Design and Evaluation of a P2P IPTV System for Heterogeneous Networks

Transcription

1 1 Desgn and Evaluaton of a P2P IPTV System for Heterogeneous Networks Meng-Tng Lu, Ju-Cheh Wu, Kuan-Jen Peng, Polly Huang, Jason J. Yao, and Homer H. Chen, Fellow, IEEE Abstract NTUStreamng s an overlay P2P-based IPTV system that ntegrates nnovatons n both overlay networkng and vdeo codng for optmal user experence. The system conssts of three key components: partnershp formaton, robust vdeo codng, and vdeo segment request schedulng. For partnershp formaton, a graph constructon mechansm TYPHOON based on epdemc algorthms s developed to reduce dsconnect tme and solated peers. For robust vdeo codng, a multple descrpton codng (MDC) scheme wth spatal-temporal hybrd nterpolaton (STHI) s proposed to adust streamng traffc accordng to the bandwdth and devce capablty of each peer. For request schedulng, an optmzaton algorthm s developed by takng the avalable bandwdth and the vdeo segment type nto account. Expermental results show that NTUStreamng s able to delver optmal vdeo qualty n lossy and dynamc networkng envronments. Index Terms IPTV, peer-to-peer (P2P), vdeo broadcast, vdeo streamng, error recovery, overlay network, multple descrpton codng. I. INTRODUCTION ITH the rapd advances n multmeda entertanment, W broadband network, and semconductor manufacturng technologes, hgh-speed multmeda communcaton s comng of age. Vdeo broadcastng over the Internet,.e., IPTV, s one of the most promsng multmeda entertanment applcatons on the rse. The key to a successful IPTV system les n the qualty of servces (QoS). For content provders wth enough fnancal power and hgh senstvty to the copyrght ssue, a conventonal dstrbuted network consstng of servers and M.-T. Lu s wth the Graduate Insttute of Communcaton Engneerng, Natonal Tawan Unversty, Tape 1617, Tawan. J.-C. Wu s wth the Graduate Insttute of Computer Scence and Informaton Engneerng, Natonal Tawan Unversty, Tape 1617, Tawan. K.-J. Peng s wth the Graduate Insttute of Communcaton Engneerng, Natonal Tawan Unversty, Tape 1617, Tawan. P. Huang s wth the Department of Electrcal Engneerng, Graduate Insttute of Communcaton Engneerng, and Graduate Insttute of Networkng and Multmeda, Natonal Tawan Unversty, Tape 1617, Tawan (phone: ; fax: ; e-mal: phuang@cc.ee.ntu.edu.tw). J. J. Yao s wth the Department of Electrcal Engneerng and Graduate Insttute of Communcaton Engneerng, Natonal Tawan Unversty, Tape 1617, Tawan. H. H. Chen s wth the Department of Electrcal Engneerng, Graduate Insttute of Communcaton Engneerng, and Graduate Insttute of Networkng and Multmeda, Natonal Tawan Unversty, Tape 1617, Tawan (phone: ; fax: ; e-mal: homer@cc.ee.ntu.edu.tw). caches may be a preferred soluton for content delvery. However, the recent success of P2P IPTV servces, such as PPStream [1], PPLve [29] and CoolStreamng [12], s an evdence of the fact that the dgtal content world s evolvng. Web 2. allows the general publc to create and share contents of ther own. In ths new content world, an economc P2P approach to content dstrbuton s attractve. Accordng to a recent measurement study, Huang et al. [34] shows that over 8% of the users on the Internet have download capacty more than 1, Kbps and upload capacty more than 384 Kbps, whch s qute enough for P2P streamng. Our obectve s to develop a scalable and robust P2P IPTV system for qualty vdeo broadcastng over the Internet. NTUStreamng, the proposed IPTV system, takes the followng desgn features nto consderatons: 1) an overlay peer-to-peer networkng approach, wth whch the system can explot the resources, such as storage and bandwdth, avalable among the peer users for better scalablty, 2) an MDC approach, wth whch heterogeneous peers can flexbly subscrbe to streams of dfferent resolutons and enoy the best qualty ther avalable resources permt, and 3) a bandwdth-aware schedulng algorthm, where the schedule of the vdeo segment transmssons s based on the resoluton of vdeo segments and network bandwdth avalable. The archtecture conssts of three maor techncal components: partnershp formaton, multple descrpton codng, and vdeo segment request schedulng. The partnershp formaton component s responsble for fndng the peers to serve vdeo segments. The multple descrpton codng determnes the encodng and playback strategy for better vdeo qualty. The vdeo segment request schedulng algorthm manages how and where to request the vdeo segments. NTUStreamng s one of the poneerng IPTV systems that ntegrate nnovatons n both overlay networkng and vdeo codng for optmal user experence. The partnershp formaton component s essental for the overlay P2P-based vdeo broadcastng. In the P2P network paradgm, a vdeo stream s dvded nto segments, whch are delvered from peers to peers. More specfcally, a user chooses a number of peers to form a partner group, and t receves vdeo segments from these partners. A user may also be chosen by other peers n the network to be ther partners. How the partner and consumer relatonshp s establshed mpacts the effcency and stablty of the network. In fact, load balancng and stablty

