Configuring Clientlink (Cli) - Cisco Mesh Access Points Deployment Manual

Configuring ClientLink (CLI)

We realized that for the current generation of 802.11n APs, while the second transmit path was being well
utilized for 802.11n clients (to implement spatial diversity), it was not being fully used for 802.11a/g clients.
In other words, for 802.11 a/g clients, some of the capabilities of the extra transmit path was lying idle. In
addition, we realized that for many networks, the performance of the installed 802.11 a/g client base would
be a limiting factor on the network.
To take advantage of this fallow capacity and greatly enhance overall network capacity by bringing 802.11
a/g clients up to a higher performance level, we created an innovation in transmit beamforming technology,
called ClientLink.
ClientLink uses advanced signal processing techniques and multiple transmit paths to optimize the signal
received by 802.11a/g clients in the downlink direction without requiring feedback. Because no special
feedback is required, Cisco ClientLink works with all existing 802.11a/g clients.
Cisco ClientLink technology effectively enables the access point to optimize the SNR exactly at the position
where the client is placed. ClientLink provides a gain of almost 4 dB in the downlink direction. Improved
SNR yields many benefits, such as a reduced number of retries and higher data rates. For example, a client at
the edge of the cell that might previously have been capable of receiving packets at 12 Mbps could now receive
them at 36 Mbps. Typical measurements of downlink performance with ClientLink show as much as 65
percent greater throughput for 802.11a/g clients. By allowing the Wi-Fi system to operate at higher data rates
and with fewer retries, ClientLink increases the overall capacity of the system, which means an efficient use
of spectrum resources.
ClientLink in the 1552 access points is based on ClientLink capability available in AP3500s. Therefore, the
access point has the ability to beamform well to nearby clients and to update beamforming information on
802.11ACKs. Therefore, even if there is no dedicated uplink traffic, the ClientLink works well, which is
beneficial to both TCP and UDP traffic streams. There are no RSSI watermarks, which the client has to cross
to take advantage of this Beamforming with Cisco 802.11n access points.
ClientLink can beamform to 15 clients at a time. Therefore, the host must select the best 15 if the number of
legacy clients exceeds 15 per radio. AP1552 has two radios, which means that up to 30 clients can be
beamformed in time domain.
Although ClientLink is applied to legacy OFDM portions of packets, which refers to 11a/g rates (not 11b)
for both indoor and outdoor 802.11n access points, there is one difference between ClientLink for indoor 11n
and ClientLink for outdoor 11n. For indoor 11n access points, SW limits the affected rates to 24, 36, 48, and
54 Mbps. This is done to avoid clients sticking to a far away AP in an indoor environment. SW also does not
allow ClientLink to work for those rates for 11n clients because the throughput gain is so minimal. However,
there is a demonstrable gain for pure legacy clients. For outdoor 11n access points, we do need more coverage.
Thus, three more additional legacy data rates lower than 24 Mbps have been added. ClientLink for outdoors
is applicable to legacy data rates of 6, 9, 12, 18, 24, 36, 48, and 54 Mbps.
Note ClientLink is enabled by default.
Configuring ClientLink (CLI)
From the 7.2 release onwards, it is not possible to configure ClientLink (beamforming) using the controller
GUI.
Step 1 Disable the 802.11a or 802.11b/g network by entering this command:
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Design Considerations
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