AnySee: Peer-to-Peer Live Streaming

Transcription

1 ysee: Peer-to-Peer Lve Streamg School of Computer Scece ad Techology Huazhog Uversty of Scece ad Techology Wuha, 40074, Cha {xflao, hj, dfdeg Xaofe Lao, Ha J, *Yuhao Lu, *Loel M. N, ad afu eg *epartmet of Computer Scece Hog Kog Uversty of Scece ad Techology Clear Water Bay, Kowloo, Hog Kog {lu, bstract Effcet ad scalable lve-streamg overlay costructo has become a hot topc recetly. I order to mprove the performace metrcs, such as startup delay, source-to-ed delay, ad playback cotuty, most prevous studes focused o tra-overlay optmzato. Such approaches have drawbacks cludg low resource utlzato, hgh startup ad source-to-ed delay, ad ureasoable resource assgmet global PP etworks. ysee s a peer-to-peer lve streamg system ad adopts a ter-overlay optmzato scheme, whch resources ca jo multple overlays, so as to () mprove global resource utlzato ad dstrbute traffc to all physcal lks evely; () assg resources based o ther localty ad delay; () guaratee streamg servce qualty by usg the earest peers, eve whe such peers mght belog to dfferet overlays; ad (4) balace the load amog the group members. We compare the performace of our desg wth exstg approaches based o comprehesve trace drve smulatos. Results show that ysee outperforms prevous schemes resource utlzato ad the QoS of streamg servces. ysee has bee mplemeted as a Iteret based lve streamg system, ad was successfully released the summer of 004 CERNET of Cha. Over 60,000 users ejoy massve etertamet programs, cludg TV programs, moves, ad academc cofereces. Statstcs prove that ths desg s scalable ad robust, ad we beleve that the wde deploymet of ysee wll soo beeft may more Iteret users. Keywords Peer-to-Peer; Lve Streamg; Iter-Overlay Optmzato; strbuted pproach; Load Balace; ysee I. INTROUCTION Wth the mprovemet of etwork badwdth, multmeda servces based o streamg lve meda, such as IPTV [], have gaed much atteto recetly. Sgfcat progress has bee made o the effcet dstrbuto of lve streams a real-tme maer over a large populato of spectators wth good QoS [4]. ue to the practcal ssues of routers, IP multcast [6] has ot bee wdely deployed. Therefore, researchers have expeded a lot of effort buldg a effcet streamg overlay multcast scheme based o PP etworks [7], whch spectators behave as routers for other users. Effcet ad scalable lve-streamg overlay costructo [8] has become a hot topc. fferet from tradtoal dstrbuted systems, streamg overlays focus o the followg three metrcs: startup delay, source-to-ed delay, ad playback cotuty, as these metrcs have a drect bearg o the teractve usablty of a lve streamg system. Large delays would exhaust user patece ad uplaed terruptos would spol the etertamet value. I order to mprove the above metrcs, prevous studes [9] focused o tra-overlay optmzato, whch each ode jos at most oe overlay. Wth the help of localty-aware strateges [0][] ad optmzato schemes such as ONet CoolStreamg [], Narada ESM [], QoS of lve streamg PPs have sgfcatly mproved. However, they stll suffer from log delay ad uplaed terruptos, especally whe a large umber of peers jo the etwork smultaeously. Fgure shows a example of tra-overlay optmzato wth two logcal streamg overlays. Peers, B, C ad jo the stream orgatg at S ad peers E, F, G, H ad K jo the stream orgatg at S. The umber o each edge represets the cost of the lk betwee two odes. I tradtoal traoverlay optmzato schemes, two multcast trees ca be establshed as show Fg. (a) ad (b). There are two obvous drawbacks. Frst, such overlay costructo s ot globally optmal. Cosderg peer Fg. (a), the cost S s 8, whle f the path S S s used, the cost s oly 4. Secod, resource utlzato of tradtoal approaches s relatvely low. Most of the exstg protocols are tree based. Cosequetly, all leaf odes fal to cotrbute ay badwdth or CPU cycles to the multcast trees. B B S (a) 4 S 6 Overlay Topology C C G G S S 6 H (c) Physcal Topology (b) Fgure. Itra-overlay optmzato: (a) optmal multcast tree rooted at S ; (b) optmal multcast tree rooted at S ; (c) physcal topology H 7 F F E E K 4 K /06/$0.00 (c)006 IEEE

