Nor Asilah Wati Abdul Hamid

An Enhanced A-MSDU Frame Aggregation Scheme for 802.11n Wireless Networks

The main goal of the IEEE 802.11n standard is to achieve a minimum throughput of 100 Mbps at the MAC service access point. This high throughput has been achieved via many enhancements in both the physical and MAC layers. A key enhancement at the MAC layer is frame aggregation in which the timing and headers overheads of the legacy MAC are reduced by aggregating multiple frames into a single large frame before being transmitted. Two aggregation schemes have been defined by the 802.11n standard, aggregate MAC service data unit (A-MSDU) and aggregate MAC protocol data unit (A-MPDU). As a consequence of the aggregation, new aggregation headers are introduced and become parts of the transmitted frame. Even though these headers are small compared to the legacy headers they still have a negative impact on the network performance, especially when aggregating frames of small payload. Moreover, the A-MSDU is highly influenced by the channel condition due mainly to lack of subframes sequence control and retransmission. In this paper, we have proposed an aggregation scheme (mA-MSDU) that reduces the aggregation headers and implements a retransmission control over the individual subframes at the MSDU level. The analysis and simulations results show the significance of the proposed scheme, specifically for applications that have a small frame size such as VoIP.

A cluster-based proxy mobile IPv6 for IP-WSNs

The Sensor Proxy Mobile IPv6 (SPMIPv6) has been designed for IP-based wireless sensor networks mobility to potentially save energy consumption by relieving the sensor nodes from participating in the handoff process. However, SPMIPv6 is dependent on a single and central Local Mobility Anchor (LMA), and thus, it inherited most of the problems observed in the Proxy Mobile IPv6 (PMIPv6) protocol, including long handoff latency, non-optimized communication path, and bottleneck issues. In addition, SPMIPv6 extends the single point of failure to include both the authentication and network information. This study presents an enhanced architecture for SPMIPv6 called Clustered SPMIPv6 (CSPMIPv6) to overcome the problems above. In the proposed architecture, the Mobility Access Gateways (MAGs) are grouped into clusters, each with a distinguished cluster Head MAG (HMAG). The HMAG is mainly designed to reduce the load on LMA by performing intra-cluster handoff signaling and providing an optimized path for data communications. The proposed architecture is evaluated analytically, and the numerical results show that the proposed CSPMIPv6 outperforms both SPMIPv6 and PMIPv6 protocols in terms of LMA load, local handoff delay, and transmission cost performance metrics.

An Adaptive Delayed Acknowledgment Strategy to Improve TCP Performance in Multi-hop Wireless Networks

In multi-hop wireless networks, transmission control protocol (TCP) suffers from performance deterioration due to poor wireless channel characteristics. Earlier studies have shown that the small TCP acknowledgments consume as much wireless resources as the long TCP data packets. Moreover, generating an acknowledgment (ACK) for each incoming data packet reduces the performance of TCP. The main factor affecting TCP performance in multi-hop wireless networks is the contention and collision between ACK and data packets that share the same path. Thus, lowering the number of ACKs using the delayed acknowledgment option defined in IETF RFC 1122 will improve TCP performance. However, large cumulative ACKs will induce packet loss due to retransmission time-out at the sender side of TCP. Motivated by this understanding, we propose a new TCP receiver with an adaptive delayed ACK strategy to improve TCP performance in multi-hop wireless networks. Extensive simulations have been done to prove and evaluate our strategy over different topologies. The simulation results demonstrate that our strategy can improve TCP performance significantly.

On-demand channel reservation scheme for common traffic in wireless mesh networks

Wireless mesh networks (WMNs) have recently gained momentum as a new broadband internet access technology to provide internet traffic. These networks have unique characteristics that make them different from ad hoc networks. These differences are as follows. First, WMNs are composed of static mesh routers that are equipped with multiple radio interfaces and turn each interface into a non-overlapping channel. These additional interfaces can create multiple concurrent links between adjacent nodes. Second, most of the traffic in WMNs is directed towards the gateway. Third, both local traffic and internet traffic are relayed by the mesh router to indeed destination. The Multi-Radio Ad hoc On-Demand Distance Vector (AODV-MR) developed to support multi-radio and does not take into account above-mentioned WMNs characteristics. In this paper, we propose an on-demand channel reservation scheme to reserve some of mesh router radio interfaces to support the gateway traffic while the remaining interfaces can be used to support the local traffic. Our scheme establishes high throughput paths for the traffic destined at the gateway, reduces the intra-flow and inter-flow interferences as well as to support full duplex node transmission. The scheme allows the gateway to assign a list of channels for each received gateway routing discovery message. Simulation results show that our proposed scheme significantly improves the performance of multi-radio multi-channel wireless mesh networks.

