Proxy‐RED: an AQM scheme for wireless local area networks

Wireless access points (APs) act as bridges between wired and wireless networks. Since the actually available bandwidth in wireless networks is much smaller than the bandwidth in wired networks, there is a disparity in channel capacity which makes the access point a significant network congestion point in the downstream direction. A current architectural trend in wireless local area networks (WLAN) is to move functionality from APs to a centralized gateway in order to reduce cost and improve features. In this paper, we study the use of RED, a well known active queue management (AQM) scheme, and explicit congestion notification (ECN) to handle bandwidth disparity between the wired and the wireless interface of an access point. Then, we propose the Proxy‐RED scheme, as a solution for reducing the AQM overhead from the access point. Simulations‐based performance analysis indicates that the proposed Proxy‐RED scheme improves the overall performance of a network. In particular, the Proxy‐RED scheme significantly reduces packet loss rate and improves goodput for a small buffer, and minimizes delay for a large buffer size. Copyright © 2006 John Wiley & Sons, Ltd.     

基于显式速率的TCP友好的UDP拥塞控制策略

本文提出了一种基于显式速率的UDP拥塞控制策略：通过源端和网络中的路由器相互配合，使得实时UDP应用能够根据网络的反馈以瓶颈链路的公平带宽为速率发送数据。此种控制策略对TCP应用是友好的，并且提高了网络的吞吐量和利用率。仿真结果表明：基于显式速率的UDP拥塞控制策略与采用TFRC(TCP—Friendly Rate Control)的UDP拥塞控制策略相比，在吞吐量、TCP友好性等方面性能有较大提高。     

Multilayer multicast congestion control in satellite environments

It is well known that long and variable link delays, link errors, and handoffs in satellite environments seriously interfere with transmission control protocol's (TCP's) congestion control mechanisms. These channel characteristics also adversely affect existing multilayer multicast congestion control schemes when they are used in satellite environments. In addition, these schemes still have problems with fairly sharing bandwidth with TCP flows, controlling the overhead of frequent grafting and pruning, and handling misbehaving receivers. In this paper, we present a new multilayer multicast congestion control scheme that is suitable for satellite environments and overcomes most of the disadvantages of existing schemes. Our scheme is not affected by the long and variable delays of satellite links. Link errors also do not decrease the performance of our scheme. Further, our scheme has very limited control overhead. In addition to these advantages specific to satellite environments, our scheme achieves good fairness in sharing bandwidth with TCP sessions and is not sensitive to misbehaving receivers.     

Improved RAID 5 controller using load-balanced destage algorithm

In the existing RAID 5 controllers, destage algorithms do not take into consideration the overall performance of the disk array but rather the optimal performance at each individual disk, and this may eventually decrease the RAID performance. This authors suggest a new RAID 5 controller using a load-balanced destage algorithm adopted at the disk array level, and show that the new controller has a higher performance than existing controllers     

Congestion control in cognitive radio networks with event-triggered sliding mode

The increasing demand for assorted services from extensive wireline and wireless users place a significant burden on the band-limited radio spectrum. To settle the demand, smart reuse and management of the spectrum are necessary. In this contribution, Cognitive Radio being an emerging technology provides a platform to share the same spectrum between Primary Users (licensed) and Secondary Users (unlicensed) for significant improvement in the spectrum efficiency. The coexistence of users for data communications in a band-limited channel calls for a robust congestion controller to maximize throughput. This work presents the design of a robust nonlinear congestion controller based on event-triggered sliding mode for Cognitive Radio Networks. The goal is to maintain desired Quality of Service of the network with optimum bandwidth and resource utilization. The controller has been designed on the notions of sliding mode, better known for its inherent robustness and disturbance rejection capabilities. An event-triggering scheme has been incorporated with the sliding mode for optimum utilization of the available resources. The signal is sampled and control is updated only when a predefined condition gets violated while ensuring acceptable closed-loop behavior of the system. The efficiency of the proposed controllers has been validated using simulations.     

