US Robotics USR2450 Informações Técnicas descarregar pdf (Página 55)

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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US Robotics USR2450 Informações Técnicas Página 55