Network Design and Appraisal

Transcription

1 Qualty-of-Servce IP QoS archtectures Ulrch Fedler Introductory Example Applcaton: IP telephony wth fxed encodng bt rate Network delay s varable, packets may get lost Network qualty-of servce requrements Network delay below 50msec Outage duraton less than 50 mcroseconds Number of outages less than fve per mnute Mcrophone Sampler, A D converter Buffer, D A Ulrch Fedler IP QoS archtectures 1 Ulrch Fedler IP QoS archtectures 2 Varablty of Network Delay Applcaton Taxonomy Playback buffers can accommodate network delay varatons. How large should the playback delay be? Do we need support from the network to meet the QoS requrements? 3 90% 97% 98% 99% Real tme vs elastc applcatons Adaptve applcatons (rate and/or delay) Applcatons Real tme Elastc Packets (%) 2 Tolerant Intolerant Interactve Interactve bulk Asynchronous 1 Adaptve Nonadaptve Rate-adaptve Nonadaptve 5 10 Delay (mllseconds) 20 Delayadaptve Rateadaptve Ulrch Fedler IP QoS archtectures 3 Ulrch Fedler IP QoS archtectures 4

2 Goals Integrated Servces You know how to classfy applcatons wth regards to QoS requrements You can gve an overvew over the IntServ archtecture Per flow servce dfferentaton. Offers guaranteed, controlled-load, and best-effort servce. Sgnalng protocol RSVP. You can gve an overvew on the DffServ archtecture Per class servce dfferentaton. At network edge classfy ncomng traffc and mark packets. Insde the network dfferentate servce for packets accordngly. Forwardng per-hop behavor (PHB) Expedted, assured, and best-effort forwardng You know that end-to-end servce guarantees are bult on PHBs addtonally requre bandwth management. You know the three key propertes of schedulng algorthms You can explan prorty, round-robn, and weghted far queueng schedulng You can explan actve queue management and random-early detecton. Server Best Effort Flows Clent Ulrch Fedler IP QoS archtectures 5 Ulrch Fedler IP QoS archtectures 6 Integrated Servces Controlled Load IP QoS archtecture that s based on per flow servce dfferentaton Best Effort Controlled-load servce relable and enhanced best effort servce Guaranteed servce Fxed delay bound Ths s acheved wth per flow resource reservatons Recever-orented Multcast capable Bandwdth s reserved Per-packet delay s not guaranteed Packet delay may vary Performs lke a lghtly loaded Best Effort network Ulrch Fedler IP QoS archtectures 7 Ulrch Fedler IP QoS archtectures 8

3 Guaranteed Servce Implementaton of IntServ Bandwdth s reserved Per-packet delay s guaranteed bounded IntServ ams at provdng QoS on a per flow bass For each flow, applcatons use a sgnalng protocol (RSVP) to reserve requred network resources requred to obtan guaranteed delay/rate. Edge routers perform Per flow admsson control All routers perform Multfeld classfcaton for each packet Packet schedulng based on the classfcaton Ulrch Fedler IP QoS archtectures 9 Ulrch Fedler IP QoS archtectures 10 RSVP Sgnalng RSVP Sgnalng Store prelmnary nformaton on the transcever n each node on the traffc path (downstream) Sender sends Path message contanng sender Tspec. Recever can then trgger resource reservatons by sendng a reservaton request (upstream). Recever sends Resv message contanng Rspec. Intermedate routers can accept or reject. Reject: Error message to recever. Accept: Lnk bandwdth and buffer space allocated, flow state nformaton nstalled, forward Resv message. Routers mantan soft state Perodc keep alve messages requred. Ulrch Fedler IP QoS archtectures 11 Ulrch Fedler IP QoS archtectures 12

