Home > Training > Wireless LAN Foundations – Day 1

Wireless LAN Foundations – Day 1

Day 1…..

It’s not surprising that wireless technologies have begun to integrate into the mainstream of our daily lives.  I would go so far as to say that in the near future we will see an exlosion of devices all connected wirelessly.    With that understanding I’ve decided to seek out formal training in this wireless arena and have cashed in on my “all you can eat” training at Global Knowledge to take a “Wireless LAN Foundations” class.  It’s meant to provide the fundamentals of wireless technologies as well as assist in preparing for the CWNA exam.  The instructors name is Ben Miller (CWNA, CWNP) and his blog is www.sniffwifi.com.  The class provided the following material:

  1. Wireless LAN Foundations course curriculum
  2. Lab Guide
  3. Official CWNA Study Guide (Certified Wireless Network Administrator)
  4. CWNA practice exam from CWNA
  5. CWNA practive exam from Sybex
  6. CWNA exam voucher
  7. Wireless enabled laptop (Dell D620)

I’m trying to document as much as possible but the amount of material that Ben ads to the slides is more then I feel needs to be included in this blog.  As I re-edit this article over the next several hours and\or days, I will remove or add content that I feel best captures the concepts of the this course.   After one full day of CWNA training I’ve come to the conclusion that, although the class is informative, the material is beyond my scope of security objectives and I will not pursue the certification.   That being said I will use the free voucher and take the exam once this course is complete and maybe with a bit of luck from the god’s I’ll pass.   Who am I kidding…If you were sitting next to me you’d have the same lost look on your face as I’ve had for the last hour or so.  I will however continue to document all class material that I feel can be best represented as “blog material” but much of the course content will be omitted. 

The first slide introduces the  3 components used for wireless networks:

  1. Transmitter
  2. RF Channel
  3. Receiver

Ben then used several questions to provide further explanations into this simple diagram.

How do we get data on the channel?

  • Amplitude = wave height
  • Frequency = # of wave cycles per second.  1 wave cycle per second is 1Hz.
  • Phase = is the starting point of wave

Frequency modulation is not used in 802.11a,b,g,n.   Modern wireless networks use amplitude (height of wave) which is used at higher WLAN speeds.    The best way to describe a phase is to compare a wave to a clock with 12 being highest and 3 lowest point.

How do we differentiate channels?

Frequencies are used to differentiate channels. 

  • Band = series of channels. 

Unlicensed frequency bands used in wireless are 2.4 & 5 GHz (billions of cycles per second).  One drawback to using these frequencies is that it is currently used by all WLANs and therefore issues will arise at times when multiple devices are using the same frequency and channel. 

What is  behind the wireless link?

  • P2P
  • WLAN
  • Wireless broadband

802.15 standard is used for wireless personal are networks.  One of the well known technologies used today is bluetooth.  Some of the characteristics of bluetooth are:

  • 2.4 GHz band
  • Fast FHSS (frequency hop spread spectrum)
  • Speeds: up to 3 Mbps
  • Range: Class 1(300 ft),  2(30 ft),  3(3 ft)

Some other less known p2p wireless technologies are ZigBee and Z-Wave.   They have much lower bandwidth transmission rates, 250Kbps which requires less power.

WLAN = specific technology used to extend a lan wirelessly

802.11 = standard for the technology

WiFi = certification for real world products

Section 2: WLAN Infrastructure

Wireless works at Layers 1 & 2 of the OSI model.  These layers deal with wireless standards such as 802.11a\b\g\n and MAC addresses.  The most common WLAN connectivity device is the Access Point.  The following are standard configuration parameters for AP’s:

  • SSID
  • Channel
  • Power
  • Security
  • Optional

In addition all AP’s have a BSSID or Basic Service Set ID. 

Some recommendations are to use a very familiar SSID name so that it will not be uniquely identified on war driving sites like www.wigle.net.  I just did a search for both of the SSID’s and to my surprise…there I was.  It was able to provide even the generalized location of the access point but no address.  So much for anonminity

Section 3: Wi-Fi Standards

 There are a few characteristics that define the wifi standards:

  • Frequency band (2.4 GHz: 3 channels)
  • Air Interference (DSSS: max 2 Mbps)
  • Data Rate: how much data can be sent in one frame
  • Throughput: how much data is actually being sent
  • Dynamic Rate Switching: all devices will negotiate data rate based on interference

There are several extra services at the MAC layer which are used to support Layer 1 wireless functionality:

  • Addressing
  • BSS membership (roaming)
  • Arbitration (channel sharing)
  • WEP
  • Fragmentation (collision handling)

There are 3 approved standards and I have included their corresponding air interference methods:

  • A (OFDM)
  • B (HR-DSSS)
  • G (ERP-OFDM \ HR-DSSS)
  • N (HT OFDM \ OFDM \ HR-DSSS) *OFDM is used with MIMO

It’s coming to a close for day 1 and the material covered so far has been…well how do I say this…technically dry and unmotivating.  This is no reflection on Ben’s teaching style but more so directed at the course content.  The saving grace has been the lab exercises and not to mention documenting all this on the blog.  Self expression always seems to elevate the spirit. 

Lab 1: WLAN Client Management

  1. Configure Basic Client Settings
  2. Configure Preferred Networks
  3. Configure Advanced Client Settings

These were simple exercises and I was aware of all settings in exercises 1 & 2 but some of the Advanced Client Settings I had yet to configure.   Some of the settings on configuring your basic wireless settings are seen below.  Anyone who has had to setup an XP wireless connection will be familiar with these settings.  As can be seen no encryption has been set and the SSID is unique, something that would be discovered on the www.wigle.net.  (of course I verfied this)

 

Some of the additional settings that I have been introduced in exercise 3 were:

  • Disable Upon Wired Connect (self explanitory)
  • Band Preference (

Both of these setting are below:

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Section 4: RF Fundamentals

Raw signal strength is measured in dBm.  So what represents a good signal in dBm?.  -70dBm or higher is good (that is a negative #).  SNR is Signal Minus Noise.  Most devices will be > or = 10 dB.  I’m still not too sure what these numbers mean but I do remember seeing them on a site I found on how to build your own wireless antenna.  I never built the antenna and after a quick review of the site realize that I still have a very limited understanding of the fundamentals of this technology.

RF energy is directed based on antenna structure.  All antenna’s give more coverage in one direction then all directions.   The concept of isotropic radiator is theoretical circular coverage area around of an antenna.  No antenna works in this fashion.  Antenna gain is measure in dBi which is calculated as the additional coverage extended in an oval pattern away from the antenna.   There are 3 types of antennas:

  • Omnidirectional – all horizontal directions
  • Semidirectional – limited vertical direction – Yagi
  • Highly directional – point to point
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