ViVUD: Vitua Seve Custe based View-Upoad Decouping fo Muti-Channe P2P Video Steaming Systems Chao Liang and Yong Liu Depatment of Eectica and Compute Engineeing Poytechnic Institute of New Yok Univesity Bookyn, New Yok, 2, USA Emai: {ciang@photon.poy.edu, yongiu@poy.edu} Abstact Despite the success to deive inceasingy age numbe of channes to miions of uses, the cuent mutichanne P2P video steaming systems sti suffe sevea fundamenta pefomance pobems, such as age stat-up deays and poo pefomance fo unpopua channes. To aeviate the impact of channe chun and esouce imbaance, the View-Upoad Decouping (VUD) [] P2P steaming design decoupes pee downoading and upoading, and enabes coss-channe esouce shaing. Howeve, VUD incus upoad bandwidth ovehead and distibution swam management cost. It is aso chaenging to adapt VUD distibution swams in exteme pee chun scenaios, such as fash-cowd. In this pape, we popose ViVUD, a Vitua Seve Custe based VUD design. In ViVUD, a vitua seve custe consisting of bandwidth-ich pees is povisioned to impove the steaming quaity of each channe. A vitua seve custe povides stabe video feeds to boost pees newy joining a channe to educe thei stat-up deays. To enabe cosschanne bandwidth shaing, foowing the VUD design, vitua seve custes fo unpopua channes ae fomed by bandwidthich pees watching popua channes. Though anaysis and simuations, we show that, compaed with the oigina VUD design, ViVUD incus ess upoad bandwidth ovehead, has ighte management equiement, achieves owe channe statup deays, and adapts faste to fash cowds. I. INTRODUCTION In these yeas, sevea age-scae commecia P2P video steaming systems have been depoyed, incuding Coosteaming [2], PPLive [3]. Recent measuement studies have veified that hundeds of thousands of uses can be simutaneousy paticipating in these systems [3]. Neay a P2P video systems offe mutipe channes. And futue use-geneate-video steaming systems wi ikey have thousands if not miions of ive channes. A common pactice in P2P video steaming today is to oganize pees viewing the same channe into a swam, with pees in the same swam edistibuting video chunks excusivey to each othe. We efe to such a design as isoated-channe o moe simpy as ISO P2P steaming systems. Howeve, ecent measuement studies [3] have identified sevea fundamenta pefomance pobems fo isoated-channe systems: age stat-up deay and poo sma-channe pefomance. Cuent stat-up deays ae typicay on the ode of -6 seconds, which is ceay undesiabe as uses ae accustomed to deays unde 3 seconds in cuent cabe and sateite teevision systems. Futhemoe, cuent P2P steaming systems geneay povide inconsistent and poo pefomance to channes with a sma numbe of pees. Recenty, a new appoach to muti-channe P2P steaming is poposed, efeed as View-Upoad Decouping (VUD) []. VUD sticty decoupes what a pee upoads fom what it views, binging stabiity to muti-channe systems and enabing coss-channe esouce shaing. In VUD, each pee is assigned to one o moe channes, with the assignments made independenty of what the pee is viewing. Fo each assigned channe, the pee heps distibute the channe. This has the effect of ceating a semi-pemanent distibution swam fo each channe, which is fomed by pees esponsibe fo upoading that channe. Athough VUD can effectivey addess the pefomance issues due to channe chun and esouce imbaance in ISO systems, it sti suffes fom the foowing issues: Upoad bandwidth ovehead. VUD intoduces upoad bandwidth ovehead since each pee now needs to upoad to its assigned channe distibution swam as we as to pees outside the distibution swam but ae the viewes of the channe. Distibution swam management cost. A viewes of a channe downoad the video fom the channe s VUD distibution swam. A VUD swam needs to be constanty monitoed and maintained to seve the time-vaying viewing demand. Suggish adaption to fash cowds. VUD distibution swams ae buit to be semi-pemanent. It is chaenging to adapt VUD swams when thee is a sudden incease in viewing demand fo a channe, such as fash cowds. In this pape, we popose a new coss-channe steaming design, ViVUD, which impoves VUD by the intoduction of vitua seve custes. In ViVUD, instead of compete Fig.. Vitua Seve Custe ISO-Mesh n u Push Data Neighbohood Souce s n 3 u n2 u New Joining Node Bootstapping Fow An iustation of the ViVUD steaming famewok.