2 2 of the partnershp n the presence of peer dynamcs are the man desgn consderatons n the partnershp formaton of NTUStreamng. Expermental results show that, relatve to the state of the art [2], the partnershp formaton scheme of NTUStreamng s able to enhance the stablty of the P2P partnershp wthout compromsng the system load balance. MDC s the component that mpacts the user percepton of the vdeo. Bult on top of the multple state vdeo codng [3], [4], [5], our proposed MDC scheme adds two streams of lower-resoluton pctures to enhance scalablty and error reslence. When a descrpton s mssng, we ntroduce a hybrd nterpolaton scheme, called Spatal-Temporal Hybrd Interpolaton (STHI) [6], whch explots both spatal and temporal nformaton to mprove the vdeo qualty. The networkng and vdeo codng components are further ntegrated through a vdeo segment request schedulng mechansm. The vdeo segment request schedulng n the state-of-the-art CoolStreamng s heurstc based. A polcy that requests the rarest segment frst could be nadequate for heterogeneous networks. We formulate the segment schedulng component as an optmzaton problem, whch allows each node n a heterogeneous network to request segments of partcular spatal or temporal resolutons based on the avalable bandwdth. As a result, the system s able to better utlze avalable resources and acheve better vdeo qualty. The rest of ths paper s organzed as follows. Secton II descrbes related work, and Secton III presents the partnershp formaton of the overlay network. Secton IV explans MDC-STHI and the ntegraton of the whole system. Secton V dscusses the comparson between MDC-STHI and layered vdeo codng. The bandwdth-aware data schedulng mechansm s gven n Secton VI. Secton VII presents expermental results and dscussons, and Secton VIII concludes ths paper. II. RELATED WORK The dstrbuton of vdeo streams over IP s a quas-relable multcast problem n nature. Solutons at the network layer have long exsted. Multcast routng protocols such as DVMRP [7] and PIM-SM [8] are wdely mplemented n commercal routers. Relable multcast solutons at the network layer such as SRM [9] have also been proposed snce The common problem of the network-layer solutons s the dffculty n deployment because every router n between the senders and recevers needs to run the requred mechansms for the multcast vdeo broadcastng to work. To acheve scalablty through adustment n the applcaton layer, several desgns have been proposed recently, ncludng Applcaton-level Multcast [1], ZgZag [11], CoolStreamng [12], SpltStream [13] and AnySee [14]. All of them explot the deployment flexblty at the applcaton level. Among the exstng systems, CoolStreamng s closest to ours but dfferent n the desgn of partnershp formaton, vdeo codng, and vdeo segment schedulng [15]. Partner Peer Consumng Peer Contact Node PartalVew InVew TABLE I NOMENCLATURE Peer of a node that serves data to the node Peer of a node that receves data from the node The node that s frst connected to by a newly oned peer The lst of partner peers for a node The lst of consumng peers for a node MDC has receved only lttle attenton n P2P streamng. Padmanabhan et al. [16] ntroduced data redundancy to CoopNet usng MDC. Znk et al. [17] dscussed the feasblty of MDC for P2P networks and compared t to herarchcally layered vdeo codng. Khan et al. [18] compared the performance of MDC over P2P networks wth that of content delvery networks (CDNs). Conventonal MDC schemes are seldom used n practce because they are too complex and usually use non-standard vdeo codecs. On the other hand, our scheme s bult on top of multple state vdeo codng, whch s easy to mplement usng standard codecs as basc components. Layered vdeo codng (LVC), such as scalable vdeo codng (SVC) [23] and MPEG-4 fne graned scalablty (FGS) profle [32], whch encodes vdeos nto streams wth temporal, spatal, and SNR scalablty, s adopted n some P2P streamng systems [19], [], [3]. The scalablty of LVC s especally sutable for heterogeneous networks. However, the maor drawback of the layered codng approach s ts hgh complexty and lack of error reslence. On the contrary, the smple MDC-STHI scheme provdes both scalablty and error reslence. III. PARTNERSHIP FORMATION The partnershp formaton component determnes for each user a lst of partner peers that can serve vdeo segments to the user. Because the peers may leave or on the overlay network at any tme, t s necessary to select substtute partners for relablty. A balanced and robust partnershp formaton polcy acheves both load balance and stablty. In ths secton, we survey a state-of-the-art partnershp formaton mechansm SCAMP and then propose TYPHOON to mprove the system stablty whle mantanng load balance. The terms used n ths secton are defned n Table I. A. SCAMP SCAMP (Scalable Membershp protocol) [2], whch s used n CoolStreamng, s a peer-to-peer partnershp formaton protocol operatng n an unstructured and fully decentralzed manner. Each node under ths protocol searches for potental neghbors to connect wth by a gossp-based messagng mechansm [21], [22]. Each node mantans a lst of partner peers, PartalVew, and a lst of consumng peers, InVew. To avod staleness, every entry n the PartalVew has a fnte lfetme, and each node sends subscrpton messages

