US 6,646,985 B1Granted

Congestion control mechanism in a network access device

AssigneeFujitsu Network Communications, Inc.

InventorsJae Park, Michael Samori

Life of this patent

Estimating the term…

Loading patent…

Abstract

A congestion control mechanism in an ATM network access device includes segmentation and reassembly (SAR) logic that sends and receives Asynchronous Transfer Mode (ATM) cells to and from interface logic that transfers the cells to and from a switch fabric. The cells are transferred on ATM connections, including flow-controlled connections for which the sending of cells by the SAR logic is controlled in response to the settings of Generic Flow Control (GFC) bits appearing in the headers of ATM cells received by the SAR logic. The interface logic receives a congestion signal indicative of the level of congestion in a transmit buffer in the switch fabric. In response to the congestion signal, the interface logic sets the GFC bits in the headers of cells transferred to the SAR logic such that the cell transmission rate is maintained at a high average level while undesirable congestion in the transmit buffer is avoided. Hysteresis is employed in the setting of the GFC bits is response to the congestion signal. The interface logic generates idle cells during periods in which no traffic-carrying cells are being transferred from the switch fabric to the SAR logic, and sends the idle cells to the SAR logic to provide GFC signalling during such periods.

Claims11

Dependent claims

Apparatus, comprising:

segmentation and reassembly (SAR) logic operative to send and receive fixed-length data units on flow-controlled connections at a flow-controlled interface, each received data unit including a flow-control field used to send flow control commands to the SAR logic in accordance with a flow-control protocol, the SAR logic being operative to send data units on the flow-controlled connections when it has received a permission indication in the flow-control fields of received data units, and to otherwise inhibit the sending of data units on the flow-controlled connections;
and
interface logic coupled to the flow-controlled interface of the SAR logic and operative to transfer data units between the SAR logic and a transmit buffer in a switch fabric, the interface logic receiving a congestion signal from the switch fabric indicating whether the fullness of the transmit buffer exceeds a threshold level, the interface logic being operative when the congestion signal is deasserted to include permission indications in data units sent to the SAR logic in accordance with the flow-control control protocol, and the interface logic being operative when the congestion signal is asserted to withhold permission indications from data units sent to the SAR logic, the interface logic being further operative to generate idle data units and transfer the idle data units to the SAR logic during periods in which no traffic-carrying data units are available for transfer from the switch fabric to the SAR logic, and wherein the data units utilized by the interface logic for sending flow control commands to the SAR logic include both the traffic-carrying data units and the idle data units.

Apparatus, comprising:

segmentation and reassembly (SAR) logic operative to send and receive fixed-length data units on flow-controlled connections at a flow-controlled interface, each received data unit including a flow-control field used to send flow control commands to the SAR logic in accordance with a flow-control protocol, the SAR logic being operative to send data units on the flow-controlled connections when it has received a permission indication in the flow-control fields of received data units, and to otherwise inhibit the sending of data units on the flow-controlled connections;
and
interface logic coupled to the flow-controlled interface of the SAR logic and operative to transfer data units between the SAR logic and a transmit buffer in a switch fabric, the interface logic receiving a congestion signal from the switch fabric indicating whether the fullness of the transmit buffer exceeds a threshold level, the interface logic being operative when the congestion signal is deasserted to include permission indications in data units sent to the SAR logic in accordance with the flow-control protocol, and the interface logic being operative when the congestion signal is asserted to withhold permission indications from data units sent to the SAR logic;
wherein:
the SAR logic maintains a flow-control counter to control the sending of data units on the flow-controlled connections, and wherein the SAR logic is operative to decrement the flow-control counter when a data unit is sent to the interface logic on a flow-controlled connection and increment the flow-control counter when a credit indication is received from the interface logic;
and
the SAR logic is further operative to inhibit the sending of data units to the interface logic on flow-controlled connections when the value of the flow-control counter reaches a predetermined value.

4 more elements

Dependencies are inferred from the claim text.