Large-Scale and Cost-Effective Video Services CS587x Lecture Department of Computer Science Iowa State University

On-demand Multicast Periodic Broadcast Application-Layer Multicast Peer-to-Peer Video Services Contents

On-demand Multicast –Patching –Double Patching Periodic Broadcast –Client Centric Approach What to Cover Today

Server Channels Videos are delivered to clients as a continuous stream. Server bandwidth determines the number of video streams can be supported simultaneously. Server bandwidth can be organized and managed as a collection of logical channels. These channels can be scheduled to deliver various videos.

Using Dedicated Channel Video Server Client Too Expensive ! Client Dedicated stream

Batching Make requests wait and then serve together Video Server Client Multicast stream Drawbacks: –If the waiting is too long, many requests may renege –If the waiting is too short, each multicast can serve only one request

Adaptive Piggybacking Video streams are merged by adjusting their playback rates new arrivals departures +5% -5% CBA Drawbacks: –The adjustment of playback rate must be small –Adjusting playback rate needs specialized hardware

Research Challenge Each request should be served immediately Each multicast should serve a large number of requests

Motivation Example video A multicast

Motivation Example video player buffer B video t skew point A multicast

Motivation Example video t patching stream skew point regular stream video player buffer B A multicast

Motivation Example video 2t regular stream video player buffer B A multicast

Proposed: Patching A r B p C p D p E r F p G p patching window Multicast group time

Optimal Patching Window Server Bandwidth Requirement = Candidates of optimal patching window : D W

Limitation of Patching Performance Patching cost increases as the time gap enlarges regular stream A t+1tt+20 t0 t0t+1 patching stream B C Serving B and C takes 2t+1 time units of data

Motivation Example Serving B and C takes only t+3 time units of data About 50% improvement when t is large! regular stream t+1tt+20 t0 0 long patching stream short patching stream t+1t+2 t+3 A B C

Observation A patching stream is shareable in the next time units if it delivers extra T time units of data T regular stream long patching stream short patching stream A B C D T 2 T / 2

Proposed: Double Patching rsp lpsp r multicast window time patching window ABCDEFGHI Multi… Patch…

The data delivered during one multicast window –by the regular stream: –by the long patching streams: –by the short patching streams: Performance Optimization

Mean Server Bandwidth Requirement (Mbit/s) Mean inter-arrival time (seconds) Standard Patching Double Patching Effect of Inter-Arrival Time

Periodic Strategy Conventional Periodic Broadcasting [Dan94, Dan96] –Broadcast period is reduced to Research Challenge –Reduce the broadcast period to ?

Motivation Example D1D1 D2D2 D3D3 D4D4 video length Design Parameters : ( K = 4, C = 2 ) Video Segmentation : [ 1, 2, 2, 4 ] Group 1: D 1 D 2 Group 2: D 3 D 4

Motivation Example (con’t) Broadcast schedule Channel 1 Channel 2 Channel 3 Channel 4 D1D1 D1D1 D1D1 D1D1 D1D1 D1D1 D1D1 D1D1 D2D2 D2D2 D2D2 D2D2 D3D3 D3D3 D3D3 D3D3 D4D4 D4D4 Group 1 Group 2

Motivation Example (con’t) Clients download segments group by group Channel 1 Channel 2 Channel 3 Channel 4 a D1D1 D2D2 D3D3 D4D4 Group 1 Group 2

Motivation Example (con’t) Clients download segments group by group Channel 1 Channel 2 Channel 3 Channel 4 a D1D1 D2D2 D3D3 D4D4 Group 1 Group 2 b

Continuity within group Continuity across group boundary D2D2 Group 1 D1D1 D1D1 D3D3 Channel 2 D2D2 Channel 3 Motivation Example (con’t) D2D2

Download Bandwidth vs. Access Latency # Channels * Segmentation [ 1, 1, 1, 1 ] [ 1, 2, 2, 4 ] [ 1, 2, 4, 4 ] [ 1, 2, 4, 8 ] Latency

Proposed: Client-Centric Approach Design Parameters – K broadcast channels and C download channels Group Video Segmentation C 1 2 : KCKC g =

Significance and Impact of CCA CCA is the first generalized technique to leverage receiving bandwidth for more efficient broadcast CCA can be modified to support receivers with different downloading bandwidth [Hua02, Hua03]

What is the limit? The first segment determines the broadcast period How to make this segment as small as possible under the condition that playback continuity is guaranteed 1.Continuity within group 2.Continuity across group boundary D2D2 Group 1 D1D1 D1D1 D3D3 Channel 2 D2D2 Channel 3 D2D2

Question What is the maximum size of S i+c ? Depend on which loader is used to download L1L1 LjLj L i+c-1

Segmentation Rule If L j is used to download, S i+c can be any size as long as 1)It is a multiple of S j 2)It is no larger than S j +S j+1 +S i+c-1 L1L1 LjLj L i+c-1

There are only three possible alignments

Download Schedules (C=2) S 1, 1 S 1, 2 S 2, 1 S 2, 2 Schedule 1 Group 1Group 2 S 2, 1 S 2, 2 Group 3 L1L1 L2L2 S 1, 1 S 1, 2 S 2, 1 S 2, 2 Group 1Group 2 S 2, 1 S 2, 2 Group 3 L1L1 L2L2 Schedule 2 Broadcast series: 1, 2, 3, 4, 6, 8, 16 …. Broadcast series: 1, 2, 2, 5, 5, 12, 12, 25, 25 …

Client-Centric Broadcast (CCB) 1.Assuming C-channel receiving capability, we have C! different download schedules 2.For each download schedule, we have one broadcast series 3.Among C! broadcast series, choose the fastest one

Segmentation Implementation S i in Group g is download by loader L[i]