Orhan Gemikonakli

Secure Live Virtual Machines Migration: Issues and Solutions

In recent years, there has been a huge trend towards running network intensive applications, such as Internet servers and Cloud-based service in virtual environment, where multiple virtual machines (VMs) running on the same machine share the machines physical and network resources. In such environment, the virtual machine monitor (VMM) virtualizes the machines resources in terms of CPU, memory, storage, network and I/O devices to allow multiple operating systems running in different VMs to operate and access the network concurrently. A key feature of virtualization is live migration (LM) that allows transfer of virtual machine from one physical server to another without interrupting the services running in virtual machine. Live migration facilitates workload balancing, fault tolerance, online system maintenance, consolidation of virtual machines etc. However, live migration is still in an early stage of implementation and its security is yet to be evaluated. The security concern of live migration is a major factor for its adoption by the IT industry. Therefore, this paper uses the X.805 security standard to investigate attacks on live virtual machine migration. The analysis highlights the main source of threats and suggests approaches to tackle them. The paper also surveys and compares different proposals in the literature to secure the live migration.

A hybrid approach to minimize state space explosion problem for the solution of two stage tandem queues

Two stage open queuing networks are used for modeling the subsystem-behaviour in computers and communication networks, mass storage devices, memory servers, and queuing analysis of wireless mobile cellular networks. The queuing analysis of wireless systems is essential in order to quantify the impact of different factors on quality of service (QoS); performance measures so that wireless protocols can be designed and/or tuned in an optimal manner. In that sense two stage open queuing systems are particularly important to model handoff phenomena, especially for the integration of two different systems such as cellular and wireless local area networks (WLANs). Analytical solutions for two-dimensional Markov processes suffer from the state space explosion problem. The numerical difficulties caused by large state spaces, make it difficult to handle multiple servers at the second stage of a tandem queuing system together with server failures and repairs. This study presents a new approach to analytical modeling of open networks offering improvements in alleviating this problem. The proposed solution is a hybrid version, which combines well known spectral expansion, and hierarchical Markov reward rate approaches. Using this approach, two-stage open networks with multiple servers, break-downs, and repairs at the second stage and feedback can be modeled as three-dimensional Markov processes and solved for performability measures. Comparative results show that the new algorithm used for solution, provides a high degree of accuracy, and it is computationally more efficient than the existing approaches. The proposed model is capable of solving other three-dimensional Markov processes.

Modelling and performability analysis of network memory servers

This paper presents an analytical method for the performability evaluation of a proposed network memory server attached to a local area network. The proposed server is expected to improve data storage and retrieval. However, the underlying network will receive an increased amount of traffic which may have a significant effect on the networks performance. The proposed analytical model and its solution can be used to evaluate the performance of such a system. Mean queue lengths and the probability that the NMS queue is full are calculated and presented.

Implementation of Non-Pipelined and Pipelined Data Encryption Standard (DES) Using Xilinx Virtex-6 FPGA Technology

Data encryption process can easily be quite complicated and usually requires significant computation time and power despite significant simplifications. This paper discusses about pipelined and non-pipelined implementation of one of the most commonly used symmetric encryption algorithm, Data Encryption Standard (DES). The platform used for this matter is, Xilinx new high performance silicon foundation, Virtex-6 Field Programmable Gate Array technology. Finite state machine is used only in non-pipelined implementation, and it is not implemented for the pipelined approach. The testing of the implemented design shows that it is possible to generate data in 16 clock cycles when non-pipelined approach is employed. When pipelined approach is employed on the other hand, 17 clock signals are required for the initial phase only, and one clock signal is sufficient afterwards for each data generation cycle. The Very High Speed Integrated Circuit Hardware Description Language (VHDL) is used to program the design.

Enabling seamless V2I communications: toward developing cooperative automotive applications in VANET systems

Cooperative applications for VANETs will require seamless communication between vehicle to infrastructure and vehicle to vehicle. IEEE 802.11p has been developed to facilitate this effort. However, in order to have seamless communication for these applications, it is necessary to look at handover as vehicles move between roadside units. Traditional models of handover used in normal mobile environments are unable to cope with the high velocity of the vehicle and the relatively small area of coverage with regard to vehicular environments. The Y-Comm framework has yielded techniques to calculate the time before vertical handover and the network dwell time for any given network topology. Furthermore, by knowing these two parameters, it is also possible to improve channel allocation and resource management in network infrastructure such as base stations, relays, and so on. In this article we explain our overall approach by describing the VANET Testbed and show that in vehicular environments it is necessary to consider a new handover model that is based on a probabilistic rather than a fixed coverage approach. Finally, we show a new performance model for proactive handover, which is then compared with traditional approaches.

