Many previous studies have shown that traditional TCP slow-start algorithm suffers performance degradation in high-speed and long-delay networks. This paper presents a sender-side enhancement, which makes use of TCP Vegas congestion-detecting scheme to monitor the router queue, and accordingly refines slow-start window evolution by introducing a two-phase approach to probe bandwidth more efficiently. Moreover, it achieves good fairness of bandwidth utilization in coexistence of multiple connections. Simulation results show that, compared with traditional slow-start and many other enhancements, it is able to significantly improve the startup performance without adversely affecting coexisting TCP connections.

This paper makes use of the fluid-based approach to model the throughput of TCP Veno flow over wired/wireless networks. A generalized formula is derived between Veno's throughput and its window evolution parameters, packet loss rate and round-trip time. Simulation experiments and real network measurements are conducted to validate the accuracy of this model.

This paper presents a semi-Markov model that evaluates the performance of TCP connections with asymmetric Additive Increase and Multiplicative Decrease (AIMD) congestion control settings involved in sharing of a common drop-tail router. We study the fairness of the connections and their individual bandwidth utilizations as well as packet loss rates. We confirm that certain asymmetric AIMD settings may achieve fairness in bandwidth sharing. We also found that while connections with asymmetric AIMD settings operate at different bandwidth utilizations, they generally experience similar packet loss rate.

In mobile ad hoc networks (MANETs), packets hop from a source to a series of forwarding nodes until they reach the desired destination. Defining the hop length to be the distance between two adjacent forwarding nodes, we observe that the two adjacent forwarding nodes tend to be farther away from each other with a higher probability in a one-dimensional MANET. We derive the probability density functions for the hop lengths to confirm our observation. Applying the developed results, we further formulate the relationship between the mean number of hops and the distance between the source and the destination.

TFRC is a TCP-friendly rate control protocol based on TCP Reno's throughput equation. It is designed to provide optimal service for unicast multimedia flow operating in the wired Internet environment. However, in wireless networks, TFRC, same as TCP Reno, suffers significant performance degradation. In this paper, we propose to make use of a more advanced equation to enhance TFRC over wireless networks. This new equation is directly derived from the modeling of the wireless TCP rather than the wired TCP. After incorporating this equation into TFRC, two achievements are obtained: 1) this enhanced TFRC has a significant throughput improvement; it is shown that in wireless networks with 10% loss rate, it can obtain 300% improvement over the original TFRC; 2) this enhanced TFRC inherits the desirable features of TFRC, namely good fairness, nice TCP-friendliness and smoothness of sending rate. The extensive experiments, including simulation and live Internet measurements, validate our proposed scheme. Moreover, our scheme only needs to modify the sender-side protocol of TFRC while the receiver-side or intermediate node protocol stack remains intact.

This paper aims to study the queue dynamics of TCP Veno with RED in the wired-wireless heterogeneous networks. The authors first develop a fluid-flow model of TCP Veno with RED over heterogeneous network, and then use the classical linear feedback control theory to analyze it. Analysis results reveal the relationship between the RED queue oscillation and the network parameters. The authors use simulation tool to validate our analysis, and show how to stabilize the router queue and improve the co-existence of TCP Veno with TFRC.

TFRC is TCP-friendly rate control protocol with TCP Reno's throughput equation based. It is designed to mainly provide optimal service for unicast multimedia flow operating in the best-effort Internet environment. However, due to Reno's significant performance degradation in wireless networks, TFRC has also led to unavoidable performance suffering from wireless links due to the poor performance of Reno throughput. This paper proposes an enhancement of TFRC based on the differentiating method used in TCP Veno. Specifically, it utilizes Veno's state differentiator to distinguish congestion losses and non-congestion losses during transmission. By discounting the impact of those non-congestion losses on the throughput calculation, it can effectively alleviate the throughput degradation caused by wireless links. The simulation results have shown that, our proposal can achieve throughput improvement up to 70% as compared to the original TFRC. Meanwhile, it maintains other merits of the original TFRC, such as sending rate smoothness, fairness, and TCP-friendliness.

