Aruba 802.11ac networks: Validated Reference Designs

Aruba 802.11ac Networks
Validated Reference Design

2 | Aruba 802.11ac Networks
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Aruba 802.11ac Networks Contents | 3
Contents
Contents 3
Introduction 5
Summary of Recommendations 7
Wired Network Considerations 7
RF Planning 7
WLAN Optimizations 8
802.11ac Features and Benefits 11
Wide RF Channel Bandwidths 11
OFDM Subcarriers 12
More Spatial Streams 13
Spatial Streams 13
Understanding MIMO and MU-MIMO 13
Space Time Block Coding, Maximum Ratio Combining, and Short Guard Interval 15
Space Time Block Coding 15
Maximal Ratio Combining 15
Short Guard Interval 15
Transmit Beamforming 15
Modulation and Rates 16
Error Correction Methods 18
Frame Aggregation, A-MPDU, and A-MSDU 18
Power-Save Enhancements 19
Backward Compatibility 20
Protection, Dynamic Bandwidth, and Channelization 20
802.11ac Planning and Deployment Guidelines 23
Wired Network Considerations 24
AP Power Requirements 24
AP Uplink Considerations 25
Access Network Uplink Consideration 25
Jumbo Frames 26

4 | Contents Aruba 802.11ac Networks
VLAN Design 26
Wireless VLAN Design 26
RF Planning 27
AP Mounting Recommendations 27
Ceiling Mount Deployment 27
Wall Deployment 27
Site Survey 28
Factors Attenuating Wireless Signals 30
Wi-Fi and Non-Wi-Fi Interference Sources 30
Forwarding Mode Recommendations 31
Tunnel Mode 31
Decrypt-Tunnel Mode 32
Channel Width Selection 32
Capacity planning 33
WLAN Optimizations 35
Adaptive Radio Management (ARM) 35
Channel and Power Settings 35
ClientMatch 37
ClientMatch Capabilities 37
Band Steering 37
Sticky Client Steering 37
Dynamic Load Balancing 38
Broadcast/Multicast (BC/MC) Optimization 38
AirGroup 39
Dynamic Multicast Optimization (DMO) 39
Dynamic Multicast Optimization 39
Multicast Rate Optimization 40
Traffic Shaping 41
Wi-Fi Multimedia and Quality of Service (QoS) 41
End-to-End QoS 42

Aruba 802.11ac Networks Introduction | 5
Chapter 1
Introduction
Wi-Fi has evolved from being a nice-to-have service to a mission-critical solution in enterprise communications.
With the introduction of 802.11ac technology, which provides gigabit speed, many companies are moving
towards all-wireless offices. Gone are the days where employees used desktops with wired connections and
desk phones. The advancements in Wi-Fi technology has made the workplace mobile. Because of mobility,
employees can have quick and easy access to data irrespective of their physical location, which improves user
productivity and reduces IT cost. It is common for an employee to carry two or more devices – for example,
smartphone, tablet, and laptop. Most of these newer devices do not come with Ethernet ports and hence Wi-Fi
is their primary mode of network access.
Mobile technology has reached the next frontier – video. Whether it is delivering buffered video like YouTube
to smartphones or streaming HDTV video around the office or home, video has become a significant driver of
network traffic. This is mainly because video requires twice more bandwidth than other IP services and is a
continuous traffic stream as compared to transactional and bursty traffic like email or Web browsing. Support
for voice and video traffic becomes important for an all-wireless workplace that uses Unified Communications
and Collaborations (UCC) applications like Microsoft Lync for webinars and video conferencing. The recent
move to cloud-based services by companies also adds stress to today's network bandwidth due to the shift to
having documents downloaded on demand to mobile devices rather than being stored locally. Ratified as a
standard by IEEE in December 2013, 802.11ac is the latest enhancement in the 802.11 standards family for
improving the network performance.
The purpose of this guide is to explain the enhancements in 802.11ac standard and provide guidance towards
migrating to 802.11ac with respect to network design, deployment, and configuration best practices for
campus environments like offices, university campus, and dorm environments.
This guide covers the following topics in detail:
l Summary of Recommendations
l 802.11ac Features and Benefits
l 802.11ac Planning and Deployment Guidelines
l Best Practice Recommendations for Deploying 802.11ac WLANs
This guide is intended for those who are willing to learn about the 802.11ac standards and understand the
best practices in deploying a high-performing 802.11ac WLAN network by using wireless LAN controllers and
Access Points (APs) from Aruba Networks, Inc.

Aruba 802.11ac Networks Summary of Recommendations | 7
Chapter 2
Summary of Recommendations
All the recommendations in this chapter are general guidelines for 802.11ac deployments. Based on your
network; radio frequency (RF) guidelines might change and hence it is strongly recommended to appropriately
tweak some RF parameters. Network admins should carefully adjust one parameter at a time and test it out
before using it in production environments.
Wired Network Considerations
The following table summarizes Aruba’s recommendation for wired networks to support 802.11ac WLAN
deployments. For detailed description, see Chapter 4: 802.11ac Planning and Deployment Guidelines.
Feature Recommendation
PoE Requirements l It is preferred to use 802.3at (PoE+) switches to power the APs.
AP Uplink
Consideration
l If this is a Greenfield deployment, it is recommended to plan two Ethernet cables per AP-
220 Series for providing PoE fallback and future-proofing your network.
Ethernet Cable l Cat 5e Ethernet cables.
l Cat 6a Ethernet Cables preferable.
Access Network
Uplink
Consideration
l Access switch terminating APs should have a 10 Gbps uplinks.
Controller Uplink l It is recommended to at least have a 10 Gbps redundant uplink from the controller.
Jumbo Frame l It is recommended to have end-to-end Jumbo Frame support on your network to get
maximum benefits of frame aggregation and improve 802.11ac performance.
VLAN Design l Design your network to have separate wired and wireless VLANs to avoid unnecessary
broadcast and multicast traffic.
l Configure a single flat VLAN for all the wireless clients.
l Configure Broadcast Multicast Optimization knobs.
Table 1: Recommendations for Wired Network
RF Planning
The following table summarizes Aruba’s recommendations for AP placement, AP mounting and channel width
selection when planning for deploying 802.11ac WLAN. For detailed description, see chapter 4: 802.11ac
Planning and Deployment Guidelines.

8 | Summary of Recommendations Aruba 802.11ac Networks
Feature Recommendation
AP Mounting
Recommendation
Ceiling Mount
AP Placement l Place AP’s approximately 40 to 60 feet apart.
l Minimum Received Signal Strength Indicator (RSSI) should be -65 dB throughout your
coverage area.
l SNR should always be greater than 25 dB.
l APs should be deployed in honeycomb pattern.
l Plan your network for 5 GHz performance.
AP Forwarding Mode l Tunnel Mode is preferred.
l Decrypt-Tunnel mode.
Channel Width
Selection
l In Greenfield deployments, deploy 80 Mhz channels including the use of DFS channels if
no radar signal interference is detected near your facility, else deploy 40 MHz channels.
Consider 40 MHz or 20 MHz channel width for better channel separation.
l In Brownfield deployments, 80 MHz channel is recommended with DFS channels only if
no radar signal interference detected near your facility. Also make sure that your legacy
clients are not having wireless issues with 80 MHz channels in which case deploy 40
MHz channels.
Client Density per AP l Plan to have around 40 to 60 active clients per radio per AP.
Table 2: Recommendations for RF Planning
WLAN Optimizations
The following table summarizes the recommendations for WLAN optimization. For detailed description, see
Chapter 5: WLAN Optimizations.
Feature Default Value Recommended Value Description
Scanning Enable Enable l Enables AP to scan other
channels
Transmit
Power
802.11a and 802.11g
radio:
Min 9/Max 127
Open Office:
5 GHz: Min 12/Max 15
2.4 GHz: Min 6/Max 9
Walled Office or Classroom:
l Sets the transmit power
value
NOTE:
l The difference between
minimum and maximum Tx
power on the same radio
should not be more than 6
dBm.
l Tx power of 5 GHz radio
should be 6 dBm higher than
that of 2.4 GHz radio.
Client Match Enable Enable l Optimizes user experience
by steering clients to the
best AP
Table 3: WLAN Optimization Recommendations

Convert
Broadcast
ARP Requests
to Unicast
Enable Enable l Helps to convert broadcast
ARP and DHCP packets to
unicast
Drop
Broadcast and
Multicast
Disable Enable l Restricts all the broadcast
and multicast traffic flooding
into AP tunnels (“Convert
Broadcast ARP Requests to
Unicast” feature must be
enabled)
AirGroup Disable Enable it if MDNS, DLNA or other
zero-configuration services are
needed.
l Allows Airplay and
ChromeCast type of
applications even if “Drop
Broadcast and Multicast”
feature is enabled
Dynamic
Multicast
Optimization
(DMO)
Disable l Enable it if multicast
streaming is needed.
l Set DMO client threshold to
80.
l Prioritize multicast stream
using controller uplink ACL.
l Converts multicast frames to
unicast frames to deliver
them at higher rates
NOTE:
l IGMP Snooping or Proxy
feature needs to be enabled
for DMO to work.
Multicast Rate
Optimization
Disable Enable l Sends multicast frames at
the highest possible
common rate
l Enable it even if DMO is
enabled
Airtime
Fairness
Default Access Fair Access l Provides equal air time to all
the clients
WMM Disable Enable it if you want to prioritize
voice/video traffic on your
network.
l Enables WMM capabilities to
prioritize voice/video traffic
Aruba 802.11ac Networks Summary of Recommendations | 9

