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Hi,
I have been reading the new PW0-104 , why is it written that HR-DSSS is clause 15 at so many pages especially at the last few chapters, is it not clause 18 which is HR-DSSS . Please confirm .

Clause 15 covers DSSS (rates of 1 & 2 Mbps).

Clause 18 covers HR/DSSS (rates of 5.5 & 11), and different modulations.

Any system claiming 802.11b, aka HR/DSSS, is also going to support the older 802.11 DSSS rates, and that may be where the confusion lies.

If you go to: http://standards.ieee.org/getieee802/download/802.11-2007.pdf you can get your own copy of the std (~ 15 MB).

BTW, the PW 104 is the exam number, not the books #.

I have the older version of the book at work, and the newer edition at home, so I couldn't check this out. Do you have a couple page numbers to look at?

To put it simply:

Clause 15: DSSS PHY (original 802.11)

Clause 18: HR/DSSS PHY (802.11b)

Since the 802.11b HR/DSSS is back compatible with the 802.11 DSSS, both PHYs can coexist in the same BSS.

there is quiet a few pages but cuz i am the last chapter will try to reference some
Page 611 HT Operation
page 612 Mode 3-HT Mixed Mode
page 619 chapter 18 review question 13

Also shouldnt there be an E-book in the CD which came along with the book ? I dont have it on the CD

I don't know for sure, but I'd imagine the e-book has been removed to prevent rascals dumping it all over the Internet. Might be wrong, but sounds a good a reason as any.

Dave

anees Escribi?3:

there is quiet a few pages but cuz i am the last chapter will try to reference some
Page 611 HT Operation
page 612 Mode 3-HT Mixed Mode
page 619 chapter 18 review question 13

Good catch. I just did a search on the book and there are 5 locations were HR-DSSS is incorrectly referred to as Clause 15 radios including the three pages you mention.

In the majority of the book, we correctly reference HR-DSSS as clause 18 radios. I will make sure that these corrections are put on the online errata at Wiley's Publishings web site and they will be corrected in the next major printing of the book which is very soon.

Thanks for catching this error.

Great catch, as they say in my business.

This is exactly the kind of attention you need to have while you're taking a CWNP exam too.

On the question section of the CD-Rom that comes with the [ excellent ] CWNA Book under Chapter 4 Q 13, it asks "What are some of the possible negative effects of an impedance mismatch?"?, reply, "signal reflection is not included in the list of answers. It is actually this factor that is the cause of the negative effects.

When there is an impedance mismatch, some of the incident energy [ called the incident signal ] is actually reflected backwards towards the source. The mixture? of incident and reflected energy is actually what causes standing waves on the transmission line. Measurement of this phenomenon is undertaken via the Voltage Standing Wave Ratio or VSWR.

http://en.wikipedia.org/wiki/Standing_wave_ratio

Signal reflection can of course occur after the antenna output, but that scenario is for an unbounded RF signal in free-space? reflecting off an object say. This reflection term? relates to reflections within the transmit chain.

Under the section Practical Implications of SWR?, can be seen the following:

When an antenna and feedline do not have matching impedances, some of the electrical energy cannot be transferred from the feedline to the antenna.[2] Energy not transferred to the antenna is reflected back towards the transmitter.[3] It is the interaction of these reflected waves with forward waves which causes standing wave patterns.[2] Reflected power has three main implications in radio transmitters: Radio Frequency (RF) energy losses increase, distortion on transmitter due to reflected power from load[2] and damage to the transmitter can occur.[4]?

The maximum power transfer theorem is used in microwave systems but also in just about every type of electronic amplifier imaginable, from home stereos to audio systems in Nintendo.

http://en.wikipedia.org/wiki/Maximum_power_theorem

For those of a mathematical bent [ or someone with insomnia ] considering a source resistance and a load resistance, and calculating power dissipation in the load and differentiating [ in the calculus sense ] with respect to the load resistance, we find that maximum power is transferred when the load resistance equals the source resistance.

This is the reason why you have to have earphones that match the resistance? of your stereo system or walkman, as otherwise, some of that energy which should be going to your ears ends up wasted in the electronics of the source.

Dave

On Bonus Exam 1 Q16 it says "Which of these devices cause all band interference in the 2.4 Ghz ISM band?

Answer D says "an 802.11a Access Point"

Dave