Jiarong Luo

Receiver-Assisted Congestion Control to Achieve High Throughput in Lossy Wireless Networks

Many applications would require fast data transfer in high-speed wireless networks nowadays. However, due to its conservative congestion control algorithm, Transmission Control Protocol (TCP) cannot effectively utilize the network capacity in lossy wireless networks. In this paper, we propose a receiver-assisted congestion control mechanism (RACC) in which the sender performs loss-based control, while the receiver is performing delay-based control. The receiver measures the network bandwidth based on the packet interarrival interval and uses it to compute a congestion window size deemed appropriate for the sender. After receiving the advertised value feedback from the receiver, the sender then uses the additive increase and multiplicative decrease (AIMD) mechanism to compute the correct congestion window size to be used. By integrating the loss-based and the delay-based congestion controls, our mechanism can mitigate the effect of wireless losses, alleviate the timeout effect, and therefore make better use of network bandwidth. Simulation and experiment results in various scenarios show that our mechanism can outperform conventional TCP in high-speed and lossy wireless environments.

Improving TCP Performance for EAST Experimental Data in the Wireless LANs

TCP is the most commonly used transport control protocol. However, its throughput and fairness performance degrades in WLANs due to the unfairness in 802.11 MAC protocol. Since more and more scientists at the EAST facility in China are relying on such set up to download and analyze their experimental data, their research productivity is severely hampered. In this paper, we propose to use a dynamical mechanism, called the AP-DDA, at the Access Point to tackle these problems. Our mechanism can decrease the number of ACKs, which in turn reduce the interference between the TCP data packets and the ACK packets, and therefore improve the channel utilization. Furthermore, fairness is enhanced by a buffer management method in addition to our delayed ACKs mechanism. Both simulation and experimental results under various scenarios show that our mechanism can have better performance than conventional methods in wireless local area networks.

Mobile-Host-Centric Transport Protocol for EAST Experiment

Some physics researchers retrieve EAST experiment data using TCP in wireless local area network (WLAN). TCP is the most commonly used transport control protocol. It assumes that every packet loss is caused by network congestion and invokes congestion control and avoidance. TCPs blind congestion control results in degraded performance in the lossy wireless networks. In a wireless network, mobile hosts have first-hand knowledge of the lossy wireless links; therefore, mobile stations can make better transmission control based on the known status of wireless link. In this paper, we proposed a new mobile-host-centric transport protocol (MCP) that integrates the characteristics of sender-centric and receiver-centric transport control schemes. MCP shifts most control policies to the mobile host side. The general behavior of MCP is similar to the TCP, but by utilizing the local information collecting from the mobile node in WLAN, MCP allows for better congestion control and loss recovery. Specifically, we designed a cross-layer implementation of MCP and ran it on NS-2. With valuable MAC (Medium Access Control) layer feedback information, MCP is able to distinguish packet loss caused by wireless random errors from network congestion more clearly and can perform a more accurate congestion control. We did extensive simulations of MCP on various WLAN scenarios, and the results show that the throughput of MCP with cross-layer feedback is higher than that of TCP Reno and Westwood.

P2P-based data system for the EAST experiment

A peer-to-peer (P2P)-based EAST data system is being designed to provide data acquisition and analysis support for the EAST superconducting tokamak. Instead of transferring data to the servers, all collected data are stored in the data acquisition subsystems locally and the PC clients can access the raw data directly using the P2P architecture. Both on-line and off-line systems are based on Napster-like P2P architecture. This allows the peer (PC) to act both as a client and as a server. A simulation-based method and a steady-state operational analysis technique are used for performance evaluation. These analyses show that the P2P technique can significantly reduce the completion time of raw data display and real-time processing on the on-line system, and raise the workload capacity and reduce the delay on the off-line system

Performance evaluation of the HT-7U data system

The HT-7U data system is being designed to support the HT-7U superconducting tokamak. For the HT-7U to achieve its mission of extremely long pulse and steady-state operation, the HT-7U data system must be flexible and robust. Corresponding to the various operation modes of the HT-7U experiment, a variety of system configurations and workload models are considered. A trace-driven simulation-based method and steady-state operational analysis technique is used for performance evaluation. These analyses show that much better performance may be obtained by applying the performance optimization techniques of fast switching networking, data compression, caching/buffering, pipelining, a real-time operating system, a real-time database, etc.