3 3 Node 3 PartalVew: 7, 1 InVew: 1, 11 Node 1 PartalVew: 2, 3, 4, 5, 6 InVew: 7 3 Node 6 PartalVew : 7, 12 InVew: 1, Standard encoder results MSVC results 4 7 Fg. 1.Illustraton of partnershp formaton. Node 7 PartalVew : 1 InVew: 3, Frame number Fg. 2. Comparson between standard encoder results and MSVC results. perodcally to reset the expraton tme. These messages are also used to update the partner lst as nodes on and leave the system dynamcally. The process of a new node onng the system s llustrated n Fg. 1. When a peer node 7 ons the system for the frst tme, t adds the contact node 1 n ts PartalVew. The contact node then advertses the dentfer of ths newly oned node to all ts partner peers and to a predetermned number of addtonal peers randomly selected from ts PartalVew. When recevng a subscrpton message, the peer adds the newly oned node to ts PartalVew wth a probablty of 1/(1+M), where M s the PartalVew sze. If the newly oned node s not added to the PartalVew, the subscrpton message s randomly forwarded to another node n the PartalVew. In SCAMP, subscrpton forwardng and partner selecton processes are purely random. Although ths acheves good load balancng, our experments show that the network becomes unstable n dynamc envronments, resultng n dsconnecton and vdeo nterrupton. B. TYPHOON The robustness of tradtonal gossp-based protocols lke SCAMP heavly reles on the success of message forwardng. When a peer leaves the overlay network, t should nform all peers n the InVew and PartalVew of ts departure. If a peer leaves the SCAMP network wthout nformng other peers, all peers n ts PartalVew can notce the partnershp change after a heart-bt cycle. However, the peers n ts InVew can not get any sgnal of ts departure. Ths knd of asymmetry results n network nstablty and frequent message losses. To solve ths problem, we propose TYPHOON an mproved SCAMP protocol based on the concept of preferental message forwardng and epdemc algorthms [21]. TYPHOON conssts of two maor parts: preferental random forwardng (PRF) and preferental random selecton (PRS). The frst part, PRF, allows preferental random forwardng of the subscrpton messages. When a node re-subscrbes tself, partners wth larger partnershp are favored and have a hgher probablty to be chosen. For the balance of the partnershp, subsequent forwardng of the subscrpton messages s sent to partners wth smaller partnershp. The second part, PRS, allows preferental selecton of partners. In SCAMP and PRF, a node s selected as a partner wth the probablty 1/(1+M). In PRS, a peer wth small partnershp sze selects peers wth hgher probablty untl reachng the lower bound of the partnershp sze. Smlarly, f the partnershp sze of a peer s larger than an upper bound, the peer smply replaces one of ts partners wth the newly selected partner and forwards the subscrpton messages of the replaced partner to others. TYPHOON s desgned as a general archtecture that works equally well regardless of the sze of membershp. Unlke SCAMP, TYPHOON mantans a moderate membershp sze for each peer. Ths helps keep the traffc between peers manageable. As the number of partners of each peer grows, the message processng traffc becomes heaver and can potentally go beyond the lmt for, for example, handheld devces n a heterogeneous network that have very lmted resource. For applcatons consdered n our work, ths s certanly undesrable. Compared to SCAMP, TYPHOON s more reslent to heavy churns that may break down or dsconnect loosely connected small overlay networks. TYPHOON and SCAMP both perodcally search for new partners to add and tme out the old partners. To make the search scalable, the subscrpton messages they send and the partner lst they record are both local. The dsconnecton n the overlay network under peer dynamcs s the problem that rses from such local dscovery of new partners. A peer may break away to add certan partners randomly or wth preference to avalable bandwdth and content. Not knowng whether the added partners are well connected to the rest of the network, a small sland can be formed and becomes dsconnected from the maor crowd. The subsequent searches for new partners are lmted to peers on the sland because none of the peers have any nformaton of the maor crowd from whom they get dsconnected by chance. In smpler words, the dsconnecton of overlay network does not mean peers physcally breaks from the network. Rather, t

4 E f E q O f O q 4 NTUStreamng vdeo source node Fg. 3. Vdeo streams n MDC-STHI. 6 frames n one segment N 1 N 2 Most powerful nodes Powerful nodes E f +O q O f +E q Less powerful nodes 64 segments n the buffer Fg. 5. NTUStreamng vdeo source node. N 3 E q +O q E f +O q E f +O f +E q +O q N 4 N 5 N 6 Fg. 4. MDC-STHI over a P2P network. means the search network for potental partners clustered so much that slands are formed. Peers on the dsconnected sland may need to spend several swarmng cycles to fgure out the fact that they are solated and some addtonal tme to re-contact the bootstrap servers to get back on the network. In delay-senstve vdeo streamng systems, such outage of vdeo streams may cause a sgnfcant amount of dsturbance to multple users. The best way to solve the solaton problem s to prevent t from happenng. Ths s why TYPHOON, consderng the connectvty of the canddate partners, can effectvely mtgate the peer solaton problem and, n return, provdes better overlay network stablty. IV. MULTIPLE DESCRIPTION CODING MDC s a crtcal component drectly affectng user satsfacton. In a P2P network, each peer downloads data from and uploads data to multple peers, but the peers many on or leave the network at any tme. MDC s especally useful for such a dynamc network wth path dversty because t allows a recever to obtan the baselne qualty as long as one suppler survves. In our system, we decompose a vdeo stream