Cheap spectrum analysis for wireless

When I was going through college for networking I learned to hate wireless.  I had come to learn that it was insecure, unreliable, unpredictable, and difficult to troubleshoot.  I got into a job I love and then the wireless era began.  We are now implemented hundreds of new wireless network devices a year.  We have built out our infrastructure with a lot of time and planning and so far have been quite successful.  We use primarily Cisco equipment with some Ubiquiti back-hauls for some of our outdoor setups.  Cisco provides some very basic spectrum information, for someone who has done some in-depth work with wireless and Cisco this is enough information.  It doesn’t seem to provide any visual representation of the network which can be had to explain to upper management.  Spectrum analyzers can be thousands of dollars and for what we are doing we don’t need something that granular.  We need something to tell use when channels are overloaded/consumed with interference and if antenna’s are aligned properly during setup.

We bought a few Ubiquiti bridges a while back and noticed the AirOS product line has a built in spectrum analysis.  This is handy when selecting channels as it ensures you are not selecting a channel already in use.  We have been watching Ubiquiti for some time now and when we started running into some issues with our client wireless access I went out and bought a Ubiquiti Bullet M5 and an M2.  I think total for the both I paid about $140 (includes adapters and some antennas I had lying around).  As you might guess the M2 runs off of the 2.4Ghz spectrum and the M5 runs off the 5.8Ghz spectrum.  With the Bullets, a switch, and a windows laptop/netbook and power source we can easily run up and diagnose a problem.  This setup is also very mobile and could be brought out into the field to be worked on (barring a power source of course).

At this point in time I have been unsuccessful in getting the spectrum analysis software working in anything other than windows.

I am going to assume you can get the default information for the Ubiquiti Bullet and login.  My bullet is completely stock, no configuration needed to do what I will show you.  After logging in you get some beautiful throughput graphs and other good troubleshooting information.  There is also a drop down menu near the logout button which provides you with an AirView option.  AirView is the spectrum analyzer software.

Screenshot - 02092013 - 01:15:35 PM

Airview is a Java Network Launch Protocol application which obviously requires Java.  The analyzer in my virtual machine runs about 9 frames a second and shows pretty close to real time the actual spectrum.  Here is a 2.4Ghz snapshot of my work where our 2.4Ghz spectrum is very overloaded. Sadly this is with only a few clients in the area.

 

Screenshot - 02092013 - 01:54:43 PM

The top visual: Waterfall ViewThis is a good representation of channel utilization over time.  You can clearly see if a client is connected and on what channel.

The middle visual: Waveform View
This is a good visual of how often you get a signal at a certain power or signal strength.

The bottom view:  Real-time View
This is good for seeing what is happening right this second compared to the average and maximum power levels recorded.  After letting this run for a few minutes you can compare spikes and hopefully identify any problems.

I plan on using these to make future recommendations to clients and potential trend information over a period of time.  This could help identify possible interferers that could be as simple and intermittent as a microwave.  These pictures will be invaluable when trying to explain to upper management how or why we are having problems, and what should be done to correct it.

 

Quick and easy MSRDP script

I love Linux, but as we all know we have to work on windows computers usually on a day-to-day basis.  We have servers we constantly have to RDP (remote desktop) into to work with active directory, etc.  The Terminal server client in 10.04 was all buggy and when you closed the window it would reconnect in 30 seconds.  This was especially annoying when you left a session open on your locked computer on the other side of the building and needed to hop on real quick to do something.

ubuntu-Terminal-Server-Client

I found out that the problem was that certain libraries had bee updated and caused this bug.   I decided using rdesktop for a while would suffice and created a launcher on my panel to run this command.  It wasn’t pretty for the longest time, a bash terminal asking for usernames, etc.  I really didn’t like it.  I stumbled across zenity a while ago and decided to use that to hide the password and pass that to the rdesktop command.  It is pretty simple actually.
I prefer to hard-code my username and domain in so that I don’t have to constantly fill it out, however more zenity windows could easily be added if more security or flexibility would be needed.  I saved this into a script, made it executable, and then created a launcher to run the script.  I haven’t spent much time on it but I could not just put this code into a launcher and run it (on XFCE, I suppose other frontends like gnome2 or unity might work).

