What do the E1/T1 Layer 1 (L1) states mean

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Sat, 08/22/2009 - 02:19

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What do the E1/T1 Layer 1 (L1) states mean?

LOS

Loss of signal. There is no signal strong enough to detect on the incoming line. In North America, this is often called a ``red alarm''.

Typical causes:

no cable plugged in, or cable plugged in to the wrong port
incorrectly wired cable
incorrect monitor point construction (i.e. the monitor point's attenuation lies outside the nominal 17-23dB range)
The GTH system not configured for monitoring even though the input signal is -20dB from nominal.

LFA

Loss of frame alignment. There is a signal on the line, but E1 (or T1) framing cannot be recovered.

Typical causes:

Incorrect L1 configuration, e.g. the incoming line may be T1 but the GTH is configured for E1, or the incoming line may be doubleframe but the L1 is configured for multiframe.
Attempting to monitor a signal which is neither E1 nor T1. For instance, attempting to monitor an HDSL modem on its analog line port instead of its E1 port will result in LFA.

LMFA

Loss of multiframe alignment. There is a signal on the line and framing can be recovered, but multiframe framing cannot be recovered.

Typical cause: incorrect L1 configuration

AIS

Alarm indication signal. The E1 receiver in the GTH has detected a fault on the signal it is receiving (too many 1-bits in a frame). This is often called a "blue alarm" in North America.

Typical cause: incorrect L1 configuration

RAI

Remote alarm indication. The E1 receiver in the equipment being monitored (i.e. not the GTH) has detected an LOS, LFA or LMFA condition in the signal it is receiving. This is often called a "yellow alarm" in North America.

Typical causes when using a monitor point:

Incorrectly wired or incorrectly installed monitor point which interrupts the signal on the line being monitored.
Fault in the line being monitored
Fault in the transmitter on the other pair of the line being monitored.
Fault in the receiver on the other pair of the line being monitored.

Typical causes when using full-duplex (normal operation):

Incorrectly wired cable
GTH L1 parameters incorrectly configured, e.g. monitoring enabled, or configured for T1 when attached to an E1 system.

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