We describe FAST TCP, a new TCP congestion control algorithm for high-speed long-latency networks, from design to implementation. We highlight the approach taken by FAST TCP to address the four difficulties, at both packet and flow levels, which the current TCP implementation has at large windows. We describe the architecture and characterize the equilibrium and stability properties of FAST TCP. We present experimental results comparing our first Linux prototype with TCP Reno, HSTCP, and STCP in terms of throughput, fairness, stability, and responsiveness. FAST TCP aims to rapidly stabilize high-speed long-latency networks into steady, efficient and fair operating points, in dynamic sharing environments, and the preliminary results are promising.

Wireless and satellite networks often have non-negligible packet corruption rates that can significantly degrade TCP performance. This is due to TCP's assumption that every packet loss is an indication of network congestion (causing TCP to reduce the transmission rate). This problem has received much attention in the literature. In this paper, we take a broad look at the problem of enhancing TCP performance under corruption losses, and include a discussion of the key issues. The main contributions of this paper are: (i) a confirmation of previous studies that show the reduction of TCP performance in the face of corruption loss, and in addition a plausible upper bound achievable with perfect knowledge of the cause of loss, (ii) a classification of the potential mitigation space, and (iii) the introduction of a promising new mitigation that employs rich cumulative information from intermediate nodes in a path to form a better congestion response.

Abstract—We prove that the XCP equilibrium solves a constrained max-min fairness problem by identifying it with the unique solution of a hierarchy of optimization problems, namely those solved by max-min fair allocation, but solved by XCP under an additional constraint. This constraint is due to the “bandwidth shuffling ” necessary to obtain fairness. We describe an algorithm to compute this equilibrium and derive a lower and upper bound on link utilization. While XCP reduces to max-min allocation at a single link, its behavior in a network can be very different. We illustrate that the additional constraint can cause flows to receive an arbitrarily small fraction of their max-min fair allocations. We confirm these results using ns2 simulations. Index Terms—Congestion control, max-min, optimization.

Achieving efficient and fair bandwidth allocation while minimizing packet loss and bottleneck queue in high bandwidthdelay product networks has long been a daunting challenge. Existing end-to-end congestion control (e.g., TCP) and traditional congestion notification schemes (e.g., TCP+AQM/ ECN) have significant limitations in achieving this goal. While the XCP protocol addresses this challenge, it requires multiple bits to encode the congestion-related information exchanged between routers and end-hosts. Unfortunately, there is no space in the IP header for these bits, and solving this problem involves a non-trivial and time-consuming standardization process. In this paper, we design and implement a simple, lowcomplexity protocol, called Variable-structure congestion Control Protocol (VCP), that leverages only the existing two ECN bits for network congestion feedback, and yet achieves comparable performance to XCP, i.e., high utilization, negligible packet loss rate, low persistent queue length, and reasonable fairness. On the downside, VCP converges significantly slower to a fair allocation than XCP. We evaluate the performance of VCP using extensive ns2 simulations over a wide range of network scenarios and find that it significantly outperforms many recently-proposed TCP variants, such as HSTCP, FAST, and CUBIC. To gain insight into the behavior of VCP, we analyze a simplified fluid model and prove its global stability for the case of a single bottleneck shared by synchronous flows with identical round-trip times. 1.

In heterogeneous networks, TCP connections that incorporate a terrestrial or satellite radio link are greatly disadvantaged with respect to entirely wired connections, because of their longer round trip times (RTTs). To cope with this problem, a new TCP proposal, the TCP Hybla, is presented and discussed in the paper. It stems from an analytical evaluation of the congestion window dynamics in the TCP standard versions (Tahoe, Reno, NewReno), which suggests the necessary modifications to remove the performance dependence on RTT. TCP Hybla performance is firstly evaluated in the case of an ideal channel, with good correlation between analytical and simulation data. Then, more realistic situations, which require the adoption of a benchmark network topology and a careful ns-2 simulation set-up, are examined. In particular, TCP Hybla performance is compared with that achievable by TCP standard in the presence of congestion and link losses, either separately or jointly considered. In all the examined cases, the superiority of TCP Hybla is evident, as it greatly reduces the severe penalization suffered by wireless, and especially satellite, TCP connections. Finally, it is worth noting that TCP Hybla does not infringe the end to end semantics of TCP and is compatible with other promising enhancements.

