Advanced RF Design & Troubleshooting

transcript

Advanced RF Design and Troubleshooting

Ken Peredia and Clark Vitek

March, 2014

CONFIDENTIAL

All rights reserved2 #AirheadsConf

Agenda

Introduction

Design

Troubleshooting

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Advanced RF Design and Troubleshooting

• Our Goals:

–RF needs to be simpler,

• (not advanced or tremendous)

–RF just has to work (Design)

–If it doesn’t work we need to figure it out

and fix it as quickly as possible

(troubleshooting)

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• Simplify RF, design for the best chance of

success, enable quick troubleshooting of RF

issues.

• Presenter’s challenge: Find a common theme we

can present in 90 minutes or less that will

advance all these goals.

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Common Theme for RF

Airtime

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Advanced RF and Airtime

• Design –Provide a stable RF environment that will

minimize the use of airtime for every task

• Troubleshooting

–Use tools that provide airtime related

information to find and fix RF problems

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Advanced RF and Airtime

• The concept of airtime is the tool that

helps us understand advanced RF topics.

• Basic RF (BRF)– Good “coverage”

• Advanced RF (ARF)– Good SNR, good signal strength, + good Airtime!

Advanced RF (ARF) = Airtime + RF

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Advanced RF Design =

Airtime + RF

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Advanced RF Design

• Advanced Design Objectives

1. All client devices can connect reliably to the

network… on the BEST AP that will minimize

impact on available airtime

2. Once connected they can do whatever they want to

do, whenever they want to do it… as quickly as

possible, finish, and open the air for someone else

3. When they move they will roam seamlessly from

one AP to another… with a minimum disruption to

airtime

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Advanced RF Design

1. All client devices can connect reliably to the network…

on the BEST AP that will minimize impact on available

airtime

Let me on

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– Acceptable Signal Strength and SNR in both directions

– Association Capacity

– Network connectivity and capacity (i.e. DHCP, Auth, etc.)• not really RF but often RF is

blamed because symptoms are the same as not meeting above 2 requirements

– Get devices connected to the BEST AP

– Before, during and after connection process minimize impact of any inidividual client on available airtime

– Secret Sauce:• Design network to limit

responses and certain traffic from APs

• Design rate controls for every stage of connection

Advanced

Basic vs. Advanced Connectivity

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Advanced Connectivity

• Step 1: Ensure Solid Coverage with Good SNR

–Goal: Provide highest data rate coverage to all

clients in the intended coverage area,

• Regardless of whether applications expected require

such rates

• Higher Rate = Less Airtime for any task with a “Fixed

Payload”

• This includes ALMOST all kinds of traffic,

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– Impact of Rates on Airtime is very significant at all stages of

connectivity: pre-association, association, and connected

– Example: Connected

• Time required to download/upload 1 Mbyte

•@6 Mbps = 1.3 secs

•@36 Mbps = 0.22 secs

• Users that can download/upload a 1 Mbyte page every 5 minutes

• @6 Mbps = 230

• @36 Mbps = 1363

– Any single 802.11 channel can support an increase in page loads

directly proportional to the client connection rate (6x in this

example)

Advanced Connectivity : Rates

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• To achieve High Data Rates requires strong

signal strength and high SNR

• Example: (from AP-220 series datasheet)

Advanced Connectivity : Coverage

(20 MHz, 1ss – 3ss)

Receive Sensitivity

per chain (dBm)

SNR (dB)

(implied, -95 dBm NF)

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

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• Common design practice of -65 dBm (~30 SNR)

is adequate is many situations to achieve

highest possible rates in all 20 MHz modes

(legacy, 11n, and 11ac)

• The corresponding throughput achieved is

based on the “Channel Capacity” and may have

to take into account an increased noise floor or

co-channel/adjacent channel AP interference

• BUT--- Wouldn’t it be a lot better if all clients

were associated at 54 Mbps and higher instead

of some at 54 and others at lower rates, i.e. down

to 6 Mbps by default in legacy 802.11a?

