Abstract: In a communication switching system controlled by a control processor, line port circuit connections are served by line call processing algorithms and trunk port circuit connections are served by trunk call processing algorithms. Trunk call processing algorithms offer the user a wide variety of call processing features and system management capabilities which are not included in normal line call processing algorithms. Host computer interconnections are typically established between digital line port circuits and therefore, host interconnections are administered by line call processing algorithms which offer only a limited set of services. To provide trunk services for host computer interconnections, an auxiliary algorithm has been added to the normal line call processing algorithms to interlink line to trunk call processing. In particular, when a host computer is served, the normal line call processing algorithm branches to the auxiliary algorithm.