Abstract: A switch segments variable length frames into cells for transmission over a cell-based switch fabric and handles rate differences between the input data rate and the switch fabric data rate. The fabric handles multiple cell packets by maintaining a switch path until a certain number of cells are transmitted as indicated in a length field in the first data cell. The first cell contains a full data payload, and a length field value sufficient to handle a maximum length frame. Subsequent cells can contain less than a full data payload, with the number of valid bytes in the cell being indicated in the length field. The last cell used to segment the frame contains an end of frame indicator. The indicator signals the destination port side of the switch to terminate the packet path in the switch fabric prematurely—before the number of cells indicated in the first data cell.

Abstract: A Fiber Channel switch is presented that tracks the congestion status of destination ports in an XOFF mask at each input. A mapping is maintained between virtual channels on an ISL and the destination ports to allow changes in the XOFF mask to trigger a primitive to an upstream port that provides virtual channel flow control. The XOFF mask is also used to avoid sending frames to a congested port. Instead, these frames are stored on a single deferred queue and later processed in a manner designed to maintain frame ordering. A routing system is provided that applies multiple routing rules in parallel to perform line speed routing. The preferred switch fabric is cell based, with techniques used to manage path maintenance for variable length frames and to adapt to varying transmission rates in the system. Finally, the switch allows data and microprocessor communication to share the same crossbar network.