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Deployment Guidelines for Highly Congested IEEE 802.11b/g Networks

Deployment Guidelines for Highly Congested IEEE 802.11b/g Networks. Andrea G. Forte and Henning Schulzrinne Columbia University. Background. IEEE 802.11b/g networks widely spread Mostly uncoordinated deployments Channel assignment not trivial Our approach

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Deployment Guidelines for Highly Congested IEEE 802.11b/g Networks

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  1. Deployment Guidelines for Highly Congested IEEE 802.11b/g Networks Andrea G. Forte and Henning Schulzrinne Columbia University

  2. Background • IEEE 802.11b/g networks widely spread • Mostly uncoordinated deployments • Channel assignment not trivial • Our approach • Test on the field (enough optimal algorithms!) • Come out with practical guidelines for network administrators

  3. Wireless Networks • IEEE 802.11a • 5 GHz band • 12 non-overlapping channels • Scarcely deployed and used • IEEE 802.11b/g • 2.4 GHz band • 3 non-overlapping channels • Widely spread  We focus on IEEE 802.11b/g  IEEE 802.11b

  4. Problems (1/3)Handoff behavior (65th IETF meeting) • Handoff is triggered • generally, by low signal strength • in congested channel, by frame loss • Effect of layer 2 handoff • Increase of traffic • Disruption of network (0.5 ~ 1.5 sec) The number of handoff per hour in each IETF session

  5. Problems (2/3)Handoff behavior (65th IETF meeting) • Handoff to the same channels : 72% • Handoff to the same AP : 55% • Handoffs between channels

  6. Problems (3/3)Handoff behavior (65th IETF meeting) • Too often handoff • Disruption of network • 0.5 ~1.5 sec per handoff • Increase of traffic due to handoff related frames – probe request and response • 10.4% of total • Distribution of session time: time between handoffs

  7. Experiments • Experiment 1 • Testing different channel configurations in existing networks • Columbia University campus (site survey) • Experiment 2 • Studying co-channel interference in highly congested scenarios (large number of users) • ORBIT wireless test-bed

  8. Site Survey – Columbia University Google Map!

  9. Site Survey – Columbia University • Found a total of 668 APs • 338 open APs: 49% • 350 secure APs: 51% • Best signal: -54 dBm • Worst signal: -98 dBm • Found 365 unique wireless networks • “private” wireless networks (single AP): 340 • “public” networks (not necessarily open): 25 • Columbia University: 143 APs • PubWiFi (Teachers College): 33 APs • COWSECURE: 12 APs • Columbia University – Law: 11 APs • Barnard College: 10 APs

  10. Experiment 1Experimental setup Sniffer AP Client Surrounding APs Surrounding APs

  11. Experiment 1 – Results (1/3)Using non-overlapping Channels • Throughput and retry rate with no interference •  Same for any channel • Throughput and retry rate with interference on channel 1

  12. Experiment 1 – Results (2/3)Using non-overlapping Channels • Throughput and retry rate with interference on channel 6 •  Most congested! • Throughput and retry rate with interference on channel 11

  13. Experiment 1 – Results (3/3)Using Overlapping Channels • Throughput and retry rate with interference on channel 4 •  Better than channel 6 • Throughput and retry rate with interference on channel 8 •  Better than channel 6

  14. Experiment 1Conclusions • Using overlapping channels does not affect performance negatively • In the experiments channel 4 and channel 8 are a much better choice than channel 6 • Use at least channels 1, 4, 8 and 11 (minimum overlapping in band) • better spatial re-use • no significant decrease in performance  USE OVERLAPPING CHANNELS!

  15. Experiment 2Experimental setup • ORBIT wireless test-bed • Grid of 20x20 wireless nodes • Used only maximum bit-rate of 11 Mb/s (no ARF) • G.711 CBR • Number of clients always exceeding the network capacity (CBR @ 11Mb/s  10 concurrent calls)

  16. Experiments 2 – Results (1/2)Non-overlapping Channels • AP1 using Ch. 1 • AP2 using Ch.6 • Num. of clients: 43 • AP1 and AP2 using Ch. 1 • Num. of clients: 43

  17. Experiments 2 – Results (2/2)Overlapping Channels • AP1 using Ch. 1 • AP2 using Ch. 4 • Num. of clients: 67 • AP1 and AP2 using Ch. 4 • Num. of clients: 67

  18. Experiment 2Conclusions • When using two APs on the same channel • Throughput decreases drastically • Physical-error rate and retry rate increase • Using two APs on two overlapping channels performs much better than using the same non-overlapping channel • Do not deploy multiple APs on the same non-overlapping channels • USE OVERLAPPING CHANNELS!

  19. One AP vs. manyVery high number of users • Network performance with single AP in highly congested scenarios • Network performance with two APs on the same channel in highly congested scenario • Using two APs on the same channel performs worst than using a single AP!

  20. Conclusions • Using overlapping channels does not affect performance negatively • Use at least channels 1, 4, 8 and 11 • Do not deploy multiple APs on the same non-overlapping channels • Using two APs on the same channel performs worst than using a single AP! • Just increasing the number of APs does not help  USE OVERLAPPING CHANNELS!

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