Transcript IEEE 802.11 in the Large: Observations at the IETF Meeting Sangho Shin

IEEE 802.11 in the Large:
Observations at the IETF Meeting
Henning Schulzrinne, Andrea G. Forte,
Sangho Shin
Department of Computer Science
Columbia University
Introduction

65th IETF meeting
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Data collection
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
Dallas, TX March 19th ~ 24th
Hilton Anatole hotel
1200 attendee
21st ~ 23rd for three days
25GB data, 80 millions frames
Goals

Identify unusual behaviors due to the highly
congested environment
Aug 5th 2006
2
Overview
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

Introduction
Related work
Wireless network setup
Measurement setup
User behavior
Load balancing
Handoff behavior
Overhead of multiple APs on a channel
Conclusion
Aug 5th 2006
3
Related Work
Target
Attendee
Clients detected
WLAN
Channels
Number of APs
Focused on
Jardosh et al.
Rodrig et al.
Balachandran et al.
62nd IETF (’05)
SIGCOMM ’04
SIGCOMM ’01
1100
500*
550
200
377
195
802.11b
802.11b
802.11b
1, 6, 11
(dynamic)
1, 8, 11
1, 4, 7, 11
38
5
4
Their new metric for
channel congestion,
‘Link reliability’
Overhead of
802.11, 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 they detected from their measurement.
Aug 5th 2006
4
Wireless network in IETF meeting
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Many hotel 802.11b APs on
channel 6
91 additional APs in
802.11a/b by IETF
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Hotel APs
802.11b channel 6
IETF APs
802.11a/b
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

ESSID : ietf65
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Aug 5th 2006
Cisco Aironet 1200 AP
Channel 1 and 11 in 802.11b
One subnet with one ESSID
‘ietf65’
The largest wireless network
measured so far
No wireless security
5
Measurement setup
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Four sniffers
IBM T42 Think Pad
Proxim ORiNOCO 11 a/b/g
Sniffer software: Airopeek NX
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Channel assignment
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Three sniffers on channel 1, 6 and 11,
respectively
Fourth sniffer on all 8 channels in 802.11a
Aug 5th 2006
6
Measurement setup
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Measurement place
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Room Chantilly
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The biggest room - 142’ x 80’, 600 persons
Two biggest IETF sessions, and the plenary
session in the evening
Session 1 (AM)
9:00
Lunch
Session 1 (PM)
11:30 13:00

Session 2
& break
15:00
17:00
Plenary
19:30
Six IETF APs + Six Hotel APs in the room
Aug 5th 2006
7
The positions of the APs in the
room
AP7
AP8
Room Chantilly
AP6
AP on channel 1
AP on channel 11
AP on channel 11
(estimated position)
AP4
AP2
Another seating area
during plenary
142 feet
AP5
sniffers
screen
Seating area during IETF
sessions and plenary
AP3
AP1
Gate
Aug 5th 2006
Lobby
80 feet
AP9
8
Overview
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
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
Introduction
Related work
Wireless network setup
Measurement setup
User behavior
Load balancing
Handoff behavior
Overhead of multiple APs on a channel
Conclusion
Aug 5th 2006
9
User behavior

Overall traffic in 802.11b
Aug 5th 2006
10
User behavior
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Number of clients
350
300
Number of clients
250
200
Ch 1
Ch 6
Ch 11
802.11a
(all 8 channels)
150
100
50
0
Session 1 (AM)
Aug 5th 2006
Lunch
Session 1 (PM)
IETF Sessions
Plenary
11
User behavior
Protocols

Protocols
HTTP
UDP
ESP
TCP
NB-NAME
BITTORR
SSH
DNS
IMAP
ARP
GRE
SNAP
ICMP
SMB
POP3
DHCP
0
5
10
15
20
25
%
Aug 5th 2006
12
Overview
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
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
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


Introduction
Related work
Wireless network setup
Measurement setup
User behavior
Load balancing
Handoff behavior
Overhead of multiple APs on a channel
Conclusion
Aug 5th 2006
13
Load balancing
Distribution of clients
No load balancing
feature was used
AP2
Client distribution is
decided by the
relative proximity from
the APs.
Ch 6 (ceiling) > Ch
1 > Ch 11
AP6
350

300
250

Number of clients

200
AP4
Another seating area
during plenary
Ch 1
Ch 6
Ch 11
802.11a
150
AP5
100

sniffers
50
0
Session 1 (AM)
Lunch
Session 1 (PM)
Seating areaIETF
during
Sessions IETF
sessions and plenary
Plenary
AP3
AP1
Aug 5th 2006
14
Load balancing
Distribution of clients
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
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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
Aug 5th 2006
160
140
120
Number of clients

100
80
AP1
AP2
AP3
60
40
20
0
Session 1 (AM)
Lunch
Session 1 (PM)
IETF Sessions
Plenary
Number of clients in channel 1
15
Load balancing

Throughput
30
9
8
25
20
Ch 1
Ch 6
Ch 11
802.11a
15
10
Throughput (KB/s)
Throughput (KB/s)
7
6
5
AP1
AP2
AP3
4
3
2
5
1
0
0
Session 1 (AM)
Lunch
Session 1 (PM)
IETF Sessions
Plenary
Average throughput in 802.11a/b
Aug 5th 2006
Session 1 (AM)
Lunch
Session2 (PM)
IETF sessions
Plenary
Average throughput in channel 1
16
Load balancing
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Throughput per client
300
160
140
250
200
100
Ch 1
Ch 6
Ch 11
802.11a
80
60
Throughput (B/s)
Throughput (B/s )
120
150
AP1
AP2
AP3
100
40
50
20
0
0
Session 1 (AM)
Lunch
Session 1 (PM)
IETF Sessions
Plenary
Average throughput per client
in 802.11a/b
Aug 5th 2006
Session 1 (AM)
Lunch
Session2 (PM)
IETF sessions
Plenary
Average throughput per client
in channel 1
17
Load balancing
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How?
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Study of Balanchandran et al.
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Number of clients? – Simple, but not accurate
Throughput ? - Accurate, but too complex
[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
Aug 5th 2006
18
Load balancing
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Number of clients vs. throughput in Ch. 6
Capacity in the channel
Aug 5th 2006
19
Load balancing
Number of clients vs. Throughput
50000
Number of frames
Throughput
45000
40000

