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Second-wave or Wave 2 products also come with a
new technology, multiuser MIMO (MU-MIMO). Whereas
802.11n is like an Ethernet hub that can transfer only a
single frame at a time to all its ports, MU-MIMO allows
an AP to send multiple frames to multiple clients at
the same time over the same frequency spectrum.
That’s right: with multiple antennas and smarts, an AP
can behave like a wireless switch. There are technical
constraints, and so MU-MIMO is particularly well suited
to Bring-Your-Own-Device (BYOD) situations in which
devices such as smartphones and tablets have only a
single antenna.
802.11ac-enabled products are the culmination of
efforts at the IEEE and Wi-Fi Alliance pipelines. IEEE
802.11ac delivered an approved Draft 2.0 amendment
in January 2012 and a refined Draft 3.0 in May 2012,
with final ratification in December 2013. In parallel, the
Wi-Fi Alliance adopted an early but very stable and
mature IEEE draft, namely Draft 3.0, and used that as
the baseline for an interoperability certification of first-
wave products in mid-2013. The Wi-Fi Alliance split its
802.11ac certification into two parts, in order to include
testing of the more advanced features. This second-
wave certification includes features that were not in the
earlier certification (Wave 1). These features include
channel bonding up to 160 MHz, four spatial streams,
and MU-MIMO. Overall, this arrangement closely follows
how 802.11n was rolled out, with 802.11ac Wave 1
coming out first and Wave 2 products being released
about 18 months later.
Enterprise networks considering an investment in
infrastructure Wi-Fi have the choice to move from an
older technology such as 802.11n while also delivering
a remarkable level of performance. If you still have an
older standard like 802.11n deployed today, upgrading
to the latest 802.11ac Wave 2 technology will provide
better performance for bandwidth-intensive applications
like streaming video and collaboration. The newer
technology will also address a common issue that
most networks are seeing today, providing consistent
performance in the face of higher density or more
wireless clients accessing the network. Cisco offers a
broad portfolio of products that support 802.11ac Wave
2, as well as the right innovation and features designed
for a variety of different network sizes and needs.
When it comes to interoperability with older standards,
802.11ac will have a few effects on existing 802.11a/n
deployments, even if the deployment is not upgraded to
802.11ac immediately: (1) the wider channel bandwidths
of neighboring APs require updates to radio resource
management, or RRM (and in particular the dynamic
channel assignment algorithm), and (2) 802.11a/n
Wireless Intrusion Protection Systems (WIPS) can
continue to decode most management frames such
as beacon and probe request/response frames (that
are invariably sent in 802.11a format) but do not have
visibility into data sent in the 802.11ac packet format.
One thing not to worry about is compatibility. 802.11ac
is designed in a deep way to coexist efficiently with
existing 802.11a/n devices, with strong carrier sense,
a single new preamble that appears to be a valid
802.11a preamble to 802.11a/n devices, and extensions
to Request-To-Send/Clear-To-Send (RTS/CTS) to
help avoid collisions with users operating on slightly
differentchannels.
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