Optical Wireless link provides high bandwidth solution to the last mile access bottleneck. However, an appreciable high availability of the link is the basic requirement of any communication application. Free Space Optics (FSO) links are highly weather dependent that reduces the link availability. Hybrid networks consisting of Free Space Optics (FSO) link and back up link in the GHz frequency range renders high availability besides providing comparable data rate. The back up link should be nearly immune to weather attenuation for achieving carrier class availability. Among all the attenuation factors for GHz back up link, rain is the most significant. In this paper effects of rain on FSO and GHz frequency range links are studied and some measurement results are presented. This analysis can help in selection of frequencies with least rain attenuation as a back up link.
An architecture for dynamic security monitoring and enforcement for client software running in Virtualized Environments for Cloud computing is presented. Monitoring mechanisms check a set of policy-defined conditions at runtime in order to detect threats or anomalous behaviour. Enforcement is achievable by using secure software execution methods that comply with the defined policies. The presented architecture allows for context adaptation of the defined policies by using a new event-sequence language. Such automatic policy runtime enforcement is crucial to achieve proper security in virtualized platforms for cloud computing.
In the context of security of Web Services, the XML Signature Wrapping attack technique has lately received increasing attention. Following a broad range of real-world exploits, general interest in applicable countermeasures rises. However, few approaches for countering these attacks have been investigated closely enough to make any claims about their effectiveness. In this paper, we analyze the effectiveness of the specific countermeasure of XML Schema validation in terms of fending Signature Wrapping attacks. We investigate the problems of XML Schema validation for Web Services messages, and discuss the approach of Schema Hardening, a technique for strengthening XML Schema declarations. We conclude that XML Schema validation with a hardened XML Schema is capable of fending XML Signature Wrapping attacks, but bears some pitfalls and disadvantages as well.
Effectively utilizing, unlocking and harnessing the data is the key to the success of organizations in the time to come. Although the software development and delivery technologies are matured, yet people are forced to start from scratch, when they encounter a new project, thus inducing cost and delay. In the proposed solution Organizations can collaborate to create a Data-center, that doesn't harm their existence or profitability. At the same time, these organizations can compete by spreading to those locations where they carry certain edge over others. This is where an ad-hoc cloud helps to venture into remote areas. We propose multitenancy for database in ad hoc cloud that helps multiple organizations to collaborate and yet compete with each other. In our proposed approach, shared database shared schema approach has been proposed that offers larger number of tenants per database server. Authentication and authorization are prime requirements when dealing with multitenancy. Kerberos authentication protocol is used on the top of multitenant database for participating educational institution.
Nowadays Cloud computing has introduced a new paradigm in distributed services, enabling the provision of services or computational resources to remote entities with no need to have them in house. In this paper, we consider two real life scenarios; 1) risk management in work areas, and 2) the execution of scientific experiments in cooperation among various computation nodes. We investigate how we can leverage Cloud capabilities and extend the aforementioned scenarios to the Cloud. We define the role of the Cloud in these scenarios and identify new dynamics between the Cloud and the services. Through these extensions, we identify security issues and vulnerabilities that need to be addressed. We describe some preliminary directions for security on the Cloud.
Storing data in the cloud poses a number of privacy issues. A way to handle them is supporting data replication and distribution on the cloud via a local, centrally synchronized storage. In this paper we propose to use an in-memory RDBMS with row-level data encryption for granting and revoking access rights to distributed data. This type of solution is rarely adopted in conventional RDBMSs because it requires several complex steps. In this paper we focus on implementation and benchmarking of a test system, which shows that our simple yet effective solution overcomes most of the problems.
