Wi-Fi / WLAN Performance Management and Optimization

Wi-Fi / WLAN

Performance Management and Optimization

Veli-Pekka Ketonen CTO, 7signal Solutions

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

Wi-Fi Networks are Everywhere!

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

Dependable Wi-Fi is Costly and Complex

Complexity of Network

Number of access points, clients, applications

Cost Needed to

Achieve Reliability _{Voice over Wi-Fi}

BYOD

Guest Networks

Mobile Computing

$ Virtual Desktop _{based on complaints} Reactive focus Video Apps

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

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 300 Mbit/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

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 overlap



APs outside channel grid



HT conflicts



Amount of APs/SSIDs

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

1

1

1

1

1

6

Without a very good reason this should not

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

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

Non Wi-Fi Interference



Bluetooth



Microwave



Video cameras

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

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

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

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.

Not ACK’d?

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

Higher QoS helps prioritize data



Voice (VO), Video (VI), Best Effort (BE) and Background (BK) classes

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

Bending the Cost Curve

Complexity of Network

Number of access points, clients, applications

Cost Needed to

Achieve Reliability _{Voice over Wi-Fi}

BYOD

Guest Networks

Mobile Computing

$ Virtual Desktop _{based on complaints} Reactive focus Video Apps

Location Svcs

Proactive focus based on continuous

Performance Management with a Systematic Approach

Listen to AP / Client Traffic (Passive Tests)

Simulate Client Traffic (Active Tests) Access Point(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

The Wi-Fi Performance Cycle

If you can’t measure it, you can’t manage it! - Peter Drucker Measure Analyze Optimize Verify Assure

4. Optimization flow,

The most important KPIs



Connection Success



Throughput



Packet Loss



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)

Asses

s Op

timi

Optimization flow at a glance

•Ensure that APs and antennas are positioned correctly

•Collect baseline data for a few days, check WLAN SW release, upgrade

1. Preparations and baseline

•Maximize available spectrum, organize channels for max capacity potential •Use manual channel plan in dense areas

2. 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 ends

4. Adjust power levels

•Remove non-WLAN interference, as much as possible

•There is always interference, understand whether it has significant impact

5. Reduce non-WLAN interference

•Make radio more robust towards remaining interference/noise

•Increased power, dropping max MCS, fragmentation, directional antennas

6. Improve radio robustness

•QoS categories, AP power levels, load balancing, SSID strategy, roaming

7. Prioritize and balance traffic

•Ensure sufficient LAN/WAN capacity and performance are present

8. LAN/WAN capabilities

•Drivers, location, models, settings

9. Improve client operation

•If performance is not sufficient, consider HW changes

#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

#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

#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 (RX SOP, or similar term)

#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

#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

#6. Improve WLAN robustness



Remove highest rates/MCS (most sensitive)



Run voice SSIDs only -g/-a mode without –n



Use radio packet fragmentation

#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

#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

#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

#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!

Uplink throughput

Average improved from ~11 to ~14 Mbit/s (27%)

The worst APs

improved from ~4 to

Downlink Throughput 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%)

Packet loss

Antenna Channel Power level Codec Core LAN

From ~2.5% to

1st 2nd 3rd 4th 5th 6th 7th

Downlink throughput (daily)

Downlink

throughput daily averages have improved 50%

1st 2nd 3rd 4th 5th 6th 7th

Downlink throughput (hour)

Minimum values increase up to ~10x

1st_{) Disabling power saving}

2nd_{) Disabling b-data rates , area 1}

3rd_{) Disabling b-data rates in other locations}

5th_{) New TxPwr settings in XXX and channel plan in YYY}

TCP downlink throughput 1 2 3 4 5 1 2 3 4 900% improvement in 1st floor 100% improvement in ground floor AP power levels More channels Beacon 300ms HT40

HTTP downlink throughput

1 2 3 4 5

90%/50% improvements

Voice Quality (MOS), downlink, hourly

1 2 3 4 5 +0.25MOS in ground

Network latency (RTT)

1 2 3 4 5

50% improvement in 1st _floor

Performance Dashboard Before Analysis and Optimization After Analysis and optimization

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

Thank You!

www.7signal.com

Email: [email protected] Presentation: http://go.7signal.com/surfwlpc