Advanced RF properties to improve Enterprise WLAN

Advanced RF properties at your disposal to
improve Enterprise WLAN deployments and
spectrum quality
BRKEWN-3010
Jim Florwick
Platform TME – Wireless
CiscoLive 2014 Milan

Cisco and/or its affiliates. All rights reserved.Presentation_ID Cisco Public
House Keeping Notes – Wednesday April 16, 2014
Thank you for attending Cisco Connect Toronto 2014, here are a few
housekeeping notes to ensure we all enjoy the session today.
 Please ensure your cellphones are set on silent to ensure no one is disturbed
during the session
 I will take questions during the session, but may ask that your hold it if we’re
ahead of the material
2

What We’re Going to Cover
3
 How important is the RF?
– The Physical Layer – we will focus exclusively on the physical
 Site Survey
– When was the last time a survey was done?
 Tools
– A word about tools
– Prime Planner, Ekahau, AirMagnet, Spectrum analysis
 What are your Priorities?
 RRM
– RF Grouping
– Dynamic Channel Assignment
 Tuning – RRM, Client Link, Band Select, HDX – RX_SOP/SmartRoam, RF Profiles
 Summary

By The End of This Session
You should understand
– Where to get information
– How to evaluate that information and use it
– Understand what tools and techniques are available to solve specific
issues
– Use the information presented to create an action plan for change
– Improve your networks capacity and your users lives
4

Wireless Trends- What’s Your Goal?

1999
Wireless Evolution
From Best Effort to Mission Critical
Hotspot System
Management Scalable
Performance
802.11n/OBSS
Self Healing &
Optimizing
802.11acGigabit Wireless
HS2.0
HDX
1999 2005
2007 2010 2013

The changing RF landscape
7
Protocol Date Characteristics Spatial
Steams
20 MHz
Channels
802.11 1997 1,2 Mbps, infra Red, spread and DSSS,
802.11FH 2.4 GHz
1 1
802.11b 1999 1,2,5.5,11 Mbps, DSSS 2.4 GHz 1 1
802.11a 1999 6,9,12,18,36,48,54 Mbps – OFDM – 5 Ghz 1 1
802.11g 2003 6,9,12,18,36,48,54 Mbps OFDM 2.4 GHz 1 1
802.11n 2005 MCS 1-15-23 1-3 SS, OFDM, 20,40 MHz, 2.4
and 5 GHz
1-3 1-2
802.11ac 2012 1-8 SS MCS 1-9, OFDM, 20-40-80-160 MHz, 5
GHz
1-8 1-8

 2013 is the first year we’ve seen higher 5 GHz adoption rates
 CiscoLive and Mobile World Congress - high tech shows –
SuperBowl different crowd 98.5% 802.11n
0.1
38 40
55
29
50
60
99
62 60
45
71
50
40
0
20
40
60
80
100
120
5 GHz
2.4 GHz
98% 802.11n for 2012 and 2013!

Key Reports – Cisco Prime
 Clean Air –
 How much of your spectrum is being used by NON Wi-Fi
devices?
 Client –
 What protocols are your client using?
 Unique Client Summary – should be a frequent
reference
 Device –
 Channel Utilization – how much spectrum do you have?
 Security
 Are Rogue Access points using your spectrum?
 Which AP’s hear them – how loud?
The above reports will tell you what/who is using
your spectrum, how efficiently you are using your
spectrum and how much you have left
9

Deploying with Spectrum in Mind

Deploying with Spectrum in Mind
 Role of site survey is as important as ever—but has evolved
 Evaluate the existing application requirements, available spectrum and
Client types/mix
 Focus should be on fixed infrastructure
– AP placement
– Density is important = capacity
– Protocols supported
– Rates supported
– Interference sources
 Mitigating issues
 Planning tools
Designing for Sustainable Spectrum Management

About Site Surveys
 When was the last time you did a site survey?
– What where the design goals when that survey was done?
– Coverage or Capacity model?
– Client/AP types and technology?
 Technologies Change – how many devices/clients where on your network the
last time you did a survey
 What are your design Priorities? What where they when you last did a survey?
 You don’t know what you don’t know and not all 802.11 technologies are
complimentary – air time rules
12