Service-orientation is an emerging paradigm for building complex systems based on loosely coupled components, deployed and consumed over the network. Despite the original intent of the paradigm, its current instantiations are limited to a single trust domain (e.g., a single organization) One of the main reasons for this is the trust gap that normally arises when software services, offered by previously unknown providers, are to be selected at run-time, without any human intervention. The idea of machine-readable security certificates (called asserts) paves the way to automated reasoning about security properties of services. Similarly to current security certification schemes, the assessment of the security properties of a service is delegated to an independent third party (certification authority), who issues a corresponding assert, bound to the service. Building on the assert concept, this paper describes our proposal for a modular architecture to realise a certification-aware service discovery framework. The architecture supports the discovery of single services based on certified security properties, as well as the dynamic synthesis of service compositions that satisfy the required security properties.
Cloud computing has achieved maturity, and there is a heterogeneous group of providers and cloud-based services. However, significant attention remains focused on security concerns. In many cases, security and privacy issues are a significant barrier to user acceptance of cloud computing systems and the advantages these offer with respect to previous systems. Biometric technologies are becoming the key aspect of a wide range of secure identification and personal verification solutions, but in a cloud computing environment they present some problems related to the management of biometric data, due to privacy regulations and the need to trust cloud providers. To overcome those problems in this paper, we propose a cryptobiometric system applied to cloud computing in which no private biometric data are exposed.
Multicast research has explored the security challenges faced in group communications. Multicast transport and multicast security need to work in close collaboration to realise a multicast service. However, there has been comparatively little work to combine the two technologies. In this paper the authors is presenting an example of partially integrating Timed Efficient Stream Loss-Tolerant Authentication (TESLA) protocol and the File Delivery over Unidirectional Transport (FLUTE) protocol. The security concern raised by the proposed algorithm is analysed for satellite network. The proposed algorithm was implemented on a testbed with multicast tunnel between University of Surrey and University of Aberdeen and the results are presented in this paper.
SatNEx aims to overcome the fragmentation in Europe's satellite communications research by bringing together Europe's leading academic institutions and research organisations in a cohesive and durable way. This paper gives an overview over the first two phases of the SatNEx Network of Excellence project, as well as an outlook to the extension, SatNEx-III, planned for the years 2009 – 2012.
This paper presents the development of a laboratory demonstrator within NEWSKY, a project co-funded by the European Commission within its 6th Research Framework Programme (FP6). The test-bed is used to demonstrate the feasibility of host and network mobility, using Mobile IPv6 (MIPv6) and Network Mobility (NEMO) protocol stack for future Air Traffic Management (ATM) networks. Representative results as an outcome of extensive network performance measurements using real satellite and emulated terrestrial links are presented at the end of the paper.
This paper aims at providing different cost-efficient solutions for the channel impairments in tropical areas. In order to extend service to isolated areas, we propose an hybrid architecture based on DVB-S2/RCS + Wi-Fi networks. In this scenario, the delay of the ACM reaction to fade changes can affect the quality of the video transmission, especially because of the characteristics of tropical deep fading events. In order to avoid QoS reduction, we focus on the DVB PHY-layer shifted threshold, which we study not only for different Amazon areas and different rain conditions, but also for different reaction delays. The performance of the PHY-layer selector is evaluated in terms of video quality (PSNR), packet error rate and bandwidth efficiency.
Distributed applications and transport protocols communicating over a satellite link may react very strongly to conditions specific to that kind of link. Providing an evaluation framework to allow tests of real implementations of such software in that context is quite a challenging task. In this paper we show how the use of the general-purpose KauNet IP-level emulator combined with satellite-specific packet loss patterns can help by reproducing losses and delays experienced on a satellite link with a simple Ethernet LAN setup. We also describe a simple experimentation platform and how a typical demonstration is carried out. Such a platform is an essential tool for developers performing continuous testing as they provide new features for e.g. video codecs or transport-level software like DCCP and its congestion control components.
This paper investigates the performance of high-rate block codes in log-normal fading atmospheric channel based on the discussion of channel characteristics. Several block codes are under study, especially two kinds of iterative decoding codes with high code rate and low encoder/decoder complexity: Hamming-based TPC codes and block circulant based LDPC codes. The code types selection and iterative decoding algorithms for the two codes are discussed. The performance of several codes under different turbulence strength are also reported. Both TPC and LDPC codes can achieve impressive coding gain based on theoretical analysis and extensive computer simulation. In term of superior property in coding gain, error floor effect and hardware implementation, we recommend TPCs as FEC scheme for FSO system.