n the temporal dmenson for dversty gans, and encode the odd frames based on the prevous odd frames and the even frames based on the prevous even frames. The two sub-streams are transmtted separately and played back wth synchronzaton at Fg. 6. Vdeo data flow of an NTUStreamng node. the recever. Such a desgn s more fault tolerant than conventonal vdeo codng because when one sub-stream s lost due to network congeston, the decoder can stll ndependently dsplay the remanng sub-stream wth controlled degradaton. Ths method would lower the codng effcency a lttle because the temporal relatonshp s not fully exploted. As shown n Fg. 2, multple state vdeo codng, usng MPEG4 for both descrptons, loses about 1 db n PSNR n comparson to normal MPEG4 vdeo at the same total bt rate. Based on the concept descrbed above, we propose a new codng scheme named MDC-STHI, whch generates four sub-streams as shown n Fg. 3. Sub-streams E f and O f represent the even and odd streams, respectvely, encoded from the orgnal full-sze vdeo. E q and O q denote the down-sampled verson encoded at a lower bt rate. In our mplementaton, a 2:1 down samplng s appled n each dmenson to the vdeo frame to generate the quarter-sze vdeo. Whle E q and O q requre extra bts to encode, we show n Secton VII that the combnaton of the four sub-streams has many desrable

5 5 features for vdeo streamng over P2P networks. Fg. 4 llustrates a possble P2P networkng scenaro usng MDC-STHI. Generally, Internet users wth varous computatonal capabltes are connected through networks of dfferent bandwdths, and they are randomly grouped as peers for vdeo streamng n a P2P envronment. In Fg. 4, the number of crcles ndcates roughly the amount of resources at the node. Thus, N 3 has enough bandwdth and computng power to retreve both E f +O q and O f +E q streams from N 1 and N 2. In turn, N 4, N 5, and N 6 can receve approprate combnatons of streams from N 3 accordng to ther avalable resources. For example, N 4 may retreve only E q and O q from N 3 because t uses a moble devce wth a narrowband wreless connecton and a small-sze screen that best dsplays quarter-sze vdeos. On the other hand, N 6 can accommodate all streams from N 3 and may further dstrbute the vdeo streams ntellgently to other peers. Compared to other MDC desgns, MDC-STHI offers superor flexblty for P2P vdeo streamng as the four sub-streams are ndependently encoded and a node may adaptvely delver sutable combnatons accordng to the peers' capabltes. The combnaton of E f +O q or O f +E q poses an nterestng challenge as t contans two streams of dfferent resolutons. Durng transmsson, the bts from O q may pggyback n the same IP packet wth E f of the prevous frame, and vce versa for O q. Ths saves the overhead and ensures same tme arrval of adacent frames. An nnovatve hybrd nterpolaton scheme s also developed for such combnatons, fully explaned n [6]. Fg. 5 shows the ntegraton of MDC-STHI wth the NTUStreamng vdeo source node. The four ndependently-encoded MDC-STHI sub-streams are read nto the vdeo source node and segmented. Each segment contans 6 frames, 15 frames for each sub-stream, thus there are 64 segments n the buffer, equvalent to 64 seconds of vdeo data. Fg. 6 shows the vdeo data flow of an NTUStreamng clent node. When recevng a segment, the MDC-STHI decoder processes the data usng the correspondng MPEG-4 decoder based on the type of the segment. The decoded frames are then put nto the STHI buffer. If the node only receves part of the descrpton due to packet loss or bandwdth constrant, the STHI module performs spatotemporal hybrd nterpolaton on the lost frames. Fnally, the nterpolated frames are sent to the dsplay buffer. V. COMPARISON BETWEEN MDC-STHI AND LVC For MDC-STHI, because all descrptons are coded ndependently, a recevng node s able to put together the full resoluton vdeo f t receves collectvely from t source nodes all descrptons of the full resoluton vdeo. In other words, dfferent descrptons of the full vdeo do not have to come from one sngle source node. If a recevng node does not receve all the descrptons of a full resoluton vdeo, t composes a scaled-down (ether spatally or temporally) verson of the full vdeo. No node s requred to receve all descrptons. Note that the system works because a recevng S node has the chance to reconstruct a full resoluton vdeo even f none of ts source peers has the complete full resoluton vdeo. Ths s n fact a novelty of MDC-STHI. In contrast to MDC-STHI where each descrpton s ndependently coded and hence mssng any descrpton does not cause catastrophc effect, the enhancement layers of LVC are dependent on the base layer. Therefore, the performance of LVC s hnged on successful transmsson of the base layer. Ths lmts ts flexblty n a dynamc P2P network where peers on and leave at any tme. Another strong dstncton between these two approaches s that thn stream s more lkely to occur for layered streamng n a dynamc P2P streamng network. Thn stream refers to the case where a low resoluton or partal vdeo s receved by a peer even f the peer has enough bandwdth for a full vdeo. Because of the codng overhead, layered vdeo codng requres more bts than the regular vdeo codng employed n MDC for each descrpton. Consequently, at a gven bandwdth, a P2P network wth layered streamng s more lkely to run nto the thn stream problem than a P2P network wth the MDC scheme. When a network bottleneck occurs that can only accommodate, for example, the base layer, a downstream peer may receve only the base layer even though t has enough bandwdth to receve the enhancement layer as well (see Fg. 7). The complexty of layered codng also poses a great challenge to system mplementaton n practce. To sum up, LVC has hgher S Source node Fg. 7. The topology of a P2P network wth bottleneck. L L L 1 L 21 L L L 42 L 33 L 43 L 44 L 1 FEC FEC L 21 L 22 FEC L 31 L 32 L 33 FEC FEC FEC Node wth low bandwdth Node wth hgh bandwdth Bottleneck L 41 L 42 L 43 L 44 Fg. 8. Illustraton of MD-FEC plus SVC wth four qualty layers. TABLE II BIT RATE OF EACH LAYER FOR SVC Qualty layer L 1 L 2 L 3 L 4 Bt rate (Kbps)

