3Com Corporation

Atrica Israel Ltd.

Yoav Honig

Eytan Mann

Golan Schzukin

Amir Lahat

Meir Ohana

Ari Halpern

A novel policer mechanism that incorporates randomization of the rate threshold which prevents 'lockup' and 'synchronization' problems associated with prior art policers that employ fixed rate thresholds. In one embodiment, a policer machine utilizes the well known sliding window technique to implement traffic control. In a second embodiment, a policer machine utilizes the well known token bucket technique to implement traffic control. In both embodiments, a random dimension is added to the rate threshold used by each policer algorithm. For the sliding window embodiment, the effect of randomization of the rate threshold is that the policer machine applies a scattering of rate values centered around the desired rate to the incoming traffic. For the token bucket embodiment, a random dimension is added to the empty bucket (i.e. zero tokens) threshold. The effect of randomization of the empty bucket threshold is that the policer machine applies a scattering of token values above the empty bucket threshold value of zero.

Policing machine incorporating randomization of rate threshold

Crossbar switch utilizing broadcast buffer and associated broadcast buffer management unit

A system for appending data to a packet whereby the original CRC calculated by the transmitting station is not modified and is retained in order to determine the occurrence of transmission errors at the receiver. The invention is applicable in communication systems whereby the data to be appended to the packet comprises a fixed length. The invention appends the data in the form of a tag to the tail of the packet after the original CRC and, in addition, determines and appends a tag CRC to the tail of the packet following the tag data. The tag CRC has a value such that the CRC machine in the receiver generates a constant CRC value even though the packet length was increased. A tag CRC is generated that when appended to the packet produces the same result as if the packet was processed through the CRC machine without any data appended.

Packet expansion with preservation of original cyclic redundancy code check indication

A novel crossbar switching matrix that improves the transmission of variable length broadcast packets by greatly reducing transmission latency time. Unicast traffic is halted in the middle of packet transmission operations and the broadcast packet is transmitted. Once the broadcast packet has finished transmission, unicast packet transmission resumes without any loss of data. A unicast buffer is used to store the unicast packet while the broadcast packet is being transmitted. A broadcast buffer is used to buffer the broadcast packet as it egresses from the switch matrix. In this fashion, the broadcast information is given high priority and passes quickly through the switch without the large delays associated with the prior art switch matrixes. The crossbar switch matrix of the present invention is applicable to any switching matrix adapted to switch variable length data units.

Crossbar switching matrix with broadcast buffering

An apparatus for and a method of collapsing multiple ports to a single queue. The invention has applications in switching devices whereby several external ports share the same resource, such as a switching fabric. In order to allocate the resources fairly to all the ports, a scanning method is used to allocate the division of the resources to each of the external ports. A port combiner circuit continuously scans or polls the external ports in a round robin fashion checking for a port ready to input data. An external port in a ready state transfers its frame data to an input queue. The frame data is written to the next available segment in the input queue which is comprised of RAM configured as a circular buffer. After a frame is written, the write pointer is incremented to point to point to the next available segment. The next frame segment read out of the input queue is always the first one written. The queue thus formed received multiple inputs but has a single output. The scanning method is operative to pass input frames to the shared resource, i.e., the switching fabric, in accordance with their arrival order and without regard to the source port the frame came in on.

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Kfar Saba, Israel

Yoav Honig