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336 IEEE TRANSACTIONS ON , VOL. 52, NO. 3, SEPTEMBER 2006 CAR: A Low Latency -on-Demand Broadcasting Scheme for Heterogeneous Receivers Chin-Tsai Lin and Jen-Wen Ding

Abstract—As different types of networks are converging wireless environments for the following two reasons. First, wire- into an all-IP network, i.e., the , it can be expected that less networks have very limited compared to conven- in the near future video-on-demand (VoD) will be widely applied tional wired networks. Second, users in wireless environments to many interesting services, and users can access these services using heterogeneous terminals via heterogeneous wired/wireless usually employ heterogeneous terminals, which are quite dif- access networks. Many periodic broadcasting protocols have ferent in terms of their processing capability, storage space, and been proposed to reduce the implementation cost of VoD systems. power. However, most of the protocols assumed homogeneity for user In the past few years, much research has been devoted to terminals, while in practice, user terminals are usually quite the design of efficient VoD servers and VoD transmission different in their processing power, buffer space, and power. To address this problem, a few periodic broadcasting protocols protocols (or protocols) [1]–[9], [11]–[15], [17]–[19], providing the same video quality for all heterogeneous clients [21]–[24]. Many studies showed that a well-designed VoD have been proposed recently. In this paper, we proposed a novel broadcasting protocol is a key technology that can effectively heterogeneous VoD broadcasting technique called Catch and Rest lower the very high I/O bandwidth and network band- (CAR) to accommodate bandwidth heterogeneity without sacri- width requirements of a large-scale VoD system. Hu and Hua ficing user video quality. Then, we provide mathematic analysis to calculate the client bandwidth and buffer space requirements of et al. provide a comprehensive survey of VoD broadcasting CAR. Finally, we present our performance evaluation results for protocols in [13], [14]. These protocols allow a large number of CAR. Our results show that under the same system resources (i.e., clients to demand different at any time with low service server and network bandwidth), CAR provides more uniform and latency ranging from a few seconds to a few minutes depending acceptable service latency for all heterogeneous clients compared on the design of the system. The service latency, in this paper, to previous works. is defined to be the time between the demand for a video and Index Terms—Broadcast channels, catch and rest, the reception of the beginning of the video. , multimedia systems, periodic broadcasting, VoD broadcasting protocols can be classified into two quality-of-service (QoS), video-on-demand (VoD). categories: reactive and proactive [13], [14]. In the reactive approach, clients make requests to a video server and the server I. INTRODUCTION employs broadcast (or multicast) to service a batch of requests that demand the same video and arrives closely in time. Ex- ITH the rapid development of multimedia and commu- amples of this type of approach include first-come-first-serve Wnication technologies over the past decade, it is (FCFS) batching, maximum-queue-length-first (MQLF) feasible to provide video-on-demand (VoD) services to a large batching [6] and maximum-factored-queued-length-first number of users using wired networks. It is antici- (MFQLF) [1], and various types of patching [3], [4], [9]. In pated that in the near future, as different types of wireless net- the proactive approach, videos are divided into a series of works are converging into all IP networks, VoD will be widely segments and broadcast periodically on dedicated channels. applied to many services (e.g., home entertainment, distance The proactive approach is delicately designed such that all learning, digital libraries, staff training, on-line games) [16], clients arriving at different times can receive and watch videos [20], and users can access these services using different termi- continuously with low service latency. For a large-scale system, nals (e.g., PDA, smart-phone, set-top box, notebook, PC) via the reactive approach is far less efficient compared to the different access technologies (e.g., 2.5G/, WLAN/WMAN, proactive approach. The VoD service provided by broadcasting xDSL) [10]. Fig. 1 shows the general architecture for providing protocols is usually referred to as near VoD service since a VoD services to heterogeneous users in hybrid wired/wireless true VoD service does not require users to wait and supports networks. However, to date, we still face many problems to video-cassette-recorder-like (VCR-like) interactivities [13], achieve the above goal. One of the main difficulties is that con- [14]. ventional VoD delivery technology cannot be readily applied to Although many proactive video broadcasting protocols have been proposed, much research has assumed that all clients are homogeneous, i.e., all clients have the same reception capability Manuscript received September 14, 2005; revised March 16, 2006. C.-T. Lin is with the Department of Information Management, Kun Shan Uni- and storage space. As discussed earlier, in the future clients at versity, Tainan 710, Taiwan (e-mail: [email protected]). different geographical locations will access VoD services using J.-W. Ding is with the Department of Information Management, National heterogeneous terminals via various wireless/wired access Kaohsiung University of Applied Sciences, Kaohsiung 807, Taiwan (e-mail: [email protected]). network technologies. This implies that a VoD broadcasting Digital Object Identifier 10.1109/TBC.2006.879856 protocol should take this heterogeneity into account and support