2 We propose a ter-overlay optmzato based scheme, ysee, whch resources ca jo multple overlays smultaeously, so as to () mprove global resource utlzato of a PP lve streamg etwork ad dstrbute traffc to all physcal lks evely; () assg resources based o ther localty ad delay; () guaratee streamg servce qualty by usg the earest peers, eve f such peers mght belog to dfferet overlays; ad (4) balace the load amog the group members. fter ysee optmzato o the example show Fg., better overlays are costructed as llustrated Fg.. Fgure. ysee ter-overlay optmzato However, for a dstrbuted approach such as ysee, to reach the above desg goal wthout global etwork kowledge s ot trval. Several key ssues, cludg effcet eghbor dscovery, resource assgmet, overlay costructo ad optmzato, must be addressed. To prove the effectveess of ysee, comprehesve trace drve smulatos are coducted based o topologes from real PP etworks []. Results show that ysee outperforms prevous schemes resource utlzato ad the QoS of streamg servces. well-kow publc mplemetato, ysee v.., was released o Jue 004. It has bee used to broadcast lve-streamg meda, cludg TV programs, moves ad the Grd ad Cooperatve Computg (GCC 04) teratoal coferece Wuha, to tes of thousads of edusers CERNET (Cha Educato ad Research Network). I the past several moths, over 60,000 users, from 40 uverstes ad 0 ctes Cha, have tested ysee PP streamg servces. The source-to-ed delay, resource utlzato, ad the startup delay were all qute ecouragg. The rest of ths paper s orgazed as follows. Secto II dscusses the related work. Secto III presets the dea of ter-overlay optmzato of ysee. Secto IV descrbes our smulato methodology ad performace aalyss. We descrbe mplemetato expereces ad show our observatos ad measuremets of ysee Secto V. We coclude ths work Secto VI. II. RELTE WORKS Two types of schemes based o tra-overlay optmzato were proposed recetly: tree-based overlays ad mesh-based overlays. Borrowg deas from IP multcast, tree-based protocols are smple, effcet, ad scalable. There are two types of tree-based protocols, cludg sgle tree protocols, such as ESM, NICE [9] ad ZgZag [8], ad multple tree protocols [4][]. The major ssue of sgle tree protocols s to buld a scalable multcast tree wth hgh effcecy. Multple tree protocols, such as MC [6], emphasze the overall reslece ad load balace of the streamg etwork. The ma dea s to dvde the vdeo of oe stream to several parts based o layer cocept CoopNet or patchg deas [0]. However, the leavg or crash behavor of odes the upper layers ofte causes buffer uderflow. They caot provde backup streamg servces, ad waste ay spare resources. To mprove the stablty of servces, mesh-based protocols have bee proposed, whch each peer ca accept meda data from multple parets as well as provdg servces for multple chldre, such as Coolstreamg, PROMISE [7] ad GNUStream []. The resource utlzato of a mesh s hgher tha that of a tree. Meshes based o Gossp protocol ca fd fresh peers the sgle mesh wth low maagemet overhead, but ot global PP etworks. ue to the radom selecto algorthm, the qualty of servce caot be guarateed, such as the startup delay. lso, to decrease the mpact of autoomy of peers o streamg servces, very large buffer space, such as used Coolstreamg, s ecessary. Zhag proposed a HT based PP resource pool, SOMO [], [] to maage global resources ad optmze multple LM (pplcato Layer Multcast) sessos, especally computato applcatos. The ma dea of such approaches s to structure all peers strctly [4], gorg the features of specfc applcatos. However the huge mateace overhead makes these approaches far from scalable. Ideed, eve f we have global kowledge of a PP etwork, fdg a optmal assgmet of resources s stll NP-hard. Based o a completely dstrbuted heurstc, our proposed approach selects streamg paths ad uses key lks or peers as backup provders. Iteroverlay optmzato s coducted ysee to complemet tradtoal tra-overlay strateges. III. NYSEE ESIGN To acheve good performace PP lve streamg systems, ysee faces the followg challeges: () how to fd paths wth low delays, cludg source-to-ed delay ad startup delay, a global PP etwork; () how to mata the servce cotuty ad stablty (decreasg the mpact of terrupto caused by peers leavg); () how to determe the frequecy of optmzato operatos; ad (4) how to reduce the cotrol overhead caused by the algorthm. We troduce the desg of ysee ths secto.. Overvew s llustrated Fg., the basc workflow of ysee s as follows. Frst, a effcet mesh-based overlay s costructed. locato detector based algorthm s employed to match the overlay wth the uderlyg physcal topology []. Secod, the sgle overlay maager, whch s based o tradtoal traoverlay optmzato, such as Narada [] ad ONet, deals wth the jo/leave operatos of peers. Thrd, the ter-overlay optmzato maager explores approprate paths, bulds backup lks, ad cuts off paths wth low QoS for each ed peer. Fourth, the key ode maager allocates the lmted resources, ad the buffer maager maages ad schedules the trasmsso of meda data.

