When the NRC-P reoptimizes the path of a PCE-controlled RSVP-TE LSP, it is possible that a path that satisfies the constraints of the LSP no longer exists. In this case, the NRC-P sends a PCUpd message with an empty ERO, which forces the PCC to bring down the path of the RSVP-TE LSP.
The NRC-P sends a PCUpd message with an empty ERO if any of the following cases are true:
the requested bandwidth is the same as the current bandwidth, which avoids bringing down the path due to a resignal during an MBB transition
local protection is not currently in use, which avoids bringing down a path that activated an FRR backup path. The LSP can remain on the FRR backup path until a new primary path can be found by the NRC-P.
the links of the current path are all operationally up, which allows the NRC-P to ensure that the RSVP control plane will report the path down when a link is down and not prematurely bring the path down with an empty ERO