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Design and Deployment of Wireless LANs for Mobile Applications
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Design and Deployment of Wireless LANs for Mobile Applications
BRKEWN-2000
Jerome Henry, Technical Marketing Engineer
© 2015 Cisco and/or its affiliates. All rights reserved.BRKEWN-2000 Cisco Public
Agenda• How Much Bandwidth do You Need?
• Determine Cell Size – Shape
• Determine Cell Size – AP Power
• Determine Cell Size – Protocols and Rates
• Determine Cell Size – 20, 40, 80 MHz?
• AP Placement Strategies
• Taking Care of the Roaming Path
• Client and AP 802.11 Optimizations
• Last Words - Troubleshooting
3
How Much Bandwidth do you Need?
© 2015 Cisco and/or its affiliates. All rights reserved.BRKEWN-2000 Cisco Public
How Much Bandwidth Is Required?
• It is most likely that you won’t be supporting just one application
• Design for the highest bandwidth demand that you intend to support
– What you need is the minimum acceptable throughput that the application will require
– Most users use only ONE high performance demanding application at a time
• Multiply this number by the number of devices that you need to support
• This is the aggregate bandwidth you will require in your space
• Often Less than You May Think
5
Application – By Use
Case
Throughput –
Nominal
Web - Casual 500 Kbps
Web - Instructional 1 Mbps
Audio - Casual 100 Kbps
Audio - instructional 1 Mbps
Video - Casual 1 Mbps
Video - Instructional 2-4 Mbps
Printing 1 Mbps
File Sharing - Casual 1 Mbps
File Sharing - Instructional 2-8 Mbps
Online Testing 2-4 Mbps
Device Backups 10-50 Mbps
© 2015 Cisco and/or its affiliates. All rights reserved.BRKEWN-2000 Cisco Public
How Much Bandwidth do You Need?
• Example, Skype (Up/Down):
• Now that you get the picture, a few other examples:– Fring (video): 135 kbps,
– Facetime (video, iPhone 4S): 400 Kbps, (audio) 32 kbps
– Viber (video) 120 kbps, (audio) 30 kbps
– Skype/Viber/other chat: around 850 to 1000 bytes (6.8 to 8 kb) per 500 character message
– Netflix (video), from 600 kbps (low quality) to 10 Mbps (3D HD), average 2.2 Mbps
– This bandwidth consumption is one way, you need to double for 2-way conversations
Call type Audio Video/screen share Video HD Group Video (5 people)
Typical
Bandwidth
30Kbps/30kbps 130kbps/130kbps 1.2 Mbps/1.2 Mbps 130 kbps/2 Mbps
6
© 2015 Cisco and/or its affiliates. All rights reserved.BRKEWN-2000 Cisco Public
Real Life Example?
• Density studies show 12 users / cell on average
– Expected 2 HD video calls (Skype type)
– 5 audio calls
– All users may browse
• Let’s do the math:
– 2 HD video calls = 1.2 Mbps x 2 x 2 ways = 4.8 Mbps
– 5 audio calls… mmm what application?• Skype too? 30 kbps x 5 x 2 ways = 600 kbps
– Others are browsing (5 people)… 250 kbps /people?
– Total = 6.65 Mbps needed
AP
Medical Center
I need 6.65 Mbps throughput everywhere in the cell- > therefore I need it here
Funny that browsing requires more than voiceShould I design for browsing?
