| Author |
MAC/Physical layer question
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| ajitkumar 2004-01-17, 11:07 am |
| For all you guys preparing for CWNA exam (including myself), here is a somewhat controversial question related to Interframe spacing in WLAN.
p.304 of study guide states that SIFS has to waited out used before sending an RTS frame
while p.312 gives an example showing DIFS being waited out before sending an RTS frame.
Which of these is correct ? Any help from the "experts" would be appreciated. | |
| jdmurray 2004-01-21, 12:56 pm |
| I'm not an expert on 802.11, but DIFS is used for checking if the channel is idle and always preceeds RTS. SIFS delimits all other elements of the handshake (e.g., CTS, data, ACK, etc.).
For example, sending a single, unfragmented packet in CSMA/CA would look like the following:
<DIFS>[RTS]<SIFS>[CTS]<SIFS>[DATA]<SIFS>[ACK]<DIFS>
Am I correct on this? | |
| ajitkumar 2004-01-21, 7:04 pm |
| Thank you so much for your reply to my query and your very crisp illustration of the use of SIFS and DIFS. I fully agree with your explanation, which means that now there are at least of 2 of us who think that the CWNA study guide contains an error on p.304 re: using SIFS in front of RTS.
BTW, I appeared for the CWNA exam this past Monday and passed it with a score of 87% 
Moving on to preparing for CWSP exam now... Wish me luck.
Ajit | |
| jdmurray 2004-01-21, 8:13 pm |
| Hey, good luck! I hope to be taking both of those exams by Summer. | |
| Devinator 2004-01-21, 11:58 pm |
| Great job guys. JDMurray is correct, and an RTS is preceded by DIFS, not SIFS. I'll make a note to the errata sheet that's downloadable from cwne.com
Thanks! | |
| jdmurray 2004-01-22, 1:04 am |
| What's the link to the errata? | |
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