The Transmission Control Protocol (TCP) has been mainly designed assuming a relatively reliable wireline network. It is known to perform poorly in the presence of wireless links because of its basic assumption that any loss of a data segment is due to congestion and consequently it invokes congestion control measures. However, on wireless access links, a large number of segment losses will occur more often because of wireless link errors or host mobility. For this reason, many proposals have recently appeared to improve TCP performance in such environment. They usually rely on the wireless access points (base stations) to locally retransmit the data in order to hide wireless losses from TCP. In this paper, we present WTCP (Wireless-TCP), a new mechanism for improving wireless access to TCP services. We use extensive simulations to evaluate TCP performance in the presence of congestion and wireless losses when the base station employs WTCP, and the well-known Snoop proposal [3]. Our results show that WTCP significantly improves the throughput of TCP connections due to its unique feature of hiding the time spent by the base station to locally recover from wireless link errors so that TCP’s round trip time estimation at the source is not affected. This proved to be critical since otherwise the ability of the source to effectively detect congestion in the fixed wireline network is hindered. Copyright c ○ 2002 John Wiley & Sons, Ltd.

Wireless and satellite networks often have non-negligible packet corruption rates that can significantly degrade TCP performance. This is due to TCP's assumption that every packet loss is an indication of network congestion (causing TCP to reduce the transmission rate). This problem has received much attention in the literature. In this paper, we take a broad look at the problem of enhancing TCP performance under corruption losses, and include a discussion of the key issues. The main contributions of this paper are: (i) a confirmation of previous studies that show the reduction of TCP performance in the face of corruption loss, and in addition a plausible upper bound achievable with perfect knowledge of the cause of loss, (ii) a classification of the potential mitigation space, and (iii) the introduction of a promising new mitigation that employs rich cumulative information from intermediate nodes in a path to form a better congestion response.

Abstract—This paper examines the impact of RED on two versions of TCP – traditional TCP Reno and a newly proposed variant, TCP Veno- over 802.11b WLAN. TCP Reno was originally designed for wired networks where packet losses are primarily due to network congestion. This assumption is not always true in wireless networks, in which packet losses can be due to transmission errors on the noisy wireless link. TCP Veno refines the algorithms in Reno by distinguishing between noncongestive and congestive states, and avoids the unnecessary reduction of TCP congestion window when packet losses are not due to congestion. Our results show that TCP Veno can achieve up to 30 % more throughput than TCP Reno when link quality is poor. Our results also show that TCP Veno is compatible with RED. In addition, although RED does not help to further improve the throughput in Veno, it can improve fairness among

Over the past decade, the modern datacenter has reshaped the computing landscape by providing a large scale consolidated platform that efficiently powers online services, financial, military, scientific, and other application domains. The fundamental principle at the core of the datacenter design is to provide a highly available, high performance computing and storage infrastructure while relying solely on low cost, commodity components. Further, in the past few years, entire datacenters have become a commodity themselves, and are increasingly being networked with each other through high speed optical networks for load balancing and fault tolerance. Therefore, the network substrate has become a key component that virtually all operations within and between datacenters rely on. Although the datacenter network substrate is fast and provisioned with large amounts of capacity to spare, networked applications find it increasingly difficult to derive the expected levels of performance. In essence, datacenters consist of inexpensive, fault-prone components running on commodity operating systems and network protocols that are ill-suited for reliable, high-performance applications. This thesis addresses several key challenges pertaining to the communication substrate of the modern

In this paper, we present an end-to-end adaptation scheme, called the wireless loss-delay based adaptation algorithm (WLDA+). WLDA+ adapts the transmission behaviour of multimedia senders in accordance with the network congestion state in wireless environments. WLDA+ is based on the loss-delay based adaptation scheme [1] which adjusts the transmission behaviour of the senders in a manner similar to TCP connections suffering from equal losses and delays. To take the specific characteristics of wireless links into account, WLDA+ incorporates error differentiation schemes to detect the loss nature in the wireless channel. The performance of WLDA+ is then investigated by simulating the behaviour of this algorithm under different network topologies.