There is a connectivity of OSN7500 with a Router. 6-SLT1-1 of OSN7500 was directly connected with Router. SNCP was made on OSN7500 and third-party-equipment to protect service on 6-SLT1-1. There were two paths one is working(DWDM) and other was protection(Third-party equipment). Later we tried to switch the services on protection path but it failed and LOOP alarms were observed on OSN7500. Please see the attachment
Later problem was found in SNCP configuration on interconnected equipment (Third party). Source was selected as Sink and Sink was selected as Source. Therefore when we tried to switch the services on protection path on OSN7500 it failed and loop occured between working and protection path. Please see the attachment for clear picture.
After analysis may be following were some possibilities
1) check all the port interface on OSN7500 and third party equipment. All ports should be non-loopback
2) May be SNCP was configured worng on either end
SNCP should be configured carefully, Source, Sink and Protection path should be clear before configuring SNCP.