0018-9316/$20.00 © 2006 IEEE LIN AND DING: LOW LATENCY VIDEO-ON-DEMAND BROADCASTING SCHEME FOR HETEROGENEOUS RECEIVERS 337

Fig. 1. General architecture for providing heterogeneous VoD services. receivers with different reception capabilities (ranging from required bandwidth and buffer space, respectively, for clients. very limited wireless bandwidth in a cafe to very high wired Section V describes the parameter settings of our simulation bandwidth at work) and different storage space (ranging from experiments and the performance evaluation results of CAR. a few mega-bytes to a few giga-bytes). However, little research Finally, Section VI concludes this paper. has been done on providing VoD services for heterogeneous receivers in hybrid wireless/wired networks. Two innovative II. RELATED WORK schemes, HeRO [2] and BroadCatch [19], have been proposed to address this problem recently. With both schemes, users can A. Overview of Periodic Video Broadcasting Schemes choose among a range of bandwidths to use to watch the video One way to broadcast popular video is to let multiple clients at the cost of their service latency, not the video quality. Specif- share the same set of channels. To reduce client access latency, ically, clients with high reception bandwidth watch videos with Staggered Broadcast [5] is the simplest broadcasting protocol low service latency, while clients with low reception bandwidth proposed in the early days. It periodically broadcasts the whole watch videos with long service latency. Although both schemes video in channels differentiated by time of the video. can provide relatively low service latency for high-end clients, Some more efficient broadcasting protocols have proposed. In- the service latency for low-end clients is quite high. In this stead of broadcasting the whole video, they broadcast a distinct paper, we propose a novel heterogeneous VoD broadcasting portion of the video periodically in each channel. In each por- scheme, termed CAR (catch-and-rest), to solve this problem. tion, the video may be further partitioned into segments that Compared to HeRO and BroadCatch, CAR greatly reduces are of fixed size or variant size depending on the broadcasting the service latency for low-end clients at the cost of slightly schedule. increasing the service latency for high-end clients. The reduced The efficiency of the proposed broadcasting schedule is service latency is one or two order of magnitude larger than always evaluated by the bandwidths that are required by the the increased service latency. This design tradeoff is significant servers and the clients. Early periodic broadcast approaches since it implies that under a limited broadcast bandwidth, it such as Pyramid Broadcast (PB) [23], Fast Broadcast [17], Har- is more likely that CAR can provide acceptable service la- monic Broadcast [15], New Pagoda Broadcast [18], Recursive tency guarantee for both high-end and low-end clients, while Frequency-Splitting [22], etc.\ aimed at reducing the server HeRO and BroadCatch can provide acceptable service latency bandwidth. However, these protocols demand that the clients guarantee for only high-end clients. In addition to service have the same bandwidth with the server and therefore result latency, CAR greatly reduces the maximum client buffer space in the requirement of high-cost clients. To minimize the client requirement as compared to BroadCatch, and has similar client bandwidth requirement, Skyscraper Broadcast [11], Client buffer space requirement as compared to HeRO. The feasibility Centric Approach (CCA) [12] and Generalized Fibonacci of CAR is proved theoretically. The performance of CAR is Broadcast [24] are proposed to limit the client bandwidth to a validated by conducting extensive simulations and comparing fixed times of the playback bandwidth. the results with that of HeRO and BroadCatch. The rest of this paper is organized as follows. Section II-A B. Review of Hero and BroadCatch provides an overview of periodic video broadcasting schemes Essentially, all the broadcasting protocol mentioned above as- proposed in the literature, and Section II-B describes the sume that all of the clients have the same reception capability. In main idea behind the latest innovative heterogeneous VoD real environment, the reception capabilities of clients vary. Re- broadcasting algorithms, HeRO and BroadCatch. Section III cently, HeRO and BroadCatch are proposed to enable periodic presents the proposed video broadcasting protocol, CAR. broadcast of constant (CBR) encoded video adaptive to Section IV shows the algorithm and the formula to calculate the clients with different reception capability. While a client with 338 IEEE TRANSACTIONS ON BROADCASTING, VOL. 52, NO. 3, SEPTEMBER 2006

