The present invention relates to a method and a network node for service instance management in telecommunications network. According to the method a plurality of network paths are monitored. A number of network paths form a protection group associated with a service instance or group of service instances. The monitoring of the network paths includes periodic transmission of CCMs on the network paths. To facilitate detection of mismatches related to protection switching, some CCMs include a mismatch information element that specifies traffic status of a working network path and of a protection network path for a set of protection groups. The set of protections groups includes the protection groups which the monitored network path is a member of. A CCM that includes the mismatch information element also includes an indication bit that indicates presence of the mismatch information element in the CCM.