第20卷第19期 系 统 仿 真 学 报© Vol 20No 192008年10月 Journalof System Simulation Oct
Server Capacity Requirements for Interactive VODitZhHi ISYintg-jEiani ,WiAN>Bhin-lqiaRn&gD,LCI Yta-Znhan h
(National Digital Sw c ng ys em ng neer ng ec no ogy en er, engz ou 450002,China)
交互式视频点播服务器容量需求
智英建,汪斌强,李雅楠
(国家数字交换系统工程技术研究中心河南郑州450002)
摘 要真正的视频一点播系统(TVOD)能够使用户在任意时刻观看任意节目且支持用户任意的VCR交互但服务器
资源消耗巨大。提出 种新的支持用户操作的流媒体调度方案规则组播固定调度RMFS。 RMFS周期调度常规组
播保证了流合并中目标流的存在。分析了RMF S方案的最佳组播间隔和服务器容量需求。仿真结果证明RMF S可
扩展性好 即使在很高的客户交互强度下 与TVOD相比也能够减少服务器带宽消耗917%。 关键词视频点
播交互调度常规组播
中图分类号 TP393 文献标识码 A 文章编号 1004-731X(2008) 19-5370-04
Introduction RMFS adopts the class-basedadmission controlpolicyto admit
expensive and non-scalable Though many efficient multicast- 1 The Proposed Scheme
which may de,grade user experiences One alternative approach, 1.1 Request admission
[5] is to use dedicated contingency channels for handling VCR The request admission determines whether a requestoperations,however, this reservation causes the waste in server should be admitted by the current state of the VOD serverresources Recently,The static full stream scheduling(SFSS) [6] RMFS divides the request at the server end into three classes:is proposed to support interactive oprations through stream the Multicast Request (MR) generated by the server every Wmerging SFSS uses the simulation method to tune the mulitcast seconds, the Interactive Request (IR)generated by the admittedinterval,which is time-consuming Another potential drawback client,and the Admission Request (AR)generated by the newlyof SFSS is that it can not assure the quality of service(QoS)for arrived clientsinteractive requests when the client interactive intensity is high Let L denote the video length The server reserves
In this paper, the Regular Multicast Fixed Scheduling L/Wchannels to serve MR So the regular multicastscheme (RMFS) is proposed to support the user interactivity (sRtrSe)amcan
FRoeucneidvaetdio:n i2te0m08: -N06at-i1o9nal Grand FRuenvdiasemde:nta2l0R08es-0a8r-c1h5973 Pro ram of whole video from the beginning to the end
Binitne-rqesitanisg,fobcoursnedinon19b6r3o,adpbroafnedssionrf,oPrmhatDionsunpetewrvoirsko;r,LhiiYs cau-nrraen,t brorsneairnch class In particular, the threshold for IR and AR is denoted as l11978,M Sc,her research interest focuses on streaming media
n 1 and n2 be the number of IR and AR requests currently in average frequency at which a client generates valid interactiveservice Suppose that the server capacity used to serve IR and playback operations We use the VCR model depicted in Fig 2AR is N, one IR or AR request is admitted if and only if the Beginning at the PLAY state, the client will randomly transit tofollowing conditions are satisfied: other VCR states or remain at PLAY state according to the
1
When one IR or AR is admitted, the server should initiate a random jump distance in the forward/backward direction,one unicast stream to serve the request immediately At the which is exponentially distributed with meanµf/µb secondssame time one target regular multicast stream should be found, The valid VCR operations include PAUSE,JF and JBif any, to consolidate the unicast stream RMFS adopts the Proposition: The CII is totally determined by the givenlogical-start-time-based method to determine the target stream interactive parameters and the video length
The actual start time defines the time the movie started Proof:Let X1 and X2 denote the mean number of interactionsplaying Suppose the actual start time of one stream is tr,and the for the session without and with ABORT, respectively Let xn,xf,requested video time offset is pr relative to the beginning of the xb and xp be the number of PLAY, JF, JB and PAU during oncevideo The logical st’art time tv for this stream is defined as video session We use the similar method in [8] to find X1tv=tr−pr In Fig 1 PS2 s actual start time is t4,but the log’ical start According to the interactive model,we havetitmet itis t4−pA3,lli eth, t3 Tl hei vildteio server retictortdsthall thte TRSTs logical xn nxb( n b)xf( nf)xpnL
