47 CFR §80.103

1. (a)Operating procedures for the use of DSC equipment in the maritime mobile service are as contained in ITU-R M.541-9 (incorporated by reference, see § 80.7), and subpart W of this part.
2. (b)When using DSC techniques, coast stations and ship stations must use maritime mobile service identities (MMSI) assigned by the Commission or its designees.
3. (c)DSC acknowledgment of DSC distress and safety calls must be made by designated coast stations and such acknowledgment must be in accordance with procedures contained in ITU-R M.541-9 (incorporated by reference, see § 80.7). Nondesignated public and private coast stations must follow the guidance provided for ship stations in ITU-R M.541-9 (incorporated by reference, see § 80.7), with respect to DSC “Acknowledgment of distress calls” and “Distress relays.” (See subpart W of this part.)
4. (d)Group calls to vessels under the common control of a single entity are authorized. A group call identity may be created from an MMSI ending in a zero, assigned to this single entity, by deleting the trailing zero and adding a leading zero to the identity.