On network bandwidth sharing for transporting rate‐adaptive packet video using feedback

While existing research shows that feedback‐based congestion control mechanisms are capable of providing better video quality and higher link utilization for rate‐adaptive packet video, there has been relatively little study on how to share network bandwidth among competing rate‐adaptive video connections, when feedback control is used in a fully distributed network. This paper addresses this issue by presenting a framework of network bandwidth sharing for transporting rate‐adaptive packet video using feedback. We show how a weight‐based bandwidth sharing policy can be used to allocate network bandwidth among competing video connections and design a feedback control algorithm using an Available Bit Rate (ABR)‐like flow control mechanism. A novel video source rate adaptation algorithm is also introduced to decouple a video source's actual transmission rate from the rate used for distributed protocol convergence. Our feedback control algorithm provides guaranteed convergence and smooth source rate adaptation to our weight‐based bandwidth sharing policy under any network configuration and any set of link distances. Finally, we show the on‐line minimum rate renegotiation and weight adjustment options in our feedback control algorithm, which offer further flexibility in network bandwidth sharing for video connections. Copyright © 2000 John Wiley & Sons, Ltd.     

HeS‐CoP: Heuristic switch‐controller placement scheme for distributed SDN controllers in data center networks

Software‐defined networking (SDN) has been widely researched and used to manage large‐scale networks such as data center networks (DCNs). An early stage of SDN controller experienced low responsiveness, low scalability, and low reliability. To solve these problems, distributed SDN controllers have been proposed. The concept of distributed SDN controllers distributes control messages among multiple SDN controllers. However, distributed SDN controllers must assign a master controller for each networking devices. Most previous studies, however, did not consider the characteristics of DCNs. Thus, they are not suitable to operate in DCNs. In this paper, we propose HeS‐CoP, a heuristic switch‐controller placement scheme for distributed SDN controllers in DCNs. With the control traffic load and CPU load, HeS‐CoP decides when our scheme should be performed in DCNs. To show the feasibility of HeS‐CoP, we designed and implemented an orchestrator that contains our proposed scheme and then evaluated our proposed scheme. As a result, our proposed scheme well distributes the control traffic load, decreases the average CPU load, and reduces the packet delay.     

Robust congestion control in cognitive radio network using dynamic event‐triggered sliding mode

The ever‐increasing service demand from wireless users under restricted bandwidth necessitates the development of suitable congestion control scheme for throughput maximization. A robust congestion controller design has been addressed in this work to sustain necessary Quality of Service in Cognitive Radio Network. The goal is to reduce packet loss while ensuring optimum utilization of available resources. Sliding mode controller proclaimed for its disturbance rejection capabilities and robustness has been used to design the proposed controller. Using the benefits of sliding mode control, dynamic event‐triggering strategies have been combined for better utilization in resource‐constrained environments. Control execution requires minimal updates while guaranteeing the desired closed‐loop system behavior. The controller efficacy has been validated in simulations.     

Adaptive Congestion Control of mSCTP for Vertical Handover Based on Bandwidth Estimation in Heterogeneous Wireless Networks

This paper proposes a new congestion control scheme of mobile Stream Control Transmission Protocol (mSCTP) for vertical handover across heterogeneous wireless/mobile networks. The proposed scheme is based on the estimation of available bandwidths in the underlying network as a cross-layer optimization approach. For congestion control of mSCTP, the initial congestion window size of the new primary path is adaptively configured, depending on the available bandwidth of the new link that a mobile node moves into. By ns-2 simulation, the proposed scheme is compared with the existing congestion control schemes in the throughput perspective. From the numerical results, we can see that the proposed mSCTP congestion control scheme could give better performance than the existing schemes in the wireless networks with an amount of background traffic.     

Robust \mathcal{H}_{\infty} State Feedback Control of Networked Control Systems with Congestion Control

This paper examines the problem of robust state feedback control of networked control systems with a simple congestion control scheme. This simple congestion control scheme is based on comparing current measurements with last transmitted measurements. If their difference is less than a prescribed percentage of the current measurements then no measurement is transmitted to the controller. The controller always uses the last transmitted measurements to control the system. With this simple congestion control scheme, a robust $\mathcal {H}_{\infty}$ state feedback controller design methodology is developed based on the Lyapunov–Krasovskii functional approach. Sufficient conditions for the existence of delay mode dependent controllers are given in terms of bilinear matrix inequalities (BMIs). These BMIs are converted into quasi-convex linear matrix inequalities (LMIs) and solved by using the cone complementarity linearization algorithm. The effectiveness of the simple congestion control in terms of reducing the network bandwidth is elaborated using simulation examples.     

