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Copyright © signal Solutions, Inc. Wi-Fi / WLAN Performance Management and Optimization Veli-Pekka Ketonen CTO, 7signal Solutions
Copyright © signal Solutions, Inc. Topics 1. The Wi-Fi Performance Challenge 2. Factors Impacting Performance 3. The Wi-Fi Performance Cycle step performance optimization flow 5. Selected example data 6. Summary / Questions 2
Copyright © signal Solutions, Inc. Wi-Fi Networks are Everywhere! But they are transitioning from “nice to have” to “must have” 3
Copyright © signal Solutions, Inc. Wi-Fi Networks are Everywhere! But they are transitioning from “nice to have” to “must have” 4 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
Copyright © signal Solutions, Inc. Dependable Wi-Fi is Costly and Complex 5 Complexity of Network Number of access points, clients, applications Cost Needed to Achieve Reliability Voice over Wi-Fi BYOD Guest Networks Mobile Computing $ Reactive focus based on complaints Virtual Desktop Video Apps Location Svcs
Copyright © signal Solutions, Inc. 2. Factors impacting the performance 6
Copyright © signal Solutions, Inc. 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 7 Down tilted pattern Attenuation upwards Max gain sideways
Copyright © signal Solutions, Inc. 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 8 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
Copyright © signal Solutions, Inc. 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! 9 Room High received neighbor AP level may drive AP power down..and cause lack of coverage here
Copyright © signal Solutions, Inc. Channel & Utilization Issues Channel overlap APs outside channel grid HT conflicts 10 Amount of APs/SSIDs Empty AP vs.. loaded AP
Copyright © signal Solutions, Inc. 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 Without a very good reason this should not ever happen
Copyright © signal Solutions, Inc. Sometimes channel automation is not working well and needs help 12 Continuous channel switching More stable operation
Copyright © signal Solutions, Inc. 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 13 * Haratcherev et.al. : Automatic IEEE Rate Control for Streaming Applications *Lakshmanan et. al. On link rate adaptation in n WLANs Optimal rate
Copyright © signal Solutions, Inc. What can rates and retries tell you? 14 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
Copyright © signal Solutions, Inc. Non Wi-Fi Interference 15 Bluetooth Microwave Video cameras Medical devices
Copyright © signal Solutions, Inc. 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 16
Copyright © signal Solutions, Inc. 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 17
Copyright © signal Solutions, Inc. Retries at different layers using TCP 18 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
Copyright © signal Solutions, Inc. Retries at different layers using UDP 19 User Application (Layer 5-7) UDP (Layer 4) WLAN (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
Copyright © signal Solutions, Inc. 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) 20 #1, 1500 B #2, 1500 B 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
Copyright © signal Solutions, Inc. Higher QoS helps prioritize data Voice (VO), Video (VI), Best Effort (BE) and Background (BK) classes 21 * Source: IEEE / aa QoS Tutorial
Copyright © signal Solutions, Inc. 3. The Wi-Fi Performance Cycle 22
Copyright © signal Solutions, Inc. Answering the Wi-Fi Challenge 23 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
Copyright © signal Solutions, Inc. Bending the Cost Curve 24 Complexity of Network Number of access points, clients, applications Cost Needed to Achieve Reliability Voice over Wi-Fi BYOD Guest Networks Mobile Computing $ Reactive focus based on complaints Virtual Desktop Video Apps Location Svcs Proactive focus based on continuous measurements
Copyright © signal Solutions, Inc. Performance Management with a Systematic Approach 25 Listen to AP / Client Traffic (Passive Tests) Simulate Client Traffic (Active Tests) Access Point(s) Sensor Mgmt Station
Copyright © signal Solutions, Inc. The Eye’s Capabilities 26 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 © signal Solutions, Inc. The Wi-Fi Performance Cycle 27 If you can’t measure it, you can’t manage it! - Peter Drucker MeasureAnalyzeOptimizeVerifyAssure
Copyright © signal Solutions, Inc. 4. Optimization flow, 10 step process 28
Copyright © signal Solutions, Inc. The most important KPIs Connection Success Throughput Packet Loss 29 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) Assess Optimize
Copyright © signal Solutions, Inc. 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 30
Copyright © signal Solutions, Inc. #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 31
Copyright © signal Solutions, Inc. #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 32
Copyright © signal Solutions, Inc. #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 33
Copyright © signal Solutions, Inc. #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 34
Copyright © signal Solutions, Inc. #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 35
Copyright © signal Solutions, Inc. #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 36
Copyright © signal Solutions, Inc. #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 37
Copyright © signal Solutions, Inc. #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 38
Copyright © signal Solutions, Inc. #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 39
Copyright © signal Solutions, Inc. #10. Physical changes to network Move APs Add APs Upgrade APs Use good quality and right type of external antennas 40 Every network can be made perform well! Every network can be made perform well!
Copyright © signal Solutions, Inc. 5. Examples 41
Copyright © signal Solutions, Inc. Akron Children’s Medical Center 42
Copyright © signal Solutions, Inc. 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
Copyright © signal Solutions, Inc. Downlink Throughput 44 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%)
Copyright © signal Solutions, Inc. Packet loss Antenna change ready Channel change Core LAN upgrade Power level change Codec changes From ~ 2.5% to ~ 0.5% 45
Copyright © signal Solutions, Inc. University, Iowa 46
Copyright © signal Solutions, Inc. 1st 2nd 3rd 4th 5th 6th 7th Downlink throughput (daily) Downlink throughput daily averages have improved 50% 1 st ) Disabling power saving 2 nd ) Disabling b-data rates, area 1 3 rd ) Disabling b-data rates in other locations 4 th ) New channel plan areas 1 &2 5 th ) New TxPwr settings in XXX and channel plan in YYY 6 th ) Beacon interval change 7 th ( Channel re-plan area 3 2.4GHz 47
Copyright © signal Solutions, Inc. 1st 2nd 3rd 4th 5th 6th 7th Downlink throughput (hour) Minimum values increase up to ~10x 1 st ) Disabling power saving 2 nd ) Disabling b-data rates, area 1 3 rd ) Disabling b-data rates in other locations 4 th ) New channel plan areas 1 &2 5 th ) New TxPwr settings in XXX and channel plan in YYY 6 th ) Beacon interval change 7 th ( Channel re-plan area 3 2.4GHz 48
Copyright © signal Solutions, Inc. Avans University of Applied Sciences 49
Copyright © signal Solutions, Inc. TCP downlink throughput % improvement in 1 st floor 100% improvement in ground floor AP power levels More channels Beacon 300ms HT40 50
Copyright © signal Solutions, Inc. HTTP downlink throughput %/50% improvements 51
Copyright © signal Solutions, Inc. Voice Quality (MOS), downlink, hourly MOS in ground +0.25MOS in 1 st floor 52
Copyright © signal Solutions, Inc. Network latency (RTT) % improvement in 1 st floor 53
Copyright © signal Solutions, Inc. Performance Dashboard 54 Before Analysis and Optimization After Analysis and optimization
Copyright © signal Solutions, Inc. 6. Summary 55
Copyright © signal Solutions, Inc. 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 56
Copyright © signal Solutions, Inc. Thank You! 57 Presentation:http://go.7signal.com/surfwlpc
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