ATM switch and a method for determining buffer threshold

A method for determining buffer threshold size in an asynchronous transfer mode (ATM) switch for controlling cells input into a switching element using aback-pressure signal, said method comprising the steps of:

• calculating ri, a buffer pool occupancy rate of an ith input port (i=1, 2, 3, . . . , N);
• calculating rH, a threshold of the buffer pool occupancy rate of the ith input port;
• calculating Li, a number of occupation of the cells in a buffer pool of the ith input port;
• calculating a difference, Dorder(k)=tj−Lj(k=1, 2, 3, . . . , N) between tj, a threshold of a jth input port and Lj, a number of cells stored in a buffer pool of the jth input port, where i≠j (j=1, 2, 3, . . . , N);
• calculating tD—order(k), a threshold when said tj−Lj is the kth value in descending order from the N input ports;
• calculating bD—order(k), a minimum threshold to guarantee minimum cell input;
• comparing Δ, the minimum unit of increase or decrease of the threshold and the value of tD—order(k)−bD—order(k);
• and
• reducing the threshold of the input port having the largest value of tj−Lj by Δ and increasing the threshold of the ith input port by Δ.

A method utilizing a buffer threshold control part for determining buffer threshold size in an asynchronous transfer mode (ATM) switch using a back-pressure signal, said ATM switch including a buffer pool control part having N input port occupancy tables to store occupancy information of N input ports, and input crosspoint control part, an output crosspoint control part, and a buffer pool including a predetermined number of priority class buffers connected to a plurality of input ports, said method comprising the steps of:

• calculating a buffer pool occupancy ratio per input port;
• calculating a threshold, at regular cell time intervals in response to said buffer pool occupancy ratio and buffer pool occupancy information output from said buffer pool control part, for each input port;
• transmitting said calculated threshold to said buffer pool control part;
• and
• generating a control signal in response to said calculated threshold to change the threshold for each priority class buffer.