Jean-Louis Rougier

Energy-aware routing: A reality check

In this work, we analyze the design of green routing algorithms and evaluate the achievable energy savings that such mechanisms could allow in several realistic network scenarios. We formulate the problem as a minimum energy routing optimization, which we numerically solve considering a core-network scenario, which can be seen as a worst-case for energy saving performance (as nodes cannot be switched off). To gather full-relief results, we analyze the energy savings in various conditions (i.e., network topology and traffic matrix) and under different technology assumptions (i.e., the energy profile of the network devices). These results give us insight into the potential benefits of different “green” technologies and their interactions. In particular, we show that depending on the topology and traffic matrices, the optimal energy savings can be modest, partly limiting the interest for green routing approaches for some scenarios. At the same time, we also show that the common belief that there is a trade off between green network optimization and performance does not necessarily hold: in the considered environment, green routing has no effect on the main network performances such as maximum link utilization.

A service plane over the PCE architecture for automatic multidomain connection-oriented services

In this article we concentrate on the automated provisioning of inter-AS services based on GMPLS-TE technology. We consider a provider alliance where TE connections are established between the members of the alliance. We propose an efficient and economically feasible architecture for the automatic provisioning of inter-AS GMPLS-TE, based on the introduction of a multidomain service plane coupled with the PCE-based architecture.

Peering equilibrium multipath routing: a game theory framework for internet peering settlements

It is generally admitted that interdomain peering links represent nowadays the main bottleneck of the Internet, particularly because of lack of coordination between providers, which use independent and “selfish” routing policies. We are interested in identifying possible “light” coordination strategies that would allow carriers to better control their peering links while preserving their independence and respective interests. We propose a robust multipath routing coordination framework for peering carriers, which relies on the multiple-exit discriminator (MED) attribute of Border Gateway Protocol (BGP) as signaling medium. Our scheme relies on a game theory modeling, with a non-cooperative potential game considering both routing and congestions costs. Peering equilibrium multipath (PEMP) coordination policies can be implemented by selecting Pareto-superior Nash equilibria at each carrier. We compare different PEMP policies to BGP Multipath schemes by emulating a realistic peering scenario. Our results show that the routing cost can be decreased by roughly 10% with PEMP. We also show that the stability of routes can be significantly improved and that congestion can be practically avoided on the peering links. Finally, we discuss practical implementation aspects and extend the model to multiple players highlighting the possible incentives for the resulting extended peering framework.

Routing Games for Traffic Engineering

Current data network scenario makes traffic engineering (TE) a very challenging task. The ever growing access rates and new applications running on end-hosts result in more variable and unpredictable traffic patterns. By providing origin-destination pairs with several possible paths, load-balancing has proved itself an excellent tool to face this uncertainty. In particular, mechanisms where routers greedily minimize a path cost function (thus requiring minimum coordination) have been studied from a game-theoretic perspective in what is known as a routing game (RG). The contribution of this paper is twofold. We first propose a new RG specifically designed for elastic traffic, where we maximize the total utility through load-balancing only. Secondly, we consider several important RGs from a TE perspective and, using several real topologies and traffic demands, present a thorough comparison of their performance. This paper brings insight into several RGs, which will help one in choosing an adequate dynamic load-balancing mechanism. The comparison shows that the performance gain of the proposed game can be important.

On the selection of optimal diverse AS-paths for inter-domain IP/(G)MPLS tunnel provisioning

This article proposes an architecture and algorithms to select optimal diverse AS paths for end-to-end LSPs computation. The multi-domain architecture relies upon a service plane consisting of a service broker and an AS Selection Agent. Through the broker, every domain advertises transit metrics representing its transit policies (cost, routing policies) and potentially some Traffic Engineering (TE) information. The metrics are assumed to be directional, i.e. depending on the incoming and outgoing ASs. The Agent uses them to compute AS paths based on both costs and TE constraints, considering also, if needed, local policies and statistics on past transactions stored by the broker. A set of diverse AS paths can be computed, in order to proactively increase the success rate of tunnel set-up, in the case of imprecision or absence of advertised TE information (each AS path being subsequently tested), or to meet end-to-end protection requirements. If an AS path can be activated, the source router trigger the router-level inter-AS path computation along the AS path, which is accomplished by the PCE-based architecture. Within this framework, we formalize the inter-AS diverse route selection problem with directional metrics, and compare a breadth-first search heuristic with limited depth to the optimal approach. Simulations on realistic topologies prove that the heuristic scales with the number of diverse routes, and that it has an optimality gap under the 5% at least once every two times.