Advanced Connectivity : Coverage

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Design Guidance

Aruba Networks produces a library of

Validated Reference Designs

The High Density (HD) WLANs VRD

covers ultra high capacity spaces

such as auditoriums, arenas,

stadiums and convention centers

The recommendations have been field

proven at dozens of customers

VRDs are free to download from

Aruba Design Guides web page:http://www.arubanetworks.com/VRD

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Design Considerations –Common Space

• Seating Capacity: The number of people in the space

• Size: Physical size of space that needs coverage

• Device count: Number of expected devices, may be more than seating capacity

• Device Capability: 2.4 or 5 GHz, 802.11n MIMO, etc.

• Device State: Sleep mode, Associated but idle, Actively sending/receiving data

• Application Bandwidth: For Active devices, how much throughput is really needed?

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Design Steps: RF Coverage

Step 1: Design RF Coverage

to achieve High Rates

Coverage should be designed for

the highest data rates (i.e. 54

Mbps+).

This requires strong signal

coverage (-65 dBm) to be provided

in all areas.

Aruba VisualRF, or other predictive

tools (Airmagnet, Ekahau) are all

good tools for this stage of the

design.

Example: 288 seats, 1 AP

covers almost entirely at -65

dBm. (green area)

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Step 2: Determine Capacity required for both 2.4

GHz and 5 GHz

a. Association Capacity – based on number of devices that will

need to associate. Typically all devices that are expected in the

environment will be included in this capacity requirement

(laptops, phones, etc.). Association capacity is typically larger

than seating count for auditoriums.

b. Active Capacity – the number of devices expected to not be

in sleep mode or “passive” association (associated but not

sending/receiving data).

c. Throughput Capacity – based on the expected applications,

how much throughput is needed to be delivered both on wireless

and wired uplinks.

Design Steps: Capacity Analysis

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• As an example, we will use the 288 seat

auditorium we saw previously needed one AP for

-65 dBm coverage

• The next step is to calculate the required

association capacity

• The assumptions shown on the following slides

are based on a “classroom” type setup

Step 2: Capacity Analysis

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Step 2: Capacity Analysis

2a: Calculate Required Association Capacity

Typically for this type of auditorium we will assume every user has 2

devices that will get used during the conference, i.e. a laptop and

smartphone

Association Capacity Required = 2 Devices x Seats =

= 2 x 288 seats = 576 Devices

We must also consider the frequency capability of the devices:

Laptops: Typical 80% are 5 GHz capable

Smartphone: Typical 30% are 5 GHz capable

Net Result :

5 GHz: (288*0.8)+(288*0.3) = 316 devices on 5 GHz

2.4 GHz: (288*0.2)+(288*0.7) = 260 devices on 2.4 GHz

Access points have a limit of 255 maximum associations

per radio (2.4 or 5 GHz).

Based on the above capacity analysis we see we will need

at least 2 Access Points to meet the needed Association

Capacity.

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Step 2: Capacity Analysis (continued)

2b Active Device Capacity Analysis

• Once the AP count to meet required association capacity is known, we need to check that AP count against the anticipated “Active User” needs

• There are a variety of adjustments that can be made to estimate the ratio of “Active” users vs “Associated”

• In this classroom example, typically user is one device active, with the second device is likely to be associated but not active or in sleeping mode. Therefore, 50% of devices would be typically assumed to be “Active” (i.e. sending/receiving data, not sleeping or idle) for this throughput analysis.

• However, in a conference center it is not unusual at times for nearly all laptops to be active concurrently.

• Therefore, for this active capacity analysis we will assume all laptops, but only 50% of smartphones are active at any time.

