The goal of the Swiss-Tx project is to develop, build and install the first Swiss tera-flop supercomputer called Swiss-T2, which is mainly based on commodity parts. Only the communication hardware and communication software is custom-made, because available off-the-shelf products, such as Ethernet with the socket interface, do not offer the necessary bandwidth, latency, and functionality. In this paper, we present a new efficient communication architecture for commodity super-computing called Fast Communication Interface (FCI), and we introduce T-NET, the custom-made high-performance communication hardware for the Swiss-Tx supercomputers. The highlights are low-latency, high-bandwidth, and portability. Portability means that the communication hardware and software is mainly platform independent and that a large number of modern workstations and standard operating systems can be used as they are. A full implementation of the standardized MPI (Message Passing Interface), written entirely on top of FCI, is also available.