Network dimensioning for elastic traffic based on flow-level QoS

Transcription

1 Network dmesog for elastc traffc based o flow-level QoS 1(10) Network dmesog for elastc traffc based o flow-level QoS Pas Lassla ad Jorma Vrtamo Networkg Laboratory Helsk Uversty of Techology

2 Itroducto (1) Network dmesog for elastc traffc based o flow-level QoS 2(10) Dmesog problem Gve the etwork (odes, lks, routg) ad the traffc demads Determe lk capactes such that a gve crtero s fulflled Coecto wth QoS: the crtero should be a meagful performace metrc for the etwork ad the applcatos Good old crcut swtched etworks QoS determed by blockg probablty Dmesog based o classcal Erlag formula Erlag formula s sestve to call holdg tme dstrbuto robustess The curret best effort Iteret No establshed QoS metrc has bee defed Maorty of Iteret traffc s elastc (cotrolled by TCP) For elastc traffc, a atural QoS metrc s the flow throughput ad dmesog could be based o that

3 Network dmesog for elastc traffc based o flow-level QoS 3(10) Itroducto (2) The mult-servce Iteret Exstg QoS archtectures (ItServ/DffServ) have prove problematc QoS s cotrol realzed at the packet level assumg substatal szed buffers but the performace of the mechasms always heavly depeds o the packet level statstcs Makg mechasms measuremet based ad adaptve helps but also adds complexty QoS parameters: packet delay, packet loss New QoSarchtecture based o flow-aware approach [J. Roberts et al.] Traffc cossts essetally of realtme traffc ad elastc traffc Routers are bufferless elmates complex self-smlarty effects at the packet level QoS cotrol realzed through flow-level cotrol of arrvg flows (access cotrol) QoS parameters: flow throughput ad servce accessblty Dmesog the mult-servce Iteret Idepedet of the chose QoS archtecture, traffc ca be largely categorzed two types: streamg ad elastc Dmesog should take to accout both types of traffc For the flow aware approach the dmesog problem ad the QoS cotrol are drectly related, but for the ItServ/DffServ approach the coecto s obvously drect

4 Itroducto (3) Network dmesog for elastc traffc based o flow-level QoS 4(10) Scope of ths study: We oly cosder elastc traffc for whch dmesog s aturally based o flow throughput Theoretcal framework We apply models based o the oto of balaced faress Idealzed badwdth sharg scheme that allows explct evaluato of throughput Mmal assumptos o traffc: sesso arrvals are Posso The models are sestve,.e., performace oly depeds o the load Balaced faress approxmates max-m faress ad proportoal faress (whch are approxmated by TCP), for whch performace ca ot be easly evaluated Thus, balaced faress s used as a computatoally effcet tool that allows robust dmesog based o flow-level throughput Practcal use of the results: Solutos ca be used as a sort of educated guess for how much badwdth s eeded to have a gve throughput performace

5 Network dmesog for elastc traffc based o flow-level QoS 5(10) Related work Geeral remarks Gve performace requremet ca be satsfed by a cotuum of possble solutos for the lk capactes Thus, a optmzato formulato s requred to choose the best soluto Ma dffereces the system model: statc/stochastc Classc Bertsekas & Gallager square-root method System model: ope etwork of M/M/1 queues Task: mmze lk costs s.t. total mea packet delay equals some target delay Problem: as such the etwork model s a packet-level model Mult-commodty flow optmzato models [M. Poro et al.] Task: maxmze flow allocato accordg to some oto of faress whe the allowed overall etwork cost s gve (budget costrat) Formulatos for max-m faress, proportoal faress, robust etworks Problem: etwork model treats traffc as flud ad gores the dyamc/stochastc ature of traffc, o oto of offered traffc (Lk dmesog: robust lk dmesog usg PS models)

6 Network dmesog for elastc traffc based o flow-level QoS 6(10) Dmesog problem decomposto ISP core etwork Detaled dmesog appled oly where badwdth s scarce,.e., the access etworks (ANs) ISP core etwork dmesoed such that t s trasparet to the users Lk loads < 0.5 (rough guess) AN1 AN2 AN3 ANs dmesoed based o per flow throughput Utlzg ew results o balaced faress

7 Network dmesog for elastc traffc based o flow-level QoS 7(10) Optmzato problem for access etworks (1) ANs have mult-level tree topology N classes (routes), J lks Optmzato formulato m s.t. C = capacty of lk ρ = load of class (bt/s) γ (C)= througput of class T (C)= througput of class F = classes that use lk Verso 1 J = 1 F γ C ρ < C = 1, K, J AN2 m max ( C ) γ, = 1, K, N T ( C) T, = 1, K, N, Verso 2 m s.t. J = 1 F C ρ < C, = 1, K, J

8 Network dmesog for elastc traffc based o flow-level QoS 8(10) Optmzato problem for access etworks (2) The throughput γ (C) ca be computed exactly usg a effcet recursve algorthm, or approxmately wth store-ad-forward lower boud or the more accurate parkg-lot approxmato Note o usg the store-ad-forward boud Coservatve boud ( some sese safe ) Dmesog problem becomes equvalet to the Bertsekas-Gallager square-root method I the square-root method, the model gves a exact dmesog rule for the packet delay a etwork of M/M/1 queues I our case, t gves a approxmate dmesog rule for the flow-level performace Other spces Possble to have per-flow rate lmtatos (SF-boud or exact soluto) Cost fucto ca be arbtrary (also olear) ρ 1 ρ 2 ρ 3 ρ 4

9 Network dmesog for elastc traffc based o flow-level QoS 9(10) Example: homogeeous tree wth braches Optmal soluto usg the SF-boud: C 0 ( 1+ ) m C0 = ρ + γ, C1 = ρ + γ Optmal costs for varous γ m as a fucto of m 1+ C 1 C γ m = 10 γ m = 5 γ m = C γ m = 10 γ m = 5 γ m = Total cos t γ m = 10 γ m = 5 γ m = Relatve error betwee SF dmesog ad exact soluto Relatve erro r γ m = 10 γ m =

10 Coclusos Network dmesog for elastc traffc based o flow-level QoS 10(10) Models based o balaced faress allow robust dmesog for elastc traffc The dmesog ca be based o a atural flow-level QoS requremet,.e., the per flow throughput Usg the SF-boud for approxmatg the performace, the optmzato problem s also umercally smple Effcet exact soluto algorthms ca be used to verfy the actual performace Future research Dmesog of etworks wth both elastc ad streamg traffc (performace bouds for such etworks are avalable) Dmesog of terferece lmted wreless etworks wth mult-hop rado lks (RANs)