Danny De Vleeschauwer

Objective and subjective evaluation of the influence of small amounts of delay and jitter on a recent first person shooter game

There have been several studies in the past years that investigate the impact of network delay on multi-user applications. Primary examples of these applications are real-time multiplayer games. These studies have shown that high network delays and jitter may indeed influence the players perception of the quality of the game. However, the proposed test values, which are often high, are not always representative for a large percentile of on-line game players. We have therefore investigated the influence of delay and jitter with numbers that are more representative for typical access networks. This in effect allows us to simulate a setup with multiplayer game servers that are located at ISP level and players connected through that ISPs access network. To obtain further true-to-life results, we opted to carry out the test using a recent first person shooter (FPS) game, Unreal Tournament 2003. It can, after all, be expected that this new generation of games has built-in features to diminish the effect of small delay values, given the popularity of playing these games over the Internet. In this paper, we have investigated both subjective perceived quality and objective measurements and will show that both are indeed influenced by even these small delay and jitter values.

Increasing the user perceived quality for IPTV services

Currently, digital television is gradually replacing analogue TV. Although these digital TV services can be delivered via various broadcast networks (e.g., terrestrial, cable, satellite), Internet Protocol TV over broadband telecommunication networks offers much more than traditional broadcast TV. Not only can it improve the quality that users experience with this linear programming TV service, but it also paves the way for new TV services, such as video-on- demand, time-shifted TV, and network personal video recorder services, because of its integral return channel and the ability to address individual users. This article first provides an overview of a typical IPTV network architecture and some basic video coding concepts. Based on these, we then explain how IPTV can increase the linear programming TV quality experienced by end users by reducing channel-change latency and mitigating packet loss. For the latter, forward error correction and automatic repeat request techniques are discussed, whereas for the former a solution based on a circular buffer strategy is described. This article further argues that the availability of larger buffers in the network enables IPTV to better offer new services (in particular, time-shifted TV, network personal video recorder, and video-on-demand) than the competing platforms.

iDASH: improved dynamic adaptive streaming over HTTP using scalable video coding

HTTP-based delivery for Video on Demand (VoD) has been gaining popularity within recent years. Progressive Download over HTTP, typically used in VoD, takes advantage of the widely deployed network caches to relieve video servers from sending the same content to a high number of users in the same access network. However, due to a sharp increase in the requests at peak hours or due to cross-traffic within the network, congestion may arise in the cache feeder link or access link respectively. Since the connection characteristics may vary over the time, with Dynamic Adaptive Streaming over HTTP (DASH), a technique that has been recently proposed, video clients may dynamically adapt the requested video quality for ongoing video flows, to match their current download rate as good as possible. In this work we show the benefits of using the Scalable Video Coding (SVC) for such a DASH environment.

Techniques for measuring quality of experience

Quality of Experience (QoE) relates to how users perceive the quality of an application. To capture such a subjective measure, either by subjective tests or via objective tools, is an art on its own. Given the importance of measuring users’ satisfaction to service providers, research on QoE took flight in recent years. In this paper we present an overview of various techniques for measuring QoE, thereby mostly focusing on freely available tools and methodologies.

Assessing voice quality in packet-based telephony

Our goal is to extend recommendations ITU-T G.114 and G.131 to cover distorted phone calls transported (partly) over a packet-based network. We assume the user terminals to be optimally tuned and focus on how network parameters-delay, packet loss, jitter, and so on-influence voice quality. We then discuss how those parameters can be quantified and incorporated into a model that lets us predict the quality of any packet-based phone call.

Access network delay in networked games

The end-to-end delay (also referred to as latency) experienced by gaming users has a significant impact on the quality of online games. In this paper we concentrate on the delay introduced in access networks. This access network delay depends on the access technology used, the network load, the link rate configured on the access links (also referred to as the last mile link) and the size of the packets generated by the games. We characterize this access network delay by means of measurements. First, we focus on this delay in actually deployed access networks: dial-up, cable and Asymmetric Digital Subscriber Line (ADSL) access. In these access networks the access network delay shoots up as soon as the gaming user (or somebody else on the users home network) saturates the users last mile link with traffic generated by applications (e.g. web browser) other than the games. Therefore, we also characterize the access network delay in a laboratory set-up of a QoS-enabled ADSL network. In this set-up we show that it is possible to (logically) segregate the game traffic from the other traffic to such an extent that the game packets are not excessively delayed while at the same time a large part of the link capacity can be consumed by the other traffic.

