Ioannis Tomkos

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Orthogonal Frequency Division Multiplexing (OFDM) has been recently proposed as a modulation technique for optical networks, due to its good spectral efficiency and impairment tolerance. Optical OFDM is much more flexible compared to traditional WDM systems, enabling elastic bandwidth transmissions. We consider the planning problem of an OFDM-based optical(More)
Two general approaches have been followed for solving the problem of upstream grant scheduling and wavelength assignment in hybrid WDM/TDMA EPON networks, i.e. the offline and the online one. The latter boasts significantly lower frame delay performance in all cases. Nevertheless, we show that simplistic online schemes do not utilize wavelength resources as(More)
Data centers are experiencing an exponential increase in the amount of network traffic that they have to sustain due to cloud computing and several emerging web applications. To face this network load, large data centers are required with thousands of servers interconnected with high bandwidth switches. Current data center networks, based on electronic(More)
1389-1286/$ see front matter 2008 Elsevier B.V doi:10.1016/j.comnet.2008.11.014 * Corresponding author. Address: Athens Informat Markopoulo Ave., 19002 Peania, Athens, Greece. Te E-mail addresses: sazo@ait.edu.gr, siamak@ac. molky), mklinkow@ac.upc.edu (M. Klinkowski), Marin), careglio@ac.upc.edu (D. Careglio), pareta@ac itom@ait.edu.gr (I. Tomkos). Optical(More)
Single and multi-carrier networks offering channel rates up to 400 Gb/s are evaluated under realistic reach parameters. It is found that efficient spectrum utilization and fine bit-rate granularity are essential to achieve cost and energy efficiency. Additionally, the break-even cost of flexible orthogonal frequency division multiplexing transponders is(More)
Fault and attack management has become a very important issue for network operators that are interested to offer a secure and resilient network capable to prevent and localize, as accurately as possible, any failure (fault or attack) that may occur. Hence, an efficient failure location method is needed. To locate failures in opaque optical networks,(More)
Physical impairments in optical fiber transmission necessitate the use of regeneration at certain intermediate nodes, at least for certain lengthy lightpaths. We design and implement impairment-aware algorithms for routing and wavelength assignment (IA-RWA) in translucent optical networks. We focus on the offline version of the problem, where we are given a(More)
We demonstrate the use of impairment constraint routing for performance engineering of transparent metropolitan area optical networks. Our results show the relationship between blocking probability and different network characteristics such as span length, amplifier noise figure, and bit rate, and provide information on the system specifications required to(More)
We consider the problem of serving traffic in a spectrum-flexible optical network, where the spectrum allocated to an end-to-end connection can change so as to adapt to the time-varying required transmission rate. In the proposed framework, each connection is assigned a route and is allocated a reference frequency over that route, using an appropriate(More)