discard threshold 422 is defined for all cells in cbp memory 302 regardless of color marking when the cell counter associated with a port reaches discard threshold 422 the port is transition to a head of line status thereafter the port may transition out of the head of line status if its cell counter falls below a reset limit threshold 424 for the xq memory 304 a guaranteed fixed allocation of xq buffers for each class of service queue is defined by a xq entry value 430 a 430 h each of xq entry value 430 a 430 h defines how many buffer entries should be reserved for an associated queue for example if 100 bytes of xq memory are assigned to a port the first four class of service queues associated with xq entries 430 a 430 d respectively may be assigned the value of 10 bytes and the last four queues associated with xq entries 430 d 430 h respectively may be assigned the value of 5 bytes according to an embodiment of the invention even if a queue does not use up all of the buffer entries reserved for it according to the associated xq entry value the head of line mechanism 406 may not assign the unused buffer to another queue nevertheless the remaining unassigned 40 bytes of xq buffers for the port may be shared among all of the class of service queues associated with the port limits on how much of the shared pool of the xq buffer may be consumed by a particular class of service queue is set with a xq set limit threshold 432 as such set limit threshold 432 may be used to define the maximum number of buffers that can be used by one queue and.