view-upoad decouping on a pees, most pees upoad and downoad the video they ae viewing in the ISO fashion. The VUD design is ony appied to a sma faction of bandwidthich pees, which ae assigned to fom semi-pemanent vitua seve custes, one fo each channe. Instead of steaming video to a viewes of a channe, the vitua seve custe is povisioned to impove the quaity of the ISO steaming between the viewes. Specificay, a vitua seve custe povides stabe video feeds to pees newy joining a channe to educe thei stat-up deays. To impove steaming quaity on existing pees, a vitua seve custe acts as a video poxy and ampifies the bandwidth of the video souce seve by activey pushing packets into the ISO mesh. To addess the upoad deficiency in unpopua channes, vitua seve custes fo unpopua channes ae fomed by bandwidth-ich pees viewing popua channes. Figue iustates the ViVUD steaming famewok fo a singe channe. We popose a set of agoithms to impement ViVUD steaming famewok in Section III. The dimensioning of vitua seve custes ae studied in Section IV. With queuing netwok mode, we compae the univesa steaming pobabiity of ViVUD with that of VUD and ISO design in Section V. Finay, though simuations in Section VI, we demonstate that, compaed with the oigina VUD design, ViVUD incus ess upoad bandwidth ovehead, has ighte management equiement, achieves owe channe stat-up deays, and adapts faste to fash cowds. II. RELATED WORK Most of the pevious eseach on P2P system design focuses on singe isoated channe, without much consideation fo muti-channe optimization. Thee ae ony few eated wok in the muti-channe setting. Seve bandwidth povisioning agoithms ae poposed to adjust the suppy of seve bandwidth among channes in steaming [4] and fie shaing appications [5]. Inte-oveay coopeation mechanisms [6] ae poposed to shae esouces among channes. Decentaized stategies ae investigated to esove the conficts among coexisting steaming oveays [7]. The above woks mosty conside the baance of bandwidth esouces. They do not diecty addess the channe chun and channe esouce imbaance pobems in muti-channe steaming systems. Recenty, the view-upoad decouping steaming design [][8] addesses those pobems by sticty decouping pee viewing and upoading. Ou wok diffes in that, we can aso esove the pefomance pobems as VUD does, but the enhanced appoach can be eadiy impemented with fa ess ovehead, and can adapt faste to fash cowd. III. SYSTEM DESIGN A. ViVUD Achitectue Oveview As iustated in Figue, in ViVUD, thee ae thee majo steaming components fo a channe: the channe souce seve, VUD Vitua Seve Custe (VSC) fomed by bandwidthich pees, and ISO steaming mesh fomed by viewes of the channe. Pees in VSC fom a mesh and coaboativey downoad video fom the channe souce seve. Due to the ich bandwidth avaiabiity on VSC pees, VSC becomes a video poxy that ampifies the bandwidth of the oigina souce seve. VSC impoves the quaity of video steaming to channe viewes in two ways. To educe the stat-up deay, when a pee joins a channe, it diecty downoads the fist x seconds of video in the downoad window quicky fom the channe s VSC. This can geaty educes the stat-up deay fo pees newy joining the system, o switching fom othe channes. To impove the steaming quaity of existing pees, VSC pushes copies of content to the main ISO mesh of viewes to acceeate the video distibution. B. VSC Fomation and Management In the oigina VUD design, the channe s distibution swam steams the video to a the viewes. Whie in ViVUD, a VSC is ony esponsibe fo bootstapping