6 6 vdeo codng effcency. To avod the thn stream problem, the peers need to be clustered by the avalable bandwdths. On the other hand, although MDC consumes more bandwdth, t s reslent to errors and smplfes the mechansm formng the peer-to-peer network. Whch approach s more approprate for a peer-to-peer desgn at hand depends on the peer and avalable bandwdth dynamcs, as well as the capacty of the underlyng physcal network. When the peers and network usage are stable and the network capacty s lmted, the LVC wth clustered peer-to-peer network approach s better. Otherwse, MDC wth the random peer-to-peer network approach appears to be a reasonable desgn choce. Although the error reslence and thn stream problem of LVC can be solved by mposng the MD-FEC structure [24], [31] on LVC, the redundancy s hgh. For MDC-STHI, the redundancy comes from the quarter-sze stream, the bt rate of whch s normally set to % of that of a full-sze stream n our smulatons. Therefore, ts redundancy rato s.4/1=%. For SVC plus MD-FEC (the layer structure of whch s shown n Fg. 8), the redundancy comes from the FEC blocks. We use the MPEG-4 SVC reference software (JSVM) [25] to encode the CIF-sze Foreman sequence nto four qualty layers correspondng to the four layers, E q, E q +O q, E f, and E f +O f, of our scheme. Table II lsts the bt rate of each layer. The total bt rate allocated for FEC s 3x3+1x2+1=1,3 Kbps, whereas the total bt rate of the layered vdeo s =1, Kbps. Therefore, the redundancy rato for ths scheme s 13/1=9%, whch s hgher than MDC-STHI. Although the redundancy of SVC plus MD-FEC can be further reduced by unequal error protecton [26] and selectve transmsson of only useful layers, the complexty of handlng these descrptons also ncreases, whch s not desred for a lve streamng system. For these reasons, MDC-STHI s adopted n our system. VI. SEGMENT SCHEDULING The segment schedulng polcy determnes how a peer requests vdeo segments from partners. In our desgn, the vdeo stream s separated nto four sub-streams and thus the decson becomes more complcated. We dvde the decson process nto two parts: segment type selecton and suppler selecton. The selecton of segment type s formulated as an optmzaton problem and solved by lnear programmng based on nformaton such as segment avalablty, sze, vdeo qualty and estmated avalable bandwdth B a. Each peer constantly estmates B a by takng a weghted average of the observed transmsson rate B obs and the prevously estmated bandwdth. The ntal B a s set to the bt rate of the vdeo. B obs s a conservatve estmaton of the nstantaneous avalable bandwdth and s calculated by dvdng the averaged segment sze by the averaged nterval between the tme the request for each segment s made and the tme the requested segment s receved for each data transmsson. Because the transmtted Fg. 9. The status of the buffer before schedulng. TABLE III DEFINITION OF THE SYMBOLS USED IN SEGMENT SCHEDULING U The PSNR value of segment wth type x P D segment traverses both the uplnk of the sendng peer and the downlnk of the recevng peer, the upload capacty of the sendng peer and download capacty of the recevng peer are both consdered. Although there are more accurate bandwdth estmaton methods reported n the lterature [27], ths smple bandwdth estmaton scheme s adopted because most other methods nvolve sendng extra probng packets, whch consumes extra bandwdth. Based on the nformaton exchanged by each peer, a node schedules the transmsson of K avalable segments at a tme by K L = xu x = 1 = 1 L L S 1 = 1 B = 1 { x } argmax The result of segment schedulng for segment wth type The subset of peers n the PartalVew that have segment wth type The estmated avalable bandwdth of the peer B mn ( D, the maxmum upload banwdth of a peer n P ) S T T L The sze of segment wth segment type The sze of the vdeo buffer after obtang segment The sze of the current vdeo buffer The nubmer of types st..( T = T + 1 x ) >, x 1, x {,1} where the symbols used n ths optmzaton problem are all defned n Table III. For the K segments to be scheduled, our mechansm determnes the segment types so that the vdeo qualty U s maxmzed subect to the constrant T >. The constrant s mposed to avod the underflow of the vdeo buffer, see Fg. 9. In our system, we actually consder both the download bandwdth of the peer and the upload bandwdth of ts partners n B. Smply consderng the download bandwdth may not work well. A node s only allowed to request one segment type for each segment. The value of x s ether or 1. If x equals 1, segment s scheduled to be type. After the type of each segment s determned, we use the rarest-frst schedulng polcy to decde the order of downloads and the supplers of segments.

