1. RELIABLE APPLICATION LAYER MULTICAST OVER COMBINED WIRED AND WIRELESS NETWORKS AUTHORS - MASAHIRO KOBAYASHI, MEMBER, IEEE, HIDEHISA NAKAYAMA, MEMBER, IEEE, NIRWAN ANSARI, FELLOW, IEEE, AND NEI KATO, SENIOR MEMBER, IEEE PRESENTED BY – ANKIT KULKARNI, SATISH ERAPPA

2. OVERVIEW Solution for reliable media content delivery over heterogeneous networks What is heterogeneous network? How is content delivery achieved? Problems in reliable media content delivery

3. HETEROGENEOUS NETWORK

4. MULTICAST Applications Approaches for multicasting IP Multicast Application Layer Multicast (ALM) Why IP Multicast can’t be used?

5. ALM IN HETEROGENEOUS NETWORKS Issues that need to be addressed by ALM Frequent node joining and departure Propagation delay between source and destination nodes High variance in availability of bandwidth for different users Multiple-tree multicast is used to address the issues mentioned above Multiple Description Coding (MDC) is used in Multiple-tree multicast Layered Multiple Description Coding (LMDC) combining MDC and layered coding to meet bandwidth constraints as well as robustness of node departure

6. SINGLE-TREE AND MULTIPLE-TREE MULTICAST

7. MULTIPLE-TREE MULTICAST CoopNet and SplitStream Do not use node disjoint trees Topology-aware Hierarchical Arrangement Graph (THAG) Does not take bandwidth constraints into account Network-aware Hierarchical Arrangement Graph (NHAG) Takes only upload bandwidth into consideration Does not offer robustness of node departure NHAG+ is proposed to address the issues

8. ARRANGEMENT GRAPHS (AG) An Arrangement Graph (AG) of size ‘s’, denoted by A s,k, is defined as a graph containing vertex set V, consisting of permutations s P k from set and edge set E, where vertices are connected by edges whenever two permutations differ in exactly one of the k positions Every vertex is denoted by x 1 x 2 ….x k An AG A s,2 contains s*(s-1) nodes and (s-2) node disjoint trees can be constructed

9. TREE STRUCTURE BASED ON ARRANGEMENT GRAPH

10. THAG THAG forms node-disjoint multicast trees using AG in hierarchical manner. When parent-AG is full, child-AG’s are created to accommodate the joining nodes The interior node in Parent-AG will act as a source node for Child-AG. The node at AG-source can have at most 2*(s-2) child nodes. If AG size is s, it can forward maximum of s-2 descriptions. The leaf node in the AG are selected as the AG entrance node. Drawback – The size of AGs is fixed. Hence it does not consider bandwidth constraints.

11. THAG AND NHAG

12. NHAG It also forms node-disjoint multicast trees using AG. The size of the AGs are dynamically changed depending on the bandwidth constraints (upload) of the nodes in AG. Size of the AG is calculated based on the available upload bandwidth of the nodes in AG. The new node is placed in the arrangement graph of appropriate size based on its available upload bandwidth. Drawback – Node departure results in QoS degradation.

13. PROPOSED METHOD (NHAG+) NHAG+ is an improvement over NHAG It solves the QoS degradation issue due to node departure in NHAG It does not change the AG size dynamically as opposed to NHAG Manages bandwidth constraints using Layered Multiple Description Coding (LMDC) The AGs receive layers according to their requested layer which is based on upload and download bandwidth of nodes. AGs with lower requested layer receive less number of layers

14. LMDC In LMDC, each video frame is split into multiple descriptions and every description is split into multiple layers. To achieve the quality Q L, all the L layers should be delivered in order. However, descriptions can be delivered in any order. Content can be played when the required number of descriptions are received. The quality of multimedia content increases with every layer of description.

