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Slobodan Milanko Manweiler, J., Franklin, P., & Choudhury, R. R. (2012, March). RxIP: Monitoring the health of home wireless networks. In INFOCOM, 2012 Proceedings IEEE (pp ). IEEE.
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Purpose Provide a solution to hidden terminals in residential networks
Mutual AP communication Hidden terminal analysis Resolution of conflict
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Motivation The bottleneck is no longer the ISP, rather the wireless network itself Significant performance degradation with increased hidden terminals RTS/CTS substantially reduces throughput Solutions requiring a backbone network Installation of other solutions is difficult
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EWLAN
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Do Controllers make sense at home?
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My home looks different
Nontechnical users / No IT staff Limited Net Infrastructure Thoughtless Deployments
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Problems One link is punished severely Client moving
Interference between clients Equal loss All loose
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Bad choice? Persistent Impacts.
Is it really noticeable? Continuous distance Becomes hidden Out of range DSL Hidden AP Placement Matters: Bad choice? Persistent Impacts.
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Solution: RxIP
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RxIP: The Contribution
1) Bootstrap: Establishing Internet Coordination 2) Detection: Verifying Hidden Terminals as the Cause 3) Fault Assessment: Identifying Hidden Terminal APs 4) Recovery: Isolating Traffic from Hidden Terminals
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RxIP: Bootstrap APs broadcast wired IP coordination address/port
Embedded in beacons Intermediate nodes forward extra hop (via wired) 2-hop coordination w/ microsecond-accuracy time sync IP Address Time Sync @ μsec accuracy IP Address Time Sync IP Address Time Sync
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? ? RxIP: Detection APs detect the presence of a hidden terminal
High loss rates when link SNR (quality) is good Link asymmetry – divergent upload/download behavior ? ? upload download We have to talk… upload download
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RxIP: Fault Assessment
APs cooperate to isolate hidden terminals APs maintain detailed records of packet transmissions Pairs of APs attempt to correlate concurrency with loss Fast record / lookup through Bloom Filters APs poll suspected hidden terminals Yes/No Questions … Did you transmit at time X? Per-peer saturating counter
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RxIP: Saturation Count
4 cases for probe response, alter sat. counter Failure, peer concurrent → large increase Success, peer concurrent → large decrease Failure, peer not transmitting → small decrease Success, peer not transmitting → small decrease Hidden Terminal Threshold
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RxIP: Recovery APs cooperate to isolate hidden terminal traffic
Hybridized CSMA/TDMA schedule Completely managed by APs, clients unaware Channel access “semaphore” between APs APs mutually agree to never transmit concurrently Initiate a pairwise token exchange to schedule timeslots My turn is later… My turn…
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Synchronized Token Passing: Pass all tokens to transmit
RxIP: Token Passing My turn… My turn… My turn… My turn… My turn… Synchronized Token Passing: Pass all tokens to transmit
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RxIP: Making my purchase
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RxIP: Benefits No deadlock in arbitrary graphs
Guaranteed by partnership establishment protocol Account for network change; Periodic re-pair No unnecessary silencing AP is only silenced if its hidden terminal is transmitting Uses internet for AP communication, and frees WIFI Transparent to clients, and users; No setup cost What happens if tokens lost/delayed? Tokens preschedule channel access time Active failure detection/recovery prevents disruptions
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RxIP: Evaluation after before
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Evaluation Cont.
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Evaluation Cont. ideal 802.11 RxIP
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RxIP: Conclusion RxIP APs can Mitigate Hidden Terminal Effects
(1) Detect the presence of a hidden terminal (2) Isolate the cause to particular nearby AP (3) Interference-aware hybrid TDMA/CSA scheduling Peer-to-peer Negotiation of the Wireless Channel Bring traditionally-centralized enterprise techniques home Room for Exploration Many successful enterprise WLAN designs Research opportunities in porting to RxIP platform
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