Improving reliability in resource management through adaptive reinforcement learning for distributed systems

Demands on capacity of distributed systems (e.g., Grid and Cloud) play a crucial role in todays information era due to the growing scale of the systems. While the distributed systems provide a vast amount of computing power their reliability is often hard to be guaranteed. This paper presents effective resource management using adaptive reinforcement learning (RL) that focuses on improving successful execution with low computational complexity. The approach uses an emerging methodology of RL in conjunction with neural network to help a scheduler that effectively observes and adapts to dynamic changes in execution environments. The observation of environment at various learning stages that normalize by resource-aware availability and feedback-based scheduling significantly brings the environments closer to the optimal solutions. Our approach also solves a high computational complexity in RL system through on-demand information sharing. Results from our extensive simulations demonstrate the effectiveness of adaptive RL for improving system reliability. Able to drive the evolution of automation networks towards higher reliability.Able to handle tasks at different states in processing.Able to adapt with system changes while leading better learning experiences.Able to sustain reliable performanceAble to deal with dynamic global network infrastructure.

Comparison of MPI Benchmark Programs on Shared Memory and Distributed Memory Machines (Point-to-Point Communication)

There are several benchmark programs available to measure the performance of MPI on parallel computers. The most common use of MPI benchmarks software are SKaMPI, Pallas MPI Benchmark, MPBench, Mpptest and MPIBench. It is interesting to analyze the differences between different benchmark. Presently, there have been few comparisons done between the different benchmarks. Thus, in this paper we discuss a comparison of the techniques used and the functionality of each benchmark, and also a comparison of the results on a distributed memory machine and shared memory machine for point-to-point communication. All of the MPI benchmarks listed above will be compared in this analysis. It is expected that the results from different benchmarks should be similar, however this analysis found substantial differences in the results for certain MPI communications, particularly for shared memory machines.

Enhancing inter-PMIPv6-domain for superior handover performance across IP-based wireless domain networks

As a network-based localized mobility management protocol, Proxy Mobile IPv6 (PMIPv6) enables a Mobile Host (MH) to roam within a localized domain without MH intervention in the mobility-related signalling. However, the PMIPv6 maintains MH mobility support in a restriction domain. Therefore, whenever the MH roams away from the PMIPv6 domain, its reachability status will be broken-down causing high handover latency and inevitable traffic loss for its communication session. This article proposes a proactive mechanism to mange the MH handover and maintain its data session continually across inter-PMIPv6-domains. The proposed mechanism introduces an intermediate global mobility anchor entity, called, which is responsible to coordinate MH handover as well as redirect its traffic across inter-PMIPv6-domains. Through various simulation evaluations, via ns-2, several experiments were conducted, revealing numerous results that verify the proposed mechanism superior performance over the conventional inter-PMIPv6-domain handover schemes in terms of handover latency, achieved throughput, protocol signalling cost and end-to-end traffic delivery latency.

An alert fusion model inspired by artificial immune system

In the recent years one of the most focused topics in the field of network security and more specifically intrusion detection systems was to find a solution to reduce the overwhelming alerts generated by IDSs in the network. Inspired by human defence system and danger theory we propose a complementary subsystem for IDS which can be integrated into any existing IDS models to aggregate the alerts in order to reduce them, and subsequently reduce false alarms among the alerts. After evaluation using different datasets and attack scenarios, our model managed to aggregate the alerts by the average rate of 97.5 percent.

Progress in various TCP variants (February 2009)

Transport Control Protocol (TCP), a basic communication language, consists of a set of rules that control communication. There are many versions of TCP which modified time to time as per need. Initially we discuss the basic functions of TCP and their role to control the congestion then graphically examine slow start, congestion avoidance, fast retransmission and fast recovery. This paper compares the performance of different TCP variants specifically Tahoe, Reno, New Reno, Westwood, Selective Acknowledgment (SACK), Forward Acknowledgement (FACK) and Vegas. TCP Vegas algorithm is explained with new structure mechanism and new congestion avoidance and modified slow start mechanisms. Subsequently, a table derived evaluates TCP variants on the basis of algorithm. We conversed the progress, and evaluated advantages and disadvantages of above TCP variants.

Review of channel assignment approaches in multi-radio multi-channel wireless mesh network

The Channel Assignment (CA) is an efficient tool to exploit multiple non-overlapping channels to minimize interference and enhance the capacity of the wireless mesh network. Even though the CA can minimize the total network interference, its result may cause some design issues which influence the network performance. First, the CA alters the network topology which in turn may produce unconnected logical topology. Second, the interaction between the CA and routing protocol where the effective capacity of each link depends on the routing decision and the result of CA. In this article we focus on multi-radio, multi-channel wireless mesh network. First, we defined the channel assignment (CA) design issues. Second, we classified the CA approaches based on the main design issues. For each CA approach, its advantages and limitations are highlighted. Third, the overall comparison for the classification is given in details. Finally, we discussed the future research direction for channel assignment.