Wi-Fi / WLAN
Performance Management
and Optimization
Veli-Pekka Ketonen
CTO, 7signal Solutions
Copyright © 2014 7signal Solutions, Inc.
Topics
1.
2.
3.
4.
5.
6.
2
The Wi-Fi Performance Challenge
Factors Impacting Performance
The Wi-Fi Performance Cycle
10 step performance optimization flow
Selected example data
Summary / Questions
Copyright © 2014 7signal Solutions, Inc.
Wi-Fi Networks are Everywhere!
But they are transitioning from “nice to have” to “must have”
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Copyright © 2014 7signal Solutions, Inc.
Wi-Fi Networks are Everywhere!
But they are transitioning from “nice to have” to “must have”
Challenges with Mission Critical Wi-Fi Networks:
 Connection issues with new devices & machines
 Bottlenecks from increasing data traffic
 Dropped or noisy voice calls
 Challenging physical environments
 Changes hourly, daily and weekly
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Dependable Wi-Fi is Costly and Complex
$
Cost Needed to
Achieve Reliability
BYOD
Video Apps
Virtual Desktop
Location Svcs
Mobile Computing
Guest Networks
Voice over Wi-Fi
Reactive focus
based on complaints
Complexity of Network
Number of access points, clients, applications
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2. Factors impacting the performance
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Improper Antenna Selection / Placement
Antenna gain pattern
Antenna gain direction
Behind metal grid?
Near to conductive or “dense”
surface?
In common ceiling mounted
APs, sideways down tilted
patterns is most useful
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Max gain
sideways
Down tilted
pattern
Attenuation
upwards
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RF power level is not that simple
 RF power isn’t always what your
datasheet and settings tell you
 Impact of:
–
–
–
–
–
–
–
–
AP/device model
Rate/MCS
HT 20/40/80
Assumed MIMO gain
Assumed diversity/STBC gain
Antenna gain
Channel #, regulation
Passing the Type Approval
– Back annotation reliability
 Lower output power and use
antenna gain to reach further with
higher rates
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+20 dBm
MIMO/TX div. gain, +3 dB
+17 dBm
No high MCS/rates, + 3dB
+14 dBm
HT40 - > HT 20, +2 dB
+11 dBm
Antenna gain, +3 dB
+8 dBm
Radio output (no antenna),
HT40, highest MCS
180Mbit/s
300
Mbit/s
300
Mbit/s
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WLAN Transmit Power Control (TPC)
can create issues
Common implementation
measures neighbor APs levels
and keep them below a fixed
value
Power levels may drift to end of
the allowed range
Clients commonly use +10 - +15
dBm power, running APs much
lower levels causes imbalance to
link budget. Both uplink and
downlink coverage are needed!
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High received neighbor
AP level may drive AP
Room
power down
Room
Room
Room
Room
Room
..and cause lack of
Room
coverage here
Room
Room
Room
Room
Room
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Channel & Utilization Issues
Channel overlap
APs outside channel grid
HT conflicts
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Amount of APs/SSIDs
Empty AP vs.. loaded AP
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Allocate channels properly
 Use all spectrum you have
 The most important way to
increase capacity -- avoid
interference and lower
utilization!
 Some devices do not support
all 5 GHz channels, but…try
really hard to use all available
channels
 Channel automation
parameters may help to make
it converge towards a better
channel plan
 If not, use manual channel
plan
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1
1
1
6
1
1
11 1
6
1
1
6
Without a very good
reason this should not
ever happen
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Sometimes channel automation
is not working well and needs help
Continuous
channel
switching
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More stable
operation
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Too high rates cause high retries
WLAN AP rate control often
uses rates that are too high
This causes high amount of
retries, which have negative
impact on performance
*Lakshmanan et. al. On link rate adaptation in 802.11n WLANs
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Optimal rate
* Haratcherev et.al. : Automatic IEEE 802.11 Rate Control for Streaming Applications
Copyright © 2014 7signal Solutions, Inc.
What can rates and retries tell you?
