What is the key feature of the Integrated Services Digital Network (ISDN)?

The key feature of the Integrated Services Digital Network (ISDN) is its ability to transmit various forms of data over digital lines. ISDN is a set of communication standards used to provide simultaneous digital transmission of voice, data, and video over traditional phone lines. This integration is significant because it allows for multiple services to be delivered over a single network infrastructure, improving efficiency and providing higher quality communication compared to analog systems.

The technology supports both circuit-switched and packet-switched communication, which enables it to handle different types of data flows. The ability to transmit voice and data simultaneously makes it especially valuable for businesses that require reliable and versatile communication channels. This multifaceted capability distinguishes ISDN from other systems that may focus solely on voice communication or purely analog signal transmission. Therefore, option B accurately captures the essence of ISDN's purpose and functionality.