7
© 2015 Cisco and/or its affiliates. All rights reserved.BRKEWN-2000 Cisco Public
VoIP Requirements
• VoIP carries voice sound with UDP and Real Time Protocol (RTP), voice control traffic uses Real Time Control Protocol (RTCP)
– Voice sound is converted to digital packets using codecs
– Resulting packet size ranges from 8 to 64 bytes per packet (+40 bytes L4/L3 headers, +L2 header)
• Voice has very strict requirements as an “application”
– Packet Error Rate (PER) <=1%
– As low jitter as possible, less than 100ms
– Retries should be < 20%
– End to end delay 150 – 200 ms, 30 ms in cell
– When these values are exceeded, MOS reduces
– Your mission is to keep MOS high
8
© 2015 Cisco and/or its affiliates. All rights reserved.BRKEWN-2000 Cisco Public
Video Applications
• Video uses video and audio codecs– Some codecs are built for real time exchange, some for streaming
– Video algorithms refresh entire images when large changes occur
– The changes generate traffic bursts
9
Cell Size and Shape
© 2015 Cisco and/or its affiliates. All rights reserved.BRKEWN-2000 Cisco Public
Cell Shape and Cell Size
Your cell shape depends on the antenna you use:
Directional
Omnidirectional
© 2015 Cisco and/or its affiliates. All rights reserved.BRKEWN-2000 Cisco Public
Cell Shape and Cell Size
Your cell shape depends on the antenna you use:
Directional
Omnidirectional
The cell size depends on 3 parameters:
The AP power level
The protocol you use (802.11a/b/g/n/ac)
The Data rates you allow
This is in open space… in real world, you also need to account for RF obstacles
Cell Size - AP Power
© 2015 Cisco and/or its affiliates. All rights reserved.BRKEWN-2000 Cisco Public
Power and Channel Plans
Many BYODs support all UNII bands
BUT: BYOD power varies with the band
Client devices cannot actively scan UNII-2e (ch 100 to 140)…
So those that support UNII-2e passively scan them only once every 6 to 18 cycles
(this means that, when on the Wi-Fi page, where an Iphone 5 scans every 11.4s, you
get UNII-2e channels every 68.4 s; when running to 8 second scans in roaming panic
mode, you get UNII-2e channels every 48 s)
Avoid UNII-2e in your channel planning if fast roaming is a concern
This may limit your options if you decide to use 40 MHz channels
15
© 2015 Cisco and/or its affiliates. All rights reserved.BRKEWN-2000 Cisco Public
Cell Size – Depends on Protocol and Rates
• Higher power does not always meanhigher SNR…
16
You are a bit quiet
Blah blah blah
Is it better now?
• Channel Utilization levels should be kept under 50%.
• You can check it using a spectrum analyzer like SpectrumExpert or Fluke AirCheck
• Noise levels should not exceed -92 dBm, which allows for a Signal to Noise Ratio (SNR) of 25 dB where a -67 dBm signal should be maintained.
© 2015 Cisco and/or its affiliates. All rights reserved.BRKEWN-2000 Cisco Public
Cell Size – Let’s get rid of the “Power” Checkbox
17
RF is symmetrical on paper:
“If your AP signal is heard by a client, the AP should hear the client signal symmetrically” (because the antenna Rx matches its Tx gain)
In real world, this is true, if the client RF parameters (Tx/Rx sensitivity, antennas, power level) are the same… otherwise, the client signal may be so weak that the AP can’t make sense out of it
2 causes:
Client rate decision is based on CLIENT perception of AP signal – if AP signal is strong, client will use high rate
The client reaches the AP mixed in surrounding noise – SNR too low and AP cannot demodulate
This is the AP signal (at phone level) This is the phone signal (at AP level)
© 2015 Cisco and/or its affiliates. All rights reserved.BRKEWN-2000 Cisco Public
Power -client Side vs AP Side
BYODs commonly have smaller power ranges than APs
18
Example: 3700i AP
(+4 dBi antenna on 2.4 GHz,
+6 dBi antenna on 5 GHz)Example: Iphone 5
Band Max Tx Power
2.4 GHz ISM 16 dBm
UNII-1 14 dBm
UNII-2 13.5 dBm
UNII-2e 12 dBm
UNII-3 13 dBm
ISM (Ch 165) 13 dBm
Source: FCC
This is the max Tx power This is the TX Power
(to the antenna)
© 2015 Cisco and/or its affiliates. All rights reserved.BRKEWN-2000 Cisco Public
Power, Spatial Streams and Data Rates
Do not think that multiple stream devices are always better
They may have higher power, but also require higher SNR
e.g.: 4 streams gives you a higher throughput
at same SNR level, than 2 streams
BUT the 2 stream device reaches its max speed
at 24 dB SNR,
while the 4 stream device needs 30+ dB
Conclusion: at same distance from the AP,
multiple stream devices will operate faster than
single stream device, but each individual stream
is slower
© 2015 Cisco and/or its affiliates. All rights reserved.BRKEWN-2000 Cisco Public
How can you tell the AP Power level?
