Wireless Challenges and Resolutions 1
Steven Shelton Senior Network Engineer Oak Ridge National Laboratory Oak Ridge, Tennessee ows@ornl.gov 2
Wireless Challenges and Resolutions Sections Common Problems with Wireless Observations Examples of Issues Improvements Review of Issues and Solutions Questions 3
Common Problems with Wireless Wireless is Slow Wireless Comes and Goes Low Signal My notebook works but not my iphone or ipad Disconnects When Walking to a New Location 4
2015 Wireless Client Observations The Most Common Characteristic of Reported Wireless Issues 2.4 GHz Averaging ~3500 Wireless Clients per Day Over 65% of Wireless Clients, ~2300, Using 2.4GHz Distribution of 2.4GHz Clients ~ 1,590 (~45%) 802.11n ~ 680 (~19%) 802.11g ~ 45 (~1.3%) 802.11b 5
2015 Wireless Client Observations Common Client Issues Low SNR High CRC Error Rates, 40% and higher Excessive Retries Significant Amount of Interference Microwave Ovens, Bluetooth, DECT phones Other Wireless Systems Operating on Same Channels Other Systems Operating on Adjacent channels Windows Notebook Prefers 2.4GHz (default driver option) Client Roaming Issues 6
2015 System Operational Notes APs Operating at Maximum Transmit Power Creates Largest Coverage Cell As Possible Serves As Many Wireless Clients As Possible Less Than Optimal AP Placement Telecom Closets Inside Cabinets Pipe Chase Antenna Orientation Out of phase with client TKIP Encryption Enabled Disables 802.11n/ac High Data Rates Sub Optimal Channel Plan Many SSIDS 7
2015 Slow to Respond Problem Resolution Difficult to Locate Clients or Other Assets Lack of Accurate AP Location Data Increases Troubleshooting Effort Lack of Wireless Event History Wireless Controllers Only Provide Current State New Deployments Custom Configuration of AP Channel and Transmit Power Very Time Consuming and Prone to Errors 8
Visual Examples 9
Normal Channel 6 and Channel 11 Power over Frequency Graph 10
Healthy Channel 6 (2.437 GHz) 11
ORNL 2.4GHz Spectrum Issues High CRC Error Rates, 40% Excessive Retries Interference Microwave Ovens, Bluetooth, DECT phones Other Wireless Systems Operating on Same Channels Other Systems Operating on Adjacent channels 12
Operational Issues APs Operating at Maximum Transmit Power Create Largest Coverage Cell As Possible Reach As Many Wireless Clients As Possible Limits Scalability Creates Intermittent Problems Difficult to Resolve 13
Operational Issues APs Operating at Maximum Transmit Power Create Largest Coverage Cell As Possible Reach As Many Wireless Clients As Possible Issue: Hidden Node Design Does Not Scale Some Clients Out of Range from Other Clients Collision Avoidance Begins to Fail Collisions Increase Dramatically Collisions Create CRC Errors CRC Errors Create Retries Retries Increase Traffic Which Creates More Collisions 14
Hidden Node AP Has Large Coverage Cell Client A Doesn t Receive or Detect Client B Client A Access Point Client B 15
Operational Issues APs Operating at Maximum Transmit Power Create Largest Coverage Cell As Possible Reach As Many Wireless Clients As Possible Issue: Dynamic Rate Shifting As the distance between the client radio and the AP increases, SNR decreases and forces the client to negotiate a lower MCS rate SNR Varies Across the Cell Range of MCS Rates Lower SNR = Slower Modulation = More Air Time All Clients Must Wait on Slowest Client 16
SNR Signal to Noise Ratio SNR is Key to High Throughput Wireless 17
Dynamic Rate Shifting 18
Operational Issues APs Operating at Maximum Transmit Power Create Largest Coverage Cell As Possible Reach As Many Wireless Clients As Possible Issue: Asymmetric Power Modern APs Have More Transmit Power Relatively Large Cell Smartphones and Tablets Have Less Transmit Power Relatively Small Cell 19
