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Network Testing and Emulation Solutions

Emulating Station Motion with a Programmable Attenuator

Goal: Test the AP migration of a station by changing the attenuation of two or more APs.

By changing the apparent distance of multiple APs, we provide an environment that emulates moving through a series of AP coverage areas. We can set the rate of change to emulate the speed of the station's movement. We can set the emulated distance for APs so it appears that the APs are further apart or closer together.

This cookbook scenario illustrates a minimal motion emulation setup: two Candela CT520 systems are providing a 1x1 AP signal to a CT703 Programmable Attenuator. A cell phone is sitting near the attenuator. (Illustration at right.)

There are many possible testing scenarios. One ideal method would be to place each AP and phone into isolation chambers, and wire a programmable attenuator to each AP, placing the antennas in the phone's isolation chamber. (Illustration below.)

It is possible to use third-party access points, but then the LANforge would not be able to report as many statistics, and would be used mostly for just operating the programmable attenuator(s). Third-party APs may be able to provide their own reporting to make this scenario more useful.

 
  1. Setup two LANforge units. The LANforge manager unit will connect to a CT703 attenuator via USB cable for control and provide a virtual AP. The LANforce resource unit will provide a second AP isolated from the first.

  2. Configure Networking on Manager node:

    1. In Ports tab, On Manager resource, Create bridge b0 and add eth1 to it.

    2. Set the address and mask of eth1 to 0.0.0.0

    3. Select wiphy0 and create Virtual Access Point vap0 with: screenshot

      1. channel: 1

      2. SSID: jedtest

      3. passphrase: jedtest1

      4. mode:ABGN

      5. IP: 0.0.0.0

      6. Mask: 0.0.0.0

      7. Enable WPA2

      8. Click OK

    4. Create bridge b0 screenshot

      1. Assign address of 10.26.1.1 to bridge

      2. Set gateway to 10.26.1.3

      3. Add vap0 to bridge b0

    5. In Netsmith, create a virtual router.

    6. Add bridge b0 to virtual router, click Apply

    7. Right clickModify b0 in the router, and enable DHCP. Create a DHCP pool with time:1200, starting address: 10.26.1.20, ending address: 10.26.1.200. Click Apply, close window. Close Netsmith.

  3. Your networking in resource 1 would look like: screenshot

  4. In Ports tab, for resource 2 node:

    1. Set address and mask of eth1 to 0.0.0.0

    2. Select wiphy0 and create Virtual Access Point vap1 with: screenshot

      1. channel: 1

      2. SSID: jedtest

      3. passphrase: jedtest1

      4. mode:ABGN

      5. IP: 0.0.0.0

      6. Mask: 0.0.0.0

      7. Enable WPA2

      8. Click OK

    3. Create bridge b1 screenshot

      1. Assign address of 10.26.1.3 to bridge

      2. Add vap1 to bridge b1

      3. and add eth1 to it.

      4. set gateway to 10.26.1.1

  5. Your networking in resource 2 would look like: screenshot

  6. Your Ports tab would show a b0, b1, vap0, vap1 and two eth1 ports like below: screenshot

  7. Open the Attenuator Motion plugin and configure a scenario. In this scenario, our attenuator is numbered 1.1.14. screenshot

    1. Change Minimum attenuation to 0.0 because we're doing an over-the-air test. You would set a higher minimum when cabling directly to the client station.

    2. Enable Loop if desired.

    3. Specify the first attenuator module wired to manager radio wiphy0 as AP #1.

      1. AP: vap0

      2. Atten: 1.1.14.0 This indicates attenuator module 1. (Ranges are 0-2 for CT703 and 0-3 CT704 models of programmable attenuators.)

      3. Distance: 100 (Meters)

    4. Specify the second attenuator module wired to resource 2 radio wiphy0 as AP #2.

      1. AP: vap1

      2. Atten: 1.1.14.1 This indicates attenuator module 2. (Ranges are 0-2 for CT703 and 0-3 CT704 models of programmable attenuators.)

      3. Distance: 100 (Meters)

    5. Configure the remaining settings so that looping does not unecessarily pause

      1. AP #3 should be at Distance 100.

      2. AP #4 should be at Distance 0.

      3. Set Speed to 1m/s

      4. Set Stop Position to Zero.

    6. Click Start and a report window will appear. The image below shows repeated looping and pausing, as well as some manual adjustment. screenshot

    7. Verify station associations. In the picture below, two cell phones are present for the test. They jump between AP ID 1.0 (AP #1) and ID 2.0 (AP #2). In our testing, it does not appear our phones do a good job of jumping to a higher quality AP when the signal to the current AP is weak. But, it will normally associate properly to the 'best' AP when it looses connection to the old AP. screenshot

      1. Click Pause

      2. Drag the position slider to distance 100 to center the station under AP #1.

      3. Check that the phone associates with AP #1.

      4. Disable phone WiFi connection.

      5. Drag the position slider to distance 200 to center the station under AP #2.

      6. Enable phone WiFi connection, and check that phone associates with AP #2.

    8. Run looping test. In graph Configured Attenuation above, and the Station rates reported by AP graph below, you can see that first cell phone had a difficult time associating to the APs while they were migrating: the reported TX and RX rates for it are zero or very sparse. A steady stream of data (fast ping, iperf download, etc) should be run to or from the phone (DUT) to ensure accurate tx/rx rate reports. That was not done in this scenario. screenshot

      1. During this test your phone will attempt to roam to anything. In your phone WiFi settings, force the phone to forget your nearby (non-testing) APs. You might have to change the WPA2 passwords kept in your phone WiFi settings for those nearby APs to force them to fail association with APs outside this test.

      2. Uncheck Pause and the test will resume automatic attenuation of each AP.

      3. At Candela Technologies, our testing showed our Android phones were not behaving optimally. Part of the problem is that we were not using isolation chambers, so even the 'out-of-range' APs were visible at around -80db signal level. We concluded that our phones were not smart enough to notice a weak AP and take proactive steps to scan for a better one.


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www.candelatech.com | sales@candelatech.com | +1.360.380.1618
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