Design of Modified RED Implemented in a Class Based CIOQ Switch

Transcription

1 Desgn of Modfed RED Imlemented n a Class Based CIOQ Swtch Chengchen Hu, Bn Lu Deartment of Comuter Scence and Technology, Tsnghua Unversty Bejng, P. R. Chna, hucc03@ mals.tsnghua.edu.cn, lub@tsnghua.edu.cn Abstract- A Combned Inut and Outut Queued (CIOQ) swtch w a certan seedu of S (1<S<N) can acheve 100% roughut and offer QoS guarantees. In s aer, we resent e deloyment of Random Early Detecton (RED) on a CIOQ swtch at has rorty queues w shared buffer (class based swtch). We frst gve an estmated model to concrete at one RED controller er outut ort s suffcent for a CIOQ swtch as long as e seedu s larger an two, and en we extend s concluson to roose a class based CIOQ swtch structure. Furermore, we modfy RED to roose two schemes based on such structure by adatvely settng RED arameters and ntroduce a dynamc rorty queue schedulng scheme. The smulaton results rove and demonstrate at our analyss s correct and e roosed algorms can acheve hgh utlzaton and rovde delay guarantees. 1. INTRODUCTION There are ree dfferent queung strateges used n swtches [1] (see Fgure 1): Inut Queue (IQ), Outut Queue (OQ) and Combned Inut and Outut Queue (CIOQ). IQ strategy can acheve 100% roughut wout any seedu by e means of rtual Outut Queue (OQ). However, t can not rovde acket delay guarantees. OQ strategy offer Qualty of Servce (QoS) guarantees, but t must run N tmes as fast as e lne rate for an N N swtch. CIOQ strategy s known to acheve 100% roughut and offer QoS guarantees w a certan seedu of S ( 1 < S < N). A CIOQ swtch s a romsng means to meet e bandwd and QoS requrement of next generaton Internet. Tradtonal queue management schemes are based on Dro Tal (DT) olcy, whch means at t doesn t dro ackets unless e queue overflows. DT olcy has two major drawbacks [2]. One s lockout henomenon. In some stuatons, DT allows a sngle connecton or a few flows to monoolze queue sace, and revent oer flows from gettng free buffer sace to squeeze nto. The oer s global synchronzaton. If a burst s arrvng when e queue s full or almost full, t wll cause multle connectons to dro ackets and ntroduce global synchronzaton at causes low lnk utlzaton and roughut. Ths has drven e IETF (Internet Inut Queue Outut Queue Combned Inut and Outut Queue Fgure 1 Queueng strateges Engneerng Task Force) to recommend e use of Actve Queue Management (AQM) n Internet routers [3]. The goal of AQM s to detect ncent congeston early and convey congeston notfcaton to e end-host, allowng em to back off before queue overflows and acket loss occurs. One of e most romnent and wdely studed AQM scheme s Random Early Detecton (RED) [4], whch has been used n commercal swtches and routers. RED gateways can mnmze bases aganst burst sources, revent global synchronzaton, and reduce acket loss usng a smle, low-overhead algorm. However, AQM have so far been studed only n e context of a sngle queue. It s necessary to study AQM on mult-queue system lke CIOQ swtch. The oneerng work s for examle [5] whch dscussed mlementaton of Rate Base (RB) AQM n a CIOQ swtch. In s aer, we consder e outut conflct and resent e deloyment of modfed RED on a CIOQ swtch at takes rorty queues w shared buffer nto account. It s showed at Backlog Based (BB) AQM lke RED s nferor to RB AQM. Unfortunately, t s dffcult and even not ractcal for ndustral mlementaton to estmate e flow arrval rate accurately whch RB AQM needed. Albet beng senstve w arameters settng, RED algorm s stll chosen as e semnal algorm. Our choce ams at consderng well-known reresentatve of

