Lianfang Zhang

Multipath source routing in wireless ad hoc networks

We propose a new multipath routing protocol for ad hoc wireless networks-multipath source routing (MSR), which is based on DSR (dynamic source routing). MSR extends DSRs route discovery and route maintenance mechanism to deal with multipath routing. Based on the measurement of RTT, we propose a scheme to distribute load between multiple paths. The simulation results show that our approach improves the throughput of TCP and UDP and the packet delivery ratio, and reduces the end-to-end delay and the queue size, while adding little overhead. As a result, MSR decreases the network congestion quite well.

Adaptive multipath source routing in ad hoc networks

In this paper, we propose a new multipath routing protocol for ad hoc wireless networks-multipath source routing (MSR), which is an extension of DSR (dynamic source routing). Based on the measurement of RTT, we propose a scheme to distribute load among multiple paths. The simulation results show that our approach improves the packet delivery ratio and the throughput of TCP and UDP, and reduces the end-to-end delay and the average queue size, while adding little overhead. As a result, MSR decreases the network congestion and increases the path fault tolerance quite well.

Traffic prediction using FARIMA models

Previous traffic measurements have found the coexistence of both long-range and short-range dependence in network traffic. Therefore, models are required to predict traffic that has both long-range and short-range dependence. This paper provides a procedure to model and predict traffic using FARIMA (p,d,q) models. Our experiments illustrate that the FARIMA model is a good model and is capable of capturing the property of actual traffic. We provide guidelines to simplify the FARIMA model fitting procedure and thus to reduce the time of traffic modeling and prediction.

Backup Routing for Multimedia Transmissions over Mesh Networks

A significant issue in mesh networks is to support multimedia transmissions while providing quality of service (QoS) guarantees to mobile users. For real-time multimedia streaming, unstable throughput or insufficient bandwidth will incur unexpected delay or jitter, and it remains difficult to provide comprehensive service guarantees for wireless mesh environment. In this paper, we target the problem of providing multimedia QoS in wireless mesh networks. We have designed and implemented a campus wireless mesh network testbed, and propose an available bandwidth estimation algorithm plus a QoS backup route mechanism to accommodate multimedia traffic flows in mobile wireless mesh networks. Moreover, to validate the correctness of our proposed algorithm, we have implemented the algorithm on the campus wireless mesh network testbed. Our implementation and experiments show that our mechanisms can improve the network stability, throughput, and delivery ratio effectively, while decreasing the number of route failures.

Energy-efficient rate adaptation for outdoor long distance WiFi links

WiLD (WiFi-based Long Distance) mesh networks have been broadly deployed for bringing extremely low-cost IT revolution to developing regions. However, external WiFi/non-WiFi interferences severely aggravate network performance. Besides, over-provisioning transmission power without considering the channel dynamics and interferences can result in unnecessary energy consumption, which will eventually lead to the network outage. In this paper, an energy efficient rate adaptation algorithm is proposed for WiLD links. It adopts an online measurement of FDR (Frame Delivery Ratio)-RSSI mapping to choose bit rate based on the joint considerations of RSSI and transmission power. Moreover, a novel algorithm called CNP-CUSUM (Continuous Non-Parameter-Cumulative Sum) is presented to detect changes of external interference intensity at receivers by leveraging beacon loss ratio statistics. Our simulation results show that it significantly outperforms fixed bit-rate, fixed transmission power schemes by achieving higher energy efficiency and considerable link throughput gain.

Flow-Level Multipath Load Balancing in MPLS Network

Multi-Protocol Label Switching (MPLS) can efficiently support the explicit routes setup by the use of Label Switched Paths (LSPs) between an ingress Label Switched Router (LSR) and an egress LSR. Hence it is possible to distribute the network traffic among several paths to achieve load balancing, thus improving the network utilization, and minimizing the congestion. The packet-level traffic characteristics in the Internet is so complex that it is natural to do traffic engineering (TE) and control at the flow level. The emerging Multi-Protocol Label Switching (MPLS) has introduced an attractive solution to TE in IP networks. The main objective of this paper is to balance traffic at the flow level among the parallel Label Switched Paths (LSPs) in MPLS networks. We introduce a multipath load-balancing model at the flow level. In this model, each LSP is modeled as an M/G/1 processor-sharing queue. The load-balancing problem is then considered as an optimization problem. Based on the analysis of the model, we propose a heuristic but efficient mechanism that can make good use of the traffic characteristics at the flow level. Packet disorder is avoided effectively by dispatching packets belonging to one flow to the same path. This mechanism only need to be implemented in the ingress LSRs and the egress LSRs, while the intermediate LSRs only forward the packets. Apart from discussing the traffic allocation granularity, and the implementation issues in details, we have also performed extensive simulations using NS-2 with MPLS modules. The simulation results show that the load through the network is well balanced so that the network throughput is improved and the delay is decreased efficiently.