3 ecodg/player dm( d, S,0) P Buffer Maager Key Node Maager S N N P P Sgle Overlay Maager Iter-overlays Optmzatos Maager dm( d, S,) N N4 P4 P6 Mesh-based Overlay Maager P Fgure. The system dagram of a ysee ode B. Mesh-based Overlay Maager I ysee, peers jo the mesh-based overlay frst. Every peer, wth a uque detfer, frst coects the bootstrappg peers ad selects oe or several peers to costruct logcal lks. Every peer matas a group of logcal eghbors. The key ssue here s to let the mesh-based overlay match wth the uderlyg physcal topology [6]. The mesh-based overlay maager, a key compoet of ysee, uses some strateges, such as a LTM (Locatoaware Topology Matchg) techque [], to optmze the overlay, fd the latest eghbors, ad elmate slow coectos. There are two major operatos: floodg-based detecto wth lmted TTL, ad updatg logcal coectos. I the frst operato, each peer perodcally floods a message, defed as dm(d, S, TTL), to ts eghbors. The message dm(d, S, TTL) meas that the peer tates a message wth I value d TTL hops. Sce our purpose s to fd the latest eghbors of peer S, we defe TTL=. To detect the dstace of peers, the message body has sx parts, cludg messagei, TTL value, sourceip (the IP address of the source peer), sourcetmestamp (the tmestamp whe the source forwards the message), rectip (the IP address of oe eghbor wth oe hop) ad recttmestamp (the tmestamp whe the eghbor wth oe hop gets the message). Fgure 4 shows the roadmap of oe message from S. Obvously, a message s broadcast to drect eghbors ad -hop away eghbors. I the secod step, logcal lks are updated. Wth the help of the tmestamps o peers, peer P compares the dstace betwee two paths, S P ad S N P. If the former legth s larger, the lk N P would be cut off ad the drect path betwee S ad P would be establshed. ll peers would do the same operatos as those The clocks of all peers are sychrozed based o NTP. Curret mplemetato of NTP verso 4.. publc doma ca reach the sychrozato accuracy dow to 7. mllsecods [7]. Fgure 4. Roadmap of detector message tated by S of peer S. fter several operatos, peers would coect wth ther earest eghbors. C. Sgle Overlay Maager The sgle overlay maager s resposble for peers leavg/jog operatos. Before ter-overlay optmzato, oe peer jos oe streamg overlay ad receves meda cotets from multple provders or sgle provder accordg to tra-overlay optmzato schemes. I ths desg, a ew attrbute s troduced called Lastelay, whch s the mmal of all source-to-ed delays from the curret ode to the streamg source o dfferet paths. Wth Lastelay, each path to the meda source ca be measured ad evaluated. Whe a meda block s delvered from the meda source to the ode, the sgle overlay maager records the tmestamp ad wrtes t to the meda block s header. Whe a peer receves the meda block wth the tal tmestamp, t computes the dfferece of the tal tmestamp ad the arrvg tmestamp. The mmal dfferece s the value of Lastelay. Peers ca jo or leave the topology accordg to Lastelay.. Iter-overlay Optmzato Maager Geerally, each peer matas oe actve streamg path set ad oe backup streamg path set. Itally all streamg paths are maaged by the sgle overlay maager. Whe the umber of backup streamg paths s less tha a threshold, the ter-overlay optmzato algorthm s called to fd approprate streamg paths the global PP etwork wth the help of the mesh-based overlay. Whe oe actve streamg path s cut off due to ts poor QoS or peer s leavg, a ew streamg path s selected from the backup set. Bascally, a peer P uder source S wth a streamg rate rate(s) matas () a actve streamg path set wth threshold sze δ a ( PS, ), ad () a backup streamg path set wth threshold sze δ b ( PS, ). Each streamg path SP from S to P has two parameters: delay (SP, S, P) s the source-to-

4 ed delay from source S to peer P; rate(sp, S, P) s the streamg rate the last hop of the path. Clearly, we have: δ ( PS, ) a rate( SP, S, P) rate( S ) () = δ ( PS, ) δ ( PS, ) b a rate( SP, S, P) = p rate( SP, S, P) () = = Let ( S ) µ deote the threshold for the delay, whch s related to the prorty of the streams oly. We also desg a probg message amed ProbM as show Fg.. Ths message cludes two major parts: () tal formato about the message, cludg sequece umber, Seq., tal peer I, Peer_0, message ssuace tme, Tmestamp0, meda source I of the tal peer, Source, curret Lastelay, ad TTL; () a array wth the sze of TTL to record peer I ad the arrvg tmestamp of the message. Cosderg that 9% of peers the Gutella system could be reached wth 7 hops by pure floodg, the maxmal TTL s set to 7. There are maly two tasks for the