WLC global level gives you the overall resulting power (this is what you care about):
(Cisco Controller) >show advanced 802.11a txpower
…/…
AP Name Channel TxPower Allowed Power Levels
-------------------------------- ---------- ------------- ------------------------
AP702W 157 *1/8 (20 dBm) [20/17/14/11/8/5/2/-1]
AP2602 48 1/4 (14 dBm) [14/11/8/5/5/5/5/5]
AP3702 (52,56) *2/5 (12 dBm) [15/12/9/6/3/3/3/3]
AP3602 (40,36) *2/7 (12 dBm) [14/12/10/8/5/-1/-4/-4]
AP is on 40 MHz channel
Power is dynamically assigned by WLC
Current level is 2 (12 dBm),
there are 7 levelsAllowed levels, 7 to 8 are the same,
so AP is configurable down to level 7
© 2015 Cisco and/or its affiliates. All rights reserved.BRKEWN-2000 Cisco Public
How can you tell the Client Power level?
You can check, live the client power levels on the AP (useful to check symmetry in AP to client and client to AP signal when building your cell edge):
AP7cad.74ff.36d2#debug dot11 dot11Radio 1 trace print rcv
*Jun 1 04:11:43.663: D5B70D90 r 6 49/46/42/48 54- 0803 000 m010B85 477AAF m010B85 33E0 477AA0 l46
*Jun 1 04:11:43.664: A2CEF918 r m15-2s 53/63/54/61 40- 8841 030 1A096F A36F20 m333300 76B0 q0 l100
This is on 5GHz radio, d0 is 2.4 GHz radio2 client signals reported
TimestampClient used MCS 15 (2SS)
Client RSSI on each antenna
Client SNR
Frame type (follows 802.11 spec)
Frame duration
Receiver and transmitter
addresses (last 3 bytes)
L+length of
rest of the frameWith WMM, shows the queue
without WMM, DCF queue index
Address 3
Sequence number
© 2015 Cisco and/or its affiliates. All rights reserved.BRKEWN-2000 Cisco Public
Some Client Max EIRPs
Model EIRP 2.4 GHz Worst* EIRP 5 GHz
Iphone 5 14.6 dBm 10 dBm
Ipad 4 15.2 dBm 22.67 dBm
Samsung S3 14.9 dBm 10.18 dBm
Samsung S4 12.05 dBm 11.24 dBm
Samsung S5 13.4 dBm 10.61 dBm
HTC One 14.4 dBm 13.8 dBm
Nokia Lumia 1520 13.1 dBm 11.6 dBm
ASUS PCE-AC66 22 dBm 22.83 dBm
* EIRP varies with sub-band, displaying worst of all sub-bands
© 2015 Cisco and/or its affiliates. All rights reserved.BRKEWN-2000 Cisco Public
So, what is the right Power?
In short: half your worst client max power
– E.g. you design for 5 GHz, worst client max is at 11 dBm, set your AP power to 8 dBm
Otherwise, you get this:
Which BYOD is the worst out there? No names, but 11 dBm is a good assumption
© 2015 Cisco and/or its affiliates. All rights reserved.BRKEWN-2000 Cisco Public
Power Levels and Client Density
– Reducing cell size by matching client
power and disabling low speed
decreases the user number per cell
– Each user has better throughput and
less risk of encountering interference
– Coverage holes might cause probing
devices to disturb the WLAN clients
© 2015 Cisco and/or its affiliates. All rights reserved.BRKEWN-2000 Cisco Public
What if I crank up my AP power a bit?
