Experimental assessment of RED in wired/wireless networks

Abstract

SUMMARYThe Internet is a heterogeneous environment comprising wired and wireless components, and transport protocols with different error recovery strategies. We use simulations to study the behaviour of random early detection (RED) gateways in such heterogeneous environments. We investigate two issues: (i) the performance trade-offs of the dropping policy of RED over Drop-Tail's, and (ii) the impact of RED's active queue management on more sophisticated protocols such as TCP-SACK. Some of our results indicate that RED does not deal adequately with heterogeneity. In particular, it may happen that RED applies congestion avoidance techniques even when wireless errors force some senders to back off prior to actual congestion. Our scenarios involve a non-monotonic transmission behaviour of transport protocols within one and the same congestion epoch; RED may escalate further bandwidth under-utilization by applying false congestion avoidance tactics. Furthermore, our results indicate that RED's dropping policy of 'proportional' fairness, which is realized through a Send-more/Drop-more scheme, can also penalize sophisticated protocols like TCP-SACK, which attempt to recover more aggressively from wireless losses. In summary, our results call for further investigation of RED's efficiency in heterogeneous networks and naturally raise the concern of RED's compliance with the end-to-end argument.

The dynamics of responsiveness and smoothness in heterogeneous networks

“…The results confirm our early findings [15] that RED can reduce the system throughput with large delaybandwidth product and small buffer sizes. More specifically, RED reduces the throughput of smooth TCPs experiencing long propagation delays.…”

“…The queueing delay can be derived by deducting the minimum RTT from the current RTT measured. Upon the detection of the following condition: (15) where the threshold is experimentally set to be 0.5, the congestion window is decreased after one RTT, with window decrease ratio set to be: (16) where is defined in (13). Equation (16) bears some similarities with (13).…”

Using active queue management to enhance performance in IEEE802.11

“…The Random Early Detection (RED) Algorithm [6] and [23] marks arriving packets for dropping with a given drop probability (or marks the ECN bit). The packet is marked if the average queue size is between a min threshold (min th ) and max threshold (max th ).…”

Simulation and evaluation of random early detection in congestion control

“…A heterogeneous network is composed of wired and wireless sub-networks, and transport protocols with different error recovery strategies. Some results indicate that RED does not deal adequately with heterogeneity [5], [6]. In particular, it may happen that RED applies congestion avoidance techniques even when wireless errors force some senders to back off prior to actual congestion.…”