Typical in
WLAN 
Retries =
HIGH
Data rates/MCS = HIGH
Target 
Unstable, high
jitter, packet
loss, limited
capacity
Good coverage,
reliable operation,
high speed and
capacity
Very slow, at the
coverage
boundary
Speed limited,
working ok
Retries =
LOW
Data rates/MCS = LOW
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Non Wi-Fi Interference
Bluetooth
Microwave
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Video cameras
Medical devices
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Legacy mode drives speed down
The largest impact from is 802.11b protection
When an AP detects an associated 802.11b client, AP
turns on protection mode (in beacons and probe
responses). AP may turn this on also when it detects
another AP using protection mode.
When protection mode is on, all clients need to start
using either RTS/CTS or CTS-to-Shelf protection to
avoid collisions
This introduces a significant overhead that usually
limits throughputs and capacity remarkably
If –b support is off, it’s useful to try to remove devices
completely. Otherwise they keep probing with –b rates
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TCP does not like lost packets or delay
TCP uses a mechanism called slow start
If a packet
loss occurs, TCP assumes that it is due to
network congestion and takes steps to rapidly reduce the
offered load to the network
With slow start, TCP starts increasing rate again when
consecutive acknowledgements are received properly
Slow-start may perform poorly with wireless networks
that are losing packets
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Retries at different layers using TCP
User data
User
Application
(Layer 5-7)
User may lose patience in 4-10s
varies
Desktop virtualization (used sometime to help with layer 1-4 problems)
TCP
(Layer 4)
WLAN
(Layer 1-2)
Not ACK’d within 2x RTT?
-> Resend w/ SLOW START
Not ACK’d?
-> Resend, 7-25 times
= A data packet, illustration purposes only
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Retries at different layers using UDP
User
VoIP call, etc.
Application
(Layer 5-7)
UDP does not retransmit,
permanently lost packet
UDP
(Layer 4)
WLAN
(Layer 1-2)
Not ACK’d?
-> Resend, 7-25 times
 Jitter
 Packet loss
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= A data packet, illustration purposes only
Copyright © 2014 7signal Solutions, Inc.
Layer 2 packet fragmentation makes
radio more robust
#1, 1500 B
#2, 1500 B
If all goes well, good efficiency
ACK
#1, 1500 B
ACK
#1, Retry 1, 1500 B
No ACK
(lost or any error)
#1, 750 B
#2, 750 B
ACK
#3, 750 B
ACK
#4, 750 B
ACK
If error is detected, content of
the whole 1500B packet is lost
and needs to be retransmitted
Probability of errors in
smaller packet is lower and
transmitting it has taken less
time in the first place
 Fragmenting packets increases robustness , but increases overhead
 Aggregating (e.g. Block ACK), reduces robustness, but increases efficiency
 Fragmentation threshold default value usually 2346B (>1500B, no fragmenting)
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Higher QoS helps prioritize data
Voice (VO), Video (VI), Best Effort (BE) and Background (BK)
classes
* Source: IEEE 802.11-08/1214-02-00aa 802.11 QoS Tutorial
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3. The Wi-Fi Performance Cycle
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Answering the Wi-Fi Challenge
Problem
 Wait for complaints
 Proactive measurements
 Limited view of network
 Check end-to-end performance
 Little historical data
 Analyze historical trends
 Guess at service levels
 Use metrics based reporting
 Remote issues costly to
 Centralize diagnosis of
resolve
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Solution
problems
Copyright © 2014 7signal Solutions, Inc.
Bending the Cost Curve
$
Cost Needed to
Achieve Reliability
BYOD
Video Apps
Virtual Desktop
Location Svcs
Mobile Computing
Guest Networks
Voice over Wi-Fi
Reactive focus
based on complaints
Proactive focus
based on continuous
measurements
Complexity of Network
Number of access points, clients, applications
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Copyright © 2014 7signal Solutions, Inc.
Performance Management with a
Systematic Approach
Simulate Client Traffic
(Active Tests)
Sensor
Mgmt
Station
Access
Point(s)
Listen to AP / Client Traffic
(Passive Tests)
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The Eye’s Capabilities
Synthetic Tests
Traffic Analysis
RF Analysis
Spectrum Analysis
Full Packet Capture
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• End-to-end view at the application layer
• Data and voice quality measurements (throughput, packet loss, latency, jitter)
• Radio frame header analysis for traffic flow between clients and APs.
