1. Robust and Efficient Path Diversity in Application-Layer Multicast for Video Streaming Ruixiong Tian, Qian Zhang, Senior Member, IEEE, Zhe Xiang, Yongqiang Xiong, Member, IEEE, Xing Li, and Wenwu Zhu, Senior Member, IEEE IEEE TRANSACTIONS ON CIRCUITS AND SYSTEMS FOR VIDEO TECHNOLOGY, VOL. 15, AUGUST 2005

2. Outline What is application-layer multicast (ALM) Consider the quality-of-service (Qos) Playback continuity Propagation delay constraint Heterogeneous Improve the reliability Utilize path diversity Random multicast forest (RMF) Topology-aware hierarchical arrangement graph (THAG) Simulation results conclusion

3. What is application-layer multicast (ALM) Main goal: Provide group communication without network infrastructure support Difficulties: Hard to promise the Qos Hard to predict the best path (reliability)

4. Quality-of-service (Qos) Issues: Playback continuity But every node may join and leave at any time Propagation delay constraint Because the media data is forwarded by a number of interior nodes Heterogeneous The hosts and network infrastructure are heterogeneous

5. Improve the reliability and effectiveness Path diversity Use Multiple description coding (MDC) Main goal: (balance load amongst hosts) Split streaming media into several sub-streams Each sub-stream is delivered through a separate multicast tree Reference: V. K. Goyal, “ Multiple description coding: Compression meets the network, ” IEEE Signal Process. Mag., vol. 18, Sep. 2001. Two schemes to construct diversity path Random multicast forest (RMF) Topology-aware hierarchical arrangement graph (THAG)

6. Random multicast forest (RMF) In RMF: A node can join several multicast trees All multicast trees are not independent A joining host can: Find m closest hosts as candidate parents (Use top-down) Step1: measure the root and all its children Step2: select the closest one and measure its children, too Step3: goto Step2, until has no child or measured previously random to select one from candidate parents One is its parent The others keep the system maintenance When current parent fails

7. Random multicast forest (RMF) Example: There are two trees denoted : solid lines and dash lines In solid lines If each host can serve two children Set m = 2 (select 2 closest node as candidate parents) When a newcomer (H 5 ) coming The candidate parents are H 2 and H 4 The similar operation in dash lines

8. Random multicast forest (RMF) Consideration When a node joining log(N) are required, where N is the multicast group size Questions When m is large (m: the size of candidate list) May select long-distance candidate Increase of transmission delay

9. Topology-aware hierarchical arrangement graph (THAG) In THAG: In ALM systems is based on structured overlays Arrangement group (AG) structure is designed Every multicast tree are independent Every path is node-disjoint Any interior node in one multicast tree at most be leaf node in all the other multicast trees What is arrangement group (AG)??

10. What is arrangement group (AG) AG is a regular interconnection topology Reference: K. Day and A. Tripathi, “ Characterization of node disjoint path in arrangement graphs, ” Computer Science Department, Univ. Minnesota, Minneapolis, Tech. Rep. 1991. Characteristics: Tree-like hierarchical structure Embedded several independent multicast trees Denoted by A n,k, 1 ≦ k ≦ n-1 Let be the set of permutations of k, and the element in is denoted as X = x 1 x 2 … x k A n,k is defined as a undirected graph G(V, E) A 4,2

11. Topology-aware hierarchical arrangement graph (THAG) In a full-filled A n,2 there are n(n-1) nodes at most n-2 independent trees the degree of each node is 2(n-2) a i,j (1 ≤ i,j ≤ n, i ≠ j) is labeled by its coordinates (i,j).

