CWNA Study Guide Chapter 2 Radio Frequency Fundamentals Key Learning Points - Part 1

I thought this chapter was probably the most important as a fundamental target to knowing how wireless interacts with its environment, what may affect a radio wave and how it may perform.

Understand what a radio wave is including the electromahnetic spectrum and radiation types such as radio, light, x-ray etc



To produce a radio wave an ac current (alternating current passes through an antenna producing a signal. ac current has a  typically sinusoidal waveform as oposed to dc current which is linear at a fixed amplitude.

The signal generated by the antenna is dependent on the changes in the ac current properties.

Properties of the ac current that may vary are wavelength, frequency, amplitude, phase and polarity.

Electromagnetic waves can travel through objects.

In a vaccuum RF travels a the speed of light which is approximately 300,000 km per second or 186,000 miles per second.

When a wave is generated it moves away from the antenna, it is said to propogate.

When a wave propogates and comes into contact with objects it can change, these changes are propogation  behaviours, these include absorption, reflection, refraction, scattering, diffraction, loss, free space path loss and multipath,

Understand RF characteristics and the relationship between wavelength and frequency. There is an inverse relationship between wavelength and frequency.

λ=c/f

where λ=wavelenth, ƒ=frequency, c=speed of light

Simple transposition of the above formula can prove the following

The higher the frequency the shorter the wavelength.

The longer the wavelength the lower the frequency.

Typical wavelengths in the 802.11 RF spectrum are

2.4 GHz = 12.5cm or 4.8"

5.0 GHz = 6.25 cm or 2.46"

A wave will attenuate or lose signal strength as it apsses through a medium, a signal with a higher wavelength and therefore a higher frequency will attenuate more for a given medium. An RF wave may attanuate to such a degree that it is below the receive sensitivity of the receiving radio and cannot be demodulated successfully and has become unuseable.

Theoretically a radio wave will travel forever in a vaccuuum.

Coverage distance of a radio wave is dependent on attenuation, brick, glass, water and even air will attanuate an RF signal.

Attenuation in air is called free space path loss.

2.4 GHz radio waves will propogate better than 5.0 GHz radio waves.

Frequenccy is the number of times an event occurs in specified time, in RF it is measured in Hertz which is cycles per second. 2.4GHz is 2.4 billion cycles per second.

Amplitude can be seen as the power or strength of a wave and when you look at an oscilloscope you would see the height of the wave vary with a change in amplitude.

Phase is the reltionship between two or more waves that share the same frequency. Phase can be measured in distance, time or more usually degrees. If two waves are in alignment they are said to be in phase. Phase is imprtant as signal amplitude may increase or decrease dependent on the phase relationship and is known as multipath

CCNA Wireless Experience

I took the CCNA Wireless exam and passed thankfully about two weeks ago, before I started blogging, I would have been gutted to get a fail with my experience and would have probably quickly resat the exam and kept quiet!

I think the exam was fair however you either needexperience or alot of reading as there are just some questions that you would find it hard to pick up.

Look at all the practice questions from Boson and on the Cisco site and it will give you a good idea what to expect. The harder part for me was definitely on the 500 series controller as I have only configured one and its alot different to the enterprise controllers so had to read some on the 500 series. Being intimately familiar with the enterprise models, the 4400 and 2100 series, I automatically think about what I would do if deploying them. Know the limitations of the 500 series access points and controllers. Also get some hands on even if its just a sandalone access point.

I studied for about a week pretty solidly but was involved in the Cisco CCNA Wireless Study Group quite actively that has helped me get into study mode and probably think more aboute the minutae that would be on the exam rather than just being able to configure and understand the processes. At the time I was on there I was studying for my CCDA, I still am, I should be sitting the CCDA tomorrow but have delayed it for about a week.

All in all I thought it was a pretty straight forward test and a fair assessment of what you could expect at that level.

I did however give myself quite a bit of stress as I also sat the Cisco AWLANFE exam on the same day, thats the Advanced Wrireless Field Engineer 642-631. I thought the material would be pretty similar and to a large degree it is. The only issue I had was time and a few of the less familiar topics like EAP-FAST that I had to read up on. The main issue is that it is based on older code so you have to think in terms of code 4.0 and also know the 1000 series access points.

Finally sitting two Cisco exams in one day is stressful even if you know the sbject matter. I have pledged to do the same for my CCDA and AWLANSE, thats the 642-681, but I know it will be a lot tougher than the CCNA and AWLANFE. Most people I spoke with thought I was mad even attempting it. I onestly can't see myself doing the same for my CCNP Wireless, R&S or teh CWNO stuff, the detail and depth is so much harder and alot of the routing stuff will be new though the concepts are alot more meaningful now and are actually making sense.

