Scalable Peer-to-Peer Video Streaming in WiMAX Networks

Transcription

1 Scalable Pee-to-Pee Video Steaming in WiMAX Netwoks Muhammad Aman, Biplab Sikda and Shyam Paekh Depatment of ECSE, Rensselae Polytechnic Institute, Toy, NY Bell Labs, Alcatel-Lucent, Muay Hill, NJ Abstact The inceasing populaity and success of web-based pee-to-pee (P2P) systems fo steaming video applications make them likely candidates fo injecting lage volumes of taffic in the emeging WiMAX netwoks. This pape develops a lightweight mechanism fo P2P steaming in WiMAX netwoks that significantly educes the load on the netwok and impoves the scalability of the steaming system. The poposed system uses the boadcast mechanism povided in the IEEE mechanism fo poviding the scalability, without beaking the P2P semantics. The scalability of the poposed system is analytically evaluated and also quantified using simulations. Ou esults show that the degee of impovement in the pefomance of the poposed system is lowe bounded by the aveage numbe of pees seved by an Access Sevice Netwok Gateway in the WiMAX netwoks. I. INTRODUCTION An inceasingly popula application in the Intenet today is pee-to-pee (P2P) video steaming [1], [2], [3]. With the advent of many commecial gade systems that ae feely available, P2P steaming has attained a lage numbe of uses. Fo example, the Chinese New Yea celebations wee boadcast by a commecial P2P steaming systems to ove 200,000 uses in the Intenet with bits ates in the ange Kbps [4]. When one consides ealistic futue scenaios with potentially millions of uses watching steams of 500 Kbps o moe, the Intenet backbone and access netwoks such as those offeed by WiMAX can be easily ovewhelmed with taffic. In the context of WiMAX as the access netwok fo the uses of these sevices, in addition to the scalability povided by the P2P steaming systems, additional WiMAX specific featues may be equied to ensue satisfactoy use expeience. Fom the pespective of WiMAX opeatos, it is thus of inteest to evaluate the scalability of video steaming in thei netwoks and facilitate the integation of featues in the P2P systems that exploit the flexibility and unique featues of the PHY and MAC layes of WiMAX netwoks. Existing wok on P2P steaming systems pimaily focuses on wied netwoks [1], [2], [3] and these solutions ae not well suited fo WiMAX netwoks and neithe ae they capable of exploiting the featues and functionalities of these netwoks. This pape addesses the above issues in two ways: (1) it poposes a mechanism fo P2P steaming specific to WiMAX netwoks that ties to maximize the sevice capacity of the video steaming system by exploiting the multicast sevices povided in IEEE and (2) it evaluates the scalability of P2P steaming sevices in WiMAX netwoks. The poposed steaming mechanism equies only mino changes to existing P2P potocols while maintaining P2P semantics and does not equie any changes to the IEEE standads. Using both analysis and simulations, we show that the poposed scheme can impove the scalability of the P2P steaming system by a magnitude at least as lage as the aveage numbe of pees seved by an Access Sevice Netwok Gateway (ASN-GW). The est of the pape is oganized as follows. In Section II we pesent an oveview the achitectue of popula P2P steaming systems. Section III pesents the poposed mechanism fo P2P steaming in WiMAX netwoks while Section IV pesents the scaling model. Finally, Section V evaluates the pefomance of the poposed system using simulation and Section VI pesents the concluding emaks. II. OVERVIEW OF P2P STREAMING SYSTEMS Existing schemes fo the delivey of steaming multimedia o IPTV content include IP multicasting [5], application level infastuctue ovelays [6], pee-to-pee multicast tees [7] and mesh-pull pee-to-pee steaming [1], [8]. Among these, the mesh-pull based steaming systems such as PPLive, PPSteam and CoolSteaming ae among the most popula. While these systems ae popietay, they follow the basic achitectue of geneic mesh-pull P2P steaming systems shown in Figue 1. A typical mesh-pull P2P steaming system consists of a tacke seve and individual pees that coopeatively distibute the media content among themselves. The media content is initially available at the channel steaming seve which beaks the content into chunks that fom the unit of infomation exchange among the pees. Each pee consists of a steaming engine and a media playe. The steaming engine at each pee downloads media chunks fom othe pees and the channel steaming seves and exchanges these chunks with othe pees. The chunks eceived at a pee ae eassembled to fom the oiginal content and played back by the media playe. When a pee desies to join the netwok and download media, it fist contacts the tacke seve to obtain a list of the media available in the P2P netwok and obtains an initial list of pees that ae cuently watching the same media o channel as the pee wishes to download. The pee then contacts the pees in the list to obtain additional lists of pees watching the same media. As the pee stats to download and view the media, it maintains a buffe with few minutes woth of chunks. These chunks may include those that have aleady been viewed as well as those that ae waiting to be played.

