The present invention relates to a protocol test device including a network processor where the network processor has the following features: protocol levels of a protocol stack can be programmed in it for at least one protocol per software; it is capable of simultaneously processing input signals of different transmission formats, in particular of different clock rates; a plurality of channel ports for network subscribers in parallel architecture; and one standardized interface for a control unit; with the network processor being designed for in-stream operation, i.e. signals arriving at the ports for network subscribers can be redirected to at least one other port for network subscribers, if necessary after a pre-processing step. A host processor which has been programmed for performing protocol emulations and/or simulations is coupled to the network processor, with the signals of the network subscribers forwarded to the channel ports terminating in the protocol test device.