4 RSVP on a Router Admsson Control Token bucket Parameters: rate: 1B/s-40TB/s Bucket depth peak rate mnmum polced unt maxmum packet sze Ulrch Fedler IP QoS archtectures 13 Ulrch Fedler IP QoS archtectures 14 Path Msg s Sender Tspec Obj. Length = 36 Class-Num = 12 C-Type=2 Verson Reserved IS Length Servce # Reserved Servce Data Length ParamID=127 Flags Parameter Data Length Token Rate (r) Token Bucket Sze (b) Peak Data Rate (p) Mnmum Polced Unt (m) Maxmum Packet Sze (M) Contans FlterSpec object Resv Message Used to set parameters n the packet-classfer process. FlowSpec object Used to set parameters n a node s packet-schedulng process Perodcally resend (e.g. all 30 sec) to mantan soft-state Ulrch Fedler IP QoS archtectures 15 Ulrch Fedler IP QoS archtectures 16

5 Mergng Reservatons (Controlled Load Style) Deployment of IntServ Most Csco Routers Support Intserv and RSVP but not enabled Mcrosoft Wndows 98+ has support for RSVP Up to now IntServ hasn t been used much Presumably ths s due large mplementaton complexty Lack of scalablty n the archtecture Ulrch Fedler IP QoS archtectures 17 Ulrch Fedler IP QoS archtectures 18 DffServ (Dfferentated Servces) DffServ IP QoS archtecture that s based on per class servce dfferentaton At network edge aggregate flows wth smlar QoS Insde the network process packets accordngly (per-hop-behavor) End-to-end servces are bult on behavoral aggregates At network edge: classfy and mark packets; polce flows In core network: servce packets accordng to classfcaton Access network At network edge aggregate flows wth smlar QoS Edge routers classfy ncomng traffc accordng to polcy specfed ( admsson control ). Packets are marked wth a code pont that reflects the desred level of servce (e.g. a bt n IPv4 TOS byte). Insde the network process packets accordngly Core routers dfferentate ncomng packets based on code pont (schedulng, queue management). End-to-end servces are bult on behavoral aggregates whch rely on per-hop-behavor (PHB) Resource manager (bandwdth broker, etc.). Ulrch Fedler IP QoS archtectures 19 Ulrch Fedler IP QoS archtectures 20

6 In Edge Routers In Core Routers Edge routers classfy and polce ncomng traffc. Classfer: classfes packets. Meter: checks whether the traffc falls wthn the negotated profle. Marker: marks traffc that falls wthn profle wth a codepont (e.g. a bt n IPv4 TOS byte). Shaper/dropper: shapes traffc/dscards packets. Core routers dfferentate ncomng packets accordng to the forwardng per-hop-behavor (PHB) specfed for the partcular packet class Schedulng Queue Management It s not specfed what mechansms to use to ensure the requred PHB performance behavor. Ulrch Fedler IP QoS archtectures 21 Ulrch Fedler IP QoS archtectures 22 Forwardng PHBs Forwardng (PHB) Expedted Forwardng (EF) Servce class that enables provders to offer leased-lne type of servce. Low delay, low jtter Intended applcatons: VoIP, vdeo etc. Assured Forwardng (AF) Preferental servce classes for data traffc Best Effort (BE) Expedted Forwardng (EF): Guarantees for the EF traffc Mnmum rate Traffc characterstcs should not sgnfcantly be nfluenced by the other traffc classes. Admtted based on peak rate. Non-conformant traffc s dropped or shaped. Ulrch Fedler IP QoS archtectures 23 Ulrch Fedler IP QoS archtectures 24

7 Forwardng (PHB) Schedulng Assured Forwardng (AF): AF defnes 4 classes wth some bandwdth and buffers allocated to them. The ntent s that t wll be used to mplement servces that dffer relatve to each other (e.g., gold, slver, ). Wthn each class, there are three drop prortes, whch affect whch packets wll get dropped frst f there s congeston. Lots of studes on how these classes and drop prortes nteract wth TCP flow control. Non-conformant traffc s remarked. Schedulng IP packets s not trval snce IP packets have varable sze Schedulng Algorthms make a trade off farness complexty sharp bounds on packet delay Ulrch Fedler IP QoS archtectures 25 Ulrch Fedler IP QoS archtectures 26 Prorty Schedulng Round Robn Schedulng The scheduler serves a packet from prorty level k only f there are no packets awatng servce n levels k+1, k+2,, n Smple mplementaton Hghest prorty level packets wll always have low delays. Starvaton s crtcal However, approprate admsson control and polcng to restrct servce rates from all but the lowest prorty level Cyclcally scan class queues, servng packets one from each class (f avalable). Smple mplementaton. Provdes protecton aganst msbehavng sources (also guarantees a mnmum bandwdth to every connecton). Hghest prorty level packets have to wat untl end of the round. Ulrch Fedler IP QoS archtectures 27 Ulrch Fedler IP QoS archtectures 28

