We present a new implementation of TCP that is better suited to today's Internet than TCP Reno or Tahoe. Our implementation of TCP, which we call TCP Santa Cruz, is designed to work with path asymmetries, out-of-order packet delivery, and networks with lossy links, limited bandwidth and dynamic changes in delay. The new congestion-control and error-recovery mechanisms in TCP Santa Cruz are based on: using estimates of delay along the forward path, rather than the round-trip delay; reaching a target operating point for the number of packets in the bottleneck of the connection, without congesting the network; and making resilient use of any acknowledgments received over a window, rather than increasing the congestion window by counting the number of returned acknowledgments. We compare TCP Santa Cruz with the Reno and Vegas implementations using the ns2 simulator. The simulation experiments show that TCP Santa Cruz achieves significantly higher throughput, smaller delays, and smaller del...

Throughout the world, GSM cellular mobile networks are being upgraded to support the "always-on" General Packet Radio Service (GPRS). Despite the apparent availability of levels of bandwidth not dissimilar to that provided by conventional fixed-wire telephone modems, the user experience using GPRS is currently considerably worse.

As local area wireless networks based on the IEEE 802.11 standard see increasing public deployment, it is important to ensure that access to the network by different users remains fair. While fairness issues in 802.11 networks have been studied before, this paper is the first to focus on TCP fairness in 802.11 networks in the presence of both mobile senders and receivers. In this paper, we evaluate extensively through analysis, simulation, and experimentation the interaction between the 802.11 MAC protocol and TCP. We identify four different regions of TCP unfairness that depend on the buffer availability at the base station, with some regions exhibiting significant unfairness of over 10 in terms of throughput ratio between upstream and downstream TCP flows. We also propose a simple solution that can be implemented at the base station above the MAC layer that ensures that different TCP flows share the 802.11 bandwidth equitably irrespective of the buffer availability at the base station. I.

This paper presents TCP Rate Control, a new technique for transparently augmenting end-to-end TCP performance by controlling the sending rate of a TCP source. The "rate" of a TCP source is determined by its window size, the round trip time and the rate of acknowledgments (or acks). TCP rate control controls these aspects by modifying the ack number and receiver window fields in acknowledgments and by modulating the acknowledgment rate.

Abstract—In this paper, we describe a receiver based congestion control policy that leverages TCP flow control mechanisms to prioritize mixed traffic loads across access links. We manage queuing at the access link to: (1) improve the response time of interactive network applications; (2) reduce congestion-related packet losses; while (3) maintaining high throughput for bulk-transfer applications. Our policy controls queue length by manipulating receive socket buffer sizes. We have implemented this solution in a dynamically loadable Linux kernel module, and tested it over low bandwidth links. Our approach yields a 7-fold improvement in packet latency over an unmodified system while maintaining link utilization at 94%. In the common case, congestionrelated packet losses at the access link can be eliminated. Finally, by prioritizing short flows, we show that our system reduces the time to download a complex web page during a large background transfer by a factor of two. I.

We study several schemes for improving the performance of two-way TCP traffic over asymmetric links where the bandwidths in the two directions may differ substantially, possibly by many orders of magnitude. The sharing of a common buffer by data segments and acknowledgments in such an environment produces the effect of ack compression, often causing dramatic reductions in throughput. We first demonstrate the significance of the problem by means of measurements on an experimental network and then proceed to study approaches to improve the throughput of the connections. These approaches reduce the effect of ack compression by carefully controlling the flow of data packets and acknowledgments. We first examine a scheme where acknowledgments are transmitted at a higher priority than data. By analysis and simulation, we show that prioritizing acks can lead to starvation of the low-bandwidth connection. The second approach makes use of a connection-level backpressure mechanism to limit the m...