In this paper, we develop a fluid-flow model of TCP Veno with RED queue management, and use this model to analyze its equilibrium state stability and throughput. On the stability side, our model reveals the relationship between Veno AIMD parameters and system stability region. On the throughput side, our model derives a closed-form throughput formula for bulk transfer TCP Veno flow. We found that, it is possible to vary Veno AIMD parameters to get higher throughput, but more throughput enhancement by TCP Veno will cause more oscillation in the router queue. The simulation results validated our analysis.

In this paper, we aim to study TCP Veno's loss distinguishing accuracy in different network conditions and its performance influence. We first propose a heuristic formula. Based on the simple math analysis and experiment results, we show the sensitivity of Veno's loss distinguishing accuracy on network parameters. Thereafter, we demonstrate two cases to study its performance influence. One case is accuracy extremely high, and another is accuracy extremely low. We observe that, even if the loss distinguishing accuracy is low, Veno still performs well without negative effect. Detailed analysis show the reason is, timeout may play the main role in TCP performance and Veno inherits from Reno the action for timeout without modification.

TCP Veno was proposed to eliminate TCP performance suffering from wireless links. Real network measurements and live Internet results have validated TCP Veno's significant throughput improvement in wireless networks and its harmonious co-existence with TCP Reno connections in wired networks. In this paper, we develop a simple analytic approach to characterize TCP Veno behavior in both wire and wireless situations. Being different from the equation of TCP Reno, a more general close formula is derived, taking into account of the refined multiplicative decrease algorithm in Veno, to model the throughput for a bulk transfer of TCP Veno flow. Our simulation and experimental results demonstrate that such an equation is able to accurately predict TCP Veno throughput over different network scenarios, ranging from very low lossy links to very heavy lossy links.

This paper observes that TCP Veno deals with random losses conservatively over high bandwidth-delay product (BDP) networks. We propose to use a variable named pBDP to help Veno handle random losses more intelligently. The simulation results demonstrate that, such enhancement can improve Veno's throughput up to 80%

In hybrid wireless/wired network, TCP suffers severe performance degradation due to the lack of inference of packet loss. TCP Veno is a novel refinement that is able to diagnose the different causes of packet loss. Based on the diagnosis, TCP Veno takes the necessary control actions, rather than "blind" reduction of throughput without any discrimination. It has been demonstrated that, in this way, TCP Veno achieves better performance than TCP Reno in wireless/wired environment. However, various uncertainties of network may impact the accuracy of TCP Veno's packet loss identification. In this paper, we consider the problem of bursty congestion, as the cause of packet loss is misdiagnosed. To solve this problem in TCP Veno, we proposed a refined packet loss distinguishing scheme. The new TCP Veno is called TCP Veno+. The experimental results show that in environment with bursty congestion, TCP Veno+ can achieve much more accurate congestion loss identification as well as better friendlessness to TCP Reno

In the field of mobile communications, there coexist various access technologies that support wireless connections, such as Bluetooth, IEEE 802.11 and GPRS. These technologies are diverse in terms of bandwidth, delay, coverage area, etc. It is not uncommon that a mobile device is equipped with multiple wireless network interfaces to achieve efficient and ubiquitous communications. In wireless overlay networks, the mobile node can even utilize multiple network interfaces simultaneously to achieve greater QoS performance. This paper presents the design of such a system that supports multi-homed communications. In particular, we design the policy for mapping different network flows to different interfaces, and propose a load-sharing algorithm based on weighted-round-robin channel selection and jump-ahead packet scheduling. Simulation results show that the algorithm can efficiently distribute data packets among multiple channels to achieve bandwidth aggregation.

TCP Veno was recently proposed to eliminate TCP performance suffering from wireless links. Real network measurements and live Internet results have validated Veno's significant throughput improvement in wireless networks and its harmonious coexistent behavior with TCP Reno connections in wired networks. In this paper, we study Veno's performance in asymmetric networks such as ADSL, HFC, where network congestion occurs on the reverse path of acks rather than on the forward path of data sending. Our real experiments demonstrate that Veno continues to reach higher throughput in these asymmetric networks, regardless of wireless or wire links being embedded. Throughput improvement up to 88% over Reno is reached.