7 7 Occurence 3 1 SCAMP PRF TYPHOON TABLE IV NORMALIZED NETWORK STABILITY STATISTICS SCAMP PRF TYPHOON Connect Tme (sec) Dsconnect Tme (sec) Number of Dsconnecton (N) Instablty Connect tme (s) (a) SCAMP PRF TYPHOON Occurence 1 1 SCAMP PRF TYPHOON Peer count In-degree Dsconnect tme (s) (b) Fg. 1. Dstrbutons of (a) connect tme and (b) dsconnect tme. Peer count SCAMP PRF TYPHOON VII. SYSTEM EVALUATION Smulatons are conducted to examne the stablty and scalablty of partnershp formaton on a large scale network and to verfy the error reslence ablty of MDC-STHI. Also, the performance of NTUStreamng mplemented on a small-scale campus testbed and PlanetLab [33] s evaluated. A. Partnershp Formaton Evaluaton The effectveness of three overlay network constructon strateges, SCAMP, SCAMP+PRF and SCAMP+PRF+PRS, s compared by usng packet-level smulatons wth ns-2 [28], and the results of the three strateges are denoted as SCAMP, PRF and TYPHOON, respectvely. The overlay network sze s set to 1 peers. The physcal network topology s not mportant n the smulaton because we do not consder the delay and bandwdth constrants. The only requrement of the physcal network s that any two nodes are always connected. The obectve of the smulaton s to test the robustness of varous partnershp formaton mechansms, so we only smulate the peer dynamcs on the overlay network. Each peer ons and leaves the overlay network wth an exponental on-off Out-degree Fg. 11. In-degree and out-degree dstrbutons. dstrbuton, and the mean values of both on and off perods equal 2 seconds. The average number of peers exst n the overlay network s. In the ntalzaton phase, all peers on the network n the frst 5, seconds. The perod of subscrpton advertsement s 128 seconds, and the smulaton tme s 75, seconds. The man performance metrcs examned here are partnershp stablty and load balance. Due to the dynamcs caused by peers onng and leavng the network, some peers may become solated and lose all the nformaton about the remanng part of the overlay network. In such a case, the whole overlay network s n the dsconnect state; otherwse t s n the connect state. The state of the overlay network vares wth tme, and each state may elapse for a perod of tme. The duraton the connect state s defned as connect tme, and that of the dsconnect state s defned as dsconnect tme. Fg. 1 shows the dstrbutons of connect tme and dsconnect tme. As we can see, both PRF and TYPHOON

8 8 Peer count SCAMP (statc) TYPHOON (statc) SCAMP (dynamc) TYPHOON (dynamc) Full Sze STHI Spatal Temporal In-degree Frame number Peer count SCAMP (statc) TYPHOON (statc) SCAMP (dynamc) TYPHOON (dynamc) 1 Out-degree Fg. 12. In-degree and out-degree dstrbutons for both statc and dynamc networks. outperform SCAMP n preventng frequent and sudden system dsconnectons (Fg. 1(a)), and fewer dsconnectons and shorter dsconnect tme than SCAMP (Fg. 1(b)). Table IV shows the statstcs of the network stablty based on the three strateges. Once the network falls nto the dsconnect state, the number of peers parttoned from the man cluster and the dsconnect tme are recorded. The nstablty ndex s defned as the sum of products of the dsconnect tme and the number of solated nodes. It ndcates how often the vdeo segment transmsson s nterrupted. The statstcs show that the nstablty of the P2P partnershp for TYPHOON s sgnfcantly lower than the other two strateges. Fg. 11 shows the hstograms of the partner sze (out-degree) and consumer sze (n-degree). For SCAMP, the peak of the out-degree s near 4 and that of the n-degree s near 3. The small n- and out-degrees mply that SCAMP networks may not work well n the presence of network dynamcs. For TYPHOON both the peaks of n-degree and out-degree are larger than the other two strateges, mplyng that the network s more stable. B. Comparson between SCAMP and TYPHOON over Both Statc and Dynamc Networks SCAMP and TYPHOON are further compared by the followng experment to show ther vulnerablty to network dynamcs. The smulaton contans two phases. In the frst phase, SCAMP and TYPHOON are compared on a statc Fg. 13. The PSNR values of the CIF-sze Stefan vdeo sequence Full Sze STHI Spatal Temporal Frame Number Fg. 14. The PSNR values of the CIF-sze Mother and Daughter vdeo sequence Full Sze STHI Spatal Temporal Frame number Fg. 15. The PSNR values of the CIF-sze Foreman vdeo sequence. network, whch means all peers stay n the network after they on. The average number of actve peers s 1. In the second phase of the experment, we start to add churns to the network, where all the peers start to on and leave the network accordng to an on-off model wth the mean values of both on and off perods equal to seconds. The frst phase starts from the begnnng of the smulaton to the 3 th second, and the second phase starts from the 31 st second to the end of the smulaton. Although the total number of peers n ths phase s 1, the average number of actve peers s. The smulaton results n Fg. 12 show that the membershp

