Hancheng Lu

A Novel Buffer Mechanism for Fast Handovers in Mobile IPv6

The anticipation time has a significant impact on the performance of fast handover, especially predictive fast handover. Predictive fast handover which generally outperforms reactive fast handover requires a sufficient anticipation time to complete necessary operations before the current network is broken. However, the anticipation time may spur packets for the mobile node (MN) to be forwarded to the new access router (NAR) while the MN is still connected to the previous access router (PAR). These packets are either delayed in the NARs buffer or lost. To address such problem, in this paper, we propose a link triggered buffer mechanism (LT-buffer). The basic idea behind the LT-buffer is to utilize the advantage of cross-layer interactions between the link layer and the network layer so that the delay time for packets in the buffer can be reduced. Moreover, the LT-buffer mechanism can trigger buffering on the PAR to reduce packet loss in reactive fast handover. Finally, we evaluate the effect of the LT-buffer.

Packet size optimization in delay tolerant networks

Studies have shown that the size of the transmitted packet has a significant impact on the performance of wireless networks, especially those in challenged environments such as Delay Tolerant Networks (DTNs) where bandwidth is a precious resource. In order to improve the end-to-end goodput in DTNs, segment size at the convergence layer and bundle size at the bundle layer are jointly optimized in this paper. Different from existing work that only performs experimentations to find the optimal packet size in single-hop DTNs, our work focuses on the theoretic analysis and formulates the relationship between packet size at two layers (i.e., the convergence layer and the bundle layer) and the performance metrics (i.e., delay, goodput) of single-hop and multi-hop DTNs. The analysis not only confirms the existence of the optimal packet size, but also quantitatively shows that the optimal packet size is determined by the number of hops, wireless channel conditions in DTNs. Furthermore, a novel Packet Size Optimization Algorithm (PASO) is proposed, in which segment size and bundle size are jointly adjusted to maximize the goodput in multi-hop DTNs. Compared with schemes where joint packet size optimization is not considered, PASO can achieve average 15% more goodput in typical DTN environments where channel conditions are usually assumed to be poor.

VNE-RFD: Virtual network embedding with resource fragmentation consideration

Virtual Network Embedding (VNE) is one of the critical techniques in network virtualization. In this paper, we attempt to improve the performance of VNE in terms of acceptance ratio of Virtual Network (VN) requests by considering resource fragmentation in a substrate network. Different from existing work, we involve a new metric called Resource Fragmentation Degree (RFD) to quantitatively measure the status of resource fragmentation at substrate nodes and links. The definition of RFD is derived from the conception of connectivity in graph theory. Actually, RFD of a node (or a link) is only determined by residual resources at its neighbor nodes and adjacent links. Thus it can be derived efficiently. For a node (or a link), maximum RFD is reached when either all of its neighbor nodes or all of its adjacent links are running out of resources. In this case, resources at the node (or the link) are entirely fragmented. With consideration of RFD, we then formulate the problem of VNE as a mixed integer program. The optimization objective includes minimizing fragmented resources indicated by RFD in the substrate network. Finally, an online algorithm called VNE-RFD is proposed to solve the problem. Simulation results show that VNE-RFD can effectively reduce resource fragmentation and thus accept more VN requests compared with some existing algorithms.

NBK: A Novel Neighborhood Based Key Distribution Scheme for Wireless Sensor Networks

Location information has been found useful in the design of key pre-distribution schemes in Wireless Sensor Networks (WSNs). In this paper, a novel key management scheme based on location is proposed to enhance the security of the wireless sensor networks. We get the idea from the previous location-based key (LBK) scheme but here the location of a sensor node is described by its neighbors logical identifiers (IDs). Through an improved authentic process between the sensor nodes, no other special infrastructures are needed to establish pair-wise keys. Further more, the scheme has a bigger probability of key establishment with a lower storage overhead, and it is suited for large scale wireless sensor networks.

Security improvement on an efficient key distribution mechanism for large-scale Wireless Sensor Network

The key issue for WSN (wireless sensor network) is designing viable security mechanisms for the protection of confidentiality, integrity and authentication to prevent malicious attacks, but with nodespsila limited capabilities. Recently, Cheng proposed an efficient key distribution mechanism for large scale wireless sensor network based on hierarchical topology. In this paper, we show that Chengpsilas scheme is vulnerable to the node capture attack. Then a security modification of the original scheme will be proposed, which can withstand the node capture attack.

