Siemens IEEE802.11 Manuale Utente Scaricare il pdf (Pagina 15)

WLAN-IEEE802.11 Tutorial (Maximilian Riegel), 021018-wlan-tutorial.ppt Page 15 © Siemens, 2002

IEEE802.11 Architecture Overview

n One common MAC supporting multiple PHYs

n Two configurations

– “Independent” (ad hoc) and “Infrastructure”

n CSMA/CA (collision avoidance) with optional “point coordination”

n Connectionless Service

– Transfer data on a shared medium without reservation

– data comes in bursts

– user waits for response, so transmit at highest speed possible

– is the same service as used by Internet

n Isochronous Service

– reserve the medium for a single connection and provide a continues stream of bits, even

when not used

– works only when cells (using the same frequencies) are not overlapping.

n Robust against noise and interference (ACK)

n Hidden Node Problem (RTS/CTS)

n Mobility (Hand-over mechanism)

n Security (WEP)

n Power savings (Sleep intervals)

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