Packet networks require queues (buffers) to absorb short term arrival rate fluctuations. Yet network implementors have always observed that queues at bottlenecks tend to fill and stay filled, which contributes extra delay and removes the ability to absorb bursts. In [1] Floyd and Jacobson proposed the RED (Random Early Detection) active queue management algorithm. RED is simple, robust and quite effective at reducing persistent queues. However, while it has been used widely and successfully on Internet routers, [1] offers little guidance on how to set configuration parameters and RED has gained the reputation of being very difficult to tune. This paper develops RED in different way, treating it as a servo control loop and deriving all the loop parameters from measurable properties of a router. The result is a `self-tuning' RED whose parameters are completely determined by the queue output bandwidth (average departure rate). This new RED performs substantially better than the original version and works for a much wider variety of traffic and link bandwidths. It also admits a substantially simpler and more efficient implementation, one particularly well suited for ASIC forwarding engines. Please note: This is an early draft of an in-progress paper. Several important sections are still missing and the simulation data needs to be reorganized so that the story it tells is clearer. 1.0

In this paper we propose an enhancement to the TCP protocol, called TCP Smart Framing, or TCP-SF for short, that enables the Fast Retransmit/Recovery algorithm even when the congestion window is small. TCP-SF is particularly effective for short-lived flows, as most of the current Internet traffic is. Without modifying the TCP congestion control based on the additive-increase/multiplicativedecrease paradigm, TCP-SF adopts a novel segmentation algorithm: while Classic TCP starts sending one segment, a TCP-SF source is allowed to send an initial window of 4 smaller segments, whose aggregate payload is equal to the connection 's MSS. This key idea can be implemented on top of any TCP flavor, from Tahoe to SACK, and requires modifications to the server behavior only.

This report investigates techniques that improve the performance of Explicit Congestion Notification for networks with a large number of heterogeneous TCP flows. Four different strategies for adaptive queue management are considered for improving goodput and fairness in a network. Basic AECN divides flows passing through a bottleneck router into flow groups, uses a mark-front strategy per flow group queue, and deploys a different max p for each flow group. A series of AECN simulations were run using ns-2. The simulations show that AECN treats each flow fairer than ECN using two fairness measurements: Jain's fairness index and visual max-min fairness. By using a higher mark probability at higher flow levels, AECN yields fewer packet drops and higher goodput than ECN. Two of the variants on AECN, selectively lowering the minimum marking threshold for robust flows and increasing the maximum mark threshold when there are many flows, are shown to further enhance AECN's ability to provide better fairness and higher goodput.

TCP Smart Framing, or TCP-SF for short, enables the Fast Retransmit /Recovery algorithms even when the congestion window is small. Without modifying the TCP congestion control based on the additiveincrease /multiplicative-decrease paradigm, TCP-SF adopts a novel segmentation algorithm: while Classic TCP always tries to send full-sized segments, a TCP-SF source adopts a more flexible segmentation algorithm to try and always have a number of in-flight segments larger than 3 so as to enable Fast Recovery. We motivate this choice by real traffic measurements, which indicate that today's traffic is populated by short-lived flows, whose only means to recover from a packet loss is by triggering a Retransmission Timeout. The key idea of TCP-SF can be implemented on top of any TCP flavor, from Tahoe to SACK, and requires modifications to the server TCP stack only, and can be easily coupled with recent TCP enhancements.