2 AQM whch can be ractcally mlemented. Some modfcatons of RED also have been done n order to deloy on shared buffer and adatvely set RED arameters. The modfcaton removes e man drawbacks of RED. The remander of s aer starts w Secton 2, whch roose a swtch archtecture alyng RED. In Secton 3 secfes e queue management utlzng a class based queue w shared buffer ncludng e modfcatons of RED algorm and a dynamc rorty queue schedulng scheme. Furer, we dscuss e arameters settng and smulate n secton 4. Fnally, conclusons are resented n Secton PROPOSED SWITCH STRUCTURE Fgure 2 shows e logcal structure of a CIOQ swtch w a seedu of S. Packets are stored at nut nterfaces and outut nterfaces. Each nut manages one Frst In Frst Out (FIFO) queue for each outut, hence, a total of N = searaton ermts to avod erformance degradatons due to well known Head of e Lne (HOL) blockng and s called rtual Outut Queueng (OQ). Each outut only mantans one queue for acket bufferng. 2 N N nut queues are resented. Ths queue λ11 u11 λ1n λ N1 λ NN u 1 N u N1 u NN Fgure 2 a CIOQ swtch structure We use OQ j ( 0 < N, 0 < j N ) to dentfy e queue whch buffer e ackets leave for outut j at nut, and we let λ j be e average acket arrval rate at OQ j. If λ j 1 and λ j j 1, e CIOQ swtch w a seedu of 2 s suffcent to acheve 100% roughut and mmc e outut queued swtch. When several nuts have ackets destne for e same outut, us t may has λ > j 1, and e congeston wll occur. Here comes e queston at wheer t s necessary to mlement RED mechansm at bo IQ (nut queue) art and OQ (nut queue) art. If not, where to mlement RED controller, at IQ art or at OQ art? 2.1. IMPLEMENTING RED IN A CIOQ SWITCH We assume end-to-end congeston control s stable and source rates converge to a steady state at or below e network caacty. Then we only need mlement RED controller at e art where congeston wll occur frst. Secfcally, f OQ (or IQ) art wll frst enter congeston state, e RED controller at s art should start congeston control rocess. As congeston control s stable, e source slow down and e oer IQ (or OQ) art can also avod congeston. To justfy where congeston occurs frst, we can aroxmately examne where e queue leng grows more aggressvely. We examne e nadmssble stuaton, where λ 1 j > to a certan outut ort j. We suose: Swtch fabrc oerates at e rate of ( 1 < S ) The average arrval rate and e average servce rate at OQj are λ j and u j resectvely ( 0 λj, u j 1). As e seedu s S, e maxmum lnk rate between lne card and swtch fabrc s S. Swtch has a work conservng scheduler to match nut ort w outut ort. Therefore e grow of OQ j s λ j u and e j grow of e queue at outut ort j s 1. We comare em below: λ j u j 1 (1) In (1), f e left term s larger an e rght term, queue leng at IQ art wll grow faster, vce versa. Consder e worst case: N nuts all have traffc destned for e same outut,.e. N nuts share e lnk rate between lne cards and swtch fabrc. So u j = / N. Substtute t nto (1), and we get: λ j 1 N λj 1/ N Now t s clear at f e nequaton (2) below s met, queue leng at OQ art wll grow faster, and t can be aroxmately to say at e OQ art wll frst enter congeston state. In oer word, we only need to mlement RED controller at OQ art, when e condton below s met. λj > (2) 1/ N The rght art of (2) s a monotonc ncreasng functon of N and S >. When N, we have λj lm S > lm = λj (3) N N 1/ N Snce 0 λ j 1, we can draw e concluson at t s suffcent to deloy one RED controller er outut queue f S > 2.

