**3. Routing and grooming framework**

provide grooming efficiency, granularity, and service classification of a packet switch along with scalability, operational efficiency, and performance of an OTN switch, as illustrated in **Figure 3**. Furthermore, the universal OTN switch can also assist in reducing router ports by distributing services from aggregated router hand-offs with virtual local area network

Naturally, several other benefits, common to first-generation OTN switches, are also present and include fast end-to-end service provisioning, rapid restoration, high scalability, subwavelength level switching, and easy support of new/multiple traffic types. Likewise, if the service data rates are the same as the data rates of the WDM wavelength channels or when only packet traffic is present, then the universal switch might not have a CAPEX advantage over traditional OTN switch or even the conventional transponder/muxponder with OTN

Depending on the location in the network and the traffic matrix, switching at the packet or STS-1/VC-4 level can have efficiency benefits over switching OTN at the ODU0 (1.25G) level or above, as long as one of two conditions are met. Either there must be a significant number of client interfaces below 1G or there must be the potential for large statistical gains from

(VLAN) to ODU mapping, as shown in **Figure 4**.

encapsulation.

**Figure 4.** Universal switching fabric [1].

**Figure 3.** Universal OTN switch.

216 Optical Fiber and Wireless Communications

The planning of a transport network requires appropriate dimensioning algorithms to guarantee that all traffic demands can be successfully supported and at the expense of minimum CAPEX, therefore giving the network operator the best positioning to run a profitable business. Moreover, the multilayer nature of transport networks exploiting both OTN switches and reconfigurable optical add/drop multiplexers (ROADMs) and the additional requirements entailed by protection and restoration mechanisms have to be taken into account by the network design framework.

The multilayer routing and grooming framework developed and implemented to support the different network scenarios analyzed in the remaining of this chapter can accommodate the different constraints imposed by the specific node architectures and available line rates and consists of the following main steps:

**Step 1**. For each node pair *sd*, compute a set of *K* routing options (*K* shortest paths for unprotected demands, *K* shortest disjoint cycles for demands with protection/restoration) over the network graph *G*(*V, L*), where *V* denotes the set of nodes and *L* denotes the set of links, and store them in set Π.

**Step 2.** Order all traffic demands from the same planning period according to a given criteria (e.g., largest first, longest first).

**Step 3.** For the next ordered traffic demand *t d* perform the following steps:

**a.** Set *k* = 1. Create an auxiliary graph, G(*V*ʹ, *L*ʹ), where each network node *v* ∈ *V* belonging to routing solution π*<sup>k</sup>* ∈ Π is mapped as node *v*ʹ ∈ *V*ʹ and where each existing light path overlapping with π*<sup>k</sup>* and with available capacity to support *td* is mapped as link *l*ʹ ∈ *L*ʹ. For unconnected nodes in *V*ʹ, determine the feasibility of a new overlapping light path with data rates of 100G and 200G. If feasible, map links *l* <sup>100</sup>ʹ ∈ *L*ʹ and *l* 200ʹ ∈ *L*ʹ.


**Step 4**. If all traffic demands have been considered, end the algorithm. Otherwise, repeat from **(Step 3)** for the next traffic demand.

Importantly, the framework is ready to support flexible-rate line interfaces, namely, capable of operating at 100G (QPSK) and 200G (16-QAM), and it can easily incorporate more line rates (e.g., 150G and 300G via 8-QAM and 64-QAM modulation formats, respectively) or can be executed for a single line rate by disabling all others. Moreover, in the case of utilizing shared restoration mechanisms to recover from failure scenarios, the fact that network resources can be shared by the backup paths of ODUs/OChs whose working paths are link- or node-disjoint also needs to be modeled. In order to control the degree of resource sharing, the number of ODUs/OChs that can share the same resource is limited by a maximum resource sharing value *S*.
