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Wifi (Point coordination function (pcf) (IFS (inter frame spacing) (SIFS…
Wifi
Point coordination function (pcf)
centralised point
PCF mode polls each station asking if they have anything to send
base station sends beacon frame (10-100 times a second) inviting stations to sign in
frame contains information like hopping frequency, dwell time and clock sync
if a station is 'signed in' it is guaranteed bandwidth. this QoS is achieved
Polling
round robin scheme
only polled can transmit
IFS (inter frame spacing)
SIFS (short inter-frame-spacing)
let the reciever transmit CTS as a response to RTS
PIFS (PCF inter-frame-spacing
AP broadcast beacon or send a poll frame
DIFT (DCF Inter-frame-spacing)
if base station has nothing to say, stations may compete for the channel, if collision - use back off
EIFS (extended inter frame spacing)
used by station having a bad frame to report
distributed coordinate function (dcf)
CSMA/CA with collision avoidence
provides multiple levels of inter-frame spacing (IFS)
MACAW = Multiple access with collision avoidance for wireless
support single or multiple access packet transmission
provide better protection against errors
adhoc style
Steps
DIFS - RTS - SIFS - CTS - SIFS - DATA - SIFS -ACK
hidden station
B - A - C
collision at A
use CSMA/CA to prevent collisions
answer
pifs
beacon frame
sifs
Polling
SIFS
300 bites recieved to s3
sifs
ack
1 more item...