Copyright © 2014 7signal Solutions, I Wi-Fi / WLAN Performance Management and Optimization Veli-Pekka Ketonen CTO, 7signal Solutions
Apr 01, 2015
Copyright © 2014 7signal Solutions, Inc.
Wi-Fi / WLANPerformance Management
and Optimization
Veli-Pekka Ketonen
CTO, 7signal Solutions
Copyright © 2014 7signal Solutions, Inc.2
Topics
1. The Wi-Fi Performance Challenge
2. Factors Impacting Performance
3. The Wi-Fi Performance Cycle
4. 10 step performance optimization flow
5. Selected example data
6. Summary / Questions
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Wi-Fi Networks are Everywhere!But they are transitioning from “nice to have” to “must have”
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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
Complexity of NetworkNumber of access points, clients, applications
Cost Needed to Achieve Reliability Voice over Wi-Fi
BYOD
Guest NetworksMobile Computing
$Reactive focus
based on complaintsVirtual DesktopVideo Apps
Location Svcs
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2. Factors impacting the performance
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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
Down tilted pattern
Attenuation upwards
Max gain sideways
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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 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
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
300Mbit/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!
Room
Room
Room
Room
Room
Room
Room
Room
Room
Room
Room
Room
High received neighbor AP level may drive AP power down
..and cause lack of coverage here
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Channel & Utilization Issues
Channel overlapAPs outside channel gridHT conflicts
Amount of APs/SSIDsEmpty AP vs.. loaded AP
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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 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
1
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Without a very good reason this should not ever happen
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1
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11
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Sometimes channel automation is not working well and needs help
Continuous channel
switching
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
* Haratcherev et.al. : Automatic IEEE 802.11 Rate Control for Streaming Applications*Lakshmanan et. al. On link rate adaptation in 802.11n WLANs
Optimal rate
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What can rates and retries tell you?
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
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Non Wi-Fi Interference
BluetoothMicrowave
Video camerasMedical devices
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Legacy mode drives speed down
The largest impact from is 802.11b protectionWhen 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
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 only
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Retries at different layers using UDP
User
Application(Layer 5-7)
UDP(Layer 4)
WLAN(Layer 1-2)
UDP does not retransmit,permanently lost packet
VoIP call, etc.
Þ JitterÞ Packet loss
Not ACK’d?-> Resend, 7-25 times
= A data packet, illustration purposes only
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Layer 2 packet fragmentation makes radio more robust
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)
#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 efficiency
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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
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 problems
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Bending the Cost Curve
Complexity of NetworkNumber of access points, clients, applications
Cost Needed to Achieve Reliability Voice over Wi-Fi
BYOD
Guest NetworksMobile Computing
$Reactive focus
based on complaintsVirtual DesktopVideo Apps
Location Svcs
Proactive focusbased on continuous
measurements
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Performance Management with a Systematic Approach
Listen to AP / Client Traffic(Passive Tests)
Simulate Client Traffic(Active Tests)
AccessPoint(s)
Sensor
Mgmt Station
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The Eye’s Capabilities
Synthetic Tests• End-to-end view at the application layer
• Data and voice quality measurements (throughput, packet loss, latency, jitter)
Traffic Analysis• Radio frame header analysis for traffic flow between clients and APs.
• KPIs for each client, SSID, AP, band and antenna beam
RF Analysis• AP settings, capabilities, signal levels, channels and noise levels
• KPIs for each AP, channel and antenna beam
Spectrum Analysis• High resolution (280kHz) for ISM band
• Interference source analysis with compass directional data on beams
Full Packet Capture• Capture remotely
• Easy export to Wireshark or other tool
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The Wi-Fi Performance Cycle
If you can’t measure it, you can’t manage it!
- Peter DruckerMeasure
Analyze
OptimizeVerify
Assure
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4. Optimization flow, 10 step
process
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The most important KPIs
Connection SuccessThroughputPacket Loss
Data ratesRetry ratesUtilizationTraffic volume
ChannelsSignal levelSpectrum data
LatencyJitterVoice quality (MOS)
End user metrics (active tests)
Layer 2 / Layer 1 metrics(passive tests)Asse
ss Optim
ize
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Optimization flow at a glance•Ensure that APs and antennas are positioned correctly•Collect baseline data for a few days, check WLAN SW release, upgrade1. Preparations and baseline
•Maximize available spectrum, organize channels for max capacity potential•Use manual channel plan in dense areas2. Channel plan
•Minimize utilization due to unnecessary 802.11 traffic•# of SSIDs, standards, beaconing, probing, data rates, protection, etc.3. Minimize utilization
•Adjust AP power levels & TPC settings for improved SNR at both ends4. Adjust power levels
•Remove non-WLAN interference, as much as possible•There is always interference, understand whether it has significant impact5. Reduce non-WLAN interference
•Make radio more robust towards remaining interference/noise•Increased power, dropping max MCS, fragmentation, directional antennas6. Improve radio robustness
•QoS categories, AP power levels, load balancing, SSID strategy, roaming7. Prioritize and balance traffic
•Ensure sufficient LAN/WAN capacity and performance are present8. LAN/WAN capabilities
•Drivers, location, models, settings9. Improve client operation
•If performance is not sufficient, consider HW changes•Directional antennas, add/move APs, replace equipment, end user devices 10. Physical network changes
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#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 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 channelIf 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
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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 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
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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 GHzUse 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 possibleObserve 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 –nUse radio packet fragmentationEnable 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 interfacesObserve packet loss metricsInternet 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 driversTurn roaming aggressiveness to medium or lowAdjust client power levelCTS-to-Self may be more efficient than RTS/CTS
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#10. Physical changes to network
Move APsAdd APsUpgrade APsUse 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
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%)
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Downlink Throughput
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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%)
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Packet loss
Antenna change ready
Channel change
Core LAN upgrade
Power level change
Codec changes
From ~2.5% to ~0.5%
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University, Iowa
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1st 2nd 3rd 4th 5th 6th 7th
Downlink throughput (daily)
Downlink throughput daily averages have improved 50%
1st) Disabling power saving2nd) Disabling b-data rates , area 13rd) Disabling b-data rates in other locations4th) New channel plan areas 1 &2
5th) New TxPwr settings in XXX and channel plan in YYY6th) Beacon interval change7th( Channel re-plan area 3 2.4GHz
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1st 2nd 3rd 4th 5th 6th 7th
Downlink throughput (hour)
Minimum values increase up to ~10x
1st) Disabling power saving2nd) Disabling b-data rates , area 13rd) Disabling b-data rates in other locations4th) New channel plan areas 1 &2
5th) New TxPwr settings in XXX and channel plan in YYY6th) Beacon interval change7th( 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 51 2 3 4 900% improvement in 1st floor
100% improvement in ground floor
AP power levels
More channels
Beacon 300ms
HT40
50
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HTTP downlink throughput
1 2 3 4 590%/50%
improvements
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Voice Quality (MOS), downlink, hourly
1 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 changesNeed knowledge of WLAN/RF to decide the actionsOptimization requires a pragmatic approach
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Thank You!
www.7signal.com
@7signal
Email: [email protected]
Presentation: http://go.7signal.com/surfwlpc