In the server, each DCU has its own SPP. An SPP must be present for its DCU to be operational.
If two or more DCUs are combined in one PDomain, one SPP is designated to manage the entire PDomain. If an SPP must be removed, its DCU cannot be part of a running PDomain.
If DCUs are operating independently of each other, the failure of one SPP in a DCU does not affect the other DCUs.