new pees and assisting steaming in ISO mesh. Theefoe, VSCs have ighte steaming wokoad than VUD swams. The numbe of pees needed in a VSC is smae than that in a VUD swam. Consequenty, the upoad bandwidth ovehead and management cost of ViVUD can be made much owe than VUD. In pactice, popua channes with a age numbe of viewes have stabe and high upoad bandwidth avaiabiity, and ae moe esiient to bandwidth fuctuations caused by pee chun [3][9]. Pees in popua channes aey suffe fom bandwidth deficiency. On the othe hand, bandwidth avaiabiity in unpopua sma channes ae vey dynamic. As a esut, the steaming quaity in unpopua channes is not consistent [3][]. To addess the esouce imbaance pobem between popua and unpopua channes, VSCs ony empoy bandwidth-ich pees watching popua channes. Cosschanne esouce shaing is enabed by assigning pees fom popua channes to VSCs of unpopua channes. Pees watching unpopua channes ae heped by stabe data feeds fom VSCs, and achieve esiience against bandwidth deficiency. To futhe educe upoad bandwidth ovehead, the VSC of a popua channe can be fomed by stabe bandwidth-ich pees watching the same channe. It is aso possibe to adopt the substeam-based swam design [] fo VSC. We esot to a tacke-based soution to manage VSCs. The tacke maintains a poo of bandwidth-ich pees fom popua channes. VSC of each channe has a tageted size (We wi discuss the VSC dimensioning issue in the next section). Fo the initia constuction, the tacke assigns pees fom the poo to each VSC to each its taget size. The tacke constanty monitos the opeations of VSCs. Wheneve a VSC expeiences bandwidth deficiency, eithe due to some pees eave the VSC, o thee is a sudden incease in the numbe of viewes fo the channe, the tacke augments the VSC by aocating moe pees to it. C. Data Shaing Stategies VSC pays two oes in the video steaming of a channe. Fist, it seves as the video poxy and souce ampifie fo the ISO mesh. (If aowed by its upoad capacity constaint, the
souce seve s can diecty steam additiona data to the ISO mesh.) A sma numbe of VSC pees ae eseved to push stabe video feeds to the ISO mesh. Second, VSC bootstaps the newy joining pees to enhance thei stat-up pefomance. When a pee joins a channe, it contacts the tacke fo a ist of VSC pees fo the channe. The new pee identifies a VSC pee as its hepe and estabishes a connection with it. The hepe bootstaps the new pee by pushing the fist x seconds of the video content in its downoad window. If the hepe can upoad to the new pee at a ate highe than the steaming ate, the bootstapping video can be upoaded in y < x seconds. The connection with the hepe is teminated afte the hepe finishes the bootstapping task. Whie bootstapped, the new pee joins the channe s ISO mesh, and downoads the video afte the fist x seconds fom its neighbos thee. VSC adaptivey adjusts the bandwidth aocation between video pushing to ISO mesh and bootstapping new pees. If the actua new pee aiva ate is owe than the expected ate, ide pees without bootstapping tasks can aso push video content to the ISO mesh to acceeate the data distibution. On the othe hand, when the new pee aiva ate is highe than the expected ate, VSC becomes unde-povisioned fo new pee bootstapping. Thee ae two ways to espond. The VSC can owe the bootstapping wokoad fo each new pee by educing x, the ength of bootstapping video, so that each new pee wi spend ess time in the bootstapping stage. It opens up some space fo VSC to bootstap moe new pees. O when newy joining pees cannot be accommodated by the VSC, they woud be diecty assigned to the ISO mesh without going though the bootstapping stage. In that way, they coud sti achieve the stat-up deay pefomance of the ISO design. IV. DIMENSIONING THE VIRTUAL SERVER CLUSTER In this section we investigate how to dimension VSCs fo efficient coss-channe shaing. Suppose in a muti-channe P2P video system, thee ae J channes. Fo channe j, the souce seve