Legacy Client Support TKIP Enabled to Support Legacy Clients WiFi Alliance Discouraged Use of TKIP by Disabling 802.11n HT Capabilities Systems Using 802.11n/ac with AES Encryption Received Full Bandwidth Capabilities Test Data Showing Throughput Increase as Client Switches to AES Test Performed Using IxChariot to Measure Throughput at the Application Layer 20
Sub Optimal AP Placement AP Coverage is Intended to Spread Across an Area, Parallel to the Floor This is the Antenna Radiation Pattern taken from the AP s Data Sheet Know Your Equipment s Capabilities 21
Sub Optimal AP Placement AP Coverage is Intended to Spread Across an Area, Parallel to the Floor Incorrect Correct Antenna radiation pattern is perpendicular to the floor 22
Manual Channel Assignment APs Operating on Same Channel Prone Coverage to Errors Cells Overlap With Too Much Power Excessively High Rate of Collisions High CRC Rates Hidden Node Issues Know as Co Channel Interference, CCI Both Cells Suffer Performance Degradation as Load Increases Should have a Minimumof 20 db of Separation 23
Manual Channel Assignment Good Example of Channel Planning and Separation 20dB Minimum of Channel Separation 25dB Better 30dB Preferred 24
Client Disconnects When I Move Around Issue: Sticky Client Roaming Decision Made by the Wireless Client 25
Improvements 26
Improvements Made for the 2.4GHz Clients 2.4GHz Options are Very Limited Only Three 20MHz Channels Inadequate Space for Channel Bonding Virtually No Control of the Air Space Migrate Clients to the 5GHz Band All New Developments are Implemented in the 5GHz Spectrum ORNL no longer supports 802.11b as of 1/1/2016 Equivalent of dropping support for Windows 98 Continue Support for 802.11g Legacy Clients As a Best Effort Service Install a 5GHz USB WLAN Adapter for Older Notebooks 27
Improvements Made for the 5GHz Service Increase Number of APs ~20% Overlap in Coverage Provides Opportunity for Seamless Roaming Small Coverage Cells Reduced AP Transmit Power From 200mW to between 10mW and ~32mW From 25,000ft 2 to between 3000ft 2 5000ft 2 Relative to Environment and Capacity Needs 28
Example of a Capacity Design More APs Less Power Optimized Transmit Power to Match Client Capabilities 29
Benefits of a Dense AP Deployment and Optimized Power Consistently Good SNR Throughout Each Cell Provides Clients an Opportunity to Achieve Their Best MCS Rate Dynamic Rate Shifting Limit DRS to the Higher MCS Rates Asymmetric Power Issue Opportunity Significantly Reduced Hidden Node Issue Opportunity Significantly Reduced High CRC Rates & Retries Reduced to Single Digits 30
Device Capabilities Cisco Publishes AP Details in Data Sheets and Deployment Guides Cisco 2802 Data Sheet Info Know Your Equipment s Capabilities 31
Device Capabilities Most Client Device Manufacturers Guard/Hide Their Products Capabilities Data can be obtained from the FCC approval application using the devices FCC ID number ipad Gen 3 1 FCC ID: BCGA1416 iphone 6s 2 FCC ID: BCGA141 f c Channels TxP mw dbm TxP mw dbm UNII 1 5180 5240 36 48 24mW 13.8 63mW 17.9 UNII 2 5260 5320 52 64 59mW 17.7 49mW 16.90 UNII 2e 5500 5700 100 140 49mW 16.9 28mW 14.5 UNII 3 5745 5825 149 161 44mW 26.4 50mW 16.98 1. https://fccid.io/bcga1416 2. https://fccid.io/bcge2816a Know The Client Capabilities 32
How to Migrate Wireless Clients to 5GHz Band Steering Not recommended for VoWLANor WiFi Calling Use Transmit Power to Steer Clients Away From 2.4GHz Make 5GHz more attractive to the client Client Driver Configuration (Desktop Support) Configure Client to prefer 5GHz» Should be part of the standard OS build for Windows Devices 33
