This memo specifies the incorporation of ECN (Explicit Congestion Notification) to TCP and IP, including ECN's use of two bits in the IP header. Table of Contents 1.

The congestion control mechanisms used in TCP have been the focus of numerous studies and have undergone a number of enhancements. However, even with these enhancements, TCP connections still experience alarmingly high loss rates, especially during times of congestion. The IETF has addressed this problem by advocating the deployment of active queue management mechanisms, such as RED, in the network. While RED can potentially improve packet loss rates, we show that its effectiveness is highly dependent upon its operating parameters. In fact, in cases where these parameters do not match the requirements of the network load, the performance of the RED gateway can approach that of a traditional drop-tail gateway. To alleviate this problem, we propose and experiment with a self-configuring active queue management mechanism which can significantly reduce loss rates across congested links. When used in the network, this mechanism can effectively reduce packet loss while maintaining high link utilizations under the most difficult scenarios. Keywords: Congestion control, Internet, TCP, RED, queue management 1

FIFO queueing is simple but does not protect traffic from flows that send more than their share or flows that fail to use end-to-end congestion control. At the other extreme, per-flow scheduling mechanisms provide max-min fairness but are more complex, keeping state for all flows going through the router. This paper proposes RED-PD (RED with Preferential Dropping), a flow-based mechanism that combines simplicity and protection by keeping state for just the high-bandwidth flows. RED-PD uses the packet drop history at the router to detect high-bandwidth flows in times of congestion and preferentially drop packets from these flows. This paper discusses the design decisions underlying RED-PD, and presents simulations evaluating RED-PD in a range of environments.

Although active networks have generated much debate in the research community, on the whole there has been little hard evidence to inform this debate. This paper aims to redress the situation by reporting what we have learned by designing, implementing and using the ANTS active network toolkit over the past two years. At this early stage, active networks remain an open research area. However, we believe that we have made substantial progress towards providing a more flexible network layer while at the same time addressing the performance and security concerns raised by the presence of mobile code in the network. In this paper, we argue our progress towards the original vision and the difficulties that we have not yet resolved in three areas that characterize a "pure" active network: the capsule model of programmability; the accessibility of that model to all users; and the applications that can be constructed in practice.

World-Wide Web server over the course a year and a half. This paper presents a longitudinal look at various network path properties, as well as the implementation status of various protocol options and mechanisms. In particular, this paper considers how WorldWide Web clients utilize TCP connections to transfer web data; the deployment of various TCP and HTTP options; the range of round-trip times observed in the network; packet sizes used for WWW transfers; the implications of the measured advertised window sizes; and the impact of using larger initial congestion window sizes. These properties/mechanisms and their implications are explored. An additional goal of this paper is to provide information to help researchers better simulate and emulate realistic networks.

Abstract not found

Theory and experiments show that as the per-flow product of bandwidth and latency increases, TCP becomes inefficient and prone to instability, regardless of the queuing scheme. This failing becomes increasingly important as the Internet evolves to incorporate very high-bandwidth optical links and more large-delay satellite links. To address

This document specifies TCP-Friendly Rate Control (TFRC). TFRC is a congestion control mechanism for unicast flows operating in a best-effort Internet environment. It is reasonably fair when competing for bandwidth with TCP flows, Handley/Padhye/Floyd/Widmer [Page 1] INTERNET-DRAFT Expires: September 2001 March 2001 but has a much lower variation of throughput over time compared with TCP, making it more suitable for applications such as telephony or streaming media where a relatively smooth sending rate is of importance. Handley/Padhye/Floyd/Widmer [Page 2] INTERNET-DRAFT Expires: September 2001 March 2001 Table of Contents 1. Introduction. . . . . . . . . . . . . . . . . . . . . . 4 2. Terminology . . . . . . . . . . . . . . . . . . . . . . 5 3. Protocol Mechanism. . . . . . . . . . . . . . . . . . . 5 3.1. TCP Throughput Equation. . . . . . . . . . . . . . . 5 3.2. Packet Contents. . . . . . . . . . . . . . . . . . . 7 3.2.1. Data Packets. . . . . . . . . . . . . . . . . . . 7 3....

Blue(SFB), a novel technique for enforcing fairness among a large number of flows. SFB scalably detects and rate-limits non-responsive flows through the use of a marking probability derived from the BLUE queue management algorithm and a Bloom filter. Using analysis and simulation, SFB is shown to effectively handle non-responsive flows using an extremely small amount of state information.

Many de nitions of fairness for multicast networks assume that sessions are single-rate, requiring that eachmulticast session transmits data to all of its receivers at the same rate. These de nitions do not account for multi-rate approaches, such aslayering, that permit receiving rates within a session to be chosen independently. Weidentify four desirable fairness properties for multicast networks, derived from properties that hold within the max-min fair allocations of unicast networks. We extend the de nition of multicast max-min fairness to networks that contain multi-rate sessions, and show that all four fairness properties hold in a multirate max-min fair allocation, but need not hold in a single-rate max-min fair allocation. We then show thatmulti-rate max-min fair rate allocations can be achieved via intra-session coordinated joins and leaves of multicast groups. However, in the absence of coordination, the resulting max-min fair rate allocation uses link bandwidth ine ciently, and does not exhibit some of the desirable fairness properties. We evaluate this ine ciency for several layered multi-rate congestion control schemes, and nd that, in a protocol where the sender coordinates joins, this ine ciency has minimal impact on desirable fairness properties. Our results indicate that sender-coordinated layered protocols show promise for achieving desirable fairness properties for allocations in largescale multicast networks. 1