Jiawei Huang

A cross‐layer TCP for providing fairness in wireless mesh networks

The fair allocation of resources among different nodes is one of the critical problems in wireless mesh networks. Existing solutions mainly focus on rate-limitation policies or distributed fair MAC schemes at the potential expense of total network utilization. This paper investigates a special starvation problem among TCP flows that are different hops away from the BS, as well as its recently proposed solution, the ‘Minimum Content Window’ policy based on IEEE 802.11e. It is found that the aggregate throughput degrades sharply because the effect of this policy on the TCP congestion mechanism has been overlooked. This paper proposes a priority-based congestion control by using ‘Cross-Layer Explicit Congestion Notification’. Analysis and simulation results demonstrate that our scheme can improve the fairness of TCP flows while the aggregate throughput is at least 20% higher than the ‘Minimum Content Window’ policy. Copyright

Vehicle Density Based Forwarding Protocol for Safety Message Broadcast in VANET

In vehicular ad hoc networks (VANETs), the medium access control (MAC) protocol is of great importance to provide time-critical safety applications. Contemporary multihop broadcast protocols in VANETs usually choose the farthest node in broadcast range as the forwarder to reduce the number of forwarding hops. However, in this paper, we demonstrate that the farthest forwarder may experience large contention delay in case of high vehicle density. We propose an IEEE 802.11-based multihop broadcast protocol VDF to address the issue of emergency message dissemination. To achieve the tradeoff between contention delay and forwarding hops, VDF adaptably chooses the forwarder according to the vehicle density. Simulation results show that, due to its ability to decrease the transmission collisions, the proposed protocol can provide significantly lower broadcast delay.

Adaptive explicit congestion control based on bandwidth estimation for high bandwidth-delay product networks

Abstract Existing congestion control protocols for high bandwidth-delay product (HBDP) networks either suffer from efficiency degradation caused by insufficient feedback of the network state, or are difficult to deploy in real networks because they require modification in IP header to provide enough feedback information. Based on VCP, this paper proposes the VCP-BE protocol that can provide more accurate network state information by estimating available bandwidth for sender with an adaptive bandwidth estimator. The estimator can dynamically adjust its parameters (e.g., observing interval) to achieve different accuracy and responsiveness to adapt to the network state indicated by two ECN bits, without no more modification in IP header than VCP. Furthermore, when the network load is high, VCP-BE calculates the ratio of current throughput to the available bandwidth to judge if network is close to the overload state. With these fine-grained network state estimation, VCP-BE can adjust the congestion window more precisely than VCP, thus greatly improves its convergence speed of achieving high bandwidth utilization and fairness. Simulation results show that VCP-BE also outperforms MLCP, which uses seven bits for explicit feedback while VCP-BE only uses two ECN bits.

A buffer management algorithm for improving up/down transmission congestion protocol fairness in IEEE 802.11 wireless local area networks

SUMMARY The fair allocation of the resources is an important issue in wireless local area network (WLAN) because all wireless nodes compete for the same wireless radio channel. When uplink and downlink transmission congestion protocol (TCP) flows coexist in WLAN, the network service is biased toward the uplink TCP flows, and the downlink TCP flows tend to starve. In this article, we investigate the special up/down TCP unfairness problem and point out that the direct cause is the uplink acknowledgement (ACK) packets occupy most buffer space of access point. We thus propose a buffer management algorithm to ensure the fairness among uplink and downlink TCP flows. In order to limit the greedy behavior of ACK packets, the proposed algorithm adjusts the maximum size of buffer allocated for the ACK packets. Analysis and simulation results show that the proposed solution not only provides the fairness but also achieves 10–20% lower queue delay and higher network goodput than the other solutions. Copyright

Performance Enhancement of Multipath TCP for Wireless Communications With Multiple Radio Interfaces

Multipath transmission control protocol (MPTCP) allows a TCP connection to operate across multiple paths simultaneously and becomes highly attractive to support the emerging mobile devices with various radio interfaces and to improve resource utilization as well as connection robustness. The existing multipath congestion control algorithms, however, are mainly loss-based and prefer the paths with lower drop rates, leading to severe performance degradation in wireless communication systems, where random packet losses occur frequently. To address this challenge and improve the performance of MPTCP in wireless networks, this paper proposes a new mVeno algorithm, which makes full use of the congestion information of all the subflows belonging to a TCP connection in order to adaptively adjust the transmission rate of each subflow. Specifically, mVeno modifies the additive increase phase of Veno so as to effectively couple all subflows by dynamically varying the congestion window increment based on the receiving ACKs. The weighted parameter of each subflow for tuning the congestion window is determined by distinguishing packet losses caused by random error of wireless links or by network congestion. We implement mVeno in a Linux server and conduct extensive experiments both in test bed and in real WAN to validate its effectiveness. The performance results demonstrate that compared with the existing schemes, mVeno increases the throughput significantly, achieves load balancing, and can keep the fairness with regular TCP.

