High-throughput multicast routing metrics in wireless mesh networks

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

3. 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 High-throughput multicast routing metrics in wireless mesh networks

4. 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 High-throughput multicast routing metrics in wireless mesh networks

5. 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 High-throughput multicast routing metrics in wireless mesh networks

6. 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 High-throughput multicast routing metrics in wireless mesh networks

7. 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 High-throughput multicast routing metrics in wireless mesh networks

8. 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 High-throughput multicast routing metrics in wireless mesh networks

9. 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 High-throughput multicast routing metrics in wireless mesh networks

10. 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 High-throughput multicast routing metrics in wireless mesh networks

11. 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 High-throughput multicast routing metrics in wireless mesh networks

12. 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 High-throughput multicast routing metrics in wireless mesh networks

13. 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 High-throughput multicast routing metrics in wireless mesh networks

14. 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 High-throughput multicast routing metrics in wireless mesh networks

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

16. 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 High-throughput multicast routing metrics in wireless mesh networks