This is the LDP identifier of the remote peer as learned from the active LDP session for this pseudowire, staying at zero until the signaling has actually completed and the peer's identity is known. Comparing this against the expected far-end PE router's LDP ID is a straightforward way to confirm a pseudowire is actually signaled to the correct remote device rather than accidentally cross-connected to the wrong peer. A pseudowire that's supposed to terminate at a router with LDP ID 10.1.1.1:0 but instead shows a different peer ID here indicates a provisioning or routing error rather than a link-layer fault.