Simple VBR Harmonic Broadcasting (SVHB)

Transcription

1 mple VBR Harmonc Broadcastng (VHB) Hsang-Fu Yu ab, Hung-hang Yang a, Y-Mng hen c, -Mng Tseng a, and hen-y Kuo a a Dep. of omputer cence & Informaton Engneerng, atonal entral Unversty, Tawan b omputer enter, atonal entral Unversty, Tawan c Dep. of Informaton Management, atonal entral Unversty, Tawan Abstract One way to broadcast a popular vdeo s to partton the vdeo nto segments, whch are broadcasted on several streams perodcally. The approach lets multple users share streams; thus, the stress on the scarce bandwdth can be allevated wthout sacrfcng vewers watng tme. One representatve approach s the Harmonc Broadcastng (HB) scheme, whch can broadcast a vdeo usng multple streams by havng new vewers wat no longer than θ ( ) tme, where s the length of a vdeo, and s the number of segments. In comparson wth other segmented schemes, the HB scheme requres mnmum bandwdth. However, the scheme manly supports transmsson of BR-encoded vdeos. In ths paper, we propose a smple VBR harmonc broadcastng (VHB) scheme for VBR-encoded vdeos. Unlke the HB scheme, the VHB scheme guarantees contnuous playout. Addtonally, the scheme mproves the varable bandwdth harmonc broadcastng (VBHB) scheme n bandwdth consumpton, maxmum buffer requrements, and maxmum requred dsk transfer rate. ome bounds on the bandwdth consumpton, the buffer requrements, and the requred dsk transfer rate are also developed. Keywords: Hot-vdeo broadcastng, vdeo-on-demand (VOD), varable-bt-rate (VBR) Introducton Wth the advancement of broadband networkng technology and the growth of processor speed and dsk capacty, vdeo-on-demand (VOD) servces have become possble [9][]. A VOD system s typcally mplemented by a clent-server archtecture, and may easly run out of bandwdth because the growth n bandwdth can never keep up wth the growth n the number of clents. Ths results n tremendous demand for computng power and communcaton bandwdth on the system. To allevate the stress on the bandwdth and I/O demands, many alternatves have been proposed by sacrfcng some VR functons, or known as near-vod servces. One way s to broadcast popular vdeos. Accordng to [2], 8% of demands are on a few ( or 2) very popular vdeos. Because the server s broadcastng actvty s ndependent of the arrvals of requests, the approach s approprate to popular or hot vdeos that may nterest many vewers at a certan perod of tme. One way to broadcast a popular vdeo s to partton the vdeo nto segments, whch are broadcasted on several streams perodcally. The schemes [][3][4][5][6][7][8][3][6][7][9] share a smlar arrangement. A vdeo server dvdes a vdeo nto segments that are smultaneously broadcasted on dfferent data streams. One of these streams transmts the frst segment n real tme. The other streams transmt the remanng segments accordng to a schedule predefned by the scheme. When clents want to watch a vdeo, they wat frst for the begnnng of the frst segment on the frst stream. Thus, ther maxmum user watng tme equals the length of the frst segment. Whle the clents start watchng the vdeo, ther set-top boxes (TB) or computers start downloadng enough data from the other streams so they wll be able to play the segments of the vdeo n turn. The smplest broadcastng scheme s the staggered broadcastng []. The server allocates K streams to transmt a vdeo. Its maxmum vewers watng tme s, where s the vdeo length. K The pyramd broadcastng [8] parttons a vdeo nto ncreasng sze of segments and transmts them on multple streams of the same bandwdth. It requres less bandwdth than the staggered broadcastng under the same maxmum watng tme. The fast broadcastng (FB) [3] dvdes a vdeo nto a geometrcal seres of, 2, 4,, 2 K. Its maxmum watng tme s K 2. In comparson wth the staggered broadcastng and the pyramd broadcastng, the FB scheme obtans shorter watng tme. The new pagoda broadcastng (PB) scheme [3] s a hybrd of the pyramd broadcastng and the fast broadcastng. It parttons a vdeo nto

