With the increased quantity of Internet traffic, improving spectrum utilization has become a hot topic in the field ofoptical communication. However, the traditional wavelength-division-multiplexing (WDM) optical networks assign aconstant spectral bandwidth (e.g. 50-GHz) to heterogeneous services and thus have limited flexibility and efficiency inspectrum utilization during service accommodation. In order to improve the efficiency in accommodating diverseservices with heterogeneous bandwidth requirements, elastic optical networks (EONs) have been proposed. In thesenetworks, spectrum resources can be allocated to different services flexibly according to their respective bandwidthrequirements, so that the flexibility and efficiency of spectrum utilization can be remarkably improved. But the spectrumcontinuity and contiguity constraints in spectrum allocation may induce some isolated, non-aligned and small-sizedspectrum segments, which are known as spectrum fragments. With the accumulation of spectrum fragments, theavailable spectral resources can be exhausted and the networking performance can be affected. Thus, spectrumfragmentation has become an important issue in EONs, and many algorithms have been proposed to reduce the numberof spectrum fragments. Among these proposed algorithms, most of them were focus on the defragmentation alongnormal working paths for services, which might induce traffic disruption for existing service connections and had limitedsurvivability for transmission failure. In order to alleviate the traffic interruption in spectrum defragmentation andimprove the survivability for any link failure in transmission, we propose a spectrum defragmentation algorithm basedon path-switching mechanism for 1+1 protection in EONs in this paper. Different from previous protection-path-baseddefragmentation algorithms, the proposed algorithm employs path-switching mechanism to realize active switchingbetween the working path and the protection path according to the usage of the spectrum in the network, so that the twopaths can be regarded as their mutual backup paths in the spectrum defragmentation along each of them. In this way, theprotection path cannot only provide the survivability for the working path, but also alleviate the traffic disruption duringthe defragmentation along the working path, while the working path can alleviate the traffic disruption during thedefragmentation along the protection path. Simulation results show that the proposed algorithm can realize low blockingprobability with reduced traffic disruption for 1+1 protection in EONs.
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