| 1. |
|
|
| 2. |
- Arvidsson, Åke, 1957-, et al.
(author)
-
Load transients in pooled cellular core network nodes
- 2015
-
In: Performance evaluation (Print). - 0166-5316 .- 1872-745X. ; 90, s. 18-35
-
Journal article (peer-reviewed)abstract
- The coverage areas of cellular networks are logically subdivided into service areas. Each service area has a local anchor node which “hides” the mobility inside the area and the entire network has a global anchor node which “hides” the mobility between areas.The concept of unique local anchor nodes per service area was invented to simplify routing but has been found to complicate expansion. The rapidly growing demand for cellular access has therefore prompted for alternative solutions with pools of local anchor nodes per service area. Such pools are now deployed by several operators all over the world.Users in pooled service areas are mapped to specific pool members according to a load distribution policy, but the mapping can change as a result of node failures or operator interventions. Such changes take a certain time to implement and cause additional load on the anchor nodes. We study these processes in detail and derive closed form expressions which allow operators to control the trade-off between rapid changes and acceptable loads.Finally we show that the key assumptions of our model are in agreement with measured data and demonstrate how the model can be applied to investigate the effects of different network settings (timers) under different user behaviour (traffic and mobility).Contrary to current solutions to this problem, which typically are slow and/or inaccurate, our results enable fast and accurate analysis of different scenarios thereby enabling operators to maximise utilisation of the existing investments and at the same time avoid potentially dangerous situations of overload.
|
|
| 3. |
- Arvidsson, Åke, et al.
(author)
-
Load transients in pooled cellular core network nodes
- 2015
-
In: Performance evaluation (Print). - : Elsevier BV. - 0166-5316 .- 1872-745X. ; 90, s. 18-35
-
Journal article (peer-reviewed)abstract
- The coverage areas of cellular networks are logically subdivided into service areas. Each service area has a local anchor node which “hides” the mobility inside the area and the entire network has a global anchor node which “hides” the mobility between areas. The concept of unique local anchor nodes per service area was invented to simplify routing but has been found to complicate expansion. The rapidly growing demand for cellular access has therefore prompted for alternative solutions with pools of local anchor nodes per service area. Such pools are now deployed by several operators all over the world. Users in pooled service areas are mapped to specific pool members according to a load distribution policy, but the mapping can change as a result of node failures or operator interventions. Such changes take a certain time to implement and cause additional load on the anchor nodes. We study these processes in detail and derive closed form expressions which allow operators to control the trade-off between rapid changes and acceptable loads. Finally we show that the key assumptions of our model are in agreement with measured data and demonstrate how the model can be applied to investigate the effects of different network settings (timers) under different user behaviour (traffic and mobility). Contrary to current solutions to this problem, which typically are slow and/or inaccurate, our results enable fast and accurate analysis of different scenarios thereby enabling operators to maximise utilisation of the existing investments and at the same time avoid potentially dangerous situations of overload.
|
|
| 4. |
- Arvidsson, Åke, 1957-, et al.
(author)
-
Modelling user experience of adaptive streaming video over fixed capacity links
- 2021
-
In: Performance evaluation (Print). - 0166-5316 .- 1872-745X. ; 148, s. 1-12
-
Journal article (peer-reviewed)abstract
- Streaming video continues to experience unprecedented growth. This underscores the need to identify user-centric performance measures and models that will allow operators to satisfy requirements for cost-effective network dimensioning delivered with an acceptable level of user experience. This paper presents an analysis of two novel metrics in the context of fixed capacity links: (i) the average proportion of a video’s playing time during which the quality is reduced and (ii) the average proportion of videos which experience reduced quality at least once during their playing time, based on an M/M/∞ system. Our analysis is shown to hold for the more general M/G/∞ system for metric (i), but not for (ii) and simulation studies show an unexpected form of sensitivity of metric (ii) to the flow duration distribution, contrary to the norm of increasing variance causing worse performance. At typical operational loads these new metrics provide a more sensitive and information rich guide for understanding how user experience degrades, than the widely used average throughput metric does. We further show that only the combined use of this existing and our new metrics can provide a holistic perspective on overall user performance.
|
|
| 5. |
- Borghol, Youmna, et al.
