# Exclusive mode

In exclusive mode, a TCP instance effectively owns its default channel. To place an outbound call, the TCP asks the network for the default channel. If the channel is not available, the network clears the call. When the TCP senses this, NaturalAccess sends NCCEVN_CALL_DISCONNECTED to the application.

For example, the application attempts to establish an outbound call using a TCP that is set up to use default B channel 5 in exclusive mode (corresponding to MVIP-95 0:4, 1:4). The TCP asks the network for B channel 5. If the channel is available, the network signals the TCP to continue with the call on that channel. Otherwise, the network clears the call. In MVIP-90 terms, this corresponds to 16:0.

In exclusive mode, any incoming call will be routed to a TCP instance only if the call is on its default channel. All calls on that channel are routed to the TCP.

To set a TCP instance to exclusive mode, set the NCC.ADI_ISDN.START_EXT.exclusive parameter to 1.

You can also use the NCC.ADI_ISDN.START_EXT.direction parameter to specify whether the channel is incoming-only, outgoing-only, or bidirectional. Incoming calls are never offered to an outgoing-only TCP channel. A call placed on an incoming-only channel is rejected.

The direction parameter setting must match the configuration of the connected equipment (for example, the network switch). If the application attempts to place a call on a channel that is configured on the connected equipment to be incoming-only, the outbound call is always rejected.

Note: DPNSS only operates in exclusive mode.