Abstract: A telephony controller for controlling a private automatic branch exchange (PABX) is disclosed that utilizes a single functionality command protocol to reduce the data traffic on a computer network or the like used to control a PABX. The telephony controller includes a functionality command converter, a communication layer for communicating with computer terminals on the computer network, and a PABX interface for communicating with the PABX. The single functionality command protocol uses a generic command format for a number of function commands that are converted by the functionality command converter into the PABX commands corresponding to the vendor specific PABX. The functionality converter generates the PABX commands to implement a function command and monitors the PABX to determine whether the command has been implemented.