, x n (p) Δίκτυα Υπολογιστών Εισαγωγή - 12

13 One lnk, wth capacty concave utlty functons More formally (I) shared by users wth Socal welfare maxmzaton problem: C max u ( ).. x s t x C { x } Mathematcal soluton (requres global nformaton) Maxmze the Lagrangan Δίκτυα Υπολογιστών Εισαγωγή - 13 (1) max L(,{ x }) ( ) ( u x x {, x } The optmal pont of (1) s characterzed by x C, u x, { x} C) for whch:

14 More formally (II) Dstrbuted soluton of the problem wth economc mechansm use prce p The user solves hs own net beneft maxmzaton: u max[ u ( x ) px ] the condton for whch s: p x Prce p dscovered teratvely by means of tattonement process provder updates market prce p n order to lead total demand to become equal to the capacty C. Under general market condtons the market prce p converges to the prce of the centralzed problem (.e. the Lagrange multpler) Approach extended by Kelly et al. to networks Δίκτυα Υπολογιστών Εισαγωγή - 14

15 Incentves A chargng scheme nfluences users demand, accordng to the ncentves t offers to the user for ndvdual optmzaton Each ndvdual user s behavor nfluences the socal well-beng (welfare) A chargng scheme s ncentve compatble f ndvdual user optmzaton also results n socal optmzaton Apples to mechansm of slde 14 Δίκτυα Υπολογιστών Εισαγωγή - 15

16 Examples of Incentves Wrong Incentves Monthly flat charge for Internet access DSL connectons left permanently open, thus gvng rse to the need for more ports n the DSLAMs Free nght use of moble telephones (U.K. late 1990s) blockng: telephones were left open for long hours Δίκτυα Υπολογιστών Εισαγωγή - 16

17 Examples of Incentves Rght Incentves Combnaton of Usage- and congeston-based chargng of Internet consdered as an effectve way to avod congeston Tme-of-day chargng n telephony and power shftng of non-busness calls off the peak perod satsfacton of both busness and non-busness users Δίκτυα Υπολογιστών Εισαγωγή - 17

18 Story on Chargng Internet and Broadband Servces produces servces from shared resources usage s hard to quantfy cost s hard to share network theorsts wrte artcles Telecom network network engneers techncal standards may leave concrete chargng solutons for later economsts complex economc models overlook many crtcal detals of technology Δίκτυα Υπολογιστών Εισαγωγή - 18