ter-overlay optmzato maager, cludg backup streamg path set maagemet ad actve streamg path set maagemet. The major operato backup streamg path set maagemet s the probg procedure, called reverse tracg algorthm. Ths algorthm starts whe the sze of backup set s less tha δ b ( PS, ). Peer_0 seds out a ProbM message to j of ts eghbors wth the recordg array empty. Each recever records the message arrval tme ad ts I to the accepted message body. The recever wll stop forwardg the message f () t fds that the delay from the tal peer Peer_0 to ths peer s greater tha Lastelay; or () the recever s the source of ths streamg servce. Otherwse, the message would be forwarded to j radom eghbors. fter reverse tracg, the meda source s able to aalyze the arrved messages wth I Seq., ad explore the best path from the source to the message ssuace peer. Iformed by the source, the peer s able to costruct the best overlay path accordgly. Fgure 6 shows a example of the reverse tracg algorthm based o the overlay show Fg., whe j= ad j=, respectvely. I ths fgure, all delays are replaced wth the cost of two peers. Peer seds out a message ad the possble routes of the message are llustrated. Some routes are cacelled due to a loger delay tha Lastelay. Evetually, a good path S S s successfully selected. The Lastelay s updated. s a large porto of ProM messages are stopped durg forwardg process, the overhead s acceptable. Mddle Peers rray Seq. Peer_0 Peer_ Tmestamp0 Tmestamp Peer_TTL Tmestamp Source Fgure. Structure of message ProbM Lastelay TTL 0 S S Ed >8 S F Ed 7 H I >8 >8 H >=8 C G 6 H >=8 S Ed >8 S Ed >=8 (a) Lastelay =8 j= B >8 S S G Ed 6 C H >=8 H S >=8 Ed >8 S Ed >=8 (b) Lastelay =8 j= Fgure 6. Examples of reverse tracg algorthm: (a) each peer forwards to three eghbors; (b) each peer forwards to two eghbors streamg path s treated as vald f () the source-toed delay s larger tha a gve threshold µ ( S ), or () the drect paret of the ed peer o the path leaves. I ths desg, we oly dscoect the overlay lk betwee the ed peer to ts paret ode because () the other coectos o the path ca be reserved to provde support for ew comg peers, ad () our observatos show that large delays ofte come from the last coecto the path, ad () frequet dscoectos cur a lot of uecessary traffc. The maagemet of a actve streamg path set has three operatos, cludg matag the states of actve streamg paths, cuttg off vald paths, ad addg ew actve paths from a backup set, whch are straghtforward. Whe the total bt rates from actve streamg paths are lower tha rate(s), the maager wll check whether a better path should be actvated to replace the curret oe. Ths maager has the followg characterstcs: () t employs a heurstc algorthm, ad the system s optmzed step by step; () probg procedures have orgated from the ormal peers, ot the source peer, so that the cotrol overhead s balaced to ormal peers; () the umber of forwardg eghbors, j, balace the tradeoff betwee the optmzato effectveess ad the overhead; (4) the frequecy of probg ad optmzato s dyamc. I ysee, probg procedure s feedback-drve based o delay. Here how to set the tal value of the threshold, µ ( S ), s of mportace. Logs from ysee, to be descrbed Fgures 9-, show that whe peers are watchg hghly popular moves, they are wllg to tolerate a hgher delay as much as 0 secods. It s reasoable that µ S. B >8 dfferet programs defe dfferet ( ) E. Key Node Maager It s of great mportace for peers to have a effectve admsso cotrol polcy whe there are too may requests. Suppose each peer has N spare coectos. ccordg to the characterstcs of requests, each request wll fall to oe of M queues wth dfferet prortes ad populartes. Whe we assg the N spare coectos to M queues, there are two

5 terestg cases. Frst, some queues are assged wth more tha oe coecto tuel, whch ca be modeled as a M/M/m/K queug system [8]. Secod, some queues oly receve oe coecto, whch follows a M/M//K queug model. The admsso cotrol polcy of a peer s desged to make the resources utlzato optmal. The problem ca be descrbed as follows. Suppose there are M queues of requests. The arrvg rate of queue j s λ j, all arrvg rates satsfy λ <... < λj <... < λm. The servce rate to assg oe coecto s µ ad each coecto processor ca buffer k requests (k ). ssumg the probablty that requests follow the M/M/m/K queug model s p, we have p ( mρ ) p0 = 0,... m =! m m ρ p0 = m, m+... K m! λ where ρ = ; we also have mµ p m m K m+ ( mρ) ( mρ) ρ + ρ! m! ρ = m m ( m) ( m) + ( K m + ) ρ = = 0! m! = 0 0 Thus, the average utlzato of N spare coectos of oe peer ca be gve by: m K m