Bad design example: Client @ 12 dBm, AP @20 dBmBased on Rx AP signal, BYOD thinks 54 Mbps rate is okay
But client message is too weak,
and AP does not ACKRetry @ 54Againand AgainOkay try 36Wow, let’s drop to 12Now I get an ACKStart over…
Each message takes 8 times more to be transmitted
(including EIFS and retries)
Cell Size - Protocols and Rates
© 2015 Cisco and/or its affiliates. All rights reserved.BRKEWN-2000 Cisco Public
Cell Throughput by Protocol
• These are average throughputs, with one client close to the AP (high SNR/RSSI)
* Two spatial streams – note most PDA’s are SISO (MCS 7) 35 Mbps max
** You could have guessed that : 256-QAM max PHY is 1.3 Gbps, max throughput is typically less than half of max PHY
Protocol Throughput (Mbps)
802.11b 7.2
802.11b/g mix (1 b client) 9.5
802.11g 22.5
802.11a 22.5
802.11n (HT20 1ss MCS7) 35
802.11n (HT20 2ss MCS15) 75*
802.11n (HT20 3ss MCS23) 110
802.11ac (VHT80 3SS MCS 9) 630**
© 2015 Cisco and/or its affiliates. All rights reserved.BRKEWN-2000 Cisco Public
Cell Size and Data Rate
Each cell’s useful radius is determined by the minimum allowed data rate
1 Mbps DSSS2 Mbps DSSS5.5 Mbps DSSS6 Mbps OFDM9 Mbps OFDM11 Mbps DSSS12 Mbps OFDM18 Mbps OFDM24 Mbps OFDM36 Mbps OFDM48 Mbps OFDM54 Mbps OFDM
© 2015 Cisco and/or its affiliates. All rights reserved.BRKEWN-2000 Cisco Public
Protocol Support and Channel Utilization
Example low rate time waste ACK frames are sent at the first mandatory speed below the speed at which the
frame was received
802.11a/n: SIFS = 16 microsec
802.11b/g/n: SIFS = 10 microsec
802.11a/g/n: slot = 9 microsec
802.11b: slot = 20 microsec
1 DIFS = 1 SIFS + 2 slots
OFDM physical header = 16 microsec (312 b at 6 Mb/s)
802.11 physical header = 192 microsec (192 b at 1 Mb/s)
ACK sent at 24 Mb/s uses 4.67 microsec. airtime
ACK sent at 1 Mb/s uses 304 microsec. Airtime
Impact on throughput higher for shorter frames
© 2015 Cisco and/or its affiliates. All rights reserved.BRKEWN-2000 Cisco Public
Protocol Support and Channel Utilization
36
5% After
60% Before
Before: 8 SSIDs, allrates allowed
After: 2 SSIDs, 802.11brates disabled
© 2015 Cisco and/or its affiliates. All rights reserved.BRKEWN-2000 Cisco Public
Protocol Support and Channel Utilization
Disabling 802.11b in this network would:
Suppress 27% of frames (slow frames would be sent faster)
Decrease airtime consumption from 62% to 18 % if using 24 Mbps (slow frames take much longer to be sent than faster frames)
Reduce cell size:
Clients nearby would benefit from higher speeds
Clients far would not sick to the AP
DSS/CCKAirtimeconsumption
OFDMAirtimeconsumption
© 2015 Cisco and/or its affiliates. All rights reserved.BRKEWN-2000 Cisco Public
Low rates impact Depends on frame size…
CCK DSSS OFDM
0
2000
4000
6000
8000
10000
12000
14000
16000
18000
20000
1 2 5.5 11 6 12 24 36 48 54 130 300
64 Byte
128 Byte
256 Byte
512 Byte
1024 Byte
2048 Bytes
Time/
μS
Mb
ps Frame
Size/Bytes
OFDMCCKDSSS
Codec & Bit
Rate
Time
consumption
per voice flow
at 1 Mb/s
Time
consumption
per voice flow
at 24 Mb/s
Time
consumption
per voice flow
at 54 Mb/s
G.711
(64 Kb/s) 102.4 ms 9.45 ms 6.49 ms
G.729
(8 Kb/s)46.4 ms 6.27 ms 5.20 ms
G.726
(32 Kb/s) 70.4 ms 7.27 ms 5.64 ms
G.728
(16 Kb/s) 42.43 ms 4.72 ms 3.74 ms
Individual theoretical time consumption:
SLOT + DIFS + (voice packet + headers) x speed x (number of packets per second) + SIFS + ACK
© 2015 Cisco and/or its affiliates. All rights reserved.BRKEWN-2000 Cisco Public
And most BYODs know that
Most BYODs take advantage of 802.11 blocks to group small frames (even if they end up sending one frame at a time):
Viber on Iphone 5S
Viber on Samsung S5
© 2015 Cisco and/or its affiliates. All rights reserved.BRKEWN-2000 Cisco Public
What should be your Minimum rate?