AS-level source routing for multi-provider connection-oriented services

In this paper, we study the inter-domain Autonomous System (AS)-level routing problem within an alliance of ASs. We first describe the framework of our work, based on the introduction of a service plane for automatic multi-domain service provisioning. We adopt an abstract representation of domain relationships by means of directional metrics which are applied to a triplet (ingress point, transit AS, egress point) where the ingress and egress points can be ASs or routers. Then, we focus on the point-to-point and multipoint AS-level routing problems that arise in such an architecture. We propose an original approach that reaches near optimal solutions with tractable computation times. A further contribution of this paper is that a heavy step in the proposed heuristic can be precomputed, independently of the service demands. Moreover, we describe how in this context AS-level path diversity can be considered, and present the related extension of our heuristic. By extensive tests on AS graphs derived from the Internet, we show that our heuristic is often equal or a few percent close to the optimal, and that, in the case of precomputation, its time consumption can be much lower than with other well-known algorithms.

Characterisation of AS-level path deviations and multipath in Internet routing

Although significant efforts have been devoted in the literature to measurements of the Internet topology, little attention has been given to the qualification of routing deviations and multipath dynamics at the Autonomous System (AS) routing level. We observed Internet AS-level routes toward thousands of destinations for several weeks between 2009 and 2010 to have a better understanding of these phenomena, nowadays. Using a modified form of traceroute at the state of the art called paris-traceroute, able to detect load-balancing, we sampled thousands of AS-level routes for several weeks. By an extensive analysis, we found that between 15% and 17% of the monitored destinations experiences AS-path deviations, and that load balancing at the AS-level (i.e., forms of BGP multipath) is not widespread at all, and, when frequently used, it is limited to a sort of AS confederation.

Cooperative multi-provider routing optimization and income distribution

We consider the problem of cooperative distributed routing optimization in multi-domain/multi-provider networks. The main object of our investigation are ASON/G-MPLS transport networks, still the results of our investigations could be extended to any multi-domain network where particular domains have limited mutual visibility of intra-domain resources. This paper refines a distributed decomposition mechanism for reliable cooperative optimization of flow reservation levels introduced, by considering the fundamental issue of fair income distribution. The proposed idea of fair income distribution mechanism has been adopted from the theory of cooperative games (Shapley value). We show the benefits of adopting the proposed income distribution scheme by numerical simulations.

Enabling sleep mode in backbone IP-networks: A criticality-driven tradeoff

The energy consumption of network devices, and, as a consequence, of communication networks, is generally independent from their level of utilization, which results in a waste of energy when the network is lightly loaded. Ideally the consumption of a network should be proportional to the amount of traffic it conveys. The most straightforward way to enforce such a proportionality between the network energy consumption and its utilization level, is to dynamically adapt the status of network devices to the load, forcing a subset of them to enter a sleep state during the low activity periods. We present in this paper an algorithm to dynamically put links into a sleep state, based on a cooperative-game approach, named “L-Game”. Our approach decides which links can be switched off based on a measure of the criticality of each link expressed as its Shapley value. This measure combines topological aspects and traffic conditions. Simulation results on real network scenarios show that our solution achieves a better trade off between energy saving and Traffic Engineering than other legacy approaches.

Internet routing diversity for stub networks with a Map-and-Encap scheme

Routing diversity has been identified as essential for network robustness and traffic engineering. The Internet possesses by its very nature a large path diversity. However this diversity cannot be fully exploited due to BGP limitations, which only keeps one single route for each available prefix. Despite some previous works in the area, no operational and non-disruptive architecture have been proposed yet to allow the networks to better exploit Internet path diversity. This paper proposes one step in this direction, focusing on the interconnection between an Autonomous System (AS) and its Internet Service Provider (ISP). We propose the use of a so-called “Map-and-Encap” scheme to bypass current BGP limitations in order to use arbitrary paths. With this scheme, an ISP may propose its rich path diversity (at least partially) to its customers, in order to perform advanced traffic engineering (e.g. fast recovery, load balancing...) based on richer and more flexible path selection policies (e.g., considering price, performance or stability of routes). To assess the potential benefits of the proposed architecture, we evaluate the potential route diversity that a Tier 1 may offer to its stub clients, based on different possible route selection policies (i.e. which routes are offered to its customers). We also analyze the overhead that is created at the control-plane (routing updates received by the mapping database) and that may impact the data-plane (path changes that may be caused by some route withdrawals/updates). Our evaluation shows that the increase in diversity has a controllable and acceptable overhead. It also gives some insights into efficient deployment strategies.