What is the name of the circuit-switched telephone network that transmits both data and voice over a digital line?

The Integrated Services Digital Network (ISDN) is the correct answer because it is specifically designed to transmit both voice and data over a digital line using circuit-switched technology. ISDN allows for the simultaneous transmission of both types of communication, making it ideal for applications that require high-quality voice along with data services, such as video conferencing or faxing. It was developed to replace traditional analog telephone services and enable more efficient and reliable communication.

ISDN utilizes digital signaling and can provide multiple channels over a single connection, enhancing the capacity for various forms of communication. This quality distinguishes ISDN from other technologies mentioned, as it directly addresses the need for integrated voice and data services over digital lines.