ρ p0 ρ = ρ( ρk) = ρ () m! Oe coecto processor ca buffer k requests, the K = mk. Whe the probablty that requests are followg the M/M//K queug model s p, we have ( ) ρ ρ ρ K + ' p = ρ 0 K ρ = K + λ ad ρ =. The the average utlzato of N spare µ coectos of oe peer ca be gve by ~ K ' ρ ρ = p0 = ρ K ρ + (7) ' ad p K s the falure probablty of requests. The, the target ca be expressed: ' () (4) (6) k ~ Max( ρ( N, N,... NM )) = Max ρ+ ρ j, j M M Subject to N = N N < N = The above optmzato problem (Eq. (8)) ca be dvded to two parts. Frst, we eumerate all (M, )-parttos (M queues ad each should be allocated at least coecto) of N spare coectos such that the best allocato ca be foud to maxmze ρ ( N, N,... NM ) Eq. (8). Secod, for all H parttos of N coectos, we ca compute all H results of average resources utlzato ad select the best partto, based o whch of the resources utlzato s maxmal. I the frst phase, we ca get H, the umber of parttos of N by ( N! ) ( M ) ( N M) N H = ( M ) =, N M (9)!! From Equato (9), the frst algorthm complexty s O(N). The secod algorthm s to select the maxmal oe N from H results. Its complexty s O( CM ) = O( N). Cosequetly, ths optmzato problem has complexty of O(N). Cosderg oe ormal peer wth 0Mbps badwdth ad average streamg rate 00Kbps, N should be set less tha. F. Buffer Maager Ths maager s resposble for recevg vald meda data from multple provders the actve streamg path set ad cotuously keepg the meda playback. ysee employs a smlar heurstc as used the Coolstreamg system [] to fetch expected meda segmets a dyamc ad heterogeeous etwork to meet two costrats: the playback deadle for each segmet ad the heterogeeous streamg badwdth from parters. s Coolstramg does ot employ ay ter-overlay optmzato, peers ofte fal to fd the closest eghbors to supply servces. To keep the meda playback cotuous, a bg buffer must be used. ue to the effectveess of the ter-overlay optmzato scheme adopted ysee, a small buffer space s eough, ad deed a small buffer ofte meas a shorter startup delay. IV. SIMULTION Before troducg our mplemetato expereces ad the observato about the real ysee system, we evaluate ysee wth comprehesve smulatos ad cotrast ts performace wth a recet lve streamg system, Coolstramg [].. Smulato Methodology We cosder two types of topologes, physcal topology ad logcal PP topology. The physcal topology represets a real topology wth Iteret characterstcs. The logcal topology represets the overlay PP topology bult o top of the physcal topology. ll PP odes are a subset of odes the physcal topology. The commucato cost betwee (8)

6 two logcal eghbors s calculated based o the shortest physcal path betwee ths par of odes. We develop a crawler based o Gutella protocol [] ad the source codes are rewrtte from Lmewre ope source clet []. The crawler s ma fucto s to probe the coectos of Gutella peers. Whe peers are recevg crawler pg messages, they reply wth correspodg pog messages. Wth the help of forty-fve depedet threads, our crawler dscovers over ffty thousads peers ad ther coectos oe week. I ths smulato we use three data sets, obtaed from dfferet tme slots. Each trace cludes aroud,000 peerg odes. For the physcal topology, we use BRITE [] geeratg three topologes, each wth,000 odes. The average umber of eghbors of each ode rages from 4 to 0. The major parameters our smulatos are lsted Table. I each ru, peers radomly jo oe of S streamg overlays (S=, 4, 8, ). Each peer radomly has C coectos ragg from 4 ( Mbps badwdth) to 40 (0 Mbps badwdth) ad matas at least M eghbors. The sze of each overlay s N (N<00). Each stream s 800- secods log, ad the streamg rate s r, ormally 00 Kbps. Based o the delay values from the trace, we set the badwdths for peers. For smplcty, the threshold µ ( S ) s set to secods, whch s estmated from logs of ysee mplemetato. The adjustmet factor p s set to, whch meas we provde oe backup streamg path for each actve streamg path. To better evaluate the performace of ysee, we use the metrcs as follows. () Resource utlzato s defed as the rato betwee the used coectos to all coectos; () Cotuty dex, represetg the playback cotuty, s defed as the umber of segmets that arrve before playback deadles over the total umber of the segmets. TBLE I. bbrevate S M N r C SIMULTION PRMETERS Commet Number of streamg overlays Number of eghbors Sze of oe overlay Streamg playback rate Number of total badwdth coectos B. Results The frst set of smulatos s coducted a stable evromet, whch peers do ot leave after jog the overlays. For each smulato setup, we take 00 rus ad report the