# Activation Process of ONU in EPON/GPON/XG-PON/NG-PON2 Networks
## 5 Simulation Results
### Epon  
In an IEEE-based standard, the connection of the units to the network is provided by the autodiscovery agent contained in the MPCP. Because of the activation process being controlled by the parent protocol, the activations for the EPON and 10G-EPON standards are identical, so only one simulation called EPON had been performed. In contrast with the ITU standard, IEEE does not directly define the accident time, discovery window, etc. Instead, these were calculated based on the number of connected units and the distance of the ONU from the OLT. However, the IEEE does not explicitly describe the procedures and mechanisms for these times in its recommendation, so the simulation was based not only on the information obtained from the recommendation, but also from [24,30]. The presented results were based on the graph comparing the EPON and GPON with 32/64 units and a 20-km ODN length. The graphs are shown in Figure 7. As shown, the activation was several times faster using EPON instead of GPON. This was primarily because the selected frame length in EPON was only 409.6 ns, whereas in GPON, it was 125 us. The total activation time was much easier to evaluate for EPON than for GPON. Fewer messages were transmitted, and they were transmitted only once (GPON sends PLOAM messages three times); the minimum message processing time of the ONU was only 16.384 us, whereas for GPON, it was 750 us, and the equalization delay was not calculated during the simulation of EPON. Figure 8 compares the activation process in XG-PON and NG-PON2. As mentioned previously, the activation process for XG-PON and NG-PON was based on GPON. However, there were some new states of substates. In other words, the PLOAM messages were almost identical. We did not consider a tuning process for changing the wavelength in the downstream or upstream because this process lies at the OLT side. Figure 6: Visualization of the NG-PON2 activation. Figure 7: Graph of activation time for EPON (**left**) and GPON (**right**) 32/64 units and 20-km ODN. On the left side, Figure 9 compares the XG-PON and NG-PON2 standards for 128 connected units and a 20-km ODN length. The maximum connection time was several ms higher for NG-PON2 than for XG-PON. The increase in connection time can be explained by the higher number of transmitted messages and the occurrence of other synchronization processes. A maximum connection time of up to 420 ms can be observed. Nevertheless, it was necessary to consider the limitations of the simulation, e.g., the simulation did not consider any collisions that can normally occur in the real network (the time necessary for the activation process would be increased in such cases), etc. If we consider the higher split ratio (1:256), which is the maximum split ratio in XG-PON and NG-PON2, we observe an almost two-fold higher value for the activation process for a 20-km ODN length. The final aim of this study was an optimization of the GPON standard. To preserve the physical essence, the calculations and the length of the messages cannot be altered. Optimization, therefore, serves to reduce the number of messages and the length of the OLT operating state, which is the time that OLT grants the ONU to process incoming messages. In GPON, all messages are transmitted three times. Hence, in theory, ONU should require less processing time. This time was set to 350 \(\upmu\)s. This is the sum of the duration of the sent message (125 \(\upmu\)s), the maximum propagation delay at 20 km, which was approximately 100 \(\upmu\)s, and the message processing time (125 \(\upmu\)s). The entire timing of the transmitted messages is indicated in Figure 10. A real GPON does not contain only 32 or 64 ONUs, and the current OLT supports up to 16 GPON ports per card. The total amount of these cards depends on the OLT chassis. We considered 16 GPON ports with 32 ONUs per port. The total amount of ONUs was 512 ONUs, which must be activated. The current activation process can activate all ONUs in \(\approx\)112 s or 74 s with our optimization, respectively.