## 7 Passive Optical Network
### Lessons Learned
This can be effectively realized as there is no wavelength overlap among the technologies. Consequently, in-band measurement can be done without any service disruption [398; 415]. A typical PON system \begin{table}
\begin{tabular}{l l l l} \hline \hline
**Solution** & **Advantages** & **Limitations** & **Reference** \\ \hline Optical systems & & & \\ \hline Dedicated fiber & \(\bullet\) & Uncomplicated as additional equipment is & \(\bullet\) & Demands fiber-rich deployment & [5,8,11,47,143,371, \\  & \(\bullet\) & not required & \(\bullet\) & Poor scalability \\  & \(\bullet\) & Colorized SFPs are not required & \(\bullet\) & Uneconomical for certain \\  & \(\bullet\) & Employs low-cost optics & \(\bullet\) & centralized deployments \\  & \(\bullet\) & Supports high capacity and low latency & & \\  & \(\bullet\) & use cases & & \\ \hline TWDM-PON (i.e., & \(\bullet\) & Relative low-cost potential & \(\bullet\) & Limitation in the supported capacity and \\ GE-PON, XG-PON, & \(\bullet\) & Enhanced fiber capacity with multiple & low-latency services & \\ and NG-PON2) & & channels per fiber & & \\  & & Capability for system reuse between FTTH & & \\  & & and FWA customers & & \\ \hline WDM-PON (i.e., & \(\bullet\) & Dedicated solution for RAN transport & \(\bullet\) & Limitation in reusing the existing & [5,8,11,25,47,143,371, \\ WS-WDM-PON, & & where ODN deployment can be adapted & \(\bullet\) & FTTH infrastructure & \\ WR-WDM-PON) & & for the preferred RAN deployment & \(\bullet\) & Potential concerns for future migration \\  & \(\bullet\) & Enhanced fiber capacity with multiple & \(\bullet\) & of customers to FTTH in which separate \\  & & channels per fiber & \(\bullet\) & ODN will be required \\  & & & Conventional scenario low fan-out limits \\  & & & the need for DWDM (i.e., CWDM \\ \hline PtP WDM overlay & \(\bullet\) & Potential reuse of the existing fiber plant & \(\bullet\) & High related footprint and costs of & [5,8,11,25,47,143,371, \\ (i.e., NG-PON2) & & for offering PtP transport solution. & ODN filters & 372,376,387] \\  & \(\bullet\) & Supports high capacity and low latency & & \\ \hline Active systems & & & \\ \hline Ethernet (i.e., CPRI & \(\bullet\) & Potential reuse of the existing & \(\bullet\) & High power consumption & [5,11,25,47,143,371, \\ over Ethernet), OTN & infrastructure & & (additional electronics) & 372,376,384,387] \\  & \(\bullet\) & Appropriate for active network & \(\bullet\) & RAN split options are virtually limited \\  & deployment & by the deployed active equipment & \\  & \(\bullet\) & Native OAM and FEC & \(\bullet\) & High footprint (cooling) \\  & \(\bullet\) & Colored SFPs no required at the DUs & \(\bullet\) & Concerns on system performance \\  & \(\bullet\) & Offers native protection & (latency, synchronization) \\  & \(\bullet\) & Enhanced scalability & & \\  & \(\bullet\) & Economical & & \\ \hline Wireless systems & & & \\ \hline LTE, 5G & \(\bullet\) & Flexible deployment & \(\bullet\) & Shared spectrum between the access & [5,11,47,143,371,372, \\  & \(\bullet\) & Offers lower deployment cost than & and transport & 376,387] \\  & & fiber solution & \(\bullet\) & More spectrum required \\  & & & Distance limited & \\ \hline MW, PSO & \(\bullet\) & Can complement fiber-based technologies & \(\bullet\) & Susceptible to weather conditions & [5,11,47,143,376,378] \\  & \(\bullet\) & Flexible deployment & \(\bullet\) & Distance limited \\  & \(\bullet\) & Cost-effective solution in areas where fiber & \(\bullet\) & LoS constraint limits network \\  & & is not available & & equipment placement \\ \hline \hline \end{tabular}
\end{table} 
Table 12: Comparison of potential transport network solutions for FWA. coexistence for supporting a gradual and pay-as-you-grow expansion for any business need, any migration scenario, and any service type is depicted in Figure 25[392]. Depending on the use cases, the ONUs on the network element can be configured to deliver services to the wireline/fixed subscribers.