40
You want to stop your cell in a place where the following happens:
Signal to your clients is still strong
Clients and overhead traffic still “reasonably fast”
Retries are low
Beyond that point, clients should be able to get to another AP if they want to. On the right:
STA1 and STA2 hear each other -> less collisions
STA 1 and STA2 send @ 54 Mb/s -> short delays
STA3 is far from AP -> lower data rate (longer transmission delay), higher PER and loss risks
STA3 does not hear STA1 and STA2 -> higher collision risk
54 Mbps
6 Mbps
STA1
STA2
STA3
© 2015 Cisco and/or its affiliates. All rights reserved.BRKEWN-2000 Cisco Public
What should be your Minimum signal level?
41
Multiple measurements show a “sweet spot” by -67 dBm:
What minimum configured data rate is that? Depends…
802.11n client still communicates at 72 Mbps (MCS 7)
Management/control frames still sent fast (24 Mbps)
But you start seeing devices (here the AP) dropping rate because signal starts to degrade
© 2015 Cisco and/or its affiliates. All rights reserved.BRKEWN-2000 Cisco Public
What should be your Minimum data rate?
42
And BER is important, because more retries means more chances that the frame will be dropped
Your job is to limit frame drops to1% or less to maintain 4.1 MOS
At -67 dBm RSSI, SNR istypically around 25 dB or more*
You can run any rate of 24 Mbpsand up, and still have good frame success rate
* well, at least in ideal conditions… see next slides
© 2015 Cisco and/or its affiliates. All rights reserved.BRKEWN-2000 Cisco Public
Signal Attenuation
Your hand position may make things worse
Object in Signal PathSignal Attenuation
Through Object
Plasterboard wall 3 dB
Glass wall with metal frame 6 dB
Cinderblock wall 4 dB
Office window 3 dB
Metal door 6 dB
Metal door in brick wall 12 dB
Phone and body position 3 - 6 dB
Phone near field absorption Up to 15 dB
There can be a 20 dB difference between these photos
© 2015 Cisco and/or its affiliates. All rights reserved.BRKEWN-2000 Cisco Public
Let’s do the signal level math
-67 dBm
-67 – 20 = -87 dBm
Signal is too weak…
APAP
But you can roam to the other AP @ -67 dBm!
© 2015 Cisco and/or its affiliates. All rights reserved.BRKEWN-2000 Cisco Public
BTW, where do you put an antenna on a BYOD?
45
Head – not good
Hand – not good
HTC One, whole
back cover is metal and
antenna
Iphone 5,
Antenna is at
bottom
Samsung S5, antenna
is at bottom, behind button
© 2015 Cisco and/or its affiliates. All rights reserved.BRKEWN-2000 Cisco Public
Disable 802.11b but not 802.11n low rates!
46
Each SSID will advertise at the minimum mandatory data rate
Disabled – not available to a client
Supported – available to an associated client
Mandatory – Client must support in order to associate
Lowest mandatory rate is beacon rate
Highest mandatory rate is default Mcast rate
© 2015 Cisco and/or its affiliates. All rights reserved.BRKEWN-2000 Cisco Public
Disable 802.11b but not 802.11n low rates!
47
Many BYODs rely on the beacon to validate that the
AP is still there (and sync their clock)
Many BYODs also ignore AP instructions about
supported 802.11n rates (disable them, and your
client talks at a speed the AP will ignore)
In standard density environment, stop your cell @ -67 dBm.
When power is @ 11 or 14 dBm, this is about 12 MbpsEverything below 12 Mbps is disabled
(but NOT 802.11n low rates)
First allowed rate (12 Mbps) is mandatory
© 2015 Cisco and/or its affiliates. All rights reserved.BRKEWN-2000 Cisco Public
Cell size strategies
In HIGH density environment, also stop your cell @ -67 dBm.
Power is usually low, 14 dBm or lower
Cells are smaller than in standard density environment
Roaming occurs faster
Rate @ -67 dBm is more commonly 24 Mbps
You want to allow your client to roam at that point -> 24 Mbps is set to Mandatory (below 24 Mbps, client does not hear the beacons and typically scans to find alternate AP)
You still want the client to communicate with the AP while getting into panic scan
Set lower rates (18, 12 Mbps) to Supported
© 2015 Cisco and/or its affiliates. All rights reserved.BRKEWN-2000 Cisco Public
Disable Slow rates, and maybe fast rates!
