The L4 application in the switch is expanded to permit functions previously performed exclusively in the L5 protocol application. Moreover, the L4 application is programmable by the system operator so that the system operator may expand the predefined set of L4 call management operations to accommodate his call processing requirements. Overall supervision of the call-management operations was previously limited to the L5 applications. However, the ability to program the L4 application enables the system operator to decide which call processing operations will be managed by the L5 applications and which operations will be managed by the L4 application. The system operator may thus define, in the L4 application, a proprietary call model that instructs the switching node to manage all incoming calls, or the system operator may specify the call model on a channel by channel basis. The latter arrangement programs the switching node to use different call-processing protocols among the various channels. In addition, the user may either re-define or define entirely new application programming interface (API) calls for communications between the host and switching node and/or between the switching node and ports.