cucsSwEthMonSrcEpRn (syntax SnmpAdminString) holds the Relative Name (RN) of this SPAN source endpoint -- the naming component that distinguishes it from sibling instances of the same class under the same parent object. Since this SPAN source endpoint is the source endpoint of an Ethernet monitoring (SPAN) session -- the port whose traffic gets mirrored, several such instances can exist side by side under one parent, so the RN is what UCSM concatenates with the parent's DN to build this instance's own unique DN. For example, comparing the RN values returned for two sibling instances under the same parent tells an admin which specific one they are looking at without walking the full DN string.