CS644 Advanced Networks

Transcription

1 Limitatios of IP CS644 Advaced Networks Lecture 7 QoS Adreas Terzis IP provides oly best effort service IP does ot participate i resource maagemet Caot provide service guaratees o a per flow basis Caot provide service differetiatio amog traffic aggregates Early efforts Teet group at Berkeley ATM IETF efforts Itegrated services iitiative Differetiated services iitiative Sprig Sprig So, what is required? Flow differetiatio Simple FIFO schedulig will ot work! Admissio cotrol Resource reservatio Flow specificatio Itegrated Services Iteret Ehace IP s service model Old model: sigle best-effort service class New model: multiple service classes, icludig best-effort ad QoS classes Create protocols ad algorithms to support ew service models Old model: o resource maagemet at IP level New model: explicit resource maagemet at IP level Key architecture differece Old model: stateless New model: per flow state maitaied at routers used for admissio cotrol ad schedulig set up by sigalig protocol Sprig Sprig

2 Itegrated Services Example Itegrated Services Example Achieve per-flow badwidth ad delay guaratees Example: guaratee 1MBps ad < 100 ms delay to a flow Receiver Seder Allocate resources - perform per-flow admissio cotrol Receiver Seder Sprig Sprig Itegrated Services Example Itegrated Services Example Seder Istall per-flow state Receiver Seder Istall per flow state Receiver Sprig Sprig

3 Itegrated Services Example: Data Path Per-flow classificatio Receiver Seder Itegrated Services Example: Data Path Seder Per-flow buffer maagemet Receiver Sprig Sprig Itegrated Services Example Per-flow schedulig How Thigs Fit Together Seder Receiver Routig Messages Routig RSVP Admissio Cotrol Cotrol Plae RSVP messages Data I Forwardig Table Route Lookup Per Flow QoS Table Classifier Scheduler Data Plae Data Out Sprig Sprig

4 Service Classes Service ca be viewed as a cotract betwee etwork ad commuicatio cliet ed-to-ed service other service scopes possible Three commo services best-effort ( elastic applicatios) hard real-time ( real-time applicatios) soft real-time ( tolerat applicatios) Hard Real Time: Guarateed Services Service cotract etwork to cliet: guaratee a determiistic upper boud o delay for each packet i a sessio cliet to etwork: the sessio does ot sed more tha it specifies Algorithm support admissio cotrol based o worst-case aalysis per flow classificatio/schedulig at routers Sprig Sprig Soft Real Time: Cotrolled Load Service Service cotract: etwork to cliet: similar performace as a uloaded besteffort etwork cliet to etwork: the sessio does ot sed more tha it specifies Algorithm Support admissio cotrol based o measuremet of aggregates schedulig for aggregate possible Role of RSVP i the Architecture Sigalig protocol for establishig per flow state Carry resource requests from hosts to routers Collect eeded iformatio from routers to hosts At each hop cosults admissio cotrol ad policy module sets up admissio state or iforms the requester of the failure Sprig RSVP Usage ad Related Issues 16

5 What is still Missig? Classificatio algorithm Schedulig algorithm Admissio cotrol algorithm QoS Routig algorithm Why did ItServ fail? Ecoomic factors Deploymet cost vs Beefit Is reservatio, the right approach? Multicast cetric view Is per-flow state maiteace a issue? What about QoS i geeral? Sprig Sprig What is the Problem? Goal: provide support for wide variety of applicatios: Iteractive TV, IP telephoy, o-lie gammig (distributed simulatios), VPNs, etc Problem: Best-effort caot do it (see previous lecture) Itserv ca support all these applicatios, but Too complex Not scalable Differetiated Services (Diffserv) Build aroud the cocept of domai Domai a cotiguous regio of etwork uder the same admiistrative owership Differetiate betwee edge ad core routers Edge routers Perform per aggregate shapig or policig Mark packets with a small umber of bits; each bit ecodig represets a class (subclass) Core routers Process packets based o packet markig Far more scalable tha Itserv, but provides weaker services Sprig Sprig

6 Diffserv Architecture Differetiated Service (DS) Field Igress routers Police/shape traffic Set Differetiated Service Code Poit (DSCP) i Diffserv (DS) field Core routers Implemet Per Hop Behavior (PHB) for each DSCP Process packets based o DSCP Igress DS-1 Egress Igress DS-2 Egress DS Filed Versio HLe TOS Legth Idetificatio Flags Fragmet offset TTL Protocol Header checksum Source address Destiatio address Data IP header Edge router Core router Sprig DS filed reuse the first 6 bits from the former Type of Service (TOS) byte The other two bits are proposed to be used by ECN Sprig Differetiated Services Two types of service Assured service Premium service Plus, best-effort service Assured Service [Clark & Wroclawski 97] Defied i terms of user profile, how much assured traffic is a user allowed to iject ito the etwork Network: provides a lower loss rate tha best-effort I case of cogestio best-effort packets are dropped first User: seds o more assured traffic tha its profile If it seds more, the excess traffic is coverted to besteffort Sprig Sprig

