# Call transfer and DPNSS

DPNSS specifications describe the behavior of nodes in a network and how they interact. NMS ISDN supports transfer-by-join operations between DPNSS nodes. In a transfer-by-join operation, the two separate calls are connected through the local node, and the local node remains involved in the call (for example, the call is not rerouted).

To transfer a call under DPNSS, the application must perform the switching required to connect calls together using standard calls to the Natural Access Switching service. The application also invokes a notify transfer operation to notify each remote party that the transfer took place.

If both parties are remote, once the notification takes place, the stack at the local node allows the two separate calls connected through the node to pass facilities information to each other without involving the local application. Basic call control signaling for the two calls (such as call clearing) must still be managed by the application. In effect, the calls have been bridged.

Before and after call transfer

The application is responsible for assuring that the B and C parties that are joined are compatible. For example, both parties should be carrying the same type of service (data, voice).

The two channels to be transferred must be on the same NMS board.