1 / 37

Challenges managing large-scale wireless networks

Challenges managing large-scale wireless networks. Lakshminarayanan Subramanian Courant Institute of Mathematical Sciences New York University Joint work with many others. Management Complexity Ladder. Indoor Wireless Access Point Network Multi-hop indoor wireless networks

hayden
Télécharger la présentation

Challenges managing large-scale wireless networks

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Challenges managing large-scale wireless networks Lakshminarayanan Subramanian Courant Institute of Mathematical Sciences New York University Joint work with many others

  2. Management Complexity Ladder • Indoor Wireless Access Point Network • Multi-hop indoor wireless networks • Outdoor Mesh Networks • Rural Wireless Networks (Long-distance +mesh)

  3. Why is management hard? • Potential causes for performance degradation • External problems • Interference, Channel fluctuations • Network performance issues • Incorrect ETX, Channel assignment. Routing problems • Physical issues • Radio separation issues • Unreliable power (Huge problem in rural wireless) • Software issues + Configuration • Forwarding problems, unexpected packet drops • Mundane problems • Loose pigtail, Card misbehavior, Card stops working

  4. Why is it hard to fix? • Potential causes are huge and interdependent • No back channels (in multi-hop cases) • Measurements vary by the second • Environmental fluctuations • Power fluctuations • Software behavior on wireless boards is not very predictable • Climbing street poles and towers is actually not fun!

  5. Some experiences ROMA: Multi-radio indoor wireless network (Aditya, Jinyang) CitySense: Outdoor wireless mesh network (Matt T, Matt W) WiLDNet: Long-distance WiFi networks (Rabin, Sergiu, Sonesh, Eric, Manuel) WiRE architecture (Matt T, Aditya) 5

  6. Cannot transmit concurrently Inter-path interference Reduce gateway gateway Cannot transmit concurrently Multi-radio mesh promises greater throughput Intra-path interference Eliminate gateway

  7. Physical constraints • Compact nodes  few radios per node • Link losses, link variability, external load

  8. Link variabilities Two radios report with diff channel conditions ETX measurements are skewed Channel 1 works very poorly, channel 11 works well!!!

  9. <C1> C1 <C1,C2> <C1,C2> C2 <C2,C3> <C2,C3> <C2,C3> C3 <C3,C4> <C3,C4> ROMA: basic idea Single-radio gateway • Each radio in a multi-radio gateway acts as an independent gateway

  10. Multi-radio route metric 1 2 1 Routing metric must consider worst link Single-radio route metric: 1 2 1 Path throughput is limited by worst link

  11. : average delivery ratio : deviation of delivery ratio : fraction of time channel is busy with external traffic ETT = Conservative metric CETT = Link metric • ETT over-estimates link performance • Link metric should incorporate: • Link variability • highly variable links result in unpredictable throughput • External load

  12. Our Indoor Testbed NSC Geode Processors, 128MB RAM, 1GB Flash Implemented on the Click Modular Router Patched Madwifi 0.9.3.3

  13. Aggregate performance • Setup: 9 UDP flows from 3 gateways to non-gateway nodes ROMA’s median aggregate throughput is 1.4X or 2.1X of alternative designs ROMA is able to utilize more channels to reduce inter-path interference CDF 2 identical channels 1 common, 1 assigned channel ROMA Aggregate throughput (Mbps)

  14. WiFi-based Long Distance Networks • WiLD links use standard 802.11 radios • Longer range up to 150km • Directional antennas (24dBi) • Line of Sight (LOS) • Why choose WiFi: • Low cost of $500/node • Volume manufacturing • No spectrum costs • Customizable using open-source drivers • Good datarates • 11Mbps (11b), 54Mbps (11g)

  15. Routers used: (a) Linksys WRT54GL, (b) PC Engines Wrap Boards, Costs: (a) $50, (b) $140 AirJaldi Network • Tibetan Community • WiLD links + APs • Links 10 – 40 Kms • Achieve 4 – 5 Mbps • VoIP + Internet • 10,000 users

  16. Routers used: PC Engines Wrap boards, 266 Mhz CPU, 512 MB Cost: $140 Aravind Eye Hospital Network • South India • Tele-ophthalmology • All WiLD links • Links 1 – 15 Kms long • Achieve 4 – 5 Mbps • Video-conferencing • 3000 consultations/month

  17. New World Record – 382 Kms Pico El Aguila, Venezuela Elev: 4200 meters

  18. Deployment

  19. Overall Impact • Both networks financially sustainable • 50000 patients/year being scaled to 500000 patients/year • Over 30000 patients have recovered sight

  20. Experience with WiLD Networks • In the field, point-to-point performance is bad • On a 60km link in Ghana • We get 0.6 Mbps TCP vs 6 Mbps UDP • On a relay (single channel) • We get only 2 Mbps TCP

  21. B A Problem: Propagation Delay • Large propagation delay  high collision probability

  22. Design Choices for WiLDNet • Use Sliding Window flow control • 802.11 MAC ACKs disabled • Packet batches sent every slot • Slot allocation determined by demand • Replace CSMA with TDMA on every link • Alternate send and receive slots

  23. B B B 1 1 1 A A A 2 2 2 C C C Inter-Link Interference Simultaneous Send Simultaneous Receive Send & Receive • 12dB isolation • Disable CCA

  24. A B I Channel Loss: From external traffic • Strong correlation between loss and external traffic • Source (A) and interferer (I) do not hear each other

  25. Sustainability Challenges • Bad quality grid power • Higher component failures, more downtimes • Limited local expertise • Local operation, maintenance, and diagnosis difficult • Lack of alternate connectivity • Complicates remote diagnosis and management • Remote locations • Traveling is difficult and infrequent (often once in 6 months)

  26. Poor Quality Power Voltage Range Number of Instances seen over 6 weeks • Spikes and Swells: • Lost 50 power adapters • Burned 30 PoE ports • Low Voltages: • Incomplete boots • HW watchdog fails • Frequent Fluctuations: • CF corruptions • Battery Damage

  27. >90% of faults are power-related HW Faults Hardware Faults at Aravind (in 2006) *Conservative Estimate

  28. SW Faults Software Faults at Aravind (in 2006) *Conservative Estimate

  29. Solutions • Power 1.1 Low Voltage Disconnect 1.2 Low-cost Solar Power Controller • Data Collection and Monitoring • Alternate Network Entry Points • Recovery Mechanisms • Safe Software

  30. Power: Low Voltage Disconnect • Low Voltage Disconnect Circuit (LVD) • Disconnect load at low voltage • Prevent battery over-discharge and hung routers • Without LVDs, roughly 50 visits per week for manual reboots at AirJaldi • Off-the-shelf LVDs oscillate too much • Too many automatic reboots • We designed new LVD circuit with better delay • No more manual visits or reboots!

  31. Power: Low-cost Solar Power Controller • Tackle spikes, swells and enable power at remote sites • Features • PPT (peak power tracking) => 15% more power draw • LVD + trickle charging => Doubles battery life • Voltage regulator => No spikes and swells • Power-over-Ethernet => Remote Mgmt • $70 (compared to $300 commercial units) • Have not lost any routers yet in 1 year

  32. Operational Results

  33. Jan’06 – Jun’06 Jul’06 – Dec’06 Jan’07 – Jun’07 Jun’07 – Dec’07 2007: 5 more clinic links Operational Results Our support Migration at Aravind Aravind Local Vendor Maintenance Management Installation Equipment Supply

  34. WiRE Architecture

  35. Questions? Thank you!

More Related