Abstract: An apparatus and method are provided for testing the ability of a digital data communications network to resolve contests for data bus control. The network includes a plurality of terminal equipment units ("TEs") coupled to a digital service unit ("DSU") by a data bus. The apparatus comprises a testing device coupled to the data bus and adapted to transmit digital control data through the data bus to the DSU for a selected time to cause the testing device to obtain control of the data bus and to cause the TEs to assume a call demand state. The testing device is further adapted to terminate transmission of the digital control data from the testing device to cause the TEs to simultaneously transmit digital control data and cause a contest among the TEs for control of the data bus.