A Word About Tools
 What you use is less important than how you use it –
 Internal vs external adapters
– Internal adapters – even the same model will have different
antenna arays and placement for different model laptops
– External adapters – can be moved with the application – and
provide consistent results – regardless of the platform used
 Use the same Tool to compare results!
 Recheck results from a known environment with version
updates
 Free Tools – Nothing is Free
How to compare Apples to Apples

What has not changed?
802.11 and Duty Cycle – Channel Utilization – Air Time
 802.11 error recovery is limited - Still
– Retransmit a packet
– Rate shift
 Duty Cycle of RF is logarithmically proportionate to Channel Utilization
 Channel Utilization is Capacity
 Busy network – less interference tolerance
 Less busy – might not even notice low levels of interference
 Bandwidth is like Money – the more you get the more you spend
 At a minimum – you have more users on your network this year than you did
last year – and a lot more than you had 5 years ago….

How does Interference impact Wi-Fi?
Separating the FUD from the Fact’s
 802.11a/b/g/n - CSMA/CA or LBT (listen Before Talk)
 Collision Avoidance – 802.11 very very polite – by design
– CCA
– Collisions
– SNR
 CCA – Clear Channel Assessment
– ED – quick – low power - prone to false positives
– Preamble – takes time – power – less prone to false
 CCA threshold for 802.11b/g is -65 dBm
 CCA for 802.11a is different -65 dBm ED, if true then 20 dB
lower for Preamble interrogation needs to be processed -85 dBm

CCA Blocked or High
802.11n traffic
Video Signal
Video Camera Duty
Cycle
90-100%

How does Interference impact Wi-Fi?
Separating the FUD from the Fact’s
 Collisions - Non Wi-Fi devices do not participate in our CA
mechanism – they have their own
 No respect for Wi-Fi – results in:
– Corrupted packets
– Increased retransmissions
– Increased Duty Cycle
– Less available bandwidth
 SNR – Signal to Noise ratio
High SNR Low SNR

802.11 and Duty Cycle – Channel Utilization
 802.11 error recovery is limited
– Retransmit a packet
– Rate shift
 Duty Cycle of interference is logarithmically proportionate to channel time
available
 Busy network – less interference tolerance
 Less busy – might not even notice low levels of interference
 Bandwidth is like Money – the more you get the more you spend

For a deep dive on CleanAir and it’s best in class
features see –
BRKEWN-3010 Orlando, Fl. June 2013
• Available on CiscoLive365

RRM – Radio Resource Management

RRM—Radio Resource Management
 What are RRM’s objectives?
– To dynamically balance the RF infrastructure and mitigate changes
– Monitor and maintain coverage for all clients
– Manage Spectrum Efficiency so as to maintain the optimal throughput under changing
conditions
 What RRM does not do
– Substitute for a site survey
– Correct an incorrectly architected network
– Manufacture spectrum

RRM Monitors the RF Group
 Continuously monitors dynamic changes in environment
– Collection of statistics and metrics used by DCA, TPC,
and CHDM
– Provides assessment of the overall “RF health” of the network
 Stats/metrics include:
– Noise (e.g., radar, Bluetooth devices, microwave ovens)
– Interference (802.11—rogue APs)
– Signal – (our AP’s)
– Load

How Does RRM Do This?
 DCA—Dynamic Channel Assignment
–Each AP radio gets a transmit
channel assigned to it
–Changes in “air quality” are monitored, AP
channel assignment changed when deemed
appropriate (based on DCA cost function)
 TPC—Transmit Power Control
–Tx Power assignment based on
radio to radio pathloss
–TPC is in charge of reducing Tx on some APs—
but may also increase Tx by defaulting back to
power level higher than the current Tx level
 CHDM—Coverage Hole Detection and Mitigation
–Detecting clients in coverage holes
–Deciding on Tx adjustment (typically Tx
increase) on certain APs based on (in)adequacy
of estimated downlink client coverage

