1. KAIS T High-throughput multicast routing metrics in wireless mesh networks Sabyasachi Roy, Dimitrios Koutsonikolas, Saumitra Das, and Y. Charlie Hu ICDCS 2006 2006. 10. 10 Hanjin Lee

2. 2 High-throughput multicast routing metrics in wireless mesh networks Contents Introduction Routing metrics for multicast protocols Methodology Simulation & testbed experiments Conclusions and future work

3. 3 High-throughput multicast routing metrics in wireless mesh networks Introduction Wireless mesh networks The routers are static, and thus dynamic topology changes are much less of a concern Main design goal for routing protocol Maintaining connectivity → finding high-throughput paths Multicast An efficient means of supporting collaborative applications Video conference, online games, webcast and distance learning All routing algorithms proposed for multicast use minimum-hop-count as the routing metric and focus on scenarios with high mobility In this paper Study the design of link-quality-based routing metrics for high-throughput multicast in mesh networks

4. 4 High-throughput multicast routing metrics in wireless mesh networks Routing metrics for multicast protocols Difference between link-layer unicast and multicast 802.11 MAC layer Unicast Virtual carrier sensing through RTS/CTS Link layer acknowledgement and data retransmission Broadcast Does not involve any RTS/CTS exchange No link layer acknowledgement and data retransmission Low reliability

5. 5 High-throughput multicast routing metrics in wireless mesh networks Routing metrics for multicast protocols Difference between link-layer unicast and multicast Two major implications on the design of link-quality metrics Bidirectional in unicast, unidirectional in multicast A successful data transfer only depends on the link quality in the forward direction No retransmission A data packet has only one chance to properly travel from one node to another For loss-rate-based link-quality metrics Adding the metric values of the individual links → multiplying

6. 6 High-throughput multicast routing metrics in wireless mesh networks Adapting unicast link-quality metrics for multicast PP (Packet Pair) Based on measuring the delay between a pair of back-to-back probes to a neighboring nodes Designed to correct the problem of distortion of RTT measurement due to queuing delays To calculate this metric A node sends two probe packets back-to-back to each neighbor periodically The first probe is small and the next one is large The neighbor calculates the delay between the receipt of the first and the second packets The delay for a link is calculated as an Exponentially Weighted Moving Average (EWMA) Modifications Broadcasting probe packets If a packet is lost, a 20% penalty is imposed

7. 7 High-throughput multicast routing metrics in wireless mesh networks Adapting unicast link-quality metrics for multicast ETX (Expected Transmission Count) The predicted number of data transmissions required to send a packet including retransmissions Modifications Not considering reverse path link quality : Forward delivery ratio : Reverse delivery ratio

8. 8 High-throughput multicast routing metrics in wireless mesh networks Adapting unicast link-quality metrics for multicast ETT (Expected Transmission Time) Bandwidth adjusted ETX Modifications To calculate ETX, the small packet is used To calculate the bandwidth of each link, divide the size of the large packet by the inter-arrival time between the small and the large packets : The size of the packet : The bandwidth of the link

9. 9 High-throughput multicast routing metrics in wireless mesh networks Adapting unicast link-quality metrics for multicast METX Routing metrics to minimize the total transmission energy Modifications Set to 1 The total expected number of transmissions needed by all the nodes along a path : The expected energy-cost of transmission form a source s to destination d : The link between u and d : The error rate of the link l : The transmission energy required between nodes u and d

10. 10 High-throughput multicast routing metrics in wireless mesh networks Adapting unicast link-quality metrics for multicast SPP (Success Probability Product) Energy efficient routing metric Modifications Set to 1 The expected number of transmissions at the source itself : The energy required to transmit over link i

11. 11 High-throughput multicast routing metrics in wireless mesh networks Methodology ODMRP (On-Demand Multicast Routing Protocol) Each node maintains a NEIGHBOR TABLE that records the cost of the links from its neighbors to itself The costs are defined according to the link-quality metric Procedure Sender Send JOIN QUERY Intermediate nodes Receive JOIN QUERY packet Look up the NEIGHBOR TABLE for the cost of the link Update the cost in the JOIN QUERY packet Rebroadcast JOIN QUERY A group member Receive JOIN QUERY After getting the first JOIN QUERY, waits for a period of δ seconds Broadcast JOIN REPLY including the best route

12. 12 High-throughput multicast routing metrics in wireless mesh networks Methodology ODMRP (On-Demand Multicast Routing Protocol) Optimization A duplicate query is forwarded only if the cost of the path it has traveled is less than that of the minimum cost query received till then Each node sets a timer for a period of α seconds when it receives the first JOIN QUERY with a particular sequence number

13. 13 High-throughput multicast routing metrics in wireless mesh networks Simulation & Testbed experiments Simulation setup 50 static nodes in 1000m*1000m Two multicast groups with ten members each The sources send CBR traffic consisting of 512-bytes packets at a rate of 20 packets/second Radio propagation range is 250m Simulation duration is 400s δ : 30ms, α : 20ms

14. 14 High-throughput multicast routing metrics in wireless mesh networks Simulation & Testbed experiments Testbed setup 8 wireless mesh routers equipped with 802.11b Implement ODMRP as an application-layer daemon 2 multicast groups Each has 1 source and 2 receivers

15. 15 High-throughput multicast routing metrics in wireless mesh networks Simulation & Testbed experiments Probe overhead Loss penalty Multiplicative Loss penalty in high loss-rate scenario

16. 16 High-throughput multicast routing metrics in wireless mesh networks Conclusions and future work In this paper Discussed the fundamental difference between unicast and multicast routing Showed how to adapt unicast routing metrics for use in multicast SPP and PP achieve the highest throughput performance Future work Optimal probing rate Multicast routing in multi-radio/multi-channel mesh networks Significantly expand the testbed