# Sending and receiving ISDN-specific messages

Some variants of the ISDN Software protocol support sending and receiving ISDN-specific messages for which there are no NCC API equivalents. ISDN Software currently supports the following ISDN-specific features:

This feature... | Allows an application to...
--- | ---
Transparent message sending and receiving | Send user-defined information elements (IEs) to the stack, and receive FACILITY messages that are not recognized by the stack.
Request call ID for call transfer | Request an identifier for one of two calls transferred together. This feature is useful when both calls are inbound.