How does Automatic Dependent Surveillance-Contract (ADS-C) differ operationally from ADS-B?

1. ADS-C establishes a point-to-point contract between the aircraft and a specific ATS unit rather than broadcasting to all receivers
2. ADS-C is only used for ground taxi operations on the airport surface
3. ADS-C requires manual transmission of reports by the flight crew every 30 minutes
4. ADS-C relies on voice radio reports instead of satellite data links