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

2. Outline Paper Survey Protocol design Conclusion 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
Parent
Discards the child from forwarding Table
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
Host 0 will…
Parent 1
Hello
Report ‘Parent Leave’ to the Server
Join Request to the other Parents
‘Leave notice’ to Child
No Reply
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
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
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)
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 :
High join rate (1 / sec) On
Off
Low leave rate(20/sec)

19. Conclusion Design and implementation of Future work
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