Signal Label. For VC-3: The SONET standard defines the C2 byte as the path signal label. The purpose of this byte is to communicate the payload type being encapsulated by the SONET Framing OverHead. It allows a single interface to transport multiple payload types simultaneously. For VC-12, VT-1.5: VT path overhead V5 byte allocates bits 5-7 for VT Path Signal Label, to indicate the content of the VT SPE. 000 Unequipped 001 Equipped : non-specific payload 010 Asynchronous mapping 011 Bit synchronous mapping (no longer valid for DS1) 100 Byte synchronous mapping 101 Unassigned 110 Unassigned 111 Unassigned Agents that do not support this feature will send SIZE 0.