Advanced WLAN Performance Analysis and Optimization · –Passing the Type Approval ......

Copyright © 2014 7signal Solutions, Inc.

Advanced WLAN

Performance

Analysis

and

Optimization

Veli-Pekka Ketonen,

CTO, 7signal

Feb 12th, 2014


Topics

1. How does 7signal Sapphire work?

2. Factors impacting the performance

3. 10 step performance optimization flow

4. Selected example data

5. Promising new technologies

6. Conclusions

2


Measures: Accessibility,

Availability, Throughput,

Packet Loss, Latency, Jitter,

MOS Score, Success Rate

Getting the data

3

Eye/Sonar performs end-to-

end active user testing:

FTP, UDP, HTTP, SIP, ICMP

Eye performs passive testing between APs

and clients: Data Rates, Retry Rates,

Utilization, Traffic Volume, Beaconing

Eye • State-of-the-art sensor

• Continually monitors Wi-Fi activity

• Performs active and passive testing

Sonar • Eyes run tests through

access points towards

test end point

Carat • Software that analyzes data and lists

specific action items for improving the

Wi-Fi network


The Eye’s Capabilities

4

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

Copyright © 2014 7signal Solutions, Inc. 5

7signal KPI Categories

Availability

Accessibility

RF signal properties

Spectrum analysis

Status codes Reason codes Failure codes

NW settings and configuration QoS categories

Utilization Traffic volume

SLA

Throughput Jitter

Latency MOS

Packet loss Success rate

Frame delivery Packet characteristics Data rates

Action Beaconing

Association/Re-/Dis- Probing

Authentication/De- Legacy

L7

L1

FTP, UDP, HTTP, SIP, ICMP


2. Factors impacting the performance

6


Understand radio environment

APs outside channel grid

Amount of APs/SSIDs

Empty AP vs loaded AP

7

Different HT

Legacy APs (802.11b)

Non-Wi-Fi interference


Select proper antenna for the purpose

Antenna gain pattern

Antenna gain pointing to…

Behind metal grid?

Near to conductive or “dense”

surface (εr, relatively permittivity)

At 30ft/10m elevation?

6dB is 2x, 3dB is a lot too!

Antenna gain is bi-directional

In common ceiling mounted APs,

sideways down tilted patterns is

most useful

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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

Error Vector Magnitude (EVM)

Lower output power and use antenna gain to reach further with higher rates

9

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


Too high rates cause high retries

WLAN AP rate control often uses too high rates/MCS

This causes high amount of retries, which have negative impact on performance

10

* 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?

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Retries = HIGH

Data rates/MCS = HIGH

Retries = LOW

Data rates/MCS = LOW

Good coverage, reliable

operation, high speed and capa

Unstable, high jitter, packet loss, limited

capacity

Speed limited, working ok

Very slow, at the coverage boundary

Typical in WLAN

Target


WLAN transmit power control

may need help No real time power control in WLAN

802.11h is used mostly for DFS

Proprietary, slow TPC functionalities

Common implementation measures neighbor APs levels and keep them below a fixed value

TPC may not be able to optimize network throughputs or avoid areas with weak signal

Power levels may drift to end of the allowed range

Clients commonly use +10 - +15 dBm power, running APs much lower levels causes in-balance to link budget. Both uplink and downlink coverage are needed!

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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


Use all spectrum and 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

1

1

6

Without a very good reason this should not ever happen

6

1

6

11

11

1


Sometimes channel automation

is not working well and needs help

14

Continuous channel

switching

More stable operation


Legacy mode drives speed down

The largest impact from 802.11b protection but also between other standards

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

15


TCP does not like lost packets

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 may lose lower layer packets

If packets are lost in TCP layer, that usually means trouble for

application performance

16


Retries at different layers using TCP

17

User

Application (Layer 4-7)

TCP (Layer 3)

Radio (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 1-3 problems)

User data

= A data packet, illustration purposes only


Retries at different layers using UDP

18

User

Application (Layer 4-7)

UDP (Layer 3)

Radio (Layer 1-2)

UDP does not retransmit, permanently lost packet

VoIP call, etc.

Jitter Packet loss

Not ACK’d? -> Resend, 7-25 times

= A data packet, illustration purposes only


Layer 2 packet fragmentation

makes radio mode 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)

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#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 over

Ad Hoc’s and other Non-Authorized APs

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

classes

20

* Source: IEEE 802.11-08/1214-02-00aa 802.11 QoS Tutorial


3. Optimization flow,

10 step process

21


What is needed?

22

Data

•Throughput, latency, packet loss, jitter

Knowledge

•Understand key principles

Changes

•Address bottlenecks

Analysis

•How did performance change?