3 2.2. EXTENDING TO CBQ When ackets enter e swtch, ey wll be classfed nto dfferent classes uon a label n a Mult Protocol Label Swtchng (MPLS) system or uon e DffServ doman for a secfc Per Hob Behavor (PHB) [6]. Class Based Queue (CBQ) sets dfferent queues, each dedcated to a dfferent acket class or an aggregate of acket classes. To suort CBQ, each queue n fgure 2, no mater each OQ or each outut queue, s relaced by m dfferent queues, where m s e number of classes e swtch suorts. Shared memory buffers ossess some advantages, alough ey face some techncal challenges, such as seed, access and memory management. They rovde hgh buffer utlzaton and us mrove acket loss erformance at e tme of congeston. We set CBQ w a sngle large shared buffer at s shared among dfferent queues (classes). Thus, ere are N shared buffers at each nut and one shared buffer at each outut. The aforementoned concluson s stll true under s stuaton as we select shared buffer to set CBQ. And at each outut ort, ere s a RED controller whch decdes e dro/mark olcy for e whole shared buffer. The dfference s at one RED controller for er outut controls a number of queues nstead of a sngle queue. Fgure 3 llustrates e roosed swtch structure. 3. QUEUE MANAGEMENT We have roosed a class based CIOQ swtch structure alyng RED, and here we have two more roblems need to be solved. Frst, whereas RED has been so far nvestgated n e context of a sngle queue, very few studes, such as [7][8], have attemted to examne e mlementaton of RED on multle queues w shared buffer. Snce we use shared buffer to set CBQ, some modfcaton should be done to RED algorm. The second roblem s how to allocate bandwd among dfferent CBQs at have dfferent rortes. To schedule ackets from a queue, a schedulng algorm has to be used to evaluate modfed RED erformance MODIFICATION OF RED ALOGRITHM The smlest meod to mlement RED on shared buffer s to ermanently dvde shared buffer nto several queues at have er own fxed bufferng sace avalable and RED s aled to each queue. It s equvalent to a set of ndeendent queues. From e smulatve and analytc results n [10] and our ror work [8], t suffers from hgher dro rato and buffer underutlzaton. Schemes roosed n [7] can also be mlemented on a shared buffer. However, ey are senstve to dfferent congeston levels [8], because ese congeston avodance Inut1 schemes start er congeston control at e same reshold under dfferent congeston levels. Here we roose two schemes whch modfy e orgnal RED algorm at e motvatons of dynamcally settng e arameters and mlementng on shared buffer. Before secfyng e schemes, we state some termnology frst. Let avg, mn, max be average queue leng, mnmum reshold and maxmum reshold of e whole buffer ndeendently, whle avg, mn, max be e same arameters of each queue. The frst scheme s RED-DT (RED w Dynamc Threshold). The rncle s: when congeston level s lght, e arameters mn and max are automatcally tuned u n order to trgger congeston control later, and when congeston level s heavy, e arameters mn and max s automatcally tuned down n order to trgger congeston control earler. At tme t, let R(t) be e remanng unused buffer sze, Q (t) be e current leng of queue, Q(t) be e sum of all e queue leng,.e. Q = Q. At any tme t, when a new acket arrves at queue, avg (t) s calculated w a gven queue weght w q usng e RED meod [4]. At e same tme t, a mnmum reshold mn (t) and a maxmum reshold max (t) are refreshed accordng to e formulas below, n whch β > α s requred and e total buffer sze s suosed to be L. mn = α R( t) = α (L Q( t)) (4) max = β R( t) = β (L Q( t)) (5) The RED-DT scheme can be descrbed by e followng seudo code: for each acket of class arrval at tme t calculate avg (t) as RED; calculate e mn,max (formula 4 and 5); f mn avg < max calculate mark robablty a as RED; w robablty a mark e arrvng acket; else f avg max RED Controller RED Controller Fgure 3 roosed CIOQ swtch structure w CBQ

