Mitsubishi Electric Information Technology Center America, Inc.

Cisco Technology, Inc.

Ross T Casley

Randy B Osborne

John H Howard

Mikhail Bershteyn

Chiahon Chien

John Benjamin Levy

Abhijit Ghosh

Donald Tarrodaychik

Michael Leigh Lipsie

Anurag Jain

Douglas J Hahn

Osamu Yamamoto

A method and apparatus for applying selective backpressure to control a multi-stage interconnection network (MIN). At one or more stages in the MIN, local information is used to define a queue status parameter for each local queue in the fabric. At the egress linecard, the upstream queue status parameter is periodically combined with the egress linecard's output queue status to generate a queue-specific backpressure signal. The backpressure signal continuously indicates to the ingress linecard that a specific fabric queue or queues is experiencing congestion and that the ingress linecard should therefore slow down or stop sending additional packets to the affected queue. Status computation mechanisms, which are state machines in one embodiment of the present invention, are incorporated in each switch element in at least the last stage of the switch fabric. In an alternate embodiment, the ingress linecard further combines the backpressure signal with its own local queue status to influence the initial queuing decision. In another alternate embodiment, queue status calculating mechanisms are present within one or more stages further upstream from the last stage of the switch fabric. Queue status information from many stages can thus be scaleably combined with egress queue status to determine fabric congestion conditions efficiently and accurately in all queues.

Selective backpressure control for multistage switches

A packet based data transmission system includes a flexible optimized nonocking transmit interface that incorporates optimized buffer modes, dynamic and static chaining, streaming and the utilization of small packet formats. Static chaining refers to connecting together the linked list for successive packets for the same transmit channel or virtual channel. Dynamic chaining refers to means by which the network interface performs this chaining automatically, thereby solving a blocking problem. On the transmit side, streaming refers to initiating the transmission of packet data before the entire packet data has been presented to the interface. This, in turn, permits more rapid recycling of the buffer space. On the receive side, streaming refers to initiating the processing of packet data before the entire packet has been received. The packet transmission system also includes a receive interface that incorporates a chunking system in which a buffer is divided into multiple chunks or segments to accommodate different size packets. Additionally, the receive interface includes an optimized linked list scheme to support chunking in which no linking element is required for the first buffer in the linked list. In one embodiment a small packet format is provided to reduce the relative overhead in sending small packets. In another embodiment the optimized buffer mode associated with the receive side can be utilized on the transmit interface for further reducing overhead.

Network interface

The speed of a hardware-software debugger is markedly increased through the use of high speed simulators which ignore all systems operations except those where design errors are expected to manifest themselves, by skipping CPU bus cycles of no interest for the simulation, by not explicitly simulating periodic clock signals and generating only schedules of clock signals, and by caching instructions when alien computers are used in the simulation process to eliminate decoding of the instructions of the target computer.

Hardware-software debugger using simulation speed enhancing techniques

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Palo Alto, CA, United States of America

Ross T Casley