Aruba 802.11ac Networks 802.11ac Features and Benefits | 11
Chapter 3
802.11ac Features and Benefits
The following section outlines the enhancements that were introduced in 802.11ac standard. 802.11ac is the
latest amendment to the 802.11 standard and it increases speed close to threefold compared to 802.11n
standard to provide an Ethernet-like user experience. Some of the key enhancements included in 802.11ac
standard are:
l Wide RF Channels
l More Spatial Streams
l MU-MIMO
l Transmit Beamforming
l 256 QAM Modulation
l Frame Aggregation, A-MPDU, and A-MSDU
l Protection, Dynamic Bandwidth, and Channelization
Wide RF Channel Bandwidths
802.11n defined 20 MHz- or 40 MHz-wide channels for wireless communication. 802.11ac added the use of
80 MHz- and 160 MHz-wide channels. In wireless communication, higher channel widths provide more
throughput. In the Modulation and Rates section of this document, a comparison of the data rates achieved by
using 80 MHz- and 160 MHz-wide channels is provided. The following figure shows the available spectrum in 5
GHz band in the US.
Figure 1 Channels defined for 5 GHz band (US Regulations) showing 20, 40, 80, and 160 MHz Channels.
In the US, Wi-Fi uses three blocks of spectrum in 5 GHz band: U-NII 1, U-NII 2, and
U-NII 3. The U-NII 1 band is restricted to indoor operations, the U-NII 2 and U-NII 2 extended bands are for
indoor and outdoor operations, and the U-NII 3/ISM band is intended for outdoor bridge products and may be
used for indoor WLANs as well. 802.11ac Wave 1 allows for use of 80 MHz channels. In future, 802.11ac Wave
2 will allow use of 160 MHz channel width. As it will be difficult to find 160 MHz of contiguous spectrum,
802.11ac Wave 2 will allow two noncontiguous channels to be used together as 80 + 80 MHz channel.
The 802.11ac standard does not operate in 2.4 GHz band and hence from the deployment standpoint all the
best practice recommendations for 802.11n APs still apply to 2.4 GHz band. For more information, refer to

12 | 802.11ac Features and Benefits Aruba 802.11ac Networks
"Aruba 802.11n Networks Validated Reference Design” document available
at:http://www.arubanetworks.com/vrd/80211nNetworksVRD/wwhelp/wwhimpl/js/html/wwhelp.htm
Aruba recommends that customers do not use 40 MHz channels in the
2.4 GHz band due to the lack of available bandwidth and high chance of interference with legacy 802.11b/g networks.
While it is possible to enable these channels, doing so will result in fewer overall channels and a decrease in
throughput.
OFDM Subcarriers
Orthogonal Frequency-Division Multiplexing (OFDM) is the encoding scheme that is used in Wi-Fi
transmissions. OFDM splits a single channel into very small subcarriers that can transport independent pieces
of data as symbols. Each symbol represents some amount of data, which depends on the encoding scheme.
The 802.11n standard only allowed for 40 MHz channel width, so you can only have 114 OFDM subcarriers.
Now, as the 802.11ac standard allows for channel width of 80 MHz, you can have 234 usable data subcarriers
and in future, 468 data subcarriers with 160 Mhz channel. This increase in channel width means that more data
subcarriers are available to carry traffic. Each additional subcarrier can carry data over the channel, which
increases the throughput. In the following figure, you can see the difference in the number of OFDM
subcarriers across different 802.11 standards. The additional channel width is the primary reason for increased
throughput with 802.11ac.
Figure 2 OFDM Subcarriers Used in 802.11a, 802.11n, and 802.11ac
Standard
Channel
Width
Total Sub-
carriers
Usable Data
Subcarriers
802.11a/802.11g 20 MHz 52 48
802.11n 20 MHz 56 52
802.11n 40 MHz 114 108
802.11ac 80 MHz 242 234
802.11ac 160 MHz 484 468
Table 4: OFDM data subcarriers with different 802.11 standards

Some of the subcarriers that do not carry data are called pilot carriers. These are used for the measurement of
channel conditions like phase shift for each subcarrier and can also be used for synchronization to avoid intersymbol
interference. This accounts for the difference in the number of total subcarriers and usable data subcarriers.
More Spatial Streams
Spatial Streams
The concept of spatial streams of data is related to the ability to transmit and receive on multiple radio chains.
More transmit and receive chains allow the AP to send independent streams of data. Multiple spatial streams
enable the AP to transmit more data simultaneously. The data is split into multiple streams and transmitted
over different radio chains. The following figure demonstrates the concept of multiple spatial streams of data.
Figure 3 Spatial Streams
Part of the merits of using Multiple Input Multiple Output (MIMO) and spatial streams is that APs can use
multipath transmissions to their advantage. Single Input Single Output (SISO) systems used in legacy 802.11
standards see performance degradation due to multipath transmissions because multipaths may add to signal
degradation. However, 802.11n and 802.11ac APs use multipath transmissions to significantly enhance
performance. The delay in the propagation of paths at different rates allows MIMO and spatial streams to be
received correctly at the other end of the transmission link. In a SISO system, that delay can cause interference.
Multiple radio chains are needed to transmit and receive multiple spatial streams. Depending on the hardware,
an AP or a client can transmit or receive spatial streams equal to the number of radio chains it has. However, it
is common to have APs with more antennas than spatial streams.
Understanding MIMO and MU-MIMO
The MIMO technology, which was introduced in 802.11n standard, increases throughput by increasing the
number of radio transmit and receive chains. The 802.11ac standard uses MIMO technology and allows for use
of up to eight spatial streams. At present, with 802.11ac Wave 1, an AP or client can have up to four transmit
and four receive chains.
Currently, the 802.11ac-certified client devices available in the market support a maximum of three spatial streams.
Figure 4 Comparison of SISO technology and MIMO technology

The 802.11ac standard also introduced Multi-User MIMO (MU-MIMO). So far, in the 802.11n and 802.11ac
Wave 1 standards, all the wireless communication is either point-to-point (that is, one-to-one) or broadcast
(that is, one-to-all). 802.11ac Wave 2 will support MU-MIMO, where an AP by using its different streams can
transmit data to multiple clients at the same time.
Figure 5 Comparison of MIMO and MU-MIMO transmission
MU-MIMO proposes that, instead of using multiple spatial streams between a given pair of devices, there
should be capability to use spatial diversity to send multiple data streams between several devices at a given
instant. The difficulty lies in coordinating between the various devices in a network – how do you discover
which pairs of radio chains or devices support diverse paths; and how does a device know that another is
transmitting, so it can safely transmit to its partner at the same instant?
802.11ac solves these problems by assuming that APs are different from client devices in that they are less
space-, power-, and price-constrained, so they are likely to have more transmitting antennas than client
devices. Therefore, since the number of spatially diverse paths depends on the number of radio chains, and the
number of opportunities depends on the amount of traffic buffered for transmission, the AP is allowed to
transmit to several clients simultaneously should it find an opportunity to do so. For example, a four-radio
chain AP could simultaneously transmit two spatial streams each to two client devices, provided the conditions
were favorable. This means that the transmissions to one client device should not cause excessive interference
at the other client and the usual MIMO Spatial Division Multiplexing (SDM) conditions should prevail, where the
streams between a given pair of devices are isolated. This downlink MU-MIMO (DL MU-MIMO) is the only
configuration supported in 802.11ac. It precludes other forms such as uplink MU-MIMO. Only one AP or client
can transmit at any instant, and while the AP can transmit to multiple clients simultaneously, clients can only
transmit to the AP one by one. The following figure shows an example of an AP with four antennas using MU-
MIMO to transmit simultaneously to four different clients.
Figure 6 Downlink Multi-User MIMO Frame Sequences

The AP is also in a good position to monitor traffic for different clients and identify opportunities to exercise DL
MU-MIMO.
Space Time Block Coding, Maximum Ratio Combining, and Short
Guard Interval
Space Time Block Coding
MIMO uses diversity techniques to improve performance. Between two communicating stations, one station
can have more antennas than the other. If there are more transmit radio chains than receive chains, Space
Time Block Coding (STBC) can be used to improve the signal-to-noise ratio (SNR) and the range for a given data
rate. For STBC, the number of transmit chains must be greater than the number of spatial streams.
Maximal Ratio Combining
The operation of Maximal Ratio Combining (MRC) depends on the number of available receive radio chains.
When there is more than one receive chain, the MRC technique combines the signals received on multiple
chains. The signals can come from one or more transmit chains. When the signals are combined, the SNR is
improved and the range for a given data rate is increased.
Short Guard Interval
The guard interval is the spacing between OFDM transmissions from or to a client. This interval prevents the
frames that are taking a longer path from colliding with those in the subsequent transmissions that are taking a
shorter path. It is the time that a receiver waits for all the transmissions to account for the delay spread of
different transmit signals reaching the receiver. For example, think of this as an echo and how long the receiver
will wait for the echo before considering the transmission complete. A shorter OFDM guard interval (from 800
ns to 400 ns) between frames means that transmissions can begin sooner in environments where the delay
between frames is low.
For more details about these features, refer to “802.11ac IN-DEPTH” white paper available at:
http://www.arubanetworks.com/pdf/technology/whitepapers/WP_80211acInDepth.pdf
Transmit Beamforming
Transmit Beamforming (TxBF) in 802.11ac works on an explicit feedback to be sent from the beamformee to
the beamformer regarding the current channel state. This information is used to modify amplitude and phase
of signal so as to direct the energy towards the receiver. If correct weightings of amplitude and phase are
chosen, the signal strength at the receive antennas is maximized in a local peak, which maximizes SNR and
hence the sustainable link rate. TxBF can be thought of as directing a beam using phase shifts towards a
particular receive antenna.
Sounding frames are used in the 802.11ac standard to achieve explicit TxBF. Following points explain how it
works:
l A transmitter sends a known pattern of RF symbols from each antenna
l The receiver constructs a matrix for how each of the receive antenna hears each transmit antenna
l This matrix is then sent back to the transmitter, allowing it to invert the matrix and use the optimum
amplitude-phase settings for best reception. With a single antenna receiver, this results in a local maximum
for SNR for an effective beamforming.

