Anticipatory Buffer Control and Quality Selection for Wireless Video Streaming

Video streaming is in high demand by mobile users, as recent studies indicate. In cellular networks, however, the unreliable wireless channel leads to two major problems. Poor channel states degrade video quality and interrupt the playback when a user cannot sufficiently fill its local playout buffer: buffer underruns occur. In contrast to that, good channel conditions cause common greedy buffering schemes to pile up very long buffers. Such over-buffering wastes expensive wireless channel capacity. To keep buffering in balance, we employ a novel approach. Assuming that we can predict data rates, we plan the quality and download time of the video segments ahead. This anticipatory scheduling avoids buffer underruns by downloading a large number of segments before a channel outage occurs, without wasting wireless capacity by excessive buffering. We formalize this approach as an optimization problem and derive practical heuristics for segmented video streaming protocols (e.g., HLS or MPEG DASH). Simulation results and testbed measurements show that our solution essentially eliminates playback interruptions without significantly decreasing video quality

Efficient partitioning strategies for distributed Web crawling

This paper presents a multi-objective approach to Web space partitioning, aimed to improve distributed crawling efficiency. The in- vestigation is supported by the construction of two different weighted graphs. The first is used to model the topological communication infras- tructure between crawlers and Web servers and the second is used to represent the amount of link connections between servers’ pages. The values of the graph edges represent, respectively, computed RTTs and pages links between nodes. The two graphs are further combined, using a multi-ob jective partitio- ning algorithm, to support Web space partitioning and load allocation for an adaptable number of geographical distributed crawlers. Partitioning strategies were evaluated by varying the number of partiti- ons (crawlers) to obtain merit figures for: i) download time, ii) exchange time and iii) relocation time. Evaluation has showed that our partitio- ning schemes outperform traditional hostname hash based counterparts in all evaluated metric, achieving on average 18% reduction for download time, 78% reduction for exchange time and 46% reduction for relocation time.Fundação para a Ciência e a Tecnologia (FCT

Pipes and Connections

This document describes the low-level Pipe and ConnectionManager objects of the Mesh- Router system. The overall MeshRouter framework provides a general scheme for interest- limited communications among a number of client processes. This generality is achieved by a carefully factorized, object-oriented software implementation. Within this framework, the Pipe and ConnectionManager (base) classes dened in this note specify the interfaces for i) ac- tual `bits on the wire' communications and ii) dynamic client insertions during overall system execution. Two specic implementations of the Pipe class are described in detail: a `Memo- ryPipe' linking objects instanced on a single processor and a more general 'rtisPipe' providing inter-processor communications built entirely from the standard RTI-s library used in current JSAF applications. Initialization procedures within the overall MeshRouter system are dis- cussed, with particular attention given to dynamic management of inter-processor connections. Prototype RTI-s router processes are discussed, and simple extensions of the standard system conguration data les are presented

A Test Suite for High-Performance Parallel Java

The Java programming language has a number of features that make it attractive for writing high-quality, portable parallel programs. A pure object formulation, strong typing and the exception model make programs easier to create, debug, and maintain. The elegant threading provides a simple route to parallelism on shared-memory machines. Anticipating great improvements in numerical performance, this paper presents a suite of simple programs that indicate how a pure Java Navier-Stokes solver might perform. The suite includes a parallel Euler solver. We present results from a 32-processor Hewlett-Packard machine and a 4-processor Sun server. While speedup is excellent on both machines, indicating a high-quality thread scheduler, the single-processor performance needs much improvement

Providing public key certificate authorization and policy with DNS

Public Key Infrastructure (PKI) instills trust in certificates commonly used to secure email, web traffic, VPNs, file transfers, and other forms of network communication. Due to a number of successful attacks against certificate authorities, malicious parties have illegitimately acquired trusted certificates for widely used online services, government agencies, and other important organizations. These incidents, and the potential for future attacks of a similar nature, present notable risk to PKI and global security as a whole. The proposed Certificate Policy Framework (CPF) offers a mechanism for organizations to control which certificates are authorized to authenticate their services. This DNS-based protocol allows organizations to publish an access control list for any given hostname, where each entry in the ACL identifies a certificate and indicates whether the certificate should be blocked, warned upon, or permitted. Similarly, any CPF-compatible application can query DNS for CPF records to verify the integrity of the certificate from an authoritative viewpoint. In this work, we review limitations in PKI and certificate-based security and review existing work in this area. We will also discuss CPF in greater detail and demonstrate how it can be used to augment PKI to strengthen this widely adopted technology