In case of video streaming services via satellite towards vehicular clients, very long blockage periods due to road infrastructures, vegetation, and so on, may lead to a complete channel outage, which may result in the loss of all packets transmitted during that period, even in the presence of interleaving and FEC techniques. But if these periods are predictable, as in the presence of known routes traced by means of a GPS navigator, it may be advisable to alert the transmitter in advance, in order to counteract the incoming outage interval. We refer to this technique as smart mode. In the following we will detail how smart mode takes advantage of FEC and interleaving techniques, in order to improve the quality of experience and to reduce the waste of bandwidth in satellite multimedia streaming.
Within this paper we examine a non-geostationary satellite constellation network with inter-satellite links (ISLs) for global air traffic control (ATC) and air passenger communication (APC). More specifically, an analysis is done to investigate the impacts of different routing policies on the end-to-end delay, and a general model describing the delays is developed. All considerations are based on a Galileo-like satellite constellation network and real global flight data of all commercial flights during one day.
The Broadband Fixed Wireless Access (BFWA) networks are terrestrial systems operating at high carrier frequencies (above 20 GHz), therefore one of the most harmful circumstantial factors in these systems is the attenuation caused by precipitation, especially by rain. Employing site diversity is a well-known method to improve the signal to interference plus noise ratio conditions within the BFWA network. The backbone of a BFWA can be wired or wireless terrestrial, however the connection between base stations and the operator's core network can be also established by high frequency satellite links. Applying a satellite backbone system and route diversity between the Earth-space links can compensate precipitation attenuation. In this paper the efficiency of the diversity scheme in a satellite backbone network for BFWA system will be presented.
This paper is focused on the measurement and evaluation of the relative timing characteristics of GPS (global positioning system) timing receivers for time synchronization application. I-Lotus M12M oncore timing modules optimized for the timing applications were utilized as tested timing modules. These modules represent the next generation of the low cost GPS timing receivers which expect accuracy of time synchronization to the so-called universal time coordinated (UTC) in the nanoseconds. The previous generation of receivers was M12+ oncore. Measurement was realized with two M12M timing receivers to obtain their relative time error. The relative time differences between generated 1PPS (one pulse per second) output signals (between rising edges of the pulses) and also 100PPS signals were measured. Error from UTC time was not needed to know but only relative time error between generated 1PPS (100 PPS) signals by the receivers. From the viewpoint of these receiver's application for precise time synchronization measured date are presented and statistically evaluated. The aim of using such timing system is a precision signal marking in different known locations.
This paper proposes a design approach to construct a high rank multiple-input multiple-output (MIMO) channel matrix in line-of-sight (LoS) propagation environment, when high altitude platforms (HAPs) are involved. This approach enhances the performance of systems, which can not utilize the MIMO gain introduced by independent and identically distributed (i.i.d.) Rayleigh fading channels or require the existence of a strong LoS signal. Geometrical design recommendations are introduced, considering Ka and V frequency bands licensed for broadband communications through HAPs. In these high frequency bands, the rain has a significant effect on the quality of the link and applications, such as Fixed Wireless Access (FWA), are feasible. The results show the potential capacity gain of the optimized LoS-HAP-MIMO architecture, under clear sky and rain conditions.
Free-space Optics (FSO) or optical wireless offers huge unlicensed bandwidth and is able to deliver the required bandwidth needed in next ten years for the next generation networks (NGN). Moreover, an increasing number of military and commercial access systems rely critically on the propagation of optical energy through the atmospheric free-space. As a result the need for predictable estimates of optical attenuation in low visibility conditions is steadily increasing, especially for fog, rain, clouds and snowfall. Cloud attenuations are the least observed/measured in case of free-space optical wireless links. We investigate here the influence of cloud attenuations on the performance of optical wireless links.
