Dynamics of random early detection

Abstract

In this paper we evaluate the effectiveness of Random Early Detection (RED) over traffic types categorized as nonadaptive, fragile and robust, according to their responses to congestion. We point out that RED allows unfair bandwidth sharing when a mixture of the three traffic types shares a link This urlfairness is caused by the fact that at any given time RED imposes the same loss rate on all jlows, regardless of their bandwidths.We propose Fair Random Early Drop (FRED), a modified version of RED. FRED uses per-active-jlow accounting to impose 011 each flow a loss rate that depends on the flow's buffer use.We sl~ow that FRED provides better protection than RED for adaptive uragile and robust) flows. In addition, FRED is able to isolate non-adaptive greedy trafic more effectively. Finally we present a "two-packet-buffer" gateway mechanism to support a large number of f7ows without incurring additional queueing delays inside the network These improvements are demonstrated by simulations of TCP and UDP traffic.FRED does not make any assumptions about queueing architecture: it will work with a FIFO gateway. FRED's peractive-jlow accounting uses memory in proportion to the total number of b@fers used: a FRED gateway maintains state only for flows for which it has packets buffered, not for all flows that traverse the gateway,

Dynamic buffer management scheme based on rate estimation in packet-switched networks

“…The per-flow buffer occupancy of flow is proportional to the per-flow output rate of flow with the FIFO discipline [9]. Therefore, we can guess that these two approaches achieve the same performance.…”

“…RED is a simple and powerful buffer management scheme that drops packets from each flow in proportion to the amount of bandwidth the flows uses on the output link [9], assuming that all flows exhibit the same behavior as TCP flows do in view of packet drop events. However, RED cannot prevent buffer overflow for many flows, cannot regulate unresponsive flows, and is unfair even among TCP flows because it drops packets randomly [9], [4], [3], [10].…”

“…However, RED cannot prevent buffer overflow for many flows, cannot regulate unresponsive flows, and is unfair even among TCP flows because it drops packets randomly [9], [4], [3], [10]. We suggest the following functions that an intelligent buffer management scheme should support: In ideal situations, routers can provide fairness even with a small buffer.…”

“…RED (Random Early Detection) [6] and FRED (Flow Random Early Drop) [9] are the foundation of buffer management schemes because they are practicable and are designed in the consideration of burstiness of TCP flows. RED prevents full exhaustion of buffers and drops packets before congestion becomes severe.…”

“…, we can achieve both of two goals, i.e., per-flow fair rate allocation and per-flow buffer management while other schemes [15], [6], [9] exhibit weaknesses in either of these two areas. Achieving these two goals at the same time is important for real-time applications that require low delay and fairness and so forth simultaneously.…”