# Function summary

The following table summarizes the NMS ISDN Messaging API functions:

Function | Synchronous/ Asynchronous | Description
--- | --- | ---
isdnReleaseBuffer | Synchronous | Indicates that the application has completed processing of an ISDN event buffer.
isdnSendMessage | Asynchronous | Sends a message to an ISDN protocol stack instance.
isdnSetMsgCapture | Asynchronous | Enables or disables debugging trace information for the selected entity in the protocol stack.
isdnStartProtocol | Asynchronous | Initializes an ISDN protocol stack instance on a D channel context.
isdnStopProtocol | Asynchronous | Shuts down a previously started ISDN protocol stack instance on a context.