4 mark all ackets; The second scheme s ARED-CS (Adatve RED w Comlete Sharng). Adatve verson of RED has been roosed w e am of auto tunng e random mark robablty max under dfferent traffc [11]. We roose algorm ARED-CS by modfyng s algorm on mult-queues comletely sharng e buffer. The rncle s to nfer wheer RED should become more or less aggressve by examnng e varatons n average queue leng. If e average queue leng oscllates around mn, en e RED s too aggressve. Thus, e algorm multlcatvely decreases e value of max. On e oer hand, f t oscllates around max, en e detecton mechansm s too conservatve. Thus, e algorm addtvely ncreases e value of max. The ARED-CS scheme can be descrbed by two arallel rocesses and e seudo code s shown below: Process 1: for each acket of class arrval at tme t calculate avg (t) & avg (t) as RED; f mn avg( t) < max f avg > mn calculate mark robablty a as RED; w robablty a mark e arrvng acket; else f avg max mark all ackets; Process 2: for every nterval seconds for each queue f avg 0.4 max mn & max 0. 5 > = max + a max f avg < 0.6max+ 0.4mn& max max = max b 3.2. DYNAMIC PRIORITY QUEUE SCHDULING A dynamc rorty queue schedulng scheme s ntroduced to allocate bandwd among dfferent CBQs. In [9], a dynamc rorty queue modeled for two traffc tyes was resented. In s aer, we extend t to multrorty case. Suose at ere are m rorty queues. Queue has hgher rorty an queue j, f 1 < j m. Then each queue ( 1 < m) s gven a redefned queue leng reshold L, whch requres L 1 < L2 < L < Lm. If no queue exceeds ts reshold, e hghest rorty queue at s not emty s scheduled. Oerwse, e lowest rorty queue at exceeds ts reshold wll be scheduled untl ts leng decreased under ts reshold. 4. PARAMETERS SETTING AND SIMULATION RED-DT and ARED-CS are bo smulated n s secton. To smlfy e smulaton, we assume at e swtch has four nuts, and suorts two classes of queues, one hgh rorty queue and one low rorty queue. Each queue at IQ art, eer hgh rorty or low rorty, has 100 TCP connectons. Every nut ort s ut under e traffc of Posson Arrval w e same load at e begnnng of e smulaton, and hgh rorty traffc occues 10% of e aggregate traffc. To study e erformance when congeston occurs, ackets at arrve at any nut all destne for e same outut. The toology for e exerments s defned n fgure 4. Fgure 4 Toology for smulaton RED Controller The shared buffer sace s set to be 100 ackets (fxed leng acket). The reshold L 2 of dynamc rorty queue scheme for low rorty queue s 50. The reason for s s to make sure at e leng of low rorty queue s around 50. Then we decde e arameters for RED controller. Whle usng RED-DT as e control algorm, e buffer occuancy wll be lmted to: Q = k max (6) k s e number of actve queues. Substtute (6) nto (5) and we get: t k β max ( ) = + L 1 k β. As mentoned above, we want to let e leng of low rorty queue be around 50, at s max = L / 2. Low rorty traffc should be much more actve an hgh rorty traffc (e arrval rate of low rorty traffc s usually 10 tmes more an at of hgh rorty traffc), us k can be aroxmately set to be one. Then we solve out at β=1. As mn s 1/3 of max at s recommended by orgnal RED, e arameter of α s set to be aroxmately 1/3 of β, α =0.3.

5 Whle usng ARED-CS as e control algorm, we choose a = mn( 0.01, max / 4) and b = 0. 9 from [10]. The reason for settng arameters a and b s secfed ere. max s set to be buffer sze, mn s set to be 1/3 of max, mn s set to be 1/2 of mn. We frst examne e outut lnk utlzaton. Every nut ort s njected w e traffc w load of 1.0. By ncreasng e seedu from 2 to 4.25, we fnd e utlzaton s almost e same for eer RED-DT algorm or ARED-CS algorm (see fgure 5). In oer word, seedu has lttle effect on lnk utlzaton. Fgure 5 also llustrates at ARED-CS has much hgher lnk utlzaton an RED-DT. We fx e seedu at two to do e followng exerments. By ncreasng e load from 0.10 to 1.00 n every nut ort, oututs come to suffer from congeston. Fgure 6 lsts roughuts under dfferent nut loads. It ndcates at two schemes behave smlarly when aggregate offer