The correct answer is: C. 400 services.
SS7, or Signaling System 7, is a set of protocols used to control telephone calls and other telecommunications services. It is a standard protocol that is used by all major telecommunications companies around the world.
SS7 provides a number of services, including:
- Call routing: SS7 is used to route calls between different telephone networks.
- Call setup: SS7 is used to set up calls between different telephones.
- Call termination: SS7 is used to terminate calls between different telephones.
- Authentication: SS7 is used to authenticate users and prevent unauthorized access to telecommunications networks.
- Billing: SS7 is used to bill users for telecommunications services.
400 services are a type of telecommunications service that is offered by some telephone companies. 400 services are typically used for customer service and support. They allow customers to call a toll-free number to reach a customer service representative.
400 services are not a service offered by SS7. SS7 is a standard protocol that is used by all major telecommunications companies around the world. 400 services are a type of telecommunications service that is offered by some telephone companies.