TON (Type of Number) indicates the scope of the address value, identifying if the number is international (including country code), national or domestic. NPI (Numbering Plan Indicator) is a type of numbering scheme to “build” telephone numbers. Most telephone numbers belong to a standardized numbering plan, like country calling codes, European Telephony Numbering Space, North American Numbering Plan, etc. Apart from the use of numbering plans for telephone numbers, the TON/NPI settings are also used in routing of SS7 signalling messages.
