Importance

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Abstract

To determine congestion within a shared memory switch, the global memory usage and the individual address queue memory usage of the switching fabric for the switch are measured. These two types of memory usage are combined to determine a net congestion state for a switching fabric. A similar congestion determination is made for line cards coupled to the main switching fabric. Specifically, the global memory usage within the line card is combined with the individual queue memory usage within the card to generate a line card congestion state. The switching fabric congestion state is then combined with the line card congestion state to determine a net congestion state. Using the net congestion state, an explicit rate can be determined for adjusting ER, CI & NI fields in the RM cell. Two methods of determining an explicit rate are disclosed. The first method modifies the explicit rate found within RM cells. The second method generates an internal 'switch explicit rate' using the Current Cell Rate value within forward RM cells. Then, when a backward RM cell is received, the internal switch explicit rate is used as a benchmark to modify the explicit rate field of the RM cell.

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First Claim