Hugh Melvin

Time synchronization for VoIP quality of service

Various approaches seek to optimize the quality of service of VoIP applications. We propose a system that uses synchronized time to combine the useful characteristics of both fixed and adaptive buffer strategies, thereby improving VoIP quality of service. Using a combination of global positioning system (GPS) technologies and the network time protocol (NTP), hosts can learn the precise end-to-end delay for each packet. This information can benefit both domestic and business Internet telephony users. We outline our proposed system and discuss issues arising from the use of synchronized time.

Can context monitoring improve QoE? A case study of video flash crowds in the internet of services

Over the last decade or so, significant research has focused on defining Quality of Experience (QoE) of Multimedia Systems and identifying the key factors that collectively determine it. Some consensus thus exists as to the role of System Factors, Human Factors and Context Factors. In this paper, the notion of context is broadened to include information gleaned from simultaneous out-of-band channels, such as social network trend analytics, that can be used if interpreted in a timely manner, to help further optimise QoE. A case study involving simulation of HTTP adaptive streaming (HAS) and load balancing in a content distribution network (CDN) in a flash crowd scenario is presented with encouraging results.

Understanding Timelines Within MPEG Standards

Nowadays, media content can be delivered via diverse broadband and broadcast technologies. Although these different technologies have somehow become rivals, their coordinated usage and convergence, by leveraging of their strengths and complementary characteristics, can bring many benefits to both operators and customers. For example, broadcast TV content can be augmented by on-demand broadband media content to provide enriched and personalized services, such as multi-view TV, audio language selection, and inclusion of real-time web feeds. A piece of evidence is the recent Hybrid Broadcast Broadband TV (HbbTV) standard, which aims at harmonizing the delivery and consumption of (hybrid) broadcast and broadband TV content. A key challenge in these emerging scenarios is the synchronization between the involved media streams, which can be originated by the same or different sources, and delivered via the same or different technologies. To enable synchronized (hybrid) media delivery services, some mechanisms providing timelines at the source side are necessary to accurately time align the involved media streams at the receiver-side. This paper provides a comprehensive review of how clock references (timing) and timestamps (time) are conveyed and interpreted when using the most widespread delivery technologies, such as DVB, RTP/RTCP and MPEG standards (e.g., MPEG-2, MPEG-4, MPEG-DASH, and MMT). It is particularly focused on the format, resolution, frequency, and the position within the bitstream of the fields conveying timing information, as well as on the involved components and packetization aspects. Finally, it provides a survey of proofs of concepts making use of these synchronization related mechanisms. This complete and thorough source of information can be very useful for scholars and practitioners interested in media services with synchronization demands.

Effective synchronisation of Hybrid Broadcast and Broadband TV

Watching a sport event via an IPTV channel and choosing a broadcast radio station as a play-out audio stream is the scenario discussed in this paper. Hybrid Broadcast and Broadband TV (hbbTV) provides an excellent platform to combine multimedia delivered via both systems. By following the recommendations in this paper, a synchronized play-out of multiple media streams delivered via the hbbTV system can be achieved.

An evaluation of the potential of synchronized time to improve voice over IP quality

Delivering PSTN-like quality over current best-effort Internet infrastructure presents many technical challenges. Much research has focused on receiver-based approaches, which adapt to varying network conditions in order to optimize playout quality. In this paper, we propose and evaluate a receiver-based approach that implements a hybrid adaptive-fixed playout regime by integrating synchronized time into the playout algorithm. Such as approach can deliver significantly better quality than existing adaptive techniques particularly when the underlying network is not heavily congested and end-to-end delays are not excessive. We present some initial results form our testbed system using the ITU-T E-model to quantify improvement.

