Apparatus and method of monitoring a queue state in an asynchronous transfer mode switch

An apparatus for monitoring the queue state in a subscriber board of an asynchronous transfer mode switching (ATM) system, said ATM system having at least one source node and at least one destination node, said apparatus comprising:

• a means for transmitting a forward resource management (FRM) cell to said ATM switch, said FRM cell containing a field having a first time difference between a present time and a previous time as said FRM cell is inputted to said ATM switch;
• a means for reading said FRM cell to determine a second time difference between a present output time and a previous output time as said FRM cell is transmitted from said ATM switch in order to calculate a switch load measurement (SLM) value, said SLM value is calculated based on the difference between said first time difference and said second time difference, said calculated SLM is inserted in the field of a backward management (BRM) cell to be transferred to said ATM switch;
• a means for storing and updating said input time of said FRM cell and said output time of said BRM cell;
• a means for calculating an explicit cell rate (ER) according to said calculated SLM value in order to explicitly control the transmission rate of said source node and to control the congestion of said ATM switch.

A method for monitoring the queue state in an asynchronous transfer mode (ATM) switch, comprising the steps of:

• (a) transmitting a forward resource management (FRM) cell from a source node connected by a virtual channel to a destination node via said ATM switch, said FRM cell containing a field having a first time difference information between a present input time and a previous input time as said FRM cell is inputted to said ATM switch;
• (b) reading, by said destination node, said FRM cell transmitted from said source node via said ATM switch and determining a second time difference information between a present output time and a previous output time as said FRM cell is read by said destination node;
• (c) determining a switch load measurement (SLM) value by calculating the difference value between said first time difference information in said FRM cell and said second time difference information;
• (d) inputting said determined SLM value by in a field of a backward management (BRM) cell to be transferred to said ATM switch;
• (e) calculating an explicit cell rate (ER) based on said SLM value contained in said BRM cell received from said destination node;
• and,
• (f) inputting said determined explicit cell rate to said BRM cell to be transferred to said source node in order to explicitly control the transmission rate of said source node and to control the congestion of said ATM switch.