This case occurs during the T1 test before a T1 service is configured between the PQM and the optical board on an OptiX OSN 2500 NE. There is not a T1 cable for the test. Therefore, the engineers conduct software loopback on the T1 interface. Then, the engineers connect an ANT-5 instrument to the optical board to test the BER of VC-12 signals. The ANT-5, however, keeps reporting the LSS alarm.
An E1 service can be tested on a VC-12 of an optical interface. A T1 service, however, cannot be tested at an optical interface. To test a T1 service, loop back the optical interface and then connect the instrument to the T1 tributary board.
A T1 service is a 1.55 Mbit/s PDH service encoded in AMI or B8ZS format. A 2 Mbit/s service, however, is HDB3 encoded. During the test, a 2 Mbit/s service is added at the optical interface. Then, the service is encoded and decoded on the PQM board. As a result, the service is different when it returns to the ANT-5, and the ANT-5 reports the LSS alarm..
Exercise caution during tests.