Delay-constrained Routing Problems: Accurate Scheduling Models and Admission Control

Frangioni, Antonio and Galli, Laura and Stea, Giovanni (2015) Delay-constrained Routing Problems: Accurate Scheduling Models and Admission Control. Technical Report del Dipartimento di Informatica, TR . Dipartimento di Informatica, Università di Pisa, Pisa, IT. (Submitted)

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Abstract

It has been recently shown that the problem of routing a new packet flow in a computer network subject to a constraint on the worst-case end-to-end delay of its packets can be formulated as a Mixed-Integer Second-Order Cone Program (MI-SOCP), and solved with general-purpose tools on instances of realistic size in time compatible with real-time use. However, that result was obtained for only one of the classes of schedulers in use in today's networks, namely Strictly Rate-Proportional ones. Furthermore, that result relies on assuming that each link is "fully loaded", so that the reserved rate of the flow coincides with its guaranteed rate. These assumptions entail both simple latency expressions, and the fact that flows are isolated from each other as far as their end-to-end delay is concerned; that is, admitting a new flow does not increase the end-to-end delay of the existing ones. However, other classes of scheduling algorithms commonly found in current networks both yield more complex latency formulae and do not enforce strict flow independence. Furthermore, the delay actually depends on the guaranteed rate of the flow, which can be significantly larger than the reserved rate if the network is less loaded. In this paper we extend the result to other classes of schedulers and to a more accurate representation of the latency, showing that, despite the increase in complexity, the problem is still efficiently solvable, even when admission control needs to be factored in, for realistic instances, provided that the right modeling choices are made.

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