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Active Capacity Analysis

Hall Associated

Devices

Active

Laptops

Active

Smartphones

Total 576 total 0% idle 50% idle

2.4 GHz 260 total =57 active

(same as associated

count)

=101 active

(50% of associated

count)

5 GHz 316 total =230 active

(same as associated

count)

=43 active

(50% of associated

count)

Consider likely idle devices

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Active Device Analysis

• After estimating the active device counts, the

required capacity depends on what we want the

clients to be able to do (bandwidth)

• To start, we need to pick a target bandwidth. This is

the number if all active clients ran speedtest at the

same time, what minimum would we want them to

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Total Channel Capacity AP-125

* This point shows 40 active 802.11n HT20 clients can sustain > 1.2 Mbps each on a single channel

50 Mbps/40

= 1.25 Mbps

18 Mbps/20

= 0.9 Mbps

30 Mbps/20

= 1.5 Mbps

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Target Bandwidth per Client

Max 40 per 5 GHz, 2ss laptops

= 1.2 Mbps

2.4 GHz smartphone target max 20, ~1 Mbps

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Step 2: Bandwidth Capacity Analysis

Band Active

Laptops

Active

Smartphones

Active

Devices

Required Channels

2.4 GHz 57 101 158 =(158/20)=8

5 GHz 230 29 259 =(259/40)=7

The above channel counts provide the number of radios

needed to maintain the target active client capacity (target

bandwidth) per channel.

Problem: Only 3 non-overlapping channels in 2.4 GHz!

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Step 3: Channel Reuse Analysis

• There are 22 available non-overlapping channels in the 5 GHz frequency range.– Channel reuse in a single open space is not required in MANY

situations

– Recommendation: Deploy the needed number of APs possible based on the 5 GHz channel count. In the example 288 seat auditorium we could increase the per user available bandwidth on 5 GHz by deploying more APs up to the available channel count. (assuming no overlap from adjacent rooms)

• There are only 3 available non-overlapping channels in the 2.4 GHz frequency range– Based on need for capacity of 7 Channels, channel reuse is suggested

– Recommendation: Plan and deploy based on channel reuse 2-3 times per channel but consider reducing to no channel reuse if active clients on 2.4 GHz are fewer than predicted.

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Design Example, 5 GHz Coverage

44 64 48

-60 dBm

-55 dBm

-65 dBm

8 APs meets:

-Coverage

-Required Association

Capacity

-Required Active Device

Capacity

-No channel reuse

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Design Example, 2.4 GHz Coverage

-55 dBm

-60 dBm

6 of 8 APs active

(vs. 3)

Meets:

-Coverage

Requirement

-Association Capacity

-Active Device

capacity not met

based on design

parameters in 2.4

-Active device

bandwidth capacity

not met increased by

channel reuse

(requires rework of 2.4

GHz objectives)

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Design Example #2Large Public Venue (LPV)

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• Typical LPV example:

– 20,000 Seat Indoor Arena: One large RF space

• Design Goals (repeat)

1. All client devices can connect reliably to the network… on

the BEST AP that will minimize impact on available airtime

2. Once connected they can do whatever they want to do,

whenever they want to do it… as quickly as possible,

finish, and open the air for someone else

3. When they move they will roam seamlessly from one AP to

another… with a minimum disruption to airtime

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• LPV Design Process

– Step 1: Provide solid coverage to every seat (-65

dBm in both 2.4 GHz and 5 GHz bands), even

when crowd is present

– Step 2: Capacity Analysis

• Association Capacity

• Active Device Capacity

• Bandwidth Considerations

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LPV RF Coverage

• Several Strategies available for providing good

coverage

• The following photos show some examples

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“Under-Seat” Installation

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“Under Concrete” Installation

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Under Concrete Example

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Coverage Strategy – Overhead Narrow Beam Antennas

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Catwalk Installation Example

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Bowl Catwalk StrategyExample Catwalk Coverage

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Outer Catwalk Example Coverage: -65 dBm from 4 APs shownOuter Catwalk CoverageANT-2x2-2314/5314

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Example Inner Catwalk CoverageANT-2x2-2314/5314

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Stadium“30 Degree Sector” Antenna Comparison

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Stadium 30 degree Sector Antenna Comparison

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Under Concrete: -50 dBm

45Aruba Confidential

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Under Concrete: -55 dBm

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Under Concrete : -60 dBm

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Capacity Analysis

• For a large public venue, it is helpful to use

manifest information to analyze association and

active user capacity on a section by section

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2013 Capacity Analysis

AP Per AP

Expected

Associations

Active

Devices Associations Active Devices

Estimated

Uplink

Area Seats APs 2.4 GHz 5 GHz Total

GHz Total

GHz 5 GHz Total

GHz 5 GHz Total Average (Mbps)

