ISDN provides two primary types of channels: B channels (Bearer channels) and D channels (Data channels). B channels carry user data, such as voice or digital information, and can be used individually or combined for higher bandwidth applications. D channels are used for signaling and control purposes, facilitating call setup, teardown, and other network management functions. ISDN also supports various protocols, including the Primary Rate Interface (PRI) and Basic Rate Interface (BRI), which offer different configurations and levels of service depending on the user’s requirements and location.

Despite its initial popularity, ISDN has largely been supplanted by newer technologies such as digital subscriber lines (DSL), cable modems, and fiber-optic networks, which offer higher data speeds and more flexible deployment options. However, ISDN remains in use in some areas, particularly for legacy systems, business applications, and specialized services that require reliable, dedicated connections. Its widespread adoption paved the way for the digital revolution in telecommunications, laying the groundwork for the development of modern broadband networks and internet-based communication technologies.