Jeonghun Noh Eric Setton Professor Bernd Girod

1. Design and Implementation of OverLay Multicast Tree Protocol Jeonghun Noh Eric Setton Professor Bernd Girod

2. Outline • Paper Survey • Protocol design • JOIN • LEAVE • HELLO • PARENT UNGRACEFUL LEAVE • Protocol State diagram for a single tree • Conclusion

3. Paper survey • Survey of the existing research work • Work by CMU, Microsoft, U. of Maryland, Etc. • Architectural overview of OLM protocol • Control plane • Membership management : JOIN, LEAVE • Data delivery • Video distribution paths • Identification of issues in designing OLM protocol • scalability | robustness | efficiency | convergence speed

4. Join Protocol - philosophy • Centralized vs. Distributed Algorithm • Whether a server controls data distribution construction • Subtle meaning of ‘distributed’ • Who should a new host contact? • A server or, • Some hosts (using Distributed Hash Table) • How to maintain a membership list • Examples • Microsoft : a dedicated server • Others : distributed algorithm

5. Server in the multicast session • Decides the distribution tree counts • Keeps a member list (potentially not accurate) • Member list updates when: • A new host reports ‘attachment’ • A host informs of ‘explicit leave’ • A child of a parent leaving ungracefully reports the leave • Server does best to keep it updated with smallest effort • Reacts to host join • Distributes video to its direct children

6. Receiver in the multicast session • Active peer (client in server-client model) • To join/leave a session • To detect parent leave and react • To send hello messages to parents • Passive peer • To react to hello messages • To forward video on attachment request • To discard a child if no more hello messages arrive • Note : • more burden on receivers than on server • Common in high-performance clients

7. Join Protocol – Design phase • [SENDER] On JoinRequest from a host • How many candidates? • too many : traffic overhead, long latency in joining • too small : low efficiency, higher failure rate to join at one time • Whom to choose? • [RECEIVER] Which parent to choose? • referred to as ‘parent selection algorithm’ • Several metrics : • depth ( from a server ) • RTT ( from a server or a parent ) • available bandwidth • Join each tree INDEPENDENLY or in a COUPLED way

8. Join Protocol – 6 way Handshaking JOIN REQUEST PROBE ATTACH SERVER PARENT CANDIDATES PARENT New Host

9. Leave Protocol – Explicit Leave SERVER Parent Leaving Host Child Child

10. Leave Protocol – What to do SERVER Discards a leaving host from the list Discards the child from forwarding Table Parent • Sends ‘Leave message’ to its children ‘Recursively’ • Rejoin ( to the server) Child

11. Hello Protocol - overview • Why we need this? • Hosts may leave ungracefully ( UNGRACEFUL LEAVE ) • Need to keep track of neighbors to check if alive • Two Design Approaches • [Approach 1] To every neighbor • First approach we took • More complex • Different handling of its parent and children • [Approach 2] To its parent only for each tree. • Less traffic • Still needs a response from its parent (why?)

12. Hello Protocol APPROACH 2 < Tree 0 > Parent Hello Hello Reply Child Child

13. Hello Protocol – timer mechanism TIMER at CHILD : Timer expiration points CHILD : say hello to parent 1st no reply 2nd no reply Time flow Notice of parent leave Time flow PARENT : respond to child Parent leaves ungracefully

14. On Parent Ungraceful Leave Parent 0 Parent 1 Host 0 will… Hello No Reply • Report ‘Parent Leave’ to the Server • Join Request to the other Parents • ‘Leave notice’ to Child Host 0 Parent 2 Child Child

15. Overall Protocol Architecture (single tree) User command Timer expires Natural flow JOIN Join Command PROBE OFFLINE LEAVE command ONLINE ATTACH HELLO

16. NAM Snapshot

17. Simulation Setup - server • Server • Preencoded video stream (H.264 with SP/SI frames) • Resides in the middle of the network • Uplink bitrate : • Parent candidate counts : • Tree counts : ( kbps per tree) • Eric, when does the server start sending video?

18. Simulation Setup - receiver • Receiver • Resides on the edge of the network • Restricted to lower uplink bitrate ( kbps supporting streams) • Downlink bitrate : • Uplink bitrate : • Heterogeneous access networks : DSL, modem, LAN.. • Repeat of Join and ungraceful leave : • Receiver • Resides on the edge of the network • Restricted to lower uplink bitrate ( kbps supporting streams) • Downlink bitrate : • Uplink bitrate : • Heterogeneous access networks : DSL, modem, LAN.. • Repeat of Join and ungraceful leave (scheduled for each receiver) High join rate (1 / sec) Off On Low leave rate(20/sec)

19. Conclusion • Design and implementation of • Building and maintaining of multiple trees • JOIN & LEAVE & HELLO protocol • Parent leave detection & rejoin procedure • Heterogeneous receiver setup based on real statistics • Detection of edge nodes in the network topology • Future work • Extension to multiple trees protocol • Integration of video data scheduling with tree construction algorithm • Optimize the timer expiration interval for each protocol state • Subtree information update algorithm to support Aggregate Rate-Distortion optimized scheduling at each host • Analysis of the effect of a mesh-style control plane