VoIP INIVITE (Call Volume) Restriction

Most Robocalls are from computer that is using VoIP which is using SIP protocol. The new phone call is using SIP method INVITE. By monitoring INVITE, telephone service provider can limit how many new calls are able to be made during certain period.
If a subscriber needs to go above this limitation, it can purchase a high rate category and required to register with FTC/local authority. With the registration, it can ensure only the legitimate organization can have higher call volume.