8 Weghted Far Queueng WFQ Emulates Flud System Hgh mplementaton complexty Guaranteed mnmal rate Tght worst-case delay bounds (for polced traffc) Far sharng of surplus bandwdth Often referred to for performance comparson reasons W W t W : flow through ppe n nterval [t k,t m ];, j contnuously backlogged: W ( tk, tm) Wj( tk, tm) j Flow delay: W Ulrch Fedler IP QoS archtectures 29 Ulrch Fedler IP QoS archtectures 30 Packetzed WFQ WFQ s Algorthm length L mux t t Ulrch Fedler IP QoS archtectures 31 Schedule packets accordng to fnshed servce n flud system L L Bounded delay Bounded unfarness: e.g. L L j j max W( tk, tm) Wj( tk, tm) f ( t) j Introduce a vrtual servce tme measure V ( t dt) V ( t) Compute schedulng tags based on updatng the set of backlogged connectons at each packet departure/arrval event k k1 k Start tag S max{ F, V( a )} next( t) L dt R B ( t ) k k k F S B( t) t ( Fmn V ( t)) next departure (real-tme) Ulrch Fedler IP QoS archtectures 32 R Fnsh tag

9 WFQ varants Queue Management Estmate vrtual servce measure: SCFQ: self-clocked far queung (Golestan et al. 1994, Infocom) SFQ: start-tme far queung (Goyal et al. 1997, IEEE/ACM ToN) MD-SCFQ: mnmum delay SCFQ (Chuss et al. 1998, Infocom) tme-shft schedulng (Gobb et al. 1998, IEEE/ACM ToN) MSFQ: mnmum startng tag far queung (Chu et al. 1997, IEICE ToC) Use two prorty queues: LFVC: leap forward vrtual clock (Sur et al. 1997, ACM Symp. PDC) WF 2 Q, WF 2 Q+ (Bennett et al. 1997, IEEE/ACM ToN) SPFQ: startng potental far queung (Stlads et al. 1998, IEEE/ACM ToN) Subsample vrtual servce measure: FBFQ: frame-based far queung (Stlads et al. 1998, IEEE/ACM ToN) VTRR: vrtual tme based Round Robn (Cho et al. 1998, ICC) DRR: Defct Round Robn (Shreedhar et al. 1996, IEEE/ACM ToN) Tal-drop FIFO queue management Random Drop queue management Ulrch Fedler IP QoS archtectures 33 Ulrch Fedler IP QoS archtectures 34 Actve Queue Management Random-Early Detecton Introduce actve queue management snce FIFO drop tal queueng has some drawbacks Full-queue problem Latency s ncreased when the queue s constantly full. A queue should only be used to accommodate short bursts. -> early drop packets Lock-out problem Small subset of flows monopolze lnk durng congeston (hgh rate flows). -> ntroduce randomzaton Random-Early Detecton (RED) Start to randomly drop packets before queue s full Vary drop probablty wth queue fll state Use smoothed queue length nstead of queue length to allow the queue to accommodate short bursts Droppng/ Markng Probablty 1 max p 0 Mn th Max th Average Queue Length Ulrch Fedler IP QoS archtectures 35 Ulrch Fedler IP QoS archtectures 36