A Distributed MAC Layer Congestion Control Method to Achieve High Network Performance for EAST Experiments

Many applications would require fast data transfer in Wireless Local Area Networks (WLANs) nowadays. A representative example is the EAST (Experimental Advanced Superconducting Tokamak) project where physics researchers need to transport massive experiment data using the TCP (Transmission Control Protocol). However, the high contention level and the high error rate in wireless networks have a great impact on the TCP performance. To alleviate this problem, this paper proposes a MAC layer congestion control method to deal with wireless packet loss due to errors (as opposed to congestion). Our mechanism is implemented at the end wireless nodes based on the IEEE 802.11 DCF mechanism but without any modification to the TCP layer. We first propose the concept of the MAC layer congestion window in which the MAC layer will send all the packets in a window when it obtains access to the wireless channel (unlike the traditional DCF mechanism that just sends only one packet). Then we allow our congestion control mechanism to adjust its MAC congestion window based on the contention degree and the packet loss rate at the MAC layer. By performing wireless congestion control at the MAC layer, our mechanism can mitigate the effect of wireless packet loss on TCP, and therefore improve the TCP performance. The simulation and experiment results show that our mechanism can achieve better performance than the traditional MAC layer mechanisms in WLANs.

Receiver assistant congestion control in high speed and lossy networks

Many applications require fast data transfer in high speed wireless networks. A representative example is that EAST experiment data are retrieved by some physics researchers using the TCP (Transmission Control Protocol). However, due to the limitation in its conservative congestion control algorithm, TCP can not effectively utilize the network capacity. Furthermore, TCP assumes that every packet loss is caused by network congestion and invokes congestion control and avoidance. TCPs blind congestion control aggravates the performance degradation in high speed and lossy wireless networks. In this paper, we propose a receiver assistant congestion control mechanism (RACC), in which the sender still performs loss-based control, while the receiver performs delay-based control. The receiver measures the network bandwidth based on the interpacket delay gaps, and computes an appropriate congestion window size according to the measured bandwidth and then feedbacks the value to the sender. The sender adjusts the congestion window size based on the value informed by the receiver and the AIMD (Additive-Increase Multiplicative-Decrease) mechanism. By integrating the loss-based and delay-based congestion controls, our mechanism can mitigate the effect of wireless losses, alleviate the timeout effect, and therefore make better use of network bandwidth. The simulation results in various scenarios show that our mechanism can have better performance than conventional TCP in high speed and lossy wireless environment.

PCI/iRMX-based front-end data acquisition for the HT-7U experiment

A PCI/iRMX-based front-end system is being designed to serve as data acquisition (DAQ) subsystem for the HT-7U superconducting tokamak. The diagnostic instruments are connected to four analog-to-digital converter (ADC) boards that are directly plugged into the peripheral component interconnect (PCI) bus of a personal computer (PC) running the iRMX real-time operating system. Each ADC board has eight channels. The sampling rate of each channel can be up to 125 K samples per second. The acquired data are directly transferred from the ADC board into the memory of the PC, and then transferred to servers through the network. As a testbed, one PCI/iRMX subsystem has been built and has acquired data from the existing HT-7 tokamak. The DAQ can easily support a wide range of pulse lengths, even matching extremely long pulse and steady-state operation. This paper describes the system design and performance evaluation in detail.

A MAC layer congestion control method to achieve high network performance for EAST experiment

Many applications would require fast data transfer in Wireless Local Area Networks (WLANs). A representative example is that EAST experiment data are retrieved by some physics researchers using the Transmission Control Protocol (TCP). However, due to the high contention degree and the high error rate in wireless networks, the packets may be loss for wireless reasons but not for congestion. This will greatly degrade the TCP performance. On one hand, the wireless packet loss is not congestion, but the traditional TCP assumes that every packet drop is congestion and thus decreases its congestion window, which will degrade its performance. On the other hand, due to the MAC layer retransmission policy employed by the IEEE 802.11 DCF mechanism, the lost packets at the MAC layer will be retransmitted for some times. Thus the waiting time of the packets in the MAC layer queue will be increased. So if we ignore all the packet loss for wireless reasons as the other improved mechanisms do, the network work congestion will be aggravated and its performance will be degraded. To alleviate the impact of the wireless packet loss to TCP in WLANs, this paper proposes a MAC layer congestion control method which is implemented at the end wireless nodes based on IEEE 802.11b DCF mechanism. At first, we propose a concept of MAC layer congestion window which means the MAC layer will send all the packets in a window when it gets access to the wireless channel, other than just sends only one packet as the traditional DCF mechanism does. Then our congestion control mechanism adjusts the MAC layer congestion window based on the contention degree and the MAC layer packet loss rate. If the MAC layer contention degree or packet error rate is high, we will increase the congestion window to improve the successful transmission rate, and we will decrease the congestion window when the packet loss rate is lower than the average wireless packet loss rate. We also use a threshold to control the increase of the congestion window. The threshold is set according to the number of wireless nodes. By performing wireless congestion control at the MAC layer, our mechanism can mitigate the effect of wireless loss to TCP, and therefore improve the TCP performance. The simulation and experiment results show that our mechanism can have better performance than traditional MAC layer mechanisms in WLANs.