RF Grouping Neighbor Messages = OTA – Over The
Air - RF analysis
 Neighbor AP messages are sent every 60
seconds at highest power and lowest
supported data rate
 Neighbor Messages are used by receiving
APs and their WLCs to determine how to
create inter and Intra-WLC RF Groups and
Physical RF Neighborhoods
 Each AP listens for other AP’s neighbor
messages – and if it’s RF Group name
matches – the message is forwarded to it’s
controller and ultimately to the RF Group
leader
 A list is maintained for each AP in the RF
Group of who heard his neighbor messages
and how loud
Neighbor messages are
sent from each AP to
multicast address
01:0B:85:00:00:00

For a deep dive on the concepts of grouping, Neighbor
Discovery, and collection of off channel metrics used in
RRM algorithm’s – please read – Radio Resource
Management (RRM) RF Grouping
• Part of the 7.4 RRM Design Guide presently under revision

RRM—DCA—
Dynamic Channel Assignment
Ensures that available RF spectrum is utilized well across frequencies/channels
Best network throughput is achieved without sacrificing stability or AP availability to clients
34
RF Channel “64”
RF Channel “44”
RF Channel “100”
Analyzes and Optimizes
Channel assignments
Coordinates 20,40, and 80 MHz OBSS
assignments Using OTA measurements
What It Does

 Who calculates DCA
– It runs on the RF Group
Leader WLC
– Decisions on channel assignment
change made on a per AP, per radio
basis
 DCA manages channel
assignments to each AP
– Assigns channels to radios
– Changes the existing assignment on
some radios, if appropriate
 What criterion is evaluated:
– RSSI-based Cost Function that
captures overall interference
(including non-802.11 noise) on a
per channel basis
Monitor=>Access Points=>Detail

 DCA represents each channel using
essentially a compound signal to noise
ratio. This is called a cost metric or
CM.
 Contributions to this metric are
– Signal – Our AP’s TX and RX neighbor
– Noise – Non Wi-Fi interference
– Interference – Managed and unmanaged
rogues
– Load – Cisco Channel Utilization
 You can manipulate what you want to
contribute to the metric – by default
Signal, Noise, and Interference are
selected.
Wireless=>802.11a/b=>RRM=>DCA

• Defaults are generally best
• Avoid Foreign AP Interference
If enabled – places a higher penalty on
rogue devices
Is to encourage DCA to work around the
neighboring AP
Encourages good neighbor borders
Can cause a lot of channel changes if
enabled with a lot of transient rogue
devices – disable if this is the case
• Load – disabled. This accounts for Cisco AP
load only. Can cause a lot of channel changes
in a heavily used network. Wireless=>802.11a/b=>RRM=>DCA

 DCA evaluates the Cost Metric to determine
optimal channels for the network
 The user defined threshold – DCA Sensitivity
Threshold – allows customization of the
algorithm
 The threshold is a Hysteresis to dampen DCA
function
 If sensitivity is medium for 2.4 GHz then in order
for a channel change to be made the new
channel must be 10 dB better than the current
channel or no change will occur.
Version Band Low Medium High
6.0 + 2.4 GHz 5 dB 10 dB 20 dB
5 GHz 5 dB 15 dB 20 dB

DCA Example
 What changes first is the CPCI selection process, randomization
prevents pinning –
 For a given CPCI, calculations permit changing first hop channels
 Second hop channels considered
 Solution is submitted to NCCF
 CPCI and 1st neighbors are removed
from the CPCI list
 Next randomized CPCI is selected

 Selection of 20 MHz – all AP’s set to 20 MHz
 Selection of 40 MHz – All 40 MHz capable AP’s set to 40 MHz
– 20 MHz only AP’s will remain 20 MHz
 Selection to 80 MHz – all 80 MHz capable AP’s set to 80 MHz
– Others – 802.11n at 40 MHz, and 802.11a at 20 MHz
Wireless=>802.11a/b=>RRM=>DCA

 Using the example of an 80 MHz OBSS – (Overlapping BSS)
 AP-AC wins contention on my primary channel and will send data on that
channel and 3 other bonded channels.
 The VHT header tells all 802.11AC stations that I’m using an 80 MHz OBSS and
even tells what 20 MHz sub channels it’s using
 But What of the lowly 802.11a station, or the 802.11n (HT) station who don’t
speak 802.11ac and it’s fancy VHT language?