9 Full Sze STHI Spatal Temporal Frame number Fg. 16. The PSNR values of the D1-sze Football sequence. Fg. 18. The 33 rd frame of the weghted nterpolated odd stream. Fg. 17. The 33 rd frame of the full-sze odd stream. Fg. 19. The 33 rd frame of the spatally nterpolated odd stream. sze of SCAMP n a statc envronment s consstently large and stable. However, n a dynamc envronment, the overlay network of SCAMP s no longer stable. The n- and out-degrees decrease from 15 to 4. Normally, the n- and out-degrees of SCAMP n a dynamc envronment are much smaller than those n a statc envronment. In contrast, the TYPHOON protocol uses PRF and PRS to prevent the overlay network from heavly weakenng. The smulaton shows that the membershp, though nfluenced by the on-off model, s stll mantaned above the lower bound. C. Multple Descrpton Codng Evaluaton To demonstrate the effectveness of MDC-STHI, four CIF-sze (36x288) vdeo sequences and one D1-sze (7x48) vdeo sequence are encoded wth only I and P frames and wth I frame nterval beng 3 frames. For CIF-sze vdeo sequences, the bt rate for each full-sze stream s set to7 Kbps, and that for each quarter-sze stream s set to 3 Kbps. For the D1-sze vdeo sequence, the bt rate for each full-sze stream s set to 1, Kbps, and 6 Kbps for each quarter-sze stream. When one descrpton stream s lost or delberately dropped due to bandwdth lmtaton, only the full-sze even frames and quarter-sze odd frames are receved. In ths case, E f and O q are nterpolated to produce a full-sze vdeo sequence. Fg.. The 121 st frame of the temporally nterpolated odd stream. The PSNR values of the nterpolated odd frames are shown n Fgs The red curve represents hybrd nterpolaton, and the green and orange ones, respectvely, represent spatal and temporal nterpolaton. These fgures show that the spatal nterpolaton scheme performs better for vdeos wth fast moton whle the temporal nterpolaton scheme performs better for vdeos wth slow moton. Furthermore, STHI outperforms both the spatal and temporal nterpolaton schemes. The frames obtaned from dfferent nterpolaton schemes for the CIF-sze Foreman vdeo sequence are shown n Fgs The crcled areas clearly show the dfference n pcture qualty between these schemes. Fg. 18, whch s

10 1 generated by STHI, shows better qualty than Fgs. 19 and. D. Evaluaton on A Small-Scale Testbed To examne the vdeo qualty based on the proposed partnershp formaton, vdeo codng, and schedulng mechansms, the system s mplemented on a campus testbed. Two sets of experments are performed. The frst set focuses on the mpact of partnershp formaton protocol on vdeo qualty, and the second compares the bandwdth-aware segment schedulng scheme wth the rarest-frst scheme. In these experments, twelve computers n the campus are used. Impact of Partnershp Formaton. In ths set of experments, SCAMP and TYPHOON separately dstrbute the CIF-sze Foreman vdeo sequence at Kbps. The bandwdth avalable for each node s sgnfcantly hgher than Kbps, so segment loss s due to segment request falure rather than bandwdth lmtaton. For each protocol, the experments are repeated three tmes to collect average PSNR values, and the smulaton tme s 18 seconds for each tral. Snce the expermental results are consstent over tme, Fg. 21 only shows the data averaged over twelve nodes and three trals for a perod of seconds. As shown n Fg. 21, the vdeo qualty of SCAMP drops occasonally due to segment request falure. In contrast, vdeo qualty drops seldom occur for TYPHOON. Impact of Segment Schedulng. In ths set of experments, MDC-STHI wth bandwdth-aware schedulng and MPEG-4 wth rarest-frst schedulng s compared. The partnershp formaton protocol used s TYPHOON. For MDC-STHI wth bandwdth-aware schedulng, the CIF-sze Foreman vdeo sequence s encoded nto four sub-streams: E f, E q, O f and O q. The bt rates of E f and O f are set to 7 Kbps and the bt rates of E q and O q are set to 3 Kbps. Three segment types are defned: E f E q +O f O q, E f +O q and O q. Segments of dfferent types are dfferent n sze, redundancy, and PSNR value. Nodes havng E f E q +O f O q segments can serve nodes requestng E f +O q or O q segments, and nodes havng E f +O q segments can serve nodes requestng O q segments. In the experment, ten nodes wth fxed bandwdth 3. Mbps always request segments wth type E f E q +O f O q. In addton, we set up two specal nodes A and B to demonstrate the performance of MDC-STHI under the bandwdth constrant. Node A s confgured wth varyng bandwdth rangng from.8 Mbps to 2. Mbps and the average bandwdth s 1.5 Mbps. Node B s also confgured wth varyng bandwdth rangng from.8 Mbps to 1.2 Mbps and average bandwdth 1. Mbps. All the twelve nodes follow the bandwdth-aware segment schedulng mechansm. The computaton tme of the optmzed schedulng for K=1 and L=3 s at most mllseconds. Ths guarantees that the optmal schedule can be obtaned n real tme. For MPEG-4 wth rarest-frst schedulng, the CIF-sze Foreman vdeo sequence s encoded at 1.5 Mbps. Ten nodes are confgured wth a fxed bandwdth 3. Mbps and two nodes C SCAMP TYPHOON Segment ndex Fg. 21. PSNR values for dfferent partnershp protocols. 3 1 Node A (MDC-STHI wth BW-aware schedulng) Node C (MPEG-4 wth rarest-frst schedulng) 1 Segment ndex Fg. 22. PSNR values for MDC wth bandwdth-aware schedulng and MPEG-4 wth rarest-frst schedulng. Node A and C both have suffcent bandwdth. 3 1 Node B (MDC-STHI wth BW-aware schedulng) Node D (MPEG-4 wth rarest-frst schedulng) 1 Segment ndex Fg. 23. PSNR values for MDC wth bandwdth-aware schedulng and MPEG-4 wth rarest-frst schedulng. Node B and D both have nsuffcent bandwdth. and D are confgured wth varyng bandwdth. Node C has the same bandwdth settng as node A, and node D has the same bandwdth settng as node B. The experments are repeated three tmes to obtan the average results, and the runnng tme for each tral s greater than seconds. Snce the expermental results are consstent over tme, only a perod of 1 seconds s extracted to show the dfference between MDC-STHI wth coded-aware schedulng and MPEG-4 wth rarest-frst schedulng. Fg. 22 shows that node A exhbts more stable vdeo qualty than node C does. However, the dfference s not qute obvous because the bandwdths of node A and C are both suffcent to retreve the vdeo of 1.5 Mbps. Fg. 23 shows the scenaro of nodes wth