average. We frst evaluate the QoS of the ysee servce a stable evromet. Fgure 7 plots the cotuty dex agast streamg rate, where we cotrast ysee ad Coolstreamg. Whe the streamg rate s creased, the cotuty of ysee s relatvely good whle the cotuty of Coolstreamg s degraded. There are two reasos. Frst, ysee ca fd more ear eghbors from all peerg odes to request servces, whle Coolstramg s oly able to fd supplers from the same overlay. Secod, the ecessary buffer sze of ysee s oly 40 secods, whle Coolstreamg eeds a 0-secod buffer. Fgure 7. Cotuty dex V.S. streamg rates whe N=400, S= ad tal buffer sze s 40 secods Fgure 8. Resources utlzato: overlay sze V.S. the umber of streamg overlays whe M=, r=00 Kbps

7 Fgure 9. Cotuty dex uder dyamc evromets whe M=, N=400, r=00 Kbps ad tal buffer sze s 40 secods Fgure 0. Resource utlzato uder dyamc evromets whe M=, N=400, ad r=00 Kbps Fgure. Servces map of ysee CERNET of Cha (red ceter pot: HUST, Wuha) Fgure. System modules of ysee Fgure 8 cotrasts resource utlzato of ysee ad Coolstreamg. See o the left part of Fgure 9, a larger umber of streamg overlays has a greater mpact o the performace of ysee, but o obvous fluece o Coolstreamg. Ths s due to the fact that Coolstreamg does ot let peers to select better relay paths usg other peers dfferet overlays. We the coduct smulatos whe peers are leavg ad jog freely. We defe the lfetme of each peer the overlay, from 00 secods to 00 secods. Peer average lfetme s expoetally dstrbuted wth a average of T secods. We ca see from Fgures 9 ad 0 that loger lfetme leads to better servce qualty ad hgher resource utlzato. However, whe the average lfetme of peers s short, the cotuty of Coolstreamg s relatvely poor. s our proposed ysee has a backup path maagemet desg ad the reverse tracg compoet keeps fdg better paths dyamcally, ysee always outperforms Coolstreamg. V. IMPLEMENTTION OF NYSEE We have mplemeted the publc free system, ysee, ad released two versos (v..0 ad v..) to provde a scalable lve-streamg servce platform based o ter-overlay optmzato CERNET of Cha. From Jue 004 to February 00, there were over 60,000 coectos to the platform ad above 40 uverstes ad 0 ctes Cha were the servce map as show Fg.. The system s mplemeted wth Java ad s platform-depedet.. rchtecture Overvew ysee system s comprsed of four compoets. They are () a redezvous pot (RP), () a meda source, () a motor, ad (4) ed systems. Each ed system cotas a IP to Network Coordates atabase (INC), whch s pre-bult ad tegrated to the ed system software.

8 Fgure shows the modules of ed systems ysee. Every ed system (cludg the Broadcaster) s composed of several fucto modules as follows: () gettg meda data (GM) module s for Broadcaster; () sedg peer selecto (SPS) module s deployed o all peers except the Broadcaster; () sesso for cotrollg message (SFCM) module s resposble for exchagg cotrol messages betwee curret peer ad ts suppler, ad motorg actos of chld peers; (4) buffer maager (BM) module gets meda packets from the upper-layer, seds them to the HTTP server module, ad deletes packets wth outdated tmestamps the buffer; () data trasmtter (T) module fetches meda packets from the buffer, ad trasmts packets to uderlyg peers uder flow cotrol polcy; (6) HTTP server (HS) module creates a vrtual HTTP servce at a local mache. fter retrevg meda data packets from the buffer, HS module seds them to meda players such as Wdows Meda Player, uder the HTTP protocol. B. Implemetato Expereces We dscuss two terestg ssues ysee mplemetato, GI based servce scheme ad localty-aware buffer maagemet scheme. ) GI based servce scheme ue to the characterstcs of streamg applcatos, t s desrable to let every peer to get meda servces from supplers wth low latecy ad hgh badwdth. May approaches have bee proposed, such as GNP. However, most of them are too complex to be feasble. I ysee, all peers are the same CERNET ad the physcal etwork map s well kow. It s effcet that the dstace s computed wth the help of the pared IP addresses. Thus, ysee requres each peer mata a INC, from whch each peer ca have a posto, amed GI the global etwork. The GI value of a ed host s a 8-bts teger ecoded by the 4-layer geometrcal formato correspodg to ISPs, ctes, campuses, ad buldgs, respectvely. Such formato s also used by ysee to estmate the physcal locatos of peers. ) Localty-aware buffer maagemet scheme s the behavor of peers upper layers have a larger mpact o QoS tha that of peers the lower layers, ysee employs a layer-aware buffer maagemet scheme. Each peer computes ts approprate buffer space sze accordg