Fig. 2. An example of HeRO with two shifted replicate channels. more reception bandwidth can benefit a shorter service latency, segments with horizontal lines. The maximum number of a client with less bandwidth takes the cost of longer service channels that are downloaded simultaneously is 3, so the latency without sacrificing the display quality. To understand bandwidth requirement is . the technique of heterogeneity, we review these two protocols If the client has not enough bandwidth, then s/he has to wait herein. until a time slot with a suitable bandwidth requirement. Once HeRO is composed of original channels identical to those beginning, the client must the broadcasting segments of Fast Broadcast plus several shifted replicate channels. All the continuously so that non-stop playback can be guaranteed. It channels are of bandwidth equal to the playback bandwidth of has been shown that replicate channels can effectively reduce the video. The video are evenly partitioned into segments, the waiting time and the buffer space requirement for the clients. denoted .For , the th original However, the more the number of replicate channels is, the more channel periodically broadcasts the segments . the latencies of high-end clients are, and the more the buffer That is, the number of distinct segments on each channel is a space requirement becomes. power of 2. One or more latest original channels are coupled BroadCatch is a new novel broadcast protocol providing het- with a shifted replicate channel that broadcasts the same series erogeneity. There are two basic channels that both broadcast of segments with the original channel except shifting half of the the whole video and differentiate each other half of the time. period. As an example, the channel schedule of HeRO with six The scheme reduces the service latency by adding recursively original channels plus two shifted replicate channels is shown more channels that periodically broadcast the leading half por- in Fig. 2. tions of the video to eventually catch the basic channels. All of To view the video, on requesting the video the client finds the channels are also of bandwidth equal to the playback band- out the first time slot to start downloading the first video seg- width . Fig. 3 shown an example of BroadCatch broadcast with ment from the first channel. Basically, the client bandwidth re- five server channels. It can be observed that clients may start quirement depends on the request time because the reception receiving the first segment of the video from any channel de- schedule varies for different startup time and the client may pending on the demanding time. Subsequent segments are al- have to download segments from multiple channels simultane- ways downloaded from the current channel or higher channels. ously so that no segment is missed. The bandwidth requirement Although there may exist many reception schedules for a Broad- of client beginning reception from the time slot, referred as the Catch client starting from a given time slot, a scheme to de- bandwidth requirement associated with the time slot, is equal rive a reception schedule with the least bandwidth requirement to the peak bandwidth occurred through the reception schedule. demands that the client avoid downloading segments from the For example, three cases of reception schedule are illustrated in trailing half of a portion while downloading segments from a Fig. 2. lower channel if possible. That is based on the fact that through 1) The client starts to download segments at the beginning of any reception schedule, the leading half of a portion can overlap time slot 0. The reception schedule follows the gray seg- in reception time with at most one higher portion, while the ments as shown. The client always segments trailing half may overlap in reception time with many higher from a channel at a time. Therefore, the bandwidth require- portions. For example, as shown in Fig. 3, the client who starts ment is . to download segments at the beginning of time slot 6 cannot 2) The client starts to download segments at the beginning of download Segments 3 and 4 from Channel 2. Otherwise, Seg- time slot 31. The reception schedule follows the dark seg- ments 3, 5, and 9 will be downloaded at the same time and the ments as shown. The client must at first download segments bandwidth requirement will be rather than . The worst case from Channels 1 to 4 simultaneously, and download seg- in Fig. 3 is that starting from time slot 7, 15, or 23. In which case, ments from both Channels 6 and 8 simultaneously during Segments 3, and 5 to 7 are inevitable to be downloaded from the some interval. Therefore, the bandwidth requirement is . trailing halves of portions. 3) The client starts to download segments at the beginning of The main advantage of BroadCatch is that the server need time slot 11. The reception schedule is illustrated by the only add more channels broadcasting the leading portions peri- LIN AND DING: LOW LATENCY VIDEO-ON-DEMAND BROADCASTING SCHEME FOR HETEROGENEOUS RECEIVERS 339