The code above in a launcher provides these dialogue boxes:

Username

password

 

Zenity provides a lot of flexibility in bash scripting so end users don’t have to see a techy/confusing bash window to do something simple.  Zenity options:

We will definitely be using zenity to make some things more user friendly…

Shattered Hard Drive

I recently had a laptop brought down for not working.  It had no cosmetic issues that looked like it had dropped however the student had noticed that when the laptop was shook…  violently shook, it sounded like there was loose parts inside.  I pulled the drive out to see if I could recover any data off of it and noticed that the sound was coming from the hard drive.  I immediately knew something was very wrong and that chances of recovery were slim to none.  Told the student I would try and sent him off.

I then took the hard drive apart… and all of my years experience I have not seen this first hand yet.  The platters were shattered.

I have stripped the sound because names were mentioned.  It also took me a minute to find the screw under the sticker.

WAN Load Balancing

We ran into an issue at work where we needed faster Internet (or more bandwidth,)…  The prices for our current ISP’s were higher than we had hoped for faster Internet, but we would like fail over as well as additional load balancing.  With teachers and students depending on the Internet so much we cannot afford not to have the Internet working well.  Our current provider’s downtime was unrealistically low (single digit hours a year) and we were VERY happy with the service.  Increasing our speed with that provider was not very cost beneficial compared to other providers.  So we started considering load balancing/fail-over with a second or third provider.

We investigated several commercial options as well as potential open source options.  We LOVE open source but something as critical as this we wouldn’t want to have to ever really troubleshoot.  We looked at solutions that were computers with specialty designed OS’s, as well as specialty hardware.

We had discussed deeply whether a standard computer hardware (with replaceable hardware) would be better than a hardware device designed to do what we wanted.  Ultimately we came to the conclusion that the software or features would make the decision.

We ended up going with a Ecessa Powerlink 600 which is a load balancer for both inbound and outbound connections,WAN fail-over, and Ecessa fail-over if two units are purchased.  We get the device setup with our current single 11Mb/11Mb fiber connection and were dieing to get more connections on the device.  A few weeks later we were able to get 100Mb/5Mb cable connection in and immediately saw the differences and how Ecessa was load balancing between the two connections.  Within the first week we had also had notices of our new cable modem dropping in and out however end user experience was not effected.

We were able to eventually load balance:

  • 11Mb down/11Mb up extremely reliable but expensive fiber connection
  • 50Mb down/50Mb up reliable wireless connection
  • 100Mb down/5Mb up least reliable cable connection

This provides us with a total usable bandwidth of 161Mb down/67Mb up, with the fastest potential download speed of 100Mb down, 50Mb up depending on the WAN interface you happen to fall on.  This also provides fail-over on any of the connections so that we can immediately fail-over to another connection without major interruption to end-users.

This link is also capable of load balancing incoming connections if set to an authoritative DNS server however we are currently not implementing that due to current network structure and time involved to implement that.  Although the time is not much, we are pressed to finish other projects right now.  That being said, we will be implementing this in the future.

I can say that installation was EXTREMELY easy with tech support.  Without the tech support the device would not be as straight forward as most would hope, advanced users ‘could’ struggle to get it setup.  We provided some simple information and they sent us a configuration file which was uploaded to the device.  They pretty well configured the device remotely and sent us the file.

We got it up and running and it has been running fantastic for over 100 days; even during ISP failures on our cable modem.  Our end users do not notice any issues when we fail-over.

When you setup Ecessa WAN links you type in the IP’s of 3 hosts to ping continuously.  When 2 of them fail the PL600 fails that link until they come back.  This ensures a good solid reliable connection for the end users.  We see out links during the day sporadically fail-over from time to time and have not had any complaints from end users.