to the layer umber. I ysee, the buffer sze of peer at the m-th layer s gve by: ( ) T = f m = ε t + t (0) ' where t deotes the total lk delay, t ' s the total trasportg delay, ad ε s the average dscoecto tmes of oe coecto. Suppose the probablty of a lk or ode falure s P b, ad a peer eeds t b tme to explore a ew paret, the border delay s t l = P b t b ad the lk delay t s the accumulato of all border delays. Suppose the trasportg delay per hop s µ ad the total hops betwee the source peer ad peer s m, the total trasportg delay of peer s t ' µ m =. If the path from source peer to peer s ls = { ls a, l,..., } a a l am, the path has the followg propertes: () the source peer would persst all the tme ad the path ls a would ot break dow; () peer would also stay the etwork ad the path l a m would exst; () the fluece that multple borders break dow smultaeously s the accumulato of fluece that multple borders break dow oe by oe; (4) f oe peer ' a leaves, oe ew peer a would jo the tree ad replace the posto of a. The the total lk delay ca be computed as = m t tl a a + = =, ad t = ( P ) t la a b l + m t tl Pb tl Pb tl the, ( )... ( ) = + + +, after computato, ( P ) m m ( ( ) ) b t = tl = tb Pb Pb () The, we have ( ( ) m ) T = ε t P + µ m () b b Gve the estmato of the above parameters Eq. (), the maxmum buffer sze of peer at the m-th layer s computed whch oly relates to layer m. C. Performace of ysee mog all log data collected, we select records from /08/004 to 9/08/004. Over 700 users from over 40 uverstes 4 ctes of Cha receved servces wth ysee. We aalyzed the performace of the multple multcast trees every te mutes. Fgure plots the average heght of ysee trees agast tree sze. lthough the heght creases whe more peers jo each servce tree, the heght s always less tha 7 eve wth a thousad peers cluded oe tree. Such a property helps shorte the source-to-ed delay as show Fg. 4. We ca see the source-to-ed delay s always less tha 00 ms. From the logs of ysee, the startup delay of most peers s less tha 0s. We have mplemeted a smple prototype, whch ca get meda servces from a Coolstreamg etwork, ad we observe the startup delays for 0 tmes. Mostly, the startup delay of Coolstreamg s aroud 60 secods. Based o the results show Fg. 4, we set µ to 0ms ad defe t b =, P = 0.4, ε =. b

9 Fgure. Heght V.S. tree sze Fgure 4. Source-to-ed delay V.S. tree sze Fgure. Maxmum umber of peers dfferet hot perods Fgure 6. Maxmum percetage of leavg peers dfferet hot perods Fgure 7. verage delay dfferet hot perods. Users Behavor ad System Optmzato It s mportat to kow the user behavor, whch ca help us optmze the system. We select three log sets to aalyze the total umber of peers, the average delay, ad the leavg peer percetage dfferet hot perods. We select 7 dfferet hot perods for three programs, Program-a, Program-b, ad Program-c. Fgures, 6, ad 7 show the maxmum umber of peers, maxmum percetage of leavg peers, ad average delay of three programs, cludg Program-a, Program-b, ad Program-c for oe hour. The results show that the overlays wth popular moves attract more users to jo, but cause larger average delays. From the fgures, we have the followg terestg observatos. Frst, larger delay s ot always the major reaso that causes people to leave the overlay. For example, the leavg percetage of Program-a s ot the largest whle ts average delay s the logest. Peers have more patece tha that maged by prevous researchers f the program s very popular. Secod, delays from 0 to 0 secods wll ot be the kller for the lve streamg servces. Most people wll stll stay the overlay eve f there s a 0 secod delay from the source peer. Based o the above observatos, ysee does ot determe the optmzato frequecy oly accordg to the average delay, but also the percetage of leavg peers. That too may users are leavg the overlay s the sgal that the overlay s uder heavy burde ad eeds to be optmzed. ysee defes the parameter optmzato dex, L, whch s gve by leavg percetage L= 00 average delay TBLE II. LS IN HOT PERIOS OF IFFERENT PROGRMS Num. Program-a Program-b Program-c verage fter computato, three Ls from dfferet perods are show Table. From Table, the average Ls for the above programs are 0.97, 0., ad 0.6, respectvely. ysee provdes a threshold o L to determe whether a overlay optmzato s ecessary.

