1,999 research outputs found
The origin of bursts and heavy tails in human dynamics
The dynamics of many social, technological and economic phenomena are driven
by individual human actions, turning the quantitative understanding of human
behavior into a central question of modern science. Current models of human
dynamics, used from risk assessment to communications, assume that human
actions are randomly distributed in time and thus well approximated by Poisson
processes. In contrast, there is increasing evidence that the timing of many
human activities, ranging from communication to entertainment and work
patterns, follow non-Poisson statistics, characterized by bursts of rapidly
occurring events separated by long periods of inactivity. Here we show that the
bursty nature of human behavior is a consequence of a decision based queuing
process: when individuals execute tasks based on some perceived priority, the
timing of the tasks will be heavy tailed, most tasks being rapidly executed,
while a few experience very long waiting times. In contrast, priority blind
execution is well approximated by uniform interevent statistics. These findings
have important implications from resource management to service allocation in
both communications and retail.Comment: Supplementary Material available at http://www.nd.edu/~network
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Performance modelling of a multiple threshold RED mechanism for bursty and correlated Internet traffic with MMPP arrival process
Access to the large web content hosted all over the world by users of the Internet engage
many hosts, routers/switches and faster links. They challenge the internet backbone to operate at
its capacity to assure e±cient content access. This may result in congestion and raises concerns over
various Quality of Service (QoS) issues like high delays, high packet loss and low throughput of the
system for various Internet applications. Thus, there is a need to develop effective congestion control
mechanisms in order to meet various Quality of Service (QoS) related performance parameters. In this
paper, our emphasis is on the Active Queue Management (AQM) mechanisms, particularly Random
Early Detection (RED). We propose a threshold based novel analytical model based on standard RED
mechanism. Various numerical examples are presented for Internet traffic scenarios containing both the
burstiness and correlation properties of the network traffic
Adaptive TTL-Based Caching for Content Delivery
Content Delivery Networks (CDNs) deliver a majority of the user-requested
content on the Internet, including web pages, videos, and software downloads. A
CDN server caches and serves the content requested by users. Designing caching
algorithms that automatically adapt to the heterogeneity, burstiness, and
non-stationary nature of real-world content requests is a major challenge and
is the focus of our work. While there is much work on caching algorithms for
stationary request traffic, the work on non-stationary request traffic is very
limited. Consequently, most prior models are inaccurate for production CDN
traffic that is non-stationary.
We propose two TTL-based caching algorithms and provide provable guarantees
for content request traffic that is bursty and non-stationary. The first
algorithm called d-TTL dynamically adapts a TTL parameter using a stochastic
approximation approach. Given a feasible target hit rate, we show that the hit
rate of d-TTL converges to its target value for a general class of bursty
traffic that allows Markov dependence over time and non-stationary arrivals.
The second algorithm called f-TTL uses two caches, each with its own TTL. The
first-level cache adaptively filters out non-stationary traffic, while the
second-level cache stores frequently-accessed stationary traffic. Given
feasible targets for both the hit rate and the expected cache size, f-TTL
asymptotically achieves both targets. We implement d-TTL and f-TTL and evaluate
both algorithms using an extensive nine-day trace consisting of 500 million
requests from a production CDN server. We show that both d-TTL and f-TTL
converge to their hit rate targets with an error of about 1.3%. But, f-TTL
requires a significantly smaller cache size than d-TTL to achieve the same hit
rate, since it effectively filters out the non-stationary traffic for
rarely-accessed objects
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
Optimal mobility-aware admission control in content delivery networks
This paper addresses the problem of mobility management in Content Delivery Networks (CDN). We introduce a CDN architecture where admission control is performed at mobility aware access routers. We formulate a Markov Modulated Poisson Decision Process for access control that captures the bursty nature of data and packetized traffic together with the heterogeneity of multimedia services. The optimization of performance parameters, like the blocking probabilities and the overall utilization, is conducted and the structural properties of the optimal solutions are also studied. Heuristics are proposed to encompass the computational difficulties of the optimal solution when several classes of multimedia traffic are considered
Performance analysis of MANET routing protocols in the presence of self-similar traffic
A number of measurement studies have convincingly demonstrated that network traffic can exhibit a noticeable self-similar nature, which has a considerable impact on queuing performance. However, many routing protocols developed for MANETs over the past few years have been primarily designed and analyzed under the assumptions of either CBR or Poisson traffic models, which are inherently unable to capture traffic self-similarity. It is crucial to re-examine the performance properties of MANETs in the context of more realistic traffic models before practical implementation show their potential performance limitations. In an effort towards this end, this paper evaluates the performance of three well-known and widely investigated MANET routing protocols, notably DSR, AODV and OLSR, in the presence of the bursty self-similar traffic. Different performance aspects are investigated including, delivery ratio, routing overhead, throughput and end-to-end delay. Our simulation results indicate that DSR routing protocol performs well with bursty traffic models compared to AODV and OLSR in terms of delivery ratio, throughput and end-to-end delay. On the other hand, OLSR performed poorly in the presence of self-similar traffic at high mobility especially in terms of data packet delivery ratio, routing overhead and delay. As for AODV routing protocol, the results show an average performance, yet a remarkably low and stable end-to-end delay
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User behaviour modelling for resource management in a hybrid UMTS/DVB-T network
Third generation mobile networks such as UMTS are designed to enhance the deployment of multimedia services providing high data rates and new flexible communication capabilities. However, these systems are interference limited and as such their performance is lowered in the case of a large number of users generating heavy traffic. A solution to this problem is to interconnect the UMTS network to a Digital Video Broadcasting-Terrestrial (DVB-T) network, so that the lack of capacity of UMTS during busy periods can be offset by the high bit rate available on the broadcast network. In order to justify this choice a prediction of the number of subscribers requesting the new multimedia applications designed for this scenario is needed. This paper focuses on the user behaviour modelling for multimedia services in a hybrid UMTS/DVB-T platform. The aim of the paper is to provide operators with a forecast of the demand for new multimedia services showing how they can be subject to a very high number of subscriptions, which UMTS would hardly be able to handle
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