The degradation of quality-of-transmission (QoT) due to the dispersion effect is a critical issue in elastic optical networks (EONs). To satisfy the required quality of transmission, a robust modulation level needs to be adopted. Thus, the number of required slots for spectrum allocation is increased. Although dispersion compensation devices reduce the effect of dispersion, they require an additional cost. This paper presents a dispersion-sensitive spectrum allocation approach for EONs to suppress the call blocking in the network. The presented spectrum allocation approach does not use any dispersion compensating device for suppressing the dispersion effect. It allocates shorter lightpath requests from the largest indexed spectrum slot, where the effect of dispersion is higher, and longer lightpath requests from the smallest indexed spectrum slot, where the effect of dispersion is lower. To satisfy the required QoT threshold level for the longer lightpath requests, the presented approach uses a less robust modulation level. Thus, for lightpath establishment, a lower number of spectrum slots are required. In the presented approach, lightpath requests are separated as longer and shorter lightpath requests using either the predetermined-threshold policy or the lightpath threshold selection algorithm. When the traffic condition is not known in advance, the predetermined-threshold policy is not applicable. In that case, the lightpath threshold selection algorithm is used to find the distance threshold value, which provides the lowest blocking probability. Simulation results indicate that the presented dispersion-sensitive spectrum allocation approach outperforms the conventional spectrum allocation scheme in terms of available contiguous aligned slot ratio and blocking probability.

由于色散效应导致的传输质量（QoT）的下降是弹性光网络（EON）中的关键问题。为了满足所需的传输质量，需要采用鲁棒的调制级别。因此，用于频谱分配的所需时隙的数量增加。尽管色散补偿装置降低了色散的影响，但它们需要额外的成本。本文提出了一种针对EON的色散敏感频谱分配方法，以抑制网络中的呼叫阻塞。提出的频谱分配方法不使用任何色散补偿装置来抑制色散效应。它从色散效果较高的最大索引频谱时隙分配较短的光路请求，而从最小索引频谱时隙分配较长的光路请求，分散效果较低的地方。为了满足更长的光路请求所需的QoT阈值水平，提出的方法使用了较不健壮的调制水平。因此，为了建立光路，需要较少数量的频谱时隙。在提出的方法中，使用预定阈值策略或光路阈值选择算法将光路请求分离为更长和更短的光路请求。当事先不知道交通状况时，预定阈值策略不适用。在那种情况下，使用光路阈值选择算法来找到距离阈值，该距离阈值提供了最低的阻塞概率。