49 research outputs found
Scale-free networks and scalable interdomain routing
Trabalho apresentado no âmbito do Mestrado em Engenharia Informática, como requisito parcial para obtenção do grau de Mestre em Engenharia InformáticaThe exponential growth of the Internet, due to its tremendous success, has brought to light some limitations of the current design at the routing and arquitectural level, such as scalability and convergence as well as the lack of support for traffic engineering, mobility, route differentiation and security.
Some of these issues arise from the design of the current architecture, while others are
caused by the interdomain routing scheme - BGP. Since it would be quite difficult to add support for the aforementioned issues, both in the interdomain architecture and in the in the routing scheme, various researchers believe that a solution can only achieved via a new architecture and (possibly) a new routing scheme.
A new routing strategy has emerged from the studies regarding large-scale networks, which
is suitable for a special type of large-scale networks which characteristics are independent of network size: scale-free networks. Using the greedy routing strategy a node routes a message to a given destination using only the information regarding the destination and its neighbours,
choosing the one which is closest to the destination. This routing strategy ensures the following remarkable properties: routing state in the order of the number of neighbours; no requirements on nodes to exchange messages in order to perform routing; chosen paths are the shortest ones.
This dissertation aims at: studying the aforementioned problems, studying the Internet configuration as a scale-free network, and defining a preliminary path onto the definition of a greedy routing scheme for interdomain routing
A survey of flooding, gossip routing, and related schemes for wireless multi- hop networks
Flooding is an essential and critical service in computer networks that is
used by many routing protocols to send packets from a source to all nodes in
the network. As the packets are forwarded once by each receiving node, many
copies of the same packet traverse the network which leads to high redundancy
and unnecessary usage of the sparse capacity of the transmission medium.
Gossip routing is a well-known approach to improve the flooding in wireless
multi-hop networks. Each node has a forwarding probability p that is either
statically per-configured or determined by information that is available at
runtime, e.g, the node degree. When a packet is received, the node selects a
random number r. If the number r is below p, the packet is forwarded and
otherwise, in the most simple gossip routing protocol, dropped. With this
approach the redundancy can be reduced while at the same time the reachability
is preserved if the value of the parameter p (and others) is chosen with
consideration of the network topology. This technical report gives an overview
of the relevant publications in the research domain of gossip routing and
gives an insight in the improvements that can be achieved. We discuss the
simulation setups and results of gossip routing protocols as well as further
improved flooding schemes. The three most important metrics in this
application domain are elaborated: reachability, redundancy, and management
overhead. The published studies used simulation environments for their
research and thus the assumptions, models, and parameters of the simulations
are discussed and the feasibility of an application for real world wireless
networks are highlighted. Wireless mesh networks based on IEEE 802.11 are the
focus of this survey but publications about other network types and
technologies are also included. As percolation theory, epidemiological models,
and delay tolerant networks are often referred as foundation, inspiration, or
application of gossip routing in wireless networks, a brief introduction to
each research domain is included and the applicability of the particular
models for the gossip routing is discussed
Virtualization and Distribution of the BGP Control Plane
L'Internet est organisé sous la forme d'une multitude de réseaux appelés Systèmes Autonomes (AS). Le Border Gateway Protocol (BGP) est le langage commun qui permet à ces domaines administratifs de s'interconnecter. Grâce à BGP, deux utilisateurs situés n'importe où dans le monde peuvent communiquer, car ce protocole est responsable de la propagation des messages de routage entre tous les réseaux voisins. Afin de répondre aux nouvelles exigences, BGP a dû s'améliorer et évoluer à travers des extensions fréquentes et de nouvelles architectures. Dans la version d'origine, il était indispensable que chaque routeur maintienne une session avec tous les autres routeurs du réseau. Cette contrainte a soulevé des problèmes de scalabilité, puisque le maillage complet des sessions BGP internes (iBGP) était devenu difficile à réaliser dans les grands réseaux. Pour couvrir ce besoin de connectivité, les opérateurs de réseaux font appel à la réflection de routes (RR) et aux confédérations. Mais si elles résolvent un problème de scalabilité, ces deux solutions ont soulevé des nouveaux défis car elles sont accompagnées de multiples défauts; la perte de diversité des routes candidates au processus de sélection BGP ou des anomalies comme par exemple des oscillations de routage, des déflections et des boucles en font partie. Les travaux menés dans cette thèse se concentrent sur oBGP, une nouvelle architecture pour redistribuer les routes externes à l'intérieur d'un AS. `A la place des classiques sessions iBGP, un réseau de type overlay est responsable (I) de l'´echange d'informations de routage avec les autres AS, (II) du stockage distribué des routes internes et externes, (III) de l'application de la politique de routage au niveau de l'AS et (IV) du calcul et de la redistribution des meilleures routes vers les destinations de l'Internet