2 Pimegy Media Playe Tacke Seve Steaming Engine Chunk Delivey Channel Steaming Seve Registation Pee discovey Repoting Chunk Request Steaming Engine Steaming Engine Media Playe Media Playe Fig. 1. Achitectue of mesh-pull P2P steaming systems. Fig. 2. Achitectue of P2P steaming in WiMAX netwoks. Each pee maintains a buffe map that indicates which chunks that it cuently has buffeed fo shaing with othes. Pees exchange buffe maps with othe pees in thei pee list and can equest one o moe chunks fom them. Chunks may also be downloaded fom the oiginal channel steaming seve in paallel with the downloads fom othe pees. While TCP is typically used fo tansfeing the chunks, some mesh-pull P2P systems use UDP as the tanspot potocol in ode to ensue timely delivey. III. PROPOSED ARCHITECTURE Conside a scenaio whee a numbe of SSs in a WiMAX netwok ae inteested in joining a P2P steaming session. When thee ae multiple SSs associated with a single BS that wish to view the same channel o content, the BS has to send the same media chunks to all the pees, sepaately. Thus an intuitive method fo educing the load on the BS and allow the P2P netwok to scale would be to develop a mechanism that can exploit the inheent boadcast natue of the tansmissions fom the BS to avoid edundant tansmissions not only in the last hop (i.e. fom the BS to the SSs), but also inside the coe netwok o the Intenet. Howeve, these need to be done without beaking the P2P semantics and without any majo changes to the undelying P2P potocol. Additionally, the desied solution should be lightweight, scalable and should be implemented without any changes to the WiMAX entities. This section highlights the challenges and the poposed solution fo a scalable P2P steaming system fo WiMAX netwoks. A. Oveview Conside Figue 2 which shows the basic achitectue of a P2P steaming system in WiMAX netwoks. If any of the SSs wants to eceive the P2P steam, it fist contacts the tacke in the same way as any othe P2P node. Howeve, the goal of ou poposed potocol is that if now anothe SS wants to eceive the same steam, it should be able do so without any additional bandwidth equiement. To solve this poblem, we popose that the ASN-GW be the poxy fo a multicast session associated with its SSs that ae involved in the P2P steaming of a paticula channel. Thus, afte one SS stats eceiving the steam, adding anothe SS to the same steam would equie only adding the next SS to the multicast session. Howeve, to do so, the SS should be able to identify and join the taget multicast session. A BS in WiMAX netwoks cannot distinguish an Laye 3 (L3) multicast goup. Consequently when an AS-GW eceives a multicast packet, it has to make a copy of the packet fo each of the SSs in the multicast goup, and delives the copies of the same packets to the BS. To eliminate this edundancy, we use a technique simila to that in [9] whee the BS needs to send the multicast IP addess along with the Multicast Polling Assignment Request (MCA- REQ) messages, so that the SS can identify the L3 multicast goup of the MCA-REQ message and join the coect goup. In the poposed scheme, in addition to the usual attibutes about the pees, the tacke includes two additional fields fo each pee. The fist field consists of one bit to indicate whethe the pee is in a WiMAX netwok o not. Fo pees that ae WiMAX SSs, the second field then stoes the multicast IP addess associated with the SS in its ASN-GW. To populate these enties, pees povide the necessay infomation eithe duing egistation, o late on acquiing a multicast IP addess. When the tacke esponds to new pees with the initial list of pees, it pefeentially lists existing pees that ae WiMAX SSs. This inceases the chances that the new WiMAX pee will be able to find othe pees that ae SSs in its own ASN- GW, if any. Afte eceiving the addesses of the pees and the multicast IP addesses of WiMAX pees, the new pee now listens to the peiodic MCA-REQ messages sent by its BS to check if any of the ongoing multicast sessions matches the ones listed by the tacke. If thee is a match, the pee joins this multicast session to eceive the multimedia steam. We now descibe the poposed mechanism in detail by consideing vaious scenaios of opeation. B. Case 1: No Existing WiMAX Pees in Same ASN-GW We fist conside the case when thee ae no existing WiMAX pees in the ASN-GW of the new pee (SS) that wishes to join the steaming session. In this scenaio, as shown in Figue 3, a new pee stats by contacting the tacke fo a list of available pees, with a pefeence fo pees in WiMAX netwoks. The tacke eplies with a list of available pees with pefeence to pees in WiMAX netwoks and thei multicast IP addesses. On eceiving this infomation, the pee then compaes the listed multicast IP addesses, if any, with the multicast IP addesses in the peiodic MCA-REQ messages sent by its BS. In this case, thee will not be any matches. To