Practical Wireless Network Coding with Constrained Decoding Buffers

Abstract- In practical wireless network coding, each node cach-es relayed packets and overheard packets in a buffer for decoding. This buffer is defined as decoding buffer. Relay nodes determine whether network coding can be performed according to cached packets in decoding buffers at their neighbors. This paper analyzes coding performance with constrained decoding buffers. Theoretical results in terms of average encoding number, network throughput and packet loss ratio are given for a line-type or X coding structure. Moreover, the effect of scheduling policies and bandwidth allocation on coding performance are also analyzed. Coding performance and the optimal bandwidth allocation are evaluated and discussed with numerical results.

Differentiated Bandwidth Allocation for Reducing Server Load in P2P VOD

P2P technology offers a promising scalable solution for Video-on-demand (VOD) service. Recent studies have found that departure misses are the major cause of server load in P2P-based VOD. Inspired by this finding, this paper addresses the design of bandwidth allocation policy to decrease departure misses and thereby reduce server load further. We first formulate the minimum departure misses problem. Then we propose a centralized algorithm which serves as our benchmark for all other schemes. The centralized algorithm makes use of surplus bandwidth to help peers prefetch chunks, thus reducing departure misses significantly. We then propose a distributed bandwidth allocation algorithm in which a stable peer with higher playback position is able to obtain a larger share of parents’ upload bandwidth. A simple predictor is developed for stable node identification. Simulation results show that our distributed protocol outperforms traditional approach, and close to the centralized one.

A Novel Bandwidth Estimation Scheme Used in Admission Control for Wireless Mesh Networks

An accurate estimation of the available bandwidth of mesh nodes is the essential prerequisite of admission control mechanism, which provides QoS assurance in wireless mesh networks. Existing bandwidth estimation schemes do not accurately consider the influence of parallel transmission due to spatial reuse and act overly conservative. In this study, we proposed an accurate bandwidth estimation scheme, the BEPTC (Bandwidth Estimation with Parallel Transmission Consideration), to reduce the parallel transmission caused estimation accuracy by solving the maximum clique problem in graph theory. The scheme is integrated into an admission control mechanism used in a hop-by-hop routing protocol (AODV). The simulation results demonstrate that the admission control mechanism based on BEPTC can effectively control the traffic load and offer QoS guarantee for admitted new flows, which can lead the network to accommodate more flows with QoS guarantee and obtain higher system throughput compared with other conservative approaches.

Viewing experience optimization based on adaptive requesting window adjustment in peer-to-peer media streaming

In the last few years, great achievements have been made in the field of peer-to-peer (P2P) streaming system. In mesh-based P2P streaming system, retrieving data from multiple parents simultaneously improves resilience of the streaming service. However, it also brings in playback lags. To improve users viewing experiences, we should consider both playback lags and resilience of the streaming service. However, it seems there is a natural trade-off between these two goals. In this paper we propose a viewing experience optimization algorithm which adjusts the position of the requesting window adaptively based on different requesting strategies. The novelty of the proposed method is that it utilizes heterogeneous real-time demands for different genres of videos, and can adjust requesting strategies adaptively. Under the condition of guaranteeing basic QoS (Quality of Service), the algorithm achieves a balance between playback lags and resilience. Finally, experiment results show the satisfactory performance of the proposed method.

Region Topology Based Route Design for Multiple Ferries in DTNs

In Delay Tolerant Networks (DTNs), message ferries exploit controlled mobility to forward messages following specific routes. One of the key challenges is how to design ferry routes to achieve desired connectivity properties and store-and-forward performance. There are some attempts at designing appropriate ferry routes, but the region topology, which denotes the adjacency relationships of ferry regions and affects the message forwarding efficiency among different ferry regions, has not been draw attention. The concept of ferry region indicates the region which a ferry route covers. In this paper, we concentrate on the Region Topology based Route Design (RTRD) for multiple ferries. RTRD dose not design the details of specific routes for each ferry independently, instead, it focuses on the interactivity of neighbor-ferries and aims to get appropriate region topologies of ferries. We analyze message delivery delay and buffer requirement in typical region topologies - Grid, Cellular and Wheel. The results show that the region topology has a significant impact on network performance, and with given performance requirements, an appropriate region topology should be chosen before designing the route details of ferries.