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.
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.
10200775
A wireless traffic probe for radio resource management and QoS provisioning in IEEE 802.11 WLANs
The emergence of real-time services such as voice over IP (VoIP) and video streaming, imposes stringent requirements on the performance of a network if quality of service (QoS) targets are to be achieved. In the case of wireless networks, some form of radio resource management (RRM) is typically required to allocate the available resources among the contending stations in accordance with their needs and respective priorities. A critical aspect of any RRM scheme is the ability to monitor resource usage and to determine the resource requirements on a per-station basis. In this paper we describe a wireless traffic probe for IEEE 802.11 WLANs capable of obtaining this information and presenting it in a compact and intuitive format. The probe also shows how the wireless stations interact with one another in competing for the resources of the WLAN in a clear and quantifiable way. The results from the WLAN traffic probe obtained in a series of video streaming test scenarios are also presented that clearly demonstrate its usefulness and importance as a network tool in RRM and QoS provisioning schemes.
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.
14605752
Experimental tuning of AIFSN and CWmin parameters to prioritize voice over data transmission in 802.11e WLAN networks
In this paper we experimentally study the impact of two EDCA parameters, namely AIFSN and CWmin, on a mixed voice/data wireless transmission. In particular we investigate how the tuning of these parameters affects both the voice transmission quality and background data throughput. We predict end-to-end voice transmission quality from time varying transmission impairments using the latest Appendix to the ITU-T E-model. Our experimental results show that the tuning of the EDCA parameters can be used to successfully prioritize voice transmission over data in real 802.11e networks. We also demonstrate that the AIFSN parameter more effectively protects voice calls against background data traffic than CWmin. To the best of our knowledge, this is the first experimental investigation on tuning of MAC layer parameters in a real 802.11e WLAN network from the perspective of end-to-end voice transmission quality and end user satisfaction.
5625582
Experimental evaluation of the Hewlett-Parkard exemplar file system
This article presents results from an experimental evaluation study of the HP Exemplar file system. Our experiments consist of simple micro-benchmarks that study the impact of various factors on the file system performance. These factors include I/O request/buffer sizes, vectored/non-vectored access patterns, read-ahead policies, multi-threaded (temporally irregular) requests, and architectural issues (cache parameters, NUMA behavior, etc.). Experimental results indicate that the Exemplar file system provides high I/O bandwidth, both for single- and multi-threaded applications. The buffer cache, with prioritized buffer management and large buffer sizes, is effective in exploiting temporal and spatial access localities. The performance of non-contiguous accesses can be improved by either using vectored I/O interfaces or tuning the read-ahead facilities. The file system performance depends on the relative locations of the computing threads and the file system, and also on various Exemplar design parameters such as the NUMA architecture, TLB/data cache management and paging policies.
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.
6966708
Countering Hostile Forensic Techniques
Digital forensic investigations can be subverted by hostile forensic techniques and tools. This paper examines various hostile forensic techniques, including the exploitation of vulnerabilities in standard forensic procedures and denial of service attacks on forensic tools during imaging and analysis. Several techniques for concealing evidence within file systems and external to file systems are highlighted. In addition, strategies for countering hostile forensic techniques and tools are discussed.
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.
34331062
A Noice Whitening approach to Multiple-Access Noise Rejection - Part II: Implementation Issues
Several practical methods are proposed for the implementation of linear filters that reject multiple-access noise in direct sequence code-division multiple-access (DS-CDMA) receivers. These methods rely on taking advantage of variations in the received chip spectrum, and do not require locking and despreading multiple signals. The resulting structures are simple, and some can operate at a high chip rate. Adaptive structures are also proposed. It is shown that a close relationship exists between noise whitening and chip-equalization for a DS-CDMA receiver. System issues affecting the choice of the chip spectrum, and thus the applicability of these methods, are described.