Advanced RF Design & Troubleshooting #AirheadsConf Italy

Advanced RF Design & Troubleshooting

Blake Krone

June 2014

CONFIDENTIAL

© Copyright 2014. Aruba Networks, Inc.

All rights reserved2 #AirheadsConf

Agenda

Who Am I?

Past and Present Design Goals

Design, Design, Design

Love Thy Patch

Demystifying RF With Tools

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All rights reserved#AirheadsConf

Who Am I?

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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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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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#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Green = Good = Coverage – no longer applicable!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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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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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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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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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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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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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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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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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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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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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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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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Patch Example

How would you cover a

long corridor that never

seems to end and provide

density coverage?

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Patch Example

Absolutely Not! Omnis Maybe

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Patch Example

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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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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Survey Tools

Ekahau Site Survey

• Predictive Design

• Active (AP on Stick) Survey

• Post Validation Survey

• Proxim 8494 Adapters

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Spectrum Analyzer

Metageek ChanalyzerPro

• USB Form Factor

• 2 x Wi-Spy DBx for 2.4 & 5GHz simultaneous

• Easy to Use

• Report Builder

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Packet Capture

Metageek Eye P.A

• Compatible with pcap files

• AirPcap direct capture

• Visualizes the packet flows

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Testing Devices

Fluke AirCheck

• Rugged handheld test device

• Consistent readings

• Fast startup

• Auto Test tool

• Import / Export data

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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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33

Thank You

#AirheadsConfCONFIDENTIAL


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Advanced RF Design & Troubleshooting #AirheadsConf Italy