Yoann Fouquet

Optimizing flow thinning protection in multicommodity networks with variable link capacity

Flow thinning (FT) is a concept of a traffic routing and protection strategy applicable to communication networks with variable capacity of links. In such networks, the links do not attain their nominal (maximum) capacity simultaneously, so in a typical network state only some links are fully available whereas on each of the remaining links only a fraction of its maximum capacity is usable. Every end-to-end traffic demand is assigned a set of logical tunnels whose total capacity is dedicated to carry the demand’s traffic. The nominal (i.e., maximum) capacity of the tunnels, supported by the nominal (maximum) link capacity, is subject to state-dependent thinning to account for variable capacity of the links fluctuating below the maximum. Accordingly, the capacity available on the tunnels is also fluctuating below their nominal levels and hence the instantaneous traffic sent between the demand’s end nodes must accommodate to the current total capacity available on its dedicated tunnels. The related multi-commodity flow optimization problem is NP-hard and its noncompact linear programming formulation requires path generation. For that, we formulate an integer programming pricing problem, at the same time showing the cases when the pricing is polynomial. We also consider an important variant of FT, affine thinning, that may lead to practical FT implementations. We present a numerical study illustrating traffic efficiency of FT and computational efficiency of its optimization models. Our considerations are relevant, among others, for wireless mesh networks utilizing multiprotocol label switching tunnels.

Elastic Routing: A Distributed Variant, Implementation Issues, and Numerical Results

This study is concerned with a specific rerouting strategy in telecommunication networks named Elastic Robust Rerouting (ERR), introduced first in [8]. We recall main points on this strategy, provide mathematical formulation and discuss in details a solution method. The second question studied in this paper is concerned with its distributed version and some related implementation issues. We report a numerical study on effectiveness of both versions in terms of dimensioning cost, restoration time and management effort.

On Protected Traffic Routing in Wireless Networks with Partial Multiple Link Failures

In this paper we study an optimization problem relevant for wireless networks. In such networks links are subject to capacity disruptions caused by changing weather/channel condition that force to adapt the modulation and coding schemes to the observed condition. To cope with this issue in network optimization, we propose a new strategy called the Flow Thinning Strategy. For traffic protection we assume (possibly) over-dimensioned normal path-flows (i.e., path-flows defined for the availability state with all links fully available, the so called normal state) that are thinned in a failure state-dependent way to adapt to fluctuating reduced capacity. What is important, the normal flows cannot be increased or restored in any way. Moreover, we assume that the demand volumes to be realized in states can be reduced as compared to the normal demands. To solve a link cost minimization problem corresponding to the above assumptions, we develop an original non-compact linear programming model together with its solution algorithm based on path generation. We also present a numerical study that compares the performance of the assumed flow-thinning routing with other routing strategies studied before. In the presented version, our model is applicable to wireless networks with non-interfering point-to-point links such as free space optical links or microwave links.

An optimization framework for traffic restoration in optical wireless networks with partial link failures

In the paper we introduce an optimization framework for traffic restoration in optical wireless networks. As such networks experience multiple partial link failures, we introduce a generic extension of restoration strategies developed for wired networks (that assume total link failures) which enables handling partial link failures as well. The particular traffic restoration strategy studied in the paper combines a known rerouting method for total link failures (Restricted Restoration – RR) and a recently developed restoration method for partial failures (Flow Thinning – FT). The paper presents a generic optimization model for link dimensioning for arbitrary sets of failure states, and its specific version that assumes the above described RR/FT strategy. For the RR/FT case, an exact solution method based on path generation is described, together with numerical results illustrating its efficiency. Next, the paper describes how the generic optimization model can be used for the FSO networks. The specific features of the failures observed in such networks (FSO is highly sensitive to atmospheric conditions) imply the necessity of treating the dimensioning problem in its chance constrained programming version which is

Generalized elastic flow rerouting scheme

NP-hard

Elastic Rerouting - models and resolution methods

by its very nature. For that we have developed an iterative heuristic scheme that makes use of the exact solution method developed for the generic case. Numerical results illustrating the so-obtained robust solutions of the dimensioning problem are also reported.

Flow adjustment methods for survivable networks

The present study deals with Elastic Flow Rerouting EFR-an original traffic restoration strategy for protecting traffic flows in communication networks including wireless networks against multiple link failures. EFR aims at alleviating the trade-off between practicability of traffic restoration and the cost of network resources observed in existing networking solutions. We present an extension of EFR capable of managing multiple partial link failures. We describe EFR and its extension, formulate the EFR related optimization problems, and discuss approaches for their resolution. We also discuss numerical results illustrating effectiveness of EFR in terms of the link capacity cost.

An optimization model for communication networks with partial multiple link failures

This study is concerned with an original traffic restoration strategy for wide-area communication networks called Elastic Rerouting (ER). ER aims at alleviating the tradeoff between the network cost and traffic restoration complexity observed in existing solutions. We present the strategy, provide a mathematical formulation for the ER related optimization problem, and discuss an approach to its resolution.We also report results of a numerical illustrating effectiveness of ER in terms of the link capacity cost.

Elastic flow rerouting

The presented study deals with a specific rerouting strategy for protecting traffic flows in communication networks called Flow Adjustment Routing. The strategy is designed to handle partial link failures. We present two variants of the strategy and analyze their pros and cons. We show that the initial strategy is not directly implementable to cope with severe link failures such as total link failures. Therefore, we propose a restricted flow adjustment version as well as its distributed variant that can be used for the total link failures case. Numerical experiments for different settings and test networks illustrate the findings.

A restoration framework for partial failures in wireless networks

This paper studies optimization issues related to a proposed traffic protection strategy referred to as flow-thinning strategy (FTS). FTS is an extension of the well known protection concept, called path diversity, to the case of partial multiple link failures. Path diversity assumes that when a certain subset of links fail, then their capacity is entirely lost and the nominal path-flows that are not affected by the failure are sufficient to realize the required demand. FTS, in turn, is designed to work also when link failures are partial, that is, the failing links in general lose only a fraction of capacity. We consider a link dimensioning problem for FTS, called flow-thinning optimization problem (FTOP), and discuss its properties. It turns out that FTOP, in its general setting, is NP-hard so that its linear programming formulations are unavoidably non-compact and require path generation. As in the general case path generation is also difficult, we propose an integer programming formulation of the pricing problem for the general case of failure scenarios. We also exhibit two special cases when the pricing problem can be solved in polynomial time. Finally, we present a numerical study illustrating cost effectiveness of FTS. The considered partial multi-link failure scenarios are relevant for wireless networks and for the upper layers of fixed communication networks, as for example the MPLS layer with greedy elastic traffic demands.