Above figure outlines the protocol stack composition if virtualized CU and DU with eCPRI between in fronthaul (where RRU and DU could be collocated or geographically distributed and active or passive antenna unit being used).
The terminology used is HLS (Higher level split), provided by 3GPP standardization, and LLS (Lower layer split) which utilize one of the CPRI splitting options. Here it is assumed that intra PHY split between gNB-DU and RRU is considered so bandwidth demands on the fronthaul network are significant for the transport network. A lower layer split in the protocol stack mandates that the fronthaul network features high bandwidth and very stringent delay/synchronization requirements.
The overall bandwidth requirements for NG-RAN deployment can vary significantly, due to range of different factors.
Table below outlines the cell bandwidth requirements for a number of MIMO, antenna port and channel size combinations (all based on 256 QAM Modulation). Values shown are approximations designed to provide a general idea of the overall bandwidth requirements. It also mention an indication of one way latency requirements. The two options outlined are option2 which is the current split point used between F1 between the gNB-CU and gNB-DU along with a potential further split point (option 7-2) which could be used for the split between gNB-DU and RRU.