4,077 research outputs found
Experimental Analysis of Subscribers' Privacy Exposure by LTE Paging
Over the last years, considerable attention has been given to the privacy of
individuals in wireless environments. Although significantly improved over the
previous generations of mobile networks, LTE still exposes vulnerabilities that
attackers can exploit. This might be the case of paging messages, wake-up
notifications that target specific subscribers, and that are broadcasted in
clear over the radio interface. If they are not properly implemented, paging
messages can expose the identity of subscribers and furthermore provide
information about their location. It is therefore important that mobile network
operators comply with the recommendations and implement the appropriate
mechanisms to mitigate attacks. In this paper, we verify by experiment that
paging messages can be captured and decoded by using minimal technical skills
and publicly available tools. Moreover, we present a general experimental
method to test privacy exposure by LTE paging messages, and we conduct a case
study on three different LTE mobile operators
zCap: a zero configuration adaptive paging and mobility management mechanism
Today, cellular networks rely on fixed collections of cells (tracking areas) for user equipment localisation. Locating users within these areas involves broadcast search (paging), which consumes radio bandwidth but reduces the user equipment signalling required for mobility management. Tracking areas are today manually configured, hard to adapt to local mobility and influence the load on several key resources in the network. We propose a decentralised and self-adaptive approach to mobility management based on a probabilistic model of local mobility. By estimating the parameters of this model from observations of user mobility collected online, we obtain a dynamic model from which we construct local neighbourhoods of cells where we are most likely to locate user equipment. We propose to replace the static tracking areas of current systems with neighbourhoods local to each cell. The model is also used to derive a multi-phase paging scheme, where the division of neighbourhood cells into consecutive phases balances response times and paging cost. The complete mechanism requires no manual tracking area configuration and performs localisation efficiently in terms of signalling and response times. Detailed simulations show that significant potential gains in localisation effi- ciency are possible while eliminating manual configuration of mobility management parameters. Variants of the proposal can be implemented within current (LTE) standards
Effect of screen presentation on text reading and revising. International Journal of Human-Computer Studies
Two studies using the methods of experimental psychology assessed the effects of two types of text presentation (page-by-page vs. scrolling) on participants' performance while reading and revising texts. Greater facilitative effects of the page-by-page presentation were observed in both tasks. The participants' reading task performance indicated that they built a better mental representation of the text as a whole and were better at locating relevant information and remembering the main ideas. Their revising task performance indicated a larger number of global corrections (which are the most difficult to make)
The economics of garbage collection
This paper argues that economic theory can improve our understanding of memory management. We introduce the allocation curve, as an analogue of the demand curve from microeconomics. An allocation curve for a program characterises how the amount of garbage collection activity required during its execution varies in relation to the heap size associated with that program. The standard treatment of microeconomic demand curves (shifts and elasticity) can be applied directly and intuitively to our new allocation curves. As an application of this new theory, we show how allocation elasticity can be used to control the heap growth rate for variable sized heaps in Jikes RVM
Persistent Memory Programming Abstractions in Context of Concurrent Applications
The advent of non-volatile memory (NVM) technologies like PCM, STT,
memristors and Fe-RAM is believed to enhance the system performance by getting
rid of the traditional memory hierarchy by reducing the gap between memory and
storage. This memory technology is considered to have the performance like that
of DRAM and persistence like that of disks. Thus, it would also provide
significant performance benefits for big data applications by allowing
in-memory processing of large data with the lowest latency to persistence.
Leveraging the performance benefits of this memory-centric computing technology
through traditional memory programming is not trivial and the challenges
aggravate for parallel/concurrent applications. To this end, several
programming abstractions have been proposed like NVthreads, Mnemosyne and
intel's NVML. However, deciding upon a programming abstraction which is easier
to program and at the same time ensures the consistency and balances various
software and architectural trade-offs is openly debatable and active area of
research for NVM community.
