- Cisco Network Router User's Manual

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CiscoAironetAccessPointDeploymentGuide 

CiscoSystems

Page42of52

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theIntelcardoropenacasewithIntelorthelaptopmanufacturerforapossibleremedy.DuringtheAP

3600 beta trials, Cisco observed differences in performance with different notebooks using the Intel

6300card.

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Note:Sometimesitcanbedifficulttoreliablymaintai na3SSlink,since

itiseasyfortheclientto

rate‐shift out of the 3SS mode. The ability to maintain a 3SS link varies with the quality of the

clientandthetestenvironment.

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TheAP 3600,withitsextraradioper band, canuse theextraredundantradioto beamform(thanks

to

ClientLink2.0)andusesthistomaintaintheadvantageof3SSlinks.ClientLink2.0canalsoimprovethe

overall performance of 802.11n clients using one, two, and three spatial streams and legacy .11a/g

clients.

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BeamforminginClientLink1.0and2.0

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ClientLink1.0wasfirstintroducedwiththeAP1250andtheAP1 140;itisamethodtocreateastronger

signalonthedownlinksidefor802.11a/gclientsbyhearingtheclientsontheuplinkandthenadjusting

thetransmittertimingsothesignalappearsmuchstrongeratthe

clientend.

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This feature was previously user configurable. However, starting with 7.2 code stream, it is now onby

defaultandisnotuserconfigurablebecausethereisnobenefittodisablingit.

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The AP 3600 fully  supports ClientLink 1.0 for 802.11a/g clients but has a greater advantage, for it

also

supportsall802.11nclientsincludingone,two,andthreespatialstreamclients.Thiscapabilityiscalled

ClientLink2.0.Thereisadistinct advantagewithClientLink2.0overthe802.11nenhancedbeamforming

specification, because ClientLink 2.0 works  with all clients today and does  not require any client

soundingorsupport.(See

Figure55.)

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Figure55:ClientLink2.0

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Withbeamformingtechnology,changingthetimingoftwotransmitterscreatesastrongersignalforthe

receiver (for example, a  client device). This is referred to as constructive interference. If the opposite

happens,andthesignalscanceleachotherout,itiscalleddestructive

interference.(SeeFigure56.)

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