Figure 7 Implicit and Explicit Feedback for Beamforming
The implicit beamforming technique is based on inferences of channel characteristics when frames are lost. The
802.11ac standard uses explicit TxBF, where beamformer transmits a sounding frame and the beamformee
analyses how it receives the frame, compresses the results to a manageable size, and transmits them back to
the beamformer. This provides accurate channel state information (CSI) and allows transmitter to direct its
transmission accurately towards the receiver.
802.11ac uses sounding frames and the full sounding sequence comprises a set of special sounding frames
sent by the transmitter (either the beamformer or the AP in case of DL MU-MIMO), and a set of compressed V
matrix frames returned by the beamformee. Because multiple clients are involved in MU-MIMO, a special
protocol ensures that they answer with feedback frames in sequence, following the reception of sounding
frame. The protocol for generating CSI at the transmitter relies on sounding or null data packet (NDP) frames,
together with announcement frames and response frames. First, the beamformer sends a null data packet
announcement (NDPA) frame identifying the intended recipients and the format of the forthcoming sounding
frame. This is followed by the sounding NDP frame itself, and the beamformee then responds with a
beamforming report frame.
The NDPA and NDP frames are quite simple. The NDPA identifies which stations should listen to the
subsequent sounding frame, along with the dimensions of that frame, depending on the number of radio
chains and spatial streams in use. The sounding frame itself is just a null data packet. After these exchanges,
the information gathered is processed and used to construct a beamforming report, which is then used to
perform TxBF.
Modulation and Rates
The 802.11ac amendment continues to extend the complexity of its modulation techniques. Building on the
rates of up to 64 Quadrature Amplitude Modulation (QAM) of 802.11n, it now extends to 256-QAM. This
means that each RF symbol represents one of the 256 possible combinations of amplitude (the signal power)
versus phase (a shift from the phase of the reference signal). The following diagram illustrates how this
complicates the task of encoding and decoding each symbol. There is very little room for error, as the receiver
has to discriminate between 16 possible amplitude levels and 16 phase shift increments; but it increases the
amount of information each symbol represents from 6 to 8 bits when comparing the top 802.11ac rate to the
802.11n rate.

Figure 8 Constellation Diagrams for 16-, 64-, and 256-QAM
While the 256-QAM 5/6 modulation provides a higher raw-data top speed, the table of available physical layer
(PHY) rates is very long, as with 802.11n, to account for various other options.
The key determinants of PHY data rate are:
1. Channel width: As we discussed earlier, 802.11ac AP can be configured to use 20 MHz, 40 MHz, 80 MHz
channel width. In future, the 802.11ac Wave 2 products will allow for 160 MHz channel width or
noncontiguous 80 + 80 MHz channel width.
2. Modulation and coding: All the earlier options are still available, and are used if SNR is too low to sustain
the highest rate. But in the modulation and coding scheme (MCS) table, the canon of 802.11n is extended
to add 256-QAM options with coding of 3/4 and 5/6.
3. Guard interval: Unchanged from 802.11n, the long guard interval of 800 ns is mandatory while the short
guard interval of 400 ns is an available option. The guard interval is the pause between transmitted RF
symbols. It is necessary to avoid multipath reflections of one symbol from arriving late and interfering with
the next symbol.
Figure 9 802.11ac data rates with respect to channel width and spatial streams
Majority of the client devices available today can support a maximum of three spatial streams.

Client Capability
802.11n – 40 MHz Chan-
nel
802.11ac – 40 MHz
Channel
802.11ac – 80 MHz
Channel
1x1 (Smart Phone) 150 Mbps 200 Mbps 433 Mbps
2x2 (Tablet, PC) 300 Mbps 400 Mbps 867 Mbps
3x3 (PC) 450 Mbps 600 Mbps 1300 Mbps
Table 5: Comparison of 802.11n and 802.11ac data rates based on client capability
As shown in the prior table, 256 QAM improves 802.11ac data rate when compared to 802.11n data rates at
40 Mhz channel width. The maximum 802.11ac Wave 1 data rates are obtained with 256 QAM modulation and
80 MHz channel width.
Increased coding in terms of bits/sec per hertz of spectrum comes at a price. The required signal level for good
reception increases with the complexity of modulation and the channel bandwidth. The following graph shows,
for instance, that whereas
-64 dBm was sufficient for the top rate (72 Mbps) of 802.11n in a 20 MHz channel, the requirement rises to -
59 dBm for the top rate (86 Mbps) of 802.11ac, single stream in a 20 MHz channel, and to -49 dBm for the top
rate (866 Mbps) in a 160 MHz channel.
Figure 10 Minimum RSSI requirements for different modulation types
Error Correction Methods
Like the 802.11n standard, 802.11ac supports two error correction methods:
1. Binary convolutional code (BCC)
2. Low-density parity check (LDPC)
The BCC method is mandatory, while the LDPC method is optional. Though LDPC is a relatively new technique,
it offers improvement over BCC and in some cases it can result in moving to the next higher-order modulation
rate (on the prior graph), or alternatively, at the same modulation rate it can significantly reduce error packets.
For more details about BCC and LDPC, refer to “802.11ac IN-DEPTH” white paper available at:
http://www.arubanetworks.com/pdf/technology/whitepapers/WP_80211acInDepth.pdf
Frame Aggregation, A-MPDU, and A-MSDU
In addition to the enhancements discussed earlier, the 802.11ac standard includes enhancements to Frame
Aggregation, Aggregated MAC Protocol Data Unit (A-MPDU), and Aggregated MAC Service Data Unit(A-MSDU).
A client (or AP) must contend for the medium (a transmit opportunity on the air) with every frame it wishes to

transmit. This results in contention, collisions on the medium, and back-off delays that waste time, which could
be better used to send traffic. The frame aggregation mechanism introduced in 802.11n, which reduces
contention events, are also supported in the 802.11ac standard.
With MAC-layer aggregation, a station with a number of frames to send can opt to combine them into an
aggregate frame (MAC MPDU). The resulting frame contains lesser header overhead than that without
aggregating, and because fewer, larger frames are sent, the contention time on the wireless medium is reduced.
In the A-MSDU format, multiple frames from higher layers are combined and processed by the MAC layer as a
single entity. Each original frame becomes a subframe within the aggregated MAC frame. Thus this method
must be used for frames with the same source and destination, and only MSDUs of the same priority (access
class as in 802.11e) can be aggregated.
An alternative method, A-MPDU format, allows concatenation of MPDUs into an aggregate MAC frame. Each
individual MPDU is encrypted and decrypted separately, and is separated by an A-MPDU delimiter, which is
modified for 802.11ac to allow for longer frames.
In 802.11ac, the A-MSDU limit is raised from 7,935 bytes to 11,426 bytes, and the maximum A-MPDU size
from 65,535 bytes to 1,048,576 bytes. The following diagram shows the MAC frame aggregation of 802.11ac.
Figure 11 MAC Frame Aggregation in 802.11ac
A-MPDU must be used with the block-acknowledgment function introduced in 802.11n. This allows a single
block acknowledgment frame to acknowledge a range of received data frames.
It is possible to combine these techniques, that is combining a number of MSDUs and A-MSDUs in an A-MPDU.
Theoretical studies have shown that this improves performance over either technique when used alone.
However, most practical implementations to date concentrate on A-MPDU, which performs well in the
presence of errors due to its selective retransmission ability.
Power-Save Enhancements
Many 802.11 devices are still battery-powered. Although other components of a smartphone, notably the
display still tax the battery much more than the Wi-Fi subsystem, power-saving additions are still worthwhile.
The new power-save enhancement is known as very high throughput transmit opportunity (VHT TXOP) power-
save. It allows a client to switch off its radio circuit after it has seen the AP indicate that a transmit opportunity
(TXOP) is intended for another client. This should be relatively uncontroversial, except that a TXOP can cover
several frames; so the AP must ensure that after having allowed a client to doze at the beginning of a TXOP, it
does not then transmit a frame for that client. Similarly, if a TXOP is truncated by the AP, it must remember
that certain clients will still be dozing and not send new frames to them.

