a system for managing communication between a client program and a server program . a port service module manages a plurality of domain ports . each domain port has predefined characteristics which are used by the port service module to direct which server computer programs or which instances of server computer programs with which a client computer program will interact . the domain port characteristics also direct the port service module whether to order messages , count messages , and / or monitor for different types of error conditions in communications between the client program and the server program .