Xianghui Liu

Requirements of Quality of Service in Wireless Sensor Network

Sensor networks are distributed networks made up of small sensing devices equipped with processors, memory, and short-range wireless communication. They differ from traditional computer networks in that they have resource constraints, unbalanced mixture traffic, data redundancy, network dynamics, and energy balance. Work within wireless sensor networks (WSNs) Quality of service (QoS) has been isolated and specific either on certain functional layers or application scenarios. However the area of sensor network quality of service (QoS) remains largely open. In this paper we define WSNs QoS requirements within a WSNs application, and then analyzing Issues for QoS Monitoring.

Using passive measuring to calibrate active measuring latency

The network performance obtained from the active probe packets is not equal to the performance experienced by users. We can obtain more exact result by using the characteristics of packets gained by passive measuring to calibrate the result of active measuring. The method of combining passive and active approaches has some advantages such as protocol-independent, negligible extra traffic, convenience and being able to estimate individual user performance. Considering the number of user data packets arriving between probe packets and the latency alteration of neighborhood probe packets, we propose the Pcoam (Passive Calibration of Active Measurement) method. It could reflect the actual network status more exactly, especially in the case of network congestion and packet loss, which has been validated by simulation.

Efficiently monitoring link bandwidth in IP networks

Link bandwidth utilization is obviously critical for numerous network management tasks. Using the flow-conservation law, we could reduce the number of activated monitor agents. The problem of efficiently monitoring link-bandwidth based on flow-conservation law could be reduced to weak vertex cover problem, which is NP-hard. In this paper, we demonstrate an approximation preserving reduction from the vertex cover problem to weak vertex cover problem. Due to this reduction, it follows that it is very difficult to get an approximation algorithm with approximation ratio lower than 2 for weak vertex cover problem. Using the primal-dual method, we give an approximation algorithm with approximation ratio 2 to solve the problem. The effectiveness of our monitoring algorithm is validated by simulations evaluation over a wide range of network topologies. We also demonstrate the problem of weak vertex cover with blackout vertices could be reduce to weak vertex cover problem. Hence we could use the approximation algorithms for weak vertex cover problem to solve the problem of weak vertex cover with blackout vertices.

On the placement of active monitor in IP network

There is increasing interest in concurrent active measurement at multiple locations within an IP network. In this paper, we consider the problem of where to place monitors within the network and how to make measurement strategy of each monitor which edges in its measurement tree are measured by the monitor. To address the tradeoff between measurement cost and measurement coverage, we consider several optimization problems on the placement of network monitor. We show that all of the defined problems are NP-hard and propose approximation algorithm to these problem.

Efficiently Link Scheduling in Wireless Sensor Network

In wireless sensor network, given a collection of source-destination pairs {(si,ti)}, how can we schedule the packet through link in wireless sensor network which can transfer data from the sources to their corresponding destinations efficiently? There are many factors effecting this question and this problem is non-trivial to solve in the case of wireless sensor networks due to interference. In this paper we focus on the problem of efficiently link scheduling algorithm in wireless sensor networks with interference

Passive calibration of active measuring latency

Network performance obtained from the active probe packets is not equal to the performance experienced by users. To gain more exact result, the characteristics of packets gained by passive measuring are utilized to calibrate the result of active measuring. Taking the number of user data packets arriving between probe packets and the latency alteration of neighborhood probe packets into account, we propose the Pcoam (Passive Calibration of Active Measurement) method. The actual network status could be reflected more exactly, especially when the network is in congestion and packet loss. And the improvement has been validated by simulation.

An approximation algorithm for weak vertex cover problem in network management

Link-bandwidth utilization and flow information are obviously critical for numerous network management tasks. The problem of efficiently monitoring the network flowing based on flow-conservation could be reduced to Weak Vertex Cover problem, which is NP-hard. In this paper, using the primal-dual method, we give an approximation algorithm with approximation ratio 2 to solve the problem. It is a near-optimal algorithm as it is very difficult to get an approximation algorithm with approximation ratio lower than 2 for Weak Vertex Cover problem. The effectiveness of our monitoring algorithm is validated by simulations evaluation over a wide range of network topologies. The practices indicate that our work is valuable to solve Weak Vertex Cover problem and its application in network management.

Efficiently passive monitoring flow bandwidth

Using the flow-conservation law, we could reduce the number of activated monitor agents used to monitor link bandwidth usage. In this paper, we address the problem of efficiently passive monitoring flow bandwidth based on flow-conservation, which could be reduced to weak vertex cover problem. And the weak vertex cover problem is NP-hard. We give an approximation algorithm with approximation ratio 2 to solve the problem. The effectiveness of our monitoring algorithm is validated by simulations evaluation over a wide range of network topologies.

Distributed active measuring link bandwidth in IP networks

Link bandwidth is obviously critical for numerous network management tasks. Taking into account the issues of measuring costs and network-wide view for large IP network, a distributed measuring system would be an ideal monitoring architecture for active measuring link bandwidth. In this paper, we address the problem of efficiently measure assignment, which optimizing goal is to reduce the cost of measuring all links bandwidth. We show that this problem is NP-hard and propose an approximation algorithm with approximation ratio 2. The effectiveness of our measuring algorithm is validated by simulations evaluation over a wide range of network topologies.

Optimizing the Distributed Network Monitoring Model with Bounded Bandwidth and Delay Constraints by Neural Networks

Designing optimal measurement infrastructure is a key step for network management. In this work the goal of the optimization is to identify a minimum aggregating nodes set subject to bandwidth and delay constraints on the aggregating procedure. The problem is NP-hard. In this paper, we describe the way of using Hopfield networks for finding aggregating nodes set. The simulation indicates that Hopfield networks can produce much better result than the current method of randomly picking aggregating nodes.