The Number Portability Dip Indicator (NPDI) shows each query to the Number Portability Data Base (NPDB). It also indicates the call should be routed using the phone number in the “rn” field (if present) instead of the original called number.
When Send NPDI enabled is enabled On an Origination Customer Trunk Group , the Orchestrator adds a Number Portability Dip Indicator (;npdi=yes) between the user and host portions of the URI in the To: header in outgoing SIP messages. NPDI indicates that a query to the Number Portability Database (e.g. the LRN Database) has been completed. This field can be included in order to prevent subsequent lookups in legacy-style PSTN databases. This feature is rarely used.