17,638 research outputs found
Computing Covers Using Prefix Tables
An \emph{indeterminate string} on an alphabet is a
sequence of nonempty subsets of ; is said to be \emph{regular} if
every subset is of size one. A proper substring of regular is said to
be a \emph{cover} of iff for every , an occurrence of in
includes . The \emph{cover array} of is
an integer array such that is the longest cover of .
Fifteen years ago a complex, though nevertheless linear-time, algorithm was
proposed to compute the cover array of regular based on prior computation
of the border array of . In this paper we first describe a linear-time
algorithm to compute the cover array of regular string based on the prefix
table of . We then extend this result to indeterminate strings.Comment: 14 pages, 1 figur
Modeling Data-Plane Power Consumption of Future Internet Architectures
With current efforts to design Future Internet Architectures (FIAs), the
evaluation and comparison of different proposals is an interesting research
challenge. Previously, metrics such as bandwidth or latency have commonly been
used to compare FIAs to IP networks. We suggest the use of power consumption as
a metric to compare FIAs. While low power consumption is an important goal in
its own right (as lower energy use translates to smaller environmental impact
as well as lower operating costs), power consumption can also serve as a proxy
for other metrics such as bandwidth and processor load.
Lacking power consumption statistics about either commodity FIA routers or
widely deployed FIA testbeds, we propose models for power consumption of FIA
routers. Based on our models, we simulate scenarios for measuring power
consumption of content delivery in different FIAs. Specifically, we address two
questions: 1) which of the proposed FIA candidates achieves the lowest energy
footprint; and 2) which set of design choices yields a power-efficient network
architecture? Although the lack of real-world data makes numerous assumptions
necessary for our analysis, we explore the uncertainty of our calculations
through sensitivity analysis of input parameters
Inferring an Indeterminate String from a Prefix Graph
An \itbf{indeterminate string} (or, more simply, just a \itbf{string}) \s{x}
= \s{x}[1..n] on an alphabet is a sequence of nonempty subsets of
. We say that \s{x}[i_1] and \s{x}[i_2] \itbf{match} (written
\s{x}[i_1] \match \s{x}[i_2]) if and only if \s{x}[i_1] \cap \s{x}[i_2] \ne
\emptyset. A \itbf{feasible array} is an array \s{y} = \s{y}[1..n] of
integers such that \s{y}[1] = n and for every , \s{y}[i] \in
0..n\- i\+ 1. A \itbf{prefix table} of a string \s{x} is an array \s{\pi} =
\s{\pi}[1..n] of integers such that, for every , \s{\pi}[i] = j
if and only if \s{x}[i..i\+ j\- 1] is the longest substring at position
of \s{x} that matches a prefix of \s{x}. It is known from \cite{CRSW13} that
every feasible array is a prefix table of some indetermintate string. A
\itbf{prefix graph} \mathcal{P} = \mathcal{P}_{\s{y}} is a labelled simple
graph whose structure is determined by a feasible array \s{y}. In this paper we
show, given a feasible array \s{y}, how to use \mathcal{P}_{\s{y}} to
construct a lexicographically least indeterminate string on a minimum alphabet
whose prefix table \s{\pi} = \s{y}.Comment: 13 pages, 1 figur
A Lightweight Approach for Improving the Lookup Performance in Kademlia-type Systems
Discovery of nodes and content in large-scale distributed systems is
generally based on Kademlia, today. Understanding Kademlia-type systems to
improve their performance is essential for maintaining a high service quality
for an increased number of participants, particularly when those systems are
adopted by latency-sensitive applications.
This paper contributes to the understanding of Kademlia by studying the
impact of \emph{diversifying} neighbours' identifiers within each routing table
bucket on the lookup performance. We propose a new, yet backward-compatible,
neighbour selection scheme that attempts to maximize the aforementioned
diversity. The scheme does not cause additional overhead except negligible
computations for comparing the diversity of identifiers. We present a
theoretical model for the actual impact of the new scheme on the lookup's hop
count and validate it against simulations of three exemplary Kademlia-type
systems. We also measure the performance gain enabled by a partial deployment
for the scheme in the real KAD system. The results confirm the superiority of
the systems that incorporate our scheme.Comment: 13 pages, 8 figures, conference version 'Diversity Entails
Improvement: A new Neighbour Selection Scheme for Kademlia-type Systems' at
IEEE P2P 201
On Maximal Unbordered Factors
Given a string of length , its maximal unbordered factor is the
longest factor which does not have a border. In this work we investigate the
relationship between and the length of the maximal unbordered factor of
. We prove that for the alphabet of size the expected length
of the maximal unbordered factor of a string of length~ is at least
(for sufficiently large values of ). As an application of this result, we
propose a new algorithm for computing the maximal unbordered factor of a
string.Comment: Accepted to the 26th Annual Symposium on Combinatorial Pattern
Matching (CPM 2015
Multi-homing tunnel broker
A proper support for communications has to provide fault tolerance capabilities such as the preservation of established connections in case of failures. Multihoming addresses this issue, but the currently available solution based in massive BGP route injection presents serious scalability limitations, since it contributes to the exponential growth of the BGP table size. An alternative solution based on the configuration of tunnels between the multihomed site exit routers and the ISP border routers has been proposed for IPv6 in RFC 3178. However, the amount of manual configuration imposed by this solution on the ISP side prevents its wide adoption. In particular, this solution requires at the ISP the manual configuration of a tunnel endpoint per each multihomed client that it serves. We present a multihoming tunnel broker (MHTB) that provides automatic creation of the tunnel endpoint at the ISP side.This work was supported by the SAM (Advanced Servers with Mobility)project, funded by the Spanish National research and Development Programme as TIC2002-04531-C04-03.Publicad
An analytical model for Loc/ID mappings caches
Concerns regarding the scalability of the interdomain routing have encouraged researchers to start elaborating a more robust Internet architecture. While consensus on the exact form of the solution is yet to be found, the need for a semantic decoupling of a node's location and identity is generally accepted as a promising way forward. However, this typically requires the use of caches that store temporal bindings between the two namespaces, to avoid hampering router packet forwarding speeds. In this article, we propose a methodology for an analytical analysis of cache performance that relies on the working-set theory. We first identify the conditions that network traffic must comply with for the theory to be applicable and then develop a model that predicts average cache miss rates relying on easily measurable traffic parameters. We validate the result by emulation, using real packet traces collected at the egress points of a campus and an academic network. To prove its versatility, we extend the model to consider cache polluting user traffic and observe that simple, low intensity attacks drastically reduce performance, whereby manufacturers should either overprovision router memory or implement more complex cache eviction policies.Peer ReviewedPostprint (author's final draft
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