upoad bandwidth is v j and the steaming ate is j. The distibution of pee viewing time is abitay. Let u i be the upoad ate of pee i. The bandwidth on a VSC pee is consumed in thee diffeent tasks: (I) within VSC, pees coaboativey etieve a copy of the video fom the souce though P2P upoad-downoad; (II) a VSC pee upoads video to a new pee to bootstap its stat-up pefomance; (III) a VSC pee pushes video to the ISO mesh to acceeate the content distibution. The pe-pee bandwidth consumption fo the fist task is oughy equa to the video steaming ate (o the substeam ate fo substeam-based VSC). Ony a few VSC pees ae sufficient fo the thid task. So, we woud mainy focus on dimensioning VSC fo the bootstapping task. ) VSC Bootstapping Capacity. Suppose fo channe j, the VSC upoads to newy joining pees the fist x seconds of content at ate β j in y seconds, i.e., x = yβ. Let X j denote the andom vaiabe of the numbe of new pees joining the channe within y seconds. We define the capacity δ of a VSC as the numbe of new pees that the VSC can simutaneousy bootstap. To achieve a bootstapping pobabiity C, the capacity of VSC fo channe j shoud satisfy P(X j < δ j ) C. () The aggegate bootstapping upoad bandwidth equied is δ j β j. 2) VSC Povisioning fo Coss-channe Shaing. Unpopua channes boow bandwidth-ich pees fom popua channes to fom thei VSCs. To educe view-upoad decouping bandwidth ovehead, we can adopt substeam-based design fo VSCs fo unpopua channes, i.e., a VSC pee ony downoads and upoads one substeam. Futhemoe, the VSC of a popua channe woud be fomed by bandwidth-ich pees viewing the same channe. Next, we discuss how to conduct coss-channe shaing between popua channes and unpopua channes. Let j s be the ate of the sth substeam in channe j and N j s be the set of VSC pees handing substeam s fo channe j. Fo an unpopua channe j J U, to satisfy the bootstapping equiement in Equation (), we obtain (u i j) s δ j βj. s (2) i N s j In addition to the bootstapping bandwidth, VSC of an unpopua channe aso addesses the bandwidth deficiency of ISO mesh. Fo this pupose, an additiona amount P j of bandwidth is needed fo pushing video to secue the steaming pefomance in ISO mesh. If channe j is divided into S j substeams with homogeneous ate, and the VSC ony accepts one type of pee with upoad capacity u p, the bandwidth ovehead atio is thus /S j and the numbe of VSC pees needed by channe j is δjβj+pj u p j/s. j Definition : The net coss-channe esouce fow σ j of channe j is defined as the net amount of outgoing/incoming bandwidth to/fom othe channes without ovehead. Suppose the eative popuaity of channe j is ρ j. The cosschanne esouce fow vecto σ is detemined as foows. Fo popua channes, we have σ j = ρ j i J\J U ρ i δ i β i + P i u p i /S iu p, j J \ J U. (3) i J U The aocation heuistic behind the ue is that the channe with moe popuaity shoud shae moe esouces to hep the unpopua ones. Fo unpopua channes, the net coss-channe esouce fow is σ j = δ j β j + P j. V. MODELING AND ANALYSIS To compae the pefomance of ViVUD with VUD and ISO design, we appy the cosed queuing netwok modes and fomuate the muti-channe P2P steaming system in the same way as [8]. Unde the same cosed queuing netwok mode, we focus on the case of a fixed numbe of pees, modeing the systems with aways-on devices o ow pee chun ate. ) Queueing netwok mode. Let λ = (λ,, λ J ) be the unique pobabiity distibution of aiva ate that satisfies λ = λp, whee P is the channe switching matix. Let /µ j denote the expected amount of time a pee continuousy views channe j and define ρ j = /µ j. Note that is the eative aiva