7 Assured Service Large spatial graularity service Theoretically, user profile is defied irrespective of destiatio All other services we leart are ed-to-ed, i.e., we kow destiatio(s) apriori This makes service very useful, but hard to provisio (why?) Traffic profile Igress Premium Service [Jacobso 97] Provides the abstractio of a virtual pipe betwee a igress ad a egress router Network: guaratees that premium packets are ot dropped ad they experiece low delay User: does ot sed more tha the size of the pipe If it seds more, excess traffic is delayed, ad dropped whe buffer overflows Sprig Sprig Cotrol Path Each domai is assiged a Badwidth Broker (BB) Usually, used to perform igress-egress badwidth allocatio BB is resposible to perform admissio cotrol i the etire domai BB ot easy to implemet Require complete kowledge about domai Sigle poit of failure, may be performace bottleeck Desigig BB still a research problem Example Achieve ed-to-ed badwidth guaratee seder 1 9 BB BB 5 BB 8 profile 6 profile 4 profile receiver Sprig Sprig

8 Compariso to Best-Effort ad Itserv Service Service scope Complexity Scalability Best-Effort Coectivity No isolatio No guaratees Ed-to-ed No setup Highly scalable (odes maitai oly routig state) Diffserv Per aggregate isolatio Per aggregate guaratee Domai Log term setup Scalable (edge routers maitais per aggregate state; core routers per class state) Itserv Per flow isolatio Per flow guaratee Ed-to-ed Per flow steup Not scalable (each router maitais per flow state) Summary Diffserv more scalable tha Itserv Edge routers maitai per aggregate state Core routers maitai state oly for a few traffic classes But, provides weaker services tha Itserv, e.g., Per aggregate badwidth guaratees (premium service) vs. per flow badwidth ad delay guaratees BB is ot a etirely solved problem Sigle poit of failure Hadle oly log term reservatios (hours, days) Sprig Sprig What is the Problem? Iteret has limited resources ad maagemet capabilities Proe to cogestio, ad deial of service Caot provide guaratees Existig solutios Stateless scalable ad robust, but weak etwork services Stateful powerful services, but much less scalable ad robust Stateless vs. Stateful Solutios Stateless solutios routers maitai o fie graied state about traffic + scalable, robust - weak services Stateful solutios routers maitai per-flow state + powerful services guarateed services + high resource utilizatio fie graied differetiatio Protectio - much less scalable ad robust Sprig Sprig

9 Existig Solutios QoS Network support for cogestio cotrol Teet [Ferrari & Verma 89] Itserv [Clark et al 91] ATM [late 80s] Stateful Roud Robi [Nagle 85] Fair Queueig [Demers et al 89] Flow Radom Early Drop (FRED) [Li & Morris 97] Diffserv - [Clark & DecBit [Ramkrisha & Jai 88] Stateless Wroclawski 97] - [Nichols et al 97] Radom Early Detectio (RED) [Floyd & Jacobso 93] BLUE [Feg et al 99] Questio Ca we achieve the best of two worlds, i.e., provide services implemeted by stateful etworks while maitaiig advatages of stateless architectures? Sprig Sprig Scalable Core (SCORE) A trusted ad cotiguous regio of etwork i which edge odes perform per flow maagemet core odes do ot perform per flow maagemet The Approach 1. Defie a referece stateful etwork that implemets the desired service 2. Emulate the fuctioality of the referece etwork i a SCORE etwork edge odes core odes edge odes Referece Stateful Network SCORE Network Sprig Sprig

10 The Idea Istead of havig core routers maitaiig per-flow state have packets carry per-flow state The Techique: Dyamic Packet State (DPS) Igress ode: compute ad isert flow state i packet s header Referece Stateful Network SCORE Network Sprig Sprig The Techique: Dyamic Packet State (DPS) Igress ode: compute ad isert flow state i packet s header The Techique: Dyamic Packet State (DPS) Core ode: process packet based o state it carries ad ode s state update both packet ad ode s state Sprig Sprig

