aruba community - wlan design and troubleshooting

ATMOSPHERE 2014AIRHEADS@

Advanced RF Design & Troubleshooting Blake Krone June 2014

CONFIDENTIAL © Copyright 2014. Aruba Networks, Inc. All rights reserved

2 #AirheadsConf

ATMOSPHERE 2014AIRHEADS@Agenda

Who Am I? Past and Present Design Goals Design, Design, Design Love Thy Patch Demystifying RF With Tools

3 CONFIDENTIAL © Copyright 2014. Aruba Networks, Inc. All rights reserved

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Who Am I?


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ATMOSPHERE 2014AIRHEADS@Who Am I?

Blake Krone [email protected] @blakekrone http://NSAShow.com All around tech junkie, programmer, RC junkie CWNA, CCIE #31229 (Wireless)


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Past & Present Design Goals


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ATMOSPHERE 2014AIRHEADS@Pre #GenMobile Design Goals

Green = Good = Coverage

•  Designed for Coverage –  Full bars, devices were connected

•  Large cells, high power

•  Less than 2 devices per person –  Laptop –  Smartphone


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ATMOSPHERE 2014AIRHEADS@#GenMobile Design Goals

Green = Good = Coverage – no longer applicable!

•  Designed for Capacity –  I’m connected, but can I send/receive with 100 other

devices?

•  Small cells, lower power

•  More than 4 devices per person –  Laptop –  Smartphone –  Tablet –  Wearables


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ATMOSPHERE 2014AIRHEADS@How To Reach the Goals?

RF is like Black Magic, the Dark Arts, etc…

Or Is it?

•  Design, Design, Design

•  Troubleshooting Accordingly


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Design, Design, Design


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ATMOSPHERE 2014AIRHEADS@About RF Design

Key to a Great Design

•  Airtime –  Be fair and play fair

•  SNR

–  Not just RSSI!

•  Frequency & Channel Reuse –  Clients are like 2 year olds, their way or the high way!

•  Don’t Forget the Backbone –  It’s never the RF, it’s those pesky servers!


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ATMOSPHERE 2014AIRHEADS@Airtime

Basic Design •  RSSI Good •  Legacy Data Rates

On •  Longer Waits to Get

On •  Longer Time On

Great Design •  RSSI Great •  Legacy Data Rates

Off •  Get On and Off

Quickly


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ATMOSPHERE 2014AIRHEADS@Airtime Example

Download/Upload 1Mb File •  6Mbps Client – 1.33s •  36Mbps Client – 0.22s

How Many Users per 5 Minute? •  6Mbps – 230 •  36Mbps - 1363


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ATMOSPHERE 2014AIRHEADS@Airtime Calculations

Mode (20Mhz, 1ss – 3ss)

Receive Sensitivity per Chain (dBm)

SNR (dB) @ -95 dBm Noise Floor

Legacy 802.11a/g 54 Mbps

-75 20

802.11n HT20 MCS7/15 65 – 216 Mbps

-71 24

802.11ac VHT20 87 – 289 Mbps

-65 30

Great Resource for Calculating Device Airtime: http://www.revolutionwifi.net/p/downloads.html - WLAN Capacity Planning Overview and Worksheets.pdf


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ATMOSPHERE 2014AIRHEADS@SNR

SNR is More Important Than RSSI!

•  RSSI is how strong I hear AP –  Doesn’t imply quality

•  SNR is relationship to noise floor

–  Changes per site per area per day per environment etc


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ATMOSPHERE 2014AIRHEADS@SNR Example

Take datasheet values for AP-220 •  802.11n HT20 •  MCS7/15 •  65 – 216 Mbps •  24 SNR Perfect world with -95 dB noise floor says -71

dBm RSSI. Reality says more like -65 dBm or better!


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ATMOSPHERE 2014AIRHEADS@Frequency & Channel Reuse

Use As Much Frequency As You Can

•  2.4GHz –  Yes it’s dirty and bloated, but we need it

•  5.0GHz

–  Don’t be shy, client adoption increasing rapidly

–  Just watch out for DFS channels

•  20MHz Channels Might Make More Sense –  We don’t always need insane speed but we do need

channels


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ATMOSPHERE 2014AIRHEADS@Frequency & Channel Reuse

•  Lower the Power –  Just cause an AP does 200mW doesn’t mean you should

allow it –  Reduce the cell size to allow more channel reuse

•  Steer When You Can - Client Ultimately Calls the Shots –  If it thinks 2.4GHz is better it’ll join there –  Always assume a roaming issue will occur


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ATMOSPHERE 2014AIRHEADS@Don’t Forget Backbone

RF Still Needs Wires & Core Services

•  DHCP –  Active clients vs Associated clients. Makes no difference,

they still use an IP if just associated. –  Short lease times for guest – example football game is 3

hours, use 3 – 4 hours for lease

•  AAA Scaling

–  Account for Web/RADIUS server calls per second for portals

–  Better yet, forget about the portal!


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Love Thy Patch


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ATMOSPHERE 2014AIRHEADS@Love Thy Patch

Learn From Interior Lighting Engineers

•  Flood or Spotlight? –  While a floodlight might work is it the right solution? –  Paint the area with RF like you would light.

•  Omni or Patch? –  Same rules apply here as they do with lights. –  More precisely control signal spread


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ATMOSPHERE 2014AIRHEADS@Patch Example

How would you cover a long corridor that never seems to end and provide density coverage?


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Absolutely Not! Omnis Maybe


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Use patch antennas alternating down a hallway.

Signal goes where you

want, antennas accessible.


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Demystifying RF With Tools


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ATMOSPHERE 2014AIRHEADS@Demystifying RF

A screwdriver makes a decent hammer, but a hammer is better.

•  Survey Tools –  Site Survey Software –  Spectrum Analysis Software

•  Packet Tools •  Testing Devices


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ATMOSPHERE 2014AIRHEADS@Survey Tools

Ekahau Site Survey •  Predictive Design •  Active (AP on Stick)

Survey •  Post Validation

Survey •  Proxim 8494

Adapters


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ATMOSPHERE 2014AIRHEADS@Spectrum Analyzer

Metageek Chanalyzer Pro

•  USB Form Factor •  2 x Wi-Spy DBx for

2.4 & 5GHz simultaneous

•  Easy to Use •  Report Builder


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ATMOSPHERE 2014AIRHEADS@Packet Capture

Metageek Eye P.A •  Compatible with

pcap files •  AirPcap direct

capture •  Visualizes the

packet flows


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ATMOSPHERE 2014AIRHEADS@Testing Devices

Fluke AirCheck •  Rugged handheld

test device •  Consistent

readings •  Fast startup •  Auto Test tool •  Import / Export data


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ATMOSPHERE 2014AIRHEADS@Testing Devices

Fluke LinkSprinter 200 •  Extremely portable •  PoE, Link, VLAN,

DHCP, Internet testing device

•  WiFi hotspot for advanced mobile display


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Questions


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DISCUSS: #AirheadsConf


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