802.11 PCF

burgi
BASIC-Programmierer
BASIC-Programmierer
Beiträge: 115
Registriert: 15. Apr 2009 18:08
Wohnort: Ludwigshafen

802.11 PCF

Beitrag von burgi » 13. Mär 2010 20:16

There is one question, which arose to me while doing some repitition on 802.11-PCF. If the point coordinator polls, within a contention-free period, a station and this station does not reply. How long does the coordinator wait before polling the next station ?
On slide 5.28 is a example for this, there the coordinator polls 3 waits for PIFS and then polls 4, but shouldn't it wait for SIFS before polling 4 ? Because D3 has to wait SIFS before it can reply to the poll.
Or did I missunderstood the slide and, the coordinator does not actually poll 3, but instead does only download some data to 3?

Thanks Dominic

Benutzeravatar
SM
Endlosschleifenbastler
Endlosschleifenbastler
Beiträge: 167
Registriert: 10. Okt 2005 18:11
Wohnort: Darmstadt
Kontaktdaten:

Re: 802.11 PCF

Beitrag von SM » 14. Mär 2010 15:41

My guess:

SIFS is shorter than PIFS (see slide 5.22).
A station contacted by the point coordinator has to reply after SIFS.
So if there was no reply after PIFS (which is SIFS+x) the point coordinator assumes that the station has no data to send and moves on to the next station.
~ Per aspera ad astra. ~

Matthias Hollick
Dozentin/Dozent
Beiträge: 99
Registriert: 21. Okt 2005 15:42

Re: 802.11 PCF

Beitrag von Matthias Hollick » 14. Mär 2010 15:44

burgi hat geschrieben: On slide 5.28 is a example for this, there the coordinator polls 3 waits for PIFS and then polls 4, but shouldn't it wait for SIFS before polling 4 ? Because D3 has to wait SIFS before it can reply to the poll.
The asnwer of SM is correct: the point coordinator waits PIFS before the next poll; would it wait SIFS, its next poll might interfere with the transmission from the station polled earlier if this station has data to send (the coordinator's transmission would drown the incoming signal of the station polled earlier).
Matthias Hollick

matthias.hollick (at) seemoo.tu-darmstadt.de

Antworten

Zurück zu „Archiv“