This value, together with tmnxDot1agCfmMepVcId, identifies the SDP binding within a bridge port that a MEP is attached to; it's only applicable to SDP-binding MEPs and must be zero when the MEP is instead attached via an interface, VLAN, service, or facility object, and can't be changed once set. An admin sets this when creating a MEP that monitors a pseudowire service binding rather than a physical port or router interface. Because it can't be modified after row creation, getting the SDP ID and VC ID pairing right at creation time matters; fixing a mistake requires deleting and recreating the MEP.