To allow clients to quickly identify if a frame is addressed to them, a new field called partial association ID
(partial AID) or Group ID for MU-MIMO is added to the preamble. If the partial AID field is not its own address,
the client can doze for the remainder of the TXOP.
One reason to introduce VHT TXOP power-save is that the frames are getting longer. 802.11ac has extended
frame lengths and now allows for frames approaching 8 KB in length, and aggregated frames (A-MPDU) of 1
MB length.
Some of this is accounted by the increased rates, so time on the medium will not be extended pro-rata. But
video and large file transfers, two of the more important use cases, drive large number of long frames (possibly
aggregated as A-MSDU or A-MPDU frames at the Wi-Fi layer); so it may well be worthwhile switching off a radio
while large numbers of frames are being delivered to other clients.
The other major power-saving feature of 802.11ac is its high data rates. Power consumption in 802.11 is
heavily dependent on the time spent transmitting the data. The higher the rate, the shorter the transmission
burst. The time spent receiving frames is also reduced by high rates, but not so significantly.
Backward Compatibility
Because 802.11ac includes new, higher-speed techniques, its transmissions are by definition not decodable by
older 802.11 equipment. But it is important that an 802.11ac AP, adjacent to older APs, is a good neighbor.
802.11ac has a number of features for co-existence, but the main one is the extension of an 802.11n
technique: A multipart RF header that uses 802.11a and 802.11n modulation. Non-802.11ac equipment can
read these headers and identify that the channel will be occupied for a given time, and therefore can avoid
transmitting simultaneously with the very high throughput frame. So 802.11ac is backward compatible with
legacy 802.11 standards and can be deployed in mixed environment with legacy APs.
Protection, Dynamic Bandwidth, and Channelization
When an 80-MHz 802.11ac network operates in the neighborhood of an older AP, or a network that is only
using a 20 MHz or 40 MHz channel, it must avoid transmitting simultaneously with a station in the neighboring
network. The question here is as to how this can be achieved without permanently reducing its channel
bandwidth.
The solution lies in answering these three questions:
1. How can a station (AP or client) that wants to operate at 80 MHz, warn older stations to stay off the air
while it is transmitting in 802.11ac mode, which they cannot decode?
2. How will the 802.11ac station know that the full channel is clear of other stations’ transmissions?
3. Finally, how can bandwidth usage be optimized if, for instance, an older station is transmitting in just 20
MHz of the 80-MHz 802.11ac channel?
Figure 12 Dynamic Bandwidth Operation, 80 MHz Channel
Sending a warning to other stations to stay off the air is achieved by Request to Send (RTS) frames. The
802.11ac station sends out multiple parallel RTS protection frames in each of its 20 MHz channel (out of the 80
MHz channel), at rates an 802.11a or 802.11n clients can understand. The multiple RTS frames use duplicate,

quadruplicate, or octuplicate transmission. Before sending RTS, it performs clear channel assessment (CCA) to
make sure it cannot hear any transmissions in progress. On receiving the RTS frame, older stations know how
long to wait for the 802.11ac transmission.
Next, the recipient runs a CCA in each of the 20 MHz channels. The RTS frame format is extended so that the
originator can indicate its channel options and replies with a Clear to Send (CTS) response to indicate whether it
hears transmissions in progress from any neighboring network. If not, the originator transmits the data frame
using the full bandwidth – 80 MHz in this case.
However, if the recipient does find transmissions in progress on any secondary channel, it can still continue
responding with CTS, while indicating which primary channels are clear (20 MHz or 40 MHz). Then, the
originator can send its transmission using only the usable part of the 80 MHz channel.
This may force a reduction in channel from 80 MHz to 40 MHz or even 20 MHz, but the frame will be
transmitted using airtime that would otherwise be unused. This feature is called dynamic bandwidth operation.
Dynamic bandwidth optimization is constrained by 802.11ac definitions of primary and secondary channels.
For each channel, such as an 80 MHz channel, one 20 MHz channel (subchannel) is designated as primary. This
is carried through from 802.11n, and in networks with a mix of 802.11ac and older clients, all management
frames are transmitted in this channel so that all clients can receive them.
The second part of the 40 MHz channel is called the secondary 20 MHz channel. And the 40 MHz of the wide
channel that does not contain the primary 20 MHz channel is the secondary 40 MHz channel. Data
transmissions can be in the primary 20 MHz channel, the 40 MHz channel including the primary 20 MHz
channel, or the full 80 MHz channel, but not in other channel combinations.
Figure 13 Dynamic bandwidth and Channelization in 802.11ac, 80 MHz Channel
Finally, the introduction of wideband channels, especially the 80 + 80 MHz channels, requires some changes to
the channel switch announcement (CSA) frame. CSA is used by an AP to inform its associated clients when it is
about to switch channels after radar has been detected in the current channel. It was first introduced in
802.11h as part of Dynamic Frequency Selection (DFS). Otherwise, the operation of DFS remains unchanged
with 802.11ac.

Aruba 802.11ac Networks 802.11ac Planning and Deployment Guidelines | 23
Chapter 4
802.11ac Planning and Deployment Guidelines
This chapter provides guidelines to plan and deploy 802.11ac WLAN network. In general, 802.11ac
deployment can be divided into the following two categories:
Greenfield:This is a deployment scenario where a network is being installed from scratch. There is no legacy
network in place, which means you can design a network with future technology support in mind. A campus
that does not have a wireless network today would be considered a Greenfield environment.
Brownfield:This is a scenario where a legacy wireless network already exists and there is plan to deploy
802.11ac. Because there is a dependency on how the network can be designed, a phased approach is typically
adopted to roll out new technology. A campus already having 802.11 a/b/g- or 802.11n-based wireless
network, and requiring you to implement 802.11ac is an example for a mixed environment. Deployment
recommendations might vary slightly based on the environment under consideration.
If you are going through a refresh cycle to transition to 802.11ac network from legacy network, Aruba
recommends consideration of the following points before doing a one-to-one replacement of legacy APs with
802.11ac APs:
l If the existing network is a capacity-based design in 5 GHz band, then one-for-one AP replacement with
802.11ac AP is viable.
l If the existing network was originally planned for legacy 802.11a/b/g or is an 802.11n network planned for
2.4 GHz based on coverage, then a network redesign is recommended. Redesigning includes a combination
of both physical and virtual survey.
Other factors to consider when planning for one-to-one replacement of legacy APs are:
Original AP density: If the answer to any of the following questions is yes, then one- to-one replacement
might not be a recommended best practice:
l Is your current network planned for coverage as opposed to capacity?
l Is there any coverage hole in your environment where you do not receive RF signals with current
deployment?
l Are there any known RF-related issues such as poor connectivity and low performance?
l Do you want to provide seamless roaming experience to users?
l Do you need location-based services?
l Is there any architectural change in you facility like new walls or metal cabinets, which are resulting in poor
Wi-Fi connection?
Number of devices on the network: Number, type, capabilities, and mix (for example, single stream vs
multiple stream, 802.11a/b/g or 802.11n or 802.11ac) of devices that are expected to be part of the network
can be a good metric to identify how many APs you need in you network. If number of devices on your
network increases, you will need to add more APs to support them, or otherwise there will be a drop in network
performance and users will start complaining for poor service. Also, you need to ensure what type of devices
you expect on your network. 802.11ac clients are much faster and take less airtime compared to legacy clients.
Application type: You need to decide on what applications you want to support on your network. Enterprise
applications like Microsoft Lync carry real-time voice and video traffic, which is delay-sensitive and requires
thorough planning regarding AP placements. Depending on different applications you want to support on your
network, identify how much bandwidth is required for each device. When you know the total number of
devices on your network and the bandwidth required per device to support applications, you can plan on the
number of clients associating per AP and total AP density required to cover the entire facility.

24 | 802.11ac Planning and Deployment
Guidelines
Although Aruba APs can support up to 255 client devices per radio, in general it is recommended to plan for 40
to 60 clients per radio so as to provide good user experience.
ArubaOS firmware version 6.4 and later used on 7200 and 7000 Series controller supports AppRF, a deep
packet inspection feature that allows you to classify and enforce policies on the applications running on your
network. AppRF supports more than 1400 applications and allows network administrators to create policies
for blocking or permitting applications depending on your network policy. You can also create bandwidth
contracts to throttle traffic or apply Quality of Service (QoS) to prioritize application based on your use cases.
Aruba Networks, Inc., supports Microsoft Lync Software-Defined Networking (SDN) API. This provides visibility
into Microsoft Lync traffic and helps prioritize Microsoft Lync traffic with respect to other background traffic so
that users can have high-quality voice and video calls. With SDN API, the Aruba Controller gets the real-time
Microsoft Lync call quality metrics from the Microsoft Lync servers. This allows network adminstrators to
quickly identify and troubleshoot issues related to Microsoft Lync voice and video calls. If any type of voice,
UCC, or multicast applications are to be used over the Wi-Fi infrastructure, this will help drive the design criteria.
After having understood the AP density requirements, the best practices and recommendations to deploy
802.11ac network using Aruba controllers and APs are provided in the following sections.
This chapter covers the following sections:
l Wired Network Considerations
l RF Planning
l Forwarding Mode Recommendations
l Channel Width Selection
l Capacity Planning
Wired Network Considerations
This section provides guidelines that will help you plan and design your wired network infrastructure to
support the deployment of 802.11ac wireless network.
AP Power Requirements
An important consideration while choosing the wired access switch for powering the 802.11ac APs is the Power
over Ethernet (PoE) capability. It is recommended to use 802.3at-capable (PoE+) switches at access layer to
supply power to the APs. Although Aruba APs support full 802.11ac functionality with 802.3af (PoE) power
source, the AP-220 Series operates with some reduced capabilities in 2.4 GHz band.
802.11ac-Capable AP
Model
802.3af (PoE) 802.3at (PoE+)
AP-224/ AP-225 5 GHz: 3x3:3
2.4 Ghz: 1x3:1
USB port: disabled
Second Ethernet port: disabled
5 GHz: 3x3:3
2.4 GHz: 3x3:3
USB port: enabled
Second Ethernet port: enabled
AP-214 / AP-215 5 Ghz: 3x3:3
2.4 Ghz: 3x3:3
USB port: disabled
Second Ethernet port: N/A
5 Ghz: 3x3:3
2.4 Ghz: 3x3:3
USB port: enabled
AP-204 / AP-205 5G Hz: 2x2:2
2.4 GHz: 2x2:2
USB port: N/A
5 Ghz: 2x2:2
2.4 Ghz: 2x2:2
USB port: N/A
Table 6: Capabilities of Aruba 802.11ac APs with respect to 802.3af and 802.3at power source