New Access Points and Code from Cisco

Cisco have just launched several new and exciting products to to enhance and extend their existing wireless portfolio.

First off is the 3500 series access point available in a variety of flavours. Theres the 3500i wth integrated 4.0 dBi antennas on the 2.4 GHz radios and 3.0 dBi on the 5.0 GHz radio. There is also a 3500e for more challenging environments supporting external antennas. Each available as single or dual band.

The key feature though is the Cisco's CleanAir Technology which makes this the industry's first 802.11n access points to create a self-healing, self-optimizing wireless network.

There is also a new isco 1260 series access point which very much looks like a replacement for the 1250. A major advantage being that it can be powered with standard 802.3af PoE. This is designed for indoor challenging environments with external antennas.

Finally there is the announcement of Cico Unified Wireless Network Software Release 7.0, hooray, well for me anyway as I hope there are one or two resolved caveat so I can get a few upgrades done.

I will get a little more time later in the week for a better update and include some details on CleanAir Technology and feature enhancements in Cisco Unified Wireless Network Software Release 7.0

CWNA or Bust

Those of who love wireless will no doubt be aware of the CWNP or Bust competition which offered a great opportunity to win some great resources to complete the CWNA or CWSP certification tracks.

The competition was hosted by George Stefanick of my80211 and sposored by the kind people of CWNP.

The winners were announced a few days ago and are posted here on my80211.

I just want to say congratulations to the guys and wish them luck on their exciting journey.

I have got to know two of them reasonably well trough forums and will be following their exploits religiously. They each have to blog their activities weekly and I know they are keen as mustard to get started.

Congratulations to John Bogard, Rick Todd and Darby Weaver. Their blogs can be followed via these links.

John Bogard http://www.my80211.com/cwna-john-bogard/

Darby Weaver http://www.my80211.com/cwna-darby-weaver/

Rick Todd http://www.my80211.com/cwna-rick-todd/

George Stefanick http://www.my80211.com/cwsp-george-stefanick/

Faster than 802.11n meet 802.11ac

Just as you thought you could breath a little easier in this fast paced wireless world that we live in there's a new kid on the block, well a new standard in the making and it will be here sooner than you think. Yes another new standard.

I can recall when I got my first 802.11g access points and panic set in about compatibility with the 802.11b we already had installed. I needn't have worried but I was still a novice. I didn't even know at that time about 802.11 or 802.11a.

A little history, the 802.11 standard was minted in 1997 provisioning 1 Mbps and 2 Mbps in the 2.4 GHz spectrum, I know it seems along time ago but it had a decent uptake in manufacturing and warehousing. Only 2 years later 802.11b and 802.11a came along, that’s 1999. 802.11a provisioned up to 54 Mbps but was slow to capture the market due to generic client support. 802.11b on the other hand took off and everything was built with 802.11b that could be. We all know the advantages of 802.11a over 802.11b, higher throughput, less congestion etc but client support meant 802.11b stormed the market. Then 802.11g came along in 2003 and there was even less need to move to 802.11a as 802.11g in the 2.4 GHz spectrum was as fast as 802.11a and more accessible.

We waited an awfully long time for 802.11n with many many false dawns, it finally became a standard on September 11th 2009, about tea time if I recall, well that’s when I got the news. Just for the record 802.3af became a standard on the same day but was eclipsed by the hoopla surrounding 802.11n.

802.11n was so different its a whole new set of rules for us wireless engineers to learn, channel bonding, MIMO, frame aggregation, block acknowledgements etc etc and promises up to 600 Mbps.

Well now we have 802.11ac, there is little out in the real world that goes into any great depth about this proposed new standard, however, it is being touted that it will be a standard in December 2012, that’s not far away at all.

All is not lost however as it seems that it will largely an evolution of 802.11n or at least some of the technologies. The basis for the enhanced speeds, over 1 Gbps, will be further channel bonding with talk of 80 MHz and even 160 MHz wide channels. Now it would appear that this would only be feasible in the 5.0 GHz spectrum as there are not enough reusable channels in the 2.4 GHz spectrum. Even with all the available channels in the 5.0 GHz spectrum it is unlikely that there would be enough non overlapping air space to deploy an enterprise cell based implementation as we do today. Slight improvements in modulation techniques will also push up the speed.

A major breakthrough could come in the form of MU-MIMO (multiple user MIMO) where simultaneous streams are given to users on the same channel.

