Ascend Communications, Inc.

Prasasth R Palnati

Mahesh N Ganmukhi

David J White

Port cards in an ATM switch store parameters for virtual channel connections (VCCs) and virtual path connections (VPCs) in separate areas of a virtual connection parameter table (VCPT), the areas being defined by a VCC pointer and a VPC pointer. Also, a number of &ldquo;free lists&rdquo; are used to identify unused single locations (for VPCs) or chunks of locations (for sets of VCCs) that are available for re-allocation. Different free lists are used for different-sized sets of VCCs, i.e., sets configured to use different maximum numbers of VCI bits. When a new VPC is created, a VCPT location identified by an entry in the VPC free list is allocated, if such an entry exists. Otherwise a VCPT location is allocated by advancing the VPC pointer. De-allocation of a VPC entry proceeds in reverse order, i.e., the VPC area is shrunk by backing up the VPC pointer if possible, and if not the de-allocated entry is placed on the VPC free list. Similar allocation and de-allocation processes are used for newly-created VCCs, using the VCC free list appropriate based on the maximum number of VCCs that may be in the set of VCCs. A consolidation technique further backs up the VCC pointer when possible to maximize space available for allocation, and also combines entries from the free lists to create larger-sized chunks. Such combined chunks may be allocated in whole or split into smaller chunks as needed for subsequent allocations.

Management of free space in an ATM virtual connection parameter table

A method and apparatus for performing virtual connection merging in an output port of a network switch are disclosed. In the event no completely assembled packets have been received and scheduled for transmission, a partially received packet is selected for cut-through transmission prior to receipt of all cells comprising the packet. Transmission of the selected packet is initiated and a timer is started. If the timer expires prior to the receipt of an end of packet indication for the packet for which transmission has commenced, and end of packet signal is generated and transmitted and the transmission of additional cells for the cut-through packet is aborted. In this manner, delays associated with packet reassembly may be avoided and buffer sizes of reassembly buffers may be reduced.

Method and apparatus for performing cut-through virtual circuit merging

A method and apparatus are disclosed for selectively accessing and independently sizing connection identification tables within a network switch. Upon receipt of a data unit, such as an asynchronous transfer mode cell at an input port of an Input Output Module, a plurality of selection bits are inserted into the cell header which are used to select one of a plurality of connection identifiers. The VPI/VCI addresses are mapped into a connection identifier and the connection identifier is also inserted within the respective cell header. The connection identifier may comprise an unicast connection identifier, a multicast connection identifier, or a redundant unicast identifier. The unicast, multicast and redundant identifiers are either stored in separate tables at call setup and the tables are independently selectable via use of the selection bits stored within the cell header. Alternatively, the selection bits are employed to specify a register which points to the first address for the respective type of identifiers. Thus, identifiers of a particular connection type are accessible via a base address plus an offset address. In the described manner, tables or portions of tables containing connection identifiers may be flexibly and independently sized.

Independently sizable memory pages for a plurality of connection ID

An apparatus and technique for facilitating mapping of a Multicast Circuit Identifier ('MID') to a Local Circuit Identifiers ('CID') is disclosed. Table entries for such mapping can be disposed in non-contiguous memory locations. A pointer is employed in ca h entry to indicate the location of any subsequent memory location associated with the MID. CIDs and associated memory locations are allocated only for ports that participate in a connection. To implement the apparatus and technique a first table provides an index into a second table based upon the MID. The second table includes entries having a port identification field, a pointer field and a CID field. The CID field indicates the CID associated with the port indicated by the port identification field. The CID is written to the header of the copy of the cell to be transmitted to the indicated port. The pointer indicates further entries in the second table that are associated with other copies of the cell to be transmitted in the multicast connection, if such entries exist. The CID is employed to obtain a Virtual Path Identifier ('VPI') and Virtual Circuit Identifier ('VCI') from a third table.

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Waltham, MA, United States of America

Prasasth R Palnati