(author)
-
Characterizing and modelling popularity of user-generated videos
- 2011
-
In: Performance evaluation (Print). - : Elsevier. - 0166-5316 .- 1872-745X. ; 68:11, s. 1037-1055
-
Journal article (peer-reviewed)abstract
- This paper develops a framework for studying the popularity dynamics of user-generated videos, presents a characterization of the popularity dynamics, and proposes a model that captures the key properties of these dynamics. We illustrate the biases that may be introduced in the analysis for some choices of the sampling technique used for collecting data; however, sampling from recently-uploaded videos provides a dataset that is seemingly unbiased. Using a dataset that tracks the views to a sample of recently-uploaded YouTube videos over the first eight months of their lifetime, we study the popularity dynamics. We find that the relative popularities of the videos within our dataset are highly non-stationary, owing primarily to large differences in the required time since upload until peak popularity is finally achieved, and secondly to popularity oscillation. We propose a model that can accurately capture the popularity dynamics of collections of recently-uploaded videos as they age, including key measures such as hot set churn statistics, and the evolution of the viewing rate and total views distributions over time.
|
|
| 6. |
- Carlsson, Niklas, et al.
(author)
-
Caching and optimized request routing in cloud-based content delivery systems
- 2014
-
In: Performance evaluation (Print). - : Elsevier. - 0166-5316 .- 1872-745X. ; 79, s. 38-55
-
Journal article (peer-reviewed)abstract
- Geographically distributed cloud platforms enable an attractive approach to large-scale content delivery. Storage at various sites can be dynamically acquired from (and released back to) the cloud provider so as to support content caching, according to the current demands for the content from the different geographic regions. When storage is sufficiently expensive that not all content should be cached at all sites, two issues must be addressed: how should requests for content be routed to the cloud provider sites, and what policy should be used for caching content using the elastic storage resources obtained from the cloud provider. Existing approaches are typically designed for non-elastic storage and little is known about the optimal policies when minimizing the delivery costs for distributed elastic storage.In this paper, we propose an approach in which elastic storage resources are exploited using a simple dynamic caching policy, while request routing is updated periodically according to the solution of an optimization model. Use of pull-based dynamic caching, rather than push-based placement, provides robustness to unpredicted changes in request rates. We show that this robustness is provided at low cost \textendash{} even with fixed request rates, use of the dynamic caching policy typically yields content delivery cost within 10\% of that with the optimal static placement. We compare request routing according to our optimization model to simpler baseline routing policies, and find that the baseline policies can yield greatly increased delivery cost relative to optimized routing. Finally, we present a lower-cost approximate solution algorithm for our routing optimization problem that yields content delivery cost within 2.5\% of the optimal solution.
|
|
| 7. |
- Carlsson, Niklas, et al.
(author)
-
Multicast Protocols for Scalable On-demand Download
- 2006
-
In: Performance evaluation (Print). - : Elsevier Science Publishers B. V.. - 0166-5316 .- 1872-745X. ; 63:9/10, s. 864-891
-
Journal article (peer-reviewed)abstract
- Previous scalable protocols for downloading large, popular files from a single server include batching and cyclic multicast. With batching, clients wait to begin receiving a requested file until the beginning of its next multicast transmission, which collectively serves all of the waiting clients that have accumulated up to that point. With cyclic multicast, the file data is cyclically transmitted on a multicast channel. Clients can begin listening to the channel at an arbitrary point in time, and continue listening until all of the file data has been received.This paper first develops lower hounds on the average and maximum client delay for completely downloading a file, as functions of the average server bandwidth used to serve requests for that file, for systems with homogeneous clients. The results show that neither cyclic multicast nor batching consistently yields performance close to optimal. New hybrid download protocols are proposed that achieve within 15% of the optimal maximum delay and 20% of the optimal average delay in homogeneous systems.For heterogeneous systems in which clients have widely varying achievable reception rates, an additional design question concerns the use of high rate transmissions, which can decrease delay for clients that can receive at such rates, in addition to low rate transmissions that can be received by all clients. A new scalable download protocol for such systems is proposed, and its performance is compared to that of alternative protocols as well as to new lower bounds on maximum client delay. The new protocol achieves within 25% of the optimal maximum client delay in all scenarios considered.
|
|
| 8. |
- Carlsson, Niklas, et al.