Design and evaluation of an efficient traffic control scheme for integrated voice,video, and data over asynchronous transfer mode networks: Explicit allowed rate algorithm

Asychronous transfer mode (ATM) networks are high‐speed networks with guaranteed quality of service. The main cause of congestion in ATM networks is over utilization of physical bandwidth. Unlike constant bit‐rate (CBR) traffic, the bandwidth reserved by variable bit‐rate (VBR) traffic is not fully utilized at all instances. Hence, this unused bandwidth is allocated to available bit‐rate (ABR) traffic. As the bandwidth used by VBR traffic changes, available bandwidth for ABR traffic varies; i.e., available bandwidth for ABR traffic is inversely proportional to the bandwidth used by the VBR traffic. Based on this fact, a rate‐based congestion control algorithm, Explicit Allowed Rate Algorithm (EARA), is presented in this paper. EARA is compared with Proportional Rate Control Algorithm (PRCA) and Explicit Rate Indication Congestion Avoidance Algorithm (ERICA), in both LAN and WAN environments. Simulations of all three algorithms are conducted under both congestion and fairness configurations with simultaneous generation of CBR, rt‐VBR, nrt‐VBR and ABR traffic. The results show that, with very small over‐head on the switch, EARA significantly decreases the required buffer space and improves the network throughput. Copyright © 1999 John Wiley & Sons, Ltd.     

Evolutionary Minority Game Model for Congestion Control Scheme

Telecommunication technology advances in the past decade have brought networking to another level in terms of reliability and link speeds. However, existing transmission control protocols do not provide satisfactory performance due to their inefficient congestion control mechanisms. In this paper, we propose a new congestion control scheme to provide Quality of Service provisioning while ensuring bandwidth efficiency. Based on the evolutionary minority game (EMG) model, the proposed algorithm adaptively controls the packet transmission to converge a desirable network equilibrium. For the efficient network management, the proposed EMG approach is dynamic and flexible that can adaptively respond to current network conditions. A simulation shows that our proposed scheme can approximate an optimized solution while ensuring a well-balanced network performance under widely different network environments.     

Performance management issues in ATM networks: traffic andcongestion control

The goal is first to introduce performance monitoring aspects of asynchronous transfer mode (ATM) networks and then to focus on traffic and congestion control schemes. To deal with this performance monitoring management, a framework for defining a generic intelligent and integrated model for network management is described. As an example of the efficiency of this intelligent management architecture, we measure the performance of a new congestion control scheme. This scheme uses the cell loss priority (CLP) bit, the explicit forward congestion indicator and the explicit backward congestion indicator. The intelligent management uses different parameters and builds a complex but efficient control scheme. We show that this new control scheme allows performance to be increased by an order of magnitude     

Bandwidth estimation schemes for TCP over wireless networks

The use of enhanced bandwidth estimation procedures within the congestion control scheme of TCP was proposed recently as a way of improving TCP performance over links affected by random loss. This paper first analyzes the problems faced by every bandwidth estimation algorithm implemented at the sender side of a TCP connection. Some proposed estimation algorithms are then reviewed, analyzing and comparing their estimation accuracy and performance. As existing algorithms are poor in bandwidth estimation, and in sharing network resources fairly, we propose TIBET (time intervals based bandwidth estimation technique). This is a new bandwidth estimation scheme that can be implemented within the TCP congestion control procedure, modifying only the sender-side of a connection. The use of TIBET enhances TCP source performance over wireless links. The performance of TIBET is analyzed and compared with other schemes. Moreover, by studying TCP behavior with an ideal bandwidth estimation, we provide an upper bound to the performance of all possible schemes based on different bandwidth estimates.     

The impact of imperfect scheduling on cross-Layer congestion control in wireless networks

In this paper, we study cross-layer design for congestion control in multihop wireless networks. In previous work, we have developed an optimal cross-layer congestion control scheme that jointly computes both the rate allocation and the stabilizing schedule that controls the resources at the underlying layers. However, the scheduling component in this optimal cross-layer congestion control scheme has to solve a complex global optimization problem at each time, and is hence too computationally expensive for online implementation. In this paper, we study how the performance of cross-layer congestion control will be impacted if the network can only use an imperfect (and potentially distributed) scheduling component that is easier to implement. We study both the case when the number of users in the system is fixed and the case with dynamic arrivals and departures of the users, and we establish performance bounds of cross-layer congestion control with imperfect scheduling. Compared with a layered approach that does not design congestion control and scheduling together, our cross-layer approach has provably better performance bounds,and substantially outperforms the layered approach. The insights drawn from our analyzes also enable us to design a fully distributed cross-layer congestion control and scheduling algorithm for a restrictive interference model.     

