1. M ULTIPLE T REE V IDEO M ULTICAST O VER W IRELESS A D H OC N ETWORKS Wei Wei and Avideh Zakhor Presented by: Jipeng Tan Hechen Liu

2. O VERVIEW Introduction Preliminary Serial Multiple Disjoint Trees Multicast Routing Protocol (Serial MDTMR) Parallel Multiple Nearly-Disjoint Trees Simulation Conclusion

3. I NTRODUCTION Multiple tree construction schemes and routing protocols for video streaming over wireless ad hoc networks. Splits the video into multiple parts and send each part over a different tree, which are constructed to be disjoint with each other Increases robustness to loss and other transmission degradations.

4. O VERVIEW Introduction Preliminary Serial Multiple Disjoint Trees Multicast Routing Protocol (Serial MDTMR) Parallel Multiple Nearly-Disjoint Trees Simulation Conclusion

5. PRELIMINARY Multiple description coding (MDC) A popular approach in multipath video streaming. A natural scheme for multiple tree video multicast communication. On demand multicast routing(ODMRP) When sending packets, the sender builds multicast mesh by periodically flooding the network with control packets to create and maintain the forwarding state of each node.

6. PRELIMINARY Tree Connectivity ( P ) Suppose we want to connect one sender to 20 receivers via 2 trees, and the resulting trees connect 18 receivers to 2 trees and 2 receivers to 1 tree, the tree connectivity M: product of the total number of receivers and the number of trees. N: the sum of all receivers connected to each multicast tree, and E[N] is the expected value of N over all topologies. P = (18 x 2 + 2 x 1) / (2 x 20) = 0.95

7. P RELIMINARY Tree Similarity The ratio of the number of shared nodes to the number of middle nodes of the tree with a smaller number of middle nodes s R1 R2 A B C D E F S = 1/3 = 33.3%

8. P RELIMINARY Dousse et at. [31] have stated that there exists one critical density λ c, for a wireless ad hoc network, such that if the density λ < λ c, all the connected clusters are almost surely bounded; otherwise, almost surely there exists one unique unbounded super connected cluster. Theorem 1: Consider an infinite wireless network, with nodes assumed to be distributed according to two- dimensional Poisson process. Let D 1 denote the required node density to achieve a given tree connectivity level, P, in a single tree case. If D 1 > λ c, there exists at least one double disjoint tree whose required node density D 2 to achieve P satisfies where is r the radio link range.

9. P RELIMINARY Multiple Tree Multicast Packet Forwarding Each packets header has a tree-flag that determine the tree to which the packet should be forward. When a node receives a data packet, it checks its forwarding table to avoid duplicate. The node forwards a non-duplicate packet forwarded in tree-y, if it is a forwarder tree-y Each packet flows is not constrained to follow present branches in the tree. Does not support packet forwarding across different trees

10. O VERVIEW Introduction Preliminary Serial Multiple Disjoint Trees Multicast Routing Protocol (Serial MDTMR) Parallel Multiple Nearly-Disjoint Trees Simulation Conclusions

11. S ERIAL MDTMR Assumption: light loaded network Mobility Poor channel condition Objective: constructs two node-disjoint trees in a distributed way Built on top of ODMRP

12. s R1 R2 Req0 A B C D E

13. Ack0 A B C D E

14. Req1 X X A B C D E

15. Ack1 A B C D E

16. A B C D E

17. S ERIAL MDTMR Each middle node only forwards the JOIN ACK msg once: disjointness guaranteed Achieve reasonable connectivity The routing overhead and construction delay are potentially twice as much as that of a parallel scheme

18. O VERVIEW Introduction Preliminary Serial Multiple Disjoint Tress Multicast Routing Protocol (Serial MDTMR) Parallel Multiple Nearly-Disjoint Trees Simulation Conclusion

19. D ESIGN G OALS Low routing overhead and construction delay High tree connectivity Low tree similarity Distributedness

20. O VERVIEW OF PARALLEL MNTMR Two types of messages Join-query (JQ) Join-reply (JR) Classifies all nodes randomly into one of two categories, i.e., group 0 or group 1 Builds two trees directly from group nodes? (Connectivity) Forces each node which connects to the sender, to forward a JQ message JQ message storing condition and JQ message forwarding condition

21. C LASSIFICATION OF JQ M ESSAGES A node forwards the earliest received JQ message of the same group immediately Otherwise it forwards the earliest received JQ message of the other group, after a short delay d from receiving it Pure JQ messages have lower overall delay, and are forwarded with a priority over mixed JQ messages

22. JQ MESSAGE STORING CONDITION Assume that the current node a is in group-0 However, if a stores every received JQ message, the tree may have loops a JQ message ba

23. JQ MESSAGE STORING CONDITION It is the first JQ message that node a receives in the current round, or The following two conditions are satisfied # of hops it has travelled that of the first received JQ msg of a plus one (shortest path) The JQ msg has not been forwarded by a (loop-free)