AP Uplink Considerations
In theory, the dual band throughput of 802.11ac APs can exceed 1Gbps, as the maximum theoretical data rate
in 5 GHz is 1.3 Gbps (802.11ac) and that in 2.4G Hz (802.11n) is 216 Mbps, assuming the recommended 20
MHz channel width for 2.4 GHz. We do not expect the actual throughput seen on the wired network to reach
that limit in any 802.11ac Wave 1 deployment. Therefore, extending an additional Ethernet cable is not an
absolute requirement today with the first generation 802.11ac deployment. However, in a Greenfield
deployment where contractors are hired to extend cables to APs for the first time, it might be a good idea to
think about the extending 2 x Ethernet cables per location to make the network future-proof. For an enterprise
where wireless is the primary method of network access, this second Ethernet cable can be used today with AP-
220 Series for providing PoE redundancy. In such deployments, when the switch terminating eth0 port of AP
fails, the AP can reboot and come up again using eth1 port terminating at a redundant switch.
Figure 14 AP Uplink Consideration
At the minimum, the cabling infrastructure in your network should be using Cat 5e cables. However if this is a
Greenfield deployment and if you can afford to deploy Cat 6a cables, that will allow your network to be future-
proof.
Access Network Uplink Consideration
Because 802.11ac is all about gigabit Wi-Fi, it is important that the supporting infrastructure is optimized to
leverage all that 802.11ac APs have to offer. To support an increased throughput without making the switches
at various layers (access, distribution, and core) a bottleneck, sizing the distribution network to provide
sufficient end-to-end bandwidth for the given number of APs and devices as well as peak throughput is critical.
The uplink recommendations for 802.11ac WLAN network are as follows:
l Have a gigabit connectivity between AP and Access switch.
l Uplink from access switch to the distribution switch should be 10 Gbps link.
l If high availability is important to your network, have redundant 10 Gbps uplink between the access and
distribution switches.
l It is recommended to plan for a minimum of redundant 10 Gbps uplink from the controller.
Link aggregation recommendations to support 802.11ac from the access layer to the core are a network best practice.
The oversubscription offered is a common practice and really not a problem.

Guidelines
Figure 15 Access Network Uplink Consideration
Jumbo Frames
With the advent of 802.11ac networks, the key factors for its improved performance over 802.11n are A-
MSDU and A-MPDU, both of which aggregate services and MAC information. With an optimum aggregation
level, an 802.11ac wireless frame is now a jumbo frame and is 4500 bytes or larger. Prior to the 802.11ac
standard, the majority of the traffic fitted in a ‘normal’ 1500 byte Ethernet frame and no special handling was
required on the wired network to achieve maximum aggregate performance. With the increased aggregation
with 802.11ac, the underlying network needs to be able to support end-to-end jumbo frames; otherwise, the
benefits of aggregation efficiency over the air will be lost due to fragmentation. So it is recommended to enable
end-to-end jumbo frame support on your network to get the maximum 802.11ac performance.
VLAN Design
When you are planning for a VLAN design of your network, it is recommended to separate your wireless VLANs
from wired VLANs, as this will eliminate unnecessary broadcast/multicast traffic in wireless VLANs and improve
network performance.
Figure 16 Wired and Wireless VLANs
Wireless VLAN Design
When you are planning a VLAN design for wireless clients, it is recommended to have a flat single VLAN design.
Single VLAN configuration simplifies network design and works well on IPv4 and IPv6 networks especially in
large campus design with thousands of users. It also simplifies network access configuration and hence makes
network operation and maintenance much easier.
In addition to single VLAN design, Aruba has an option to use VLAN pools. VLAN pool is a group of equal-sized
VLANs that can be referenced as a single entity. A VLAN pool can be associated with an interface to allow for
devices that are connecting via the interface to obtain an IP address from that pool of addresses. VLAN pools
are used for networks where using a single VLAN option is not feasible due to IP address limitation.
However, if you want IPv6 support on your network, it is not recommended to use VLAN pools. With IPv6,
most clients use Stateless Address Auto Configuration (SLAAC) for address derivation, where the router
announcements (RA) are sent as multicast packets to all clients. With Multiple VLANs in a VLAN pool and an
IPv6 subnet associated with each VLAN in the pool, each client gets multiple RAs and can pick up any of the RAs

and derive an address from it. There is a very high probability that a client may pick an address in a VLAN that
we did not associate it with. This breaks IPv6 connectivity.
So Aruba recommends using a single flat VLAN for wireless clients. To optimize the wireless performance, it is
recommended to use broadcast/multicast (BC/MC) optimization knobs of Aruba controller to prevent
unnecessary broadcast/multicast traffic from occupying spectrum bandwidth. For more details, see the
Broadcast/Multicast optimization section in Chapter 5: WLAN Optimizations.
RF Planning
When you are planning to deploy a WLAN network, it is important to understand how and where your APs will
be mounted to have a seamless Wi-Fi experience. You should identify the attenuation and interference sources
in you environment, which can degrade your network performance. Following section provides RF planning
guidelines to deploy an 802.11ac WLAN network.
AP Mounting Recommendations
Indoor APs are typically deployed in either of the following methods:
l Ceiling mount deployment
l Wall mount deployment
Aruba recommends against desk or cubicle mounts. These locations typically do not allow for a clear line-of-
sight throughout the coverage area, which in turn can reduce WLAN performance.
Ceiling Mount Deployment
The majority of modern WLAN deployments are at the ceiling level. A ceiling deployment can occur at or below
the level of the ceiling material. In general, it is not recommended to mount APs above any type of ceiling
material, especially suspended or “false” ceilings. There are two reasons for this: First, many ceiling tiles contain
materials or metallic backing that can greatly reduce signal quality. Second, the space above the ceiling is full of
fixtures, air conditioning ducts, pipes, conduits, and other normal mechanical items. These items directly
obstruct signal and can harm the user experience.
Figure 17 Ceiling mounted Access Point
Wall Deployment
Wall deployments are not as common as ceiling deployments, but are often found in hotels and dormitory
rooms. Walls are a common deployment location for large spaces such as lecture halls because reaching the
ceiling is difficult. Wall deployments may also be preferable in areas with a hard ceiling where cabling cannot be
run. If you are not using the AP-103Hor AP-205H, which was designed for wall mounting, consider the antenna
pattern before you deploy wall-mounted APs.

Guidelines
Figure 18 Wall Mounted Access Point
Site Survey
One of the important steps in RF planning is site survey analysis, which helps to identify AP placements to
provide high-quality wireless experience throughout the facility. There are different types of site survey
methods available such as virtual site survey, passive site survey, active site survey, and spectrum clearing site
survey.
A virtual site survey, which is generally done using softwares like Aruba’s VisualRF Plan, can be a good starting
point to identify the coverage pattern. It can generate heat map showing RSSI values and can also help in
generating bill of material (BoM) for your project. Although virtual site survey is a quick way to simulate AP
placements and understand coverage patterns, it is recommended to conduct a physical site survey to validate
the estimates of virtual site survey and verify the coverage and capacity of your network.
For more details regarding wireless site survey, refer to the indoor site survey and planning VRD available at:
http://community.arubanetworks.com/t5/Validated-Reference-Design/tkb-p/ArubaVDRs.
When conducting site survey to plan for AP placements for a ubiquitous Wi-Fi coverage, it is important to
remember that RF signals with higher frequency cover short distance compared to the low-frequency signals.
You should plan your network in such a way that the 5 GHz band signals cover the area where you need to
provide Wi-Fi to the users. If you plan the network based on 2.4 GHz band coverage, you might create a
coverage hole as shown below.
Figure 19 Comparison of 2.4 GHz and 5 GHz coverage pattern
Aruba Recommendations for AP Placements
AP placement recommendations for an enterprise network, which needs to support high-performing 802.11ac
network along with real-time voice and video applications, are as follows:
l Distance between two APs should be approximately 40 to 60 feet.
l Minimum RSSI should be -65 dBm throughout the coverage area.

