Asynchronous transfer mode switch with logical multicasting

An Asynchronous Transfer Mode (“ATM”) switch having a plurality of input ports for receiving cells, each cell with a header including address fields Virtual Path Index (“VPI”) and Virtual Channel Index (“VCI”) and a plurality of output ports for transmitting a outgoing cells to their destination, said input ports and output ports coupled by a routing fabric, a controller for adding a Control Index (“CI”) to each header, including a base address, to direct the received cells to their respective output ports, each CI based on a received port as well as the VPI and VCI fields of a corresponding cell;

• and a lookup table;
• wherein
• said controller is adapted for using the CI to control flow through the routing fabric and for updating the VPI and VCI on the outgoing cells by use of said lookup table;
• said controller is adapted for assigning a block of consecutive CIs, starting at the base address CI of an original received cell for creating leafs whereupon each leaf is assembled with individual VPIs and VCIs and is destined for the same physical output port as the original received cell;
• said controller is adapted to block out N consecutive CIs, wherein N represents the maximum number of leafs;
• said controller is adapted for taking a received cell for delivery to the physical port, wherein the CI number of the received cell is used to index the VPI/VCI for the leafs;
• said controller is adapted for directing the CI to the lookup table which provides a corresponding predetermined Logical Multicast Offset field (“LMO”) which defines the offset from the base address of the CI of the next leaf of a logical multicast;
• a zero value indicative that a connection is not a logical multicast connection or that the CI is the last leaf of a logical multicast connection;
• and
• said controller is adapted for repetitively adding said offset to the base address of the cell to index a next VPI/VCI and a next offset which is added to the repetitively added offset until the LMO offset from the lookup table is equal to zero.

A computer program for logical multicasting information of original cells, said original cells including a header with VPI and VCI fields, on the same physical port of an ATM Switch, said ATM switch including receiving ports and outputting ports, comprising the steps of:

• adding a CI, a control index including a base address, to the headers of the original cells, wherein the CI is based on the VPI, the VCI, and a received port, wherein said CI directs a cell to its respective output port,
• determining the number of times an original cell is to be replicated,
• creating a number of replicated cells of each original cell, herein defined as leafs, said leafs having VPIs and VCIs, and LMOs defining offsets from said base address,
• assigning a block of consecutive CIs, wherein the first CI is the base address of the CI of the original cell, and block length being the maximum number of times the cell is to be replicated for said multicasting, and
• accessing LMO offsets for each leaf until a LMO offset value is zero, wherein the multicasting is complete.