1. Wi-Fi / WLAN Performance Management and Optimization
Veli-Pekka Ketonen
CTO, 7signal Solutions
7signal has developed Wi-Fi Performance platform.
Based in Akron, Ohio
Akron claims to invented many things – things like oatmeal, the first synthetic tire, the first artificial fish bait. and it also played a key role in developing Wi-Fi at Aironet, which became part of Cisco
Poll – Education, Government. Healthcare, Other Enterprise, Sell solutions to these people?

2. The Wi-Fi Performance Challenge Factors Impacting Performance
Topics
The Wi-Fi Performance Challenge
Factors Impacting Performance
The Wi-Fi Performance Cycle
10 step performance optimization flow
Selected example data
Summary / Questions
10:30 – 10:40 – INTRO (10 Minutes)
10:40 – 11:00 – FACTORS (20 Minutes)
11:00 – 11:10 – PERFORMANCE CYCLE
11:10 – 11:30 – OPTIMIZATION
11:30 – 11:40 – EXAMPLES & SUMMARY
11:40 – 11:45 -- QUESTIONS

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

4. 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
Changes hourly, daily and weekly

5. Dependable Wi-Fi is Costly and Complex
BYOD
Video Apps
Reactive focus
based on complaints $
Virtual Desktop
Location Svcs
Mobile Computing
Cost Needed to Achieve Reliability
Guest Networks
Voice over Wi-Fi
Today, you might use a series of troubleshooting steps and tools in order to identify and fix problems.
But as your network gets more and more complex over time, the cost of deploying those tools and resources becomes enormous….and this is not a scalable solution. <click>
Complexity of Network
Number of access points, clients, applications

6. 2. Factors impacting the performance

7. Improper Antenna Selection / Placement
Max gain sideways
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
Attenuation upwards
Down tilted pattern
Typically antennas built in
More challenging physical environments, may be external
In an environment having issues, good to be aware of what type – are they omnidirectional (typical) or some type of directional and whether they are near some type of structure like a metal grid or cement beam that effects transmissions
In common APs, you want a radiated patter tilled downwards to reach clients

8. RF power level is not that simple
+20 dBm
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
MIMO/TX div. gain, +3 dB
+17 dBm
No high MCS/rates, + 3dB
+14 dBm
HT40 - > HT 20, +2 dB
+11 dBm
Antenna gain, +3 dB
+8 dBm
Radio output (no antenna), HT40, highest MCS
Another factor impacting performance is RF Power Level, and you have to be careful here, because the power is not always what the datasheet on controller settings tell you, and there are a lot of components to RF power.
MCS – modulation / coding scheme (QAM, rate, spatial streams, data rate, etc.)
STBC gain – space/time/block code
You may think the higher the radio output power, the better, but that is not always the case
Transmitters are not linear, so at higher rates, the APs cut back on power to provide a non-distorted signal, so you may be better off with a TX power setting slightly lower than max and use antenna gain to be successful transmitting higher rates further distances
180Mbit/s
300
Mbit/s
300
Mbit/s

9. 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 dBm power, running APs much lower levels causes imbalance to link budget. Both uplink and downlink coverage are needed!
High received neighbor AP level may drive AP power down
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..and cause lack of coverage here
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Other problem with too high power is causing interference with other APs.
WLAN manufacturers have automatic TX Power Control, try to create the ideal cell size
We’ve found that they tend to drive TX Power tool low, so clients can’t actually hear the APs!
Most manufacturers you can tweak the range, and we’ve found it is better to reduce the range – raise the lower limits and lower the higher limits
But you don’t want to do this without having data that shows the impact – we’ll talk more about that later
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10. Channel & Utilization Issues
Get the antennas and power right and have ideal coverage, but then have issues with channels being used
There are some manufacturers that have invented their own protocol to enhance the basic Collision Avoidance in CSMA/CA but in general
Adjacent APs need to use different channels or else they will spend most of the time waiting to talk in a very ineffective
2.4 GHz – 5 MHz spacing, but 20 MHz wide, so there will be overlap unless you stick with 1, 6, 11
5 GHz – 20 MHz spacing so you can use adjacent channels, but when you combine channels to get more bandwidths you need to make sure you don’t create overlap
On this graph, which comes from our software console, each line represents a BSSID
Channel 4 – neighbor, commercial grade rogue AP that someone has brought in because they’re unhappy with the Wi-Fi, which sometimes look for an “empty” channel, or it could be a default setting on a device like a printer – not a total disaster but it raises the noise floor
Performance also impacted by other factors like the number of SSIDs, which create overhead from beaconing and probe responses and cuts down on airtime availability
Channel overlap
APs outside channel grid
HT conflicts
Amount of APs/SSIDs
Empty AP vs.. loaded AP