Fig. 3. An example of BroadCatch broadcast with five server channels

segment on Channel 3 is late for one time slot, the client cannot rest and must download segments from all three channels simultaneously. It results in more bandwidth and buffer space requirement. Previous research [2] has addressed the problem of Fast Broadcast: there are considerable consecutive time slots (in the last part of every broadcasting period) with high bandwidth requirements for all clients entering the system during these time slots. Therefore, for clients with insufficient number of Fig. 4. Fibonacci Broadcast with three server channels. download channels, it takes a long waiting time to startup a video. Consequently, HeRO adds shifted replicate channels to eliminate such a sequence of bandwidth requirements and odically without resegmentation in order to shorten the latencies reduce the waiting time. for the clients with more bandwidths. From the above discussion, we find that “catch and rest” and “replicate channels” are two effective approaches to reducing III. CATCH AND REST BROADCASTING SCHEME the client bandwidth requirements. We also find that the effect is more significant when these techniques are applied to the A. Idea of Catch and Rest highest channels, especially for reducing the buffer space re- The concept of “catch and rest (CAR)” is motivated by the quirement also. In view of this, first, we combine Fast Broad- special case of Fibonacci Broadcast with three channels as cast and “catch and rest” to obtain a low-latency heterogeneous shown in Fig. 4. We begin by observing the reception schedule broadcasting scheme, called CAR without replicate channels. indicated by the blank arrows. At time slot 3, a client begins By applying the channel structure in Fig. 4 to Fast Broadcast, to receive the first two segments from Channels 1 and 2. Be- we modify the channel design of Fast Broadcast as follows: cause the client receives the first two segments simultaneously for some , the number of distinct segments of Channel (“catch”), it will buffer one segment and need not receive the triples that of Channel , and the number of distinct segments fourth segment immediately from Channel 3. At time slot 4, the of Channel doubles that of Channel . Secondly, as with client receives the third segment. At time slot 5, since the client HeRO, we employ the concept of using replicate channels with has received the first three segments and only consumed two, it shifted time slots to further reduce the service latency of CAR. can playback the buffered segment, the third segment, without As a whole, what CAR sacrifices is a small degradation of the re- receiving any segment (“rest”). At time slot 0 in the next duction rate of the maximum service latency for high-end clients broadcasting period, the client can receive and playback the as the number of channels increases, but what CAR gains is fourth segment on time. The combination of “catch” and “rest” a large reduction of the maximum service latency for low-end is significant since it reduces the maximum client reception clients. bandwidth requirement and also reduces the maximum client There are several points needed to be addressed. First, Fi- buffer space requirement. In Fig. 4, for every possible time slot bonacci Broadcast was designed to minimize the service laten- we also put the required number of download channels and cies for clients with only two download channels [14] and does buffer space (in segments). It can be observed that the user not adapt to client bandwidth heterogeneity. Fig. 5 shows the bandwidth requirement is no more than two. broadcasting schedule of Fibonacci Broadcast with 5 channels. In contrast, in Fast Broadcast the number of distinct segments Second, we apply only the structure of the lowest three chan- of Channel always doubles that of Channel . Therefore, nels of Fibonacci Broadcast, as shown in Fig. 4, to our proposed the number of distinct segments of Channel 3 is four instead scheme. The reason is as follows. In Fibonacci Broadcast, the of three. Again, consider a client beginning to receive the lengths (in time slot) of periods of different broadcast channels first segment at time slot 3. Since the repetition of the fourth are a Fibonacci series, i.e., 1, 2, 3, 5, 8, etc. In contrast, in Fast 340 IEEE TRANSACTIONS ON BROADCASTING, VOL. 52, NO. 3, SEPTEMBER 2006

Fig. 5. A server schedule of Fibonacci Broadcast. A reception schedule with the maximum buffer space requirement (maximum overlaps) is indicated by gray color.

