ANI Normalization when enabled, will determine if a 10 digit ANI provided in the incoming SIP Invite (taken from the PAI, RPID, or From Header in that order) is a valid US number by checking the LERG. If the ANI is valid then it will prepend the number with 1 as the country code and continue to process the SIP Invite. If the ANI is not in the LERG the number will be treated as an International number.
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