US Robotics USR2450 Informacje Techniczne Strona 55

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V 2.2 Copyright SystemExperts 2001,2002,2003
109
Anatomy of 802.11b
n Looking at some of the guts of the protocol to
help us understand:
n Modulation determines speed/distance
n What effects the transmission rate
n other than distance or barriers
n Congestion resolution
n Hidden nodes
n The MAC layer is our friend!
V 2.2 Copyright SystemExperts 2001,2002,2003
110
Anatomy of 802.11b: the bits
n As we said before, data is encoded using
DSSS
n i.e., The data stream is modulated (XOR’d) with a
sequence called the Barker code (11 bits:
10110111000 it’s just a really good pattern for
generating radio waves) to generate a series of data
objects called chips
n These chips are then sent out by the wireless radio
(i.e., the wireless card)
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