Understanding T3 Loopback tests

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May 16th, 2009
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Per Cisco for T3 Interface loopback testing:

Syntax Description


Sets the loopback after the LIU toward the terminal.


Sets the loopback after going through the framer toward the terminal.

network {line | payload}

Sets the loopback toward the network before going through the framer (line) or after going through the framer (payload).


Sends a far-end alarm control (FEAC) to set the remote framer in loopback.

I am sorry, but I am trying to understand the components involved in the testing.

It the path of traffic from


What is the difference between the DTE test and the Local test?

What is the LIU and the Framer?

These are both testing the local equipment before hitting the "network", but are not actually testing any connection to the providers equipment (which would include my cabling), is this correct?

What is the "Line" test actually testing and what is the "Line" and what is the "Payload"?

Would these be testing my cabling going through the providers equipment local to me?

The "Remote" is the only one that seems clear to me, which is putting the remote port in loopback, which would test my cabling, the local providers equipment and remote providers equipment?

Is this correct?

Which would include the customers remote cabling?

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Overall Rating: 5 (1 ratings)
paolo bevilacqua Sat, 05/16/2009 - 13:54
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You are correct, liu and dte are mostly diagnostic tests with little difference and even less practical use.

Network and remote are the only ones that also test the circuit, to be used sometime.

wilson_1234_2 Sat, 05/16/2009 - 20:33
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Does the "network loopback" loop through the cables and connection to the telco equipment on the local side where the interface or controller is looped?

paolo bevilacqua Sat, 05/16/2009 - 22:28
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As indicated above, yes.


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