hase alignment budget. The downside is that this means you must deploy a larger number of PRTC and T-GM devices when they are distributed like this. The next factor to consider is the technology split between the DU and RU and what the connection is between them. Additionally, the location where the DU and the RU are situated matters-whether they are co-located or distributed over a FH network (third and fourth cases depicted in Figure 11- In summary, this decision comes down to whether the architecture of the RAN is centralized or dis- tributed, or, in other words, whether the goal is a DRAN or a CRAN; and for a CRAN, where the various components are located. 11.4.1 Centralized RAN and Distributed RAN Recall from Chapter 10 that there are numerous positive benefits to building a CRAN over building a DRAN. These benefits materialize (or become cost effective) only when the CRAN is applied to cell sites in dense metro areas-the DRAN is still the dominant architecture outside those areas. But the selected approach influences the timing design quite markedly; the lesson to take away here is that if timing the DRAN is difficult, timing the CRAN can be even more SO. Although the selected architecture of the RAN determines the timing requirements, there are also other con- sequences of the decision that limit the layout of the various RAN components. The major consideration is latency, and the selected RAN type and the technology split can have dramatic effects on the latency require- ments. Some of these latency budgets are very small (say, 100 us), and that imposes severe geographical con- straints on distance between these elements. A centralized RAN is still distributed out close to the radio units for this reason-it is only partially centralized. Latency is also why a CRAN can be a problem to deploy in more remote locations because the distances between elements are too large. For many types of small cell and devices based on mmWave, the DU and RU are commonly co-loc- ated, and there is no FH network. These can ha