# Supporting Heterogenous Traffic on Top of Point-to-Multipoint Light-Trees +
## 4 Illustrative Results
### Quantitative Analysis
To this goal, we model the cost of P2P transceivers and apply the needed constraints to find the targeted cost of OCS and DSCM ones. For the P2P lightpath solution, we consider the optical transceivers availability as in Table 2. Based on the cost model in [24], we model the cost (\(C\)) of these transceivers in monetary units (m.u.) as a function of the bit rate (\(BR\)), as:  
\[C=\alpha\cdot BR^{\beta}, \tag{5}\]  
where \(\alpha\) is a normalization factor to set the cost of the 100 G transceiver to 1 and \(\beta\) is a positive constant \(<\) 1 that we use to define different cost profiles. Two cost profiles are considered for analysis, \(\beta\) = 0.5 and \(\beta\) = 0.6 (see Figure 11), which reproduces the technology costs trend to exponentially decrease by generations [24]. Figure 11: Cost profile for lightpath transceivers. Figure 10: Reduction in number of transceivers. However, to enable optical P2 MP connectivity, DSCM-600, DSCM-300, DSCM-150, and OCS-600 transceivers require additional DSP features, which translates into an additional cost. Although the cost of such transceivers still needs to be determined, it is worth noting that we imposed these relations among costs following the proportions in Figure 11, for \(\beta=0.5\) and \(\beta=0.6\). In the aggressive availability (Figure 12a), DSCM outperforms OCS for P2P traffic. For 2 destinations, DSCM provides 12% and 9% extra cost savings than OCS for \(\beta=0.5\) and \(\beta=0.6\), respectively. The cost savings are more evident for 4 destinations, where DSCM provides 35.4% and 34% more cost savings than OCS. However, both OCS and DSCM provide the same savings in the case of mixed P2P + P2 MP traffic. For \(\beta=0.5\), we observe savings of 40% and 32% for 2 and 4 destinations, respectively, similarly as for \(\beta=0.6\), where the savings are 42.2% and 31.4%, respectively. In the non-aggressive availability (Figure 12b), the same savings as for aggressive availability for P2P only traffic are observed because the installed transceivers remain the same in both the cases. However, for mixed P2P + P2 MP traffic, OCS outperforms DSCM mainly because additional transceivers for enabling P2 MP traffic need to be installed. For 2 destinations, OCS provides 24.6% and 25.8% more cost savings than DSCM for \(\beta=0.5\) and \(\beta=0.6\), respectively. The cost savings are lower for 4 destinations, where OCS provides 12.9% and 14.5% more cost savings than DSCM. Figure 12: Cost savings: aggressive approach (**a**) and non-aggressive approach (**b**). Finally, we study the efficiency of DSCM and OCS for optical P2 MP, as this metric provides us with an insight into how efficiently a source can utilize the total capacity to serve the requested dynamic traffic profile. For example, in Figure 9a at 8 h, destination 1 requires 250 Gb/s and destination 2 requires 100 Gb/s. In this case, the efficiency of OCS and DSCM will be 58.33% (350/600), whereas for the P2P lightpath solution, the efficiency will be 43.75% (350/800). Figure 13 shows the efficiency for the case of two destinations for the aggressive and non-aggressive availabilities for P2P (Figure 13a) and P2P + P2 MP (Figure 13b) traffic profiles. In the case of the aggressive availability, the efficiency of OCS and DSCM is the same throughout the traffic profiles, whereas the efficiency of the P2P lightpath solution is always under that of OCS and DSCM. Under P2P only traffic, the OCS and DSCM approaches are utmost 14.6% more efficient than the P2P lightpath solution that is observed at 8 h. At that same hour of the day, the maximum efficiency improvement of 25% for P2P + P2 MP traffic is observed. In the case of the non-aggressive availability, the same pattern as the aggressive availability is observed for P2P only traffic. However, for mixed P2P + P2 MP traffic, OCS provides a abetter efficiency than DSCM and achieves a maximum efficiency improvement of 12% at 8 h.  
In view of these results, let us examine implementing OCS on top of DSCM.