copyright © 2014 7signal solutions, inc. wi-fi / wlan performance management and optimization...

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


Wi-Fi Networks are Everywhere!But they are transitioning from “nice to have” to “must have”


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


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


2. Factors impacting the performance


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


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


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


Channel & Utilization Issues

Channel overlapAPs outside channel gridHT conflicts

Amount of APs/SSIDsEmpty AP vs.. loaded AP


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

1

1

1

1

1

6

Without a very good reason this should not ever happen

6

1

6

11

1

1


Sometimes channel automation is not working well and needs help

Continuous channel

switching

More stable operation


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


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


Non Wi-Fi Interference

BluetoothMicrowave

Video camerasMedical devices


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


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


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


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


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


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


3. The Wi-Fi Performance Cycle


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


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


Performance Management with a Systematic Approach

Listen to AP / Client Traffic(Passive Tests)

Simulate Client Traffic(Active Tests)

AccessPoint(s)

Sensor

Mgmt Station


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


The Wi-Fi Performance Cycle

If you can’t measure it, you can’t manage it!

- Peter DruckerMeasure

Analyze

OptimizeVerify

Assure


4. Optimization flow, 10 step

process


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


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

30


#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


#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


#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


#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


#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


#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


#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


#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


#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


#10. Physical changes to network

Move APsAdd APsUpgrade APsUse good quality and right type of external antennas

Every network can be made perform well!


5. Examples


Akron Children’s Medical Center


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%)

43


Downlink Throughput

44


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%)


Packet loss


Channel change

Core LAN upgrade

Power level change

Codec changes

From ~2.5% to ~0.5%

45


University, Iowa


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

47


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

48


Avans University of Applied Sciences


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


HTTP downlink throughput

1 2 3 4 590%/50%

improvements

51


Voice Quality (MOS), downlink, hourly

1 2 3 4 5 +0.25MOS in ground+0.25MOS in 1st floor

52


Network latency (RTT)

1 2 3 4 5

50% improvement in 1st floor

53


Performance Dashboard

Before Analysis and Optimization

After Analysis and optimization


6. Summary


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


Thank You!

www.7signal.com

@7signal

Email: [email protected]

Presentation: http://go.7signal.com/surfwlpc

http://www.7signal.com/

copyright © 2014 7signal solutions, inc. wi-fi / wlan performance management and optimization...

Documents

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mbits slide

weekly slide

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ap power

high rates

wlan target slide

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