3 SS Tacke BS ASN GW Pee/Seve Registation/Pee discoey (WiMAX node pefeence) No WiMAX pees/wimax pees in diffeent ASN GW IGMP join with the IP addess of seve/pee IGMP join Video steaming packet MCA REQ MCA RSP Peiodic MCA REQ message containing multicast IP Goup table check Fig. 3. Potocol opeation in the absence of pees in the same ASN-GW. SS Tacke BS Registation/Pee discoey (WiMAX node pefeence) SS Tacke BS ASN GW Registation/Pee discoey (WiMAX node pefeence) WiMAX pee(s) + multicast IP WiMAX pee(s) + multicast IP Peiodic MCA REQ message containing multicast IP MCA RSP Peiodic MCA REQ message containing multicast IP IGMP join with multicast IP eceived duing egistation MCA REQ MCA RSP Fig. 4. Potocol opeation in the pesence of pees in the same BS and ASN-GW. check if any of the multicast sessions in the eceived list exist in anothe BS seved by its ASN-GW (see case 3 below), the pee then sends IGMP join equests to its ASN-GW fo these multicast IP addesses. The ASN-GW checks its goup table and in the cuent case does not find any match, and dops these equests. Thus the pee concludes that thee thee is no active multicast session fo the equested P2P media steam within its ASN-GW. Thus the new pee initiates a new P2P session with the seve o one of the pees outside its ASN-GW by sending it an IGMP join message. Simila messages may be sent to multiple pees. Moeove, the new pee will equest the seve and the othe pees to send the media steam to its destination multicast addess instead of a unicast addess. Once the seve o the pees join the multicast session, all steaming packets to the new pee ae sent ove the multicast session. At the last hop, the steaming packets ae sent to the pee SSs using MCA-REQ and MCA-RSP exchanges. Finally, the new pee updates the tacke with the multicast IP addess of the sessions that it has initiated. C. Case 2: Existing WiMAX Pee in Same BS and ASN-GW The second scenaio deals with the case when a pee exists in the same BS and ASN-GW as the SS which wants to join the P2P steam. As in the pevious case, when the new pee contacts the tacke fo P2P nodes, it will notify the tacke that it is a WiMAX node, as shown in Figue 4. Fig. 5. Potocol opeation in the pesence of pees in the same ASN-GW but diffeent BS. In tun the tacke will povide the new pee with a list of pees in WiMAX netwoks and othe infomation such as the associated multicast IP addesses. The pee then listens to the MCA-REQ messaged boadcast by its BS and compaes the multicast IP addesses in the list with those in the MCA-REQ messages. In this case thee is a match and the pee then joins the multicast session. Subsequently, it can listen on to the steaming multimedia packets that ae boadcast by the BS. D. Case 3: Existing WiMAX Pee in Same ASN-GW but Anothe BS The thid scenaio deals with the case when no pee exists in the same BS as the new pee but thee exists a pee in the egion of a BS being seved by the same ASN-GW as the BS of the joining SS. In this scenaio, as shown in Figue 5, the new pee will pefom pee discovey as in the pevious two cases. As usual, the tacke eplies with a list of existing pees, with a pefeence to pees in WiMAX netwoks. Howeve, when the SS compaes the multicast IP addesses obtained fom the tacke with the multicast IP addesses eceived in the peiodic MCA-REQ messages fom its BS, the compaison fails. Thus the pee SS sends IGMP join messages to the ASN-GW with the same multicast IP addesses as it eceived fom the tacke. The ASN-GW checks it s goup table and finds out that a multicast session with one of the multicast IP addesses is aleady in pogess and thus adds the new BS

