1. IEEE 802.11 in the Large: Observations at the IETF Meeting
Andrea G. Forte
Sangho Shin
Henning Schulzrinne
Department of Computer Science
Columbia University

2. Introduction 65th IETF meeting Data collection Goals
Dallas, TX March 19th ~ 24th
Hilton Anatole hotel
1200 attendee
Data collection
21st ~ 23rd for three days
25GB data, 80 millions frames
Goals
Identify unusual behaviors due to the highly congested environment
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3. Overview Introduction Related work Wireless network setup
Measurement setup
User behavior
Load balancing
Handoff behavior
Overhead of multiple APs on a channel
Conclusions
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4. Related Work Jardosh et al. Rodrig et al. Balachandran et al. Target
62nd IETF (’05)
SIGCOMM ’04
SIGCOMM ’01
Attendee
1100
550
200
Clients detected
500
377
195
WLAN
802.11b
Channels
1, 6, 11
(dynamic)
1, 8, 11
1, 4, 7, 11
Number of APs 38 5 4
Focused on
New metric for channel congestion, ‘Link reliability’
Overhead of , the data transmission rate
Load balancing: “No correlation b/w num of clients and traffic load” *
* The number does not mean the total number of wireless clients in the IETF meeting,
but the number of clients detected from the measurements.
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5. Wireless network in IETF meeting
Many hotel b APs on channel 6
91 additional APs in a/b by IETF
Cisco Aironet 1200 AP
Channel 1 and 11 in b
One subnet with one ESSID ‘ietf65 ’
No wireless security
The largest wireless network measured so far
Hotel APs
802.11b channel 6
IETF APs
802.11a/b
ESSID : ietf65
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6. Measurement setup Four sniffers Channel assignment IBM T42 Think Pad
Proxim ORiNOCO 11 a/b/g
Sniffer software: Airopeek NX
Channel assignment
Three sniffers on channel 1, 6 and 11, respectively
Fourth sniffer on all 8 channels in a
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7. Measurement setup Measurement place Room Chantilly
The biggest room - 142’ x 80’, 600 persons
Two biggest IETF sessions, and the plenary session in the evening
Six IETF APs + Six Hotel APs in the room
Session 2
& break
Session 1 (AM)
Lunch
Session 1 (PM)
Plenary
9:00
11:30
13:00
15:00
17:00
19:30
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8. The positions of the APs in the room
Room Chantilly
AP5
AP4
Seating area during IETF sessions and plenary
Another seating area during plenary
AP1
AP2
AP3
AP6
sniffers
AP on channel 1
AP on channel 11
AP on channel 11
(estimated position)
142 feet
screen
Gate
80 feet
Lobby
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AP9

9. Overview Introduction Related work Wireless network setup
Measurement setup
User behavior
Load balancing
Handoff behavior
Overhead of multiple APs on a channel
Conclusions
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10. User behavior
Overall traffic in b
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11. User behavior
Protocols
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12. User behavior
Number of clients
(all 8 channels)
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13. Overview Introduction Related work Wireless network setup
Measurement setup
User behavior
Load balancing
Handoff behavior
Overhead of multiple APs on a channel
Conclusions
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14. Load balancing Distribution of clients
No load balancing feature was used
Client distribution is decided by the relative proximity from the APs
Ch 6 (ceiling) > Ch 1 > Ch 11
AP5
AP4
Seating area during IETF sessions and plenary
Another seating area during plenary
AP1
AP2
AP3
AP6
sniffers
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15. Load balancing Distribution of clients
No load balancing feature was used
Client distribution is decided by the relative proximity from the APs
Ch 6 (ceiling) > Ch 1 > Ch 11
AP1 > AP2 > AP3
Number of clients in channel 1
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16. Load balancing Throughput Average throughput in 802.11a/b
Average throughput in channel 1
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17. Load balancing Throughput per client Average throughput per client
in a/b
Average throughput per client
in channel 1
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18. Load balancing How? Study of Balanchandran et al. [1]
Number of clients? – Simple, but not accurate
Throughput ? - Accurate, but too complex
Study of Balanchandran et al. [1]
“No correlation between the number of clients and traffic load”
“Throughput per client needs to be considered”
In the large scale wireless network like IETF meeting?
[1] A. Balanchandran et al. “Characterizing user behavior and network
performance in a public wireless LAN”, SIGMETRICS ‘02
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19. Capacity in the channel
Load balancing
Number of clients vs. throughput in Ch. 6
Capacity in the channel
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20. Capacity in the channel
Load balancing
Number of clients vs. Throughput
Capacity in the channel
Clear correlation between the number of clients and throughput
The number of clients can be used for load balancing with low complexity of implementation, in large scale wireless networks
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21. Effect of screen Small number of clients on AP3 Effect of a screen?
Number of clients in channel 1
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22. Effect of screen
An experiment
30 ~ 100 feet
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23. Overview Introduction Related work Wireless network setup
Measurement setup
User behavior
Load balancing
Handoff behavior
Overhead of multiple APs on a channel
Conclusions
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24. The number of handoff per hour
Handoff behavior
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
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25. Handoff behavior Handoffs between channels
Handoff to the same channels : 72%
Handoff to the same AP : 55%
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26. Handoff behavior Distribution of session time: time between handoffs
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
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27. (based on the number of handoffs during the whole day)
Handoff behavior
Handoffs per vendor
Distribution of vendors
Distribution of handoffs per vendor
(based on the number of handoffs during the whole day)
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28. Handoff behavior Handoffs per vendor (session time) 9/22/2018 Cisco
Apple
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29. Overview Introduction Related work Wireless network setup
Measurement setup
User behavior
Load balancing
Handoff behavior
Overhead of multiple APs on a channel
Conclusions
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30. Overhead of having multiple APs
Overhead from replicated multicast and broadcast frames
All broadcast and multicast frames are replicated by all APs  Increase traffic
Router
A channel
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31. Overhead of having multiple APs
Overhead from replicated multicast and broadcast frames
All broadcast and multicast frames are replicated by all APs
DHCP request (broadcast) frames are replicated and sent back to each channel
Router
A channel
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32. Overhead of having multiple APs
Overhead from replicated multicast and broadcast frames
All broadcast and multicast frames are replicated by all APs.
DHCP request (broadcast) frames are replicated and sent back to each channel.
Multicast and broadcast frames : 10%
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33. Overhead of having multiple APs
Co-channel interference
14 APs around the room Chantilly in channel 6
Co-channel interference and too many clients are responsible for the very low throughput of channel 6.
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34. Conclusions
Uneven distribution of clients and throughput among channels and APs
Correlation between the throughput and the number of clients
The number of clients can be used for load balancing with low complexity in highly congested wireless networks
Too many inefficient handoffs
Disrupt network and increase traffic
Need better handoff algorithms
Having multiple APs on a channel
Increases the traffic due to replication of multicast and broadcast frames
Decrease throughput due to co-channel interference
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35. Most Recent Results
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36. Ongoing Work Apple vs. Intel (Thank you Norbert!) Apple
When to scan?
Who to associate to?
Intel (newest chipset)
Roaming aggressiveness
Too many handoffs?
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37. Thank you!
Questions ?
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38. Backup slides
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39. Handoff behavior Total number of handoffs Total number of handoffs
Number of handoffs per hour
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