We study the NVthreads, Mnemosyne and NVML libraries by building a concurrent
and persistent set and open addressed hash-table data structure application. In
this process, we explore and report various tradeoffs and hidden costs involved
in building concurrent applications for persistence in terms of achieving
efficiency, consistency and ease of programming with these NVM programming
abstractions. Eventually, we evaluate the performance of the set and hash-table
data structure applications. We observe that NVML is easiest to program with
but is least efficient and Mnemosyne is most performance friendly but involves
significant programming efforts to build concurrent and persistent
applications.Comment: Accepted in HiPC SRS 201
Semi-persistent RRC protocol for machine-type communication devices in LTE networks
In this paper, we investigate the design of a radio resource control (RRC) protocol in the framework of long-term evolution (LTE) of the 3rd Generation Partnership Project regarding provision of low cost/complexity and low energy consumption machine-type communication (MTC), which is an enabling technology for the emerging paradigm of the Internet of Things. Due to the nature and envisaged battery-operated long-life operation of MTC devices without human intervention, energy efficiency becomes extremely important. This paper elaborates the state-of-the-art approaches toward addressing the challenge in relation to the low energy consumption operation of MTC devices, and proposes a novel RRC protocol design, namely, semi-persistent RRC state transition (SPRST), where the RRC state transition is no longer triggered by incoming traffic but depends on pre-determined parameters based on the traffic pattern obtained by exploiting the network memory. The proposed RRC protocol can easily co-exist with the legacy RRC protocol in the LTE. The design criterion of SPRST is derived and the signalling procedure is investigated accordingly. Based upon the simulation results, it is shown that the SPRST significantly reduces both the energy consumption and the signalling overhead while at the same time guarantees the quality of service requirements
VIRTUAL MEMORY ON A MANY-CORE NOC
Many-core devices are likely to become increasingly common in real-time and embedded systems as computational demands grow and as expectations for higher performance can generally only be met by by increasing core numbers rather than relying on higher clock speeds.
Network-on-chip devices, where multiple cores share a single slice of silicon and employ packetised communications, are a widely-deployed many-core option for system designers. As NoCs are expected to run larger and more complex programs, the small amount of fast, on-chip memory available to each core is unlikely to be sufficient for all but the simplest of tasks, and it is necessary to find an efficient, effective, and time-bounded, means of accessing resources stored in off-chip memory, such as DRAM or Flash storage.
The abstraction of paged virtual memory is a familiar technique to manage similar tasks in general computing but has often been shunned by real-time developers because of concern about time predictability. We show it can be a poor choice for a many-core NoC system as, unmodified, it typically uses page sizes optimised for interaction with spinning disks and not solid state media, and transports significant volumes of subsequently unused data across already congested links.
In this work we outline and simulate an efficient partial paging algorithm where only those memory resources that are locally accessed are transported between global and local storage. We further show that smaller page sizes add to efficiency. We examine the factors that lead to timing delays in such systems, and show we can predict worst case execution times at even safety-critical thresholds by using statistical methods from extreme value theory. We also show these results are applicable to systems with a variety of connections to memory
Concept-based Interactive Query Expansion Support Tool (CIQUEST)
This report describes a three-year project (2000-03) undertaken in the Information Studies
Department at The University of Sheffield and funded by Resource, The Council for
Museums, Archives and Libraries. The overall aim of the research was to provide user
support for query formulation and reformulation in searching large-scale textual resources
including those of the World Wide Web. More specifically the objectives were: to investigate
and evaluate methods for the automatic generation and organisation of concepts derived from
retrieved document sets, based on statistical methods for term weighting; and to conduct
user-based evaluations on the understanding, presentation and retrieval effectiveness of
concept structures in selecting candidate terms for interactive query expansion.
The TREC test collection formed the basis for the seven evaluative experiments conducted in
the course of the project. These formed four distinct phases in the project plan. In the first
phase, a series of experiments was conducted to investigate further techniques for concept
derivation and hierarchical organisation and structure. The second phase was concerned with
user-based validation of the concept structures. Results of phases 1 and 2 informed on the
design of the test system and the user interface was developed in phase 3. The final phase
entailed a user-based summative evaluation of the CiQuest system.
The main findings demonstrate that concept hierarchies can effectively be generated from
sets of retrieved documents and displayed to searchers in a meaningful way. The approach
provides the searcher with an overview of the contents of the retrieved documents, which in
turn facilitates the viewing of documents and selection of the most relevant ones. Concept
hierarchies are a good source of terms for query expansion and can improve precision. The
extraction of descriptive phrases as an alternative source of terms was also effective. With
respect to presentation, cascading menus were easy to browse for selecting terms and for
viewing documents. In conclusion the project dissemination programme and future work are
outlined
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