10011177
MeshScan: fast and efficient handoff in IEEE802.11 mesh networks
Handoff delay is one of the major problems in Wireless Mesh Network (WMN) that needs to be solved in order to allow time-critical and real-time applications run continuously during handoff. We have developed a fast handoff scheme called MeshScan to provide a novel use of channel scanning latency by employing open system authentication. This scheme comprises two steps: firstly a client device takes advantage of the WMN architecture to maintain a list of active mesh nodes. Secondly when handoff is required, a client transmits Authentication Request frames to all mesh nodes (MNs) from the list instead of broadcasting Probe Request frames as in an active scan to discover the available MNs. This fast handoff scheme is feasible by upgrading the software only on the client side. This paper compares the theoretical handoff latency of MeshScan with other approaches and we demonstrate the effectiveness of our scheme through experiment.
571649
An Evaluation of a Conservative Transmit Power Control Mechanism on an Indoor 802.11 Wireless Mesh Testbed
Power control techniques for IEEE 802.11 wireless networks have already gained considerable attention. Such techniques are particularly attractive because they can improve various aspects of wireless network operation such as interference mitigation, spatial reuse in dense wireless deployments, topology control, and link quality enhancement. In this paper we propose a novel delivery ratio based Conservative Transmit Power Control (ConTPC) mechanism. Our implementation is conservative when it comes to deciding if the transmit power should be reduced for a given link. This is because we do not want poor quality wireless links to further reduce their quality and be overwhelmed by other links transmitting at maximum power. We have experimentally evaluated the benefit of the proposed power control scheme when compared with fixed power level systems. We show that our ConTPC mechanism can increase the throughput, however the magnitude of this enhancement largely depends on the topology of the wireless network.
18478829
Gauging VoIP call quality from 802.11 WLAN resource usage
In this paper we experimentally study the relationship between resource utilization in the wireless LAN and the quality of VoIP calls transmitted over the wireless medium. Specifically we evaluate how its overall capacity is shared between three basic MAC bandwidth components (load, access, and free) as the number of VoIP calls increases and how it influences transmission impairments (delay, loss, and jitter) and thus call quality. Resource utilization (under the MAC bandwidth components framework) is calculated by a WLAN probe application that passively "sniffs" packets at the L2/MAC layer of the wireless medium and analyses their headers and temporal characteristics. The quality of VoIP calls is predicted using an extended version of the ITU-T E-model, which estimates user satisfaction from time varying transmission impairments. Through experimentation with various codecs and packetization schemes we found that as the load (number of calls) reaches the available capacity level, packet delays and jitter increase dramatically resulting in the call quality becoming degraded. We show how these MAC bandwidth components maybe used to assess the VoIP call quality on 802.11 WLANs
553221
An Experimental Investigation of Parallel Multimedia Streams Over IEEE 802.11e WLAN Networks Using TXOP
In this paper we perform an experimental investigation of the IEEE 802.11e TXOP facility to enhance the transmission of parallel multimedia streaming sessions through efficient bandwidth reservation and explicitly consider both the audio and video streams. The delay constraints associated with the audio and video streams that comprise a multimedia session pose the greatest challenge since real-time multimedia is particularly sensitive to delay as the packets require a strict bounded end-to-end delay. We show how the TXOPLimit parameter can be efficiently dimensioned to reduce the transmission delay for the video frames. Due to its frame-based nature, video applications are considered to be bursty as each video frame is typically transmitted as a burst of packets. The size of the burst is related to the size of the video frame and the number of packets required to transmit the video frame. The TXOP facility is particularly suited to efficiently deal with this burstiness since it can be used to reserve bandwidth for the duration of the packet burst. Through experimental investigation, we show that there is a significant performance improvement for the video streams by using the TXOPLimit parameter however there is no such improvement for the audio streams. We show that over-dimensioning the TXOPLimit parameter can cause the video stream to seize too much bandwidth which results in a deterioration in performance for the other competing traffic streams. This deterioration becomes more prominent as the number of parallel multimedia streams increases. We show that there is a performance improvement to all traffic streams by providing differentiated service to the constituent I, P, and B video frame types in conjunction with the TXOP facility.