(author)
-
Performance Modeling of Anonymity Protocols
- 2012
-
In: Performance evaluation (Print). - : Elsevier. - 0166-5316 .- 1872-745X. ; 69:12, s. 643-661
-
Journal article (peer-reviewed)abstract
- Anonymous network communication protocols provide privacy for Internet-based communication. In this paper, we focus on the performance and scalability of anonymityprotocols. In particular, we develop performance models for two anonymityprotocols from the prior literature (Buses and Taxis), as well as our own newly proposed protocol (Motorcycles). Using a combination of experimental implementation, simulation, and analysis, we show that: (1) the message latency of the Buses protocol is O(N2), scaling quadratically with the number of participants; (2) the message latency of the Taxis protocol is O(N), scaling linearly with the number of participants; and (3) the message latency of the Motorcycles protocol is O(log2N), scaling logarithmically with the number of participants. Motorcycles can provide scalable anonymous network communication, without compromising the strength of anonymity provided by Buses or Taxis.
|
|
| 9. |
- Carlsson, Niklas, et al.
(author)
-
Worst-case bounds and optimized cache on Mth request cache insertion policies under elastic conditions
- 2018
-
In: Performance evaluation (Print). - : ELSEVIER SCIENCE BV. - 0166-5316 .- 1872-745X. ; 127, s. 70-92
-
Journal article (peer-reviewed)abstract
- Cloud services and other shared third-party infrastructures allow individual content providers to easily scale their services based on current resource demands. In this paper, we consider an individual content provider that wants to minimize its delivery costs under the assumptions that the storage and bandwidth resources it requires are elastic, the content provider only pays for the resources that it consumes, and costs are proportional to the resource usage. Within this context, we (i) derive worst-case bounds for the optimal cost and competitive cost ratios of different classes of cache on Mth request cache insertion policies, (ii) derive explicit average cost expressions and bounds under arbitrary inter request distributions, (iii) derive explicit average cost expressions and bounds for short tailed (deterministic, Erlang, and exponential) and heavy-tailed (Pareto) inter-request distributions, and (iv) present numeric and trace-based evaluations that reveal insights into the relative cost performance of the policies. Our results show that a window-based cache on 2nd request policy using a single threshold optimized to minimize worst-case costs provides good average performance across the different distributions and the full parameter ranges of each considered distribution, making it an attractive choice for a wide range of practical conditions where request rates of individual file objects typically are not known and can change quickly. (C) 2018 Elsevier B.V. All rights reserved.
|
|
| 10. |
- Dán, György, et al.
(author)
-
Stability and performance of overlay multicast systems employing forward error correction
- 2010
-
In: Performance evaluation (Print). - : Elsevier BV. - 0166-5316 .- 1872-745X. ; 67:2, s. 80-101
-
Journal article (peer-reviewed)abstract
- The two main sources of impairment in overlay multicast systems are packet losses and node churn. Yet, little is known about their effects on the data distribution performance. In this paper we develop an analytical model of a large class of peer-to-peer streaming architectures based on decomposition and non-linear recurrence relations. We analyze the stability properties of these systems using fixed-point analysis. We derive bounds on the probability that nodes in the overlay receive an arbitrary packet of the stream. Based on the model, we explain the effects of the overlay's size, node heterogeneity, loss correlations and node churn on the overlay's performance. Our findings lead us to the definition of an overlay structure with improved stability properties. We show how and under what conditions overlays can benefit from the use of error control solutions, prioritization and taxation schemes. Based on our results, we identify the components that are needed to achieve good data distribution performance in multi-tree-based overlay multicast.
|
|
