This is the numeric ID of the parent logical (physical) ring that this virtual ring rides on top of. Because multiple virtual rings share the fate of their underlying physical ring's links, an admin troubleshooting why several seemingly unrelated virtual rings all show a fault at the same time should check whether they all share the same value here, pointing to a single underlying physical ring problem rather than several independent virtual ring issues. For example, if virtual rings for three different customers all show this value as 2 and all report a fault simultaneously, the root cause is very likely a shared physical fiber cut on logical ring 2, not three coincidental unrelated failures.