164 research outputs found
Randomized rounding algorithms for large scale unsplittable flow problems
Unsplittable flow problems cover a wide range of telecommunication and
transportation problems and their efficient resolution is key to a number of
applications. In this work, we study algorithms that can scale up to large
graphs and important numbers of commodities. We present and analyze in detail a
heuristic based on the linear relaxation of the problem and randomized
rounding. We provide empirical evidence that this approach is competitive with
state-of-the-art resolution methods either by its scaling performance or by the
quality of its solutions. We provide a variation of the heuristic which has the
same approximation factor as the state-of-the-art approximation algorithm. We
also derive a tighter analysis for the approximation factor of both the
variation and the state-of-the-art algorithm. We introduce a new objective
function for the unsplittable flow problem and discuss its differences with the
classical congestion objective function. Finally, we discuss the gap in
practical performance and theoretical guarantees between all the aforementioned
algorithms
Merlin: A Language for Provisioning Network Resources
This paper presents Merlin, a new framework for managing resources in
software-defined networks. With Merlin, administrators express high-level
policies using programs in a declarative language. The language includes
logical predicates to identify sets of packets, regular expressions to encode
forwarding paths, and arithmetic formulas to specify bandwidth constraints. The
Merlin compiler uses a combination of advanced techniques to translate these
policies into code that can be executed on network elements including a
constraint solver that allocates bandwidth using parameterizable heuristics. To
facilitate dynamic adaptation, Merlin provides mechanisms for delegating
control of sub-policies and for verifying that modifications made to
sub-policies do not violate global constraints. Experiments demonstrate the
expressiveness and scalability of Merlin on real-world topologies and
applications. Overall, Merlin simplifies network administration by providing
high-level abstractions for specifying network policies and scalable
infrastructure for enforcing them
Fast network configuration in Software Defined Networking
Software Defined Networking (SDN) provides a framework to dynamically adjust and re-program the data plane with the use of flow rules. The realization of highly adaptive SDNs with the ability to respond to changing demands or recover after a network failure in a short period of time, hinges on efficient updates of flow rules. We model the time to deploy a set of flow rules by the update time at the bottleneck switch, and formulate the problem of selecting paths to minimize the deployment time under feasibility constraints as a mixed integer linear program (MILP). To reduce the computation time of determining flow rules, we propose efficient heuristics designed to approximate the minimum-deployment-time solution by relaxing the MILP or selecting the paths sequentially. Through extensive simulations we show that our algorithms outperform current, shortest path based solutions by reducing the total network configuration time up to 55% while having similar packet loss, in the considered scenarios. We also demonstrate that in a networked environment with a certain fraction of failed links, our algorithms are able to reduce the average time to reestablish disrupted flows by 40%
Randomized rounding algorithms for large scale unsplittable flow problems
Unsplittable flow problems cover a wide range of telecommunication and transporta-
tion problems and their efficient resolution is key to a number of applications. In
this work, we study algorithms that can scale up to large graphs and important num-
bers of commodities. We present and analyze in detail a heuristic based on the linear
relaxation of the problem and randomized rounding. We provide empirical evidence
that this approach is competitive with state-of-the-art resolution methods either by its
scaling performance or by the quality of its solutions. We provide a variation of the
heuristic which has the same approximation factor as the state-of-the-art approxima-
tion algorithm. We also derive a tighter analysis for the approximation factor of both
the variation and the state-of-the-art algorithm. We introduce a new objective function
for the unsplittable flow problem and discuss its differences with the classical con-
gestion objective function. Finally, we discuss the gap in practical performance and
theoretical guarantees between all the aforementioned algorithms
Data transfer scheduling with advance reservation and provisioning
Over the years, scientific applications have become more complex and more data intensive. Although through the use of distributed resources the institutions and organizations gain access to the resources needed for their large-scale applications, complex middleware is required to orchestrate the use of these storage and network resources between collaborating parties, and to manage the end-to-end processing of data. We present a new data scheduling paradigm with advance reservation and provisioning. Our methodology provides a basis for provisioning end-to-end high performance data transfers which require integration between system, storage and network resources, and coordination between reservation managers and data transfer nodes. This allows researchers/users and higher level meta-schedulers to use data placement as a service where they can plan ahead and reserve time and resources for their data movement operations. We present a novel approach for evaluating time-dependent structures with bandwidth guaranteed paths. We present a practical online scheduling model using advance reservation in dynamic network with time constraints. In addition, we report a new polynomial algorithm presenting possible reservation options and alternatives for earliest completion and shortest transfer duration. We enhance the advance network reservation system by extending the underlying mechanism to provide a new service in which users submit their constraints and the system suggests possible reservation requests satisfying users\u27 requirements. We have studied scheduling data transfer operation with resource and time conflicts. We have developed a new scheduling methodology considering resource allocation in client sites and bandwidth allocation on network link connecting resources. Some other major contributions of our study include enhanced reliability, adaptability, and performance optimization of distributed data placement tasks. While designing this new data scheduling architecture, we also developed other important methodologies such as early error detection, failure awareness, job aggregation, and dynamic adaptation of distributed data placement tasks. The adaptive tuning includes dynamically setting data transfer parameters and controlling utilization of available network capacity. Our research aims to provide a middleware to improve the data bottleneck in high performance computing systems
Time4: Time for SDN
With the rise of Software Defined Networks (SDN), there is growing interest
in dynamic and centralized traffic engineering, where decisions about
forwarding paths are taken dynamically from a network-wide perspective.