2 fxed-sze segments and maps them nto data streams of equal bandwdth at the proper decreasng frequences. Accordngly, the PB scheme obtans shorter watng tme than the FB scheme. The recursve frequency splttng (RF) scheme [6] further mproves the PB scheme n watng tme by usng a more complex segment-to-stream mappng. The harmonc broadcastng (HB) scheme [5] frst dvdes a vdeo nto several segments equally, and further dvdes the segments nto sub-segments accordng to the harmonc seres. Yang, Juhn, and Tseng [2] proved that the HB scheme requres the mnmum bandwdth under the same watng tme. An mplementaton of the FB scheme on IP networks was reported n [2]. The above schemes assume that vdeos are encoded n constant-bt-rate (BR). Accordngly, they cannot support varable-bt-rate (VBR) vdeos well. ome schemes were proposed to address ths problem. The perodc broadcastng wth VBR-encoded vdeo (VBR-B) [5] ntegrates the pyramd broadcastng scheme wth the technques of the GoP smoothng, server bufferng, and clent prefetchg to transmt VBR vdeos. Based on the VBR-B, the trace adaptve fragmentaton (TAF) scheme [] takes the trace of each vdeo nto account to predct the bandwdth requrements, and then uses complex technques to smooth the bandwdth consumpton. The varable bandwdth harmonc broadcastng (VBHB) [4] frst dvdes a VBR vdeo nto fxed sze segments. The frst and second segments are broadcasted at the transmsson rate guaranteeng on tme delvery of all frames. All other segments are dvded nto equal-sze sub-segments, whch are dstrbuted n the way of the cautous harmonc broadcastng (HB) scheme [2]. In ths paper, we propose a smple VBR harmonc broadcastng (VHB) scheme for VBR-encoded vdeos. It s systematc and smple n concept. A VBR vdeo s dvded nto multple equal-length segments by tme. Each segment s further equally dvded nto sub-segments by sze. The scheme then broadcasts sub-segments at constant bt rate n the way of the HB scheme; thus, the total requred bandwdth s constant. The VHB scheme s the same as the VBHB scheme n segment partton and the maxmum vewers watng tme under the same vdeo length and number of segments. The VHB scheme manly dffers from the VBHB scheme n two areas. Frst, the VHB scheme and the VBHB scheme are based on the HB scheme and the HB scheme, respectvely. econd, the schemes employ dfferent approaches to ensure contnuous playout. The VHB scheme requres clents to receve a segment completely before playng t. That s clents cannot receve and play a segment concurrently. In contrast, the VBHB scheme allows clents to receve and play a segment synchronously. The scheme derves the maxmum bandwdth requrements for the frst segment and leaves the second segment undvded such that vdeo data can be played contnuously. Fnally, the VHB scheme mproves the VBHB scheme n bandwdth consumpton, maxmum buffer requrements, and maxmum requred dsk transfer rate at the cost of longer average vewers watng tme. The rest of ths paper s organzed as follows. In ecton 2, we present the VHB scheme for VBR vdeos. ome analyss and smulaton results are presented n ecton 3. We make bref conclusons n ecton 4. 2 Harmonc Broadcastng cheme for VBR Vdeos 2. Harmonc Broadcastng cheme To help understand the new scheme, we frst revew the HB scheme n the lterature. uppose we equally dvde a vdeo nto segments. The segments are denoted by, 2,, n sequence. egment s further dvded nto sub-segments equally, denoted by,,, 2,,,. We then allocate streams, denoted by,,, to broadcast the vdeo segments. s responsble for dstrbutng all the sub-segments of sequentally and perodcally. uppose the bandwdth requred for s equal to the data consumpton rate b of the vdeo. Because s dvded nto equal-sze sub-segments, the,,,, 2, 2,2 2, 2,2 3, 3,2 3,3,, 2, 2,2 3, 3,2 3,3, 2, 2,2 3, 3,2 3,3 4, 4,2 4,3 4,4 4, 4,2 4,3 4,4 4, 4,2 b/4 5, 5,2 5,3 5,4 5,5 5, 5,2 5,3 5,4 5,5 5, b/5 6, 6,2 6,3 6,4 6,5 6,6 6, 6,2 6,3 6,4 6,5 6,6 b/6 7, 7,2 7,3 7,4 7,5 7,6 7,7 7, 7,2 7,3 7,4 7,5 7,6 Fgure : An example for the stream allocaton for the harmonc broadcastng scheme. b b/2 b/3 b/7

3 Bt rate (Kbps) Tme (seconds) Fgure 2: The data consumpton rate of the vdeo, Jurassc Park III. bandwdth requred for s b. Therefore, the total requred bandwdth s the summaton of the frst terms of harmonc seres, equal to n b. Fgure llustrates the stream = allocaton for a vdeo wth seven segments by the HB scheme. 