Congestion Control Behavior Research Articles

Enhancing HTTP Web Protocol Performance with Updated Transport Layer Techniques

Popular Internet applications such as web browsing, and web video download use HTTP protocol as application over the standard Transport Control Protocol (TCP). Traditional TCP behavior is unsuitable for this style of application because their transmission rate and traffic pattern are different from conventional bulk transfer applications. Previous works have analyzed the interaction of these applications with the congestion control algorithms in TCP and the proposed Congestion Window Validation (CWV) as a solution. However, this method was incomplete and has been shown to present drawbacks. This paper focuses on the ‘newCWV’ which was designed to address these drawbacks. NewCWV provides a practical mechanism to estimate the available path capacity and suggests a more appropriate congestion control behavior. This paper describes how this algorithm was implemented in the Linux TCP/IP stack and tested by experiments, where results indicate that, with newCWV, the browsing can get 50% faster in an uncongested network.

DX: Latency-Based Congestion Control for Datacenters

Since the advent of datacenter networking, achieving low latency within the network has been a primary goal. Many congestion control schemes have been proposed in recent years to meet the datacenters’ unique performance requirement. The nature of congestion feedback largely governs the behavior of congestion control. In datacenter networks, where round trip times are in hundreds of microseconds, accurate feedback is crucial to achieve both high utilization and low queueing delay. Proposals for datacenter congestion control predominantly leverage explicit congestion notification (ECN) or even explicit in-network feedback to minimize the queuing delay. In this paper, we explore latency-based feedback as an alternative and show its advantages over ECN. Against the common belief that such implicit feedback is noisy and inaccurate, we demonstrate that latency-based implicit feedback is accurate enough to signal a single packet’s queuing delay in 10 Gb/s networks. Such high accuracy enables us to design a new congestion control algorithm, DX, that performs fine-grained control to adjust the congestion window just enough to achieve very low queuing delay while attaining full utilization. Our extensive evaluation shows that: 1) the latency measurement accurately reflects the one-way queuing delay in single packet level; 2) the latency feedback can be used to perform practical and fine-grained congestion control in high-speed datacenter networks; and 3) DX outperforms DCTCP with 5.33 times smaller median queueing delay at 1 Gb/s and 1.57 times at 10 Gb/s.

A rate-based TCP traffic model to accelerate network simulation

Traditional discrete-event simulation of large-scale networks at the packet level is computationally expensive. This article presents a fast rate-based transmission control protocol (RTCP) traffic model designed to reduce the time and space complexity for simulating network traffic whilst maintaining good accuracy. A distinct feature of the proposed model is that the transmission control protocol (TCP) congestion control behavior is represented using analytical models that describe the send rate at the traffic source as a function of the round-trip time and the packet loss rate at different phases of a TCP connection. Rather than modeling at the granularity of individual packets visiting the intermediate routers, the model approximates traffic flows as a series of rate windows, each consisting of a number of packets considered to possess the same arrival rate. The model calculates the queuing delays and the packet losses as these rate windows traverse the individual network queues along the flow path. The proposed RTCP model is able to achieve a performance advantage over other TCP models, by integrating analytical solutions and aggregating traffic using rate windows. Empirical results show that the RTCP model can correctly capture the overall TCP behavior and achieve a speedup of more than two orders of magnitude over the corresponding detailed packet-oriented simulation.

Restrictive mechanism of flow control among non-cooperative Internet users

The flow and congestion control methods based on one-shot game model with non-cooperative game theory can explain the non-cooperative behavior of Internet users. However, the low efficiency of equilibrium solutions affects their utility. Here the behavior of flow and congestion control based on infinitely repeated game models is addressed; the repeated and infinitely repeated flow and congestion control game model is presented; the existence and optimization of the Nash equilibrium point are proved; the discount factor in repeated game is discussed; the punishment and threat strategy to users’ misbehavior is studied in N-users infinitely flow control game; the punishment restrictive method of users’ behavior is designed in infinitely and finitely games; finally, a flow control algorithm based on repeated game, FCAR, is provided based on the conclusions of repeated game model. The results of experiment and simulation show that FCAR algorithm could regularize and restrict users’ misbehavior effectively. FCAR algorithm can also make non-cooperative Internet users achieve cooperation in order to optimize the utility of the whole flow and congestion control system.

Exploiting the predictability of TCP steady-state to speed up network simulation

In discrete-event network simulations, a significant portion of resources are dedicated to the processing of packet events. For large-scale network simulations, the processing of packet events is the most time consuming aspect of the simulation. In this work, we develop a technique that saves on the processing of packet events for TCP flows using the well established results showing that the average behavior of a TCP flow is predictable given a steady-state path condition. We exploit this to predict the average behavior of a TCP flow over a future period of time where steady-state conditions hold, thus allowing for a reduction (or elimination) of the processing required for packet events. We call the flows simulated with our scheme “predicted flows”, in contrast to the “packet-based flows” in usual packet level simulations. We design a simulation framework that provides the flexibility to incorporate this method of simulating TCP packet flows. Our goal is (1) to accommodate different network configurations, on/off flow behaviors and interaction between predicted flows and packet-based flows; and (2) to preserve the statistical behavior of every entity in the system so as to maintain the accuracy of the network simulation as a whole. In order to illustrate the promise of this idea, we implement it in the context of the ns2 simulation system. A set of experiments illustrate the speedup and approximation of the simulation framework, and relate the effectiveness of the scheme to the transient behavior of TCP congestion control. We compare two approaches to predicting TCP throughput and show that formula-based prediction suffers inaccuracy under certain scenarios due to the simple assumptions made about inter-loss time, as most fluid models do, but otherwise achieves a good approximation faster than direct measurement prediction.