load s below 1.00 (0.25 for each nut). As load ncreases contnuously, e roughut decreases. It s ndcated at RED-DT obtans hgher roughut, alough e decreasng sloe of two algorms are aroxmately e same. Fgure 7 shows e queue leng of bo IQ and OQ art whle RED-DT algorm s used. Note at e mean queue lengs of IQ art, no matter hgh rorty queue or low rorty queue, are extremely low. It agrees w e analyss n secton 2 at t doesn t need to mlement RED controller at IQ art. And t also agrees w e fact at a CIOQ swtch w a seedu of two can mmc an outut swtch. The leng of low rorty outut queue, as we exected, s around 50, and w lttle oscllaton. The leng of hgh rorty outut queue s at very low level, and also w lttle oscllaton. Short leng means short delay, and lttle leng oscllaton means lttle delay jtters. Fgure 8 demonstrates e queue leng of bo IQ and OQ art whle ARED-CS algorm s used. As e same w RED-DT, e mean queue lengs of IQ art are extremely low. The leng of low rorty outut queue, as we exected, s around 50, and w lttle oscllaton. However, e leng of low rorty outut queue oscllates serously whch wll brng delay jtter. It s clear rough our smulaton at RED-DT has better jtter erformance and ARED-CS has hgher lnk utlzaton. One can choose schemes deends on what he cares. 5. CONCLUSION Ths aer addresses e desgn of RED mlemented on a CIOQ swtch at has rorty queues w shared buffer. The frst major contrbuton of s aer s to gve an estmated model to rove at one RED controller er outut ort s suffcent for a CIOQ swtch when e Fgure 5 Seedu vs. Lnk utlzaton Fgure 6 Load vs. Throughut seedu s larger an 2, and en extend s concluson to roose a class based CIOQ swtch structure w shared buffer based on rorty queues. The second major contrbuton of s aer s to roose two novel algorms whch dynamcally set RED arameters and can be mlemented on shared buffer. The smulaton results show at our analyss s correct and demonstrate at e roosed schemes can acheve hgh utlzaton and offer delay guarantees. ACKNOWLEDGMENT Ths research s suorted by NSFC (No and No ) and Chna 863 Hgh-tech Plan (No. 2003AA and No. 2002AA ). Furermore, e auors ank Yang Xu and We L for suggestng e roblem and dscussons. REFERENCES [1] Shang-Tse Chuang, Ashsh Goel, Nck McKeown and Balaj Prabhakar. Matchng Outut Queueng w a Combned Inut Outut Queued Swtch [A]; INFOCOM '99 [C], vol. (3): , March 1999 [2] H. Jonaan Chao and Xaole Guo. Qualty of Servce Control n Hgh-Seed Network [M]. John Wley &Sons, Inc, New York, [3] B. Braden, D. Clark, et al. Recommendatons on Queue Management and Congeston Avodance n e Internet [S]. RFC [4] S. Floyd and. Jacobson. Random early detecton gateways for congeston avodance [J]. IEEE/ACM Transactons on Networkng. ol. 1(4): , August [5] Bartek Wydrowsk and Moshe Zukerman; Imlementaton of actve queue management n a combned nut and outut queued swtch[a]; ICC '03 [C], ol. 1, 2003 [6] S. Blake, D. Black, M. Carlson, E. Daves, W. Wess, and Z.

6 Wang, An archtecture for dfferentated Servces [S] RFC 2475, December [7] Farshd Agharebarast and ctor C. M. Leung; Imrovng e erformance of RED deloyment on a class based queue w shared buffers [A]; GLOBECOM '01[C], vol.(4): Nov [8] Chengchen Hu and Bn Lu; RED w Otmal Dynamc Threshold Deloyment on Shared Buffer [A]; AINA 2004 [C], March, [9] Knessl C, Cho DI and Ter C; A dynamc rorty queue model for smultaneous servce of two traffc tyes [J]; SIAM Journal on Aled Maematcs ol. 63 (2): JAN 2003 [10] Farshd Agharebarast; ctor C. M. Leung; On e deloyment of RED on shared-memory buffers [J]; Communcatons Letters, IEEE, ol. 6(10) : , Oct [11] S. Floyd, R. Gummad, and S. Shenker. Adatve RED: An Algorm for Increasng e Robustness of RED's Actve Queue Management [R]. ACIRI Techncal Reort, 2001 [12] W.-C. Feng, D.D. Kandlur, D. Saha, K.G. Shn A self-confgurng RED gateway [A]; INFOCOM '99 [C], ol.(3) : , March 1999 Fgure 7 queue leng of nut & outut queue (RED-DT) Fgure 8 queue leng of nut & outut queue (ARED-CS)