ate into channe j, and ρ j is the eative channe popuaity. Sma channes have eativey ow vaues of ρ j. We nomaize the ρ j s so that ρ + +ρ J =. Let M j be a andom vaiabe denoting the numbe of pees viewing channe j. Each of n pees is viewing some channe. Because the tota numbe of pees viewing channes is fixed at n, we have M + +M J = n. Thus, the andom vaiabes M,...,M J ae dependent. By viewing the system as an infinite-seve Jackson queuing netwok [], with each channe being a node in the netwok, and each pee as a custome which sojouns at node j fo a andom amount of time with mean /µ j, we immediatey aive at the foowing esut: Lemma : Fo any m,...,m J with m + + m J = n, we have P(M = m,...,m J = m J ) = n! ρm m! ρmj J m J! Note that (M,..., M J ) has a mutinomia distibution. It foows diecty fom the emma that E[M j ] = nρ j and that M j has the binomia distibution P(M j = m j ) = (4) n! m j!(n m j )! ρmj j ( ρ j ) (n mj). (5) With the distibution of the numbe of viewes in each channe, we now detemine the distibution of the numbe X j of newy joining pees to be bootstapped. Let y j be the bootstapping peiod fo channe j. Given y j is shot, we ignoe the ae case that a newy joining pee eaves channe j befoe the bootstapping is ove, and assume a new pees ae bootstapped fo y j seconds. Each channe coud be modeed by a tandem of two queues, as iustated in Fig. 2. The fist queue has the deteministic sevice time of y j, whie the aveage sevice time fo the second queue is /µ j y j. The numbe X j of pees in bootstapping stage coesponds to the numbe of viewes in the fist queue. The eative popuaity of the fist queue fo channe j can be cacuated as ρ j = y jµ j ρ j. Hence, we can deive the distibution of X j based on Lemma. And we can futhe detemine the dimensioning of VSCs, and the net coss-channe esouce fow σ. i k t j t j = /µ j Fig. 2. i k t j t j = y j Tansfomation of channe queue. t 2 j t 2 j = /µ j y j Let M j be the set of pees viewing channe j. The pobabiity of system-wide univesa steaming of ViVUD is PS = P(v j + i M j u i + σ j M j j, j =,...,J) whee M j is a andom set and M j = M j. We can cacuate this pobabiity using Monte Cao methods and impotance samping [2]. We epeatedy geneate sampes {M,..., M J }, evauate the event in the above pobabiity (as o ) and take aveages. Suppose thee ae two casses of pees: n pees with ow upoad ate u ; and n h pees with high upoad ates u h. Fo a given channe j in ViVUD, the pobabiity of univesa steaming is given by PU j = P(v j + i M j u i + σ j M j j ) = P(v j + u h M h j + u M j + σ j (M h j + M j ) j) = n h M h j = n M j = I(v j + u h m h j + u m j + σ j (m h j + m j ) j)p(m h j = mh j )P(M j = m j ), whee P(M h j = mh j ) = ( n h m j ) = ( n m j m h j ) ρ m j j ( ρ j ) n m j. ) ρ m h j j ( ρ j ) nh m h j and P(M j = 2) Numeica esuts. In the simuation setting, thee ae, 8 pees and 2 channes. Each channe has the same ate and the channe popuaity foows a Zipf distibution. Thee ae two casses of pees with upoad bandwidth u =.2 and u h = 3. These two casses of pees have the equa distibution. Fo the dimensioning of ViVUD, we set C = and β =. VSC pees downoad the fu video steam. In VUD, the steaming in each channe is divided into substeams. A channe with the aveage numbe of viewes ess than 3 is teated as an unpopua channe. We assume the bootstapping time fo an unpopua channe j is set to be y j = θ/µ j, θ <. Fig. 3(a) shows ViVUD can achieve PS.95.9 5.75.7 ISO VUD 5 ViVUD θ=.5 ViVUD θ=.2.2.2.4 Zipf Paamete (a) PS PU j.99.98.97.96.95.94 ISO VUD.93 ViVUD θ=.5 ViVUD θ=.2.92 5 5 2 Channe ID (b) PU j Fig. 3. The univesa steaming pobabiity of PS and PU j. highe pobabiity of system-wide univesa steaming unde diffeent channe popuaity distibutions. Fig. 3(b) pots the pobabiity of univesa steaming fo each channe when the Zipf paamete is.5. We can obseve that the unpopua channes in ViVUD ae moe esiient to bandwidth fuctuation than VUD and ISO, the coss-channe shaing does not have much negative impact on the popua channes, thanks to the eativey sma esouce demands fom unpopua channes. Futhemoe, ViVUD incus much ess ovehead, which is ess than % even when θ =.2, whie the ovehead of VUD is % with substeams in each channe. VI. PERFORMANCE EVALUATION In this section, we conduct extensive packet-eve simuations to evauate the pefomance of the poposed stategies.
