Live Streaming over Subscription Overlay Networks CS587x Lecture Department of Computer Science

1. Live Streaming over Subscription Overlay Networks CS587x Lecture Department of Computer Science Iowa State University

2. Outline • Subscription Overlay Network (SONet) • Subscription and topology management • Streaming over SONet • Performance Study • Concluding Remarks

3. Subscription Overlay Network • Two components • One central server • Streaming source (eg., live TV broadcast, etc.) • A number of subscribing nodes • Pay monthly fee in return of video services • A node can be offline/online/idling/playing • One Service • Streaming video data from source to all online nodes • Three goals • Minimize the server workload • Minimize network traffic • Minimize data latency 4 1 3 r r 2 r 5 r 6 S

4. Solution I: Unicast • Dedicating one stream for each online node • Advantages • Simple implementation • Good data freshness (shortest distance) • Disadvantages • Server bottleneck: not scalable

5. Solution II: IP Multicast • One multicast stream can serve many clients simultaneously • Advantages • Simple implementation • Achieve all three goals • Disadvantages • IP Multicast is not widely deployed on the Internet (due to security issues, etc.)

6. Solution III: Application Layer Multicast • A node receiving data can forward its incoming stream to serve others • Existing ALM techniques • Chaining/ESM • NICE/ZIPZAG, etc. c5 c3 c6 s c4 c1 c2

7. Solution III: Application Layer Multicast • A node receiving data can forward its incoming stream to serve others • Existing ALM techniques • Chaining/ESM • NICE/ZIPZAG, etc. • Advantages • each server stream can serve many clients • Leverage the entire network resource c5 c3 c6 s c4 c1 c2

8. Solution III: Application Layer Multicast • A node receiving data can forward its incoming stream to serve others • Existing ALM techniques • Chaining/ESM • NICE/ZIPZAG, etc. • Advantages • each server stream can serve many clients • Leverage the entire network resource • Disadvantages • Only the playing nodes can contribute • Difficult to maintain topology, etc. c5 c3 c6 s c4 c1 c2

9. Observation and Motivation • A SONet may consist of a large number of subscribers, but at any one time, only a small percentage of them are playing • American watch TV 4 hours/day in average • A majority of SONet not playing may be idling • Unlike regular TV sets, a node not playing is likely to be online • Recruiting appropriate idling nodes for data forwarding can effectively reduce network traffic

10. Motivation Examples • Server workload? • Network traffic? • Data freshness?

11. Subscription/Topology Management • Account database • The server maintains all subscriber information, including IP, password, the amount of data forwarded (for discount purpose), etc. • Topology graph • When a new member M joins, the server S detects its path to the members • A path is denoted as PATH(S, M) = SR1R2M • When a member M1 is asked to forward data to another member M2, M1 reports the actual PATH(M1, M2) to the server • The connections among the members are detected and updated as needed • The topology graph becomes more and more accurate to the server • For each stream, the server records its actual streaming path • Given a router, the server can find out the set of streams flowing through it.

12. Notations/Definitions • Path(X, Y) • The sequence of routers on the shortest path from X to Y (as known to the server) • Ring(R, i) • The set of routers that are i-hop away from R • Capacity(N) • The number of streams N can forward • Local node and local router • A node and a router is local to each other if they connect directly

13. Changing of Node Status • A node can make itself only offline, idling, or playing • Only the server can decide when a node can become an incentive node

14. A node becomes online • When an offline node becomes online, the server may bundle the streams flowing through N’s local router

15. Bundling Procedure

16. A node becomes playing • The node is in incentive • Simply turn on its player • The node was in idling • Find a parent (should be as close as possible to N) • Find the joint router Rj • Search Ring(Rj, 0) • Prefer playing node • If not, recruit an incentive node, more than one candidates may be available (choosing criteria?) • Repeat on Ring(Rj, 1), …, until a parent is found

17. Find Parent Candidates

18. Choosing Incentive Node Cost(XY, I, N) = Hop(X, I) + Hop(I, Y) + Hop(I, N) – Hop(X, Y)

19. If N’s capacity is not 0 • It can help serve others • The server finds the parent by searching Ring(Rj, 0), …, but stops at Ring(Rj, d), where d is Hop(N, Rj) • Since N can serve at least one child, it can redirect its incoming stream to its parent’s current child

20. A node becomes offline or idling • Find a new parent for each child of this node • The parent can be either an incentive or playing node

21. Performance Study • Performance Metrics • Mean Relative Delay (MRP) • The MRP of a node X is to defined to HOP(S, X)/StreamingPath(S, X) • Measure the data freshness • Link Stress • The total amount of traffic flowing through each network links • Our study focus on • Effect of subscription size • Effect of topology size • Effect of active rate

22. Effect of Subscription Size

23. Concluding Remarks • SONet: a framework for video streaming over the Internet • Similar to cable/satellite broadcast networks • Allows effective incentive mechanisms • Centralized subscription and topology maintenance • A new topology-oriented technique for building application layer multicast • Unique in its ability of incorporating idling nodes to assist in data forwarding • Simulation confirms its performance advantage • Future work???