Section 118 734 5 138 46 184 69 23 92 28 10 38 14 5 18 0.490666667

Section 117 1366 9 257 86 343 129 43 172 29 10 39 14 5 19 0.508148148

Section 116 1066 7 200 67 267 100 34 134 29 10 39 14 5 19 0.508571429

Section 314 811 5 153 51 204 77 26 102 31 11 42 15 5 20 0.544

Section 321 1002 7 188 63 251 94 32 126 27 9 36 13 5 18 0.478095238

Section 110 378 3 71 24 95 36 12 48 24 8 32 12 4 16 0.422222222

• List Sections and seat counts, and APs planned per

section

• Estimate expected Associations and Active devices

• Per AP Values – Assocations and Devices

• Uplink Estimate – Based on Per Session Usage, 5 min

average (2014 is about double now)

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2013 Capacity Analysis

• Typical per-user bandwidth required (average) is

~20 kbps even in environments where individual

speedtests can support >50 Mbps!

• How? Most Clients get on, get done quickly, get

out of the way for the next guy.

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Example: Moda Center 3/5/2014

Client Session Summary

Sessions: 32146

Unique clients: 4217

Unique APs: 289

Avg session duration: 11 mins

Total traffic (MB): 94107.51

Avg traffic per session (MB): 2.93

Avg traffic per client (MB): 22.32

Avg bandwidth per client (Kbps): 26.75

Avg signal quality: 24.51

Airwave stats:

~20% of capacity

(20,000 seats)

50-60% of this value

typically concurrent

Total Traffic

94 Gbytes

Per session, Per user

Total Traffic

94 Gbytes

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Design Configuration Best Practices

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Design Configuration

• Goal: Maximizing available Airtime by Design

– In previous section we designed for high rate coverage

– Now, lets really take advantage of it!

• Increase Beacon and Basic Rates

– These rates are used for most types of management traffic

including beacons, probe responses, association requests, etc.

– In environments with lots of APs to meet high association capacity

requirements it is critical to increase these rates as high as

possible that will allow clients to still connect

– Increasing these rates has side effect of encouraging clients to

move to their “best AP” since they can not decode higher rate

frames as they get farther away

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• Increase data rates: Once a client is on an AP, require it to use a

high rate to maximize available airtime.

• Use 20 MHz channels in dense environments, or environments

with mixes of clients. At present 4x VHT20 or HT20 channels

appear to still provide more aggregate throughput than a single

80 MHz channel when there are a lot of clients and APs in range.

• Increase max retries: Whenever channel reuse is happening,

potential for collisions increases. Allowing more retries reduces

drops.

• Limit Probe Responses: In environments with lots of

unassociated clients, probe responses can be a significant use

of airtime.

• Limit broadcast and multicast to known applications requiring

these protocols

Design Configuration

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Configuration – SSID Profile

Items in italics are ArubaOS default

values.

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Configuration – Other Profiles

Items in italics are ArubaOS default

values.

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Controller Troubleshooting

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What could affect Airtime?

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Low Client Health

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Investigating Low Client Health

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Investigating Low Client Health

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AP Neighbors

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Using Airtime to Troubleshoot RF Problems

AP Client Table

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Channel Quality

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Channel Quality

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Channel Quality

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Airwave Troubleshooting

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Client Health Dashboard

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Low Client Health

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Low Signal Strength

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RF Capacity

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<1% Time Exceeded Threshold

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AP with High Channel Utilization

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Channel Utilization Revealed

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How many RF Neighbors?

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Mobile Wi-Fi Tools

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Aruba Utilities – Handover Tab

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Aruba AirO – Easy Health Check

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Quick Internet Throughput Test

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Ping & DNS

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Ping & DNS

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Aruba Spectrum Analyzer

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Real Time FFT

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Real Time FFT

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Channel Summary

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3rd Party Analysis

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Airmagnet Spectrum

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Questions?

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91CONFIDENTIAL

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Thank You

#AirheadsConfCONFIDENTIAL

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