Layered Range Multicast for Video On Demand

1
Layered Range Multicast for Video On Demand

• Duc A. Tran
• Kien A. Hua
• Tai T. Do

2
Agenda

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

3
Introduction

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

4
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

5
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

6
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)

7
Quality of Service

• Video Stream V is encoded into L layers
• Basic layer v1
• Enhancement layers v2, v3, ,vL
• Decode v1 and some enhancement layers according
  to the required QoS
• QoS level j Vj (v1, v2, ,vj)
• Clients request video stream by specifying j

8
Overlay Cache Design

• Non-root nodes reserve an amount of local storage
• Divided into equally sized chunks C1, C2, , CN
• CK is divided into sub-chunks, CK1, CK2, , CKL
• N depends on the capability of the node

9
Caching Algorithm

• When Vj arrives
• For each layer l of Vj (l ? 1, 2, , j)
• Find an empty sub-chunk of layer l for caching vl
• Otherwise, select a sub-chunk of layer l that is
  in free state for the longest time
• Otherwise, vl will not be cached

10
Caching Algorithm
11
Caching Algorithm
12
Service Procedure

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

13
Seeking Phase

• On receiving find()
• Root node return found()
• Non-Root node
• Compute list L vl1, vl2, , vlj ? Vj 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 (R1, L1), (R2, L2), , (Rn, Ln)

14
Seeking Phase

• Use the following greedy algorithm to select
  nodes
• Set L EMPTY, i 0
• Put all the current found messages into Qx
• WHILE (L Vj)
• WHILE (Qx EMPTY) Waiting
• Dequeue (Ri, Li) from Qx
• Send node Ri an ack message asking it to send the
  layers specified in Li \ L to the client
• L L ? Li, i i 1
• If there are more coming found messages to
  Rep(X), then put them into Qx
• Send each of the rest of nodes in Qx a nack
  message to deny its offer.

15
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

16
Service Procedure
17
Performance Evaluation

• Metrics
• Bandwidth Saving
• System Throughput
• Ratio of served requests to total simulated time

18
Performance Evaluation
19
Performance Evaluation
20
Conclusion

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

21
Thought

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