two sites. Figure 10-28 provides an overview of the different possible split options for a disaggregated 5G RAN architecture. In both upstream and downstream directions, the radio signals go through series of signal processing blocks; and the interfaces between these blocks are potential split options for 4G as well as 5G RAN. The functions on the left up to the point of the split are centralized, and the functions to the right of the split are decentralized to the radio site. CPRI option 8 is on the far right. Option 1 Option 2 Option 3 Option 4 Option 5 Option 6 Option 7 Option 8 (CPRI) eCPRI Scope ~10-0s GB Bandwidth Latency >10-ms ~10-0 us Figure 10-28 Functional Split Options Options with the lower numbers (1, 2) are known as high-level splits, whereas those with large numbers (7, 8) are known as low-level splits. When RAN engineers talk of low-level splits, they mean the split is lower down the processing stack, but the option number is higher. Conversely, a high-level split has a low option number. With each split option, the latency requirements change, and the amount of bandwidth required to carry a specific amount of user traffic also changes. Selecting a low-level split option (toward the right) increases the bandwidth (and thus the ineffi- ciency) and tightens the latency requirements. But the high level of centralization with these low- level splits allows much tighter coordination between radios at the BBU/DU, improving the quality and spectrum efficiency using methods seen in the preceding sections. With high-level split options (toward the left), the bandwidth requirement scales more in line with user traffic and allows statistical multiplexing advantages. Being able to deploy high-layer splits (for example, option 2) relaxes the latency and bandwidth requirements. Therefore, option 2 is a commonly chosen split level for those use cases that require high bandwidth. Controlling multiple RUs with a centralized DU deployment allows load-balancing between differ- ent RUs, real-time interference manage