11 The Techique: Dyamic Packet State (DPS) Egress ode: remove state from packet s header Why Guarateed Service Example? Illustrate power ad flexibility of our solutio guarateed service - strogest sematic service proposed i cotext of stateful etworks best-effort cogestio cotrol support differetiated services statistical services guarateed services worse service quality better Sprig Sprig Example: Guarateed Services Goal: provide per-flow delay ad badwidth guaratees How: emulate ideal model i which each flow traverses dedicated liks of capacity r Guarateed Services Defie referece etwork to implemet service cotrol path: per-flow admissio cotrol, reserve capacity r o each lik data path: eforce ideal model, by usig Jitter Virtual Clock (Jitter-VC) scheduler flow (reservatio = r ) r r r Jitter-VC Jitter-VC Jitter-VC Jitter-VC Jitter-VC Jitter-VC Jitter-VC Per-hop packet service time = (packet legth) / r Sprig Referece Stateful Network Sprig

12 Guarateed Services Use DPS to elimiate per-flow state i core cotrol path: emulate per-flow admissio cotrol data path: emulate Jitter-VC by Core-Jitter Virtual Clock (CJVC) Data Path Ideal Model Jitter-VC Jitter-VC Jitter-VC Jitter-VC CJVC CJVC CJVC Stateful solutio: Jitter Virtual Clock Jitter-VC Jitter-VC Jitter-VC CJVC CJVC Stateless solutio: Core-Jitter Virtual Clock Referece Stateful Network CJVC SCORE Network Sprig Sprig Ideal Model: Example legth(p1) / r p1 arrival p2 arrival legth(p2) / r packet arrival time packet trasmissio time (service) i ideal model Sprig time Stateful Solutio: Jitter Virtual Clock (Jitter-VC) With each packet associate eligible time start time of servig packet i ideal model deadlie fiish time of servig packet i ideal model eligible times deadlies Sprig time

13 Jitter-VC Algorithm: schedule eligible packets i icreasig order of their deadlies Property: guaratees that all packets meet their deadlies deadlies Jitter-VC: Eligible Time Computatio Miimum betwee arrival time deadlie at previous ode + propagatio delay deadlie of previous packet eligible time = arrival time eligible times Sprig time eligible time = packet deadlie at previous ode Sprig time Jitter-VC: Eligible Time Computatio Miimum betwee arrival time deadlie at previous ode + propagatio delay deadlie of previous packet eligible time = arrival time Stateless Solutio: Core-Jitter Virtual Clock (CJVC) Goal: elimiate per-flow state elimiate depedecy o previous packet deadlie eligible time = packet deadlie at prev. ode eligible time = prev. packet deadlie usig previous packet s Sprig 2004 deadlie Ë per flow state51time Sprig time

14 Core-Jitter Virtual Clock (CJVC) Solutio: make eligible time greater or equal to previous packet deadlie Sprig time Core-Jitter Virtual Clock (CJVC) How: associate to each packet a slack variable s Delay eligible time at each ode by s eligible time = packet deadlie at prev. ode + s Sprig s time CJVC Properties Theorem: CJVC ad Jitter-VC provide the same edto-ed delay bouds s ca be computed at igress: depeds o curret ad previous packet eligible times (e ad e p ) curret ad previous packet legths (l p ad l) slack variable associated to previous packet (s p ) flow reservatio (r) umber of hops (h) computed at admissio time s = max 0, s p l + p l e + r p e + l h 1 / r Sprig p CJVC Algorithm Each packet carries i its header three variable slack variable s (computed ad iserted by igress) flow s reserved rate r (iserted by igress) ahead of schedule a (iserted by previous ode) Eligible time = arrival time + a + s Deadlie = eligible time + (packet legth) / r NOTE: usig a istead of the deadlie at previous ode Ë o eed for sychroized clocks Sprig

15 Jitter-VC: Core Router CJVC: Core Router Data path Per-flow classificatio Per-flow buffer maagemet Per-flow schedulig Cotrol path istall ad maitai per-flow state for data ad cotrol paths Classifier Per flowl State flow 1 flow 2 flow Buffer maagemet Scheduler Data path Per-flow classificatio Per-flow buffer maagemet Per-packet schedulig Cotrol path Istall ad maitai per-flow state for data ad cotrol paths Cotrol State Buffer maagemet Scheduler Sprig Sprig Cotrol Path: Admissio Cotrol Goal: reserve resources (badwidth) for each flow alog its path Approach: light-weight protocol that does ot require core odes to maitai per-flow state yes yes yes yes Per-hop Admissio Cotrol A ode admits a reservatio r, if C output lik capacity R = r i r C R i R aggregate reservatio: Need: maitai aggregate reservatio R Problem: it requires per flow state to hadle partial reservatio failures ad message loss Sprig Sprig