2.2 mple VBR Harmonc Broadcastng Fgure 2 shows the data consumpton rate of a MPEG-2 vdeo, Jurassc Park III. The varance of the rate s very large, and so s ts requred bandwdth. If we drectly partton a VBR vdeo nto multple segments, and then dstrbute the segments usng the HB scheme. Vdeo servers may easly stop ther vdeo servces because the dsk transfer rate and bandwdth requrements exceed ther capabltes. In addton, clents probably cannot receve the vdeo data n tme when the networks cannot satsfy the peak bandwdth requrements. To elmnate the varance of bandwdth requrements for VBR vdeos, we propose the smple VBR harmonc broadcastng (VHB) scheme. The VHB scheme and the HB scheme dffer n two areas. Asynchronous download and playout for a segment. The data consumpton rate of a VBR vdeo vares wth tme so the rate s probably larger than ts data transfer rate. In the HB scheme, a clent receves and plays a segment concurrently; thus, the vdeo playout may be blocked when the consumpton rate s larger than the transfer rate. To ensure the contnuous playout, the VHB scheme requres a clent to buffer a segment completely before playng t. That s the clent cannot receve and play a vdeo segment concurrently. Ths restrcton causes the VHB scheme havng larger average watng tme than the HB scheme; however, the two schemes have the same maxmum watng tme. Hybrd dvson by length and sze. The VHB scheme dvdes a VBR vdeo nto segments by length, and then further dvdes the segments nto sub-segments by sze. The scheme transmts each sub-segment at constant bt rate on each stream. Thus, the varance of requred bandwdth s zero. On the server sde, the VHB scheme nvolves the followng steps.. A vdeo s equally dvded nto segments by length. uppose s the th segment of the vdeo, and ts sze s. The concatenaton of all the s segments consttutes the whole vdeo, = s then dvded nto equal-sze sub-segments. uppose, j s the jth sub-segment of. The concatenaton of all the sub-segments consttutes the whole segment, =.,2,,... The sze of s s., j 2. The vdeo server broadcasts the on stream sub-segments of sequentally and perodcally at constant bt rate. Fgure 3 llustrates the dstrbuton of a vdeo, whch s dvded nto eght equal-length-but-unequal-sze segments. In the fgure, the rectangles represent the segments of the vdeo, and the area reflects the sze of a segment. At the clent end, suppose there s plenty of dsk space to buffer portons of the playng vdeo. For watchng a vdeo, the followng steps are nvolved:. Download all of the sub-segments concurrently durng each tme slot. 2. To ensure a segment was buffered completely before ts use, we delay the

4 playout a perod of tme. If the clent begns to download the vdeo segments at t, the vdeo can be played n the order of 2 l at t top loadng data from networks when we have receved all of the segments. Requred bandwdth (Mbps) VHB VBHB Analyss and omparson 3. Vewers Watng Tme uppose the clent has enough dsk space to buffer portons of the playng vdeo on dsk. The vewer s watng tme comes from the access tme of vdeo segments on networks. To ensure contnuous playout, the access tme of a segment cannot be larger than ts length. Thus, the vewers watng tme δ s equal to the length of a segment. δ = () Thus, the VHB scheme has longer average watng tme than the VBHB scheme. However, ther maxmum watng tme s the same. 2, 2, 3,, 5,. 2, 2 3, 2 3, , 2 4, 3 4, 4 5, 5, 5, 5,, 6 6, 2 6, 3 6, 4 6, 5 6, 6 7 7, 2 7, 3 7, 4 7, 5 7, 6 7, 7, (a) The vdeo segments 8 8, 2 8, 3 8, 4 8, 5 8, 6 8, 7 8, 8 (b) The segment arrangement by the VHB scheme Fgure 3: An example for vdeo dstrbuton by the VHB scheme. Because the vdeo server broadcasts the sub-segments of on stream sequentally and perodcally, the requred bandwdth on B stream s equal to bandwdth s B = s δ = δ. The total requred s = Gven a bandwdth allocaton B, the access tme δ B equals the transferred data sze over the bandwdth; thus, δ =. B B = Fgure 4 depcts the bandwdth requrements for the move, Jurassc Park III, usng the VHB scheme and the VBHB scheme. The vdeo s encoded by MPEG-2. Its length and sze s 48 seconds and 2.66 Gbytes. Wth the ncreasng of segment length, the number of segments decreases so the number of the requred streams (or the requred bandwdth) becomes small. The fgure also ndcates that the requred bandwdth for the VHB scheme s smaller than that for the VBHB scheme. It reflects the segment partton by the HB scheme s more effcent than that by the HB scheme. s 3.2 Buffer Requrements The clent needs to buffer portons of the playng vdeo on dsk because the arrval rate of the vdeo data s larger than the consumpton rate. In addton, the clent merely buffers same vdeo data once. uppose the tme that a clent begns to receve vdeo data s t. Durng ( ) δ t + to t + δ egment length (seconds) Fgure 4: The requred bandwdth versus segment length n the move, Jurassc Park III., the sub-segments that come from.

