# Planning of Optical Connections in 5G Packet-Optical xHaul Access Network
## 6 Concluding Remarks  
We have studied the problem of planning optimal transmission paths, realized using optical fiber connections and optical add-drop multiplexers, in a 5G packet-optical xHauI access network. The planning problem has concerned the selection of routing paths in the network, between a set of remote nodes and a hub site, and placement of OADMs onto the paths for traffic aggregation with the goal to minimize the number of transmission paths in the network. The mentioned optimization problem was formulated as an integer linear programming problem. To estimate maximum transmission distances and determine the maximum number of OADMs allowable on particular paths, we have developed a transmission model based on optical power budget calculation. In network analysis, we have considered the functionality and parameters of a commercial packet-optical xHauI system and optical components available on the market. The evaluation was performed in two different network topologies, including an urban typology developed based on real antenna locations and realistic transmission distances.  
We have shown that the application of OADMs allows to decrease the number of required transmission paths significantly when compared to the network in which aggregation of traffic from remote sites by means of OADMs is not realized. The reduction in the number of transmission paths in both evaluated networks can reach up to 65% under a low load, which translates into a lower demand for fiber resources and, consequently, cost savings. Even at higher traffic loads, with an average demand corresponding to 75% of the WDM system capacity, i.e., for 3 wavelengths requested on average per remote site, the savings of about 15% can be achieved. Provisioning of multiple candidate routing paths, instead of using the shortest path only, is beneficial as it allows for a more effective traffic aggregation and, hence, reduction of the number of transmission paths, between 16% and 32%, depending on traffic and MUX loss scenario. Finally, the application of MUXs with lower attenuation can be advantageous for low load scenarios; however, under moderate and higher traffic, they have not offered any performance gains in the analyzed networks.  
In future works, we will address packet-optical xHauI network scenarios in which diverse types of OADMs are applied instead of a fixed OADM assumed in this work. In addition, we will extend the optimization models to account for WDM systems in which the power loss levels are not the same for particular wavelengths. Eventually, we plan to study multi-layer xHauI scenarios in which routing decisions concern both the packet and optical layer.  
Figure 7: Number of transmission paths (**left**) and relative gain versus the network without OADMs (**right**) in a function of traffic load (\(\rho\)) for different MUX loss values in MESH38.  
**Author Contributions:** Conceptualization, M.K.; Funding acquisition, M.K.; Investigation, M.K. and M.J.; Methodology, M.K. and M.J.; Project administration, M.K.; Software, M.K.; Supervision, M.K.; Visualization, M.K.; Writing--original draft, M.K. and M.J.; Writing--review & editing, M.K. and M.J. All authors have read and agreed to the published version of the manuscript.  
This research was funded by National Science Center, Poland under grant number 2018/31/B/ST7/03456.  
The author declares no conflict of interest.