ve a centralized CU and SO are connected to the MH network (see the third case in Figure 11-12). These tend to be deployed at very high-traffic locations in dense urban settings. Wherever the location of the CU, the timing is only required at the cell site and the requirement for +1.1 us absolute phase alignment always applies. There may also be additional, tighter requirements to achieve inter-cell radio coordination (see the upcoming section "Relative Versus Absolute Timing"). The design is similar for many macro cells, especially those in more remote and rural locations; everything is at the cell site, and there is only a connection to the BH network (the first case from Figure 11-12). As in the small cell case, the timing is only required at the cell site and the same +1.1-us phase requirement always applies. It is commonly the mobility or mid-band sites that tend to centralize their DU or BBU equipment into a shared facility remote from the cell site, and these are deployed mainly in high-traffic, metro areas (the first and fourth cases depicted in Figure 11-12). This CRAN architecture connects the DU/BBU to the RU over the FH network. In 4G deployments, the FH network was based on the lowest level option 8 split that used transport methods such as the Common Public Radio Interface (CPRI). CPRI is a TDM-like synchronous protocol, SO the same +1.1-us phase was delivered to the DU/BBU, and CPRI took care of the fre- quency and phase out to the RU at the cell site. For phase timing of mobile networks, this is one of the easiest deployments to build a timing solution for. For 5G, CPRI now shows its limitations (mainly excessive bandwidth needs in the FH because of the option 8 split), SO there is now a migration to transform the CRAN to use an FH network utiliz- ing packet-based transport. 11.4.1 Packetized Radio Access Network With the option 8 (CPRI) split, the timing signal only needs to be made available at the DU/BBU, with CPRI doing the job for the last few kilometers (limited to about 20 km for latency re