5 s j,, +, h j= need to be buffered. et I =, where. (2) j represent the sze of the ncreasng data that are wrtten nto the buffer by the clent durng ths tme nterval. Durng the same nterval, the clent consumes prevous receved segments because the clent cannot download and play a segment concurrently. et O =, and O = s, where 2 + (3) represent the output sze of the data that are read out from the buffer by the clent durng + ( ) δ t + δ. et Z t to represent the sze of the requred buffer durng t + ( ) δ to δ t +. At, all the data that come from t + δ,, 2 obtan, need to be buffered. Hence, we (4) Durng Z I Z Z = + O =, and t + δ I t, where 2. to + ( + ) δ, the clent stops downloadng the data, and begns consumng the last segment. There s no wrte requrement, and all the buffered data wll be consumed durng ths nterval. Hence, we obtan I = and + Z =. + Accordng to equatons (2), (3), and (4), we can calculate,,, } for a fxed. { Z Z 2 Z From equaton (), we can obtan = ; thus we δ can derve the relatonshp between the max { =,, } and the segment length δ. Z δ Fgure 5 depcts the curve for the move, Jurassc Park III. The fgure ndcates the VHB scheme requres less buffer than the VBHB scheme. 3.3 Dsk Transfer Rate Accordng to the storage requrements, the dsk transfer rate requrements can be broken nto wrte requrements and read requrements. From equaton (2), the wrte requrements durng t + ( )δ to δ t + are W = δ s j, where, and j= j W =. (5) + The read transfer rate s equal to the data consumpton rate. Because the vdeo s VBR-encoded, the rate vares wth tme. For smplcty, we merely consder the maxmum consumpton rate of each segment. et b represent the rate of. Durng t to t + δ, the read transfer rate s zero because the clent cannot download and play the frst segment concurrently. et =, and R R b =, where 2 + (6) represent the maxmum read transfer requrements durng t + ( ) δ to δ t +. Thus, the maxmum dsk transfer rate requrements are Maxmum requred buffer (GBytes) VHB VBHB Maxmum requred dsk transfer rate (Mbps) VHB VBHB egment length (seconds) egment length (seconds) Fgure 5: The maxmum buffer requrements versus segment length n the move, Jurassc Park III. Fgure 6: The maxmum dsk transfer rate versus segment length n the move, Jurassc Park III.