 Never Fear – LBT (Listen before Talk) to the rescue – CCA! (Clear Carrier Assessment)
 CCA thresholds where adjusted in the 802.11ac specification to allow Overlapping BSS
and IBSS stations coexist by adjusting the contention requirements for Sub Channels
 In the table above – you can see that all 3 protocols have equal contention on the primary.
 Any primary operating within a secondary 20 or 40 will loose contention
 Any secondary 20 operating in a secondary 40 will win contention over other secondary's!
Protocol Primary Secondary 20 MHz Secondary 40 MHz
802.11a -82 dBm
802.11n -82 dBm -62 dBm (20 dB liberty)
802.11ac -82 dBm -72 dBm (10 dB liberty) -76 to -79 (3-6 dB liberty)

 The 802.11AC specification allows for an RTS to be sent on all sub channels as
an 802.11a frame, and expects a CTS if a primary channel is assigned to one of
the sub channels
– The specification says that RTS is optional, but CTS is mandatory
– Will clients implement this?
Even when the secondary40 channel is
occupied by a transmission, an 80 MHz
11ac AP can select to transmit 40 MHz
for the time being, thus the system still
fully utilizes the channel. (The
placement of the primary on which half
of the secondary40 is no longer a
critical concern.)

 The level of constructive coexistence
among OBSS’s is based on these
criteria:
– Fair channel access
– Fairness between 11ac and 11ac is
neutral
 Fairness between 11ac and legacy
(11n and 11a)
 Number of hidden nodes decreases
 Number of collision decreases
 Overall performance and efficiency
increases

In simulations and analysis, the general level of constructive coexistence
decreases between two OBSSs in the order for these possible scenarios:
1. Primary and secondary20 channels mismatched
2. Primary channel on secondary40 or secondary 80 channels
3. Primary channels aligned

Cisco and/or its affiliates. All rights reserved.Presentation_ID Cisco Public 49
Channel 40,44
802.11n 802.11ac
Channel 48,52,40,44
-54 dBm
120 Mbps
50 Mbps
-64 dBm
50 Mbps
120 Mbps
-74 dBm
220 Mbps
10 Mbps
-84 dBm
210 Mbps
90 Mbps

Channel 48,52
802.11n 802.11ac
Channel 48,52,40,44
-54 dBm
120 Mbps
50 Mbps
-64 dBm
120 Mbps
50 Mbps
-74 dBm
120 Mbps
50 Mbps
-84 dBm
200 Mbps
90 Mbps

How does DCA keep track of all the other AP’s and the channels their using?
 Remember the DCA cost Metric?
 Add Bias to a given channels CM to reinforce good channel solutions
 Bias values match the given 3 performance scenarios – B1, B2, B3 for our AP’s
and R1, R2, R3 for rogues increasing the bias for lower coexistence values
 For instance - Not using Channel 60, and the resulting CM for channel 60 is
+128!

 DCA will search for a 20, 40, 80 MHz solution for each AP
– and only populate up to the AP’s capabilities
 DCA channel Width settings determines the DCA mode
 The AP Type determines the possible Channel Widths
 DCA search’s for 20, then 40, then 80MHz channel widths
and presents the solution as a grouping of cost metrics
 Metrics for the same channel– can and will change for the
channel width solution searched due to BIAS settings