An integrated NTP-RTCP solution to audio skew detection and compensation for VoIP applications

The circuit switched POTS (plain old telephone system) preserves the timing relationship between media samples from sender to receiver through use of a common clock. For PC-based Internet multimedia, the existence of separate audio and system clocks on either end-host can introduce significant complications. Much work has taken place in recent years that addresses the issue of system clock skew and its effect on precise delay measurement. In a voice over IP (VoIP) environment, where adaptive buffering techniques are employed, system and audio clock skew can distort both delay measurement and playout control as well as lead to poor buffer performance. This paper presents a high level mechanism to measure and compensate for the skew relationships between system and audio clocks at each end of a multimedia session. The mechanism utilises both the network time protocol (NTP) and the RTP (realtime transport protocol) control protocol or RTCP. Preliminary and positive results are presented from a testbed system and plans for further work are outlined.

Dynamic Flooding Time Synchronisation Protocol for WSNs

This paper describes and validates an extension to the widely used Flooding Time Synchronisation Protocol (FTSP) namely Dynamic Flooding Time Synchronisation Protocol for Wireless Sensor Networks. The extension enhances FTSP by dynamically optimising communication exchange with the dual aim of conserving energy whilst improving accuracy. This optimisation is realised by altering the transmission rate of motes based on real-time monitoring and the WSN application accuracy requirements. The proposed mechanism, thus, eliminates the need with FTSP to determine and pre-configure a suitable transmission interval for a particular environment. Our results show that the proposed protocol extension can perform as well as FTSP in a stable temperature environment and can achieve similar accuracies with a much reduced (up to 75 percent) number of transmissions in an environment whereby motes are exposed to temperature fluctuations.

Enhanced IPTV services through time synchronisation

User interactivity and customisation are key features that must be promoted to help distinguish IPTV from satellite/aerial/cable TV alternatives. Furthermore, IPTV providers also have to compete with Internet TV by providing extra features to justify the cost. In this paper, we present a number of scenarios whereby IPTV providers can achieve this through the use of synchronised time. Integrating and tightly synchronising multiple user-selected media streams in Real-Time that are logically and temporally related potentially adds significant extra value to any IPTV platform. It also raises significant research challenges. We outline the prototype developed for a TV/Text Feed scenario and present some details of ongoing and future work.

Detailed comparative analysis of PESQ and VISQOL behaviour in the context of playout delay adjustments introduced by VOIP jitter buffer algorithms

This paper undertakes a detailed comparative analysis of both PESQ and VISQOL model behaviour, when tested against speech samples modified through playout delay adjustments. The adjustments are typical (in extent and magnitude) to those introduced by VoIP jitter buffer algorithms. Furthermore, the analysis examines the impact of adjustment location as well as speaker factors on MOS scores predicted by both models and seeks to determine if both models are able to correctly predict the impact on quality perceived by the end user from earlier subjective tests. The earlier results showed speaker voice preference and potentially wideband experience dominating subjective tests more than playout delay adjustment duration or location. By design, PESQ and VISQOL do not qualify speaker voice difference reducing their correlation with the subjective tests. In addition, it was found that PESQ scores are impacted by playout delay adjustments and thus the impact of playout delay adjustments on a quality perceived by the end user is not well modelled. On the other hand, VISQOL model is better in predicting an impact of playout delay adjustments on a quality perceived by the user but there are still some discrepancies in the predicted scores. The reasons for those discrepancies are particularly analysed and discussed.

The role of ICT in evolving SmartGrids

Energy Systems are rapidly evolving, driven by a combination of factors, including cost, efficiency, environmental impact and security-of-supply, while being facilitated by increased deregulation. This complexity is facilitated by the rollout of complex Information & Communications Technology (ICT) systems that will play a significant role in operating, managing, planning, and securing the energy infrastructure. SmartGrid is an umbrella term used to describe the broad scope of interdependent systems that make up this modernized grid. These systems cover the full life cycle of energy from generation to transmission, distribution, and consumption. SmartGrid through use of ICT enables bidirectional flows of energy between these component systems and uses two-way communication and control capabilities to maintain efficiency, availability, and robustness. SmartGrid will bring about significant economic and environmental benefits to consumers, organisations, and countries, all facilitated by ICT. This paper provides a high level overview of the role of ICT in SmartGrid, focusing on some of the key issues.