Radio Resource Management, RRM Dynamically Manages and Balances RF Infrastructure Automatically Adjusts Channel and TxPto maintain Optimum Coverage Configurable Thresholds Configurable in RF Profiles Requires Proper AP Location and Density Creating a Self Healing, Self Optimizing Wireless Network 34
Improvements in Wireless Management Implemented Prime Infrastructure Online Floor Maps Shows AP placement, etc. Previously Used Printed Floor Maps and Notes Maintains History of Wireless Clients Connectivity APs, Signal Strength, SNR Maintains History of AP Utilization Number of Clients, Noise, Interference Performance Reporting and Fault Management Significant Reduction in Troubleshoot Time Troubleshoot by Alarms and Events 35
Improvements in Wireless Management Implemented Mobility Services Engine, MSE RFID Location Services Detect/Classify/Mitigate 802.11 Interference Track and Trace Interferers and L1 Exploits Track and Trace Rogues Rogue Mitigation Maintain Air Quality System wide Interferer Details and Event Correlation Maintains Real Time and Historical Information Back in Time Analysis Zone of Impact and Interferer Notification 36
Results of Improvements Reduced Number of 2.4GHz Clients Significantly In 2015, Averaging ~ 3500 Clients per Day 65% of Clients Used the 2.4GHz Service In 2018, Averaging ~ 4000 Clients per Day 40% of Today s Clients Using 2.4GHz ~ 1,570 802.11n (Down 25% in 2015) ~ 30 802.11g (Down 95% in 2015) 0 802.11b (No Longer Supported) Ongoing Implementation of New Design Criteria 37
Review of Issues and Resolutions 38
Wireless Improvements Issue: Wireless is Slow Increased Overall Cell Throughput by Reducing Cell Size Provides client with best opportunity for highest MCS Rate Removed Opportunity for Hidden Node Issue Limit Dynamic Rate Shifting to Upper MCS Rates Migrated Clients to 5GHz Decommissioned TKIP Encryption Option 39
Wireless Improvements Issue: Wireless Comes and Goes Issue: My notebook Works but Not My iphone or ipad Removed Asymmetric Power Issue Reduced Cell Size and Transmit Power Cell Diameter Appropriately Designed Cell Matches Client s Transmit Range 40
Wireless Improvements Issue: Disconnects When Moving to a New Location AKA Sticky Client Implemented Custom RF Profiles Deployed in Specific WLAN Groups Designed for the Environment Attempt to Help/Force Client into a Roaming Decision On the Client Side (Desktop Support Team) Research Known Issues with Manufacturer & Chipset Use Manufacturer Recommended Driver Provide the Best Opportunity for Wireless Client to Make Best Decision 41
New Design Model Small Cell Diameter and Low Transmit Power Accommodate Low Powered Devices Increase Wireless Client Capacity per a Given Area Implement Channel Bonding on All New Deployments Increase Client Throughput Promote Clients to 5GHz Reduce the 2.4GHz Client Population Control Number of SSIDs Broadcast SSIDs where needed RF Profiles and AP Groups RRM Self Healing, Self Optimizing Mitigates Interference 42
Wireless Health Analysis Cell Edge: 67 dbm (allows ~20% overlap) Co Channel Separation > 20dB Minimum 5 GHz Channel Separation > 100MHz SNR >= 20 db Minimum SNR >= 30 db Preferred If Supporting Voice Channel Utilization < 30% CRC Rate < 10% If Supporting Data Only Channel Utilization < 40% CRC Rate < 15% 43
Wireless Analysis Tools Site Survey Application Spectrum Analyzer Wireless Analysis Application Wireless Packet Capture Ixia IxChariot 44
Questions? 45
Thank You Steven Shelton sheltonws@ornl.gov 46
https://d2cpnw0u24fjm4.cloudfront.net/wp content/uploads/802.11n and 802.11ac MCS SNR and RSSI.pdf 47
Limited MCS Rates Example 48