Airewave Director: metrics20 After Normaliz( 52, -81.68)( 56, -74.51)( 60, 128.00)( 64, -55.38) <snip>
*RRM-MGR-5_0-GRP: Sep 23 15:59:38.556: 64:d9:89:42:29:50 <snip>
Note – there are 3 similar but different answers - It is
3 different questions with 3 different set’s of rules. What determines
Which answer is used?
*RRM-MGR-5_0-GRP: Sep 23 15:59:38.551: 64:d9:89:42:29:50 Airewave
Director RRM Chan Assignment Mode: 2 Lrad Capability: 2 DCA Channel Width:
2 0= 20 MHz
1 = 40 Mhz
2 = 80 Mhz

 802.11ac and 80 MHz - lets see what this baby can do!
 Likely already a full spectrum (the network was already there
right?)
– Using DFS channels already?
– Already have 40 MHz assigned for 802.11n?
 Likely DCA is at medium Sensitivity 10 dB Hysteresis
– Changing Channel Width – is a major change
– Expanding some channel Width’s to 80 Mhz and others to 40 Mhz is not trivial
– Don’t limit the possible solutions to within 10 dB!

5 GHz 20/40/80/160 MHz Channels
56
36
40
44
48
52
56
60
64
68
72
76
80
84
88
92
96
100
104
108
112
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120
124
128
132
136
140
144
149
153
157
161
165
169
173
177
181
20
40
80
160
US
Europe
20
40
80
160
Indi
a
20
40
80
160
China
Existing Channel New Channel
UNII-2UNII-1 NEW! UNII-2 NEW! UNII-2 UNII-3 NEW!
5250
MHz
5350
MHz
5470
MHz
5725
MHz
5825
MHz
5925
MHz

Feature Benefit
256-QAM 5/6 coding 30% faster – at any #ss
Rate vs Range – significantly
increased
Faster speeds – further from the AP –
faster overall cell – less airtime
consumed
802.11ac – ONLY 5 Ghz Finally,Seriously, overdue….
Optional 802.11n Specifications
Removed – discarded - junked
Less implementation choices = less
client variability
Manufacturers already committed to
implementation
Many already delivering product

 Do you have spectrum available for 80 Mhz?
– Evaluate by Regulatory
 Do you use 40 MHz for 802.11n AP’s today?
– If not – why not?
– Does it make sense to use 80 MHz?
 Plan the Implementation – and understand that this is a Major
Change to your existing spectrum plan
 Let DCA help you

Best Practices for Implementing 802.11ac
 Decide what Channel Width you
will use
 Implement new hardware –
 Initialize DCA in Startup Mode –
FROM the RF group Leader(s)
 Remember – all of this is 5 GHz
only!
7.3 and above – from the CLI - Config 802.11a/b channel global restart

RX Utilization 36
TX Utilization 7
Channel Utilization 96

Channel Utilization – what is it?
 Channel Utilization is the physical – and the logical Air Time consumed
 It is – physical signal in the air above CCA
 It is - the logical CW and NAV
 It is – All RF in the air – ours as well as rogues – if it’s 802.11 and we hear it –
it counts
 It is the metric which represents the AP’s TX_op in the current channel
 And- it represents the whole channel – not the AP’s utilization
Root Cause for Channel Utilization must be isolated
– Self Interference – SSID’s, Data Rates, AP isolation vs Density – control with
Configuration
– Non – Wi-Fi interference – possibly controllable
– Rogue Devices/networks – configuration management

Spectrum Is a Shared Finite Resource
Understand Protocol Selection 802.11 b/g/a/n/ac
and Duty Cycle—Important? Why?
75
0
500
1000
1500
2000
2500
3000
3500
6 12 36 54 130 173.3 300 540
64 Bytes
128 Bytes
256 Bytes
512 Bytes
1024 Bytes
2048 Bytes
Data Bytes
Time μS
Data Rate - Mbps
HT/VHT 40
3ss
HT/VHT 20
2ss
OFDM

Every SSID Counts!
76
 Each SSID requires a separate Beacon
 Each SSID will advertise at the minimum
mandatory data rate
 Disabled – not available to a client
 Supported – available to Existing
associated client
 Mandatory – Client must support to
associate
 Lowest mandatory rate is beacon rate
 Highest mandatory rate is default mcast
rate

