1. Brief Announcement: Randomized Rumor Spreading with Fewer Phone Calls Kirsten Hildrum Sean Ma Satish Rao

2. The Problem Soccer game time change! Must tell everyone

3. Pushing a rumor Soccer game time change! Must tell everyone

4. A Phone Tree Soccer game time change! Must tell everyone

5. Phone tree problem Soccer game time change! Must tell everyone

6. Our Observation Combine the approaches: 1.Rumor spreading to get around faults 2.Tree to finish spreading rumor Metrics –Success rate: % of players who know the rumor –Number of phone calls Idea: Rumor spreading efficient when few know rumor, when many know, use tree. Long history of rumor spreading algorithms, lots of related work, combo idea also used by others (eg. Birman et al)

7. Reduces failure rate of tree Percent of nodes notified using % failed Tree alone Push alone Push +tree 010088100 1026388 2003060 3001027 40038 Success rate vs. failure rate

8. Fewer phone calls than push Phone calls per node Num playersPush+treeRumor spreading 163842.215.3 655362.117.4 262,1442.019.6 1,048,5762.022.0 4,194,3042.023.4 10% nodes have failed (note that with push+tree not all nodes know message)

9. Thanks!