16 Solutio 1. Estimate aggregate reservatio R est 2. Accout for approximatios ad compute a upper boud R boud, i.e., R boud >= R 3. Use R boud, istead of R, to perform admissio cotrol, i.e., admit a reservatio r if r C R boud Estimatig Aggregate Reservatio (R est ) Observatio: If all flows were sedig at their reserved rates, computig R est is trivial: just measure the traffic throughput, e.g., R est = i S ( a, a+ T ) legth( i) T where S(a, a+t) cotais all packets of all flows received durig [a, a+t) R est 5 Mbps r = 1 2 Mbps r = 2 3Mbps Sprig Sprig Virtual Legth Problem: What if flows do ot sed at their reserved rates? Virtual Legth Problem: What if flows do ot sed at their reserved rates? Solutio: associate to each packet a virtual legth such that if legths of all packets of a flow were equal to their virtual legths, the flow seds at its reserved rate The, use virtual legths istead of actual packet legths to compute R est Sprig Sprig

17 Virtual Legth Defiitio: virtuallegth = r ( crt _ time prev _ time) r flow reserved rate crt_time trasmissio time of curret packet prev_time trasmissio time of previous packet Example: assume a flow with reservatio r = 1 Mbps sedig 1000 bit packets 1.9 ms 1.3 ms 1.2 ms legth Sprig virtual legth Estimatig Aggregate Reservatio (R est ) Use Dyamic Packet State (DPS) Igress ode: upo each packet departure computes the virtual legth ad iserts it i the packet header Core ode: Estimate R est o each output lik as R est = i S ( a, a+ T ) virtuallegth( i) T where S(a, a+t) cotais of all packets of all flows received durig [a, a+t) Sprig Aggregate Reservatio Estimatio: Discussio Core Router The estimatio algorithm is robust i presece of cotrol message loss ad duplicatio their effect is forgotte after oe estimatio iterval If o packet of a flow departs durig a predefied iterval (i.e., maximum iterdeparture time), igress ode geerates a dummy packet Utilizatio <= 1 f, where f = (max. iter-departure time) / (estimatio it.) e.g.: max. iter-departure time = 5s; estimatio it. = 30s Ë utilizatio <= 0.83 Sprig Data path Per-flow classificatio Per-flow buffer maagemet Per-packet schedulig Cotrol path Istall ad maitai per flow state for data ad cotrol paths Cotrol State Buffer maagemet Scheduler Sprig

18 Core Router Data path Per-flow classificatio Per-flow buffer maagemet Per-packet schedulig Cotrol path Istall ad maitai per flow state for data ad cotrol paths Cotrol State Buffer maagemet Scheduler o eed to maitai cosistecy of per-flow state Implemetatio: State Ecodig Problem: Where to isert the state? Possible solutios: betwee lik layer ad etwork layer headers as a IP optio (IP optio 23 allocated by IANA) fid room i IP header Sprig Sprig Implemetatio: State Ecodig Curret solutio 4 bits i DS field (belog to former TOS) 13 bits by reusig fragmet offset Ecodig techiques Take advatage of implicit depedecies betwee state values Temporal multiplexig: use oe field to ecode two states, if these states do ot eed to be simultaeously preseted i each packet Implemetatio FreeBSD Petium II 400 MHz ZNYX etwork cards 10/100 Mbps Etheret Fully implemets cotrol ad data path fuctioalities Maagemet ad moitorig ifrastructure Sprig Sprig

19 Moitorig Ifrastructure Light weight mechaism that allows cotiuous moitorig at packet level Implemetatio Record each packet (28 bytes) IP header ad port umbers arrival, departure or drop times Use raw IP to sed this iformatio to a moitorig site A Simple Experimet Three flows sharig a 10 Mbps lik Flow 1: 1 Mbps reservatio Flow 2: 3 Mbps reservatio with ON/OFF traffic Flow 3: best-effort UDP sedig at > 8 Mbps Moitorig machie aruba (igress) cozumel (core) Sprig Sprig Aggregate Reservatio Computatio 0.5 Mbps reservatio active durig etire iterval 0.5 Mbps reservatio startig at 18 sec; edig at 39 sec 1.2 Rate (Mbps) accept reservatio (0.5 Mbps) termiate reservatio (0.5 Mbps) Aggregate Time (sec) 35 Sprig 45 Sprig Rboud R

20 Coclusios SCORE ad DPS bridge the gap betwee stateless ad stateful solutios Key ideas Istead of core routers maitai per-flow state have packets carry this state Use state to coordiate edge ad core router actios Coclusios (cot d) SCORE architecture ca provide: Service guaratees Network support for cogestio cotrol Service differetiatio DPS compatible with Diffserv: ca greatly ehace the fuctioality while requirig miimal chages Referece Stateful Network SCORE Network Sprig Sprig