• KPIs for each client, SSID, AP, band and antenna beam
• AP settings, capabilities, signal levels, channels and noise levels
• KPIs for each AP, channel and antenna beam
• High resolution (280kHz) for ISM band
• Interference source analysis with compass directional data on beams
• Capture remotely
• Easy export to Wireshark or other tool
Copyright © 2014 7signal Solutions, Inc.
The Wi-Fi Performance Cycle
If you can’t measure it, you can’t
manage it!
Measure
- Peter Drucker
Assure
Verify
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Analyze
Optimize
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4. Optimization flow,
10 step process
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The most important KPIs
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Connection Success
Throughput
Packet Loss
Latency
Jitter
Voice quality (MOS)
Layer 2 / Layer 1 metrics(passive tests)
Data rates
Channels
Retry rates
Signal level
Utilization
Spectrum data
Traffic volume
Optimize
Assess
End user metrics (active tests)
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Optimization flow at a glance
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1. Preparations and baseline
•Ensure that APs and antennas are positioned correctly
•Collect baseline data for a few days, check WLAN SW release, upgrade
2. Channel plan
•Maximize available spectrum, organize channels for max capacity potential
•Use manual channel plan in dense areas
3. Minimize utilization
•Minimize utilization due to unnecessary 802.11 traffic
•# of SSIDs, standards, beaconing, probing, data rates, protection, etc.
4. Adjust power levels
•Adjust AP power levels & TPC settings for improved SNR at both ends
5. Reduce non-WLAN interference
•Remove non-WLAN interference, as much as possible
•There is always interference, understand whether it has significant impact
6. Improve radio robustness
•Make radio more robust towards remaining interference/noise
•Increased power, dropping max MCS, fragmentation, directional antennas
7. Prioritize and balance traffic
•QoS categories, AP power levels, load balancing, SSID strategy, roaming
8. LAN/WAN capabilities
•Ensure sufficient LAN/WAN capacity and performance are present
9. Improve client operation
•Drivers, location, models, settings
10. Physical network changes
•If performance is not sufficient, consider HW changes
•Directional antennas, add/move APs, replace equipment, end user devices
Copyright © 2014 7signal Solutions, Inc.
#1. Understand the baseline
Collect and review all radio parameter settings
Verify AP type, antenna performance and placement
Collect baseline performance data for 3-5 days
– Understand peaks and valleys in performance
– Nighttime data is extremely useful - If empty network can’t
provide good throughput, it won’t do that under load either!
Analyze and find likely bottlenecks
Draft a plan for optimization steps
– Make small changes and verify each step
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#2. Plan the channels carefully
Understand # of AP/channel in the whole area
Use maximum amount of radio spectrum & channels
Align all APs to a common channel grid (1, 6, 11, etc)
Fix HT bonding side, HT40+ or HT40Do not overlap bonded with main channel
If automation does not provide a balanced plan,
assign channels manually
Rotate channels evenly within floor
Rotate with offset between floors
Remove out of grid devices is possible
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#3. Minimize utilization
Reduce number of SSIDs/AP to max. 3-4
– Note: Every SSID sends an own beacon, days and nights
– Its common that networks run high utilization w/o clients!
Remove 802.11b rates (1, 2, 5.5, 11) and their support
Remove low MCS and SS multiples
Increase beacon interval from 100ms to 300ms
– Note: Some devices do not allow this. E.g. Vocera badges,
older VoIP phones and in general older equipment
Increase CCA threshold
Remove printers and other devices that keep air busy
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#4. Adjust power levels
Define a limited range for TPC algorithms instead of
default
Observe power level changes also from metrics. Do
they correlate with settings?
Assign 3-5 dB higher power range for 5 vs. 2.4 GHz
Use manual power levels if TPC noes not yield good
results
If possible, do not exceed the power level that still
supports all data rates/MCSs. Consider
compensating with higher gain antennas if needed
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#5. Reduce non-Wi-Fi interference
Interference is present, always! Understand level of impact
– How are end user metrics impacted?
– Correlate spectrum data with metrics
Analyze spectrum, where does the noise come from?