Fig. 6. A server schedule of CAR without replicate channels.

TABLE I NOTATIONS IN THE RECEPTION ALGORITHM

Broadcast, the lengths of periods of different broadcast chan- channels. The broadcasting period of each channel is defined re- nels are a geometric series of factor 2, i.e., 1, 2, 4, 8, 16, etc. cursively as follows: Obviously, given the same number of broadcasting channels, Fi- bonacci Broadcast divides the video into a set of larger segments if in comparison to Fast Broadcast. The difference is even large if as the number of broadcast channels increases. Because larger if segments imply a longer average service latency for clients, we cannot excessively apply Fibonacci Broadcast in terms of net- Like Fast Broadcast, the segments indexed from to work bandwidth utilization. Finally, the channels conforms to are repeatedly broadcasted on Channel for . the 1:2:3 period ratio (“catch and rest”) must be at the top, not The last channels are modified. The number of distinct segments at the bottom, of Fast Broadcast so that the length of the con- triples that of Channel instead of doubling that of Channel secutive time slots with high bandwidth requirements can be re- . To align the receiving time, the offset of the first broad- duced. cast on channel , , relative to the beginning of channel is equal to time slots. Fig. 6 show B. Channel Design an example of server channel design of CAR without replicate channels (Table I). We first describe the channel design of the scheme called CAR Next, we introduce the channel design of CAR with shifted without replicate channels. Server uses several channels, each replicate channels. Above the modified channel, we can add with the bandwidth equal to the playback bandwidth . Video more channels and associate each of them with a replicate are divided into equal-size segments . Each channel, which broadcasts the same series of segments except channel repeatedly broadcasts a set of contiguous segments, one shifting half of the period. We call an original channel and its segment in each time slot. Let denote the number of server shifted replicate channel a shifted pair. Like Fast Broadcast, LIN AND DING: LOW LATENCY VIDEO-ON-DEMAND BROADCASTING SCHEME FOR HETEROGENEOUS RECEIVERS 341

Fig. 7. A server schedule of CAR with one replicate channel.

Fig. 8. A server schedule of CAR with two replicate channels. accompanied with the period of the modified channel, the pe- the first segment of the next (original or replicate) channel as it riods of these original channels also forms a geometrical series appears except the following two situations. with a ratio of 2. To align the receiving time, the offset between 1) The next occurrence of the first segment of the next (orig- the beginning of some original channel and the beginning of inal or replicate) channel just aligns with the end of the its previous original channel is also equal to the period of the last segment of the most current reception channel. For ex- previous one (i.e., half of its own period). Fig. 7 shows a server ample, in Fig. 7, the client who starts receiving the first schedule of CAR with one replicate channel. The reception segment at time slot 8 cannot download segments 8 and 14 schedules using the idea of “catch and rest” are indicated by simultaneously from Channels 4 and 5. blank arrows. In this figure, Channels 5 and 6 are a shifted 2) The clients are receiving segments from both Channels pair, where Channel 5 is the original channel and Channel 6 and . For example, in Fig. 7, is the shifted replicate channel. Fig. 8 shows a schedule of the client who starts receiving the first segment at time slot CAR with two replicate channels. There are two shifted pairs: 7 cannot download segment 8 at time slot 7. Channel 5 coupled with Channel 6, and Channel 7 coupled In which cases, clients defer reception of the first segment of the with Channel 8. next channel until its previous segments have all been received. Let denotes the number of replicate channels. By summing In the other words, clients receive a segment only when the the periods, we derive for CAR with replicate channels segment will miss the deadline in the next broadcast time. Let the number of segments as follows. the drift reception time be the difference between the current time and the time starting download . Then, a segment is downloaded on time if the corresponding reception drift time (in time slot) is less than its segment number. The pseudo code (1) of the reception algorithm is shown in Fig. 9. As shown in Fig. 7, the arrows illustrates the reception The repeating pattern of the broadcasting schedule can be found schedule from on to on Channel 6. “Catch by tracing down the channels from high to low. Since the pattern and rest” is shown by blank arrows: once a reception schedule depends on the period of the highest channel, we can verify that has passed a blank arrow, it will follow another blank arrow in the whole schedule repeats every time slots, where the next step. According to the reception schedule, channels are down- if (2) loaded from low to high without jump except the pairs. if Furthermore, the download of a lower channel always complete prior to that of a higher channel. For CAR with , while one of the channels belonging to the shift pair are downloading, C. Reception Schedule for Playback all of the lower channels have been completely downloaded. The reception schedule for clients is simple. Clients always Therefore, if or 1, then clients always download seg- start with receiving segments from Channel 1 and start receiving ments from adjacent channels at a time. LIN AND DING: LOW LATENCY VIDEO-ON-DEMAND BROADCASTING SCHEME FOR HETEROGENEOUS RECEIVERS 349