11 MDC-STHI wth BW-aware schedulng MPEG-4 wth rarest-frst schedulng Segment ndex Fg. 24. PSNR values for MDC wth bandwdth-aware schedulng and MPEG-4 wth rarest-frst schedulng on PlanetLab. nsuffcent bandwdth. MDC wth bandwdth-aware schedulng allows bandwdth-lmted nodes to acqure lower qualty frames to preserve a stable and smooth dsplay. Ths also proves that the NTUStreamng system adapts to the bandwdth heterogenety n the network. E. Evaluaton on PlanetLab In ths experment, MDC-STHI wth bandwdth-aware schedulng and MPEG-4 wth rarest-frst schedulng are further compared usng the PlanetLab testbed. For MPEG-4, the CIF-sze Foreman sequence s encoded at Kbps. For MDC-STHI, the bt rates of E f and O f are set to Kbps, and the bt rates of E q and O q are set to Kbps. The overlay network conssts of 1 nodes, some of whch are connected va DSL. Because the performance of MPEG-4 s the same as that of MDC-STHI for nodes wth hgh bandwdth, we only show the average vdeo qualty of four DSL nodes wth bandwdth rangng from 3 Kbps to 3 Kbps n Fg. 24. The results are smlar to the one n the prevous secton and prove that MDC-STHI wth bandwdth-aware schedulng can acheve better qualty for bandwdth-lmted nodes. VIII. CONCLUSION In summary, we have presented the networkng and vdeo codng co-desgn of NTUStreamng, whch conssts of three key components: TYPHOON, MDC-STHI, and coded-aware schedulng. TYPHOON makes our system work equally well over both statc and dynamc networks. MDC-STHI makes our system reslent to data loss and adaptve to network heterogenety. Bandwdth-aware schedulng ntegrates the above two components to provde the best vdeo qualty. The expermental results ndcate that the combnaton of P2P streamng wth multple descrpton codng s a promsng approach to adaptve provsonng of vdeo broadcast on large-scale heterogeneous networks. 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Conf. on Multmeda and Expo, Amsterdam, Netherlands, Jul. 5. [31] X. Xu, Y. Wang, S. S. Panwar, and K. W. Ross, A peer-to-peer vdeo-on-demand system usng multple descrpton codng and server dversty, n Proc. IEEE Int. Conf. on Image Processng, pp , Sngapore, Oct. 5. [32] Codng of Audo-Vsual Obects, Part-2 Vsual, Amendment 4: Streamng Vdeo Profle, ISO/IEC /FPDAM4, Jul.. [33] PlanetLab. [34] C. Huang, J. L, and K. W. Ross, Can Internet vdeo-on-demand be proftable? n Proc. ACM SIGCOMM, Kyoto, Japan, Aug. 7. Meng-Tng Lu was born n Peng-Hu, Tawan. He receved the B.S degree n Electrcal Engneerng from Natonal Tawan Unversty, Tawan, n 3. He s currently workng toward the Ph.D. degree n the Graduate Insttute of Communcaton Engneerng, Natonal Tawan Unversty. Hs research nterests nclude vdeo streamng, peer-to-peer streamng, and vdeo codng. Ju-Cheh Wu s currently a research assstant n Natonal Tawan Unversty. He receved hs B.S degree n year 4 and M.S degree n year 6 from the Computer Scence and Informaton Engneerng department, Natonal Tawan Unversty. Hs research nterests nclude overlay network entertanment and sensor networks. Engneerng and Networks Laboratory (TIK) of the Swss Federal Insttute of Technology (ETH) Zurch and a post-doctoral fellow at the Insttute of Pure and Appled Mathematcs of UCLA. Dr. Huang s research nterest ncludes sensor networkng, multmeda networkng, and Internet characterzaton. She s a member of ACM and IEEE and serves currently on the edtoral board of the Journal of Communcatons and Networks. Jason J. Yao receved hs B.S. degree n Electrcal Engneerng from Natonal Tawan Unversty, Tawan, and hs Ph.D. degree n Electrcal and Computer Engneerng from Unversty of Calforna, Santa Barbara. Hs research nterests span from dgtal sgnal processng, telecommuncatons, audo/vdeo systems to Internet traffc engneerng and bonformatcs. Dr. Yao has worked for AT&T Bell Labs, Futsu Network Transport Systems, Futsu Laboratores of Amerca wth ob functons n advanced research, proect management and strategc plannng. Dr. Yao also holds an MBA from Santa Clara Unversty. Kuan-Jen Peng s currently a software engneer n VIA Telecom. He receved hs B.S. degree n 4 from the Computer Scence and Informaton Engneerng department, Natonal Tawan Unversty and M.S degree n 6 from the Graduate Insttute of Communcaton Engneerng, Natonal Tawan Unversty. Hs research nterests nclude network plannng, vdeo streamng and overlay network entertanment. Polly Huang receved her Ph.D. (1999) and M.S. (1997) n Computer Scence from Unversty of Southern Calforna, and her B.S. (1993) n Mathematcs from Natonal Tawan Unversty. In February 3, she oned the Department of Electrcal Engneerng of the Natonal Tawan Unversty at whch she currently holds an assocate professor poston. Pror to onng NTU, she worked as a post-doctoral research scentst at the Computer Homer H. Chen (S 83-M 86-SM 1-F 3) receved the Ph.D. degree from Unversty of Illnos at Urbana-Champagn n Electrcal and Computer Engneerng. Snce August 3, he has been wth the College of Electrcal Engneerng and Computer Scence, Natonal Tawan Unversty, where he s Irvng T. Ho Char Professor. Pror to that, he had held varous R&D management and engneerng postons n leadng US companes ncludng AT&T Bell Labs, Rockwell Scence Center, Vast, and Dgtal Island over a perod of 17 years. He was a US delegate of the ISO and ITU standards commttees and contrbuted to the development of many new nteractve multmeda technologes that are now part of the MPEG-4 and JPEG- standards. Hs research nterests le n the broad area of multmeda processng and communcatons. Dr. Chen s an IEEE Fellow.