1,942 research outputs found
Estimating Dynamic Traffic Matrices by using Viable Routing Changes
Abstract: In this paper we propose a new approach for dealing with the ill-posed nature of traffic matrix estimation. We present three solution enhancers: an algorithm for deliberately changing link weights to obtain additional information that can make the underlying linear system full rank; a cyclo-stationary model to capture both long-term and short-term traffic variability, and a method for estimating the variance of origin-destination (OD) flows. We show how these three elements can be combined into a comprehensive traffic matrix estimation procedure that dramatically reduces the errors compared to existing methods. We demonstrate that our variance estimates can be used to identify the elephant OD flows, and we thus propose a variant of our algorithm that addresses the problem of estimating only the heavy flows in a traffic matrix. One of our key findings is that by focusing only on heavy flows, we can simplify the measurement and estimation procedure so as to render it more practical. Although there is a tradeoff between practicality and accuracy, we find that increasing the rank is so helpful that we can nevertheless keep the average errors consistently below the 10% carrier target error rate. We validate the effectiveness of our methodology and the intuition behind it using commercial traffic matrix data from Sprint's Tier-1 backbon
Energy management in communication networks: a journey through modelling and optimization glasses
The widespread proliferation of Internet and wireless applications has
produced a significant increase of ICT energy footprint. As a response, in the
last five years, significant efforts have been undertaken to include
energy-awareness into network management. Several green networking frameworks
have been proposed by carefully managing the network routing and the power
state of network devices.
Even though approaches proposed differ based on network technologies and
sleep modes of nodes and interfaces, they all aim at tailoring the active
network resources to the varying traffic needs in order to minimize energy
consumption. From a modeling point of view, this has several commonalities with
classical network design and routing problems, even if with different
objectives and in a dynamic context.
With most researchers focused on addressing the complex and crucial
technological aspects of green networking schemes, there has been so far little
attention on understanding the modeling similarities and differences of
proposed solutions. This paper fills the gap surveying the literature with
optimization modeling glasses, following a tutorial approach that guides
through the different components of the models with a unified symbolism. A
detailed classification of the previous work based on the modeling issues
included is also proposed
Towards Robust Traffic Engineering in IP Networks
To deliver a reliable communication service it is essential for
the network operator to manage how traffic flows in the network.
The paths taken by the traffic is controlled by the routing function.
Traditional ways of tuning routing in IP networks are designed
to be simple to manage and are not designed to adapt to the
traffic situation in the network. This can lead to congestion in
parts of the network while other parts of the network is
far from fully utilized. In this thesis we explore issues related
to optimization of the routing function to balance load in the network.
We investigate methods for efficient derivation of the
traffic situation using link count measurements. The advantage
of using link counts is that they are easily obtained and yield
a very limited amount of data. We evaluate and show that estimation
based on link counts give the operator a fast and accurate description
of the traffic demands. For the evaluation we have access to a unique data
set of complete traffic demands from an operational
IP backbone.
Furthermore, we evaluate performance of search heuristics to
set weights in link-state routing protocols. For the evaluation
we have access to complete traffic data from a Tier-1 IP network.
Our findings confirm previous studies who use partial traffic data or
synthetic traffic data. We find that optimization using estimated
traffic demands has little significance to the performance of
the load balancing.
Finally, we device an algorithm that finds a routing setting that is
robust to shifts in traffic patterns due to changes in the
interdomain routing. A set of worst case scenarios caused by the interdomain routing changes
is identified and used to solve a robust routing problem. The evaluation
indicates that performance of the robust routing is close to optimal for
a wide variety of traffic scenarios.
The main contribution of this thesis is that we demonstrate that it is
possible to estimate the traffic matrix with good accuracy and to develop
methods that optimize the routing settings to give strong and robust network
performance. Only minor changes might be necessary in order to implement our
algorithms in existing networks
Aspects of proactive traffic engineering in IP networks
To deliver a reliable communication service over the Internet
it is essential for
the network operator to manage the traffic situation in the network.
