1

Less-than-Best-Effort Service for Community Wireless Networks:

Challenges at Three Layers

GAIA meeting, 89th IETF Meeting6. 3. 2014Michael Welzl

michawe@ifi.uio.no

2

Context: the LCDNet vision

From http://publicaccesswifi.org/the-research/paws-approach/

3

Layer 2 LBEOutsidenot under control

Insideunder control

• Can control:– Both ways: PHY rates, PCF? 802.11e QoS?– Download: RA algorithm, DCF parameters like CW

download

upload

4

RA alg. impact

From:Naeem Khademi, Michael Welzl, Stein Gjessing: "Experimental Evaluation of TCP Performance in Multi-rate 802.11 WLANs”, IEEE WoWMoM 2012.

5

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)

6

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.

7

Conclusion

• LEDBAT isn’t enough, it’s a larger story– Research needed

Thank you!

Questions?