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Elastic optical network (EON) is a type of telecommunications network.

EONs evolved from Wavelength switched optical network allowing optical connections to use arbitrary portion of spectrum. While WSONs all established optical connections have to fit in one channel of the rigid WDM grid standardized by ITU-T, in EONs the spectrum of the optical fibre is exploited by means of a flexible grid with fine granularity.

As a WSON, an EON consist of two planes: the data and the control planes.

The data plane comprises Wavelength-division multiplexing (WDM) fiber links connecting optical cross-connect (OXCs) through a comb of several tens of wavelength channels, with typical data rates of 10 or 40 Gb/s. Optical end-to-end connections (i.e., lightpaths) are established in the optical domain and switched by OXCs at the wavelength granularity.

In WSONs the optical signal is switched at the wavelength granularity, therefore the wavelength assignment process, selecting the carrier of each established lightpath, plays a crucial role in dynamic network operation.

The dynamic provisioning and maintenance of lightpaths is managed by the control plane. The control plane is implemented on a separate network and typically employs one network controller for each node in the data plane, as shown in the figure. The GMPLS protocol suite is the de facto standard control plane for WSONs proposed by the IETF, is composed of three protocols.

In EONs high spectral efficiency can be achieved because eachlightpath can use a different amount of spectrum and can therefore exploit advanced modulation formats~\cite{Jinno-CommMag2009,Gerstel-CommMag}. Moreover, the deploying of EONs is also fostered by the operators because they can easily evolve current WSONs towards EONs by means of gradual upgrades~\cite{idealist}. Specifically, while modifications are required in both the data and the control planes, the current fibre infrastructure can be kept as it is.