What about the other rates?
For Voice, rates faster than 24 Mbps do not bring any clear advantages
Codec & Bit
Rate
Time
consumption
per voice flow
at 1 Mb/s
Time
consumption
per voice flow
at 24 Mb/s
Time consumption
per voice flow
at 54 Mb/s
G.711 (64 Kb/s) 102.4 ms 9.45 ms 6.49 ms
G.729 (8 Kb/s) 46.4 ms 6.27 ms 5.20 ms
G.726 (32 Kb/s) 70.4 ms 7.27 ms 5.64 ms
G.728 (16 Kb/s) 42.43 ms 4.72 ms 3.74 ms
Time consumption = SLOT + DIFS + (voice packet + headers) x speed x (number of packets per second) + SIFS + ACK
© 2015 Cisco and/or its affiliates. All rights reserved.BRKEWN-2000 Cisco Public
Disable Slow rates, and maybe fast rates!
Faster rates DO have an impact on rate shifting:
200 byte frame @ 54 Mbps is sent in 3.7 μs
200 byte frame @ 24 Mbps is sent in 8.3 μs
Rate shifting from 54 Mbps to 24 Mbps wastes 1100 μs(65 times longer to send the next frame), in ideal (no congestion) conditions
54 Mbps
48 Mbps36 Mbps24 Mbps
54 Mbps
36 Mbps
24 Mbps
© 2015 Cisco and/or its affiliates. All rights reserved.BRKEWN-2000 Cisco Public
Disable Slow rates, but not 802.11n rates!
51
Conclusion: disable low rates
If your real time applications are Voice only,
disable rates higher than 24 Mbps, and set
channels to 20 MHz
If your real time applications are Voice AND
Video, then you need higher rates
In 5 GHz, set channels to 40 MHz… if your
clients support 40 MHz
Leave all 802.11n / ac rates enabled
(if your clients support 802.11n and 802.11ac)
Cell Size - 20, 40, 80 MHz?
© 2015 Cisco and/or its affiliates. All rights reserved.BRKEWN-2000 Cisco Public
Cell Size – Depends on Power, Protocol and Rates
53
With the explosion of 802.11ac, majority of devices are dual-band
98% of devices observed are 802.11n
5 GHz 802.11n devices are not always 40/80 MHz-able
0.1
38 40
55
29
5060
99
62 60
45
71
5040
0
20
40
60
80
100
1205 GHz
© 2015 Cisco and/or its affiliates. All rights reserved.BRKEWN-2000 Cisco Public
Cell Size – Depends on Power, Protocol and Rates
54
What about YOUR network?
If there is no network deployed yet, capture traffic at different times and observe
Example: large airport on US East Coast, last month 12 captures of 10 minutes each at different times / days, with wireshark – display rates
In this network, enabling 40 MHz is a waste40 MHz rates
20 MHz rates
AP Placement Strategy
© 2015 Cisco and/or its affiliates. All rights reserved.BRKEWN-2000 Cisco Public
Real Time AP Placement
56
A huge percentage of problems come from incorrectly defined coverage areas
Coverage areas: where the real time service should be offered
Typical errors: “not needed in the bathrooms”, “not in the elevators”, “not in the stairs”, “not in the outdoor smoking area”
Talk to end-users. Think what they will need and when
Coverage Areas
© 2015 Cisco and/or its affiliates. All rights reserved.BRKEWN-2000 Cisco Public
AP Placement Guidelines
Mount APs so that antennas are vertical (we use vertical polarization)
© 2015 Cisco and/or its affiliates. All rights reserved.BRKEWN-2000 Cisco Public
AP Placement Guidelines
Avoid metallic objects that can affect the signal to your clients
© 2015 Cisco and/or its affiliates. All rights reserved.BRKEWN-2000 Cisco Public
RF Design Matters
62
Highly reflective environments
Multipath distortion/fade is a consideration
Legacy SISO technologies (802.11a/b/g) are most prone
802.11n improvements with MIMO
Devices are susceptible
Things that reflect RF– Irregular metal surfaces
– Large glass enclosures/walls
– Lots of polished stone
© 2015 Cisco and/or its affiliates. All rights reserved.BRKEWN-2000 Cisco Public
AP Placement – Bad Examples
Issue is sometimes in the environment
Ceiling is highly reflective
metallic mesh
AP behind ceiling
(yes they did that)
© 2015 Cisco and/or its affiliates. All rights reserved.BRKEWN-2000 Cisco Public
AP Placement – Bad Examples
AP too high:– Low rate to the ground
– Client signal too weak at the AP level
> 20ft
Nice… but you won’t cover the
jetway as soon as the door closes
© 2015 Cisco and/or its affiliates. All rights reserved.BRKEWN-2000 Cisco Public
AP Antenna Guidelines
Use matching antennas
When RF cluelessness becomes art…
These are dual band plugs (2.4 and 5 GHz)
They require dual band antennas… they are labelled “a,b,c,d”
These are single band antennas…
are you going to get 2.4 or 5 GHz? Antenna gain mismatch: AP
won’t know which to believe
Coverage pattern mismatch:
Are you covering through the
wall?
