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Multicast Service Overlay Design Li Lao (UCLA), Jun-Hong Cui (UCONN), Mario Gerla (UCLA) Multicast Overview IP Multicast Application Layer Multicast SPECTS 2005 Overlay Multicast 2 Multicast Overview IP multicast (network level, routers) Application layer multicast (end hosts) Easy to deploy Inefficient and difficult to scale to large groups Multicast Service Overlay Network (MSON) (proxies) Efficient Faces deployment and marketing problems Efficient and scale to large groups Need careful overlay design A Comparative Study of Multicast Protocols: Top, Bottom, or In the Middle? (Lao, et al. GI 2005) SPECTS 2005 3 An Example of MSON TOMA F MSON D C E B A Application-Layer Multicast SPECTS 2005 4 Our Goal Investigate MSON provisioning Where to place proxies How to connect these proxies (overlay links) How much bandwidth to be reserved on each overlay link Examine effects of design algorithms Performance of TOMA (as example) SPECTS 2005 5 An Example of MSON Design A D E I SPECTS 2005 6 Roadmap Motivation Problem Formulation Our Approach Simulation Study Conclusion SPECTS 2005 7 Problem Formulation Input: a network N = (V, E), multicast groups G with membership distribution and bandwidth requirement Output: a virtual network N’ = (V’, E’) V’ V, and E’ path(E) Each e’ is assigned bandwidth, e’E’ Objective: minimize multicast overlay cost and average end-to-end delay SPECTS 2005 8 Our Approach Divide and Conquer Overlay proxy placement: determine V’ Overlay link selection: determine E’ Bandwidth dimensioning: determine bandwidth for e’ E’ SPECTS 2005 9 1. Overlay Proxy Placement Given: the number of members wi for each router i (1 i n), and the shortest distance dij between every two routers i and j Find: no more than K (1 K n) routers as proxies Objective: the weighted sum of distances from each router to its nearest proxy is minimized SPECTS 2005 10 Solution ILP Formulation 1, xi 0, if router i is selected as a proxy otherwise 1, yij 0, if router j subscribes to proxy i otherwise A lot of approaches to solve, but expensive Greedy In each step, a router i is selected if this reduces the weighted sum of distances by the largest amount O(Kn2) SPECTS 2005 11 2. Overlay Link Selection E C A A D D B B E C A Complete Graph E C A D D B E C B 1-MST SPECTS 2005 Adjacent Connection 12 Solutions Complete Graph Shortest path length Highest tree cost n( n 1) Largest number of overlay links: 2 Adjacent Connection Shortest path length Reduced tree cost Reduced number of overlay links Minimum Spanning Tree Long path length Minimum tree cost Minimum number of overlay links: n 1 SPECTS 2005 13 3. Bandwidth Dimensioning Given: an overlay network N’ = (V’, E’), a set of groups G with member distribution and bandwidth requirements, and a multicast routing algorithm Compute the amount of bandwidth reserved on each overlay link e’ E’ SPECTS 2005 14 Solution Simulation-based approach Compute the multicast trees Sum up the traffic volume of these trees for each overlay link Over-dimensioning SPECTS 2005 15 Simulation Study Abstracted AT&T backbone Rocketfuel 1755 54 nodes, 9 proxies Weight-based membership model ~300 nodes, 20 proxies Uniform membership distribution Metrics Multicast tree cost, path length, request rejection ratio SPECTS 2005 16 Overlay Proxy Placement SPECTS 2005 17 Overlay Proxy Placement SPECTS 2005 18 Overlay Link Selection Number of overlay links Multicast Tree Cost Path Length Complete Graph 190 81.9 4.24 Adjacent Connection 76 48.3 4.24 1-MST 19 31.2 6.05 2-MST 38 35.0 4.98 SPECTS 2005 19 Bandwidth Dimensioning SPECTS 2005 20 Bandwidth Dimensioning SPECTS 2005 21 Conclusions & On-going Work Formulated the problem and divided it into three subproblems Proposed solutions to each sub-problem Greedy algorithm very effective for overlay proxy placement MST and Adjacent Connection perform better than Complete Graph Over-dimensioning is needed for bandwidth dimensioning to reduce join request rejection ratio On-going work: Overlay link selection: trade-off of overlay cost and delay Probe a comprehensive optimal approach SPECTS 2005 22 Questions ??? SPECTS 2005 23