Cisco Cisco Aironet 1140 Access Point 백서
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White Paper
© 2009 Cisco Systems, Inc. All rights reserved. This document is Cisco Public Information.
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Cisco ClientLink: Optimized Device Performance with 802.11n
Overview
Over the next few years Wi-Fi networks will transition to 802.11n technology. During this time many networks will
support a mix of 802.11a/g and 802.11n clients. Because they operate at lower data rates, the older clients can
reduce the capacity of the entire network. ClientLink technology can help solve problems related to adoption of
802.11n in mixed-client networks by making sure that 802.11a/g clients operate at the best possible rates, especially
when they are near cell boundaries.
Introduction
802.11n provides remarkable performance improvements in the areas of throughput, link reliability, and
predictability. The transition to 802.11n provides significant benefits, but most organizations will take a phased
approach to migration. Over the next few years, many installations can be expected to support a mix of older
802.11a/g clients and newer 802.11n clients. The reasons that older clients will continue to operate for some time is
that it takes 3 to 5 years for a full refresh cycle of enterprise laptops. And certain industries such as manufacturing,
retail, and healthcare can take even longer to replace their devices.
In mixed environments, older 802.11a/g clients delay communications for 802.11n clients and reduce system
performance. Recognizing the need for businesses to protect their investment in these 802.11a/g devices, Cisco has
developed a new technology that allows businesses to deliver the performance benefits of 802.11n to 802.11a/g
devices, thereby increasing their useful life.
Most 802.11n solutions offer improvements in the uplink communication from client to access point. Cisco ClientLink
technology is unique in that it offers uplink improvements as well as downlink communication from access point to
client. This is significant because the majority of daily communication on the WLAN such as web browsing, email,
and file downloads occur in the downlink direction. Improving the downlink throughput of the slowest clients improves
the experience not only for the clients, but also for all other clients on the network. The result is a more reliable
roaming experience and increased capacity of the network.
Cisco has added advanced signal processing into the Wi-Fi chipset. Multiple transmit antennas are used to focus
transmissions in the direction of the 802.11a/g client, increasing the downlink signal-to-noise ratio and the data rate
over range, thereby reducing coverage holes and enhancing the overall system performance. This technology
essentially learns the optimum way to combine the signal received from a client, and then uses that information to
send packets in an optimum way back to the client. This technique is also referred to as MIMO (multiple-input
multiple-output) beamforming, transmit beamforming, or cophasing, and it is the only enterprise-class solution on the
market that does not require expensive antenna arrays.
Basics of MIMO and 802.11n
MIMO, which refers to a radio system that has multiple separate receive and transmit paths, is at the heart of
802.11n. MIMO systems are described using the number of transmitters and receivers in the system. For example,
2x1 or "two by one" refers to a system with two transmitters and one receiver. 802.11n defines a number of different
combinations from 2x1 to 4x4.