few troubles

6 posts by 3 authors in: Forums > CWNA - Enterprise Wi-Fi Admin
Last Post: August 10, 2006:
  • i have some confusion regarding following questions:

    1.what kind of impact jet engines have on 802.11 RF signals

    2.Elevators cause RF shadows b/c elevators are basically dead RF zones.

    3. what does 802.11n recommend??

    4. the study guide does not mention Null Function frame though the

    practice tests include questions about do i learn about it...

    5.what is IEEE 802.3-2005 Clause 33 (PD and PSE)??

    6. when 802.11b/g are used in mixed mode then the 'g' STA uses CTS-to-

    Self protection mechanism while in one of the questions of practice

    tests the correct answer is RTS/ that true?

    7. one question in practice test asks which wireless solution offers

    greatest tolerance to delay spread....the answers include both 802.11g

    and 802.11a...i selected 802.11g which was marked wrong...both 'a' and

    'g' are OFDM...any of them can be the answer....

    8. where do i find information about 802.11r??

  • Hi Kapil:

    Which certification, practice test, and study guide are you referring to?

    Several of your questions are rather general and could be answered by judicious use of google. You might want to ask here just the questions you can't answer on your own.

    Thanks. /criss

  • I'll address a few:

    2) Think about what elevators are primarily made up of, and then consider why they create RF shadows.

    3) Check the 802.11n working group for more info here.

    5) IEEE 802.3-2005 Clause 33 is PoE (Formerly 802.3af). The standard is freely available for download, which is highly recommended.

    7) Look for the correction to this PT question in the next update (~ 2 weeks or less)

    8) Check the IEEE 802.11r working group for more info. Know how it relates to 802.11F

  • well i m going for CWNA, using version 3 of study guide and using the practice tests of this forum......

    though i havnt gone thru google b/c i though i will be directly answered here without wasting time in searching as i have very limited time to appear..

    well elevators are made of metals so they may cause RF shadows...i just wanted to conform it...

    regarding the correction of qs....i hope the question in the exam wont need any correction b/c there wont be any chance after that...lolz...

    what abt qs number 4 and 6 that i asked...any ways thanx for ur support...i will check for the PoE standard and 802.11n and 802.11r...thanx again

  • Hi Kapil:

    4. I find IEEE 802.11 null function data frames discussed in the CWAP study guide, but not in the CWNAv3 study guide. I suspect they are discussed in CWNA courseware, but I don't have that on hand to check.

    The IEEE 802.11 TGm appears poised to rename data frame subtype 0100 from "Null function (no data)" to simply "Null (no data)", bowing to the obvious that even though this data frame subtype has no frame body and carries no data, other than the details in its frame header, it performs some function based solely on the data in the frame header.

    There are six other data frame subtypes that have no frame body. Three for the dead PCF coordination function (subtype values 0101, 0110, 0111) and three for the dead PCF coordination function plus QoS (subtype values 1100, 1110, and 1111).

    TGm draft 5.2 section 7.2.2 says in part: "For data frames of subtype Null (no data), CF-Ack (no data), CF-Poll (no data), and CF-Ack+CF-Poll (no data) and for the corresponding QoS data frame subtypes, the Frame Body field is omitted; these subtypes are used for MAC control purposes. For data frames of subtypes Data, Data+CF-Ack, Data+CF-Poll, and Data+CF-Ack+CF+Poll and for the corresponding four QoS data frame subtypes, the Frame Body field contains all of, or a fragment of, an MSDU after any encapsulation for security."

    So what good is a disembodied data frame, in particular subtype 0100 "Null (no data)"? The standard has much to say about null frames and PCF, but PCF knowledge appears to be of vanishing interest to the CWNP Program. Vendors have found it convenient for non-AP STAs to use null frames to signal their APs of an impending change in power save mode, and the CWNP Program wants you to know that.

    6. ERP protection mechanisms include both CTS-to-self and RTS/CTS.

    I hope this helps. Thanks. /criss

  • thanx for ur support....

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