4 into the multicast goup. The join messages fo IP addesses not in its goup table ae dopped. Next time when the BS eceives the multicast packet fom the ASN-GW, it will send the MCA-REQ message with multicast IP addess of the P2P steam. Thus, the new pee accepts the MCA-REQ message by sending an MCA-RSP message and stats eceiving the multimedia steam. E. Effect on the P2P Steaming Potocol The poposed potocol can scale a P2P multimedia steam to a lage numbe of WiMAX uses with vey mino changes to the existing P2P potocols. Fistly, each pee adds a bit in the egistation message it sends to the tacke to indicate that it is in a WiMAX netwok. Secondly, the tacke now needs to save the multicast IP as well as the unicast IP addess of the pees in the case of nodes in WiMAX netwoks. The thid change that is equied is that if a non-wimax P2P node eceives an IGMP join message, it should stat sending the chunks to a multicast IP addess athe than to an unicast IP addess. The upload potion of the P2P potocols emains the same, i.e. if a non-wimax node equests a chunk fom a WiMAX node, the pocedue followed will be simila to existing P2P potocols. IV. SCALING BEHAVIOR OF THE PROPOSED PROTOCOL In a steaming session, the usability of any chunk aiving at a pee depends on the time that has elapsed since the chunk was fist geneated by the steaming seve (souce). Thus the numbe of pees that may be suppoted in a P2P steaming session depends on the delay bound as well as the ovelay P2P topology. In this section we evaluate a bound on the numbe of pees that may be suppoted by the poposed P2P system and compae it with that of a native P2P system. We stat with a chaacteization of an optimal P2P steaming session. The optimal session is defined as one that achieves the lagest numbe of pees eceiving data at a given ate within a maximum toleated delay, without consideing fainess among pees. Now, the delay incued by a chunk is a sum of the queueing delays and the popagation delays. Queueing delays ae incued when chunks ae enqueued at a pee waiting to be played o to be elayed to othe pees. It is obvious that thee is no queueing delay in an optimal session. This is because if all pees eceive data at ate, then buffeing is not equied and a pee may immediately play a block it eceives. Consequently, we need to conside only popagation delays. Let d i be the popagation delay fom the souce to pee i, measued in tems of the numbe of P2P ovelay hops. A pee is consideed seved if the upload capacity of the souce and all the existing seved pees have the capacity to seve it at ate, while ensuing that the downloads of none of the existing pees is disupted. We conside a netwok with N pees and without loss of geneality we assume that the N pees ae seved in the ode 1,2,,N. Then the popagation delay fo pee i is k+1 (i.e. d i = k + 1) if k is the smallest intege fo which i 1 + u j I(d j k) i (1) j=1 whee and u j ae the upload bandwidths of the souce and pee j espectively, and I(x) is an indicato function that takes the value of 1 if x is tue and 0 othewise. The optimal steaming session ties to maximize the numbe of pees seved while ensuing that the maximum delay at any pee is not moe than a theshold. Intuitively, placing pees with lage upload capacities close to the souce will incease the numbe of pees that can successfully join the P2P steaming session. This esult can be fomalized as: Claim 1: Conside a P2P steaming session with N pees whee the seve s bandwidth is and the othe pees have a bandwidth dawn fom a distibution F(u). By placing the pees with highe upload capacities close to the souce, the numbe of pees suppoted with delays lowe than a theshold is no less than that of an optimal session. Poof: Assume that thee exists an optimal session Π in which thee exists at least one set of pees (a,a v ) such that the upload capacity u < u v but d > d v. The numbe of pees suppoted by the optimal P2P session is then Ω(Π) = = I(d i < ) 1 I(d i < ) + I(d < ) + +I(d v < ) + i=+1 I(d i < ) I(d i < ) (2) Now conside an altenate topology Π which is identical to Π in all espects except that the positions of a and a v ae swapped. Let the distance fo pee i in this topology be d i. The numbe of pees suppoted by Π is then Ω(Π ) = 1 I(d i < ) + I(d < ) + +I(d v < ) + i=+1 I(d i < ) I(d i < ) (3) Since a pee with highe upload capacity has been placed in position, the new distance d = d. Also, the pees in positions 1 to 1, +1 to, and v+1 to N ae not changed. Thus we have d i = d i fo 1 i 1. The diffeence in the numbe of pees suppoted in the two sessions is then Ω(Π) Ω(Π ) = I(d i < ) + I(d v < ) + I(d i < ) i=+1 i=+1 I(d i< ) I(d v < ) I(d i< ) (4) Now d i = k + 1 if k is the smallest value fo which + i 1 j=1 u ji(d j k) i, i.e. d i = 1 + ag min k i 1 u j I(d j k) + i (5) j=1

