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The merging trend of three separate networks, i.e. telephone, cable TV and computer networks, demands underlying communication systems to provide a mechanism to transmit and switch bit streams at very high speed, and to satisfy different users' QoS requirements. DWDM, with its transmission rate at tens of tera bits per second in a single fiber, becomes the most promising candidate for such convergence. However, switching techniques in DWDM have not yet fledged for such a merged high-speed network. We present a novel concept called the physical frame time-slot switching (PFTS). With PFTS, transmission time of a fixed-length physical frame is defined as a "time-slot", and used for multiplexing a single lambda channel and for user data switching over a DWDM platform. A maximum length of Ethernet MAC frame is exactly fitted into a PFT (physical frame time-slot), and one or more PFT(s) can be assigned to a time-critical user data stream according to required QoS parameters, such as throughput and time delay. PFT switching operates in an asynchronous mode on the basis of single PFT in a lambda; and hence eliminates the need of lambda switching and global synchronization among clocks in a network. In an "out-band signaling" network, PFTS enables user data transfer platform to be reduced to a single physical layer.