Corruption‐aware adaptive increase and adaptive decrease algorithm for TCP error and congestion controls in wireless networks

The conventional TCP tends to suffer from performance degradation due to packet corruptions in the wireless lossy channels, since any corruption event is regarded as an indication of network congestion. This paper proposes a TCP error and congestion control scheme using corruption‐aware adaptive increase and adaptive decrease algorithm to improve TCP performance over wireless networks. In the proposed scheme, the available network bandwidth is estimated based on the amount of the received integral data as well as the received corrupted data. The slow start threshold is updated only when a lost but not corrupted segment is detected by sender, since the corrupted packets still arrive at the TCP receiver. In the proposed scheme, the duplicated ACKs are processed differently by sender depending on whether there are any lost but not corrupted segments at present. Simulation results show that the proposed scheme could significantly improve TCP throughput over the heterogeneous wired and wireless networks with a high bit error rate, compared with the existing TCP and its variants. Copyright © 2008 John Wiley & Sons, Ltd.     

TCP Window Control for Variable Bandwidth in Wireless Cellular Networks

Most of TCP schemes in wireless networks assume that the bandwidth of the bottleneck link remains constant over time. However, in wireless cellular networks, to effectively manage the limited resources, the bandwidth is controlled based on radio condition over time. Such varying bandwidth can cause the networks congestion or underutilization. In this letter, we propose a new window control algorithm to improve TCP performance in wireless cellular networks with variable bandwidth. Simulation results illustrate that our proposal improves the performance of TCP in terms of fairness and link utilization     

Queue length‐based load balancing in data center networks

Traffic load balancing in data centers is an important requirement. Traffic dynamics and possibilities of changes in the topology (e.g., failures and asymmetries) make load balancing a challenging task. Existing end‐host–based schemes either employ the predominantly used ECN or combine it with RTT to get congestion information of paths. Both congestion signals, ECN and RTT, have limitations; ECN only tells whether the queue length is above or below a threshold value but does not inform about the extent of congestion; similarly, RTT in data center networks is on the scale of up to few hundreds of microseconds, and current data center operating systems lack fine‐grained microsecond‐level timers. Therefore, there is a need of a new congestion signal which should give accurate information of congestion along the path. Furthermore, in end‐host–based schemes, detecting asymmetries in the topology is challenging due to the inability to accurately measure RTT on the scale of microseconds. This paper presents QLLB, an end‐host–based, queue length–based load balancing scheme. QLLB employs a new queue length–based congestion signal that gives an exact measure of congestion along the paths. Furthermore, QLLB uses relative‐RTT to detect asymmetries in the topology. QLLB is implemented in ns‐3 and compared with ECMP, CONGA, and Hermes. The results show that QLLB significantly improves performance of short flows over the other schemes and performs within acceptable level, of CONGA and Hermes, for long flows. In addition, QLLB effectively detects asymmetric paths and performs better than Hermes under high loads.     

Class-Based Service Connectivity Using Multi-level Bandwidth Adaptation in Multimedia Wireless Networks

Due to the fact that quality of service requirements are not very strict for all traffic types, more calls of higher priority can be accommodated by reducing some bandwidth allocation for the bandwidth adaptive calls. The bandwidth adaptation to accept a higher priority call is more than that of a lower priority call. Therefore, the multi-level bandwidth adaptation technique improves the overall forced call termination probability as well as provides priority of the traffic classes in terms of call blocking probability without reducing the bandwidth utilization. We propose a novel bandwidth adaptation model that releases multi-level of bandwidth from the existing multimedia traffic calls. The amount of released bandwidth is decided based on the priority of the requesting traffic calls and the number of existing bandwidth adaptive calls. This prioritization of traffic classes does not reduce the bandwidth utilization. Moreover, our scheme reduces the overall forced call termination probability significantly. The proposed scheme is modeled using the Markov Chain. The numerical results show that the proposed scheme is able to provide negligible handover call dropping probability as well as significantly reduced new call blocking probability of higher priority calls without increasing the overall forced call termination probability.     

Improving TCP performance with fast adaptive congestion control during soft vertical handoff

Recently, the research on the interworking between 3G cellular networks and WLANs is actively being constructed. To integrate these two technologies, there are many issues such as the network architecture, mobility management, and security which should be solved. During vertical handoff, some undesirable phenomena may mistakenly trigger TCP congestion control operations and thus degrade TCP performance. In this paper, we propose an approach that can quickly estimate available bandwidth when a mobile node (MN) handoff occurs. A sender updates the adaptive slow-start threshold (ssthresh) and congestion window size (cwnd) to improve TCP performance during soft vertical handoff in hybrid mobile networks. Our scheme requires only minor modifications of the transport layer of the end hosts. Simulation results show that our scheme effectively improves the TCP performance.