l SNR should be greater than 25 dB.
l APs should be deployed in a honeycomb pattern as shown in the following diagram. This pattern ensures
that distance is normalized along all directions to have the best coverage.
Figure 20 Honeycomb Pattern AP Deployment
The AP placement recommendations will vary if you are planning for ultra-high density environment such as
conference halls, auditoriums, and public venues. For more information on these types of deployments, refer to “Very
High Density 802.11ac Networks Validated Reference Design” guide available at:
http://community.arubanetworks.com/t5/Aruba-Support-Documentation /tkbc-
p/ArubaSupportDocumentation?_ga=1.65699885.224949537.1405570350
When you design an 802.11ac network using dual band APs in such a way that 5 GHz band signal covers the
entire facility, it might create co-channel interference (CCI) in 2.4 GHz band. This is because 2.4 GHz signals
have greater coverage range compared to 5 GHz signals. To avoid this scenario, you can disable the 2.4 GHz
radio on some of the APs on your network as show in the following figure.
Figure 21 Mitigating CCI in 2.4 GHz band

Guidelines
In this figure, as 3 APs are enough to have a 2.4 GHz coverage, you can disable the
2.4 GHz radio on AP-4 to avoid co-channel interference. You can use the 2.4 GHz radio on AP-4 either as a
dedicated spectrum monitor to collect spectrum analysis data or as a dedicated air monitor to perform wireless
intrusion detection and wireless intrusion protection.
Factors Attenuating Wireless Signals
It is important to understand the physical environment where we are planning to deploy 802.11ac WLAN
because different materials have different attenuation characteristics which can impact the wireless
performance. The following table compares the attenuation caused in 2.4 Ghz and 5 Ghz bands due to walls,
glass window, or other such things.
Indoor
Environment
Attenuation in 2.4 GHz Attenuation in 5 GHz
Fabric, blinds, ceiling tiles Approximately 1 dB Approximately 1.5 dB
Interior drywall 3–4 dB 3–5 dB
Cubicle wall 2–5 dB 4–9 dB
Wood door (Hollow –Solid) 3–4 dB 6–7 dB
Brick/concrete wall 6–18 dB 10–30 dB
Glass/window (not tinted) 2–3 dB 6–8 dB
Double-pane coated glass 13 dB 20 dB
Steel/fire exit door 13–19 dB 25–32 dB
Table 7: Comparison of Attenuation Losses in 2.4 GHz and 5 GHz band
Wi-Fi and Non-Wi-Fi Interference Sources
One of the common causes of degradation in wireless performance is interference. It can be Wi-Fi interference
caused by neighboring APs or a non-Wi-Fi interference caused by a microwave lying in break room. You should
conduct spectrum analysis to identify any potential Wi-Fi or non-Wi-Fi interference in your environment which
can result in poor user experience. Some of the known interference sources are shown in the following table.
Wi-Fi Interference Source Non-Wi-Fi Interference Source
l Your APs (overdesigned)
l Somebody else’s APs (neighbor)
l Muncipal Wi-Fi Network
l iPhone Personal Hotspots
l Neighboring clients
l Faulty clients
l Blue-tooth (headset, keyboards,
mouse, speaker)
l Microwave Oven
l Cordless phones, mouse
l Very strong out-of-band source (GSM
tower/DAS)
l Baby monitor
l WiMax (2.5 GHz)
l ZigBee (802.15.4)
l Video or security cameras
Table 8: List of Wi-Fi and Non-Wi-Fi Interference Sources

Aruba APs can act as a dedicated spectrum analyzer which will scan all the Wi-Fi channel in regulatory domain or it can
at as a hybrid spectrum analyzer where the AP will serve clients and simultaneously scan the channel on which it is
serving clients. For more details about Spectrum Monitors, refer to “Aruba 802.11n Networks Validated Reference
Design” document available at: http://community.arubanetworks.com/t5/Validated-Reference-Design/tkb-
p/ArubaVDRs.
Forwarding Mode Recommendations
For campus AP deployment, Aruba supports three different forwarding mode — Tunnel Mode, Decrypt-Tunnel
mode, and Bridge mode.
In general, bridge mode is not recommended to be used in campus environments.
This section provides information on the most common AP forwarding modes and the recommended mode
for 802.11ac deployments.
Tunnel Mode
The bulk of today's deployments utilize tunnel mode as the de-facto AP forwarding mode, where the AP sends
the 802.11 traffic back to the controller. One of the advantages of the tunnel mode is centralized encryption
of control and data traffic. That is, in this mode, the control and data traffic between the AP and the mobility
controller is encrypted, which increases network security.
Figure 22 Tunnel Mode
Tunnel mode is our preferred mode of operation and has met the requirements of Aruba customers. As
discussed earlier, with frame aggregation techniques, 802.11ac frame is now a jumbo frame. Without jumbo
frame support, Aruba controller and APs with service set identifiers (SSIDs) in tunnel mode do not participate in
A-MSDU negotiations and hence there will be an impact on performance. To achieve high performance, it is
always recommended to enable jumbo frames end-to-end, that is your switches and routers should also
support jumbo frames.
The forwarding mode does not affect the controllers' maximum AP limit and performance, for example a 7240
controller can handle 2048 campus APs operating in tunnel mode without any performance issues.

Guidelines
Decrypt-Tunnel Mode
When an AP uses decrypt-tunnel forwarding mode, it decrypts and decapsulates all 802.11 frames from a
client and sends the 802.3 frames through the GRE tunnel to the controller, which then applies firewall policies
to the user traffic. When the controller sends traffic to a client, the controller sends 802.3 traffic through the
GRE tunnel to the AP, which then converts it to encrypted 802.11 and forwards to the client. In decrypt-tunnel
mode, the encryption/decryption of traffic happens at the AP. The mobility controller still acts as the
aggregation point for terminating data traffic. In this mode, the AP-Client pair can take full advantage of A-
MSDU and A-MPDU aggregation on the WLAN radio side without requiring the wired network to transport the
jumbo frames, because the AP is performing all assembly aggregation and de-aggregation locally.
Figure 23 Decrypt-Tunnel Mode
The performance of decrypt-tunnel mode is equivalent to tunnel mode with jumbo frames enabled; however,
there is no centralized encryption because the user data traffic is decrypted by the AP and sent to the
controller through a GRE tunnel.
Channel Width Selection
At present, 802.11ac Wave 1 products can be deployed to transmit in 20 MHz, 40 MHz, and 80 MHz channels
in 5 GHz band. To get the maximum performance, 802.11ac APs should be deployed to use 80 MHz channel
width. However, as discussed earlier, in the US there are only 5 available 80 MHz channel out of which 3
channels require DFS support to protect radar operation. We can design a network using the available five 80
Mhz channels in 5 GHz band using DFS channels support; however, it might be a problem if there is radar
interference near your environment, because when an AP operating in DFS channel detects a radar signal, it will
disconnect the clients and move to a non-DFS channel. This will affect the users connected on that AP and
might also create a co-channel interference with the neighboring AP, thereby degrading the network
performance.
Selection of channel width depends on site environment and network requirements. Some ultra-high density
networks would even prefer deploying APs with 20 Mhz channel width so as to have more channel to reuse
throughout the network without causing Wi-Fi interference.
You should also consider the clients' capabilities when planning for deploying APs with DFS channels to verify if
all of your clients support DFS channels. Even if some clients support DFS channel, they may not actively probe
on those channels and only learn of them through passive scanning. This can lead to roaming issues. It is
recommended to perform roaming test using different clients to analyze their roaming pattern with DFS
channels.

With 802.11ac standard, Federal Communications Commission (FCC) allowed the use of Channel 144. However, legacy
and 802.11n clients do not support Channel 144 and hence they cannot associate to the AP if its primary channel is
Channel 144. So make sure when you plan for 80 Mhz channel, avoid using channel 144 as primary channel.
General guidelines for channel width selection is as follows:
Channel Width Selection for Greenfield Deployments: When planning for Greenfield deployment, you
can go with 80 Mhz channel width deployment; however, DFS channels need to be assessed on a case-by-case
basis. Certain verticals like healthcare try to avoid deploying APs in the DFS channel to avoid radar-triggered
channel shifts, given that mission-critical services like heart rate monitors and IV pumps are running on Wi-Fi. In
case where use of DFS channels is not feasible either due to regulatory domain constraints or due to radar
interference, it is recommended to use 40 MHz channel width so that more channels are available for reuse.
Channel Width Selection for Brownfield Deployments: In a Brownfield deployment, where the customer
is migrating from a legacy 802.11a/b/g/n AP to 802.11ac AP and there will be a mix of Wi-Fi technologies, you
can utilize 80 MHz or 40 Mhz channels.
If you are utilizing the wider 80 MHz channels, then you should perform interoperability tests with a sample set
of your client devices to ensure that the legacy clients do not cause implementation issues. In such case, you
would need to limit your network to 40 MHz channels until your clients are updated. This is more pronounced
in environments such as universities, where the IT department does not have control over the devices that
users bring in.
For environments where IT has control over the device, it is recommended to update the client wireless chipset
driver to the latest version and run some tests between 802.11n and 802.11ac APs when 802.11ac is
deployed using 80 MHz channels. It is also recommended to deploy the new 802.11ac APs together in an area
rather than a mix (salt and pepper) of legacy and 802.11ac APs.
Capacity planning
When planning for capacity, the most important things to consider are how many devices will access the
network and what will be the type of client mix. Generally, people carry at least three devices – for example, a
laptop, a tablet, and a smartphone. The number of devices per user also has ramifications in the design of
VLANs and subnets. Expected number of active devices trying to access the network will be one of the metrics
to calculate the required AP density.
When calculating AP density for a capacity design, plan to have around 40 to 60 active devices per radio.
Although APs can support 255 associated devices per radio, having less users will allow facilitation of
bandwidth requirements and provides for high quality user experience. It is also important to select right
devices to support your network requirements. Aruba Networks, Inc., have a wide portfolio of Controllers and
APs that allows you to select the best combination of devices to meet your network requirements.
For detailed information about WLAN products, refer to http://www.arubanetworks.com/products/.
Active devices are the clients which are associated to the AP and actively sending and receiving data on the wireless
network. Associated devices are clients that are just associated to the AP and might not be involved in active data
transfer activity.
As can be seen from the following figure, typically in a capacity-based design, you will have to deploy more APs
compared to coverage-based design. In a capacity design, users are generally associated with high data rates
and get better wireless experience.