Taking Care of the Roaming Path
© 2015 Cisco and/or its affiliates. All rights reserved.BRKEWN-2000 Cisco Public
Rates and Cell Overlap
Cell overlap is designed so that when a VoWLAN device gets to the
–67 dBm area, it is already in good range of another access point.
20-percent overlap between cells is recommended
How much is that? Use the -75 dBm rule if you are not sure.
© 2015 Cisco and/or its affiliates. All rights reserved.BRKEWN-2000 Cisco Public
Network Design
70
Try to design small cells, with clever overlap…
© 2015 Cisco and/or its affiliates. All rights reserved.BRKEWN-2000 Cisco Public
Channel Plan and Data Rate
Each cell’s useful radius is determined by the minimum allowed data rate
RF
edge
24 Mbps OFDM36 Mbps OFDM48 Mbps OFDM54 Mbps OFDM
© 2015 Cisco and/or its affiliates. All rights reserved.BRKEWN-2000 Cisco Public
Client Signal Detection Optimization
AP Rx sensitivity is MUCH higher than that of most BYODs… and improved over the years beyond the 802.11 requirements
E.g. 1242 Rx sensitivity at 1 Mbps is -96 dBm, with a typical SNR of 3 dB (so you need -96 dBm signal, with background noise not more than -99 dBm, to recognize and read a frame sent at 1 Mbps). With the 3700 AP, that threshold is -101 dBm (with the same SNR requirements), so we are 5 dB better
We need more signal to read 802.11n than legacy protocols. If we disable legacy protocols on our new APs, the problem would probably more or less go away by itself, but the issue is that we keep the old protocols and at the same time build smaller cells to benefit from the additional throughputs.
Rate Recommended RSSI (3700AP) Recommended SNR
1 Mbps -91 dBm 1
6 Mbps -87 dBm 2
MCS 0 (6.5 Mbps) -82 dBm 1
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Sending modulation depends on Received RSSI and SNR
74
802.11 determines “minimum RX performance values” – RSSI based
Vendors achieve “at least” these values
Example: Cisco 3700e Rx performances:
© 2015 Cisco and/or its affiliates. All rights reserved.BRKEWN-2000 Cisco Public
RX-SOP – (Receive - Start of Packet) – What is it?
75
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.
