Frame-based transmission of data

Abstract

A network for transferring packet data in a frame structure, preferably mixed with isochronous data is provided. The frame structure is a continuously repeating structure, with each frame having a number of time slots. Certain ones of the time slots are available for transmitting packet data. The packet data is re-timed, e.g., by using a FIFO to output the data nibble-wise as required by the frame structure. Similar re-timing can be used for isochronous data so that the frame structure defines time-division multiplexing of the packet data and isochronous data. A four/five encoding scheme provides sufficient encoding efficiency that both the packet data and other data can be accommodated without degrading the data rate of the packet data. The encoding scheme provides extra symbols which can be used for transferring 'no carrier' information, or 'frame alignment' messages. Preferably, the frame structure is translated to and from a packet structure to permit the present invention to be used with previously available packet circuitry such as a media access controller and a hub repeater circuit. Latency of the FIFO can be reduced by pre-filling with packet preambles, and/or sub-latency propagation of preamble bytes, or providing special MACs which do not output preambles, and using the buffer circuitry to output preambles.