Performance analysis of a caching algorithm for a catch-up television service

The catch-up TV (CUTV) service allows users to watch video content that was previously broadcast live on TV channels and later placed on an on-line video store. Upon a request from a user to watch a recently missed episode of his/her favourite TV series, the content is streamed from the video server to the customer's receiver device. This requires that an individual flow is set up for the duration of the video, and since it is hard to impossible to employ multicast streaming for this purpose (as users seldomly issue a request for the same episode at the same time), these flows are unicast. In this paper, we demonstrate that with the growing popularity of the CUTV service, the number of simultaneously running unicast flows on the aggregation parts of the network threaten to lead to an unwieldy increase in required bandwidth. Anticipating this problem and trying to alleviate it, the network operators deploy caches in strategic places in the network. We investigate the performance of such a caching strategy and the impact of its size and the cache update logic. We first analyse and model the evolution of video popularity over time based on traces we collected during 10 months. Through simulations we compare the performance of the traditional least-recently used and least-frequently used caching algorithms to our own algorithm. We also compare their performance with a "perfect" caching algorithm, which knows and hence does not have to estimate the video request rates. In the experimental data, we see that the video parameters from the popularity evolution law can be clustered. Therefore, we investigate theoretical models that can capture these clusters and we study the impact of clustering on the caching performance. Finally, some considerations on the optimal cache placement are presented

Distributional little's law for queues with heterogeneous server interruptions

Distributional forms of Little's law relate the steady-state distributions of the number of customers in a queueing system (system content) and the time a customer spends in the system (delay). A new law for discrete-time multiserver queues is discussed, with single-slot service times, a first-come-first-served discipline and heterogeneous server interruptions

Anomalieë in die geskiedenis van die Griekse Wysbegeerte

Die geskiedskrywing van die wysbegeerte is sowel ’n saak van historiese aanvoeling as van metodologiese geskooldheid. Sistematies aangelegde wysgere kan selde meer as ’n rasiona- listiese maakwerk van die geskiedenis tot stand bring by ge- brek aan daardie aanvoelingsvermoë wat enkel in ’n beperkte mate leerbaar is. ’n Mens besit daardie gawe of besit dit nie, net soos vir die een verstand vir die logika en vir die ander een vir die etiek voorbestem is. Daarom is ’n bepaalde „genia liteit” (die woord in etimologiese sin, nie in aksiologiese sin opgevat nie) ’n algemene voorvereiste om die lewe, ook die lewe van gedagtes te rekonstrueer. Gedagtes leef immers in die gees van mense en nie daarbuite as selfstandige wesens nie, en mense is voorasnog nie elektroniese masjienes, rasionalis- tiese of wiskundige deduksies of rasionalistiese formules nie. Daarbenewens veronderstel die geskiedenis ook metode, en metode is op sy beurt nie iets wat ’n mens somaar uit ’n pocket-boekie kan leer nie, maar wat spontaan uit die per- soonlike lewens- en werkervaring van die historikus self ont- staan en daardeur aan voortdurende korreksie blootgestel is. En dit lei tot ’n tweevoudige resultaat, eerstens dat ’n lewe van historiese ondersoek die enigste grondslag kan wees om met ’n ernstige kennis van sake oor die metode en sy veeler- hande vraagstukke te kan praat en tweedens dat die historikus gewoonlik gedurende die grootste gedeelte van sy historiogra- fiese loopbaan verplig word om met metodes te werk wat hy met verloop van tyd meer as een keer sal wysig

End-to-end QoE optimization through overlay network deployment

In this paper an overlay network for end-to-end QoE management is presented. The goal of this infrastructure is QoE optimization by routing around failures in the IP network and optimizing the bandwidth usage on the last mile to the client. The overlay network consists of components that are located both in the core and at the edge of the network. A number of overlay servers perform end-to-end QoS monitoring and maintain an overlay topology, allowing them to route around link failures and congestion. Overlay access components situated at the edge of the network are responsible for determining whether packets are sent to the overlay network, while proxy components manage the bandwidth on the last mile. This paper gives a detailed overview of the end-to-end architecture together with representative experimental results which comprehensively demonstrate the overlay network's ability to optimize the QoE

