Windows XP makes an optimized use of the bandwidth, 100% of the bandwidth is available
almost all the time for shared application, unless an application specifically request priority
bandwidth through the QoS. By default 20% of the bandwidth is allocated for these
special requests, but under normal circumstances this reserved bandwidth
can be freely used by any shared application or data flow.
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Enable this option and then modify the % bandwidth.
You can reset it from 20% to 0%, though this will not bring any increase in connection.