Cascade Communications Corporation

Phil Malloy

Andrew T Hebb

Gregory S Goss

Bing Yang

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.

Growing community of inventors

Andover, MA, United States of America

Phil Malloy