Archive for the ‘802.11n’ Category

802.11n Deployment Considerations – Troubleshooting & Analysis Tools

This is the second in a series of 802.11n Deployment Considerations to include cabling, power, system architecture, etc. The focus of this particular post is to discuss the deployment considerations related to troubleshooting and analysis tools when deploying 802.11n wireless LANs.  

Packet Analysis 

One of the main troubleshooting & analysis tools for WLAN engineers is a wireless packet capture program. Personally, I use both OmniPeek Professional as well as the AirPcap device from CACE Technologies.  With wireless packet capture programs, it is important for you to ensure both the wireless NIC you are using and the software support 802.11n functionality.  Otherwise, 802.11n features such as channel bonding, frame aggregation, and block acknowledgement might not display properly (or show up in your display at all).  AirPcap sells a specific model for 802.11n, called their AirPcap Nx.  

Spectrum Analysis 

Another important troubleshooting tool for WLAN engineers is a Spectrum Analyzer.  I use both the AirMagnet Spectrum Analyzer and the Wi-Spy Spectrum Analyzer from MetaGeek.  If you read my rant (post) regarding 2.4 GHz vs. 5 GHz for 802.11n networks, hopefully you realize the increasing importance of the 5 GHz spectrum.  Therefore, I would suggest you utilize a dual band spectrum analyzer.   The only Wi-Spy product that is dual band is the Wi-Spy DBx.  

Another spectrum analyzer troubleshooting tool that I am curious to try is the AirMagnet Airmedic Product.  If anyone has used the Airmedic product, leave a comment letting me know your thoughts!  

Wireless IDS/IPS 

While most people think of wireless intrustion detection & intrusion detection as a security tool, they can also be used monitor and preserve the overall well being of the WLAN.   Therefore, it makes sense to deploy 802.11n capable sensors for security, troubleshooting, & analysis.  

Related Posts: 

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WiFi Jedi Featured as Top Blog Post on CWNP.com

In case you haven’t seen it already, my post on 2.4 GHz vs. 5 GHz for 802.11n Deployments was featured in the CWNP newsletter, which has over 100k subscribers!   Here is a snap shot that I took: 

cwnp-top-blog-post

While, I am extremely honored to be chosen and excited to share the news, I am equally grateful for all those that read and comment on my blog posts here at WiFiJedi.com and on CWNP.com  

Please pass along the web address or RSS feed info to anyone else you think would find value in good discussion around wireless networking & security. The comments, sense of community, and spirited debates are what I enjoy most – keep them coming!  

Related Posts: 

What is the greatest obstacle to deploying enterprise 802.11n?

Welcome CWNP.com Readers!

Welcome CWNP.com readers!  I hope you enjoyed my guest blog post at http://www.cwnp.com regarding frequency band utilization for 802.11n networks.  

Since you’re here, I am guessing that you interested in wireless networking and security!  

Below are a some of my most popular blog posts to-date: 

Technical

  • How Stuff Works – 802.11n and MIMO 
  • How Stuff Works – 802.11n and Spatial Multiplexing 
  • How Stuff Works – 802.11n and Channel Bonding
  • How Stuff Works – 802.11n, Fame Aggregation, & Block Acknowledgement
  • How Stuff Works – 802.11n and Short Guard Interval
  •  

    Opinion

    Polls 

    For Project Managers

    802.11n Deployment Considerations – Cabling

    My 802.11n How Stuff Works Series was so popular, I thought I would start another series.  This time I am going to talk about the various deployment considerations for 802.11n networks, such as: 

    • Cabling 
    • Power 
    • Trobleshooting/Analysis Tools 
    • WIDS/WIPS Sensors
    • Etc. 

    Let’s take a look at the first of these considerations, cabling.  With 802.11n, the data rates are drastically improved.  Rates can be as high as 600 Mbps, but most practical implementations of 802.11n today have data rates of approximately 300 Mbps.  

    Therefore, the cable used should have higher capacity than 10/100 Mbps.  What cables have 1 Gbps cabability?  Category 5e or Category 6 cables can support the neccessary speed for 802.11n networks.   IEEE 802.3ab also specifies 1000-Base-T over Category 5 cables, although I would personally recommend Cat 5e or Cat 6 cable.

    Many newer access points or arrays have multiple physical interfaces to include console ports, 10/100 out of band management ports, and one or more 10/100 or Gigabit uplink ports.  If your access points or arrays support multiple uplink ports, you should run separate cables to each.  

