Advanced RF Design & Troubleshooting

Advanced RF Design and Troubleshooting
Ken Peredia and Clark Vitek
March, 2014

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© Copyright 2014. Aruba Networks, Inc.
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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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Goals
• 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
Let me on

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Basic
– 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
Mode
(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
see?

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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 ch
TotalChannelCapacity
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
Total
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
36 52
4060
44 64 48
56
-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
6
6
111
11
1
-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
GHz
-Active device
bandwidth capacity
not met increased by
channel reuse
(requires rework of 2.4
GHz objectives)

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Design Example #2
Large 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
Design Example #2

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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
Design Example #2

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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 Strategy
Example Catwalk Coverage

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Outer Catwalk Example Coverage: -65 dBm from 4 APsOuter Catwalk Coverage
ANT-2x2-2314/5314

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Example Inner Catwalk Coverage
ANT-2x2-2314/5314

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Stadium“30 Degree Sector”
Antenna Comparison
Other

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Stadium 30 degree Sector
Antenna Comparison
Other

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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
basis

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2013 Capacity Analysis
Per
AP
Per
AP Per AP
Expected
Associations
Active
Devices Associations Active Devices
Estimated
Uplink
Area Seats APs 2.4 GHz 5 GHz Total
2.4
GHz
5
GHz Total
2.4
GHz 5 GHz Total
2.4
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
stats
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

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Configuration – Other Profiles
Items in italics are ArubaOS default

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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

Advanced RF Design & Troubleshooting

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