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The automatically switched optical networks (ASONs) and the generalized multi protocol label switching (GMPLS) control plane are envisaged to play an important role in the next generation Internet. ASON/GMPLS networks enable the multilayer traffic engineering (MTE) paradigm which facilitates the interaction between the IP and the dense wavelength division multiplexing (DWDM) layers. In such dynamic scenario the lightpaths are considered to be on-demand services rather than static aggregation core pipes and therefore the quality of service (QoS) and the service differentiation (DiffServ) are issues to be addressed in both IP and optical layer and preferably in an integrated fashion. This paper proposes a DiffServ scheme for ASON/GMPLS networks which logically divides the IP/MPLS virtual topology into two virtual topologies used to carry high priority and low priority traffic, respectively. The control plane uses different routing/grooming and topology reconfiguration strategies offering more stability - and therefore strict QoS commitments - to the topology carrying high priority traffic. The fairness problem is also addressed by defining a parameter that allows the operator to control the quantity of resources assigned to the two virtual topologies. The performance of the proposed scheme has been evaluated by means of a simulation study.