Francisco Garcia

Integrated quality of service for multimedia communications

The integration of distributed multimedia systems around the unifying theme of quality of service (QOS) is addressed. A set of key QOS requirements is presented and mapped onto a provisional QOS architecture (QOS-A) that has emerged from a experimental system designed and implemented at Lancaster. The scope of the discussion is limited to aspects of a QOS-A for the support of continuous media communications. Also, the focus is on asynchronous transfer mode (ATM) at the network layer rather than the full range of multiservice networks. Functions and mechanisms for QOS support are examined and placed within the evolving QOS-A.<<ETX>>

Filters: QoS support mechanisms for multipeer communications

The nature of distributed multimedia applications is such that they require multipeer communication support mechanisms. The multimedia traffic needs to be delivered to end-systems, networks, and end-users in a form that they can handle while satisfying the constraints imposed by the multimedia application. Quality-of-service (QoS) mechanisms that can ensure full quality media playout at high-performance workstations, while at the same time providing appropriately filtered lower quality media for playout at other end-systems, are required. Existing multicast support mechanisms are deficient for this purpose, in a heterogeneous environment, because they work on a common denominator premise where the quality delivered depends on the least capable link or node involved in the multicast session. This paper begins by discussing video compression; it proposes and analyzes the use of filtering mechanisms as means of supporting disparate receiver capabilities and QoS requirements. The paper describes the implementation of a number of filtering mechanisms and highlights the communications architecture within which these mechanisms are built. This architecture constitutes a specific network topology and a new protocol family developed within a UNIX-like operating system.

A continuous media transport and orchestration service

The desire to transfer continuous media such as digital audio and video across packet switched networks imposes a number of new requirements on transport level communication services. This paper identifies a number of these requirements in the context of an experimental distributed multimedia infrastructure, and reports on research which addresses some of the associated issues. Particular attention is paid to two areas: (i) extended Quality of Service (QoS) provision; and (ii) support for the co-ordination of multiple related connections. We then describe an application level service, known as an orchestrator, which performs synchronisation functions over multiple related transport connections. We also outline the design and implementation of a continuous media transport service which meets the identified requirements. Finally, we outline the way in which the orchestrator and transport services are integrated into an object-based distributed multimedia application platform.

Protocol support for distributed multimedia applications

In this paper we describe ongoing work in protocol support for distributed multimedia applications. This work concerns the provision of suitable transport mechanisms to convey multimedia information (text, and digital voice and video) between multimedia workstations in a distributed system. There are two parts to the Lancaster multimedia work. First, we have developed an abstract model for multimedia communications that is based on the use of streams; and second, we have built an experimental system on which to test the implementation of protocols based on this model. This paper reports on both aspects of the Lancaster work, describing the results so far and identifying areas to be investigated further.

QoS Adaption and Flow Filtering in ATM Networks

The integration of multimedia systems which handle text, graphics, digital audio and video together with other media types is being encouraged by the development of international compression standards [JPEG 92, H.261 90, MPEG-I 93, MPEG-II 93]. Graphics, still images, high quality digital audio, and moving pictures in their uncompressed forms consume digital storage and network resources which far exceed likely availability in the near future. Compression can considerably support developing multimedia applications and will be a prerequisite in future multimedia systems engineering. Together with technological developments in high speed networks and multimedia workstations, new classes of distributed applications such as distance learning, desktop video-conferencing and video on demand are now possible. These applications place new and diverse Quality of Service (QoS) requirements on operating systems support, communication protocols and networks. The task of meeting these diverse QoS requirements is being assisted by the use of compression.

A microscopic look at WiFi fingerprinting for indoor mobile phone localization in diverse environments

WiFi fingerprinting has received much attention for indoor mobile phone localization. In this study, we examine the impact of various aspects underlying a WiFi fingerprinting system. Specifically, we investigate different definitions for fingerprinting and location estimation algorithms across different indoor environments ranging from a multi-storey office building to shopping centers of different sizes. Our results show that the fingerprint definition is as important as the choice of location estimation algorithm and there is no single combination of these two that works across all environments or even all floors of a given environment. We then consider the effect of WiFi frequency bands (e.g., 2.4GHz and 5GHz) and the presence of virtual access points (VAPs) on location accuracy with WiFi fingerprinting. Our results demonstrate that 5GHz signals are less prone to variation and thus yield more accurate location estimation. We also find that the presence of VAPs improves location estimation accuracy.

Urban WiFi characterization via mobile crowdsensing

We present a mobile crowdsensing approach for urban WiFi characterization that leverages commodity smartphones and the natural mobility of people. Specifically, we report measurement results obtained for Edinburgh, a representative European city, on detecting the presence of deployedWiFi APs via the mobile crowdsensing approach. They show that few channels in 2.4GHz are heavily used; in contrast, there is hardly any activity in the 5GHz band even though relatively it has a greater number of available channels. Spatial analysis of spectrum usage reveals that mutual interference among nearby APs operating in the same channel can be a serious problem with around 10 APs contending with each other in many locations. We find that the characteristics of WiFi deployments at city-scale are similar to that of WiFi deployments in public spaces of different indoor environments. We validate our approach in comparison with wardriving, and also show that our findings generally match with previous studies based on other measurement approaches. As an application of the mobile crowdsensing based urban WiFi monitoring, we outline a cloud based WiFi router configuration service for better interference management with global awareness in urban areas.

QoS Filters: Addressing the Heterogeneity Gap

Disparities in current computer technologies exist between networks, end-systems and user applications. Problems resulting from this heterogeneity gap are at their most acute in distributed multipeer environments. This paper addresses Quality of Service (QoS) disparities in heterogeneous multipeer internetworking and proposes the use of filters to bridge this aspect of the heterogeneity gap. These filter mechanisms must be sufficient adaptive to handle dynamic changes in both end-system and network capabilities. This paper discusses various filter mechanisms implemented at Lancaster University and the software developed to evaluate the feasibility of these mechanisms within a dynamic QoS controlled architecture.

A network interface unit to support continuous media

The combination of high-speed multiservice networks and multimedia workstations offers considerable potential for the development of distributed multimedia applications. A key problem is how to integrate continuous-media types such as audio and video into a distributed workstation environment. An experimental system architecture based on a specialized multimedia network interface that attempts to provide this integration is described. The design and implementation of this system are discussed in depth in terms of workstation enhancement and distributed system support. A new approach to the problem of media synchronization is introduced, and the importance of quality of service in the architecture is highlighted. Experiences encountered during this work are described, comparison with other approaches is made, and likely future developments in multimedia network interfacing are discussed. >

Visibility of individual packet loss on H.264 encoded video stream: a user study on the impact of packet loss on perceived video quality

Assessing video content transmitted over networked content infrastructures becomes a fundamental requirement for service providers. Previous research has shown that there is no direct correlation between traditional network QoS and user perceived video quality. This paper presents a study investigating the impact of individual packet loss on four types of H.264 main-profile encoded video streams. Four artifact factors to model the degree of artifacts in video frames are defined. Further, the visibility of artifacts considering the video content characteristics, encoding scheme and error concealment is investigated in conjunction with a user study. The individual and joint impacts of artifact factors are explored on the test video sequences. From the results of user tests, the artifact factor-based assessment method shows superiority over PSNR-based and network QoS based quality assessment.