Layered Range Multicast for Video On Demand Duc A. Tran Kien A. Hua Tai T. Do

Agenda Introduction Layered Range Multicast (LRM) Network Model Quality of Service Overlay Cache Design Service Procedure Performance Evaluation Conclusion

Introduction Problems Clients requests arrive at different times cannot be batched to share a single multicast stream easily VoD services to heterogeneous clients

Introduction Layered Range Multicast (LRM) Layered video coding Video streams are encoded into several layers Video quality improves by receiving more layers “Range Multicast” Transmit a range of continuous frames to the participating clients If requested play point is in the range, new clients can still join a multicast group without additional server bandwidth

Layered Range Multicast (LRM) Rationale Prolong the usefulness of a multicast stream Overview Root node, non-Root nodes (application-level routers) Clients receive video stream from root with QoS, through some non-root nodes Non-root nodes cache some video streams layers

Network Model LRM-enable nodes Interconnected by unicast path Root nodes, non-Root nodes Root Nodes Front-end node for video server Store full quality (all layers) video streams Non-Root Nodes Representatives of local community of clients, Rep(X) Root NR client

Quality of Service Video Stream V is encoded into L layers Basic layer: v 1 Enhancement layers: v 2, v 3, …,v L Decode v 1 and some enhancement layers according to the required QoS QoS level j = V j (={v 1, v 2, …,v j }) Clients request video stream by specifying j

Overlay Cache Design Non-root nodes reserve an amount of local storage Divided into equally sized chunks C 1, C 2, …, C N C K is divided into sub-chunks, C K 1, C K 2, …, C K L N depends on the capability of the node C1LC1L C 1 L-1 C11C11 C1C C2LC2L C 2 L-1 C21C21 C2C CNLCNL C N L-1 CN1CN1 CNCN …

Caching Algorithm When V j arrives For each layer l of V j (l ∈ {1, 2, …, j}) Find an empty sub-chunk of layer l for caching v l Otherwise, select a sub-chunk of layer l that is in “free” state for the longest time Otherwise, v l will not be cached

Caching Algorithm

Service Procedure Seeking Phase Client node X requests a video V j (video V with quality level j) to Rep(X) Rep(X) send request find(X, V, J) to all adjacent-on-overlay nodes

Seeking Phase On receiving find() Root node return found() Non-Root node Compute list L = {v l1, v l2, …, v lj } ⊂ V j s.t. it got L in cache If L is empty, forward find() to adjacent nodes, except root If L is non-empty, send found(L) to Rep(X) Rep(X) receives (R 1, L 1 ), (R 2, L 2 ), …, (R n, L n )

Seeking Phase Use the following greedy algorithm to select nodes: Set L = EMPTY, i = 0 Put all the current found messages into Q x WHILE (L = V j ) WHILE (Q x = EMPTY) Waiting Dequeue (R i, L i ) from Q x Send node R i an ack message asking it to send the layers specified in Li \ L to the client L = L ∪ L i, i = i + 1 If there are more coming found messages to Rep(X), then put them into Q x Send each of the rest of nodes in Q x a nack message to deny its offer.

Transmission & Leaving Phase Transmission Phase Each serving node transmits to client a stream consisting of the layers specified in ack Delivery path is the reversal of the path that the serving node received find() from Rep(X) Leaving Phase Client send quit() to Rep(X) Rep(X) send quit() to all serving nodes

Service Procedure

Performance Evaluation Metrics Bandwidth Saving System Throughput Ratio of served requests to total simulated time Data provided by intermediate nodes Total amount of data provided

Performance Evaluation

Conclusion LRM provides: Better service latency Reduced server bandwidth demand Efficient and feasible implementation on Internet

Thought Is layering existing video contents (e.g. DVD, VCD, …) feasible? What is the performance impact when non- root nodes fail?