Management and Optimization VeliPekka Ketonen CTO 7signal Solutions T opics The WiFi Performance Challenge Factors Impacting Performance The WiFi Performance Cycle 10 step performance optimization flow ID: 634760
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Slide1
Wi-Fi / WLANPerformance Management and Optimization
Veli-Pekka KetonenCTO, 7signal SolutionsSlide2
Topics
The Wi-Fi Performance ChallengeFactors Impacting PerformanceThe Wi-Fi Performance Cycle10 step performance optimization flow
Selected example data
Summary / Questions2Slide3
Wi-Fi Networks are Everywhere!But they are transitioning from “nice to have” to “must have”
3Slide4
Wi-Fi Networks are Everywhere!But they are transitioning from “nice to have” to “must have”
4
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 weeklySlide5
Dependable Wi-Fi is Costly and Complex
5
Complexity of Network
Number of access
points, clients
, applications
Cost Needed to Achieve Reliability
Voice over Wi-Fi
BYOD
Guest Networks
Mobile Computing
$
Reactive focus
based on complaints
Virtual Desktop
Video Apps
Location SvcsSlide6
2. Factors impacting the performance
6Slide7
Improper Antenna Selection / Placement
Antenna gain patternAntenna gain directionBehind metal grid?Near to conductive or “dense” surface?In common ceiling mounted APs, sideways down tilted patterns is most useful
7
Down tilted pattern
Attenuation upwards
Max gain sidewaysSlide8
180Mbit/s
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 gainAntenna gainChannel #, regulation
Passing the Type ApprovalBack annotation reliabilityLower output power and use antenna gain to reach further with higher rates
8
Radio output (no antenna), HT40, highest MCS
Antenna gain, +3 dB
HT40 - > HT 20, +2 dB
No high MCS/rates, + 3dB
MIMO/TX div. gain, +3 dB
+17 dBm
+14 dBm
+11 dBm
+8 dBm
+20 dBm
300
Mbit/s
300
Mbit/sSlide9
WLAN Transmit Power Control (TPC)
can create issuesCommon 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!
9
Room
Room
Room
Room
Room
R
oom
Room
Room
Room
Room
R
oom
R
oom
High received neighbor AP level may drive AP power down
..and cause lack of coverage hereSlide10
Channel & Utilization Issues
Channel overlapAPs outside channel gridHT conflicts10
Amount of APs/SSIDs
Empty AP vs.. loaded APSlide11
Allocate channels properly
Use all spectrum you haveThe 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 channelsChannel automation parameters may help to make it converge towards a better channel plan
If not, use manual channel plan
11
1
1
1
1
1
6
Without a very good reason this should not ever happen
6
1
6
11
1
1Slide12
Sometimes channel automation is not working well and needs help
12
Continuous channel switching
More stable operationSlide13
Too high rates cause high retries
WLAN AP rate control often uses rates that are too highThis causes high amount of retries, which have negative impact on performance13
* Haratcherev et.al. : Automatic
IEEE 802.11 Rate Control for Streaming Applications
*Lakshmanan et. al. On
link rate adaptation in 802.11n WLANs
Optimal rateSlide14
What can rates and retries tell you?
14
Retries
=
HIGH
Data rates/MCS = HIGH
Retries
=LOW
Data rates/MCS
=
LOW
Good coverage, reliable operation, high speed and capacity
Unstable, high jitter, packet loss, limited capacity
Speed limited, working ok
Very slow, at the coverage boundary
Typical in WLAN
Target
Slide15
Non Wi-Fi Interference15
Bluetooth
Microwave
Video cameras
Medical devicesSlide16
Legacy mode drives speed downThe 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 rates16Slide17
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
17Slide18
Retries at different layers using TCP
18User
Application
(Layer 5-7)
TCP
(Layer 4)
WLAN
(Layer 1-2)
Not ACK’d within 2x RTT?
-> Resend w/ SLOW START
Not ACK’d?