160
140
35000
Number of Frames
180
120
30000
100
25000
80
20000
60
15000
40
10000
20
5000
Capacity in the channel
0
30
40
50
60
70
80
90
0
100
Throughput (KB/s)
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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
Number of clients
Aug 5th 2006
20
Effect of screen
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160
140
Number of clients
120
Small number of
clients on AP3
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Effect of a screen?
100
80
AP1
AP2
AP3
60
40
20
0
Session 1 (AM)
Lunch
Session 1 (PM)
IETF Sessions
Plenary
Number of clients in channel 1
Aug 5th 2006
21
Effect of screen
An experiment
45%
With screen
W/O screen
40%
35%
Retry rate
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30%
25%
20%
15%
30 ~ 100 feet
10%
30
40
50
60
70
80
90
100
Distance from the AP
Aug 5th 2006
22
Overview


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




Introduction
Related work
Wireless network setup
Measurement setup
User behavior
Load balancing
Handoff behavior
Overhead of multiple APs on a channel
Conclusion
Aug 5th 2006
23
Handoff behavior
Handoff is triggered
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generally, by low
signal strength
in congested channel,
by frame loss
Effect of layer 2
handoff
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Increase of traffic
Disruption of
network (0.5 ~ 1.5
sec)
Aug 5th 2006
700
600
84
162
500
Number of handoffs

131
222
400
227
C11
C6
183
300
C1
36
200
306
112
262
218
100
111
0
S1
Lunch
S1
IETF Sessions
P
The number of handoff per hour
in each IETF session
24
Handoff behavior
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Handoffs between channels
11→11
17%
11→6
2%

1→1
22%
11→1
3%
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6→11
2%
Handoff to the same
channels : 72%
Handoff to the same
AP : 55%
1→6
9%
1→11
3%
6→6
33%
Aug 5th 2006
6→1
9%
25
Handoff behavior
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Distribution of session
time : time between
handoffs
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Too often handoff
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>= 10 min
32%
< 10 min
12%
Aug 5th 2006
< 1 min
23%
< 5 min
33%
Disruption of network
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0.5 ~1.5 sec per handoff
Increase of traffic due
to handoff related
frames – probe request
and response
10.4% of total
26
Handoff behavior
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Handoffs per vendor
Agere
6%
Others
18%
Others
7%
Nokia
4%
Intel
40%
Agere
7%
Ambit
8%
Lucent
3%
Nokia
7%
Ambit
6%
Lucent Cisco
2%
3%
Intel
57%
Cisco
11%
Apple
17%
Distribution of vendors
Apple
4%
Distribution of handoffs per vendor
(based on the number of handoffs during the whole day)
Aug 5th 2006
27
Handoff behavior
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Handoffs per vendor (session time)
1 ≤ session time < 5 min
session time < 1 min
90
80
% of such sessions
70
60
50
40
30
20
10
0
Nokia
Agere
Cisco
Intel
Lucent
Ambit
Apple
Apple
Vendors
Aug 5th 2006
28
Overview
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


Introduction
Related work
Wireless network setup
Measurement setup
User behavior
Load balancing
Handoff behavior
Overhead of multiple APs on a channel
Conclusion
Aug 5th 2006
29
Overhead of having multiple APs
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Overhead from replicated multicast and
broadcast frames
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All broadcast and multicast frames are
replicated by all APs  Increase traffic
Router
A channel
Aug 5th 2006
30
Overhead of having multiple APs

Overhead from replicated multicast and
broadcast frames
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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
Aug 5th 2006
31
Overhead of having multiple APs
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Overhead from replicated multicast and
broadcast frames
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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%
Aug 5th 2006
32
Overhead of having multiple APs
30
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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.
Throughput (KB/s)
Co-channel
interference
20
Ch 1
Ch 6
Ch 11
802.11a
15
10
5
0
Session 1 (AM)
Lunch
Session 1 (PM)
IETF Sessions
Plenary
25
20
Retry rate (%)

25
15
Ch 1
Ch 6
Ch 11
10
5
0
Session 1 (AM)
Aug 5th 2006
Lunch
Session 1 (PM)
IETF Sessions
Plenary
33
Conclusions
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Uneven distribution of clients and throughput among
channels and APs
Correlation between the throughput and the number
of clients
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Too many inefficient handoffs
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The number of clients can be used for load balancing with
low complexity in highly congested wireless networks
Disrupt network and increase traffic
Need better handoff algorithms
Having multiple APs on a channel
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Increases the traffic due to replication of multicast and
broadcast frames.
Decrease throughput due to co-channel interference
Aug 5th 2006
34

Aug 5th 2006
Thank you
35
Backup slides
Aug 5th 2006
36
Handoff behavior

Total number of handoffs
1600
700
211
1400
600
323
500
555
1000
800
454
457
600
400
765
162
327
131
222
400
227
524
C11
C6
183
300
C1
36
200
54
168
C11
C6
C1
Number of handoffs
Number of handoffs
1200
84
306
544
112
262
218
200
100
167
111
0
S1
Lunch
S1
IETF Sessions
P
Total number of handoffs
Aug 5th 2006
0
S1
Lunch
S1
IETF Sessions
P
Number of handoffs per hour
37