This is the Relative Name of a SasPortDescriptor object, the naming component that distinguishes one port descriptor from its sibling descriptors under the same parent in UCSM's object tree. An admin uses it together with the parent path to reconstruct which specific SAS port a descriptor entry describes. For example, when parsing SNMP output for a multi-port storage controller, the admin relies on this Rn to tell descriptor entries for port 1 and port 2 apart.