1) Check that Linear MS 1+1 on both sides
2) Check the parameters like WRT and Revertive/Non-Revertive in Linear MS on both sides (OSN and HIT)
3) After creating Linear MS 1+1 protection at third vendor HIT end alarms from OSN were successfully cleared.
After further analysis it was found that Linear MS 1+1 was not created at HIT end between their STM boards. Due to this, at OSN end services were successfully mapped on protection board which is 16-N1SL16, but at third vendor HIT end as there was no Linear MS 1+1 so no services were mapped on protection board. Due to which the protection board of OSN was showing AU_LOP alarm.