In Fig 1, the client c1 arrives at time t1, and caches video Assume that the arrival of the clients follows a Poisson processdata from RS 1 The missed part of the video is delivered by the with an arrival rateλWe consider the worst case in wh’ich eachdedicated unicast stream PS 1, called patching stream, to enable interactive command leads to a jump out of the user s bufferit to begin playback Assume the client issues one jump backward data and the user is completely merged with the RM before herequest at time t4 and the requested playback time offset relative issues another VCR operation Then arrival rates for IR and ARto the beginning of the video is p3 If the admission condition is are λ1=(1−PB2)λCII and λ2=λ, respectively Under thissatisfied, t’he server initiates one patching stream PS2 to continue cSiurmcumisntanuce, the umnuicltaisctastreaanmdsuonnicavsetracogme aroenoenftlsentghthe Wto/t2altheclient svideodisplay At the sametimetheserverfindsone g p p ,target RS(RS 1 in this example)based on the logical start time of serveRr=resLo/uWrc+e c1o−nPsumpλtioWn ra/2te+R1−isP
PS2 to merge this client back to RS1 The client concurrently buffers h r d ( hB2) id2 bri ( DBi1)ffλ1 Wir/2idata from RS1 and PS2 The length of PS2 is (p4−p3) seconds w ere ri enoithes t e v eo t rdate i erhent at nl g the above2 T
2.1 Client interactive intensity T
The client interactive intensity (CII) is defined as the server channel number requirement achieving the target QoS level
第20卷第19期 系 统 仿 真 学 报 Vol 20No 192008年10月 Journal of System Simulation Oct ,2008
PB1<P1 N l2=l2−1 3.3 Scalability of RMFS
EYxit TVOFDig 7 sihowt-sbthatdthebrethquired servericthapalciitytof RiMFlS atnd
3 Simulation and Numerical Results of 01, 05 and 10 reque,sts/s when C, II is equal to 20 The
and HI=(03, 03, 01, 001,µ) Set C=100,W=1200s, l1=94, Fig 8 CapaCcCI IiItIy vs CII Fig 9 ClliCienatpAarrciviviatalylRRavatsete((raererqqruiuevesstastsl/s/sr))atel2=94, λ=001requests/s, µ=300s-700s Fig 4 shows that the scalculation results fit simulation ones very well In reality,CII Fig 8 shows that the capacity requirement of RMFSis usually less than 10[9],and the calculation error is below 1% increases with CII,while the channel requirement of TVODin this case,which verifies the correctness of the analytical does not change But we can see that RMFS can reduce servermethod for CII. resource by as much as 917%compared to TVOD, even at
Fig 4 CII vs distance Fig 5 Probability vs multicast interval Wi e cl atni see thltat Acalctuhlatedb valuetsi arie tchont stihstent fwith thes mu a on resu s no er o serva on s a e per ormance
· 5372·
RMFS can reduce capacity requirements by as much as 40%at 4 ShovemWerY B L D: i H, t l :D i dhigh interactive level [ ] Alganorithm, Seupport,ing aVCR, FeunactionsesbgynEaxntendIemdplSetmreeanmtatMioenr:giAnng
4 Conclusions [J] Computer Science(S1002-137X),2005,32(3): 88-94
indteriactiive platybalck lciontrolds RMFlSid atdopths the i clatss-bt ased [6] Wong Y W, ,Lee J,Y B, Li V O K, et al Supporting Interactivea m ss on con ro po cy an conso a es e un cas s ream Video-on-Demand with Adaptive Multicast Streaming[J] IEEE Transthrough stream merging We derive the optimal multicast on circuits and systems for video technology(S 1558-2205), 2007,interval and server capacity requirement for RMFS Numerical 17(2): 129-142and simulation results show that RMFS scales well compared to [7] MDiutnrdiburt Pd,VSiodod-An-KD,mSiamndonS Rt CmlassJ-BaIEseEdEATcrcaenss Ciontritol afnodrTVOD and Patching even at high interactive intensity RMFS s stemufoer videoeotecohnoleo (S15y5s8e-22s05[)]2005 15(7):s84c4-c8u53scan achieve zero-delay service, and can be generalized to many [8] Mya H D, Shin K G Pegrfyormance Analy,sis of, the Interactivity f
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