pour tous les routeurs clients présents dans l'AS. ABSTRACT : The Internet is organized as a collection of networks called Autonomous Systems (ASes). The Border Gateway Protocol (BGP) is the glue that connects these administrative domains. Communication is thus possible between users worldwide and each network is responsible of sharing reachability information to peers through BGP. Protocol extensions are periodically added because the intended use and design of BGP no longer fit the current demands. Scalability concerns make the required internal BGP (iBGP) full mesh difficult to achieve in today's large networks and therefore network operators resort to confederations or Route Reflectors (RRs) to achieve full connectivity. These two options come with a set of flaws of their own such as route diversity loss, persistent routing oscillations, deflections, forwarding loops etc. In this dissertation we present oBGP, a new architecture for the redistribution of external routes inside an AS. Instead of relying on the usual statically configured set of iBGP sessions, we propose to use an overlay of routing instances that are collectively responsible for (I) the exchange of routes with other ASes, (II) the storage of internal and external routes, (III) the storage of the entire routing policy configuration of the AS and (IV) the computation and redistribution of the best routes towards Internet destinations to each client router in the AS
Virtualization and Distribution of the BGP Control Plane
The Internet is organized as a collection of networks called Autonomous Systems (ASes). The Border Gateway Protocol (BGP) is the glue that connects these administrative domains. Communication is thus possible between users worldwide and each network is responsible of sharing reachability information to peers through BGP. Protocol extensions are periodically added because the intended use and design of BGP no longer fit the current demands. Scalability concerns make the required internal BGP (iBGP) full mesh difficult to achieve in today's large networks and therefore network operators resort to confederations or Route Reflectors (RRs) to achieve full connectivity. These two options come with a set of flaws of their own such as route diversity loss, persistent routing oscillations, deflections, forwarding loops etc. In this dissertation we present oBGP, a new architecture for the redistribution of external routes inside an AS. Instead of relying on the usual statically configured set of iBGP sessions, we propose to use an overlay of routing instances that are collectively responsible for (I) the exchange of routes with other ASes, (II) the storage of internal and external routes, (III) the storage of the entire routing policy configuration of the AS and (IV) the computation and redistribution of the best routes towards Internet destinations to each client router in the AS
Software-based and regionally-oriented traffic management in Networks-on-Chip
Since the introduction of chip-multiprocessor systems, the number of integrated cores has been steady growing and workload applications have been adapted to exploit the increasing parallelism. This changed the importance of efficient on-chip communication significantly and the infrastructure has to keep step with these new requirements.
The work at hand makes significant contributions to the state-of-the-art of the latest generation of such solutions, called Networks-on-Chip, to improve the performance, reliability, and flexible management of these on-chip infrastructures
Geographic Routing for Point to Point Data Delivery in Wireless Sensor Network
Ph.DDOCTOR OF PHILOSOPH
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
Bandwith allocation and scheduling in photonic networks
This thesis describes a framework for bandwidth allocation and scheduling in the Agile All-Photonic Network (AAPN). This framework is also applicable to any single-hop communication network with significant signalling delay (such as satellite-TDMA systems). Slot-by-slot scheduling approaches do not provide adequate performance for wide-area networks, so we focus on frame-based scheduling. We propose three novel fixed-length frame scheduling algorithms (Minimum Cost Search, Fair Matching and Minimum Rejection) and a feedback control system for stabilization.MCS is a greedy algorithm, which allocates time-slots sequentially using a cost function. This function is defined such that the time-slots with higher blocking probability are assigned first. MCS does not guarantee 100% throughput, thought it has a low blocking percentage. Our optimum scheduling approach is based on modifying the demand matrix such that the network resources are fully utilized, while the requests are optimally served. The Fair Matching Algorithm (FMA) uses the weighted max-min fairness criterion to achieve a fair share of resources amongst the connections in the network. When rejection is inevitable, FMA selects rejections such that the maximum percentage rejection experienced in the network is minimized. In another approach we formulate the rejection task as an optimization problem and propose the Minimum Rejection Algorithm (MRA), which minimizes total rejection. The minimum rejection problem is a special case of maximum flow problem. Due to the complexity of the algorithms that solve the max-flow problem we propose a heuristic algorithm with lower complexity.Scheduling in wide-area networks must be based on predictions of traffic demand and the resultant errors can lead to instability and unfairness. We design a feedback control system based on Smith's principle, which removes the destabilizing delays from the feedback loop by using a "loop cancelation" technique. The feedback control system we propose reduces the effect of prediction errors, increasing the speed of the response to sudden changes in traffic arrival rates and improving the fairness in the network through equalization of queue-lengths