 analog signal, amplifies it, and then radiates the signal over the air. Control and management data and synchronization information are delivered through CPRI subchannels, more specifically through control words in the CPRI basic frames. This infor- mation is only used by the REC (on the BBU side) and the RE (on the RRH side). CPRI subchannels are created per CPRI hyper-frame, which is 66.67 us and a hyperframe consists of 256 basic frames (260.42 ns). Each basic frame has one byte of a control word and 15 bytes of payload. A group of 256 control words in one hyperframe collectively constitute 64 subchannels. Fig. 1.29 shows a CPRI subframe and how the control and management data and synchronization information are mapped and transported [75]. eCPRI Transport The concepts of CPRI-over-Ethernet and replacing the TDM-like CPRI format with Ethernet messaging both hold the promise of reducing the bandwidth require- ments of CPRI transport and making fronthaul affordable and available to all mobile opera- tors. Ethernet is a very cost-effective transport technology that is widely deployed in the 010001000100111 0100010001001117 LTE/NR LTE/NR RF User data LTE/NR IP backhaul Control and management Synchronization Optical fiber medium Fast C&M information (Ethernet) Fast C&M information (Ethernet) Slow C&M information (HDLC) Slow C&M information (HDLC) L1 Inband protocol 16 bits/260.42 ns L1 Inband protocol Vendor specific information Vendor specific information Timing and synchronization Timing and synchronization Radio equipment (RE)/RRH/RRU W= 15 Radio Equipment Control (REC)/BBU/DU CPRI payload (I/Q data block 120 bits) CPRI interface Figure 1.29 Illustration of CPRI framing [60]. 5G Network Architecture backhaul transport network. However, it is also an asynchronous best effort technology that has not been originally designed to meet the low latency, low jitter, and tight synchroniza- tion requirements of baseband signal transmission. The new specification, known as eCPRI, introduces improved transport efficiency t