24. JQ MESSAGE FORWARDING CONDITION A JQ message satisfies the forwarding condition, if Node a has not forwarded a JQ message in this JOIN- QUERY round The messages last hop is the sender or of the same group with a

25. U PSTREAM NODE SELECTION RULE Goal: maximize the disjointness of two trees Let JQM a denote the set of all the messages in the JQ message cache of a If there exist both group-0 and group-1 msgs Upstream Node for tree 0 Upstream Node for tree 1

26. U PSTREAM NODE SELECTION RULE Goal: maximize the disjointness of two trees Let JQM a denote the set of all the messages in the JQ message cache of a If all msgs in JQ Message Cache of a are from the same group Upstream Node for tree 0 Upstream Node for tree 1

27. U PSTREAM NODE SELECTION RULE Goal: maximize the disjointness of two trees Let JQM a denote the set of all the messages in the JQ message cache of a If JQM a has only one element the last hop of the only JQ message is selected as upstream nodes for both tree-0 and tree-1

28. U PSTREAM NODE SELECTION RULE When nodes select an upstream node for tree-0, other close-by nodes are likely to select the same node for tree-0, thus avoid the upstream node for tree-1 chosen by other nodes Increases the likelihood of disjointness of two trees.

29. T REE C ONSTRUCTION The source triggers a multicast tree construction by broadcasting a JQ message. Each middle node performs the JQ message processing

32. T REE C ONSTRUCTION When receiving a group- y JQ message, if it is a pure JQ msg and the node has not initiated a JR msg for tree-y, select the last hop of this JQ msg as its upstream node for tree-y The receiver unicasts a JR msg to the sender All nodes receiving and forwarding the JR msg for tree-y, become middle nodes of tree-y The receiver sets a timer upon receiving the earliest JQ message

33. T REE C ONSTRUCTION When the timer expires, for each tree having not initiated a JR message, receiver selects an upstream node and unicast a JR msg to the sender When a middle node receives a non-duplicate JR msg for tree-y, it selects an upstream node and forwards the JR msg to the upstream node Obtain one tree mainly containing group-0 nodes and another mainly containing group-1 nodes Periodically update the to maintain the tree structure

34. E XAMPLE Upstream node for tree-0 Upstream node for tree-1 Upstream node for tree-0 Upstream node for tree-1

35. 1 2 3 4 5 R1 R2 S E XAMPLE

36. D ISCUSSION Since the Parallel MNTMR builds two trees simultaneously, the routing overhead and the construction delay is similar to that of a typical single tree multicast routing protocol. The protocol requires it to send JR messages for both trees, therefore the tree connectivity is the same as that of a single tree protocol.

37. D ISCUSSION If two nodes in different trees share the same first two JQ messages in their JQ message caches, they will not select the same node as their upstream nodes. The Parallel MNTMR reduces the number of shared nodes between two trees.We use a three-bit code to denote the classification of nodes 1, 2, and 3, with the x th bit representing the class to which node belongs

38. D ISCUSSION The averaged probability that two nodes share an upstream node using Parallel MNTMR is 1/6, while choosing at random would have resulted in 1/4.

39. O VERVIEW Introduction Preliminary Serial Multiple Disjoint Trees Multicast Routing Protocol (Serial MDTMR) Parallel Multiple Nearly-Disjoint Trees Simulation Conclusion

40. S IMULATION Simulation Scenario Use a simulation model based on NS-2. The random waypoint model is used to model mobility. Each run, the author simulate a 50 node wireless ad hot network with 1500x300m ² area. Each simulation is 900s long, and results are averaged over 30 runs. The author randomly choose one sender and eight receivers.

41. PERFORMANCE METRICS AND COMPARISON SCHEMES Performance Metrics The ratio of bad frames The number of bad periods Normalized packet overhead Forwarding efficiency Average hops of each packet Tree similarity Comparison Schemes: Parallel MNTMR and MDC Serial MDTMR and MDC ODMRP and MDC ODMRP and SDC

42. P ERFORMANCE M ETRICS AND S CHEMES Normalized forwarded data packets.

43. P ERFORMANCE M ETRICS AND S CHEMES Number of bad periods.

44. P ERFORMANCE M ETRICS AND S CHEMES Bad period varies on different node density

45. P ERFORMANCE M ETRICS AND S CHEMES Normalized control packets

46. C ONCLUSION The authors proposed multiple tree video multicast with MDC to provide robustness for real-time video multicast communication over ad hoc networks. There are two different multiple disjoint tree multicast routing protocol (MDTMR). Serial MDTMR: simple but involved high routing overhead and construction dely. Parallel MNTMR: construct two nearly trees simultaneously in a distributed way. The simulation shows that proposed method can achieved significantly higher video quality than single tree multicast video communication, with similar routing overhead and forwarding efficiency.

47. Questions?

48. Thank you!