gure 4.5.6 Control (left), user (center), and synchronization (right) message protocol stack. (Source: Reproduced by permission of © O-RAN). 4 NG-RAN Architecture Destination Source MAC Preamble Type/Length VLAN Tag Payload MAC Address Address (8 Bytes) (EtherType) (4 Bytes) (6 Bytes) (42-1500 Bytes) (4 Bytes) (12 Bytes) (6 Bytes) (2 Bytes) O-RAN Native Ethernet Package with VLAN Destination Source MAC Preamble Type/Length VLAN Tag IPv4/IPv6 Address (EtherType) Payload MAC Address (8 Bytes) (6 Bytes) (6 Bytes) (4 Bytes) (20/40 Bytes) (8 Bytes) (2 Bytes) (0-1472 Bytes) (4 Bytes) (12 Bytes) O-RAN Native IPv4/IPv6 Package wnn VLAN eCPRI/RoE Transport Header O-RAN Transport Payload (8 Bytes) Figure 4.5.7 O-RAN transport protocol stack diagram. The eCPRI Transport Header, shown in Figure 4.5.8, carries the following information: ecpriVersion - The eCPRI protocol version. Default Value: 0001b (eCPRI version 1.0). ecpriReserved - The reserved field, not used. Default Value: 000b. ecpriConcatenation - The indicator of multiple eCPRI messages concatenation within single payload. Default value: 0 b (no concatenation). ecpriMessage - The message type. Valid Values: 0x0 (user-plane data) or 0x2 (control-plane data) or 0x5 (network delay measurement messages). ecpriPayload - The eCPRI message payload size in bytes. ecpriRtcid/ecpriPcid - The component_eAxC identifier (c_eAxC ID) which is used to identify the specific data flow associated with each control-plane (ecpriRtcid) or user-plane (ecpriPcid) message. ecpriSeqid - The message sequence ID to identify the message ordering within an eAxC message stream. The IEEE1914.3 header, shown in Figure 4.5.9, carries the following information: RoEsubType - The payload type of the IEEE 1914.3. Value range 128-131, which maps to the eCPRI header field combination of ecpriMessage and cpriConcatenation. RoEflowID - The flow ID between endpoints. It is not used in O-RAN. RoElength - The message payload size in bytes. RoEorderInfo - The field is split into seven subfields: DU_Port_ID - Id