15. REQUESTED LAYER In NHAG+, each node calculates the requested layer rl which is the largest layer required to stably receive and deliver descriptions. In NHAG, the requested size is computed using only the upload bandwidth of nodes, whereas in NHAG+, both upload and download bandwidth are considered while determining requested layer. rl = min(rl up, rl down )where, rl = requested layer rl up = requested upload layer rl down = requested download layer Bw up = upload bandwidth of node BW down = download bandwidth of node L = number of layers M = number of descriptions R = Rate of media content delivered by ALM C n = Maximum number of child nodes for a particular node

16. NODE JOINING PROCEDURE Case 1 – Is AG completely filled? The new node can join the AG if AG is not completely filled Case 2 – When does it replace node in AG? If the AG is full, every node e in the AG computes the value G NHAG+ (e) as given: G NHAG+ (e) = RL(e)/RL(j) Where, RL(e) = Request layer of node e in AG RL(j) = Requested layer of node j (joining node) If the value of G NHAG+ (e) < 1, then the node with the least value of G NHAG+ (e) is replaced. Case 3 – If node not replaced AG entrance finds closest AG member h to joining node and checks if it can have a new child-AG.

17. NODE LEAVING PROCEDURE When a node leaves, it generally sends a leaving message to the AG entrance and its neighbors Control messages often fail in wireless environments due to packet errors and handovers In THAG and NHAG, this problem is handled by using heartbeat messages In NHAG+, when a node leaves (which is not AG entrance), its parent node in the same tree will undertake the position’s task. If it is AG entrance, parent node in the same tree takes over the AG entrance tasks. If the leaving node has child-AGs, one of its child-AGs promotes a node with maximum requested layer to replace the vacated position.

18. RENEWAL OF AG LAYER Due to frequent leaving and joining of nodes, the AG layer is dynamically renewed according to the nodes’ states. It is done after every node joins, leaves, node replacement occurs or after periodic time interval. The requested layer of AG can potentially change at every event. Therefore, a smoothing scheme is implemented to avoid abrupt changes of the request layer.

19. SIMULATION SETUP Network topology used – transit stub topology created by GT-ITM tool Network topology consisted of – 1010 routers connected by 5000 edges Link delay – 1 to 10 ms for each edge Upload and Download Bandwidths of each node – randomly chosen from 2 to 5 Mbps Number of end-nodes was varied from 200 to 500 Nodes joined the ALM every 2 seconds. After all the nodes have joined, nodes leave the ALM every 2 seconds. When a wireless node leaves, it does so without any prior notice. NHAG+ is compared with three methods: SplitStream, THAG and NHAG.

20. SIMULATION SETUP CONTD. The performance evaluation is done in 3 different cases: CASE 1 – All the nodes are wired CASE 2 – Half of the nodes are wired and the rest are wireless CASE 3 – All the nodes are wireless The packet error rates are set to 0% in wired nodes and 1% in wireless nodes Rate of source media data is 2 Mbps MDC divided data in 4 descriptions, with each description rate = 500 Kbps In LMDC, number of descriptions = 4 and number of layers = 4. Hence, rate of layer of each description = 125 Kbps. The number of multicast trees = 4 (for all the methods). In THAG and NHAG+, AG size = 6, for NHAG, maximum AG size allowed was 6.

21. PERFORMANCE METRICS Total Throughput – Defined as the sum of throughput of each description. Where M = number of descriptions Relative Delay Penalty (RDP) – The average ratio of propagation delay on the paths from the source to receiver node in ALM trees over the end to end unicast latency between these nodes. where mDelay = multicast delay uDelay = unicast delay Relative Delay Variation (RDV) – The normalized difference of delay of the paths from source to a node in a different multicast tree. where Dmax = maximum delay Dmin = minimum delay

22. SIMULATION RESULTS TOTAL THROUGHPUT

23. SIMULATION RESULTS CONTD. Relative Delay Penalty (RDP)

24. SIMULATION RESULTS CONTD. Relative Delay Variation (RDV)

25. CONCLUSION The authors proposed a new method (NHAG+) for an efficient content delivery system in combined wired and wireless networks. They have studied and examined THAG and NHAG in detail. THAG has constant AG size, making it difficult to deliver descriptions appropriately across a heterogeneous network. NHAG solves the limitations of THAG, however, robustness of node departure is degraded. NHAG+ alleviates all the above mentioned limitations of THAG and NHAG by using LMDC. Simulation results demonstrate that NHAG+ out-performs SplitStream, THAG and NHAG in terms of total throughput, RDP and RDV.

26. QUESTIONS?