A Hybrid Double-Threshold Based Cooperative Spectrum Sensing over Fading Channels

This paper investigates double-threshold-based energy detector for cooperative spectrum sensing mechanisms in cognitive wireless radio networks. We first propose a hybrid double-threshold-based energy detector (HDTED) to improve the sensing performance at secondary users (SUs) by exploiting both the local binary/energy decisions and global binary decisions feedback from the fusion center (FC). Significantly, we derive closed-form expressions and bounds for the probabilities of missed detection and false alarm considering a practical scenario where all channel links suffer from Rayleigh fading and background noise. The derived expressions not only show the improved performance achieved with the HDTED scheme but also enable us to analyze the impacts of the number of the SUs and the fading channels on the cooperative spectrum sensing performance. Furthermore, based on the derived bounds, we propose an optimal SU selection algorithm for forwarding the local decisions to the FC, which helps reduce the number of forwarding bits for a lower-complexity signaling. Finally, numerical results are provided to demonstrate the validity of the analytical findings.

Path Loss Effect on Energy Consumption in a WSN

Energy consumption of nodes is a crucial factor that constrains the networks life time for Wireless Sensor Networks (WSNs). WSNs are composed of small sensors equipped with low-power devices, and have limited battery power supply. The main concern in existing architectural and optimisation studies is to prolong the network lifetime. The lifetime of the sensor nodes is affected by different components such as the microprocessor, the sensing module and the wireless transmitter/receiver. The existing works mainly consider these components to decide on best deployment, topology, protocols and so on. Recent studies have also considered the monitoring and evaluation of the path loss caused by environmental factors. Path loss is always considered in isolation from the higher layers such as application and network. It is necessary to combine path loss computations used in physical layer, with information from upper layers such as application layer for a more realistic evaluation. In this paper, a simulation-based study is presented that uses path-loss model and application layer information in order to predict the network lifetime. Physical environment is considered as well. We show that when path-loss is introduced, increasing the transmission power is needed to reduce the amount of packets lost. This presents a tradeoff between the residual energy and the successful transmission rate when more realistic settings are employed for simulation. It is a challenging task to optimise the transmission power of WSNs, in presence of path loss, because although increasing the transmission power reduces the residual energy, it also reduces the number of retransmissions required.

Multi-Channel Distributed Coordinated Function over Single Radio in Wireless Sensor Networks

Multi-channel assignments are becoming the solution of choice to improve performance in single radio for wireless networks. Multi-channel allows wireless networks to assign different channels to different nodes in real-time transmission. In this paper, we propose a new approach, Multi-channel Distributed Coordinated Function (MC-DCF) which takes advantage of multi-channel assignment. The backoff algorithm of the IEEE 802.11 distributed coordination function (DCF) was modified to invoke channel switching, based on threshold criteria in order to improve the overall throughput for wireless sensor networks (WSNs) over 802.11 networks. We presented simulation experiments in order to investigate the characteristics of multi-channel communication in wireless sensor networks using an NS2 platform. Nodes only use a single radio and perform channel switching only after specified threshold is reached. Single radio can only work on one channel at any given time. All nodes initiate constant bit rate streams towards the receiving nodes. In this work, we studied the impact of non-overlapping channels in the 2.4 frequency band on: constant bit rate (CBR) streams, node density, source nodes sending data directly to sink and signal strength by varying distances between the sensor nodes and operating frequencies of the radios with different data rates. We showed that multi-channel enhancement using our proposed algorithm provides significant improvement in terms of throughput, packet delivery ratio and delay. This technique can be considered for WSNs future use in 802.11 networks especially when the IEEE 802.11n becomes popular thereby may prevent the 802.15.4 network from operating effectively in the 2.4 GHz frequency band.

Performability Modelling of Handoff in Wireless Cellular Networks with Channel Failures and Recovery

Mobility is one of the major issues in the performance characterization of wireless communication systems. Wireless communication systems encounter failures. These failures can occur because of software, hardware, human error, or a combination of these factors. The probability of an ongoing call being dropped due to a handoff failure and the probability of a new call being blocked due to the temporary unavailability of an idle channel are main metrics that affect the performance of wireless cellular systems. In order to overcome this problem, availability and performance of these systems should be considered together. In this paper, cellular networks with failures and recovery are modelled. The model is based on previous work in performance modelling and availability modelling of such systems. A Markov Reward Model is used to represent such a system with handoffs. Mean queue length and blocking probability are calculated using an analytical model and presented.

Providing ubiquitous communication using road-side units in VANET systems: Unveiling the challenges

Vehicular Ad-Hoc Networks (VANETs) are a long-term solution contributing significantly towards Intelligent Transport Systems (ITS) in providing access to critical life-safety applications and services. Although Vehicular Ad Hoc Networks (VANETs) are attracting greater commercial interest, current research has not adequately captured the real-world constraints in VANET handover techniques. Therefore, in order to have the best practice for VANET services, it is necessary to have seamless connectivity for optimal coverage and ideal channel utilization: this comes at the cost of overlapping signals of adjacent RSUs. This overlapping effect can be investigated using concepts such Network Dwell Time, Time Before Handover and Exit Times. In this simulation study we investigate the feasibility and benefits of providing a ubiquitous communication in VANET under different mobile environments. We also study the impact of beacon frequency and velocity on Network Dwell Time, Time Before Handover and Exit Times, which will help us to predict the handover times and thus make proactive handover possible. Therefore understanding handover issues is critical in supporting life-safety applications and services in VANETs.