Cooperative announcement-based caching for video-on-demand streaming

Recently, video-on-demand (VoD) streaming services like Netflix and Hulu have gained a lot of popularity. This has led to a strong increase in bandwidth capacity requirements in the network. To reduce this network load, the design of appropriate caching strategies is of utmost importance. Based on the fact that, typically, a video stream is temporally segmented into smaller chunks that can be accessed and decoded independently, cache replacement strategies have been developed that take advantage of this temporal structure in the video. In this paper, two caching strategies are proposed that additionally take advantage of the phenomenon of binge watching, where users stream multiple consecutive episodes of the same series, reported by recent user behavior studies to become the everyday behavior. Taking into account this information allows us to predict future segment requests, even before the video playout has started. Two strategies are proposed, both with a different level of coordination between the caches in the network. Using a VoD request trace based on binge watching user characteristics, the presented algorithms have been thoroughly evaluated in multiple network topologies with different characteristics, showing their general applicability. It was shown that in a realistic scenario, the proposed election-based caching strategy can outperform the state-of-the-art by 20% in terms of cache hit ratio while using 4% less network bandwidth

Real-time media: spiegel van de zintuigen

‘Beauty lies in the eye of the beholder’. Bij de uitvinding van de lp en de videoband lieten ingenieurs zich in de eerste plaats leiden door hun kennis van fysica. De maatstaf voor de kwaliteit van audio of video was een set van technisch meetbare parameters. Deze aanpak heeft plaats geruimd voor zogeheten subjectieve maatstaven, die zo dicht mogelijk aansluiten bij de menselijke waarneming. In deze voordracht lichten we toe hoe de menselijke perceptie vormgegeven heeft aan hedendaagse real-time mediastandaarden, met toepassingen in online radio, video en telefonie

Decomposing SLAs for Network Slicing

In Press / En PrensaWhen a network slice is requested, multiple technology and/or administrative domains are invoked to ensure that the slice end-to-end service level agreement (SLA) is met. Therefore, this SLA requirement needs to be decomposed in portions that each of the domains can support. In this paper we consider a management architecture consisting of an end-to-end service orchestrator responsible for decomposing the SLA, and domain controllers that govern their respective domain. The orchestrator has no detailed knowledge of the state of the resources in each of the domains when the network slice is requested. The orchestrator is only aware of the responses of the domains to previous requests, and captures this knowledge in a risk model associated with each domain. In this study, we propose an approach for decomposing the end-to-end SLA based on the best current estimate of the risk models of all involved domains. We further describe how the risk model for a particular domain is determined (and updated) based on historical data.Work partially funded by the EU H2020 5GROWTH Project (grant no. 856709)

An autonomic delivery framework for HTTP adaptive streaming in multicast-enabled multimedia access networks

The consumption of multimedia services over HTTP-based delivery mechanisms has recently gained popularity due to their increased flexibility and reliability. Traditional broadcast TV channels are now offered over the Internet, in order to support Live TV for a broad range of consumer devices. Moreover, service providers can greatly benefit from offering external live content (e. g., YouTube, Hulu) in a managed way. Recently, HTTP Adaptive Streaming (HAS) techniques have been proposed in which video clients dynamically adapt their requested video quality level based on the current network and device state. Unlike linear TV, traditional HTTP- and HAS-based video streaming services depend on unicast sessions, leading to a network traffic load proportional to the number of multimedia consumers. In this paper we propose a novel HAS-based video delivery architecture, which features intelligent multicasting and caching in order to decrease the required bandwidth considerably in a Live TV scenario. Furthermore we discuss the autonomic selection of multicasted content to support Video on Demand (VoD) sessions. Experiments were conducted on a large scale and realistic emulation environment and compared with a traditional HAS-based media delivery setup using only unicast connections

On the merits of SVC-based HTTP adaptive streaming

HTTP Adaptive Streaming (HAS) is quickly becoming the dominant type of video streaming in Over-The-Top multimedia services. HAS content is temporally segmented and each segment is offered in different video qualities to the client. It enables a video client to dynamically adapt the consumed video quality to match with the capabilities of the network and/or the client's device. As such, the use of HAS allows a service provider to offer video streaming over heterogeneous networks and to heterogeneous devices. Traditionally, the H. 264/AVC video codec is used for encoding the HAS content: for each offered video quality, a separate AVC video file is encoded. Obviously, this leads to a considerable storage redundancy at the video server as each video is available in a multitude of qualities. The recent Scalable Video Codec (SVC) extension of H. 264/AVC allows encoding a video into different quality layers: by dowloading one or more additional layers, the video quality can be improved. While this leads to an immediate reduction of required storage at the video server, the impact of using SVC-based HAS on the network and perceived quality by the user are less obvious. In this article, we characterize the performance of AVC- and SVC-based HAS in terms of perceived video quality, network load and client characteristics, with the goal of identifying advantages and disadvantages of both options