-> Resend, 7-25 times
User may lose patience in 4-10s
varies
Desktop virtualization (used sometime to help with layer 1-4 problems)
User data
= A data packet, illustration purposes onlySlide19
Retries at different layers using UDP
19User
Application
(Layer 5-7)
UDP
(Layer 4)
WLAN
(Layer 1-2)
UDP does not retransmit,
p
ermanently lost packet
VoIP call, etc.
Jitter
Packet loss
Not ACK’d?
-> Resend, 7-25 times
= A data packet, illustration purposes onlySlide20
Layer 2 packet fragmentation makes radio more robust
Fragmenting packets increases robustness , but increases overheadAggregating (e.g. Block ACK), reduces robustness, but increases efficiency
Fragmentation threshold default value usually 2346B (>1500B, no fragmenting)
20
#1
, 1500 B
#2, 1500 B
ACK
ACK
#1
, 750 B
ACK
#2
, 750 B
ACK
#3
, 750 B
#4
, 750 B
ACK
#1
, 1500 B
#1, Retry 1
, 1500 B
No ACK
(lost or any error)
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
If all goes well, good efficiencySlide21
Higher QoS helps prioritize data
Voice (VO), Video (VI), Best Effort (BE) and Background (BK) classes21
*
Source:
IEEE
802.11-08/1214-02-00aa 802.11 QoS TutorialSlide22
3. The Wi-Fi Performance Cycle
22Slide23
Answering the Wi-Fi Challenge23
Wait for complaints
Limited view of network
Little historical data
Guess at service levels
Remote issues costly to resolve
Problem
Solution
Proactive
measurements
Check end-to-end
performance
Analyze historical trends
Use metrics based reporting
Centralize diagnosis of
problemsSlide24
Bending the Cost Curve
24
Complexity of Network
Number of access points, clients, applications
Cost Needed to Achieve Reliability
Voice over Wi-Fi
BYOD
Guest Networks
Mobile Computing
$
Reactive focus
based on complaints
Virtual Desktop
Video Apps
Location Svcs
Proactive focus
based on continuous
measurementsSlide25
Performance Management with a Systematic Approach
25
Listen to AP / Client Traffic
(Passive Tests)
Simulate Client Traffic
(Active Tests)
Access
Point(s)
Sensor
Mgmt StationSlide26
The Eye’s Capabilities26Slide27
The Wi-Fi Performance Cycle27
If you can’t measure it, you can’t manage it!
- Peter DruckerSlide28
4. Optimization flow, 10 step process
28Slide29
The most important KPIs
Connection SuccessThroughputPacket Loss29
Data rates
Retry rates
Utilization
Traffic volume
Channels
Signal level
Spectrum data
Latency
Jitter
Voice quality (MOS)
End user metrics (active tests)
Layer 2 / Layer 1 metrics(passive tests)
Assess
OptimizeSlide30
Optimization flow at a glance
30Slide31
#1. Understand the baseline
Collect and review all radio parameter settingsVerify 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 stepsMake small changes and verify each step
31Slide32
#2. Plan the channels carefully
Understand # of AP/channel in the whole areaUse maximum amount of radio spectrum & channelsAlign 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 floorRotate with offset between floorsRemove out of grid devices is possible
32Slide33
#3. Minimize utilization
Reduce number of SSIDs/AP to max. 3-4Note: Every SSID sends an own beacon, days and nightsIts common that networks run high utilization w/o clients! Remove 802.11b rates (1, 2, 5.5, 11) and their supportRemove low MCS and SS multiplesIncrease 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 thresholdRemove printers and other devices that keep air busy
33Slide34
#4. Adjust power levels
Define a limited range for TPC algorithms instead of defaultObserve power level changes also from metrics. Do they correlate with settings?Assign 3-5 dB higher power range for 5 vs. 2.4 GHzUse manual power levels if TPC noes not yield good resultsIf possible, do not exceed the power level that still supports all data rates/MCSs. Consider compensating with higher gain antennas if needed
34Slide35
#5. Reduce non-Wi-Fi interference