AP-3700 – Supports Client Link 3.0
So why Client Link 3.0?
• ClientLink’s beamforming capability unlike the standard improves
the SNR for all clients including legacy clients.
• Because this technology does not depend on any client-side
hardware or software capabilities, it works with mixed-client
networks seamlessly with 802.11ac and 802.11a/n clients that co-
exist on the same Access Point
• Standards based beamforming only works with .11ac clients and
most of them do not support it at this time.
A real “purpose built” AP is one that can support Cellular modules, Monitor radios, Wave-2
upgrades and can future protect your investment.
We also didn’t “accidently” build the AP-3700 you might say “purpose built” includes
ClientLink innovation, Spectrum Intelligence and Quality RF performance from the center
of RF Excellence located in Richfield Ohio… Yes QUALITY DOES MATTER… 

52.4
Optimized RF Utilization by Moving 5 GHz Capable Client Out of the
Congested 2.4 GHz Channels
802.11?
BandSelect
Access Point Assisted 5 GHz Band Selection
Dual-Band Client Radio
2.4/5GHz
Discovery Probes
Looking for AP
Discovery
Response
Solution
BandSelect directs clients to 5 GHz optimizing RF
usage
 Better usage of the higher capacity 5GHz band
 Frees up 2.4 GHz for single band clients
Challenge
Dual-Band clients persistently connect to 2.4 GHz
 2.4GHz may have 802.11b/g/n clients causing
contention
 2.4GHz is prone to interference

RF Profiles to Manage your RF Configurations
 RF Profiles work in Conjunction with AP Groups (beginning in release 7.2)
 You can create separate RF profiles for both 2.4 and 5 GHz
 1 profile for each band (802.11a/802.11b) can be assigned to an AP group
 What can be adjusted within a profile continues to expand with DCA expected
in version 8.1
 Today
– 802.11 data rates
– TPC Power Threshold and Min max Power settings
– DCA (in 8.0!)
– Coverage hole algorithm settings
– High Density – HDX configurations RX_SOP, Client Limit, Mcast data rate
– Client Distribution
82

RF Profiles – RRM – Create
 RF Tuning parameters can be
applied through profiles assigned in
AP groups
 2 Profiles per AP group – 1 ea. 2.4
and 5 GHz
 Profiles must be applied on ALL
WLC’s from which AP’s will be
assigned (same as AP Group)
 Permits control of granular groups
of AP’s
 We love it…
83
Wireless=>RF Profiles

Profiles : Granular Control
84
Data Rates
Load Balancing
TPC, DCA,Coverage Hole
High Density

Profiles – Applied Through AP Groups
87
 Create Profiles
 Create or edit AP Groups
 Apply Profiles (2.4/5 Ghz)
to AP groups
 Assign AP’s

HDX – High Density Experience

Bigger Cells, More Users
Control Cell Size by Data Rate selection and RX tuning
 The Cell is the unit of bandwidth
 Manage the per user bandwidth
by managing the size of the Cell
 RF Profiles allows you to treat 2
groups of AP’s differently in
order to tune the deployment to
peak performance
 Here are some additional tools
to manage higher density
encounters and win
90
167
PAX
40 PAX/per

When Coverage meets Capacity
 You’ve eliminated several SSID’s
 You’ve raised your data rates to fit
the coverage areas
 You’ve added AP’s to areas where
additional coverage is needed…..
 Channel Utilization won’t come
down – and power is already at
the lowest settings
Welcome to High Client Density
91

RX-SOP – Receive Start of Packet threshold
92
 The AP has a threshold on each radio at which it logically honors a packet
 Below this threshold – it is treated as noise
 Above this threshold it is treated as Wi-Fi – and all the logical utilization that
goes with that
 When you start to add more channels for capacity – you will tune data rates
and placement to decrease your transmit footprint
 Use Antenna’s to focus your receive sensitivity
 RX-SOP allows you to tune the receive cell size to match the Tx cell size
 If you hear less – you will have less Channel Utilization

RX-SOP – (Receive - Start of Packet) – What is it?
 Receiver Start of Packet Detection Threshold (RX-SOP) determines the Wi-Fi
signal level in dBm at which an AP radio will demodulate and decode a packet.
 The higher the level, the less sensitive the radio is and the smaller the receiver
cell size will be
 By reducing the cell size we can affect every thing from the distribution of clients
to our perception of channel utilization
 This is for High Density designs – and requires knowledge of the behavior you
want to support
 A client needs to have someplace to go if you ignore it on the current cell
WARNING – This setting is a brick wall – if you set it above where your clients are being
heard – they will no longer be heard. Really.