6 Φ = W + R, where +. Fgure 6 depcts the requrements for the move, Jurassc Park III. The fgure shows the VHB scheme requres smaller dsk transfer rate than the VBHB scheme. 4 onclusons The vdeo broadcastng servce s already popular on Internet. In ths paper, we propose a HB-based broadcastng scheme for VBR vdeo servces. Unlke the HB scheme, the smple VBR harmonc broadcastng (VHB) scheme ensures contnuous playout. We further analyze the scheme by the vewers watng tme, buffer requrements, and requred dsk transfer rate. Fnally, we use a VBR vdeo to evaluate the VHB scheme and the VBHB scheme. The results ndcate that the VHB scheme outperforms the VBHB scheme on bandwdth consumpton, maxmum buffer requrements, and maxmum requred dsk transfer rate. Future research could be drected toward fndng new approaches to broadcastng lve VBR vdeos. Acknowledgement The authors would lke to thank the atonal cence ouncl of the Republc of hna for fnancally supportng ths research under ontract o E-8-4. References [] K.. Almeroth and M. H. Ammar, The use of multcast delvery to provde a scalable and nteractve vdeo-on-demand servce, IEEE Journal on elected Areas n ommuncatons, vol. 4, no. 5, pp. -22, Aug 996. [2] Ast Dan, Dnkar taram, Perwez hahabuddn, Dynamc batchng polces for an on-demand vdeo server, Multmeda ystems, vol. 4, no. 3, pp. 2 2, June 996. [3].-. Juhn, and.-m. Tseng, Fast broadcastng for hot vdeo access, n Proceedngs of the 4 th Internatonal Workshop on Real-tme omputng ystems and Applcatons, pp , Oct 997. [4].-. Juhn and.-m. Tseng, tarcase data broadcastng and recevng scheme for hot vdeo servce, IEEE Transactons on onsumer Electroncs, vol. 43, no. 4, pp. -7, ovember 997. [5].-. Juhn and.-m. Tseng, Harmonc broadcastng for vdeo-on-demand servce, IEEE Transactons on Broadcastng, vol. 43, no. 3, pp , eptember 997. [6].-. Juhn and.-m. Tseng, Fast data broadcastng and recevng scheme for popular vdeo servces, IEEE Transactons on Broadcastng, vol. 44, no., pp. -5, March 998. [7].-. Juhn, and.-m. Tseng, Enhanced harmonc data broadcastng and recevng scheme for popular vdeo servce, IEEE Transactons on omputer Electroncs, vol. 44, no. 2, pp , May 998. [8].-. Juhn, and.-m. Tseng, Adaptve fast data broadcastng scheme for vdeo-on-demand servces, IEEE Transactons on Broadcastng, vol. 44, no. 2, pp , June 998. [9] T.. Kun et al., Issues n storage and retreval of multmeda data, Multmeda ystems, vol. 3, no. 5, pp , 995. [] F., and I. kolads, Trace-adaptve fragmentaton for perodc broadcastng of VBR vdeo, n Proceedngs of 9 th Internatonal Workshop on etwork and Operatng ystem upport for Dgtal Audo and Vdeo (ODAV 99), June 999. [] B. Ozden, R. Rastog, and A. lberschatz, On the desgn of a low cost vdeo-on-demand storage system, Multmeda ystems, vol. 4, no., pp. 4 54, 996. [2] J.-F. Pars,. W. arter, and D.D. E. ong, Effcent broadcastng protocols for vdeo on demand, n Proceedngs of the 6 th Internatonal ymposum on Modelng, Analyss and mulaton of omputer and Telecommuncaton ystems, Montreal, anada, pp , July 998. [3] J.-F. Pars, A smple low-bandwdth broadcastng protocol for vdeo-on-demand, n Proceedngs of Internatonal onference on omputer ommuncatons and etworks, pp. 8 23, 999. [4] J. F. Pars, A broadcastng protocol for compressed vdeo, n Proceedngs of Euromeda 99 onference, Munch, Germany, pp 78-84, Apr 999. [5] D. aparlla, K. Ross, and M. Resslen, Perodc broadcastng wth VBR-encoded vdeo, IEEE IFOOM 999, pp , 999. [6] Yu-hee Tseng, Mng-Hour Yang, and h-he hang, A recursve frequency-splttng scheme for broadcastng hot vdeos n VOD servce, IEEE Transactons on ommuncatons, vol. 5, no. 8, pp , August 22.

7 [7] Yu-hee Tseng, Mng-Hour Yang, h-mng Hseh, Wen-Hwa ao, and Jang-Png heu, Data broadcastng and seamless channel transton for hghly demanded vdeos, IEEE Transactons on ommuncatons, vol. 49, no. 5, pp , May 2. [8]. Vswanathan and T. Imelnsk, Pyramd Broadcastng for vdeo on demand servce, n Proceedngs of IEEE Multmeda omputng and etworkng onference, vol. 247, pp , an Jose, alforna, 995. [9] H.-. Yang, H.-F. Yu, and.-m. Tseng, Adaptve ve Broadcastng for Hghly-Demanded Vdeos, Journal of Informaton cence and Engneerng, vol. 9, no3, May 23. [2] Z.-Y. Yang,.-. Juhn, and.-m. Tseng, On Optmal Broadcastng cheme for Popular Vdeo ervce, IEEE Transactons on Broadcastng, vol. 45, no. 3, pp , eptember 999. [2] Z.-Y. Yang, The Telepresentaton ystem over Internet wth atecomers upport, Ph.D. Dssertaton, Department of omputer cence and Informaton Engneerng, atonal entral Unversty, Tawan, 2.