eCPRI Message Format: Header and Types Explained

This document explains the eCPRI message format, covering the eCPRI header, payload structure, transmission order, and different message types.

Introduction to eCPRI

• eCPRI stands for Enhanced Common Public Radio Interface.

• The core concept involves dividing the functionalities of a Base Station (BS) into two blocks: Radio Equipment Control (REC) and Radio Equipment (RE). These are connected via a packet-based fronthaul transport network, such as Ethernet or IP. Figure 1 illustrates this concept.

  Figure 1: eCPRI fronthaul connection

• While CPRI uses the terms REC and RE, eCPRI refers to the same entities as eREC and eRE, respectively.

• eCPRI manages the following service points: User Plane Traffic, Synchronization, and Control & Management.

• eCPRI can be implemented between single eRECs and eREs, as well as multiple eRECs/eREs.

• The eREC and eRE are physically separated. The eRE is typically located closer to the antenna, while the eREC is at a remote location.

eCPRI Message Format

Figure 2: eCPRI message format

Figure 2 shows the general eCPRI message format.

• For User Plane data transmitted over Ethernet, eCPRI messages are sent within standard Ethernet frames. The minimum size of the data field in an Ethernet frame is 46 octets. Frames with payload sizes exceeding 1500 octets are also supported.

• When using IP for User Plane, eCPRI messages are transmitted within UDP/IP packets.

• The structure of an eCPRI message is as follows:

  eCPRI message = { eCPRI header (4 bytes) eCPRI payload (variable size) }
  

eCPRI Header Format (Common Header)

Figure 3: eCPRI header format

Figure 3 illustrates the eCPRI header format, highlighting the common header fields. The eCPRI message common header contains the following fields:

eCPRI header = {
eCPRI protocol revision (4 bits)
Reserved (3 bits)
C bit (1 bit)
C = 0 indicates that the current eCPRI message is the last one inside the eCPRI PDU
C = 1 indicates that another eCPRI message follows this current one within the eCPRI PDU.
eCPRI message type (8 bits) - Type of service carried by the message.
eCPRI payload size (16 bits) - Maximum supported payload size is 2^16 - 1.
}

eCPRI Message Types

The following table outlines the various eCPRI message types.

Message Type	Name of message
0	IQ Data
1	Bit Sequence
2	Real time control data
3	Generic Data transfer
4	Remote Memory Access
5	One way delay measurement
6	Remote reset
7	Event Indication
8 to 63	Reserved
64 to 255	Vendor Specific

Refer to the eCPRI protocol stack documentation for more information on how different eCPRI message types flow through the stack.

References

• eCPRI Specification V1.2 (2018-06-25)