Multiplex communications – Data flow congestion prevention or control – Control of data admission to the network
Reexamination Certificate
1998-01-06
2001-12-11
Nguyen, Chau (Department: 2663)
Multiplex communications
Data flow congestion prevention or control
Control of data admission to the network
C370S412000, C370S428000, C370S468000
Reexamination Certificate
active
06330223
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates generally to asynchronous transfer mode (ATM) networks, and more specifically to an ATM network node wherein a plurality of servers of different classes are examined in a round robin fashion to forward buffered cells according to the frequency weights allocated to their service classes.
2. Description of the Related Art
Weighted round-robin cell multiplexing is described in a paper titled “Weighted Round-Robin Cell Multiplexing in a General-Purpose ATM Switch Chip”, Manolis Katevenis et al., IEEE Journal on Selected Areas in Communications, Vol 9, No. 8, October 1991, pages 1265 to 1279. According to this prior art, ATM Cells of different traffic (or service class) are stored in corresponding buffers and counters are associated respectively with the buffers. Different values of frequency weights are loaded into the counters corresponding to the service classes. In a round-robin fashion, a cell is forwarded from each buffer until the associated counter is decremented to zero. At the end of a round robin cycle, all the counters are reset and the frequency weights are reloaded into the counters to begin a new cycle.
However, the arrival of cells in a rapid succession would form a queue in a buffer if the other buffers are also receiving rapidly arriving cells. When this occurs, the counter is decremented to zero and the stored cells must wait for their turn until the next round robin cycle begins. If these cells are of the type which must be processed on a real-time basis, delays caused by the weighted round robin multiplexing cannot be ignored.
SUMMARY OF THE INVENTION
It is therefore an object of the present invention to provide an ATM network node wherein cells are multiplexed on a weighted round-robin fashion with reduced delays for cells arriving at short time intervals.
According to a first broader aspect of the present invention, there is provided an ATM network node which comprises a plurality of buffers for respectively storing cells of different service classes and a plurality of counters respectively associated with the buffers, the counters being initially loaded with initial weight values respectively corresponding to the service classes. Updating circuitry is provided for respectively updating the initial count values with output values of the counters. Control circuitry sequentially interrogates the buffers and the counters in a round-robin fashion. If the output value of each interrogated counter is not decremented to a predetermined value, a cell is forwarded from the associated buffer and the counter is decremented by one. At the end of a round robin cycle, all of the counters are reloaded with the initial count values of the updated count values depending on the number of cells forwarded from each of the buffers.
According to a first specific aspect, the updated count values are smaller than the initial count values by amounts corresponding to negative output values of the counters.
According to a second specific aspect, the updated count values are respectively greater than the initial count values by amounts corresponding to positive output values of the counters but respectively smaller than predetermined upper limit values.
According to a third specific aspect, the updated count values are respectively smaller than the initial count values by amounts corresponding to negative output values of the counters or respectively greater than the initial count values by amounts corresponding to positive output values of the counters but respectively smaller than predetermined upper limit values.
According to a second broader aspect, the present invention provides a method for an ATM network node which comprises a plurality of buffers for respectively storing cells of different service classes, and a plurality of counters respectively associated with the buffers, the counters being initially loaded with full-count values respectively corresponding to the service classes. The method comprises the steps of (a) determining whether the output value of a successive one of the counters is not decremented to a predetermined count value, (b) if the counter is not decremented to the predetermined count value, causing the buffet associated with the counter to forward a cell and decrementing the counter by one, (c) updating the full-count value of the counter with an output value thereof, (d) repeating the steps (a) to (c) in a round robin fashion, and (e) reloading each of the counters with the initial weight or the updated weight at the end of a round robin cycle depending on the number of cells forwarded from the buffer associated with the counter.
According to a third broader aspect, the present invention provides a method for an ATM network node which comprises a plurality of buffers for respectively storing cells, and a plurality of counters of different service classes respectively associated with the buffers, the counters being initially loaded with respective full-count values corresponding to weight values of the service classes, wherein each of the counters produces a first indication when the counter is decremented to a predetermined value and each of the buffers produces a second indication when there is no cell to transmit. The method comprisies comprises the steps of (a) setting a counter-pointing variable “i” to one, and (b) making an affirmative decision when the counter pointed by variable “i” is producing the first indication or the buffer associated with the counter is producing the second indication or a negative decision when both of the counter and the associated buffer are not producing the respective indications. If the decision at step (b) is negative, step (c) is performed by forwarding a cell from the associated buffer, decrementing the counter by one and updating the full-count value with an output value of the counter. Decision step (d) is then performed: If, in each of the service classes, the counter is producing the first indication or the buffer is producing the second indication, all of the counters are reloaded with thin initial full-count values or the updated full-count values of the counters depending on the number of cells forwarded from the buffers associated with the counters. If, in at least one of the service classes, both of the counter and the buffer are not producing the respective indications, the variable “i” is incremented by one and the step (b) and those that follow are repeated. If the decision at step (b) is affirmative, decision step (d) and those that follow are repeated.
Step (c) may further include the step of resetting the variable “i” to zero. With the variable resetting step, cells of higher priority levels are forwarded preferentially over those of lower priority levels.
REFERENCES:
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patent: 5561663 (1996-10-01), Klausmeier
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patent: 6069893 (2000-05-01), Parruck et al.
M. Katevenis, et al., “Weighted Round-Robin Cell Multiplexing in a General-Purpose ATM Switch Chip”,IEEE Journal on Selected Areas in Communications, vol. 9, No. 8, Oct. 1991, pp. 1265-1279.
Hyun Soon-Dong
NEC Corporation
Nguyen Chau
Ostrolenk Faber Gerb & Soffen, LLP
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