How to Run Loopback Test with Auto Loopback

With ApexPlus and GigaPlus 3.0 firmware or later, you can use loopback auto function to test the OMU or IDU for normal operation. This can be used for diagnosing poor link conditions to rule out or identify if there is a defective IDU or OMU. This test is typically only run at the request of technical support and would not normally be used during installation or to troubleshoot alignment or low RSSI issues.

Login to the web interface and go to the config node. For those that are new to the 3.0 interface, the username is config and the default password is trango, all lowercase.

Under the Diagnostics heading, select Loopback Auto. You'll see a mostly blank page if the test has not yet been run and a box at the top where you can enter a number of iterations to run the loopback test. Go ahead and enter 10 in the upper box and hit submit. A warning will pop-up to ensure you understand that this will break the link to perform the test. As long as you have default opmode enabled, when the test is done, the link should be restored to normal operation.

Click OK to proceed with the test.

The software will now turn your ODU power off to try and eliminate the signal coming from the other side of the link. Best practice, when possible, would be to disable the transmitter on the opposite side of the link to completely eliminate that signal from interfering with the test, but under most conditions turning off the ODU will reduce the signal enough for an accurate test. If you still have management access, you'll notice that the Active link and remote link indicators on the top of the page go grey to indicate that the ODU is powered off. On the opposite side of the link, the indicators will be red as there is no signal coming in and therefore no link.

Ethernet data ports will also be shut off during the test. When loopback is activated, the signal is actually looped inside the IDU or OMU and any Ethernet or T1 traffic coming in will be looped back out the same port. Since this can cause numerous problems in an Ethernet network, the data ports are shut off for the test. If testing manually, you'll need to ensure that the data ports are disconnected or disabled before enabling loopback. If you're using IBM, auto loopback will allow loopback tests to be run without having to switch to out of band management.

Note that it is possible to control the number of iterations and use a number other than ten in the entry field. A number as small as one may be entered here for a quick test, or a larger number like 50 may be entered for a longer test. Any integer from 1 to 99 may be used for the number of test iterations. Ten seems to be good number for most tests as it gives you enough information to detect if a longer test is needed, which most of the time it is not. The number of iterations controls how many times the software will run and capture linktest for each of the loopback modes.

As the ODU power has been turned off and the Ethernet ports disabled, it will run loopback IF where it loops the signal just before it would normally go out to the IF cable to the ODU. 

After the loopback IF test results are captured, the software will change the loopback mode to Digital, which performs a digital loopback before the signal is sent to the IF card.

When the tests are done and the results captured, the ODU power will be turned back on and the Ethernet ports will be enabled again. As long as the default opmode was on, the link to the opposite side will be re-established. When the test is done, you may need to log back into the radio if this was a remote radio that you could no longer manage during the test. You'll be able to determine when the test is complete because the link will be restored, or the ODU power turned back on so the grey link status indicators will turn back to red or green depending on the condition of your link.

Click show result to see the data that was logged. Primarily what you want to look for is that the link is locked, indicated by a 1, and examine the MSE. In the IF section the MSE should be -36 or better. -38 is a better MSE value than -36. If the MSE showed -32 or anything worse than -36, it would indicate a problem with the IDU or OMU or there is interferance getting into the IF cable. It is possible to run the tests manually with the IF cable disconnected to rule out a cable, but obviously this test must be run on site to detach the cable. 

If the IF results are not good, then the digital results can be examined. The MSE is Digital should be -38 or better, but is typically only examined in comparison to the MSE from the loopback IF test. Technical support can offer specific advice given your situation as to what poor loopback MSE values could indicate.