Bluetooth is the most common non-WLAN source
– Keyboard, mouse, headset, handheld readers
– Many other potential sources especially at 2.4 GHz band
Remove sources when possible
Observe impact to throughput and other end user metrics
when changes are made
If changes are helping, it’s visible in active data
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#6. Improve WLAN robustness
Remove highest rates/MCS (most sensitive)
Run voice SSIDs only -g/-a mode without –n
Use radio packet fragmentation
Enable interference resistant mode if supported
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#7. Prioritize and balance traffic
Separate SSIDs (but keep quantity to minimum)
Assign QoS classes with WMM (Wireless
Multimedia Extensions)
Adjust relative AP power levels to move clients
Consider use of load balancing, band steering/select
and admission control features
Different features offered depending on vendor
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#8. Ensure sufficient LAN/WAN capacity
Observe utilization at the switch/router interfaces
Observe packet loss metrics
Internet connection speed may be a bottleneck at
remote sites
Routing data packets always to controller may
impact performance
Understand what is sufficient throughput for end
user and dimension connections accordingly
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#9. Improve client operation
Review all client devices and understand where are
their antennas
Ensure that antennas are not hidden within metal
enclosures and have space to operate properly
Upgrade WLAN drivers
Turn roaming aggressiveness to medium or low
Adjust client power level
CTS-to-Self may be more efficient than RTS/CTS
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#10. Physical changes to network
Move APs
Add APs
Upgrade APs
Use good quality and right type of external antennas
Every network can be
made perform well!
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5. Examples
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Akron Children’s Medical Center
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Uplink throughput
Average improved
from ~11 to ~14
Mbit/s (27%)
The worst APs
improved from ~4 to
~13 Mbit/s. (225%)
Antenna
change ready
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Channel
change
Power level
change
Codec
changes
Core LAN
upgrade
Copyright © 2014 7signal Solutions, Inc.
Downlink Throughput
Average improved
from 13 to 17 Mbit/s
(30%)
The worst APs
improved from 7 to
15 Mbit/s. (110%)
Antenna
change ready
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Channel
change
Power level
change
Codec
changes
Core LAN
upgrade
Copyright © 2014 7signal Solutions, Inc.
Packet loss
From ~2.5% to
~0.5%
Antenna
change ready
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Channel
change
Power level
change
Codec
changes
Core LAN
upgrade
Copyright © 2014 7signal Solutions, Inc.
University, Iowa
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Downlink throughput (daily)
Downlink
throughput daily
averages have
improved 50%
1st
2nd
1st) Disabling power saving
2nd) Disabling b-data rates , area 1
3rd) Disabling b-data rates in other locations
4th) New channel plan areas 1 &2
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3rd
4th
5th
6th
7th
5th) New TxPwr settings in XXX and channel plan in YYY
6th) Beacon interval change
7th( Channel re-plan area 3 2.4GHz
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Downlink throughput (hour)
Minimum values
increase up to
~10x
1st
2nd
1st) Disabling power saving
2nd) Disabling b-data rates , area 1
3rd) Disabling b-data rates in other locations
4th) New channel plan areas 1 &2
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3rd
4th
5th
6th
7th
5th) New TxPwr settings in XXX and channel plan in YYY
6th) Beacon interval change
7th( Channel re-plan area 3 2.4GHz
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Avans University of Applied Sciences
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TCP downlink throughput
1
2
3
4
5
900% improvement in 1st
floor
100% improvement in
ground floor
HT40
More channels
AP power levels
Beacon 300ms
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HTTP downlink throughput
1
2
3
4
5
90%/50%
improvements
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Voice Quality (MOS), downlink, hourly
1
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2
3
4
5
+0.25MOS in ground
+0.25MOS in 1st floor
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Network latency (RTT)
1
2
3
4
5
50% improvement in
1st floor
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Performance Dashboard
Before
Analysis and
Optimization
After
Analysis and
optimization
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6. Summary
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Summary
Wi-Fi is very sensitive to the surroundings and
network parameters, even though it somehow works
almost no matter where you put it
Performance can often be improved significantly
by adjusting the network parameters
Need relevant continuous data to validate changes
Need knowledge of WLAN/RF to decide the actions
Optimization requires a pragmatic approach
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Thank You!
Email:
veli-pekka.ketonen@7signal.com
Presentation:
http://go.7signal.com/surfwlpc
www.7signal.com
@7signal
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