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Th`ese de Doctorat de l'université Paris VI Pierre et Marie Curie Mlle ...

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of which there exist extensive theories and algorithms such as the Karush-Kuhn-Tucker<br />

conditions and duality theorem.<br />

Kelly has suggested in [7] that the problem of bandwidth allocation should be posed<br />

as one of achieving maximum aggregate utility for the users. These users are assumed to<br />

be of elastic traffic, and can adjust their rates based on the feedback from the n<strong>et</strong>work.<br />

Further, in [7], pricing is used to <strong>de</strong>compose the overall problem into subproblems for the<br />

n<strong>et</strong>work and for the individual users.<br />

Authors in [14] have also investigated the problem of achieving the optimal bandwidth<br />

allocation that maximizes the aggregate utility of the users, using only the information<br />

available at the end hosts. The users are assumed of elastic traffic, but differently from [7],<br />

in [14], the users adjust their rates based on their estimates of n<strong>et</strong>work congestion level.<br />

On the other hand, the authors in [15] have addressed the problem of allocating trans-<br />

mission data rates distributedly to users who have concave as well as sigmoidal utility<br />

functions, to take into account the behavior of different applications. Moreover, it is<br />

<strong>de</strong>monstrated in [15] that applying rate control algorithms <strong>de</strong>veloped for concave utility<br />

functions in a more realistic s<strong>et</strong>ting can lead to instability and high n<strong>et</strong>work congestion.<br />

In our service mo<strong>de</strong>l, we do not restrict the utility functions to be concave; in line<br />

with [15], we allow users to have more general utility functions that arise naturally in<br />

the context of various applications. However, to solve the problem of extra-bandwidth<br />

allocation, we distinguish b<strong>et</strong>ween two cases: 1) all users have concave utility functions; or<br />

2) users have concave as well as non concave utility functions. In the first case, we propose<br />

a mathematical formulation of the bandwidth allocation problem that maximizes the total<br />

n<strong>et</strong>work revenue, while in the second case we introduce two heuristic online measurement-<br />

based bandwidth allocation algorithms.<br />

In [2], a generic pricing structure is presented to characterize the pricing schemes cur-<br />

rently used in the Intern<strong>et</strong>, and a dynamic, congestion-sensitive pricing algorithm is in-<br />

troduced to provi<strong>de</strong> an incentive for multimedia applications to adapt their transmission<br />

27

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