# Integrated Services Digital Network (ISDN)

Integrated Services Digital Network (ISDN) is a continually evolving international standard for networking services, including voice and non-voice services. The network is completely digital, from one end to the other. Voice information is digitized and sent in digital form. Signaling information is sent separately using a method called common channel signaling (CCS).

The NMS ISDN Management (IMGT) service is a Natural Access service that interacts with the NMS ISDN protocol stack and provides access to information and messages that are not part of traditional call control. The IMGT service provides functions that enable you to put B channels in and out of service and query the stack about the status of a particular B channel or D channel. The service also reports some variant-specific messages.

IMGT applications run independently from call control applications, whether the call control application is based on the ISDN Messaging API or the Natural Call Control (NCC) API.