11747548
A multiplex-multicast scheme that improves system capacity of voice-over-IP on wireless LAN by 100%
Voice-over-IP (VoIP) is.an important application on the Internet. With the emergence of WLAN technology and its various advantages compared with the traditional wired LAN, it is fast becoming the "last-mile" of choice for the overall Internet infrastructure. This work considers the support of VoIP over 802.11b WLAN. We show that although the raw WLAN capacity can potentially support more than 500 VoIP sessions, various overheads bring this down to only 12 VoIP sessions when using GSM 6.10 codec. We propose a novel multiplexing scheme for VoIP which exploits multicasting over WLAN for the downlink VoIP traffic. This scheme can achieve nearly 100% improvement in system capacity. In addition, we present results showing that the delay and delay jitter introduced by the proposed scheme are small. We believe that the scheme can reduce the blocking probability of VoIP sessions in an enterprise WLAN significantly.
12623712
A transparent rate adaptation algorithm for streaming video over the Internet
The lack of end-to-end quality of service support in the current Internet has caused significant difficulties to ensuring playback continuity in video streaming applications. This study addresses this challenge by investigating a new adaptation algorithm to adjust the bit-rate of video data in response to the network bandwidth available to improve playback continuity. Unlike previous works, the proposed algorithm is transparent to the video client, requires no parameter tuning, and yet can outperform existing algorithms. This paper presents this algorithm, evaluates and compares its performance with the best algorithm currently available using extensive trace-driven simulations.
1459613
PK-tree: A Spatial Index Structure for High Dimensional Point Data
In this chapter we present the PK-tree which is an index structure for high dimensional point data. The proposed indexing structure can be viewed as combining aspects of the PR-quad or K-D tree but where unnecessary nodes are eliminated. The unnecessary nodes are typically the result of skew in the point distribution and we show that by eliminating these nodes the performance of the resulting index is robust to skewed data distributions. The index structure is formally defined, efficiently updateable and bounds on the number of nodes and the mean height of the tree can be proved. Bounds on the expected height of the tree can be given under certain mild constraints on the spatial distribution of points. Empirical evidence both on real data sets and generated data sets shows that the PK-tree outperforms the recently proposed spatial indexes based on the R-tree and X-tree by a wide margin. It is also significant that the relative performance advantage of the PK-tree grows with the dimensionality of the data set.
8299246
HyLog: A High Performance Approach to Managing Disk Layout
Our objective is to improve disk I/O performance in multi-disk systems supporting multiple concurrent users, such as file servers, database servers, and email servers. In such systems, many disk reads are absorbed by large in-memory buffers, and so disk writes comprise a large portion of the disk I/O traffic. LFS (Log-structured File System) has the potential to achieve superior write performance by accumulating small writes into large blocks and writing them to new places, rather than overwriting on top of their old copies (called Overwrite). Although it is commonly believed that the high segment cleaning overhead of LFS makes it a poor choice for workloads with random updates, in this paper we find that because of the fast improvement of disk technologies, LFS significantly outperforms Overwrite in a wide range of system configurations and workloads (including the random update workload) under modern and future disks. 
 
LFS performs worse than Overwrite, however, when the disk space utilization is very high due to the high cleaning cost. In this paper, we propose a new approach, the Hybrid Log-structured (Hy-Log) disk layout, to overcome this problem. Hy-Log uses a log-structured approach for hot pages to achieve high write performance, and Overwrite for cold pages to reduce the cleaning cost. We compare the performance of HyLog to that of Overwrite, LFS and WOLF (the latest improvement on LFS) under various system configurations and workloads. Our results show that, in most cases, Hylog performs comparably to the best of the other three approaches.
15045713
Visual Specification and Optimization of XQuery Using VXQ
As the popularity of XML increases, the need for querying collections of XML data from various systems becomes imperative. Proposed by W3C, XQuery is becoming a standard for querying such systems. However, the complexity of XQuery prevents its usage by broad audience. This paper proposes a visual XQuery specification language called VXQ to address this issue. By intuitive abstractions of XML and XQuery, the proposed system can generate XQueries for users that have little knowledge about the language. We show that our visual language is more expressive than previous proposals. Finally, we extend our proposed visual XQuery to support query rewriting and optimization for multiple XQuery systems.
39024705
The Linear 2-Arboricity of Planar Graphs
Abstract. Let G be a planar graph with maximum degree Δ and girth g. The linear 2-arboricity la2(G) of G is the least integer k such that G can be partitioned into k edge-disjoint forests, whose component trees are paths of length at most 2. We prove that (1) la2(G)≤⌈(Δ+1)/2⌉+12; (2) la2(G)≤⌈(Δ+1)/2⌉+6 if g≥4; (3) la2(G)≤⌈(Δ+1)/2⌉+2 if g≥5; (4) la2(G)≤⌈(Δ+1)/2⌉+1 if g≥7.
36275833
Generalized pre-scheduler
A preschedule is a list of "executives" generated offline for a set of time-driven jobs. If in addition there exists event-driven workload competing for resources, sufficient slacks must be embedded in a valid preschedule. A prescheduler was defined in Wang et al. (2003) with the following assumptions: the competing workload is modeled as sporadic tasks and the time-driven jobs to be prescheduled are independent. In this paper, the prescheduling problem is generalized. First, the event-driven workload is no longer limited to sporadic tasks or any specific task model. Instead, a concept called "prescheduling space" is introduced so that the time-driven jobs to be prescheduled are inside the space, the competing event-driven workload is outside the space, and resource competition is abstracted to the space bounded by a supply function and a supply contract. Second, precedence constraints between the time-driven jobs to be prescheduled are allowed. The generalized prescheduler presented in this paper produces a valid preschedule if and only if one exists under the constraints of execution time bounds, valid scopes, precedence requirements and supply contract; otherwise, it returns a notice of failure. The generalized prescheduler runs in time polynomial to the number of time-driven jobs.