Frequent path reconfiguration can significantly improve the network
performance, but should be handled with care, so as to minimize disruptions
that may occur during network updates.
In this paper we introduce Time4, an approach that uses accurate time to
coordinate network updates. Time4 is a powerful tool in softwarized
environments, that can be used for various network update scenarios.
Specifically, we characterize a set of update scenarios called flow swaps, for
which Time4 is the optimal update approach, yielding less packet loss than
existing update approaches. We define the lossless flow allocation problem, and
formally show that in environments with frequent path allocation, scenarios
that require simultaneous changes at multiple network devices are inevitable.
We present the design, implementation, and evaluation of a Time4-enabled
OpenFlow prototype. The prototype is publicly available as open source. Our
work includes an extension to the OpenFlow protocol that has been adopted by
the Open Networking Foundation (ONF), and is now included in OpenFlow 1.5. Our
experimental results show the significant advantages of Time4 compared to other
network update approaches, and demonstrate an SDN use case that is infeasible
without Time4.Comment: This report is an extended version of "Software Defined Networks:
It's About Time", which was accepted to IEEE INFOCOM 2016. A preliminary
version of this report was published in arXiv in May, 201
Department of Computer Science Activity 1998-2004
This report summarizes much of the research and teaching activity of the Department of Computer Science at Dartmouth College between late 1998 and late 2004. The material for this report was collected as part of the final report for NSF Institutional Infrastructure award EIA-9802068, which funded equipment and technical staff during that six-year period. This equipment and staff supported essentially all of the department\u27s research activity during that period
Approximating the single source unsplittable min-cost flow problem
In the single source unsplittable min-cost flow problem, commodities must be routed simultaneously from a common source vertex to certain destination vertices in a given graph with edge capacities and costs; the demand of each commodity must be routed along a single path and the total cost must not exceed a given budget. This problem has been introduced by Kleinberg and generalizes several NP-complete problems from various areas in combinatorial optimization such as packing, partitioning, scheduling, load balancing and virtual-circuit routing
Heuristic algorithms for wireless mesh network planning
x, 131 leaves : ill. ; 29 cmTechnologies like IEEE 802.16j wireless mesh networks are drawing increasing attention of
the research community. Mesh networks are economically viable and may extend services
such as Internet to remote locations. This thesis takes interest into a planning problem in
IEEE 802.16j networks, where we need to establish minimum cost relay and base stations to
cover the bandwidth demand of wireless clients. A special feature of this planning problem
is that any node in this network can send data to at most one node towards the next hop,
thus traffic flow is unsplittable from source to destination.
We study different integer programming formulations of the problem. We propose four
types of heuristic algorithms that uses greedy, local search, variable neighborhood search
and Lagrangian relaxation based approaches for the problem. We evaluate the algorithms
on database of network instances of 500-5000 nodes, some of which are randomly generated
network instances, while other network instances are generated over geometric distribution.
Our experiments show that the proposed algorithms produce satisfactory result
compared to benchmarks produced by generalized optimization problem solver software
Networks, Communication, and Computing Vol. 2
Networks, communications, and computing have become ubiquitous and inseparable parts of everyday life. This book is based on a Special Issue of the Algorithms journal, and it is devoted to the exploration of the many-faceted relationship of networks, communications, and computing. The included papers explore the current state-of-the-art research in these areas, with a particular interest in the interactions among the fields
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