This paper presents Random Early Detection (RED) gate-ways for congestion avoidance in packet-switched networks. The gateway detects incipient congestion by com-puting the average queue size. The gateway could notify connections of congestion either by dropping packets ar-riving at the gateway or by setting a bit in packet headers. When the average queue size exceeds a preset threshold,the gateway drops or marks each arriving packet with a certain probability, where the exact probability is a func-tion of the average queue size. RED gateways keep the average queue size low while allowing occasional bursts of packets in the queue. During congestion, the probability that the gateway notifies a particular connection to reduce its window is roughly proportional to that connection's share of the bandwidth throughthe gateway. RED gateways are designed to accompany a transport-layer congestion control protocol such as TCP.The RED gateway has no bias against bursty traffic and avoids the global synchronization of many connectionsdecreasing their window at the same time. Simulations of a TCP/IP network are used to illustrate the performance of RED gateways.

Network arrivals are often modeled as Poisson processes for analytic simplicity, even though a number of traffic studies have shown that packet interarrivals are not exponentially distributed. We evaluate 24 wide-area traces, investigating a number of wide-area TCP arrival processes (session and connection arrivals, FTP data connection arrivals within FTP sessions, and TELNET packet arrivals) to determine the error introduced by modeling them using Poisson processes. We find that user-initiated TCP session arrivals, such as remotelogin and file-transfer, are well-modeled as Poisson processes with fixed hourly rates, but that other connection arrivals deviate considerably from Poisson; that modeling TELNET packet interarrivals as exponential grievously underestimates the burstiness of TELNET traffic, but using the empirical Tcplib [Danzig et al, 1992] interarrivals preserves burstiness over many time scales; and that FTP data connection arrivals within FTP sessions come bunched into “connection bursts,” the largest of which are so large that they completely dominate FTP data traffic. Finally, we offer some results regarding how our findings relate to the possible self-similarity of widearea traffic.

In this paper we explore the bias in TCP/IP networks against connections with multiple congested gateways. We consider the interaction between the bias against connections with multiple congested gateways, the bias of the TCP window modification algorithm against connections with longer roundtrip times, and the bias of Drop Tail and Random Drop gateways against bursty traffic. Using simulations and a heuristic analysis, we show that in a network with the window modification algorithm in 4.3 tahoe BSD TCP and with Random Drop or Drop Tail gateways, a longer connection with multiple congested gateways can receive unacceptably low throughput. We show that in a network with no bias against connections with longer roundtrip times and with no bias against bursty traffic, a connection with multiple congested gateways can receive an acceptable level of throughput. We discuss the application of several current measures of fairness to networks with multiple congested gateways, and show that diff...

Abstract — The paper considers a network with many apparently-independent periodic processes and discusses one method by which these processes can inadvertent Iy become synchronized. In particular, we study the synchronization of periodic routing messages, and offer guidelines on how to avoid inadvertent synchronization. Using simulations and analysis, we study the process of synchronization and show that the transition from unsynchronized to synchronized traffic is not one of gradual degradation but is instead a very abrupt ‘phase transition’: in general, the addition of a single router will convert a completely unsynchronized traffic stream into a completely synchronized one. We show that synchronization can be avoided by the addition of randomization to the tra~c sources and quantify how much randomization is necessary. In addition, we argue that the inadvertent synchronization of periodic processes is likely to become an increasing problem in computer networks.

this paper we define the notion of traffic phase in a packet-switched network and describe how phase differences between competing traffic streams can be the dominant factor in relative throughput. Drop Tail gateways in a TCP/IP network with strongly periodic traffic can result in systematic discrimination against some connections. We demonstrate this

As the most widely used reliable transport in today’s Internet, TCP has been extensively studied in the past decade. However, previous research usually only considers a small or medium number of concurrent TCP con-nections. The TCP behavior under many competing TCP flows has not been sufficiently explored. In this paper we use extensive simulations to investigate the individual and aggregate TCP performance for network model that captures the essence of wide-area Internet connections. Second, we study the performance of a single TCP flow with many competing TCP flows by evaluating the best-known analytical model proposed in the literature. Finally, we examine the aggregate TCP behavior exhibited by many concurrent TCP flows, and derive general conclusions about the overall throughput, goodput, and loss probability. 1

A congestion control algorithm fairly distributes network resources under various load and fault conditions. Congestion control for reliable multicast is an active and important area of current research. Simple approaches to this problem have suffered from the "drop-towards-zero" phenomenon, resulting in some cases with performance significantly worse than what would be achieved by using separate TCP connections from the sender to each receiver. This presents a strong disincentive to use reliable multicast. One of the primary reasons that progress in this area has been so slow is that there has not been a formal definition of what a congestion control algorithm should be trying to accomplish. In particular, there has been no agreed upon definition for what it means to fairly share the network. This paper does the following. . It specifies an abstract model for a network, and summarizes the notion of a response function for TCP. . It proposes a set of metrics to evaluate a congestion ...

As the most widely used reliable transport in today’s Internet, TCP has been extensively studied in the past decade. However, previous research usually only considers a small or medium number of concurrent TCP connections. The TCP behavior under many competing TCP flows has not been sufficiently explored. In this paper 1, we use extensive simulations to systematically investigate the performance of a large number of concurrent TCP flows. We start with a simple scenario, in which all the connections have the same round-trip time, and the gateways use Drop-Tail policy. We examine how the aggregate throughput, goodput, and loss rate vary with different underlying topologies. We also look at the behavior of each individual connection when competing with other connections. We observe global synchronization in some cases. We break the synchronization by either adding random processing time or using RED gateways, and examine their effects on the TCP performance. Finally we investigate the TCP performance with different RTT’s, and quantify the roundtrip bias using both analysis and simulations. Keywords: TCP, congestion control, drop-tail, RED, simulation.

The congestion control mechanisms of TCP make it vulnerable in an environment where flows with different congestionsensitivity compete for scarce resources. With the increasing amount of unresponsive UDP traffic in today's Internet, new mechanisms are needed to enforce fairness in the core of the network. We propose a scalable Diffserv-like architecture, where flows with different characteristics are classified into separate service queues at the routers. Such class-based isolation provides protection so that flows with different characteristics do not negatively impact one another. In this study, we examine different aspects of UDP and TCP interaction and possible gains from segregating UDP and TCP into different classes. We also investigate the utility of further segregating TCP flows into two classes, which are class of short and class of long flows. Results are obtained analytically for both Tail-drop and Random Early Drop (RED) routers. Class-based isolation have the following salient features: (1) better fairness, (2) improved predictability for all kinds of flows, (3) lower transmission delay for delay-sensitive flows, and (4) better control over Quality of Service (QoS) of a particular traffic type.

The dominant transport protocol for the Internet is TCP (Transmission Control Protocol). The applications using this protocol range from simple email exchanges to web browsing and live audio or video streaming. Approximately 90 % of the data carried by the Internet are governed by TCP. TCP provides an end-to-end (application-to-application) service that ensures the