/38 2 Motivation multi-agent path planning (MAPP) is important necessity of building reliable systems cutting-edge studies assume perfect agents robot faults are common => fault-tolerance e.g., mean time between failure of one robot: 125days* *https://fr.autostoresystem.com/benefits/reliable aws.amazon.com path planning where agents may unexpectedly crash at runtime MAPPCF (w/crash faults)
/38 13 Problem Formulation of MAPPCF given solution s.t. all non-crashed agents eventually reach their destination, regardless of crashes (up to f ) & transition rules & maximum number of crashes f defined with failure detector & execution model centralized planning followed by decentralized execution
/38 14 Failure Detectors oracle that tells status of neighboring vertices response: 1. no agent query 2. non-crashed agent named FD 3. crashed agent anonymous FD unable to identify who crashes c.f., [Chandra+ JACM-96]
/38 16 Model Power Analyses SYN + AFD SYN + NFD SEQ + NFD SEQ + AFD synchronous model sequential model named failure detector anonymous FD SYN SEQ NFD AFD strictly stronger SEQ+AFD SYN+AFD solvable instances weakly stronger SYN+AFD SYN+NFD SYN+AFD SYN+NFD or solvable in SYN unsolvable in SEQ
/38 17 Computational Complexity 1. finding solutions is NP-hard 2. verification is co-NP-complete regardless of FD types or execution models the proofs are reductions from 3-SAT MAPPCF is computationally intractable
/38 18 Solving MAPPCF proposal: decoupled crash faults resolution framework (DCRF) synchronous model + named FD number of maximum crashes f =2 example* *DCRF is applicable to other models 1. find initial paths 2. identify unresolved events 3. compute backup path & update solution 4. back to step-2
success rate #crashes f fixed #agents: 15 SYN SEQ solving MAPPCF becomes difficult with more {agents, crashes} SEQ is harder than SYN random-32-32-10 32x32 (|V|=922) from [Stern+ SOCS-19] 30sec timeout with named FD synchronous SYN v.s. sequential SEQ
/38 37 Empirical Results MAPPCF provides better solution concept than finding disjoint paths random-32-32-10 32x32 (|V|=922) from [Stern+ SOCS-19] 30sec timeout with named FD
success rate #agents DCRF/SYN disjoint paths
costs / lower bound #agents DCRF/SYN disjoint paths fixed #crashes: f =1 adapted from CBS [Sharon+ AIJ-15] v.s. finding vertex disjoint paths traveling time when no crashes
/38 38 Concluding Remarks MAPPCF novel path planning problem for multiple agents that may crash at runtime fault solution multiple paths assuming crashes https://kei18.github.io/mappcf future directions: complete algorithms, optimization, other types of failure detectors
kei18
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kneath
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