Product may hit markets as early as next year however I get the general feeling that it will have more specific applications than 802.11n due to the channel bonding and would be ideal for streaming HD video or high speed PtP or PtmP implementations.

802.11ac also has a big sister, 802.11ad, similar technologies but working up to 60GHz where I believe there is a lot of spectrum available. This however would be severely limited in its signal propagation as we all know the higher the frequency the poorer the range so 60GHz is going to be working between two devices in relatively close proximity.

One thing is for sure, the wireless market place is technologically innovative and our jobs and skills will only be more valuable as we ride the crest of the wave.

Wireless Standards

I was looking for info on the next generation wireless standard 802.11ac and came across this.

http://www.ieee802.org/11/Reports/802.11_Timelines.htm

Its a good outline of all the current standards, ammendments and recommended practices and includes download links for some standards that are freely available.

I have thoughtfully copied the links to the download locations to save you the hassle of clicking everything and put in a few additional links that I could find.

IEEE 802.11: The WLAN standard was originally 1 Mbit/s and 2 Mbit/s, 2.4 GHz RF and infrared [IR] standard (1997), all the others listed below are Amendments to this standard, except for Recommended Practices 802.11F and 802.11T.

IEEE 802.11-2007 A new release of the standard that includes amendments a, b, d, e, g, h, i & j. (July 2007)

IEEE 802.11a-1999 54 Mbit/s, 5 GHz standard (1999, shipping products in 2001)

IEEE 802.11b-1999 Enhancements to 802.11 to support 5.5 and 11 Mbit/s (1999)

IEEE 802.11d-2001 International (country-to-country) roaming extensions (2001)

IEEE 802.11e-2005 Enhancements: QoS, including packet bursting (2005)

IEEE 802.11F-2003 Inter-Access Point Protocol (2003) Withdrawn February 2006

IEEE 802.11g-2003 54 Mbit/s, 2.4 GHz standard (backwards compatible with b) (2003)

IEEE 802.11h-2003 Spectrum Managed 802.11a (5 GHz) for European compatibility (2004)

IEEE 802.11i-2004 Enhanced security (2004)

IEEE 802.11j-2004 Extensions for Japan (2004)

IEEE 802.11k-2008 Radio resource measurement enhancements (2008)

IEEE 802.11n-2009 Higher throughput improvements using MIMO (multiple input, multiple output antennas) (September 2009)

IEEE 802.11p: WAVE—Wireless Access for the Vehicular Environment (such as ambulances and passenger cars) (working—June 2010)

IEEE 802.11r-2008 Fast BSS transition (FT) Working "Task Group r" (2008)

IEEE 802.11s: Mesh Networking, Extended Service Set (ESS) (working—September 2010)

IEEE 802.11T: Wireless Performance Prediction (WPP)—test methods and metrics Recommendation cancelled

IEEE 802.11u: Interworking with non-802 networks (for example, cellular) (working—September 2010)

IEEE 802.11v: Wireless network management (working—June 2010)

IEEE 802.11w-2009 Protected Management Frames (September 2009)

IEEE 802.11y-2008 3650–3700 MHz Operation in the U.S. (2008)

IEEE 802.11z: Extensions to Direct Link Setup (DLS) (August 2007 – December 2011)

IEEE 802.11aa: Robust streaming of Audio Video Transport Streams (March 2008 – June 2011)

IEEE 802.11ac: Very High Throughput <6 GHz; potential improvements over 802.11n: better modulation scheme (expected ~10% throughput increase); wider channels (80 or even 160MHz), multi user MIMO; (September 2008 – December 2012)

IEEE 802.11ad: Very High Throughput 60 GHz (December 2008 – December 2012)

IEEE 802.11ae: QoS Management

IEEE 802.11af: TV Whitespace

IEEE 802.11mb: Maintenance of the standard. Will become 802.11-2011. (Expected publication 8/02/11)

For those withh some money to spare at the end of all the books and lab gear you will be buying 80211n

Blogger

Well after a few days with blogger I have spent far too much time trying to get it how I want it but its looking OK at the moment.

I think there are certainly things that would be easier to accomplish with more control but I am not an HTML guru so I will stick with it for now. I also have a great deal on at the present time.

Eventually I think I will host my blog elsewhere and rid myself of the shackles that are imposed by Google Blogger.

Don't get me wrong I wouldn't have this up and running if it wasn't as easy as it is but there are restrictions that I think I could get around by hosting it myself. I also think that I will outgrow the capabilities of Blogger before the year is out.