RBS analysis of front contacts for surface-barrier detectors

Surface-barrier detector structures based on Au, WTi and Au/WTi contacts on (111) n-Si were analysed. The metal layers were deposited by evaporation or sputtering to 40–100 nm thicknesses. The aim was to improve the thermal stability of the surface-barrier structures and retain the favourable detector properties of the Au/Si system. Contact structures which contain WTi layers have shown a much better thermal stability compared to the Au/Si system, but the properties of the detectors were poorer. The probable reasons are the reactivity of W and Ti with the thin oxide layer on the silicon surface and perhaps the higher energy of adatoms during sputter-deposition. Both effects can influence the degradation of the surface-barrier properties.     

On the quality of VoIP with DCCP for satellite communications

We present experimental results for the performance of selected voice codecs using Datagram Congestion Control Protocol (DCCP) with CCID4 congestion control over a satellite link. We evaluate the performance of both constant and variable data rate speech codecs for a number of simultaneous calls using the ITU E‐model. We analyse the sources of packet losses and additionally analyse the effect of jitter, which is one of the crucial parameters contributing to Voice over IP (VoIP) quality and has, to the best of our knowledge, not been considered previously in the published DCCP performance results. We propose modifications to the CCID4 algorithm and demonstrate how these improve the VoIP performance, without the need for additional link information other than what is already monitored by CCID4. We also demonstrate the fairness of the proposed modifications to other flows. Although the recently adopted changes to TCP‐Friendly Rate Control specification alleviate some of the performance issues for VoIP on satellite links, we argue that the characteristics of commercial satellite links necessitate consideration of further improvements. We identify the additional benefit of DCCP when used in VoIP admission control mechanisms and draw conclusions about the advantages and disadvantages of the proposed DCCP/CCID4 congestion control mechanism for use with VoIP applications. Copyright © 2012 John Wiley & Sons, Ltd.     

Privacy in targeted advertising on mobile devices: a survey

Targeted advertising has transformed the marketing landscape for a wide variety of businesses, by creating new opportunities for advertisers to reach prospective customers by delivering personalised ads, using an infrastructure of a number of intermediary entities and technologies. The advertising and analytics companies collect, aggregate, process, and trade a vast amount of users’ personal data, which has prompted serious privacy concerns among both individuals and organisations. This article presents a comprehensive survey of the privacy risks and proposed solutions for targeted advertising in a mobile environment. We outline details of the information flow between the advertising platform and ad/analytics networks, the profiling process, the measurement analysis of targeted advertising based on user’s interests and profiling context, and the ads delivery process, for both in-app and in-browser targeted ads; we also include an overview of data sharing and tracking technologies. We discuss challenges in preserving the mobile user’s privacy that include threats related to private information extraction and exchange among various advertising entities, privacy threats from third-party tracking, re-identification of private information and associated privacy risks. Subsequently, we present various techniques for preserving user privacy and a comprehensive analysis of the proposals based on such techniques; we compare the proposals based on the underlying architectures, privacy mechanisms, and deployment scenarios. Finally, we discuss the potential research challenges and open research issues.

     

On the impact of link layer retransmission schemes on TCP over 4G satellite links

We study the impact of reliability mechanisms introduced at the link layer on the performance of transport protocols in the context of 4G satellite links. Specifically, we design a software module that performs realistic analysis of the network performance, by utilizing real physical layer traces of a 4G satellite service. Based on these traces, our software module produces equivalent link layer traces, as a function of the chosen link layer reliability mechanism. We further utilize the link layer traces within the ns‐2 network simulator to evaluate the impact of link layer schemes on the performance of selected Transmission Control Protocol (TCP) variants. We consider erasure coding, selective‐repeat automatic request (ARQ) and hybrid‐ARQ link layer mechanisms, and TCP Cubic, Compound, Hybla, New Reno and Westwood. We show that, for all target TCP variants, when the throughput of the transport protocol is close to the channel capacity, using the ARQ mechanism is most beneficial for TCP performance improvement. In conditions where the physical channel error rate is high, hybrid‐ARQ results in the best performance for all TCP variants considered, with up to 22% improvements compared to other schemes. Copyright © 2014 John Wiley & Sons, Ltd.     

A mobility toolbox architecture for all-IP networks: an ambient networks approach [architectures and protocols for mobility management in all-IP mobile networks]

The future Internet will need to cater to an increasing number of mobile devices and mobile networks, roaming across different access networks and trust domains. In addition, various limitations imposed by the end user, service provider, or network operator agreements and preferences will need to be considered. A plethora of mobility management protocols have been proposed to handle different and mostly limited sets of these mobility requirements. In this article we make the case for coexistence of mobility protocols in order to support the large range of mobility scenarios possible in future all-IP networks. This coexistence takes the form of a mobility toolbox that enables mobility handling mechanisms to be selected according to the context. We then present a design for the mobility toolbox as a component of the ambient networks architecture, including a simplified mobility tool interface toward protocol modules, and show how it meets the requirements of future all-IP networks. We further demonstrate the feasibility and performance gains of the mobility toolbox architecture with a prototype implementation based on network mobility.     

Resources-aware trusted node selection for content distribution in mobile ad hoc networks

We propose a novel trust and probabilistic node selection mechanism for content distribution in mobile ad hoc networks. Due to the open nature of such networks which as a rule do not have strict node membership control, the selection of trustworthy nodes is an important challenge, especially as the resources (e.g., battery, bandwidth) of the mobile devices are limited and should not be wasted on erroneous or malicious content. Our proposal, in addition to considering the trustworthiness of nodes, ensures that the traffic load is equally shared amongst the population of nodes, thus further conserving mobile node resources. We analyse the proposed mechanisms and evaluate it against selected previously proposed trust schemes which, in the majority, favour the selection of the most trustworthy node. We demonstrate the benefits of our proposal which provides load balancing and prevents overuse of a single node’s resources, while still providing a good performance in regards to accurately choosing trustworthy nodes to provide the required content.