5 Since u > u and u j > u j, j with j v, we have j u i > j u i and d i d i fo < j < v. This in tun implies I(d j < ) I(d j < ) (6) fo < j < s. Now since the nodes in positions and v of Π ae swapped in Π, we have u + u v = u + u v. This implies j u i = j u i fo j > v. As befoe, we again have I(d j < ) I(d j < ) (7) fo j > s. Fom Eqns. (6) and (7) we then have Ω(Π ) Ω(Π) 0 (8) This shows that the session unde Π is no wose than the optimal session. Fom the esult above, we can also conclude that in an optimal session, the seve neve uploads media to pees that ae moe than one hop away. Next we conside a means to obtain a lowe bound on the numbe of suppoted pees by any P2P steaming system. Fo this, we conside the case whee all pees have the same, constant upload capacity. We show that such a system seves as a lowe bound on the numbe of pees that can be suppoted by any P2P steaming system. Claim 2: Conside an abitay upload capacity distibution F a (u) that has the same mean as a constant upload capacity distibution F c (u) = δ(). As the netwok size inceases, the numbe of pees that can be suppoted with delays less than when the pees have upload capacities dawn fom F a (u) is no less than the coesponding numbe of pees suppoted when the upload capacities ae constant. Poof: Fom Claim 1, to maximize the numbe of suppoted pees, we place the pees with the highe upload capacities close to the souce. Also, the pee upload capacities, in deceasing ode, in the abitay distibution ae denoted by a 1,a 2,,a N and in the constant capacity case by b 1,b 2,,b N with b i = b j, i,j. Since the means of the two distibutions is the same, we have lim N 1 N a i = 1 N b i w.p. 1 (9) whee w.p. stands fo with pobability. The pobability that thee exists at least one pee (i.e. the pee with the highest upload capacity) with upload capacity geate than is P[a 1 > ] = 1 As N, we have P[a 1 > ] = N P[a i ] = 1 [P[a ]] N lim 1 [P[a N ]]N = 1 (10) Also since fom Eqn. (9) we have N a i = N b i, Eqn. (10) implies that j a i > j b i, fo 1 j < N, and thus d aj d bj. This in tun implies I(d ai < ) I(d bi < ) (11) fo 1 j < N and hence I(d ai < ) I(d bi < ) (12) which concludes the poof. Next we poceed to obtain the numbe of pees that may be suppoted fo a given delay bound in the native as well as the poposed P2P steaming system using the methodology in [10]. Hee we assume that all pees ae in WiMAX netwoks. Also, the numbe of pees unde each ASN-GW is denoted by M. Note that fom Claims 1 and 2, to compae the wost case pefomance of the two systems, it suffices to compae thei pefomance unde the case of constant upload capacity distibution. We conside the native P2P system fist and assume that / and / ae integes. Based on the atio of and, we have two cases and the following esults summaize the pefomance in each case. Claim 3: The numbe of pees suppoted in the native P2P steaming system fo a delay constaint when is N max = ( ) 1 1 (13) Poof: The steaming seve seves / pees and each of these in tun can seve / pees. With a delay constaint of, we can have 1 such hops. The total numbe of pees suppoted is then N max = 1 i=0 ( ) i = ( ) 1 1 (14) which concludes the poof. When <, the addition of a pee intoduces less upload bandwidth in the netwok than that used by the pee. Thus if is lage, thee will not be sufficient bandwidth to suppot any moe pees afte a numbe of hops, h. In paticula, h is given by the smallest i such that cs ( )i 1 <, i.e. i > log ( ) ( 2 ) + 1 (15) since log α (x) > log α (y) if α < 1 and x < y. The numbe of pees suppoted in this case is given by the following esult. Claim 4: The numbe of pees suppoted in the native P2P steaming system fo a delay constaint when < is N max < ( 3 2 ) cs 1 = cs ( ) 1 1 fo h = log ( ) ( 2 ) + 1 < othewise (16) Poof: In the fist case, the bandwidth is exhausted befoe the delay bound is met. The numbe of suppoted pees is then N max = & log ( ) i=0 2 cs ( ) i < ( 3 2 ) cs 1 (17) In the case whee the delay bound is eached befoe the available bandwidth is exhausted, we can use Eqn. (14) to deive the numbe of suppoted pees. This completes the poof.