© 2015 Cisco and/or its affiliates. All rights reserved.BRKEWN-2000 Cisco Public
RX-SOP configuration
76
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
© 2015 Cisco and/or its affiliates. All rights reserved.BRKEWN-2000 Cisco Public
Radiation Pattern and Roaming Buffer
When users are expected to roam while communicating, make sure their BYOD can detect neighboring APs BEFORE roaming
Directional vs omnidirectional antenna
Floor
AP signal drops fast
AP signal drops slowly
User does not have much space/time
to find the next AP
© 2015 Cisco and/or its affiliates. All rights reserved.BRKEWN-2000 Cisco Public
VoWiFi Rate Shifting and Transition AP
79
1
3
2A B
C
At “A” the phone is connected to AP 1
At “B” the phone has AP 2 in the neighbor list, AP 3 has not yet been scanned due to the RF shadow caused by the elevator bank
At “C” the phone needs to roam, but AP 2 is the only AP in the neighbor list
The phone then needs to rescan and connect to AP 3
– 200 B frame @ 54 Mbps is sent in 3.7 μs
– 200 B frame @ 24 Mbps is sent in 8.3 μs
– Rate shifting from 54 Mbps to 24 Mbps can waste 1100 μs
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VoWiFi Rate Shifting and Transition AP
80
AB
C
1
2
3
At point A the phone is connected to AP 1
At point B the phone has AP 2 in the neighbor list as it was able to scan it while moving down the hall
At point C the phone needs to roam and successfully selects AP 2
The phone has sufficient time to scan for AP 3 ahead of time
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Controller Redundancy and Roaming Paths
Design expected roaming paths and make sure all APs connect to the same controller, and overlap allows for next AP discovery
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Avoid Ping Pong Zones
Ping-pong effect occurs when a wireless client is at the edge of two cells
and hops between them.
Client stays here
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Avoid Ping Pong Zones
“Pacing back and forth” zone
Ping Pong zone recipe:
Set overlap along pacing path
Let user head force the roam
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Cisco ClientLink Technology• Advanced Beam Forming Technology
84
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BandSelect – Test Before Full Deployment
90
Caveat – Possible Increased Roaming Delay2.4G band
5G bandNo Delay
Some Delay
(1.5s)
Possible Delay
Client and AP 802.11 Optimizations
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Cisco VideoStream - How Does it Work?
.
.
1
2
34
5
67
8
9
1. Client sends IGMP join
2. WLC intercepts IGMP join
3. WLC sends AP RRC request
4. AP sends RRC response
5. WLC forwards join request
6. Multicast sourcesends IGMP join response
7. Multicast stream sent
8. WLC forwards multicast stream to AP
9. AP converts stream to unicast and delivers to client
98
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Thinking BANDWIDTH in Terms of Directions
102
In a standard cell, 70% of traffic is downstream (from AP to client)
30% is upstream
We can definitely control downstream, especially as 802.11n/ac stations are necessarily WMM
Can we control the upstream? Not directly, but we may have an indirect way of controlling it…
Don’t
send!
I decide, alone,
when to send (thank
you CSMA/CA)
10
2
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Bandwidth Control
103
You can also control upstream and downstream bandwidth consumption:
Per QoS Profile (Gold etc.)
Per SSID
Per user type (guest etc)
Per device type
Per individual user
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If you have Several Traffic Types to Target: Use Application Visibility and Control
107
Identify Applications using NBAR2
VoiceVideoBest-Effort
Background
Client Traffic
Control Application Behavior
Don’t Allow
Rate Limiting
Last Words - Troubleshooting
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Troubleshooting Tools
112
Wireless sniffer
Omnipeek/Wireshark (multichannel, for roaming issues)
Mac with OS X 10.6 and above, Windows 7 with Netmon 3.4
AP in Sniffer mode
L1 analysis: SpectrumExpert
WLCCA (WLC Configuration Analyzer) – TAC support
NCS / Cisco Prime Infrastructure for Historical viewand « Client Troubleshooting tool »
Wireless Captures, RF Analysis, Configuration Analysis
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Support Community
113
https://supportforums.cisco.com/community/5771/wireless-ip-voice-and-video
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Continue Your Education
• Demos in the Cisco Campus
• Walk-in Self-Paced Labs
• Table Topics
• Meet the Engineer 1:1 meetings
115
© 2015 Cisco and/or its affiliates. All rights reserved.BRKEWN-2000 Cisco Public
Call to Action
• Visit the World of Solutions for
– Cisco Campus
– Walk in Labs
– Technical Solution Clinics
• Meet the Engineer
• Lunch time Table Topics
• DevNet zone related labs and sessions
• Recommended Reading: for reading material and further resources for this session, please visit www.pearson-books.com/CLMilan 2015
116
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Complete Your Online Session Evaluation
• Please complete your online sessionevaluations after each session.Complete 4 session evaluations& the Overall Conference Evaluation(available from Thursday)to receive your Cisco Live T-shirt.
• All surveys can be completed viathe Cisco Live Mobile App or theCommunication Stations
117