Draytek Vigor2920 Series User Manual page 257

Item
Long Preamble
Packet-OVERDRIVE
Description
This option is to define the length of the sync field in an
802.11 packet. Most modern wireless network uses short
preamble with 56 bit sync field instead of long preamble with
128 bit sync field. However, some original 11b wireless
network devices only support long preamble. Check it to use
Long Preamble if needed to communicate with this kind of
devices.
This feature can enhance the performance in data transmission
about 40%* more (by checking Tx Burst). It is active only
when both sides of Access Point and Station (in wireless
client) invoke this function at the same time. That is, the
wireless client must support this feature and invoke the
function, too.
Note: Vigor N61 wireless adapter supports this function.
Therefore, you can use and install it into your PC for matching
with Packet-OVERDRIVE (refer to the following picture of
Vigor N61 wireless utility window, choose Enable for
TxBURST on the tab of Option).
Note: * means the real transmission rate depends on the
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Vigor2920 Series User's Guide