RX-SOP – Why Use It?
 Reduce sensitivity to interference and noise – reduce Channel Utilization
 It sharpens the cell edge – we will hear what we intend to cover
 Caveats –
– You can significantly reduce coverage
– You can make it impossible for intended clients to associate or communicate with your
AP
 This feature is to be used in conjunction with a known design to solve a specific
problems when you understand the coverage and usage of the network by the
users
 RX-SOP is available at the global level as well as in RF profiles – Strongly
recommend applying only through profiles – to solve specific problems with
HDX

RX-SOP configuration
 Settings High, Medium, Low,
Auto
 Auto is default behavior, and
leaves RX-SOP function linked
to CCA threshold for automatic
adjustment
 Most networks can support a
LOW setting and see
improvement
 This affects all packets seen at
the receiver

Optimized Roaming- help for clients that are not so
smart….
97
Optimized Roaming Disabled Optimized Roaming enabled

Optimized Roaming
 Sets a threshold RSSI value and or
Minimum Data rate that a client will
be sent a Disassociate
 Developed to support Cellular Hand
Off
 Global configuration of 4 Parameters
available
– Enable/Disable
– Interval (seconds)
– Data Rate threshold
– RSSI threshold configured through
Data CHD
 Trigger is Pre-Coverage hole event –
set under CHDM config

Optimized Roaming configuration
 Enable/Disable – Global command
 Interval = #seconds between checks at the
Radio
 Data Rate threshold-
 Used in conjunction with RSSI threshold, if
set is a gating function where both data
rate and rssi must be true for action –
default is disabled
 RSSI threshold – set through data RSSI
config in Coverage at the global level, and
under RRM in RF Profile

Optimized Roaming Logic
Data RSSI Data Rate Result
True Disable (default) Disassociate
True False No Action
True True Disassociate
• Uses CHDM Data RSSI for trigger Alone – decision
is based on RSSI seen at the radio
• Combined with Data Rate – provides additional
gate for action – and preserves CHDM Function
• If Used with Client Low RSSI check, and the higher
of the two values is used (with 6 dB hysteresis).

Optimized Roaming & Low RSSI feature “WARNING”
 Low RSSI check is a completely separate feature – and sets a low RSSI
threshold which a client must be above to associate to the AP
 Optimized Roaming has a 6 dB hysteresis built in to prevent thrashing
 i.e. If Optimized roaming is set to -75, then to rejoin the AP the clients signal
must improve to -69 dBm
 The logic checks low RSSI – AND Optimized roaming before allowing a client
to Join – and both must pass

For a deep dive on High Client Density design practices
see BRKEWN-2019 RF design for the Mobile Device
Explosion 2013 CL Orlando
• Available on CiscoLive365

Summary
 Evaluating what the goal of your network is on a regular basis will enable you
to make better design decisions
 Good tools make and defend good decisions
 Eliminating spectrum hogs should be first priority – strongly consider
eliminating anything not OFDM all together (Legacy 802.11b)
 Understand how RRM gathers information and makes it’s decisions
 Allow RRM DCA to do it’s job – best practice to restart DCA after major
changes to numbers, types, placements of AP’s
 Not all your coverage zones have the same needs – use RF profiles!
104

Links/References
 Cisco 802.11n Design and Deployment Guidelines
 Cisco High Density Wireless Lan Design Guide
 Cisco Client Link White Paper
 Client Link testing – Miercom
 Client Link 2 Testing - Miercom Report Cisco 3600e/i
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