T1 / T3 Alarms

Posted on in Networking

The following is a list of alarms you may receive on your T1 or T3 (or E1/E3) interface. Where applicable, troubleshooting hints are included.

Loss of Signal (LOS)

A Loss of Signal (LOS) alarm indicates that the interface is not receiving a valid T1 or T3 signal. This is indicative of a physical problem and the cabling between the interface and service provider should be checked. In the case of T3 circuits with individual transmit and receive pairs, it's common for the cables to be "rolled" and the transmit and receive should be swapped.

Loss of Frame (LOF)

A Loss of Frame (LOF) alarm might also be called a red alarm. In this case, the interface is not receiving the expected frame type, or there are errors in the incoming framing pattern. In the case of T1s, ensure the service provider is set to use the same framing (most likely ESF (Extended Super Frame)). T3 framing is usually transparent to the service provider and may indicate a framing mismatch on the other end of the circuit.

Alarm Indication Signal (AIS)

AIS is also known as a blue or "all 1s" alarm. It indicates an error has occurred upstream from the interface. This alarm indicates a problem in the service provider's network such as link failure or misconfiguration.

Remote Alarm Indication (RAI)

RAI is also known as a yellow alarm. This alarm indicates that the remote interface has a problem with signal received from the local interface. This could indicate a hardware problem, or a configuration mismatch.

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