10 VI. CONCLUSION N FUTURE WORK Effcet ad scalable lve-streamg overlay costructo has become a hot topc recetly. I order to mprove the metrcs, such as startup delay, source-to-ed delay, ad playback cotuty, most prevous studes focused o traoverlay optmzato. Such approaches have drawbacks cludg low resource utlzato, hgh startup ad sourceto-ed delay, ad effcet resource assgmet global PP etworks. I ths paper, we propose a ter-overlay optmzato based lve streamg scheme. Istead of selectg better paths the same overlay, ysee peers are able to costruct effcet paths usg peers dfferet overlays. We evaluate the performace of ysee by comprehesve smulatos. Our expermetal results show that ysee outperforms exstg tra-overlay lve streamg schemes, such as Coolstreamg. The practcal ysee system has bee released for several moths ad ts clet code s free to be dowloaded CERNET of Cha. To date, over 60,000 users beeft from ysee to ejoy two teratoal academc cofereces, amely GCC 04 (Grd ad Cooperatve Computg) ad NPC 04 (Network ad Parallel Computg), ad other massve etertamet programs. Logs from ysee show that users have great patece for lve streamg servces wth large delay f they have eough terest the programs. We hope the system ca serve more people ad atta better qualty the future. We are curretly buldg peer-to-peer vdeo-o-demad servces for large-scale users based o ter-overlay optmzato schemes. We are gog to observe more user behavors to further mprove the system performace. CKNOWLEGMENT Ths work was partally supported by Cha Natoal Natural Scece Foudato (NSFC) uder grat No.6008, , 6079, 60740, Specalzed Research Fud for the Ph. Program from Mstry of Educato uder grat No , ad Hog Kog RGC Grats HKUST664/04E, G 0/06.EG44 ad oe/e-0/99. REFERENCES [] The Gutella protocol specfcato 0.6, [] Lmewre, [] BRITE, [4] J. Lu, B. L, ad Y.-Q Zhag, "daptve Vdeo Multcast Over the Iteret", IEEE Multmeda, 00. [] B. lfos, "I Wat My IPTV: Iteret Protocol Televso Predcted a Wer", IEEE strbuted Systems Ole, 00. [6] R. Perlma, "Models for IP Multcast", Proceedgs of IEEE Iteratoal Coferece o Networks, 004. [7]. Gajam ad H. Zhag, "Iteret Multcast Vdeo elvery", IEEE Proceedg, 00. [8] S. Baerjee, C. Kommareddy, K. Kar, B. Bhattacharjee, ad S. Khuller, "Costructo of a Effcet Overlay Multcast Ifrastructure for Real-Tme pplcatos", Proceedgs of IEEE INFOCOM, 00. [9]. Myers, T.S.E. Ng, ad H. Zhag, "Rethkg the Servce Model: Scalg Etheret to a Mllo Nodes", Proceedgs of CM SIGCOMM HotNets, 004. [0] Y. Lu, X. Lu, L. Xao, L. N, ad X. Zhag, "Locato- ware Topology Matchg PP Systems", Proceedgs of IEEE INFOCOM, 004 [] T.S.E. Ng ad H. Zhag, " Network Postog System for the Iteret", Proceedgs of USENIX, 004. [] X. Zhag, J. Lu, B. L, ad T. P. Yum, "ONET: ata- rve Overlay Network for Effcet Lve Meda Streamg", Proceedgs of IEEE INFOCOM, 00. [] Y. Chu, S. G. Rao, ad H. Zhag, " Case for Ed System Multcast," Proceedgs of CM SIGMETRICS, 000. [4] M. Castro, P. ruschel,. Kermarrec,. Nad,. Rowstro, ad. Sgh, "SpltStream: Hgh-badwdth Cotet strbuto Cooperatve Evromets", Proceedgs of CM SOSP, 00. []. Kostc,. Rodrguez, J. lbrecht, ad. Vahdat, "Bullet: Hgh Badwdth ata ssemato Usg a Overlay Mesh", Proceedgs of CM SOSP, 00. [6] V. N. Padmaabha, H. J. Wag, P.. Chou, ad K. Srpadkulcha, "strbutg Streamg Meda Cotet Usg Cooperatve Networkg", Proceedgs of CM NOSSV, 00. [7] M. Hefeeda,. Habb, B. Botev,. Xu, ad B. Bhargava, "PROMISE: Peer-To-Peer Meda Streamg Usg Collectcast", Proceedgs of CM Multmeda, 00. [8]. Tra, K. Hua, ad S. Sheu, "Zgzag: Effcet Peer-To- Peer Scheme for Meda Streamg", Proceedgs of IEEE INFOCOM, 00. [9] S. Baerjee, B. Bhattacharjee, ad C. Kommareddy, "Scalable pplcato Layer Multcast", Proceedgs of CM SIGCOMM, 00. [0] Y. Guo, K. Suh, J. Kurose, ad. Towsley, "PCast: PP Patchg Scheme for Vo Servce", Proceedgs of WWW, 00. [] X. Jag, Y. og, ad X., B. Bhargava, "GNUSTREM: PP Meda Streamg System Prototype", Proceedgs of IEEE ICME, 00. [] Z. Zhag, Y. Che, S. L, B. Lu, S. Sh, X. Xe, ad C. Yua, "PP Resource Pool ad Its pplcato to Optmze Wde- rea pplcato Level Multcastg", Proceedgs of Iteratoal Coferece o Parallel Processg Workshops, 004. [] Z. Zhag, S. Sh, ad J. Zhu, "SOMO: Self-Orgazed Metadata Overlay for Resource Maagemet PP HT", Proceedgs of IEEE IPTPS, 00. [4] S. Ratasamy, P. Fracs, M. Hadley, R. Karp, ad S. Sheker, " Scalable Cotet-ddressable Network", Proceedgs of CM SIGCOMM, 00. [] Y. Lu, L. Xao, X. Lu, L.M. N, ad X. Zhag, "Locato wareess Ustructured Peer-To-Peer Systems", IEEE Trasactos o Parallel ad strbuted Systems, 00. [6] M. Rpeau ad I. Foster, Mappg Gutella Network, IEEE Iteret Computg, 00. [7] NTP: The Network Tme Protocol, [8] L. Klerock, Queueg Systems, Joh Wley, 974. [9] Y. Lu, -H. Esfahaa, L. Xao, ad L. M. N, "pproachg Optmal Peer-to-Peer Overlays", Proceedgs of IEEE MSCOTS, 00.