A. Simuation Setting To compae the pefomance of diffeent muti-channe steaming design, we impement an event-diven P2P steaming simuato which can simuate packet-eve tansmissions and end-to-end atency among pees. In ou simuation, it is assumed that the botteneck ony happens at the edge of netwoks, and a the paticipating pees have enough downoad bandwidth. The video steaming ate is 4kbps. The souce seve upoad bandwidth is set to be Mbps as defaut fo each channe. Thee types of pees ae assigned with upoad bandwidth.6mbps, 384kbps and 28kbps. The coesponding factions of them ae (.5,.5,.34), and the esouce index of the system is amost.2. To compement the anaysis based on cosed-queuing netwok, we simuate an open muti-channe system. Thee ae 5 channes and the popuaity of the channes foows Zipf distibution. Pees aive at the system accoding to a Poisson pocess. Pee viewing time in a channe foows a Weibu distibution. Afte a pee finishes viewing a channe, it eaves the system with cetain pobabiity, o switches to anothe channe with a pobabiity popotiona to the channe popuaity. The aveage numbe of active pees in the system is 2,. B. Simuation Resuts ) Muti-channe Pefomance: VSCs ae fomed by the cass of pees with.6mbps upoad bandwidth. Each VSC is povisioned with twice of the equied bootstapping bandwidth. The bootstapping time fo new pees is 2 seconds. The stat-up deay is counted as the time that a new pee needs to fi up at east 7% of the fist 5 seconds of buffe since it joins the channe. Figue 4(a) pots the CCDF of the video deivey atio pefomance. ViVUD geaty impoves steaming quaity fo unpopua channes. Amost 8% unpopua channes have deivey atio above 9%, whie the deivey atio is aound 7% in ISO design. Futhemoe, Figue 4(b) shows that ViVUD can achieve owe stat-up deay with neay 9% pees having stat-up deay ess than 5 seconds. CCDF ViVUD popua.2 ViVUD unpopua ISO popua ISO unpopua.7.75 5.9.95 Deivey Ratio (a) Deivey Ratio Fig. 4. CDF ViVUD popua.2 ViVUD unpopua ISO popua ISO unpopua 2 3 4 Stat up Deay (Second) Muti-channe pefomance. (b) Stat-up Deay 2) Robustness against fash cowds: We compae the singe channe pefomance of ViVUD and ISO unde fash cowd scenaio. In this simuation, the pee aiva foows the Poisson distibution with mean λ =. The pee ifetime is distibuted with Weibu distibution paametes (6,2). In ViVUD, each VSC is povisioned with 6 pees fo bootstapping, and 5 pees eseved fo pushing to ISO mesh. Between time 4 and 45, thee is a batch aiva of pees at a ate of 6 pees pe second. Figue 5(a) shows the evoution of numbe of onine pees and deivey atio of both schemes. We can obseve that ViVUD can povide highe deivey atio than ISO. Figue 5(b) pesents the stat-up deay of pees with diffeent joining time. We can obseve that pees cannot get satisfactoy stat-up deay pefomance duing the shot fash cowd peiod. Othe than that peiod, ViVUD can aways bootstap new pees we and aow them to achieve owe stat-up deay than ISO. Aveage Deivey Ratio.9.7.5.3.2 # of Onine Pees ViVUD ISO 2 4 6 8.2 Time (Second) (a) Deivey Ratio Fig. 5. Numbe of Onine Pees (K) Stat up Deay (Second) 5 4 3 2 ViVUD ISO 2 4 6 8 Pee Joining Time (Second) (b) Stat-up Deay Singe channe pefomance unde fash cowd. VII. CONCLUSION In this pape, we poposed a vitua seve custe based VUD design (ViVUD) to addess the pefomance pobems in the oigina VUD and ISO design. ViVUD empoys vitua seve custes to bootstap newy joining pees, and enabes coss-channe shaing by assigning bandwidth-ich pees fom popua channes to VSCs of unpopua channes. Though modeing, anaysis and simuation, we demonstated that, compaed with the oigina VUD design, ViVUD has ighte management equiement, achieves owe channe statup deays, and adapts faste to fash cowds. REFERENCES [] D. Wu, C. Liang, Y. Liu, and K. 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