deployment guidelines for highly congested ieee 802.11b/g networks
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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 - PowerPoint PPT PresentationTRANSCRIPT
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– Test on the field (enough optimal algorithms!)– Come out with practical guidelines for network
administrators
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
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)
306
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36
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sS1 Lunch S1 P
IETF Sessions
C11
C6
C1
The number of handoff per hour in each IETF session
Problems (2/3)Handoff behavior (65th IETF meeting)
1→122%
1→69%
1→113%
6→19%
6→633%
6→112%
11→13%
11→62%
11→1117%
• Handoff to the same channels : 72%
• Handoff to the same AP : 55%
• Handoffs between channels
Problems (3/3)Handoff behavior (65th IETF meeting)
< 5 min33%< 10 min
12%
< 1 min23%>= 10 min
32%
• 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
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
Site Survey – Columbia University
Google Map!
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
Experiment 1Experimental setup
AP Client
Sniffer
Surrounding APs Surrounding APs
Experiment 1 – Results (1/3)Using non-overlapping Channels
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Experiment
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•Throughput and retry rate with no interference
Same for any channel
•Throughput and retry rate with interference on channel 1
Experiment 1 – Results (2/3)Using non-overlapping Channels
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Experiment
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Experiment
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• Throughput and retry rate with interference on channel 6
Most congested!
•Throughput and retry rate with interference on channel 11
Experiment 1 – Results (3/3)Using Overlapping Channels
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• 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
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!
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)
Experiments 2 – Results (1/2)Non-overlapping Channels
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• AP1 using Ch. 1
• AP2 using Ch.6
• Num. of clients: 43
• AP1 and AP2 using Ch. 1
• Num. of clients: 43
Experiments 2 – Results (2/2)Overlapping Channels
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• AP1 using Ch. 1
• AP2 using Ch. 4
• Num. of clients: 67
• AP1 and AP2 using Ch. 4
• Num. of clients: 67
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!
One AP vs. manyVery high number of users
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•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!
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!