Nx Networks 3000 - Manual (Page 56)

Monitoring Your 3000 Series Secure Gateway Router
42 3000 Series User Guide
T1 CSU/DSU Module
This module has three amber status lights.
Light Indicates . . .
ALM Alarm condition indicating standard blue, yellow, or
red alarm conditions.
TST Module is in loopback test mode.
LOS Loss of sync indicating that the module is unable to
sync to the incoming data stream.
ALM
T1 CSU/DSU
TST
LOS