Guidelines
Figure 24 Capacity Planning
Capacity planning along with Aruba’s unique features like Adaptive Radio Management and ClientMatch allows clients
to associate at higher data rates.
Parameter Recommendation
AP forwarding mode Tunnel mode
Distance between APs Neighboring APs should be 40 to 60 feet
apart
AP mounting Ceiling mount or wall mount
Channel width recommendation 80 MHz channel will give maximum
performance but will require DFS support.
Consider using 40 MHz or 20 MHz
channels in 5 Ghz band to have better
channel separation.
Number of devices per radio 40 to 60 active client devices
Power It is recommended to use PoE+ enabled
switches to power the APs.
AP Uplink 1 Gpbs link between AP and access switch
Access Switch Uplink 10 Gbps uplink for access switch
terminating APs
Controller Uplink At least 10 Gbps uplink with redundancy
VLAN design Single Flat VLAN design is recommended
along with the broadcast/multicast
optimization configuration.
Jumbo Frame support Enable end-to-end jumbo frame support.
Ethernet cable At least Cat 5e cable is needed. Cat 6
would be preferred if cost is not an issue.
Table 9: Summary of Aruba recommendations

Aruba 802.11ac Networks WLAN Optimizations | 35
Chapter 5
WLAN Optimizations
This chapter provides guidelines and recommendations on some of the unique features supported by Aruba’s
WLAN architecture to optimize WLAN network performance. We will provide recommendations for following
topics:
l Adaptive Radio Management (ARM)
l ClientMatch (CM)
l Broadcast/Multicast Optimization
l Dynamic Multicast Optimization
l Traffic Shaping
l QoS
Adaptive Radio Management (ARM)
Radio Frequency (RF) spectrum is a limited and shared resource, and as many factors as possible must be
controlled to provide an optimal user experience. ArubaOS supports Adaptive Radio Management (ARM)
feature that allows WLAN infrastructure to make decisions about radio resources and client connections
without manual intervention by network administrators or client-side software.
Aruba APs or Air Monitors (AM) periodically scan the networks to gather information about the RF
environment. This information is then fed to the ARM algorithm that optimizes the network and improves the
user experience. ARM is a part of the base ArubaOS™ and is available on all Aruba Mobility Controllers and APs.
One of the important functions of ARM is to dynamically select channel for the APs as a means to avoid Wi-Fi
and non-Wi-Fi interference and to adjust transmit power so as to mitigate the issues of coverage hole and
optimize network performance.
Channel and Power Settings
Initially, when 802.11n WLANs were introduced, network administrators had to manually build a channel and
power plan based on onetime site survey. The following figure shows a typical 2.4 Ghz RF channel plan where
the network engineer must manually change the power and channel on each AP. Remember that in the 2.4
GHz band, only three channels are practical for use in most regulatory domains. A similar plan exists in the 5
GHz band, but generally more channels are available.

36 | WLAN Optimizations Aruba 802.11ac Networks
Figure 25 Typical Channel Plan 20 MHz channel width
After all the APs are configured, they will remain in this state until the administrator changes them manually.
The problem with manual channel plans is that they were based on a snapshot in time of the RF environment.
The presence of devices, walls, cubes, office doors that open and close, microwave ovens, and even the human
body, all have an effect on the RF environment. This fluid environment generally cannot be tested and
compensated for in a static channel and power plan. First of all, it is very time consuming to configure each and
every AP on the network manually. Additionally, the static plan does not automatically work around AP failure
and new sources of interference. If an AP in a particular area fails, the administrator will have to manually
increase power on the surrounding APs to compensate for the RF “hole” until that AP can be replaced. If
persistent interference makes a channel unusable, that AP must be configured with a new channel. New
channels typically have a cascade effect and require that changes be made to other adjacent APs in the area,
eventually propagating through the entire local wireless network. Consider the scenario shown in the following
figure, when a wireless camera interferes with the AP's channel, the entire plan must be adjusted to
compensate.
Figure 26 Dynamic Channel Selection Using ARM to Avoid Interference
At the most basic level, ARM allows the network to consider Wi-Fi and non-Wi-Fi interference and other APs
before it configures power and channel settings for APs. APs and AMs continuously scan the environment. If
an AP goes down, ARM automatically fills in the “RF hole.” ARM increases power on the surrounding APs until
the original AP is restored. When the AP is restored, ARM sets the network to the new optimal setting. If an
interfering device (Wi-Fi or non-Wi-Fi) appears on the network, such as a wireless camera that consumes a
channel, ARM adjusts the AP channels appropriately.

The important thing here is that the Aruba WLAN controller learns networkwide information and takes decision
dynamically to change channel and power of the APs to avoid interference and improve network performance.
ClientMatch
There is a better understanding of all the improvements that come with 802.11ac standard and how clients
can get higher data rates. Even though clients can achieve high speeds, it is difficult to ensure that each client in
a network has a good user experience especially when we have smartphones, tablets, and other clients that
control their own connectivity and roaming decision. Prior to ClientMatch, clients were steered to the best AP
only during the initial association. In case of any RF environment changes, for example if SNR or signal level of
client falls below a certain level, the AP will not make any intelligent decision on steering the client to a better AP
and will rely on clients to make its own decision. Similarly, during roaming scenario, some clients stick to an old
AP even when it can hear another AP with better signal strength. This can result in poor connectivity and can
bring down the performance of other associated clients on that AP.
ClientMatch technology from Aruba Networks, Inc., is a patented, standards-based RF management
technology that puts the WLAN infrastructure in control of client connectivity and roaming. Leveraging a
system-level view of the network, ClientMatch monitors clients and automatically matches them to the right
radio on the right AP, boosting the overall WLAN performance and delivering a consistent, predictable
performance to every user and client, while eliminating the sticky client problem for good. ClientMatch is an
ArubaOS function and no software changes are required on the client side to achieve this functionality.
ClientMatch works with all clients, including all the latest 802.11ac clients across all operating systems.
ClientMatch is supported on ArubaOS 6.3.0 and later firmware versions.
ClientMatch leverages industry standards to accomplish its monitoring and control functions, including the 802.11k and
the 802.11v standards. As a result, IT is assured of interoperability with no additional overhead.
ClientMatch Capabilities
ClientMatch has number of capabilities that enables it to connect the client to the best AP and improve the
user experience. In general, here are some of the client/AP mismatch conditions that are managed by
ClientMatch.
Band Steering
Dual band clients scan all the channels on both 2.4 GHz and 5 GHz radios and may attempt to connect to the
basic service set identifier (BSSID) with the strongest signal or the BSSID that responds first to the client’s
probe request. This sometimes results in a client connecting to an SSID in 2.4 GHz at lower PHY rates when it
could connect to the same SSID in a clear 5 GHz channel at better PHY rates. In such scenarios, the ClientMatch
band steers clients to the appropriate band.
Figure 27 Band Steering
Sticky Client Steering
Once attached to an AP, many clients tend to stay attached – even when users begin to move away from the
AP and WLAN signal weakens. As a result of this stickiness, performance for mobile users and clients often

degrades, dragging down overall network throughput. ClientMatch intelligently steers such sticky clients to a
better AP and improves user experience and overall network performance.
Dynamic Load Balancing
Dynamic Load Balancing enables APs and controllers to dynamically load-balance Wi-Fi clients to the APs within
the same RF neighborhood on underutilized channels. This technique helps stationary and roaming clients in
dense office environments, conference rooms, lecture halls, and environments that have high-bandwidth
applications owing to client density being dynamically balanced among the APs in the same vicinity.
ClientMatch performs dynamic load balancing and ensures that individual APs are not overtaxed and client
performance is continually optimized, even in dense environments.
All the features mentioned here work dynamically and improve client and network performance. Some of the
benefits of ClientMatch are:
l Faster network connections for individual clients, which translates to better overall performance for
everyone.
l Vastly improved performance for roaming smartphones, tablets, and laptops.
l A standards-based solution that works with all client types, including 802.11a/b/g, 802.11n, and 802.11ac
clients.
l There is no need to purchase new clients or install new software.
l Operates automatically, so there is nothing for IT to configure, monitor, or manage.
l The network continuously optimizes client connections so overall network capacity and performance
remains consistent.
l Dramatically reduced help desk calls due to a better user experience.
ClientMatch is enabled by default and supports band steering, sticky client steering, and dynamic load balancing
features on AP-200 Series (802.11ac APs). The legacyArubaOS knobs to perform similar functions (band steering, client
handoff assist, and spectrum load balancing) do not work with AP-200 Series.
For more information on how ClientMatch configuration can be optimized for roaming, refer to the “RF and
Roaming Optimization for Aruba 802.11ac Networks” VRD available at:
Broadcast/Multicast (BC/MC) Optimization
In the VLAN design section, we recommended using a single flat VLAN design for wireless users. In a high-
density environment, this can create large broadcast domain. To control the unnecessary broadcast and
multicast traffic from consuming airtime, Aruba recommends configuring the broadcast/multicast optimization
knobs as discussed in the following table.
Feature Default Value
Recommended
Value
Comments
Convert Broadcast ARP
Requests to Unicast
Enable Enable Helps to convert broadcast ARP and
DHCP packets to unicast
Drop Broadcast and
Multicast
Disable Enable Restricts all the broadcast and
multicast traffic flooding into AP
tunnels
(“Convert Broadcast ARP to Unicast”
feature must be enabled)
Table 10: Recommendations for Broadcast/Multicast Optimization Knobs

