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the study guide mentions at one place that when two stations having overlapping coverages can cause hidden node problem...how is it possible as in chapter 11, only three reasons are mentioned that can cause hiddeen node problems and the above mentioned is not one of them..??

Where is that statement in the study guide?

Hi Kapil:

The CWNAv3 study guide is correct in all four instances. The "three main ways" on page 403 are just that. And it is true in a more general way that, as you say, "two stations having overlapping coverages can cause hidden node problem."

IEEE 802.11-1999 5.1.1.2 says: "IEEE 802.11 PHYs lack full connectivity, and therefore the assumption normally made that every STA can hear every other STA is invalid (i.e., STAs may be ?¡é?€??hidden?¡é?€?? from each other)."

The phrase "hidden STA" appears twice after this in the standard but is not defined. The 1999 IEEE 802.11 Handbook describes what it calls "the hidden node problem" in some detail.

The IEEE 802.11 Task Group M is revising 802.11-1999. It's draft 5.2 uses the phrases "hidden STA", "hidden station", and "hidden node" nine times and includes the following definition:

"3.66 hidden station (STA): A STA whose transmissions cannot be detected using carrier sense (CS) by a second STA, but whose transmissions interfere with transmissions from the second STA to a third STA."

I observe that there must be at least three STAs involved in a hidden station scenario. Two STAs will be out of range or "hidden" from each other's transmissions. The third STA will be in range of each of the first two and susceptible to having reception of a frame from one of the hidden stations corrupted by an overlapping transmission of a frame from the other hidden station despite the normal best efforts of CSMA/CA.

I hope this helps. Can you add your location to your forum profile? Thanks. /criss

the page number 368 mentions


" Therefore,a situation can occur in which two stations with overlapping coverage are unable to hear each other. this situation is known in the trade as the hidden node problem."

from this statement i think only STAs are being considered not three...its quite confusing...i think there is some mistake...i would like the author to have a look on it and try to remove my ambiguity..efforts from others are also appreciated...thanx

Hi Kapil:

When you include the previous sentence you find the example has three STAs:

"The 802.11 standard requires only that all stations in a BSS be able to hear the AP in the BSS. Therefore, a situation can occur in which two stations with overlapping coverage are unable to hear each other. This situation is known in the trade as the hidden node problem."

The two client stations in the example are out of range of each other but are both within range of the AP station to which they are both associated. Their "coverage" "overlaps" only at the AP. Each of the two client stations is said to be hidden from the other.

I hope this helps. Thanks. /criss

P.S. I like your location!

thanx for ur views...they were supportive...have u ever been to my country before ...as u mentioned that u like my place

Hi Kapil:

No, but I would like to. Your location caught my eye because of my last name -- Hyde.

Take care. /criss