[7] J. W. Ding and Y. M. Huang, “Packet permutation: a robust transmis- sion technique for continuous media streaming over the Internet,” Mul- timedia Tools and Applications, vol. 21, no. 3, pp. 281–305, Dec. 2003. [8] ——, “Resource-based striping: an efficient striping strategy for video servers using heterogeneous disk-subsystems,” Multimedia Tools and Applications, vol. 19, no. 1, pp. 29–51, Jan. 2003. [9] D. Eager, M. Vernon, and J. Zahorjan, “Optimal and efficient merging schedules for video-on-demand servers,” in Proc. ACM Multimedia’99, 1999, pp. 199–202. [10] E. Gustafsson and A. Jonsson, “Always best connected,” IEEE Wireless , vol. 10, no. 1, pp. 49–55, Feb. 2003, (also in IEEE Personal communications). [11] K. A. Hua and S. Sheu, “Skyscraper broadcasting: A new broadcasting scheme for metropolitan video-on-demand services,” in Proc. of the ACM SIGCOMM’97, Cannes, France, Sep. 1997, pp. 89–99. [12] K. A. Hua, Y. Cai, and S. Sheu, “Exploiting client bandwidth for more efficient video broadcast,” in Proc. 1998 Int. Conf. Computer Commu- nications and Networks, Lafayette, LA, USA, Oct. 1998, pp. 848–856. [13] K. A. Hua, M. A. Tantaoui, and W. Tavanapong, “Video delivery tech- nologies for large-scale deployment of multimedia applications,” Pro- ceedings of the IEEE, vol. 92, no. 9, pp. 1439–1451, Sep. 2004. Fig. 22. The buffer space requirement for clients with maximal download chan- [14] A. Hu, “Video-on-demand broadcasting protocols: a comprehensive nels. study,” in IEEE INFOCOM 2001, Apr. 2001, vol. 1, pp. 508–517. [15] L. Juhn and L. Tseng, “Harmonic broadcasting for video-on-demand VI. CONCLUSION service,” IEEE Trans. on Broadcasting, vol. 43, no. 3, pp. 268–271, Sep. 1997. In this paper, we proposed a novel VoD broadcasting tech- [16] Y. L. Jeng, Y. M. Huang, and Y. H. Kuo et al., “ANTS: Agent-based navigational training system,” Lecture Notes in Computer Science, vol. nique called CAR to support client heterogeneity. The schedule 3583, pp. 320–325, 2005. of CAR is very deterministic. We showed that the reception [17] L. Juhn and L. Tseng, “Fast data broadcasting and receiving scheme schedule of clients can be formulated by the indices of arrival for popular video service,” IEEE Trans. on Broadcasting, vol. 44, no. 1, pp. 100–105, Mar. 1998. time in one broadcasting period. [18] J.-F. Paris, “A simple low-bandwidth broadcasting protocol for Our performance evaluation shows that CAR can greatly re- video-on-demand,” in Proc. Int. Conf. Computer Communication and duce the service latency for clients with low reception capability Network, Boston, MA, USA, Oct. 1999, pp. 118–123. [19] M. A. Tantaoui, K. A. Hua, and T. T. Do, “BroadCatch: A periodic at the cost of slightly increasing the service latency for clients broadcast technique for heterogeneous video-on-demand,” IEEE with high reception capability. This design tradeoff produces ac- Trans. on Broadcasting, vol. 50, no. 3, pp. 393–400, Sep. 2004. ceptable service latency for all heterogeneous clients. With CAR, [20] M. Topic, Streaming Media Demystified. : McGraw-Hill, 2002. [21] S. L. Tsao and Y. M. Huang, “Making a cost-effective storage server as long as two downloading channels are available, the clients for broadcasting services,” IEEE Transactions on Broad- can achieve near VoD on moderate number of server channels. casting, vol. 44, no. 3, pp. 300–308, Sep. 1998. Our results also show that compared to the latest two innovative [22] Y.