Performance of Caching Algorithms for IPTV On-Demand Services

Due to its native return channel and its ability to easily address each user individually an IPTV system is very well suited to offer on-demand services. Those services are becoming more popular as there is an undeniable trend that users want to watch the offered content when and where it suits them best. Because multicast can no longer be relied upon for such services, as was the case when offering linear-programming TV, this trend risks to increase the traffic unwieldy over some parts of the IPTV network unless caches are deployed in strategic places within it. Since caches are limited in size and the popularity of on-demand content is volatile (i.e., changing over time), it is not straightforward to decide which objects to cache at which moment in time. This paper introduces and studies a caching algorithm that tracks the popularity of objects to make intelligent caching decisions. We will show that when its parameters are set equal or close to their optimal values this algorithm outperforms traditional algorithms as LRU (least-recently used) and LFU (least-frequently used). After a generic study of the algorithm fed by a user demand model that takes the volatility of the objects into account we will discuss two particular cases of an on-demand service, video-on-demand and catch-up TV, for each of which we give guidelines on how to dimension their associated caches.

Efficient HTTP-based streaming using Scalable Video Coding

HTTP-based video streaming has been gaining popularity within the recent years. There are multiple benefits of relying on HTTP/TCP connections, such as the usage of the widely deployed network caches to relieve video servers from sending the same content to a high number of users and the avoidance of traversal issues with firewalls and NATs typical for RTP/UDP-based solutions. Therefore, many service providers resort to adopt HTTP streaming as the basis for their services. In this paper, the benefits of using the Scalable Video Coding (SVC) for a HTTP streaming service are shown, and the SVC based approach is compared to the AVC based approach. We show that network resources are more efficiently used and how the benefits of the traditional techniques can even be heightened by adopting the Scalable Video Coding (SVC) as the video codec for adaptive low delay streaming over HTTP. For the latter small playout-buffers are considered hence allowing low media access latency in the delivery chain and it is shown that adaptation is more effectively performed with the SVC based approach.

Optimization of HTTP adaptive streaming over mobile cellular networks

Video streaming, in particular, hypertext transfer protocol based (HTTP) adaptive streaming (HAS) of video, is expected to be a dominant application over mobile networks in the near future. The observation that the base station can alter the video quality requested by a HAS client to its server by controlling the over-the-air throughput from the base station to the client implies that the base station can jointly maximize aggregate video quality of all the HAS flows and throughput of data flows that it serves. We formulate a utility maximization problem that separately takes into account different utility functions for video and data flows and show that the utility maximization can be achieved through an algorithm, we term adaptive guaranteed bit rate (AGBR), wherein target bit rates are calculated for each HAS flow and passed on to an underlying minimum rate proportional fair scheduler that schedules resources across all the flows. This approach has the advantage that it retains the existing scheduling function in the base station with a separate function to compute the target bit rates for the video flows allowing them to only change slowly over time in order to avoid frequent video quality changes. Through analytical modeling and simulations we show that the proposed algorithm can achieve required fairness among the video flows as well as automatically and fairly adapt video quality with increasing congestion thereby preventing data flow throughput starvation.

Analysis and Modeling of Video Popularity Evolution in Various Online Video Content Systems: Power-Law versus Exponential Decay

Internet evolved from a world communication network with restricted information transmission capabilities into an entertainment and information network with many broadband clients and more multimedia-rich applications. In particular, video (streaming) applications are gaining in popularity and usage, but those are also notorious for their high resources demand. A study of the popularity evolution of videos in different online video content systems can give insight and have implications for adequate network dimensioning. In this paper we study and model the popularity evolution of some video traces from YouTube, one Dutch catch-up TV online portal, and historical data on DVD rentals in the US. The model we put forward can degenerate into either a power-law distribution or an exponential distribution depending on its form-determining parameter. We find out that not all traces have a power-law decay as suggested in other works, but also a significant part of those expose an exponential popularity evolution.