    Many times the multiple uplink ports can be configured in several different “modes” to include daisy chaining, port failover, port mirroring, or 802.3ad link aggregation.  In port failover mode, running multiple uplink cables  gives you a level of redundancy to survive a single port failure on either the access point or the uplink switch, increasing the overall reliability of the system.  

      Related Posts:
  • How Stuff Works – 802.11n and MIMO 
  • How Stuff Works – 802.11n and Spatial Multiplexing 
  • How Stuff Works – 802.11n and Channel Bonding
  • How Stuff Works – 802.11n, Fame Aggregation, & Block Acknowledgement
  • How Stuff Works – 802.11n and Short Guard Interval
  • 802.11n Poll Question

    Take other polls at WiFiJedi.com:

    Adventures in Capturing Wireless Packets

    Just a quick FYI for those *true* WiFi packet analysis junkies out there – I installed OmniPeek Professional 5.1.4 on my HP 6910 laptop.  The software “works” with embedded Intel wireless NIC, but reports invalid data rates for 802.11n traffic.

    The work around that I came too was to purchase a 3rd party, dual-band 802.11n USB adapter that has a supported API within the OmniPeek software.

    I also have an AirPcap Nx device from CACE Technologies that I like *very* much – USB form factor that allows for wireless packet capture in Windows.  AirPcap integrates directly into Wireshark, which is nice since I “grew up” taking wireless captures in Lib PCAP format under Linux and looking at them in Ethereal.

    How Stuff Works – 802.11n Frame Aggregation and Block ACKs

    Here’s another guest post that I wrote for a friend of mine.  Check out his blog “Hip Technology“.  Again, the “How Stuff Works” posts have been so popular on https://wifijedi.wordpress.com that I am re-posting what I wrote here.

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    I have posted several times on technical improvements related to 802.11n and thought that I would continue that format here.  For this post, I would like to discuss frame aggregation and block acknowledgment.

    In normal 802.11 operation, each directed data and management must be acknowledged.  This ACK takes the form of a 14 byte packet.  This is shown in the top row of the graphic.

    802.11n MAC Improvements

    802.11n MAC Improvements

    With frame aggregation, up to 64 MSDUs (MAC Service Data Units – essentially layer 2 frames) can be sent at one time.  This “super” frame has one physical layer header, then data frames (each with their own MAC header).  Once all the data has been sent, a block acknowledgment is sent.   This is shown in the bottom row of the graphic.

    This is more efficient for several reasons:

    • A physical layer header does not have to be transmitted for each data frame.  
    • The block acknowledgment is much shorter than 64 separate ACKs.   
    • There are far fewer interframe spaces as all the data is aggregated into one burst and all the acknowledgments are bundled together.  

    Block Acknowledgments are also used under 802.11e Quality of Service.

    How Stuff Works – 802.11n and Short Guard Interval

    This is a post that I wrote the other day as a “guest post” for a co-worker’s blog.   It is a Xirrus sponsored blog, titled “Geekster”.  The URL for the blog is http://geekster1.blogspot.com/ The guest post was part of a series, “How Stuff Works”, which has been one of the most successful portions of my own blog, so I am going to re-post for my faithful readers.  🙂

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    In the first several “How Stuff Works” posts, I have been talking about technical improvements to 802.11n such as MIMO antennas, Spatial Multiplexing, and Channel Bonding.  In this post, I want to talk about another such technical improvement, Short Guard Interval.

    The guard interval is the space between symbols (characters) being transmitted.  This is often confused with the space between packets, which is the interframe space (IFS).  The guard interval is there to eliminate intersymbol interference, which is referred to as ISI.  ISI happens when echos or reflections from one symbol interfere with another.  Adding time between symbol transmission allows these echos and reflections to settle in before the next symbol is transmitted.  In normal 802.11 operation, the guard interval is 800 ns.

    With 802.11n, short guard intervals are possible.   The short guard interval time is 400ns, or half of what it used to be.  Shorter wait time (guard interval) between symbols increases throughput.  However, if it’s too short, the amount of ISI will increase, and throughput will decrease.  On the other hand, if the guard interval is too long, there is increased overhead due to the additional idle time.    If you look at an 802.11 Modulation and Coding Scheme (MCS) chart, you will see that Short Guard Interval increases the data rate by roughly 10-11%.

    Check out my blog at http://wifijedi.wordpress.org for other “How Stuff Works” postings as well as other information and opinions on wireless networking and security!

    IEEE Ratification of 802.11n Standard

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