-C. Tseng, M.-H. Yang, and C.-H. Chang, “A recursive frequency- splitting scheme for broadcasting hot videos in VoD service,” IEEE heterogeneous VoD broadcasting schemes, namely BroadCatch Trans. Comm., vol. 50, no. 8, pp. 1335–1348, Aug. 2002. and HeRO, CAR outperforms BroadCatch in many aspects, in- [23] S. Viswanathan and T. Imielinski, “Pyramid Broadcasting for video on cluding the service latency and buffer space requirement; CAR demand service,” in Proc. of IEEE Multimedia Computing and Net- working, San Jose, California, 1995, vol. 2417, pp. 66–77. alsooutperformsHeROwithrespecttotheservicelatencyforlow [24] E. M. Yan and T. Kaneda, “An efficient VoD broadcasting scheme with capability clients while achieving a comparable performance for user bandwidth limit,” in Proc. ACM Multimedia Computing and Net- high capability clients. In conclusion, CAR is an efficient data working, Santa Clara, CA, Jan. 20–24, 2003, vol. 5019, pp. 200–208. broadcasting scheme that can provide low-latency VoD services Chin-Tsai Lin received his B.S. degree in computer for heterogeneous receivers in wired/wireless networks. science from National Chiao Tung University, Hsinchu, Taiwan, in 1987. He received his M.S. and Ph.D. degrees in computer science and information REFERENCES from National Taiwan University, [1] C. C. Aggarwal, J. L. Wolf, and P. S. Yu, “On optimal batching policies Taipei, Taiwan, in 1989 and 1996, respectively. He for video-on-demand storage servers,” in Proc. IEEE Int. Conf. Multi- is currently an assistant professor of Dept. of Infor- media Computing and Systems, 1996, pp. 253–258. mation Management, Kun Shan University, Tainan, [2] O. Bagouet, K. A. Hua, and D. Oger, “A periodic broadcast protocol for Taiwan. His research interests include multimedia heterogeneous receivers,” in SPIE Conf. Multimedia Computing and communications, parallel and distributed computing. Networking 2003 (MMCN’03), Santa Clara, California, Jan. 2003, pp. 220–231. [3] Y. Cai and K. A. Hua, “Sharing multicast videos using patching streams,” Multimedia Tools Appl. J., vol. 21, no. 2, pp. 125–146, Nov. 2003. Jen-Wen Ding received his B.S., M.S., and Ph.D. [4] S. W. Carter and D. D. E. Long, “Improving bandwidth efficiency degrees in engineering science from National Cheng of video-on-demand servers,” Comput. Netw. ISDN Syst., vol. 31, pp. Kung University, Tainan, Taiwan, in 1996, 1998, 99–111, Mar. 1999. and 2001, respectively. He is currently an assistant [5] T. Chiueh and C. Lu, “A periodic broadcasting approach to video-on- professor of Dept. of Information Management, demand service,” in Proc. SPIE-Int. Soc. Optical Eng., Oct. 1995, vol. National Kaohsiung University of Applied Sciences, 2615, pp. 162–169. Kaohsiung, Taiwan. His research interests include [6] A. Dan, D. Sitaram, and P. Shahabuddin, “Dynamic batching poli- multimedia communications, mobile computing, cies for an on-demand video server,” Multimedia Systems, vol. 4, pp. and video-on-demand. 112–121, June 1996.