11. 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 1 6 6 1 11
Really want to use all the spectrum you have – both 5GHz and 2.4GHZ
Really want channel separation, not only on the same floor but between floors, so you have to think 3 dimensionally
Manufacturers have mechanisms for channel automation work fine in the lab or small environment, but sometimes they get confused, and you end up with something looking like this
Without a very good reason this should not ever happen

12. Sometimes channel automation is not working well and needs help
Continuous channel switching
More stable operation
Here is an example of channel automation at one university – we call this channel flapping and is not very productive – end users waste a lot of time getting disconnected and reconnected
Channel Fly, ARM, RRM

13. 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
Optimal rate
Data rates also impact performance
In general you’d think that you’d like to transmit at the highest rate possible – if you can send your information quickly, you can get off the air and let someone else talk. But the faster you transmit, the higher the SNR you need at the receiver to accurately receive the data.
The general algorithm is to transmit at higher rate – and if you don’t get acknowledgement different manufacturers will decide to transmit again at the same rate or immediately go to a lower rate.
If you see a lot of retransmissions, you might be better off lowering the max rate
Acknowledgements may go out at lower rate.
*Lakshmanan et. al. On link rate adaptation in n WLANs
* Haratcherev et.al. : Automatic IEEE Rate Control for Streaming Applications

14. What can rates and retries tell you?
Data rates/MCS = HIGH
Typical in WLAN 
Target 
Unstable, high jitter, packet loss, limited capacity
Good coverage, reliable operation, high speed and capacity
Retries =
HIGH
Retries =
LOW
Very slow, at the coverage boundary
Speed limited, working ok
It really is a balance between data rates and retransmissions as illustrated by this chart. You would like to operating in the green area.
Data rates/MCS = LOW

15. Non Wi-Fi Interference
Impact of devices at 2.4G, not so much at 5G
Important to understand that Wi-Fi will work in the presence of other devices, but the noise floor will be higher.
A big mistake people make is to focus on these non-wifi devices without understanding how the network is working at a higher level with metrics like throughput, delay and jitter, which I will talk about later
Bluetooth
Microwave
Video cameras
Medical devices

16. Legacy mode drives speed down
The largest impact from is b protection
When an AP detects an associated b 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
is backward protocol is designed to be backward compatible with slower older devices, but this supports has a big impact.
Not only do .11b packets take longer to transmit, but the APs and clients have to go into protection mode because b clients can’t detect the higher rate carrier, which means the added overhead of using RTS/CTS
In practice, it is best to disable .b – a lot of universities are doing this, in hospitals, not so easy because of medical devices or VoIP badges still using .b
JOKE – WHY DID IT TAKE GOD ONLY 6 DAYS TO CREATE THE WORLD? He didn’t have to deal with legacy systems!

17. 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
Let’s start to look at higher protocol issues.
TCP is of course the basic mechanism to transfer files or web traffic, and it is very sensitive to delay and lost packets. It has a mechanism called slow start where it sends a few packets, waits for an acknowledgement, and based on that decides to increase the window and send more data before getting an acknowledgment.
So a lost packet or acknowledgement can impact the overall data transfer rate

18. Retries at different layers using TCP
User
User data
User may lose patience in 4-10s
Application
(Layer 5-7)
varies
Desktop virtualization (used sometime to help with layer 1-4 problems)
TCP
(Layer 4)
Not ACK’d within 2x RTT?
-> Resend w/ SLOW START
WLAN
(Layer 1-2)
This shows this process – at the TCP layer you have one level of transmit / acknowledge and below that you have the transmit / acknowledge at the Wi-Fi layer.
A lost or delayed packet will impact the overall speed of the perceived connection and the user could get frustrated.
Not ACK’d?
-> Resend, 7-25 times
= A data packet, illustration purposes only

19. Retries at different layers using UDP
User
VoIP call, etc.
Application
(Layer 5-7)
UDP does not retransmit,
permanently lost packet
UDP
(Layer 4)
WLAN
(Layer 1-2)
With UDP used in Voice over IP, no high level acknowledgements, so a lost or delayed packet results in jitter or noise
How many of you have been on a conference call where one guy is on a bad Wi-Fi connection and the echo cancellers start going crazy – not a pleasant experience.
Not ACK’d?
-> Resend, 7-25 times
Jitter
Packet loss
= A data packet, illustration purposes only

20. Layer 2 packet fragmentation makes radio more robust
If all goes well, good efficiency
#1, B
#2, 1500 B
ACK
ACK
If error is detected, content of the whole 1500B packet is lost and needs to be retransmitted
#1, 1500 B
#1, Retry 1, 1500 B
No ACK
(lost or any error)
Probability of errors in smaller packet is lower and transmitting it has taken less time in the first place
#1, 750 B
#2, 750 B
#3, 750 B
#4, 750 B
Fragmentation is another factor that can actually improve performance in a noisy environment.
By breaking up the packet into smaller fragments, there is a better chance of getting through. Tradeoff is more overhead.
ACK
ACK
ACK
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)