10 RED The RED algorthm Instantaneous queue length Max queue length Max threshold Mn threshold Tme Forced drop Probablstc early drop No drop for each packet arrval: calculate the average queue sze avg f avg mnth do nothng else f mnth avg maxth calculate drop probablty p drop arrvng packet wth probablty p else f maxth avg drop the arrvng packet Ulrch Fedler IP QoS archtectures 37 Ulrch Fedler IP QoS archtectures 38 Average Queue Length n RED RED Parameter Settngs Use an exponental average of the queue length where q s the newly measured queue length. Ths exponental weghted movng average s desgned such that short-term ncreases n queue sze from bursty traffc or transent congeston do not sgnfcantly ncrease average queue sze. RED s controlled by 5 parameters qlen The maxmum length of the queue w q Weghtng factor for average queue length computaton mn th Mnmum queue length for trggerng probablstc drops max th Queue length threshold for trggerng forced drops max p The maxmum drop probablty Ths s what S. Floyd suggests <= w q <= Set max th dependng on the maxmum tolerable delay. Set max th at least twce mn th Ulrch Fedler IP QoS archtectures 39 Ulrch Fedler IP QoS archtectures 40

11 RED Issues Extremely senstve to parameter settngs Wld queue oscllatons upon load changes Fal to prevent buffer overflow as the number of sources ncreases Does not help fragle flows (e.g.: small wndow flows or retransmtted packets) Does not adequately solate cooperatve flows from non-cooperatve flows RED varants Adaptve RED -- ARED (Feng, Kandlur, Saha, Shn 1999) Snce RED s extremely senstve to #sources and parameter settngs adapt max p to load No per-flow nformaton needed Flow RED -- FRED (Lng, Morrs 1997) Use per-flow accountng to penalze flows that frequently lead to buffer overflows BLUE (Feng, Kandlur, Saha, Shn 1999) On buffer overflow, ncrement markng probablty, on dle lnk decrease markng probablty to avod wld oscllatons of RED that typcally lead to cyclc overflow and underutlzaton Stochastc Far Blue (Feng, Kandlur, Saha, Shn 2000) Protecton aganst non-adaptve flows Generalzed Random Early Evason Network -- GREEN (Feng, Kapada, Thulasdasan, 2002) Ensure farness between TCP flows usng knowledge on TCP steady state Ulrch Fedler IP QoS archtectures 41 Ulrch Fedler IP QoS archtectures 42 ACM n Dffserv Fnal Word on DffServ RIO (random drop n/out of profle) Use dfferent (max,mn) thresholds to mplement P(drop) drop precedence 1.0 MaxP Mn out Mn n Max out Max n AvgLen No scalablty problem Servces are allocated per class Complexty at network edge Markng, shapng, etc. Buldng end-to-end servces based on per-hop-behavor s a dffcult ssue Buldng premum servce based on expedted forwardng requres bandwdth management/traffc engneerng n addton to DffServ Dffcult over doman boundares EF/BE has been deployed on the Qbone So far lttle success Ulrch Fedler IP QoS archtectures 43 Ulrch Fedler IP QoS archtectures 44

12 References QoS X. Xao, L. N Internet QoS: A Bg Pcture, IEEE Network March/Aprl 1999 P. Ferguson, G. Huston, Qualty of Servce, Delverng QoS on the Internet and n Corporate Networks, John Wley&Sons, Inc., 1998 IntServ RFC 1633 (Integrated Servces), 2205 (RSVP), 2210 (Usng RVSP wth IntServ), 221 (Controlled Load Servce), 2212 (Guaranteed Servce) DffServ K. Nchol, V. Jacobsen, L. Zhang, A two-bt dfferentated servces archtecture for the Internet, RFC 2638, July 1999 Summary Introductory example VoIP, applcaton taxonometry IntServ archtecture Per flow servce dfferentaton. Offers guaranteed, controlled-load, and best-effort servce. Sgnalng protocol: RSVP. DffServ archtecture Per class servce dfferentaton. At network edge classfy ncomng traffc and mark packets. Insde the network dfferentate servce for packets accordngly. Forwardng per-hop behavor (PHB) Expedted, assured, and best-effort forwardng Schedulng Prorty, round-robn, and weghted far queueng schedulng Actve queue management Random-early detecton End-to-end servce guarantees bult on PHBs addtonally requre bandwth management. Ulrch Fedler IP QoS archtectures 45 Ulrch Fedler IP QoS archtectures 46