Interference is present, always! Understand level of impactHow are end user metrics impacted?Correlate spectrum data with metricsAnalyze 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 possibleObserve impact to throughput and other end user metrics when changes are madeIf changes are helping, it’s visible in active data
35Slide36
#6. Improve WLAN robustnessRemove highest rates/MCS (most sensitive)
Run voice SSIDs only -g/-a mode without –nUse radio packet fragmentationEnable interference resistant mode if supported36Slide37
#7. Prioritize and balance trafficSeparate 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 featuresDifferent features offered depending on vendor
37Slide38
#8. Ensure sufficient LAN/WAN capacity
Observe utilization at the switch/router interfacesObserve packet loss metricsInternet connection speed may be a bottleneck at remote sitesRouting data packets always to controller may impact performanceUnderstand what is sufficient throughput for end user and dimension connections accordingly
38Slide39
#9. Improve client operationReview all client devices and understand where are their antennas
Ensure that antennas are not hidden within metal enclosures and have space to operate properlyUpgrade WLAN driversTurn roaming aggressiveness to medium or lowAdjust client power levelCTS-to-Self may be more efficient than RTS/CTS
39Slide40
#10. Physical changes to network
Move APsAdd APsUpgrade APsUse good quality and right type of external antennas
40
Every network can be
made perform well!Slide41
5. Examples
41Slide42
Akron Children’s Medical Center
42Slide43
Uplink throughput
Antenna change ready
Channel change
Core LAN upgrade
Power level change
Codec changes
Average improved from
~
11 to
~
14 Mbit/s (27%)
The worst APs improved from
~
4 to
~
13 Mbit/s. (225%)
43Slide44
Downlink Throughput
44
Antenna change ready
Channel change
Core LAN upgrade
Power level change
Codec changes
The worst APs improved from 7 to 15 Mbit/s. (110%)
Average improved from 13 to 17 Mbit/s (30%)Slide45
Packet loss
Antenna change ready
Channel change
Core LAN upgrade
Power level change
Codec changes
From
~
2.5% to
~
0.5%
45Slide46
University, Iowa
46Slide47
1st
2nd
3rd
4th
5
th
6th
7
th
Downlink throughput (daily)
Downlink throughput daily averages have improved 50%
1
st
) Disabling
power
saving
2
nd
) Disabling
b-data
rates , area 1
3
rd
) Disabling b-data rates in
other locations
4
th
)
New channel plan
areas 1 &2
5
th
)
New
TxPwr
settings in
XXX and
channel plan in
YYY
6
th
) Beacon interval
change
7
th
( Channel re-plan area 3 2.4GHz
47Slide48
1st
2nd
3rd
4th
5
th
6th
7
th
Downlink throughput (hour)
Minimum values increase up to ~10x
1
st
) Disabling
power
saving
2
nd
) Disabling
b-data
rates , area 1
3
rd
) Disabling b-data rates in
other locations
4
th
)
New channel plan
areas 1 &2
5
th
)
New
TxPwr
settings in
XXX
and channel plan in
YYY
6
th
) Beacon interval
change
7
th
( Channel re-plan area 3 2.4GHz
48Slide49
Avans University of Applied Sciences
49Slide50
TCP downlink throughput
1
2
3
4
5
1
2
3
4
900%
improvement in 1
st
floor
100%
improvement in
ground floor
AP power levels
More channels
Beacon 300ms
HT40
50Slide51
HTTP downlink throughput
1
2
3
4
5
90%/50% improvements
51Slide52
Voice Quality (MOS), downlink, hourly
1
2
3
4
5
+0.25MOS in ground
+0.25MOS in 1
st
floor
52Slide53
Network latency (RTT)
1
2
3
4
5
50% improvement in 1
st
floor
53Slide54
Performance Dashboard54
Before
Analysis and
Optimization
After Analysis and optimizationSlide55
6. Summary
55Slide56
Summary
Wi-Fi is very sensitive to the surroundings and network parameters, even though it somehow works almost no matter where you put itPerformance can often be improved significantly by adjusting the network parametersNeed relevant continuous data to validate changes
Need knowledge of WLAN/RF
to decide the actionsOptimization requires a pragmatic approach
56Slide57
Thank You!
57
www.7signal.com
@7signal
Email: veli-pekka.ketonen@7signal.com
Presentation:
http://go.7signal.com/surfwlpc