Forum

explanation about 11n radio chains (3x3, 2x2 etc) on page 40 seems to be wrong, differs from what I've red before. e.g https://www.cwnp.com/index/cwnp_wifi_blog/first-certification-3x33

You are correct, Leonardo. Correct terminology is very important here, as "conventional radio terms" can be confusing enough as it is, even without .11n.

For example, what exactly is a "radio". There are many definitions. For example, most of can think of the radio in our cars. That device is receive only. That is, for conventional consumer grade radios, we can only receive, yet we still call the device a "radio". Data communications ( HDLC, SDLC anybody ? ) took some terms from the "radio industry". In the case of the car radio, it is said to operate in "receive only" or "simplex" mode. That is, we have a simplex radio.

We have also walkie-talkies and CB radio used by big strapping truck drivers "That's a 21 good buddy....". With these systems, we operate on the same frequency ( transmit and receive ) between two stations or endpoints. Wi-Fi works a little bit like this, using the same frequency to both transmit and receive information to and from each other' s equipment. We say that this a "half-duplex radio".

The next type of "radio" is used in many microwave and satellite links, where we have separate, dedicated frequencies for both transmit and receive ( bandwidth is a big issue here ). In this mode, we use the term "full duplex radio".

There are still data transmission circuits out there that can change direction of transmission via "line turnaround" commands.

Another "radio term" you will see out there concerns "transceivers". Short for "Transmitter/Receiver".

These devices are capable of transmission and reception.

The information given by Marcus sums things up well. Like Leonardo, I find the explanations in the book confusing, and a bit misleading.

Dave

P37, last paragraph:

Clause 15 and 18 should read:

Clause 18 and 19

P5 of the following gives some information re ?clause numbering?

http://www.invictusnetworks.com/faq/802.11n%20Information/Ensuring%20802.11n%20and%20802.11abg%20Compatiblity%20by%20AirMagnet%208-08.pdf

Dave

Practice Exam Questions for CWDP

I found the following two questions with incorrect answers, at least according to the reading and explinations:

Practice Exam 1 Question 4 reads:
When asking a customer about their network design, what type of VLAN information will you find helpful in determining how traffic flows are restricted? (Choose all that apply.)
A. ACLs
B. VLAN ID
C. Firewall rules
D. Gateway devices

The explination reads:
Access control lists (ACLs) or inter-VLAN firewall rules are likely the most obvious answers to this question because they restrict or allow certain traffic between VLANs. Information about gateway devices and what device(s) are responsible for routing in a particular VLAN can tell you whether or not the VLAN is routable.

The correct answers should be A, C, D based on this but the test wants you to answer A, B, D

The only other error I found on ALL the tests was Question #38 from this same Practice Exam 1 that reads:

Which of the following are examples of business requirements? (Choose all that apply.)
A. The network must decrease operating expenses.
B. The network must increase employee productivity by 10%.
C. The network must support 802.11n devices.
D. The network must maintain a 99.999% network uptime.

The explination reads:
Examples like decreasing expenses, increasing productivity, and uptime are all business-driven requirements. Support for any particular technology is a technical requirement.

The correct answers should be A, B, D but the test wants you to answer A, B, C

Great book and practice tests....I believe I'm ready for the CWDP, thanks to your help in understanding all these complex topics. I would recommend this book to anyone who is seriously thinking of entering, advancing or adding Wi-Fi Engineering to their career. It is right along the quality of my IEEE 802.11 Handbook and 802.11 Hands-On Analysis books that I reference frequently. Thanks again,

Page 665 in the spanning tree section states that MSTP is proprietary, it isn't.
http://en.wikipedia.org/wiki/Spanning_Tree_Protocol#Multiple_Spanning_Tree_Protocol_.28MSTP.29

Page 421, last paragraph: "The signal is somewhat of a carotid pattern from front to back." This refers to Figure 9.14 on page 442 (polar directional chart). The term should be "cardioid" or "heart-shaped" polar pattern. (Carotid is an artery in the neck. :-) )

If no one responds to your CWDP errata note, would your comment have been in vein?

(sorry, that probably sounded a bit too sanguine)...

Questions/possible errata in assessment test:
Please correct me if I'm wrong.

15. Which architecture is most prevalent?
According to the discussion about chipsets (pg 183), "the difference in volume between purchases of consumer and enterprise chipsets is staggering". That would certainly lead one to believe that autonomous architecture is more prevalent. Had the question been qualified with "Which enterprise architecture is most prevalent? ", I would agree that centralized makes more sense.

22.....first action that needs to be completed....
When we get a call from a customer, the first thing we do is a quick satellite image review to see if the link is even possible without erecting towers. Saves a lot of time. Just saying......

24. .....802.11n....throughput
Are you saying that the security protocol you choose will have no effect on throughput. I would think that it might very well have a big impact on a busy network.

26. ...passive survey....limited...
I would think that the RSSI downlink info would give at least [i]some [/i]estimate of what PHY rates you could expect. No?

Comments and explanations please.

This is not errata in book but in the definition of CWDP cert on this page https://www.cwnp.com/certifications

"CWDP is [b]an[/b] professional level career certification " I believe it needs to be [b]a[/b]. Also for the CWAP.