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Less-than-Best-Effort Service for Community Wireless Networks:
Challenges at Three Layers
GAIA meeting, 89th IETF Meeting6. 3. 2014Michael Welzl
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Context: the LCDNet vision
From http://publicaccesswifi.org/the-research/paws-approach/
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Layer 2 LBEOutsidenot under control
Insideunder control
• Can control:– Both ways: PHY rates, PCF? 802.11e QoS?– Download: RA algorithm, DCF parameters like CW
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RA alg. impact
From:Naeem Khademi, Michael Welzl, Stein Gjessing: "Experimental Evaluation of TCP Performance in Multi-rate 802.11 WLANs”, IEEE WoWMoM 2012.
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Layer 3 LBE
• Shortest path routing is THE routing method– This overloads the shortest path– If there are multiple paths, LBE traffic could take a
detour • Tools exist: e.g. MPLS TE, ECMP… but typically still shortest
paths used• multi topology (MT) routing, meant for IP fast reroute, could
be a good fit
• Small packets could be costly (power consumption)– May want to aggregate + tunnel them (TCMTF)
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Layer 4 LBE
• End systems: LEDBAT isn’t great– Much more stuff exists– LBE != LBE…
• Routers / AP / Modem:AQM can differentiate (early mark/drop)Queue scheduling can differentiate (CBQ etc)
From: David Ros, Michael Welzl: "Assessing LEDBAT's Delay Impact", IEEE Communications Letters 17(5), pp. 1044-1047, 2013.
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Conclusion
• LEDBAT isn’t enough, it’s a larger story– Research needed
Thank you!
Questions?
