11 research outputs found
Probabilistic Analysis of Buffer Starvation in Markovian Queues
International audienceOur purpose in this paper is to obtain the \emph{exact distribution} of the number of buffer starvations within a sequence of consecutive packet arrivals. The buffer is modeled as an M/M/1 queue. When the buffer is empty, the service restarts after a certain amount of packets are \emph{prefetched}. With this goal, we propose two approaches, one of which is based on \emph{Ballot theorem}, and the other uses recursive equations. The Ballot theorem approach gives an explicit solution, but at the cost of the high complexity order in certain circumstances. The recursive approach, though not offering an explicit result, needs fewer computations. We further propose a fluid analysis of starvation probability on the file level, given the distribution of file size and the traffic intensity. The starvation probabilities of this paper have many potential applications. We apply them to optimize the quality of experience (QoE) of media streaming service, by exploiting the tradeoff between the start-up delay and the starvation
Multipath streaming: fundamental limits and efficient algorithms
We investigate streaming over multiple links. A file is split into small
units called chunks that may be requested on the various links according to
some policy, and received after some random delay. After a start-up time called
pre-buffering time, received chunks are played at a fixed speed. There is
starvation if the chunk to be played has not yet arrived. We provide lower
bounds (fundamental limits) on the starvation probability of any policy. We
further propose simple, order-optimal policies that require no feedback. For
general delay distributions, we provide tractable upper bounds for the
starvation probability of the proposed policies, allowing to select the
pre-buffering time appropriately. We specialize our results to: (i) links that
employ CSMA or opportunistic scheduling at the packet level, (ii) links shared
with a primary user (iii) links that use fair rate sharing at the flow level.
We consider a generic model so that our results give insight into the design
and performance of media streaming over (a) wired networks with several paths
between the source and destination, (b) wireless networks featuring spectrum
aggregation and (c) multi-homed wireless networks.Comment: 24 page
Flow Level QoE of Video Streaming in Wireless Networks
The Quality of Experience (QoE) of streaming service is often degraded by
frequent playback interruptions. To mitigate the interruptions, the media
player prefetches streaming contents before starting playback, at a cost of
delay. We study the QoE of streaming from the perspective of flow dynamics.
First, a framework is developed for QoE when streaming users join the network
randomly and leave after downloading completion. We compute the distribution of
prefetching delay using partial differential equations (PDEs), and the
probability generating function of playout buffer starvations using ordinary
differential equations (ODEs) for CBR streaming. Second, we extend our
framework to characterize the throughput variation caused by opportunistic
scheduling at the base station, and the playback variation of VBR streaming.
Our study reveals that the flow dynamics is the fundamental reason of playback
starvation. The QoE of streaming service is dominated by the first moments such
as the average throughput of opportunistic scheduling and the mean playback
rate. While the variances of throughput and playback rate have very limited
impact on starvation behavior.Comment: 14 page
Analysis of Buffer Starvation with Application to Objective QoE Optimization of Streaming Services
Our purpose in this paper is to characterize buffer starvations for streaming
services. The buffer is modeled as an M/M/1 queue, plus the consideration of
bursty arrivals. When the buffer is empty, the service restarts after a certain
amount of packets are \emph{prefetched}. With this goal, we propose two
approaches to obtain the \emph{exact distribution} of the number of buffer
starvations, one of which is based on \emph{Ballot theorem}, and the other uses
recursive equations. The Ballot theorem approach gives an explicit result. We
extend this approach to the scenario with a constant playback rate using
T\`{a}kacs Ballot theorem. The recursive approach, though not offering an
explicit result, can obtain the distribution of starvations with
non-independent and identically distributed (i.i.d.) arrival process in which
an ON/OFF bursty arrival process is considered in this work. We further compute
the starvation probability as a function of the amount of prefetched packets
for a large number of files via a fluid analysis. Among many potential
applications of starvation analysis, we show how to apply it to optimize the
objective quality of experience (QoE) of media streaming, by exploiting the
tradeoff between startup/rebuffering delay and starvations.Comment: 9 pages, 7 figures; IEEE Infocom 201
Subjective quality assessment of longer duration video sequences delivered over HTTP adaptive streaming to tablet devices
HTTP adaptive streaming facilitates video streaming to mobile devices connected through heterogeneous networks without the need for a dedicated streaming infrastructure. By splitting different encoded versions of the same video into small segments, clients can continuously decide which segments to download based on available network resources and device characteristics. These encoded versions can, for example, differ in terms of bitrate and spatial or temporal resolution. However, as a result of dynamically selecting video segments, perceived video quality can fluctuate during playback which will impact end-users' quality of experience. Subjective studies have already been conducted to assess the influence of video delivery using HTTP Adaptive Streaming to mobile devices. Nevertheless, existing studies are limited to the evaluation of short video sequences in controlled environments. Research has already shown that video duration and assessment environment influence quality perception. Therefore, in this article, we go beyond the traditional ways for subjective quality evaluation by conducting novel experiments on tablet devices in more ecologically valid testing environments using longer duration video sequences. As such, we want to mimic realistic viewing behavior as much as possible. Our results show that both video content and the range of quality switches significantly influence end-users' rating behavior. In general, quality level switches are only perceived in high motion sequences or in case switching occurs between high and low quality video segments. Moreover, we also found that video stallings should be avoided during playback at all times
Impact of flow-level dynamics on QoE of video streaming in wireless networks
International audienceThe Quality of Experience (QoE) of streaming service is often degraded by frequent playback interruptions. To mitigate the interruptions, the media player prefetches streaming contents before starting playback, at a cost of delay. We study the QoE of streaming from the perspective of flow dynamics. First, a framework is developed for QoE when streaming users join the network randomly and leave after downloading completion. We compute the distribution of prefetching delay using partial differential equations (PDEs), and the probability generating function of playout buffer starvations using ordinary differential equations (ODEs). Second, we extend our framework to characterize the throughput variation caused by opportunistic scheduling at the base station in the presence of fast fading. Our study reveals that the flow dynamics is the fundamental reason of playback starvation. The QoE of streaming service is dominated by the average throughput of opportunistic scheduling, while the variance of throughput has very limited impact on starvation behavior
Duality relations in finite queueing models
Motivated by applications in multimedia streaming and in energy systems, we study duality relations in fi nite queues. Dual of a queue is de fined to be a queue in which the arrival and service processes are interchanged. In other words, dual of the G1/G2/1/K queue is the G2/G1/1/K queue, a queue in which the inter-arrival times have the same distribution as the service times
of the primal queue and vice versa. Similarly, dual of a fluid flow queue
with cumulative input C(t) and available processing S(t) is a fluid queue
with cumulative input S(t) and available processing C(t). We are primarily interested in finding relations between the overflow and underflow of the primal and dual queues. Then, using existing results in the literature regarding the probability of loss and the stationary probability of queue being
full, we can obtain estimates on the probability of starvation and the probability of the queue being empty. The probability of starvation corresponds to the probability that a queue becomes empty, i.e., the end of a busy period.
We study the relations between arrival and departure Palm distributions and their relations to stationary distributions. We consider both the case of point process inputs as well as fluid inputs. We obtain inequalities between the probability of the queue being empty and the probability of the queue being full for both the time stationary and Palm distributions by interchanging arrival and service processes. In the
fluid queue case, we show that there is an equality between arrival and departure distributions that leads to an equality between the probability of starvation in the primal queue and the probability of overflow in the dual queue. The techniques are based on monotonicity arguments and coupling. The usefulness of the bounds is illustrated via numerical results.1 yea