AirGroup
After you configure the broadcast/multicast optimization knobs, we drop the broadcast/multicast traffic in the
air. However, in enterprise or campus deployments, multicast-based services like DLNA, MDNS, and other zero-
configuration protocols are essential. To allow such services for AirPlay and Chromecast type of application,
Aruba WLAN with AirGroup technology enables context-aware access to DLNA, Apple Bonjour, and other
shared devices without constraining WLAN performance.
When AirGroup is enabled, the controller maintains the list of the servers and clients that are using one of the
multicast services. Each time a new client tries to access a service, or a server broadcasts the service, the
controller stores it and proxy it on behalf of clients or servers. When you think about thousands of users in the
campus environment and hundreds of servers, AirGroup can save significant bandwidth on wired and wireless
side.
Feature Default Value Recommended Value Comments
AirGroup Disable Enable it if MDNS, DLNA or
other zero-configuration
services are needed.
Allows AirPlay and Chromecast type of
applications even if “drop broadcast and
multicast” is enabled
Table 11: AirGroup Recommendation
Dynamic Multicast Optimization (DMO)
AirGroup helps to allow and optimize multicast-based services like Airplay and Chromecast. However, in large
enterprises or campus networks, there could be other type of multicast traffic that needs to be allowed. Many
companies or universities have multicast video streams running in their network for business and educational
purpose. There might be other custom applications that runs on multicast. To meet these requirements, Aruba
controller provides knobs to optimize multicast traffic over the air.
This section provides details about the following knobs:
l Dynamic Multicast Optimization
l Multicast Rate Optimization
Dynamic Multicast Optimization
The 802.11 standard states that multicast over WLAN must be transmitted at the lowest basic rate so that all
the clients are able to decode it. The low transmission rate results in increased airtime utilization, and decreased
overall throughput. Due to decrease in speed, it is advisable to transform multicast traffic to unicast when a
few clients have subscribed to a multicast stream.

Figure 28 Multicast Traffic Flow in WLAN With and Without Optimization
The previous figure illustrates how Dynamic Multicast Optimization (DMO) parameter converts multicast
packets to unicast and transmits it at a higher unicast rate over the air. In case of tunnel mode, the conversion
is executed in the Aruba controller while in Decrypt-Tunnel mode, it is executed at the AP level. In Decrypt-
tunnel mode, as conversion of multicast traffic to unicast is distributed across multiple APs, it is known as
Distributed Dynamic Multicast Optimization (D-DMO). By default, DMO threshold has a default value of six
clients. When threshold is reached, multicast traffic will be sent as is to other clients. The value of the DMO
threshold should be high enough to match the expected number of clients on an AP.
IGMP snooping or IGMP proxy needs to be enabled for DMO to work. IGMP refers to the Internet Group Management
Protocol. Multicast stream should be prioritized by configuring uplink ACL and correct Wi-Fi Multimedia (WMM)
parameter to match DSCP values.
Multicast Rate Optimization
Multicast rate optimization keeps track of the transmit rates sustainable for each associated client and uses the
highest possible common rate for multicast transmission. For example, if all the clients connected to the virtual
access point (VAP) are transmitting at a data rate of 24 Mbps or higher, multicast frames are transmitted at 24
Mbps, rather than the lowest basic rate, which ranges between 1 Mbps and 6 Mbps.
Multicast Rate Optimization should be enabled along with DMO to optimize the multicast traffic when the DMO client
threshold is hit.

Feature Default Value Recommended Value Comments
Dynamic
Multicast
Optimization
(DMO)
l Set DMO client
threshold to 80.
l Prioritize multicast
stream using controller
uplink access control
list (ACL).
l Converts multicast frames to unicast
frames to deliver them at higher rates
NOTE:
l IGMP snooping or proxy needs to be
enabled for DMO to work.
Multicast Rate
Optimization
Disable Enable l Sends multicast frames at highest
possible common rate
l Enable it even if DMO is enabled.
Table 12: Multicast Traffic Optimization Recommendation
Depending on your network requirements, you will have to configure some or all of the following
broadcast/multicast optimization knobs:
l Convert Broadcast ARP Requests to Unicast
l Drop Broadcast and Multicast
l AirGroup
l Dynamic Multicast Optimization (DMO)
l Multicast Rate Optimization
Traffic Shaping
Wi-Fi uses a shared medium and is used by many different client types and applications. So, fair access to send
data becomes critically important, especially during times of high contention amongst multiple clients. First, it is
important that all clients receive access to that medium when they have data to transmit. At the same time, it is
also important that high-speed clients can take advantage of their speed without being unduly slowed by
legacy clients that unfairly consume airtime.
Following traffic shaping policies can be applied to Aruba APs:
l Default access: Traffic shaping is disabled, and client performance is dependent on MAC contention
resolution. This might result in less-capable clients getting more time on the air than faster clients, thereby
decreasing the aggregate network performance.
l Fair access: Each client gets the same airtime, regardless of client capability and capacity. This option is
useful in environments like a training facility or exam hall, where a mix of legacy, 802.11n ,and 802.11ac
clients need equal amount of network resources, regardless of their capabilities.
l Preferred access: In preferred access, more airtime is allocated to the clients with higher speeds – that is,
802.11ac clients will get more airtime compared to 802.11n and legacy clients. This mode gives the highest
aggregate network performance but your legacy clients might get less performance.
It is recommend to use fair access traffic shaping policy to provide equal airtime to each client irrespective of
their 802.11 capabilities (Legacy vs. 802.11n vs. 802.11ac).
Wi-Fi Multimedia and Quality of Service (QoS)
Quality of service (QoS) is a set of packet markings and queuing mechanisms that prioritize classes of traffic
through the network. Wi-Fi Multimedia (WMM) is based on the 802.11e amendment. It is a system for marking
traffic as higher priority and adjusting the packet timers to allow delay-sensitive data to have precedence on

the air. Streams that are commonly designated for special treatment include voice and video streams, where
bandwidth, packet loss, jitter, and latency must all be controlled.
End-to-End QoS
For QoS and WMM to work effectively, they must be deployed end-to-end throughout the network. All
components must recognize the packet marking and must react in the same way to ensure proper handling.
Complete deployment of QoS ensures consistent delivery of data. With proper planning, high-quality voice and
video can be achieved over the WLAN. The following figure shows how DSCP, 802.11p, and WMM marking is
used in an Aruba deployment.
Figure 29 QoS Segments
The network uses WMM/802.11e mechanism on the wireless side, and DiffServ Code Point (DSCP) and 802.1p
tagging mechanism on the wired side. WMM handles prioritization, queuing of packets, and servicing of
queues. WMM also has additional power-save mechanisms to extend battery life. DSCP/802.1p tagging
ensures appropriate delivery on the wired side of the network. To be effective, this tagging must be
implemented throughout the network with the same values at all nodes.
Aruba recommends you to enable WMM, if you are planning to support Voice/Video applications on your
network. For detailed information about QoS over Aruba products and how we classify and prioritize traffic,
refer to “Lync over Aruba Wi-Fi” validated reference design document available at:
Scanning Enable Enable l Enables AP to scan other
channels
Transmit
Power
802.11a and 802.11g
radio:
Min 9/Max 127
Open Office:
Walled Office or Classroom:
l Sets the transmit power
value
NOTE:
l The difference between
minimum and maximum Tx
power on the same radio
should not be more than 6
dBm.
l Tx power of 5 GHz radio
should be 6 dBm higher than
that of 2.4 GHz radio.
Client Match Enable Enable l Optimizes user experience
by steering clients to the
best AP

Convert
Broadcast
ARP Requests
to Unicast
Enable Enable l Helps to convert broadcast
ARP and DHCP packets to
unicast
Drop
Broadcast and
Multicast
Disable Enable l Restricts all the broadcast
and multicast traffic flooding
into AP tunnels (“Convert
Broadcast ARP Requests to
Unicast” feature must be
enabled)
AirGroup Disable Enable it if MDNS, DLNA or other
zero-configuration services are
needed.
l Allows Airplay and
ChromeCast type of
applications even if “Drop
Broadcast and Multicast”
feature is enabled
Dynamic
Multicast
Optimization
(DMO)
l Set DMO client threshold to
80.
l Prioritize multicast stream
using controller uplink ACL.
l Converts multicast frames to
unicast frames to deliver
them at higher rates
l IGMP Snooping or Proxy
feature needs to be enabled
for DMO to work
Multicast Rate
Optimization
Disable Enable l Sends multicast frames at
the highest possible
common rate
l Enable it even if DMO is
enabled
Airtime
Fairness
Default Access Fair Access l Provides equal air time to all
the clients
WMM Disable Enable it if you want to prioritize
voice/video traffic on your
network.
l Enables WMM capabilities to
prioritize voice/video traffic

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