A system including: (a) a processor, adapted to generate first type descriptors, second type descriptors and second type descriptor pointers; wherein the first type descriptors and the second type descriptors describe data entities received by the system, and wherein a size of a second type descriptor pointer equals a size of a first type descriptor; and (b) a memory unit, connected to the processor, adapted to maintain a queue that stores at least one first type descriptor and at least one second type descriptor pointer.