Integrated Services Digital Network (ISDN) is a telecommunications standard that allows for the simultaneous transmission of voice, video, and data over traditional phone lines. It was developed to improve the quality and speed of communication by providing a digital connection, which is more efficient than the older analog systems. ISDN offers two main types of services: Basic Rate Interface (BRI) and Primary Rate Interface (PRI). BRI is typically used for home and small business connections, providing two 64 Kbps channels for voice or data. PRI, on the other hand, is designed for larger organizations, offering up to 30 channels, making it suitable for high-capacity communication needs.