An accurate model for analyzing wireless TCP performance with the coexistence of Non-TCP traffic

Our work reported in this paper attempts to develop a detailed analytical model of the TCP congestion control algorithm in wide-cum-wireless environments with regular TCP traffic that could coexist with other exogenous connections such as voice and video traffic. Thus our model is unlike previous models that did not explicitly consider the impact of non-TCP traffic on the referenced TCP connection. We think that it is extremely difficult and also unnecessary to try to use a single closed-form model to accurately describe the TCP performance. Based on an approximated fluid model, we deduce the TCP throughput performance with arbitrary connection size and the coexistence of non-TCP traffic. Most previous literature on TCP models focused on steady-state TCP congestion control behavior. However, a wealth of evidence suggests that many popular TCP connections are short, often below 30 KB. This paper examines how well our proposed model could capture the behavior of short TCP connections with wireless error losses. The simulation results show that our hybrid method approximates the throughput performance of an arbitrary-sized TCP connection with wireless losses much better than other proposed models. In addition, the throughput performance of multiple TCP connections is analyzed and simulated. Based on our analysis results, we make some suggestions for TCP performance enhancement for overcoming the serious effect from wireless losses.

Selfish behavior and stability of the internet:

For years, the conventional wisdom [7, 22] has been that the continued stability of the Internet depends on the widespread deployment of "socially responsible" congestion control. In this paper, we seek to answer the following fundamental question: If network end-points behaved in a selfish manner, would the stability of the Internet be endangered?.We evaluate the impact of greedy end-point behavior through a game-theoretic analysis of TCP. In this "TCP Game" each flowattempts to maximize the throughput it achieves by modifying its congestion control behavior. We use a combination of analysis and simulation to determine the Nash Equilibrium of this game. Our question then reduces to whether the network operates efficiently at these Nash equilibria.Our findings are twofold. First, in more traditional environments -- where end-points use TCP Reno-style loss recovery and routers use drop-tail queues -- the Nash Equilibria are reasonably efficient. However, when endpoints use more recent variations of TCP (e.g., SACK) and routers employ either RED or drop-tail queues, the Nash equilibria are very inefficient. This suggests that the Internet of the past could remain stable in the face of greedy end-user behavior, but the Internet of today is vulnerable to such behavior. Second, we find that restoring the efficiency of the Nash equilibria in these settings does not require heavy-weight packet scheduling techniques (e.g., Fair Queuing) but instead can be done with a very simple stateless mechanism based on CHOKe [21].

Design and Simulation of Asynchronous Transfer Mode-Available Bit Rate End System Congestion Control

The authors develop a simulation model for asynchronous transfer mode available bit rate (ATM ABR) service and use it to engineer ABR congestion control behavior. Although significant work has been performed on ABR rate allocation algorithms at network switches, little work has focused on the end system behavior, which is examined in this article. The effect of (1) the speed of the links on the path from the source to the destination and (2) the connection round trip time on the selection of ABR parameter values is studied. Simulation results illustrate the impact of the key parameters that control rate reduction in the absence of network feedback on performance, in terms of connection throughputs, queue lengths at the switches, and link utilizations. These results have been incorporated into the ABR standards and can be generalized to cooperative congestion control with explicit congestion notification in the Internet.

A rate regulating traffic conditioner for supporting TCP over Diffserv

The ever-growing usage of the Internet and the popularity of multimedia applications result in a need to extend its simple best-effort service model. Differentiated Services (Diffserv) is a promising architecture for supporting a wide range of network services over the Internet. While scalable and flexible, Diffserv must still overcome several challenges including providing per-flow service guarantees and fairness. A critical problem is the difficulty faced by TCP flows in achieving their guaranteed or fair-share rates, especially when competing with flows that do not support congestion control mechanisms, such as UDP. In this paper, we present a traffic conditioner based on Rate Regulation via Early Adaptive Detection (READ). READ uses knowledge of TCP congestion control behavior to proactively regulate flow throughput in order to achieve the desired rate. Our simulation results demonstrate READ's effectiveness in providing TCP flows with their guaranteed or fair share rates. Its adaptive early detection mechanism leads to highly predictable TCP flow behavior, even under dynamic load environments with high priority traffic and competing UDP flows.

Dynamics of congestion control and avoidance of two-way traffic in an OSI testbed

An extensive set of measurements were made in an OSI testbed to study the behavior of congestion control and avoidance. Testbed systems used the Connectionless Network Protocol (CLNP) and Transport Protocol Class 4 (TP4), which had been modified to perform the CE-bit [10] congestion avoidance and the "CUTE" [6] congestion recovery algorithms.We found that two-way traffic has dynamics which can significantly decrease fairness among competing connections using congestion avoidance. We present experiments that demonstrate this problem and our analysis of how two-way traffic results in reduced fairness. This analysis led us to develop an effective modification to the congestion avoidance algorithms to maintain fairness with two-way traffic.Our analysis of experimental results also points to undesirable interactions between two-way traffic dynamics and a sending strategy that times data transmissions, by the receipt of acknowledgements. These interactions reinforce burstiness of transmissions. therefore increasing buffering requirements and delay in routers. They may also decrease throughput.