This is an index value for this virtual ring specifically exposed so it can be included in SNMP notification (trap) PDUs, distinct from the table index used for regular GET/SET access. Because it's accessible-for-notify rather than a standard readable object, this value is meant to be read by a trap receiver parsing an incoming notification, letting an alarm-management system identify which of up to 240 virtual rings triggered a given trap without a separate lookup. For example, a NOC's trap receiver getting a RAPS protection-switch notification would use this index value from the trap payload to look up which specific virtual ring the alarm applies to.