A D-Channel is a communication channel used in Integrated Services Digital Network (ISDN) systems. It primarily carries signaling information, which helps establish and manage calls, rather than transmitting voice or data directly. The D-Channel operates alongside B-Channels, which are responsible for carrying the actual voice or data traffic. In an ISDN setup, the D-Channel typically operates at a speed of 16 or 64 kilobits per second. It plays a crucial role in ensuring efficient communication by managing call setup, teardown, and other signaling tasks, allowing for seamless connectivity between different devices and networks.