Cheng Peng Fu

TCP Veno: TCP enhancement for transmission over wireless access networks

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.

Network connectivity of one-dimensional MANETs with random waypoint movement

An analysis of network connectivity of one-dimensional mobile ad hoc networks with a particular mobility scheme is presented, focusing on the random waypoint mobility scheme. The numerical results are verified using simulation to show their accuracy under practical network conditions. Observations on RWP properties further lead to approximations and an eventual simple network connectivity formula.

A remedy for performance degradation of TCP Vegas in asymmetric networks

Many previous studies have indicated that TCP Vegas outperforms TCP Reno. This letter shows that in asymmetric networks in which the bottleneck is on the reverse path rather than on the forward path, Vegas underutilizes the available bandwidth on the forward path by a large margin. A solution that makes use of the TCP timestamp option can effectively restore the throughput on the forward path.

A hierarchical scheme for data aggregation in sensor network

Sensor networks are wireless networks that are capable of obtaining and processing physical world information from scattered sensor devices. Its performance is largely constrained by limited power, slow processor, and less memory in each device. Recently, a data-centric scheme called directed diffusion has been proposed to provide efficient data transmission over sensor networks. In this paper, we enhance this scheme by a hierarchical aggregation technique. Experiments demonstrate that our enhanced scheme can save transmission energy to 50% over directed diffusion. Moreover, with the principle of parent selection embedded, our enhanced scheme can obtain higher reliability and provide more applicable data aggregation.

HDA: A hierarchical data aggregation scheme for sensor networks

Sensor networks are wireless networks that can obtain and process physical world information from scattered sensor devices. Due to the limited power, slow processor, and less memory in each device, routing protocols of sensor networks must be designed carefully. Recently, a data-centric scheme called directed diffusion has been proposed to provide efficient data transmission over sensor networks. In this paper, we enhance this scheme by a hierarchical data aggregation technique (HDA). Experiments demonstrate that our enhanced scheme can save transmission energy up to 50% over directed diffusion, without any reliability or delivery efficiency being compromised. At the same time, our scheme can facilitate greater data-level aggregation in data-centric routing.

TFRC Veno: An Enhancement of TCP Friendly Rate Control over Wired/Wireless Networks

TFRC is a TCP-friendly rate control protocol based on TCP Renos 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.

A Simple Throughput Model for TCP Veno

TCP Veno was proposed to eliminate TCP performance suffering from wireless links. Real network measurements and live Internet results have validated TCP Venos 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.

Dynamics comparison of TCP Veno and Reno

TCP Veno was recently proposed to eliminate TCP performance suffering from wireless links. Real network measurements and live Internet results have validated Venos 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.

TCP Veno revisited

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 TCPs suffering in wireless environments. Real network measurements and live Internet results validated Venos 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 Venos advantages, but also illuminate some basic philosophies behind Veno, which could provide helpful guidelines for future protocol design.

Modeling Hop Length Distributions for Reactive Routing Protocols in One Dimensional MANETs

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.