CWAP book comments after first read
Last Post: January 7, 2005:
On page 86, we actually meant bytes/octets, but you can quickly calculate the bits if you know there's 8 bits in a byte/octet. I'll add that to the errata. I'd rather it say octets.
How do you know that AiroPeek sets the first one to 1 instead of 0? If it's doing this, that means it's displaying wrong information. A transmitter is required to set the fragment number to 0000 (which is zero obviously). My guess is that what happened when you took a trace is that your analyzer missed the first frame altogether. Remember, in a WLAN environment, you're NEVER guaranteed to get all of the frames. I highly doubt that AiroPeek is seeing 0000 and interpreting it as a "1", but if it is, that's bad and we need to report it to the development team at Wildpackets.
Page 175 - you're correct. Consider it fixed. ;-)
Page 199 - DIFS is correct. DIFS-RTS-SIFS-CTS-SIFS-DATA-SIFS-ACK which would then be followed by whatever the appropriate interframe space would be. A transmitter has to contend for the medium in order to transmit the RTS frame. This happens after a DIFS and a contention period.
Page 268 - you're correct - should be PPTP. Added to errata sheet.
Pages 227 and 379 are both correct. There is no standard for this acronym, and both are used equally. I tend to hear "Check" most often myself, but the 802.11-1999 (R2003) standard defines it as "Code"
One last thing.....
Please do not think that ANY exam is perfect. If you've ever taken Cisco, Microsoft, Novell, CompTIA, or any other certification exams, I'm sure you've experienced questions that are absolutely horrible. I have taken close to 100 IT certification exams now, and I absolutely break into laughter at how bad some of these questions are when I'm sitting an exam. You would think that companies such as these could afford to QA their questions a little better, but alas, they do not. I consider our exams far more accurate, worded more precisely, and testing more focused topics than any of the aforementioned company's exams. Having said that, our exams still are not perfect. We get regular feedback from test-takers, and we review the suspect questions periodically.
No probs on the practice exam I noticed one of the questions had a duplicate answer radio button. When I see it again I will note it down.
As for the airopeek trace I can send it to you. My traces are in a lab which means, for this particular trace, the WS and AP are the only stations
on the bss. My fragements traces were to and from a wired ws. I saw the same thing in my lab just using two ws pinging between each other in a singel bss. I am using airopeek with a dedicated WIDS based
analyzer(Network Chemistry's RF Protect). So I am confident that no packets are missed.
As for the exams I understand about cisco et. al. Please do not take my posts too personal. My post is from a "candidates" perspective.
I remember the old ccie written and the ccdp design exams frought with errors and I know yours are better from my experience with the cwna.
I'll take a look at AiroPeek and see what they're doing. If it is as you suspect, I'll go make some inquiries with the right people at Wildpackets.
802.11-1999 (R2003), section 184.108.40.206.1 says,
"The Sequence Number field is a 12-bit field indicating the sequence number of an MSDU or MMPDU. Each MSDU or MMPDU transmitted by a STA is assigned a sequence number. Sequence numbers are assigned
from a single modulo 4096 counter, starting at 0 and incrementing by 1 for each MSDU or MMPDU. Each
fragment of an MSDU or MMPDU contains the assigned sequence number. The sequence number remains
constant in all retransmissions of an MSDU, MMPDU, or fragment thereof."
by the way, I don't take it personal. ;-D just the facts ma'am, just the facts. hehe.
Okay I am wrong and stand corrected on the fragment trace. After another check I know where I made my mistake. I had in my mind defined the first fragment to be the first msdu flagged as a fragment in a decode. So when I looked again for my three packet ping the first packet( shown as ping req) in the summary has a seq# of 1 for example and a frag# of 0. Then the next msdu shown(as an 802.11 frag) in the summery has a seq# of 1 and a frag# of 1 and the last msdu again shown(as an 802.11 frag) in the summery has a seq of#1 an a frag# of 2. So I, the analyst was incorrectly thinking of what is the first fragment. I mistakenly taken the first instance of 802.11 frag in the trace to be the first fragment with 0 which is incorrect.
Traces never lie. Just the facts mamm
I was reviewing the errata and I noticed that you have "page 177 delete Lines 23-30".
Does this mean that on page 177 the entire paragrapgh that starts with "Access points (as well as stations in IBSSs)" should be ignored?
How come I don't get credit in the errata? Why does cwnp hate me? :(
ON page 2 of the errata you have Page 86 - EAP Framework. Page 86 is the chapter's review questions. I think you meant page 82.
Why does the errata hate me:(
Yes, we meant page 82, and I found that yesterday while updating the errata. I fixed it then. Yes, that entire paragraph is to be deleted because it's duplicate material (on the same page even). ;) The new errata file will be posted to the website shortly. I've submitted it to the webmaster for posting. The reason Westcott (one of our instructors) got his name in the errata is that he put several hours into drawings. I wanted to say thanks somehow. ;-D
I know I think I am overstudying a little too much now. I did see the reference to the standards. the reason I didnt read any of the standards was I wanted something digestable that explained the topics much clearer than a standard document.
Reading standards and rfcs are tough for they are dry and no anologies are made. They are great for reference but not for learning topics the first time IMHO. That is why I may have missed some of the things in the errata that I did not submit. It makes sense now. I was hoping to not cross reference the study guide to the standards often or at all.
I know that the guide is very good and will even be better. It makes a great all in one reference and a fantasitc read to grasp such difficult concepts for the first time. The more accurate it is the better and then one can go to the standards for more information if applicable. Will PDF versions of the guide be available like the CWNA?
As for the credits I am just busting chops;)
hehehe. I really appreciate your posts to this forum and for your valuable feedback and possible errata. Please do us the favor and post a review of the CWAP Study Guide on Amazon.com when you have time. You're certainly right about the standards - they are dry, interwoven piles of confusion. If they were written plainly in their entirety, they would be 8000 pages long each. :-) No PDF version will be made available - sorry.