Learning

•Learn from every change


The most important KPIs

Throughput

Latency

Packet loss

23

Data rates

Retry rates

Utilization

Traffic volume

Channels

Signal level

Spectrum data

Jitter

Voice quality (MOS)

Success rates

End user metrics

Radio operation Ass

ess O

ptim

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, 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, client roaming,…

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

•Directional antennas, add/move APs, replace equipment, end user devices 10. Physical network changes

24


#1. Understand the baseline

Collect and review all radio parameter settings

Verify AP type, antenna performance and placement

Upgrade controller/AP SW if clearly outdated

Collect baseline performance data for 3-5 days

Analyze and find likely bottlenecks

Draft a plan for optimization steps

Note: Night time data is extremely useful

If empty network can’t push good throughputs, it’s won’t do that under load either

If empty network utilization is significant, that’s a problem

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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 802.1b rates (1, 2, 5.5, 11) and their support

Remove gradually low MCS and SS multiples

Beacon at higher rate than lowest allowed

Consider disabling removing power save mode

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

27


#4. Adjust power levels

Define a limited range for TPC algorithms instead of

default (-10 dBm - +30dBm or similar).

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

28


#5. Reduce non-Wi-Fi interference

Interference is present, always! Understand level of impact

What is the throughput performance?

Correlate spectrum data with throughput data

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, often not

Observe impact to throughput and other end user metrics’ when changes are made

If changes are helping, it’s visible in active data

29


#6. Improve radio robustness

Remove highest rates/MCS (most sensitive)

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

Assign higher WMM QoS class (voice the highest)

Use radio packet fragmentation

Increase AP power

Enable interference resistant mode if supported

30


#7. Prioritize and balance traffic

Separate SSIDs (but keep quantity to minimum)

Assign WMM QoS classes

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

cause slowness, drop packets locally

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 to terminals

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

Use good quality and right type of external antennas

Upgrade APs

Add LAN/WAN capacity

Upgrade client terminals

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Every network can be made perform well!


4. Examples

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Akron Childrens 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 AP’s improved from ~7 to ~15 Mbit/s. (110%)

37


Voice quality, downlink


Channel change

Core LAN upgrade

Power level change

Codec changes

Daily average variance practically zero

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Packet loss


Channel change

Core LAN upgrade

Power level change

Codec changes

From ~2.5% to ~0.5%

39


Avans University of Applied Sciences

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TCP downlink throughput

1 2 3 4 5 1 2 3 4 5 900% improvement in 1st

floor

100% improvement in ground floor

AP power levels

More channels

Beacon 300ms

HT40

41


HTTP downlink throughput

1 2 3 4 5 90%/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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Retransmission by AP

towards clients

1 2 3 4 5

Lowered by 25% until HT40 is turned on at

step 5

HT40 increases significantly

retransmissions from AP

45


Retransmission by

Clients toward AP

1 2 3 4 5

Lowered by 50% until HT40 is turned on at

step 5

HT40 increases significantly

retransmissions from clients

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5 GHz, Learning center,

1st floor, 8am-6pm BEFORE

AFTER

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University

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

Downlink throughput (daily)

Downlink throughput daily averages have improved 50%

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

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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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 4th) New channel plan areas 1 &2

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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5. Promising new technologies for

enhanced performance

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Promising technologies

Asymmetric priority control

– AP’s send more often than clients. Giving AP’s shorter back-off times increases

overall efficiency

Dynamic Sensitivity Control (DSC)

– In dense environments, Clear Channel Assessment (CCA) may too easily keep

channel busy and APs & clients do not get opportunities for transmitting

Full duplex Wi-Fi

– AP transmission may be cancelled at AP receiver. This enabled simultaneous

transmission and receiving on the same channel

Multipath TCP

– TCP connection using two parallel radio connections (for example Apple, Siri)

Self Organizing Networks (SON)

– Automated network reconfiguration

– WLAN has been early adopter of this kind functionalities for channel and

general AP power level control, but results have been mixed

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Many of these have been presented and discussed in 802.11HEW SG meetings See https://mentor.ieee.org/802.11/documents?is_dcn=DCN%2C%20Title%2C%20Author%20or%20Affiliation&is_group=0hew

https://mentor.ieee.org/802.11/documents?is_dcn=DCN, Title, Author or Affiliation&is_group=0hew

https://mentor.ieee.org/802.11/documents?is_dcn=DCN, Title, Author or Affiliation&is_group=0hew


SON in the works,

7signal Auto-Analysis and Optimization

Analyzing the data and concluding bottlenecks

needs experience that’s not always available

Automating the analysis (Auto-Analysis) helps to

find bottlenecks

Limiting factors need to be addressed. Auto-

Optimize provides a suggested action plan

Eventually Wi-Fi needs to be continuously Self-

Optimizing and Re-Configuring (“SON”). It may

still take some time to get that in place everywhere

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Summary

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Summary

Wi-Fi is very sensitive to the surroundings and

network configuration, even though works somehow

almost no matter where you put it

Performance can often be improved significantly

by adjusting the configuration

Need relevant continuous data to validate changes

Need knowledge of WLAN/RF to decide the actions

Optimization requires a pragmatic approach

55


Thank You!

56

Email [email protected] Twitter @VPonwireless

This material is available at: http://go.7signal.com/wlpc

Advanced WLAN Performance Analysis and Optimization · –Passing the Type Approval ......

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