Flow-level multipath load balancing in MPLS network

The packet-level traffic characteristics in the Internet are so complex that it is natural to do traffic engineering (TE) and control at the flow level. The emerging multi-protocol label switching (MPLS) has introduced an attractive solution to TE in IP networks. The main objective of this paper is to balance traffic at the flow level among the parallel label switched paths (LSPs) in MPLS networks. We first introduce a multipath load-balancing model at the flow level. In this model, each LSP is modeled as an M/G/1 processor-sharing queue. Based on the analysis of the model, we propose a heuristic but efficient mechanism that is implemented only at the ingress label switched routers (LSRs) and egress LSRs in the network. Extensive simulations using NS2 are performed with MPLS modules. The simulation results show that the load through the network is well balanced so that the network throughput is improved and the delay is decreased significantly.

Fast track article: A multi-layer experimental study of multimedia and QoS communication in wireless mesh networks

A significant issue in Mesh networks is to support multimedia transmissions while providing Quality of Service (QoS) guarantees to mobile users. For real-time multimedia streaming, unstable throughput or insufficient bandwidth will incur unexpected delay or jitter, and it remains difficult to provide comprehensive service guarantees for a wireless mesh environment. In this paper, we target the problem of providing multimedia QoS in wireless mesh networks. We design and implement a campus test-bed for supporting multimedia traffic in mobile wireless mesh networks, and investigate in detail some possible improvements on a number of layers to enable multimedia transmission over wireless networks with QoS support. We first study a number of improvements of some existing routing protocols to support multimedia transmissions. Some new admission control and rate control mechanisms are studied and their performance gains are verified in our experiments. In our new cross-layer adaptive rate control (CLARC) mechanism, we adaptively change the video encoders output bit rate based on the available network bandwidth to improve the quality of the received video. We also design a mobile gateway protocol to connect the MANET to Internet and a wireless LAN management protocol to automatically manage WLAN to provide some QoS.

A fast clustering algorithm based on grid and density

The efficiency of data mining algorithms is a very important issue as data becoming larger and larger. Density-based clustering analysis can discover clusters with arbitrary shape and is insensitive to noise data. The advantage of grid-based clustering method is linear time complexity. In this paper, we present a new clustering algorithm CLUGD relying on grid and density. We first construct a grid of relevant portion. Then the algorithm finds references by grid and classifies these references to core references and bound references. Then it attaches the data of the bound references to the nearest core references and aggregation the core references in neighboring portions. At last, in-direct graph is used to classify these core references and maps cluster to original data. We performed an experimental evaluation of effectiveness and efficiency of CLUGD using synthetic data and the data of the SEQUOIA 2000 Benchmark. Both theory analysis and experimental results confirm that CLUGD can discover clusters with arbitrary shape and is insensitive to noise data. In the meanwhile, its executing efficiency is much higher than DBSCAN algorithm based on R*-tree

Collaborative learning system based on wireless mobile equipments

With the popularization of wireless mobile equipment, long distance education based on such equipment, e.g., PDAs, attracts increasing attention. However, two problems are: how to transform current Web pages to display correctly on PDA; how to deal with long distance discussions between PDA users and PC users. We have developed a mobile learning system, composed of a collaborative learning model and a network agent service model. The system can be deployed over a heterogeneous network of mobile wireless devices and wired devices, ranging from PDAs to desktop PCs. The collaborative learning system, based on traditional C/S (client-server) architecture, includes some basic discussion tools. The client side is implemented in the form of an applet, which can communicate with the server side located on the Web server. Teachers and students can communicate through the Web page browsers of PDAs or PCs. The network agent service model, which acts as an HTTP agency, can transform the text and images in HTML pages into an appropriate size and format that can be displayed by the PDA browser, according to the size of its screen. The architecture and framework of the mobile learning system, which includes some key technologies, such as the realization of image conversion, is introduced. We demonstrate the use and effect of the system in the context of long distance education.