Signal Label Mismatch stems from mismatched values of the SONET frame Path overhead C2 byte.

The Signal Label indicates the content of the SONET SPE or the content of the SONET VT. Signal Label Mismatch (SLM) is an alarmed error in which a Path or VT connection is not correctly provisioned. A received Signal Label is considered mismatched if it does not equal either the locally provisioned value or does not match the value equipped non-specific (1 hex). The Signal Label resides on the C2 byte of the SONET Path Overhead and/or the V5 byte of the VT Superframe. The following are some of the possible values of the C2 byte:

Hex Payload Type:

The Signal Label of Unequipped indicates that the line connection is completed, but there is no path origination equipment.

Equipped/non-specific can be used for all payloads that need no further differentiation or that achieve differentiation by other means such as messages from operations systems.