# Supporting Heterogenous Traffic on Top of Point-to-Multipoint Light-Trees +
###### Abstract  
New 5 G and beyond services demand innovative solutions in optical transport to increase efficiency and flexibility and reduce capital (CAPEX) and operational (OPEX) expenditures to support heterogeneous and dynamic traffic. In this context, optical point-to-multipoint (P2 MP) connectivity is seen as an alternative to provide connectivity to multiple sites from a single source, thus potentially both reducing CAPEX and OPEX. Digital subcarrier multiplexing (DSCM) has been shown as a feasible candidate for optical P2 MP in view of its ability to generate multiple subcarriers (SC) in the frequency domain that can be used to serve several destinations. This paper proposes a different technology, named optical constellation slicing (OCS), that enables a source to communicate with multiple destinations by focusing on the time domain. OCS is described in detail and compared to DSCM by simulation, where the results show that both OCS and DSCM provide a good performance in terms of the bit error rate (BER) for access/metro applications. An exhaustive quantitative study is afterwards carried out to compare OCS and DSCM considering its support to dynamic packet layer P2P traffic only and mixed P2P and P2 MP traffic; throughput, efficiency, and cost are used here as the metrics. As a baseline for comparison, the traditional optical P2P solution is also considered in this study. Numerical results show that OCS and DSCM provide a better efficiency and cost savings than traditional optical P2P connectivity. For P2P only traffic, OCS and DSCM are utmost 14.6% more efficient than the traditional lightpath solution, whereas for heterogeneous P2P + P2 MP traffic, a 25% efficiency improvement is achieved, making OCS 12% more efficient than DSCM. Interestingly, the results show that for P2P only traffic, DSCM provides more savings of up to 12% than OCS, whereas for heterogeneous traffic, OCS can save up to 24.6% more than DSCM. optical point-to-multipoint; multilayer optical networks; metro and access networks 2023232325  
be devised that provide the required agility in terms of dynamic traffic management and flexibility in terms of topology upgrade [4]. In this regard, point-to-multipoint (P2 MP) networking has been recently proposed at the optical layer to connect several mobile sites to a single metro datacenter [5]. In P2 MP connections, one single source node _(hub)_ is connected to a set of destinations (_spokes_) that may be scattered over a geographical area. Note, in contrast, that point-to-point (P2P) connectivity has been generally implemented in transport networks, which does not fit well to support _hub-and-spoke_ arrangements such as the above one. However, P2 MP also has disadvantages, such as the loss of data privacy, since all the leaves can receive all the data being sent. Implementing P2 MP at the optical layer requires not only establishing _light-trees_[6; 7], but also innovative optical transmission technologies based on advanced digital signal processing (DSP) [8]. DSP is commonly used to implement high-order modulation formats that increases the speed and reach of coherent optical systems [9]. DSP can also be used to implement new optical communications technologies, such as digital subcarrier multiplexing (DSCM) [10; 11]. The primary advantage of DSCM is that it enables fixed bandwidth granularity, i.e., instead of generating a single carrier at the transmitter, several subcarriers (SC) are generated and multiplexed digitally before transmission. Additionally, SCs can be dynamically activated and deactivated to meet capacity requirements [12]. DSCM was recently proposed for P2 MP coherent communications in [5; 13; 14; 15], where a subset of independent SCs can be dedicated to support P2P traffic between the source and each destination with the benefit of using one single optical transceiver in the source supporting all the P2P traffic flows. A different optical communications technology for optical P2 MP supporting P2P traffic is optical constellation slicing (OCS) [16].