TCP Veno was recently proposed to eliminate TCP performance suffering from wireless links. Real network measurements and live Internet results have validated Veno's significant throughput improvement in wireless networks and its harmonious coexistence with TCP Reno connections in wired networks. We demonstrate the out-of-phase synchronization of Veno in one-way traffic, as opposed to the in-phase synchronization of Reno. The detailed studies of this behavior and its interaction with Reno are reported. Moreover, our careful study shows that this out-of-phase synchronization benefits network link utilization, and reduces the occurrence of congestion loss.

In wireless networks, random loss due to bit error leads to significant performance degradation to conventional multicast congestion control schemes. In this paper, we propose and study an enhanced multicast congestion control scheme, called EPGMCC (enhanced PGMCC), which achieves significant performance improvement over PGMCC over loss-prone wireless links. The key idea of EPGMCC is to discriminate random loss from congestion loss according to the measured network congestion level, and perform different actions accordingly. Specifically: 1) at the sender, it adapts the AIMD algorithms in TCP Veno (Cheng Peng Fu et al., 2003) to avoid the unnecessary window-halving induced by random loss and 2) at the receiver, a new scheme is designed to better measure the loss rate and thus help the sender to select the right representative of the group. Our extensive simulation results demonstrate that EPGMCC achieves significant throughput improvement over PGMCC in hybrid wired/wireless networks, furthermore, the improved throughput achieved by EPGMCC is not grabbed from the bandwidth of coexisting connections but from the utilization of available bandwidth that left unused. Throughput improvement of up to 40% can be demonstrated over typical wireless access link with 1% random loss rate.

Diverse links (i.e., wireless links, satellite links and ADSL links) are being widely deployed in current Internet, unlike wired links, these heterogeneous links are causing significant performance degradation of TCP. Recently one sender-side enhancement of TCP, called Veno TCP, is proposed to mainly eliminate TCP's suffering in wireless environments. Real network measurements and live Internet results validated Veno's throughput improvement and its harmonious co-existence with legacy TCP connections. In this paper, we revisit Veno TCP and evaluate its performance in more practical way. Specifically, we measure Veno from four metrics - compatibility, flexibility, robustness and deployablity. Our extensive arguments not only prove Veno's advantages, but also illuminate some basic philosophies behind Veno, which could provide helpful guidelines for future protocol design.

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 co-existing TCP flows.

Wireless access networks in the form of wireless local area networks, home networks, and cellular networks are becoming an integral part of the Internet. Unlike wired networks, random packet loss due to bit errors is not negligible in wireless networks, and this causes significant performance degradation of transmission control protocol (TCP). We propose and study a novel end-to-end congestion control mechanism called TCP Veno that is simple and effective for dealing with random packet loss. A key ingredient of Veno is that it monitors the network congestion level and uses that information to decide whether packet losses are likely to be due to congestion or random bit errors. Specifically: (1) it refines the multiplicative decrease algorithm of TCP Reno-the most widely deployed TCP version in practice-by adjusting the slow-start threshold according to the perceived network congestion level rather than a fixed drop factor and (2) it refines the linear increase algorithm so that the connection can stay longer in an operating region in which the network bandwidth is fully utilized. Based on extensive network testbed experiments and live Internet measurements, we show that Veno can achieve significant throughput improvements without adversely affecting other concurrent TCP connections, including other concurrent Reno connections. In typical wireless access networks with 1% random packet loss rate, throughput improvement of up to 80% can be demonstrated. A salient feature of Veno is that it modifies only the sender-side protocol of Reno without changing the receiver-side protocol stack.

TCP Vegas employs congestion avoidance, early detection of packet loss and conservative slow-start algorithms to improve TCP performance. With its proactive congestion detection, it utilizes network bandwidth more efficiently and achieves a higher throughput than TCP Reno. This paper shows that in asymmetric networks in which the bottleneck is on the reverse path rather than on the forward path, its performance can be significantly lower than that of Reno. In particular, Vegas may erroneously converge to an operating region in which the available bandwidth on the forward path is under-utilized by a large margin. Even worse, when connections running Vegas and Reno co-exist and compete on the same network, Vegas suffers a severe penalty. We propose an approach to improve Vegas' throughput in asymmetric networks.