Abstract: In a digital switch high data rate data communications system, such as a "Datapath" system following the "T Link" protocol, to intercouple data terminal equipment operating at different data rates, voice messages are concurrently interleaved in transmitted bit streams. The system includes echo suppression modules for voice transmissions, but for data transmissions the echo suppression means is disabled in a channel by digital simulation of a monofrequency tone to open the channel. The preparatory sequence includes predetermined byte sequences which initiate the exchange of version identifier and parameter data prior to selection of a common data rate for intercommunication.