Abstract—As third-generation (3G) wireless networks with high data rate get widely deployed, optimizing the Transmission Control Protocol (TCP) performance over these networks would have a broad and significant impact on data application performance. In this paper, we make two main contributions. First, one of the biggest challenges in optimizing the TCP performance over the 3G wireless networks is adapting to the significant delay and rate variations over the wireless channel. We present Window Regulator algorithms that use the receiver window field in the acknowledgment (ACK) packets to convey the instantaneous wireless channel conditions to the TCP source and an ACK buffer to absorb the channel variations, thereby maximizing long-lived TCP performance. It improves the performance of TCP selective ACK (SACK) by up to 100 percent over a simple drop-tail policy, with small buffer sizes at the congested router. Second, we present a wireless channel and TCP-aware scheduling and buffer sharing algorithm that reduces the latency of short flows while still exploiting user diversity for a wide range of user and traffic mix. Index Terms—TCP, 3G network, long and short flows, delay and rate variation. Ç 1

In this paper, we propose an extension of TCP Westwood allowing the management of the Efficiency/Friendliness-toNewReno tradeoffs. We show that the extended TCP Westwood is able to achieve higher total link utilization, yet at the same time maintain friendliness. TCP Westwood (for short, TCPW) implements a novel window congestion control algorithm based on eligible rate estimation. The performance of TCPW has been promising, exceeding that of TCP NewReno in "large leaky pipes"; i.e. network paths with high bandwidth-delay product and non-negligible random error rate. Consider the situation where TCPW and TCP NewReno connections coexist and share common bottlenecks. Friendliness in this shared environment is paramount. Under certain conditions TCP NewReno may experience some performance degradation since TCPW "learns" more about connection performance and thus can take better advantage of available bandwidth. To manage the efficiency/friendliness tradeoffs, we propose to combine the original TCPW Bandwidth Estimation (BE) strategy with a new Rate Estimation (RE) strategy. One finds that BE provides significantly higher utilization, but may, under certain conditions, overestimates a connection fair share. RE, on the other hand, tends to be closer to the achieved rate of a connection, but it may underestimate the connection fair share. The question is: which estimate -- RE or BE -- yields better throughput/friendliness tradeoffs? Our studies show that RE works best when packet loss is mostly due to congestion. If, on the other hand, packet loss is mostly due to link errors, BE gives better performance. To achieve the "best of all worlds", we introduce a method we call Combined Rate and Bandwidth estimation (CRB.) A connection first infers the predominant cause of packet lo...

Abstract — Virtually all network applications requiring reliable end-toend communication depend on TCP. Unfortunately, the performance of any stock TCP is abysmal over wide-area networks (WANs) and even over localarea networks (LANs) with very high-bandwidth links. Currently, network researchers manually optimize TCP buffer sizes to achieve acceptable performance over a given connection. Unfortunately, this manual optimization requires changes to the kernel on both end hosts involved in the network connection (changes that are only effective for connections between these two hosts). Furthermore, because two administrative domains must be coordinated to perform this optimization, this process can be tedious and time consuming. To address these problems, this paper illustrates the benefits of a new technique called dynamic right-sizing. This technique dynamically and automatically determines the best buffer size, and hence flow-control window size in TCP. Our simulation study shows that dynamic right-sizing can improve the performance of flows by two orders of magnitude over stock TCP implementations that have static flow-control windows.

In this survey, we first review the concept of congestion control with a focus on the Transmission Control Protocol/Internet Protocol (TCP/IP). We describe many recently proposed algorithms to combat congestion and improve performance, particularly active queue management (AQM) algorithms such as random early detection (RED) and its variants. We then survey control-theoretic analysis and design of TCP congestion control with an AQM scheme. In addition, we discuss three problems associated with AQM proposals: parameter setting, the insensitivity to the input traffic load variation, and the mismatch between macroscopic and microscopic behavior of queue length dynamics. As alternatives to AQM algorithms, we also survey architectural approaches such as modification of source or network algorithms, and economic approaches including pricing or optimization of allocated resources. Finally, we list many open issues that persist in the design, operation, and control of the Internet. Internet congestion occurs when the aggregate demand for