The traffic situation is controlled by
the routing function which determines what path traffic follows from source
to destination.
Current practices for setting routing parameters in IP networks are
designed to be simple to manage. This can lead to congestion in
parts of the network while other parts of the network are
far from fully utilized. In this thesis we explore issues related
to optimization of the routing function to balance load in the network
and efficiently deliver a reliable communication service to the users.
The optimization takes into account not only the traffic situation under
normal operational conditions, but also traffic situations that appear
under a wide variety of circumstances deviating from the nominal case.
In order to balance load in the network knowledge of the traffic
situations is needed. Consequently, in this thesis
we investigate methods for efficient derivation of the
traffic situation. The derivation is based on estimation of
traffic demands from link load measurements. The advantage
of using link load measurements is that they are easily obtained and consist
of a limited amount of data that need to be processed. We evaluate and demonstrate how estimation
based on link counts gives the operator a fast and accurate description
of the traffic demands. For the evaluation we have access to a unique data
set of complete traffic demands from an operational
IP backbone.
However, to honor service level agreements at all times the variability
of the traffic needs to be accounted for in the load balancing.
In addition, optimization techniques are often sensitive to errors and
variations in input data. Hence, when an optimized routing setting is
subjected to real traffic demands in the network, performance often
deviate from what can be anticipated from the optimization. Thus,
we identify and model different traffic uncertainties and describe
how the routing setting can be optimized, not only for a nominal case,
but for a wide range of different traffic situations that might appear
in the network.
Our results can be applied in MPLS enabled networks as well as in
networks using link state routing protocols such as the widely used
OSPF and IS-IS protocols. Only minor changes may be needed in current
networks to implement our algorithms.
The contributions of this thesis is that we: demonstrate that it is
possible to estimate the traffic matrix with acceptable precision, and
we develop methods and models for common traffic uncertainties to
account for these uncertainties in the optimization of the routing
configuration. In addition, we identify important properties in the
structure of the traffic to successfully balance uncertain and
varying traffic demands
Computer programs for the geomagnetic field Final report
Spherical-harmonic expansion - least squares program for improving parameter precision and statistical program for field mappin
Crop-livestock interactions and livelihoods in the Indo-Gangetic Plains, India: A regional synthesis
The research and development community faces
the challenge of sustaining crop productivity
gains, improving rural livelihoods, and securing environmental sustainability in the Indo-Gangetic Plains (IGP). This calls for a better understanding of farming systems and of rural livelihoods, particularly with the advent of, and strong advocacy for, conservation farming and resource-conserving
technologies. This report presents a regional
synthesis of four scoping studies to assess croplivestock interactions and rural livelihoods in each of the four subregions of the Indian IGP: the Trans-Gangetic Plains (TGP: Punjab and Haryana), the Gangetic Plains of Uttar Pradesh (UP), Bihar, and
West Bengal
Optimal route reflection topology design
An Autonomous System (AS) is a group of Internet Protocol-based networks with a single and clearly defined external routing policy, usually under single ownership, trust or administrative control. The AS represents a connected group of one or more blocks of IP addresses, called IP prefixes, that have been assigned to that organization and provides a single routing policy to systems outside the AS.
The Internet is composed of the interconnection of several thousands of ASes, which use the Border Gateway Protocol (BGP) to exchange network prefixes (aggregations of IP addresses) reachability advertisements. BGP advertisements (or updates) are sent over BGP sessions administratively set between pairs of routers.
BGP is a path vector routing protocol and is used to span different ASes. A path vector protocol defines a route as a pairing between a destination and the attributes of the path to that destination. Interior Border Gateway Protocol (iBGP) refers to the BGP neighbor relationship within the same AS. When BGP neighbor relationship are formed between two peers belonging to different AS are called Exterior Border Gateway Protocol (eBGP). In the last case, BGP routers are called Autonomous System Border Routers (ASBRs), while those running only iBGP sessions are referred to as Internal Routers (IRs).
Traditional iBGP implementations require a full-mesh of sessions among routers of each AS
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