Cascade Communications Corporation

Ascend Communications, Inc.

Gregory S Goss

Andrew T Hebb

Kurt A Melden

Bing Yang

Phil Malloy

A method and apparatus for performing logical multicasting within a network switch are disclosed so as to permit a downstream network device to perform cell forwarding in a manner which resembles spatial multicasting. A logical multicast cell has a connection identifier associated with the cell within the switch. 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 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 associated with the output port of the switch so as to minimize the likelihood of blocking and so as to minimize cell delay variation. In one embodiment, the output cell buffers having cells to transmit are afforded transmit opportunities in a round robin sequence.

Logical multicasting method and apparatus

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.

Remapping of ATM cells for multicast transmission

A method and apparatus are disclosed for multicasting through a single physical port in a switch, i.e., logical multicasting. An incoming cell is logically multicast by providing a first copy of the cell to the desired output port and providing a second copy of the cell to a loop-back element which includes standard input and output ports dedicated to loop-back operation. The cell provided to the loop-back element is subsequently provided to the desired output port such that the first and second copies of the cell are serially transmitted from the single desired output port. Further, the cell provided to the loop-back element may be repeatedly copied, provided to the loop-back element, and provided to the desired output port. Thus, the incoming cell may be transmitted through a single output port as many times as is desired. When utilized in conjunction with a switch configured for unicast operation, multicast type capability can be provided in the unicasting switch by logically multicasting from the multicasting switch to the unicasting switch.

Logical multicast from a switch configured for spatial multicast

Prioritized subclasses of cells within at least one quality of service (QoS) level in an asynchronous transfer mode (ATM) network element are described. Corresponding QoS queues are provided with one or more thresholds for intelligent discard of incoming cells within a QoS, based upon cell priority, at the onset of queue congestion. Cells having a first priority within a QoS are discarded as a first queue threshold is achieved; cells having a higher priority are enqueued. A cell loss priority (CLP) bit is employed to provide a further degree of cell discard prioritization. Different traffic streams within a single queue have different priorities, enabling intelligent discard of lower priority traffic prior to complete queue congestion.

Quality of service priority subclasses

Method and apparatus are disclosed for maintaining operational and statistical information in a high speed network switch for each of a plurality of supported connections. A high speed array is provided which includes a plurality of high speed registers for each of a plurality of connections supported by the switch. Upon receipt of a cell/frame, a connection identifier is generated to identify the connection within the network switch and the connection identifier is stored in an index register. The connection identifier stored within the index is used to select a plurality of registers within the high speed register array of registers pertaining to the specified connection. Information pertaining to each received cell/frame is generated upon receipt of the cell or retrieved from the respective cell header and is employed to generate an operand for each of the plurality of registers addressed by the connection identifier. Operands may allow for the clearing, setting, incrementing, decrementing or maintenance of the register contents. Each of the plurality of registers identified by the connection identifier is updated in parallel within the time frame associated with the receipt of a frame/cell.

Growing community of inventors

Lowell, MA, United States of America

Gregory S Goss