Cascade Communications Corporation

Bing Yang

Andrew T Hebb

Gregory S Goss

Phil Malloy

Improved methods and apparatus are disclosed for remapping Asynchronous Transfer Mode ('ATM') cells in an ATM switch to convert a single Virtual Path Identifier ('VPI')/Virtual Connection Identifier ('VCI') address pair to multiple outgoing VPI/VCI pairs for multicast transmission. An incoming cell is examined to determine the ports through which the cell will exit and a local header is generated which includes a field specifying the I/O modules ('IOMs') through which the cell will exit. The VPI/VCI pair of an incoming multicast cell is mapped to a global multicast identifier ('MID') which is written into the local header. The cell, including the local header is then forwarded to the IOMs specified in the header. A first lookup table on each IOM is employed to provide a port bitmask indexed by MID to direct the cell to the previously identified ports, and to map the MID into a connection identifier ('CID'). A second lookup table is employed to map the CID provided from the first table to a destination VPI/VCI. The second table is shared among all ports on the IOM. Memory utilization efficiency is improved by using global MIDs and by distinguishing multiport-multicast cells from single-port-multicast cells. If the cell is being sent to a single port within the IOM then a single location is allocated in the second table. If the cell is being sent to multiple ports within the IOM then multiple locations are allocated within the second table.

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Lee, NH, United States of America

Bing Yang