6 10 3 native poposed native poposed Numbe of Pees Suppoted Numbe of Pees Suppoted Fig. 6. Scalability of the poposed system when >. Fig. 7. Scalability of the poposed system when <. Fo the poposed P2P steaming system, we can use the same esults as above by intepeting N max in the equations above to epesent ASN-GWs athe than pees. Then since each ASN-GW can suppot M pees while using the same download capacity equied by one pee in the native system, the poposed system is at least M times as scalable. Futhe impovements may occu when we conside the fact that each of the M pees in the ASN-GW may now contibute upload bandwidth. V. SIMULATION RESULTS In this section we use simulations to demonstate and quantify the impovement in scalability of the poposed P2P steaming system fo WiMAX netwoks. The simulations wee conducted using a custom built simulato. In the scenaio consideed, the netwok had a total of 100 ASN-GWs with thee BSs in each ASN-GW. Also, each BS had five SSs that ty to paticipate in the P2P steaming session. The equied download ate at each pee is = 340 Kbps and the upload capacity at each pee depends on its distance fom its BS and the coesponding highest modulation and coding scheme that can be suppoted. The possible modulation and coding schemes wee BPSK(1/2), QPSK(1/2), QPSK(3/4), 16 QAM(1/2), 16 QAM(3/4), 64 QAM(2/3) and 64 QAM(3/4). Fo each simulation setting, the esults pesented ae the aveage ove 10 uns of the simulato. In the fist scenaio, the nodes ae andomly placed such that they ae moe likely to be close to the BS and the aveage upload capacity of the pees was Kbps, i.e. >. Fo this case, Figue 6 compaes the numbe of pees suppoted by the poposed P2P steaming system with that of the oiginal, native system. We see that the impovement in the poposed system povides is of the ode of the numbe of pees in an ASN-GW, as shown in the pevious section. The degee of impovement inceases as the delay bound inceases. Figue 7 shows the coesponding esults fo the case whee the aveage upload capacity of the pees was 323 Kbps, i.e. <. In this case, the numbe of pees suppoted satuates much faste in the native P2P steaming system. Also, the impovement in the poposed system inceases as the delay bound inceases. VI. CONCLUSION In this pape we poposed a mechanism fo impoving the scalability of P2P steaming potocols in WiMAX netwoks. The poposed potocol is based on exploiting the multicast featue of WiMAX netwoks to avoid edundant, multiple tansmissions of the same packet fom the BS to multiple pee SSs. A potocol fo facilitating the multicast tansmissions is poposed and the scalability of the poposed system is evaluated. Ou esults show that the poposed system can significantly impove the scalability of P2P steaming systems when the pees ae pat of a WiMAX netwok. REFERENCES [1] X. Zhang, J. Liu, B. Li and T.-S. Yum, DONet/CoolSteaming: A Data-diven Ovelay Netwok fo Live Media Steaming, Poc. IEEE INFOCOM, Mach [2] M. Zhang, Q. Zhang, L. Sun and S. Yang, Undestanding the powe of pull-based steaming potocol: Can we do bette?, IEEE Jou. on Sel. Aeas in Comm., vol. 25, no. 9, pp , Decembe [3] F. Pianese, D. Peino, J. Kelle and E. Biesack, Pulse: an adaptive, incentive-based, unstuctued p2p live steaming system, IEEE Tansaction on Multimedia, vol. 9, no. 8, pp , Decembe [4] X. Hei, C. Liang, J. Liang, Y. Liu and K. Ross, A Measuement Study of a Lage-Scale P2P IPTV System, IEEE Tansactions on Multimedia, vol. 9, no. 8, pp , Decembe [5] S. Deeing and D. Cheiton, Multicast outing in datagam intenetwoks and extended LANs, ACM Tansactions on Compute Systems, vol. 8, no. 2, pp , May [6] L. Kontothanassis et. al., A Tanspot Laye fo Live Steaming in a Content Delivey Netwok, Poceedings of the IEEE, vol. 92, no. 9, pp , [7] Y. Chu, S. Rao and H. Zhang, A Case Fo End System Multicast, Poc. ACM SIGMETRICS, pp. 1-12, Santa Claa, CA, June [8] X. Hei, Y. Liu and K. Ross, IPTV ove P2P Steaming Netwoks: the Mesh-pull Appoach, IEEE Communications Magazine, vol. 46, no. 2, pp , Feb [9] K. Lee, S. Rhee and H. Youn, A MAC Laye Multicasting Appoach fo WiMAX Access Netwoks, Poc. IEEE PeCom, Mach [10] T. Small, B. Liang and B. Li Fundamental Scaling Laws of Pee-to-Pee Live Multimedia Steaming, Poc. ACM Multimedia, Octobe 2006.