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.
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.
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.
10980387
Classical optimizations in Ada
Ada contains several features which have posed problems for optimizers when included in other languages. These features are subprograms, exception handling, and multi-tasking. They are defined in Ada in such a way that classical optimizations, such as common sub-expression elimination and code motion, are minimally affected. This paper discusses the impact of Ada's semantics on classical optimizations and the information needed for the correct application of these transformations.
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.
36665753
Extracting Concealed Data from BIOS Chips
The practice of digital forensics demands thorough, meticulous examinations of all data storage media seized in investigations. However, BIOS chips and other firmware are largely overlooked in forensic investigations. No forensically sound procedures exist for imaging BIOS chips and no tools are available specifically for analyzing BIOS image files. Yet, significant amounts of data may be stored on BIOS chips without hindering machine performance.
59792527
International text in JDK 1.2