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Routing with Elastic Characteristics

An EON has the capability to slice the spectrum into slots with finer granularity than WDM-based networks. Jinno et al. [29] presented, for first time, the method referred to as single slot on the grid approach, see Fig. 4.3. In this approach, the frequency slots are based on the ITU-T fixed grids, where the central frequency is set at 193.1 THz. The width of a frequency slot depends on the transmission system. In this example, one frequency slot is 12.5 GHz. According to the bandwidth demand of a connection request, a group of frequency slots, usually consecutive in the frequency domain, are allocated.

Frequency slot approach for elastic optical networks

Figure 4.3: Frequency slot approach for elastic optical networks.

In EONs, single path routing via the RSA approach can create the spectrum fragmentation problem and thus inefficiency. The spectrum fragmentation issue is explained in detail in the following chapters. To overcome this problem, multi- path routing [88-93] has been considered for the EON. An example of this routing is shown in Fig. 4.4. We consider a lightpath request L(F,S,D), where F, 5, and D are the number of required contiguous slots, source, and destination, respectively. We assume that lightpath requests arrive in the system in serial manner. We refer to the available slots as fragmented slots after the spectrum allocation of lightpath requests L, Li, ■ ■ ■, Lf,. In this context, if lightpath request L7 arrives at node A for destination node C with demand of four consecutive slots, it is rejected as the required slots are unavailable. However, two lightpaths (i.e., A — B — C and A — D — C), each of which will utilize two consecutive slots, can be setup to service L7. This type of routing, called multi-path routing or sometimes spectrum-split routing, is caused by spectrum fragmentation. Multi-path routing

Concept of multi-path or spectrum-split routing in EONs

Figure 4.4: Concept of multi-path or spectrum-split routing in EONs.

can be used to handle the spectrum fragments that are very common in dynamic traffic scenarios.

 
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