Dear friend!
The OptiX OSN 2500 has the following 155 Mbit/s boards:
SL1: 1-port STM-1 optical interface board
SL1A: 1-port STM-1 optical interface board
SLQ1: 4-port STM-1 optical interface board
SLQ1A: 4-port STM-1 optical interface board
SLO1: 8-port STM-1 optical interface board
SLT1:12-port STM-1 optical interface board
SEP1: 8-port STM-1 line processing board
Thanks!