Transwitch Corporation

Joseph C Lau

Subhash Chandra Roy

John F Gilsdorf

Ivo Edmond Vandeweerd

Dirk L Callaerts

A method for the fair and efficient transfer of variable length packets using fixed length &ldquo;segments&rdquo; utilizes a modified UTOPIA interface with three additional signals added, i.e. start of packet (SOP), end of packet (EOP), and most significant byte (MSB). Packets are broken into &ldquo;segments&rdquo; of fixed, but programmable, length. The start of a segment is marked by a pulse on the UTOPIA start of cell (SOC) signal line. The start of a packet is marked by a pulse on the SOP signal line. The end of a packet is marked by a pulse on the EOP signal line. According to a presently preferred embodiment, bytes are transferred via a 16-bit bus. When a packet ends with a single byte on the bus, the MSB signal line is asserted to distinguish it from a packet which ends with two bytes on the bus. The invention can be expanded to accommodate buses wider than 16-bits by making the EOP a multiple bit signal. The extra signals added to the standard UTOPIA interface by the invention are not involved in segment transfer. Segments are transferred in the same manner that ATM cells are transferred using standard UTOPIA technology. Rather, the extra signals are used by a PHY device to reconstruct packets which were transferred over the interface. Accordingly, a single interface according to the invention can be used to transfer both variable length packets and ATM cells.

Method and apparatus for the fair and efficient transfer of variable length packets using fixed length segments

Apparatus and methods for allocating shared memory utilizing linked lists are provided which are particularly useful in telecommunications applications such as ATM. A management RAM contained within a VLSI circuit is provided for controlling the flow of data into and out of a shared memory (data RAM), and stores information regarding a number of link lists and a free link list in the shared memory, and a block pointer to unused RAM locations. A head pointer, tail pointer, block counter and empty flag are stored for each data link list. The head and tail pointers each include a block pointer and a position counter. The block counter contains the number of blocks used in the particular queue. The empty flag indicates whether the queue is empty. The free link list includes a head pointer, a block counter, and an empty flag. Each memory page of the shared data RAM receiving the incoming data includes locations for storing data. The last location of the last page in a block of shared data RAM memory is preferably used to store a next-block pointer plus parity information. If there are no more blocks in the queue, that last location is set to all ones. An independent agent is utilized in the background to monitor the integrity of the link list structure. Using the methods and apparatus of the invention, four operations are defined for ATM cell management: cell write, cell read, queue clear, and link list monitoring.

Method and apparatus for allocation and management of shared memory with

An ATM destination switch includes an ATM layer device coupled to a physical layer device. The ATM layer device includes a ATM layer interface which receives incoming ATM cells, a processor which is typically with an associated translation RAM, and an ATM layer to physical layer interface. The processor decodes the incoming ATM cell to obtain a VPI/VCI, and provides additional routing information (session number) for the cell for multicast purposes. The cell with the additional routing information is forwarded to the physical layer device which has a header processor, a multicast indicator storage table, preferably in the form of a bit map, for storing output line indications by session number, and a plurality of ATM line output interfaces. The header processor receives the cell with the additional routing information, reads the additional routing information, accesses the multicast indicator storage table based on the additional routing information to determine to which output lines the cell is to be provided, and controls the copying of the cell for each output line so that it may be received at multiple destinations. Thus, an incoming cell which is to be multicast to multiple users connected to the physical layer side of the switch will be multicast to the multiple users using the single VPI/VCI chosen for the local multicast.

Method and apparatus for providing multiple multicast communication

Methods and apparatus for generating and clearing an excessive bit error rate (EBER) alarm are provided and utilize a reset window algorithm. The BIP-8 bytes (e.g., B2 bytes) of incoming data blocks (each block being B frames long) of an STSn telecommunications signal are monitored in an 'idle state' for code violation counts (CV). Upon receiving a data block having a code violation count meeting or exceeding a code violation count threshold (CVSET), a counter is initialized in a 'crossing calculation state', and a window comprising a plurality (W) of blocks is monitored. The counter counts the number of incoming blocks in the window having a CV which meets or exceeds CVSET. If in the crossing calculation state, the count meets or exceeds its own threshold (X), an alarm state is entered and an EBER alarm is set. If not, the system returns to the 'idle state'. Once in the alarm state, every received block is monitored for its code violation count. The first received block with a CV count of CVCLR (code violation clear) or less initializes a clearing calculation state' which sets a clearing-counter CC. The clearing counter CC is used to count the number of incoming blocks in the window having a CV of CVCLR or less. If the CC count meets a third threshold value Y within the time window, the alarm is cleared and the system returns to the idle state. Otherwise, the system reverts to the alarm state.

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Shelton, CT, United States of America

Joseph C Lau