LOGICAL MULTICASTING METHOD AND APPARATUS

摘要

A method and apparatus for performing logical multicasting within a network switch (10) are disclosed so as to permit a downstream network device to perform cell forwarding in a manner which resembles spatial multicasting. Each input cell (26) received at an input port (12a---12n) is checked to determine if it is a logical multicast cell. A logical multicast cell has a connection identifier associated with the cell within the switch (10). The connection identifier is employed to initiate a series of lookup operations to generate unique VPI/VCI addresses which are transmitted out of an output port (14a---14n) of the switch as copies or leaves of the multicast cell. Successive look-ups of outgoing VPI/VCI addresses for a logical multicast cell are performed using a chain bit to indicate when all leaves of the cell have been transmitted. Leaves of a logical multicast cell are transmitted to the downstream network device from one output cell buffer of a plurality of output cell buffers (20) associated with an output port (14) of the switch (10) so as to minimize the likelihood of blocking and so as to minimize cell delay variation. In one embodiment, the output cell buffers (20) having cells to transmit are afforded transmit opportunities in a round robin sequence by a scheduler (22) associated with the output port (14).