6738991
An Experimental Investigation of IEEE 802.11e TXOP Facility for Real-Time Video Streaming
Real-time multimedia streaming applications require a strict bounded end-to-end delay and are considered to be bursty as each video frame is typically transmitted as a burst of packets. In this paper we show how the distribution of video frame sizes can be used to efficiently dimension the IEEE 802.lie TXOP limit parameter to efficiently deal with this burstiness in order to enhance the transmission of real-time video streaming services. Through experimental investigation, we show that by using the mean video frame size to dimension the TXOP limit parameter, the transmission delay for the video frame is reduced by 67% under heavily loaded conditions. Other techniques investigated in this paper include applying the TXOP facility separately to each of the constituent I, P, and B video frame types.
12221702
The capability of the EDCA mechanism to support voice traffic in a mixed voice/data transmission over 802.11e WLANs - an experimental investigation
In this paper we experimentally evaluate the capability of the EDCA mechanism to support voice traffic in a mixed voice/data transmission over 802.1 le WLANs. In particular we investigate how real-time voice transmission can be supported by tuning four EDCA parameters, namely AIFSN, CWmin , CWmax, and TXOP and how this impacts on background data transmission. The experimental set-up involves fifteen VoIP terminals sending bi-directional traffic between wired and wireless subnets and another station injecting various types of heavy background loads to the wireless subnet. End-to-end voice transmission quality is predicted from time-varying transmission impairments with the use of the latest appendix to the ITU-T E-model. Our experimental results show that the AIFSN parameter more effectively protects voice calls against background data traffic than CWmin. We also demonstrate that tuning of the TXOP parameter does not improve the quality of voice transmission. To the best of our knowledge, this is the first experimental investigation regarding tuning of MAC layer EDCA parameters in a real 802.1 le WLAN network from the perspective of end-to-end voice transmission quality and end user satisfaction.
45315809
Forensic Analysis of BIOS Chips
Data can be hidden in BIOS chips without hindering computer performance. This feature has been exploited by virus writers and computer game enthusiasts. Unused BIOS storage can also be used by criminals, terrorists and intelligence agents to conceal secrets. However, BIOS chips are largely ignored in digital forensic investigations. Few techniques exist for imaging BIOS chips and no tools are available specifically for analyzing BIOS data.
41330468
Detecting Data Concealment Programs Using File System Analysis
An improved closure and nozzle system for containers for air-curable materials such as cartridges for sealant and caulking compounds is disclosed. A container such as a caulking cartridge is provided with a threaded neck for attachment of a correspondingly threaded nozzle having a tapered tip portion designed to be cut off to provide a desired orifice size. A cap having a snap-fit ring is designed to mate with a corresponding snap-fit ring on the nozzle short of the tip and also having a threaded external portion designed to mate with the container neck so that the cartridge can be resealed after opening.
215753551
The Unicode Standard, Version 3.0
Disclaimer These charts are provided as the online reference to the character contents of the Unicode Standard, Version 8.0 but do not provide all the information needed to fully support individual scripts using the Unicode Standard. For a complete understanding of the use of the characters contained in this file, please consult the appropriate sections of The Unicode Standard, Version 8.0, online at http://www.unicode.org/versions/Unicode8.0.0/, as well as Unicode Standard Annexes #9, #11, #14, #15, #24, #29, #31, #34, #38, #41, #42, #44, and #45, the other Unicode Technical Reports and Standards, and the Unicode Character Database, which are available online.
27004101
A Network-Based Architecture for Storing Digital Evidence
The storage and handling of digital evidence are creating significant challenges for federal, state and local law enforcement agencies. The problems include acquiring and processing massive amounts of digital evidence, maintaining the integrity of the evidence, and storing digital evidence for extended periods of time. This paper describes a network-based storage architecture that helps address these issues. The architecture also supports collaborative efforts by examiners and investigators located at geographically dispersed sites.
31126198
Detecting Hidden Data in Ext2/Ext3 File Systems
The use of digital forensic tools by law enforcement agencies has made it difficult for malicious individuals to hide potentially incriminating evidence. To combat this situation, the hacker community has developed anti-forensic tools that remove or hide electronic evidence for the specific purpose of undermining forensic investigations. This paper examines the latest techniques for hiding data in the popular Ext2 and Ext3 file systems. It also describes techniques for detecting hidden data in the reserved portions of these file systems.