Adaptive-Acceleration Data Center TCP

Providing deadline-sensitive services is a challenge in data centers. Because of the conservativeness in additive increase congestion avoidance, current transmission control protocols are inefficient in utilizing the super high bandwidth of data centers. This may cause many deadline-sensitive flows to miss their deadlines before achieving their available bandwidths. We propose an Adaptive-Acceleration Data Center TCP, A2DTCP, which takes into account both network congestion and latency requirement of application service. By using congestion avoidance with an adaptive increase rate that varies between additive and multiplicative, A2DTCP accelerates bandwidth detection thus achieving high bandwidth utilization efficiency. At-scale simulations and real testbed implementations show that A2DTCP significantly reduces the missed deadline ratio compared to D2TCP and DCTCP. In addition, A2DTCP can co-exist with conventional TCP as well without requiring more changes in switch hardware than D2TCP and DCTCP.

Packet Slicing for Highly Concurrent TCPs in Data Center Networks with COTS Switches

Modern data center nowadays leverages highly concurrent TCP connections between thousands of computer servers to achieve high system performance and service reliability. However, recent works have shown that, in the many-to-one and barrier-synchronized communication pattern, a large number of concurrent TCP connections suffer the TCP Incast problem due to packet drops in shallow-buffered Ethernet switches. This problem unavoidably leads to severe under-utilization of link capacity. In this work, we first reveal theoretically and empirically that controlling the IP packet size reduces the Incast probability much more effectively than controlling the congestion windows in the presence of severe congestion. We further present the design and implementation of Packet Slicing, a general supporting scheme that adjusts the packet size through a standard ICMP signaling method. Our method can be deployed on commodity switches with small firmware updates, while making no modification on end hosts. Another highlight of our work is Packet Slicings broad applicability and effectiveness. We integrate Packet Slicing transparently (i.e., without modification) with three state-of-the-art TCP protocols designed for data centers on NS2 simulation and a physical testbed, respectively. The experimental results show that Packet Slicing remarkably improves network goodput across different TCP protocols by average 26× under severe congestion, while introducing little I/O performance impact on both switches and end hosts.

A Congestion Level based end-to-end acknowledgement mechanism for Delay Tolerant Networks

End-to-end reliability in Delay Tolerant Networks (DTNs) is challenging and complicated because of high delay and absence of stable end-to-end path in the intermittently-connected mobile environment. Some existing acknowledgement mechanisms use active forwarding to provide the end-to-end reliability, while incurring excessive retransmissions or replications. The other passive mechanisms aim to reduce the storage overhead but may suffer a large delay. To improve the storage-delay tradeoff, we propose a Congestion Level based end-to-end ACKnowledgement (CL-ACK) mechanism, which adaptively adjusts the spread manner of ACK packets according to the ratio of drops over replications. Simulation results show that CL-ACK effectively controls resources consumption, reduces end-to-end delay, and achieves high message delivery rate.

Adaptive marking threshold method for delay-sensitive TCP in data center network

Due to the highly dynamic traffic load, providing delay-sensitive services is a challenge in data centers. Many recent transport protocols, such as DCTCP, D 2 TCP , and L2DCT, use Explicit Congestion Notification (ECN) to control the switch queue length for achieving low-latency transmission. However, the original ECN marking threshold fails to make real-time tradeoff between bottleneck link utilization and queueing delay, thereby increasing the flow completion time. In this paper, we propose Adaptive Marking Threshold (AMT), which proactively tunes the marking threshold to eliminate the unnecessary queueing delay, and maintains high link utilization at the same time. The experimental results of NS2 simulation and physical testbed show that AMT significantly reduces the flow completion time of typical applications across different network scenarios with negligible change in the data center switch.

ECN-Based Congestion Probability Prediction over Hybrid Wired-Wireless Networks

Network congestions and wireless link errors are both potential reasons for packet losses in hybrid wired-wireless networks. Their coexistence necessitates the design of new mechanisms that can differentiate network states more precisely. In this paper, a method is proposed to distinguish between the two reasons of packet losses in hybrid wired-wireless networks (i.e., congestions and wireless link errors) and calculate the probability of network congestion in the former case. This method combines the information contained in CE bits of a sequence of ECN-enabled acknowledge packets to calculate the probability of network congestion; thus it is more accurate than methods using CE bits of a single acknowledge packet. Analysis on the effectiveness of the proposed method in calculating congestion probability is performed via simulations. The ability to differentiate precise network states helps a TCP source response to ECN feedback more adaptively. We discuss how to enhance existing TCP variants with the proposed method. Simulation results show that the enhanced TCP variants can effectively improve network performance.