21. Higher QoS helps prioritize data
Another mechanism is assigned QoS traffic classes to help prioritize data within the network; a lot of times this gets translated to different SSIDs for Voice and Video, which are more delay sensitive.
Voice (VO), Video (VI), Best Effort (BE) and Background (BK) classes
* Source: IEEE / aa QoS Tutorial

22. 3. The Wi-Fi Performance Cycle

23. Answering the Wi-Fi Challenge
Problem
Solution
Proactive measurements
Check end-to-end performance
Analyze historical trends
Use metrics based reporting
Centralize diagnosis of problems
Wait for complaints
Limited view of network
Little historical data
Guess at service levels
Remote issues costly to resolve

24. Cost Needed to Achieve Reliability
Bending the Cost Curve
BYOD
Video Apps
Reactive focus
based on complaints $
Virtual Desktop
Location Svcs
Mobile Computing
Cost Needed to Achieve Reliability
Guest Networks
Proactive focus
based on continuous
measurements
Voice over Wi-Fi
Complexity of Network
Number of access points, clients, applications

25. Performance Management with a Systematic Approach
Simulate Client Traffic
(Active Tests)
Sensor
Access
Point(s)
Mgmt Station
Listen to AP / Client Traffic
(Passive Tests)

26. 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

27. The Wi-Fi Performance Cycle
If you can’t measure it, you can’t manage it!
- Peter Drucker
Measure
Analyze
Optimize
Verify
Assure

28. 4. Optimization flow, 10 step process

29. The most important KPIs
End user metrics (active tests)
Connection Success
Throughput
Packet Loss
Latency
Jitter
Voice quality (MOS)
Assess
Optimize
Layer 2 / Layer 1 metrics(passive tests)
Data rates
Retry rates
Utilization
Traffic volume
Channels
Signal level
Spectrum data
Want to use high level end user metrics to assess the network while making changes to the lower level network.

30. 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 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
Directional antennas, add/move APs, replace equipment, end user devices
10. Physical network changes

31. #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

32. #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

33. #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 b 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
Remove printers and other devices that keep air busy
Why do people assign different SSIDs? Different authentications (guest, etc.), traffic types. What are examples that we have found? (typically we find 3 – guest, VoIP, general). (worse we’ve seen – 15-30)
What is a typical beaconing rate? (100 msec). What do you change to from 3 to 1 (Dtim – dynamic traffic interval map)

34. #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 compensating with higher gain antennas if needed

35. #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
If changes are helping, it’s visible in active data

36. #6. Improve WLAN robustness
Remove highest rates/MCS (most sensitive)
Run voice SSIDs only -g/-a mode without –n
Use radio packet fragmentation
Enable interference resistant mode if supported

37. #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
Balancing AP (by forcing highly utilized APs to lower power levels) – do we do this a lot?

38. #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 user and dimension connections accordingly

39. #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
CTS-to-Self may be more efficient than RTS/CTS

40. #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!

41. 5. Examples

42. Akron Children’s Medical Center

43. Uplink throughput Average improved from ~11 to ~14 Mbit/s (27%)
The worst APs improved from ~4 to ~13 Mbit/s. (225%)
Antenna change is step 10 in optimization process, but this was step 1?
Antenna change ready
Channel change
Power level change
Codec changes
Core LAN upgrade

44. Downlink Throughput Average improved from 13 to 17 Mbit/s (30%)
The worst APs improved from 7 to 15 Mbit/s. (110%)
Antenna change is step 10 in optimization process, but this was step 1?
Antenna change ready
Channel change
Power level change
Codec changes
Core LAN upgrade

45. Packet loss From ~2.5% to ~0.5% Antenna change ready Channel change
Power level change
Codec changes
Core LAN upgrade

46. University, Iowa

47. Downlink throughput (daily)
1st
2nd
3rd
4th
5th
6th
7th
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

48. Downlink throughput (hour)
Minimum values increase up to ~10x
2nd
3rd
4th
5th
6th
1st
7th
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

49. Avans University of Applied Sciences

50. TCP downlink throughput1 2 3 4 5
900% improvement in 1st floor
100% improvement in ground floor
AP power levels
More channels
Beacon 300ms
HT40

51. HTTP downlink throughput1 2 3 4 5
90%/50% improvements

52. Voice Quality (MOS), downlink, hourly
+0.25MOS in ground
+0.25MOS in 1st floor 1 2 3 4 5

53. 50% improvement in 1st floor
Network latency (RTT) 1 2 3 4 5
50% improvement in 1st floor

54. Performance Dashboard
Before Analysis and
Optimization
After Analysis and optimization
We baseline, then we optimize.
Tracking the trends

55. 6. Summary

56. 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
Optimization requires a pragmatic approach

57. Thank You! www.7signal.com @7signal
Presentation:
@7signal