Assigning incoming calls to TCP instances

When a call arrives on a B channel, a TCP instance is assigned to the channel as follows:

1. If a TCP instance is currently assigned to the channel in exclusive mode (and is not set up as outgoing-only), the call is routed to the TCP.
   
   If the TCP instance is outgoing-only, the call is rejected.

2. If a TCP is currently assigned to the channel in non-exclusive mode (for example, the channel is the TCP's default channel), the call is routed to the TCP if it is not already handling another call (and is not set up as outgoing-only).

3. Otherwise, the call is passed to any free TCP that is in non-exclusive mode and is not set up as outgoing-only.

4. If no TCP is available, the call is rejected.