During troubleshooting we can VERY easily see what WAN links are up and down, if there were problems, and what speeds are.  Screenshot - 01152013 - 09:30:12 PM

 

 

We have found the Powerlink Extremely effective and  HUGE cost savings.  In about 1 year the device will pay itself off compared to if we would purchase a very fast reliable Internet connection.  We are looking for a second to setup as a redundant fail-over in the years to come.

Linux Vinyl Plotting With A Gerber enVision Plotter

I recently had the opportunity to work with an older Gerber enVision plotter from a township.  I had major difficulties getting the old version of Omega working with their USB licensing stick, and I knew that getting anything like this working on Windows without proper licensing would be an inadvisable, and rocky road ahead.

I decided to look into open source solutions, and I found out that Inkscape can do vinyl plotting with an extension called InkCut.

This tutorial will attempt to comprehensively explain how I got this working.  I am by no means an expert, but I found very limited web resources out there on this topic, and I am hopeful that someone will eventually stumble on this article and find it useful.

Background
A simple, free, and open source solution to an expensive and complex problem: How do we plot stuff with our vinyl plotter?

Assumptions
This tutorial will assume that you have some prior experience with the Linux terminal and the Linux desktop.  On my test computer, I was working with a clean installation of Ubuntu 12.04 (12.04.1) LTS.  However, any Ubuntu or Debian flavor should be acceptable.  I am also assuming you have an older Gerber enVision series plotter.  If this is not the case, I imagine most of these instructions will apply fairly well to any kind of vinyl plotter.

The Plotter
Here are some photos of the Gerber enVision plotter I was working with.

2013-01-01 13.20.33

2013-01-01 13.20.42

 

The plotter interfaced with the computer using a serial connection.

Ubuntu & This Plotter
In order to establish proper communications between the computer and the plotter, I had to ensure some things were true.  I reset my plotter to the factory default settings, which resulted in a condition where I could assume this about my serial connection:

Baud: 9600
Data Length: 8
Parity: None
Stop Bit: 1

In order to ensure communication with non-root users, I took a questionable approach, and I decided to:

This did not need to be a very secure environment (we didn’t even password protect the workstation’s desktop) so I figured this would be a reasonable approach, rather than troubleshooting why CUPS was getting permission denied errors while printing to the serial port.

Configure The Plotter In CUPS
To install this plotter in CUPS, you’ll want to open up your Printer configuration area from the System menu.

Click “Add” to add a printer.

CUPS Add A Printer

If you don’t have the option for “Serial Port #1”, then use the Device URI “serial:/dev/ttyS0“.

Serial Printer

 

You will want to select Generic as the make of printer.

Generic Printer

 

Then, select “Raw Queue”  This will work with InkCut providing the HPGL instructions.

Generic Printer - Raw Queue

Obviously, it doesn’t matter what you name your plotter, or what description you give it, just give it something that makes sense.

Finalize Printer Settings

Install Inkscape

Next, we want to install Inkscape.  You can do this from Apt on Ubuntu, as such:

Once you’re done with the installation, start Inkscape for the first time.  This will create blank default configuration folders in your profile which are necessary for the next step.

Inkscape

 

Then, go ahead and close Inkscape, and move on to installing InkCut!

Install InkCut
You can download the latest version of InkCut from their website.  At the time of this writing, the version is 1.0, and can be found here.

Once you’ve downloaded InkCut, go ahead and extract the file using this command.  It will put the files right where they need to be for you!

Now, when you start Inkscape, you should see InkCut on the Extensions menu, under Cutter/Plotter.

InkCut

Screencast How-To’s
 I have also created some screencasts to explain how to set up the document for your plotter, as well as how to plot some basic text.

Document Setup – Screencast
(Download OGV)

Let’s Plot Some Text! – Screencast
(Download OGV)

Remember, when plotting your text, you need to make sure your objects are converted to paths, by highlighting your text and going to Path > Object To Path.  You also want to make sure your paths aren’t grouped, by right clicking each block of text and clicking Ungroup.

Then you should be good to go to Extensions > Cutter/Plotter > InkCut v1.0 and start plotting!