12. Topology-aware hierarchical arrangement graph (THAG) The algorithm of n-2 multicast trees into an A n,2 : Step 1: a k,1 (k=3,4, … n) as the root for multicast tree T k Step 2: Let a k,y (y=2,3, … n, y ≠ k) and a x,1 (x=2,3, …,n, x ≠ k) join the tree T k, a k,1 is the parent node Step 3: Let a x,y (x=1,2, … n, x ≠ k, y=2,3, … n, y ≠ k) join the tree T k, a k,y is the parent node Step 4: If k is odd, let node a 1,k join the tree T k, node a 1,k-1 is parent node. Let a x,k (x=2,3, … n, x ≠ k) join the tree T k, a k,1 is the parent node Step 5: If k is even, let node a 2,k join the tree T k, node a 2,k-1 is parent node. Let a x,k (x=1,3, … n, x ≠ k) join the tree T k, a 2,k is the parent node root : full-leaf nodes

13. Topology-aware hierarchical arrangement graph (THAG) Characteristics: All parents are its children ’ s neighbors A node reach any other node in at most 4 AG is resilient If a node leaves One neighbor will create the virtual node for the position The virtual node can be replaced by the actual node later only (n-2) new connections are required The overhead is small Considerations: Problems: the size of A n,2 is limited Ex: there are at most 90 nodes in an A 10,2 Solution: Extend AGs into hierarchical architecture

14. Extend AG to hierarchical architecture When A 4,2 is fulfilled, it derives child-AGs. A column node in AG {ai,j | i=1, …,n, i ≠ j, i ≠ (j+1)mod2 +1} can derive one or more child-AGs

15. Extend AG to hierarchical architecture Considerations: How does the THAG protocol design How to join THAG How to fast switch when a node cannot receive parent ’ s data

16. How does the THAG protocol design : actual node : virtual node Must very stable

17. How to join THAG Propose a locating-replacing-sinking algorithm (LRS) Use a top-down way

18. How to fast switch when a node cannot receive parent ’ s data If s trees are utilized to deliver data in A n,2, called delivery tree, where n >s +2 There are n-2-s trees are not utilized called nondelivery tree When a node cannot receive data from parent Asks a parent in nondelivery tree to send data

19. Simulation results Demonstrate fault-tolerance and Qos-provision THAG and RMF with 1000 hosts Each node will fail with probability P THAG is constructed on A 8,2 At most has (8-2) = 6 multicast trees

20. Simulation results THAG has better fault-tolerant performance than RMF In THAG, a failure of one node only affect a tree P=0 P=10% (RMF) P=5% (RMF) P=2% (RMF) P=2% (THAG) P=5% (THAG) P=10% (THAG) ( s= 2~6, N = 1000 )

21. Simulation results Hosts in THAG have higher probability to receive more flows than in RMF (s=4, N=1000, P=5%) RMF THAG

22. Evaluation of Qos-Provision Relative delay penalty (RDP): show the propagation delay on the paths The data delivery in THAG is much shorter latency than that in RMF Simulation results (RMF) 90%-tile (RMF) 90%-tile (THAG) Average (RMF) Average (THAG) ( s= 3)

23. Evaluation of Qos-Provision Link Stress: The total number of duplicate copies of a packet that a link has to carry The link stress increases slowly Small link stress indicate that they have the ability of avoiding the serious link congestion problem Simulation results (RMF) 90%-tile (RMF) 90%-tile (THAG) Average (RMF) Average (THAG)

24. Simulation results Evaluation of Qos-Provision Delay Variation: the average of delay on the paths in multicast tree Relative delay variation (RDV), where D max and D min are maximum and minimum propagation delay

25. Conclusion In ALM Use path diversity to improve the reliability of streaming Two schemes: RMF and THAG Summary In reliability THAG has been improved up to 20% compared with RMF In Qos In RDP, link stress, and delay variation THAG is also smaller than RMF or almost the same as that in RMF

26. Replacing procedure Use GNP algorithm to compute the distance Reference: T. S. E. Ng and H. Zhang, “ Predicting internet network distance with coordinates-based approaches, ” Proc. IEEE INFOCOM, Jun. 2002. The replacement gain, G(x,y), for each node a x,y (1 ≦ x,y ≦ n, x ≠ y) If G(x,y) > 1, replaced by the joining host h: join host s i : ith AG source d: the distance of network coordinate