RFIFO: “Retreat FIFOs” for the Head-of-Line Blocking problem

Abstract: The Head-of-Line (HoL) blocking problem, which occurs in input-buffered service systems, degrades their performance, especially in “hot-spot” traffic conditions. In this paper, we present a variation of the design of FIFO queues, called “Retreat FIFOs” or “FIFOs with Retreat” (RFIFOs), which significantly improves the performance of plain FIFOs, with respect to the HoL blocking problem. Each FIFO element is tagged with two status bits. When the HoL element is blocked, a “retreat” process is initiated, i.e., the blocked packet is continuously swapped with its next-in-line packet, until the end of the FIFO is reached. Simulation results indicate that the performance of the RFIFO is significantly improved compared to plain FIFOs, especially for hotspot traffic.