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EL873
Advanced Networking Systems and Technology
Short Report

eCPRI Protocol layer

School of Engineering and Digital Arts
The University of Kent
March 2020

Introduction
Common public radio interface(CPRI), a serial interface, is a communication protocol between the
baseband unit(BBU) and radio resource unit(RRU) [1]
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As 5G will carry a lot more
traffic, an ethernet based CPRI protocol is introduced called enhanced CPRI (eCPRI), which by using
functional splits divides the baseband functions, in this way it reduces high data rate demand between
eCPRI Radio Equipment Control (eREC) and eCPRI Radio Equipment (eRE)[3]
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In industry seminar, analysis of eCPRI protocol was discussed, where eCPRI protocol layer was
highlighted along with eCPRI header and payload format
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e Data plane and Control plane
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Data Plane/User plane
eCPRI itself defines the user plane[4]
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For user plane over Ethernet, standard ethernet frames (AEFE) are used for the transmission of eCPRI
messages with ethernet rates of 10Gbps to 100Gbps
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In the data field of both ethernet frame and UDP datagram, eCPRI header of four bytes is placed at
beginning
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For UDP datagram, no padding is required
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This is then appended at the transport network layer header as a payload of
transport network layer as shown below:

eCPRI
Message/Messages
eCPRI
eCPRI
Common Payload
Header
Figure 2_Mapping_of_eCPRI_messages_on_transport_network_layer

Transport Network
layer Header

A unique ethernet MAC/IP address is given to every eCPRI node which tells about the source and
destination of eCPRI message
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It is now totally dependent on the vendor’s choice that which
functional decomposition between eREC and eRE they want[3]
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eCPRI focuses in these 3 splits of PHY layer; one for uplink (Iu) and two for downlink (ID, IID)
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Real time control information is transferred before the
transmission of IQ data/bit sequence to let the remote node know about the processing of IQ samples/bit
sequence
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In order to carry either of these data type between the PHY
processing elements in eREC and eRE, vendor specific information of respective real-time control data
(e
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eCPRI can co-exist with
both new and legacy network(CPRI nodes)
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Control plane
If the splits are more towards the MAC frame, then control data bits increase
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C&M and synchronization plane together makes the
control plane[5]
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2
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This control information is then
transmitted to higher protocol layers
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The information flow of this plane is divided
into background traffic, and interactive traffic which is responsible for the control functions of
eCPRI nodes [3]
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2 Synchronization Plane
Synchronization data is used for the alignment of frames and time synchronization between
nodes
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For
air transmission, as eRE generates the frequency locally, so eRE 3GPP synchronization and
timing requirements should be available for eRE’s air interface[3]
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With the help of that eREC sends the data
to eRE at the right time, which provides enough time for eRE to process the data and handle
network latency before transmitting it into air interface
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To get maximum accuracy, it
uses a combination of PTP and SyncE
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Conclusion
eCPRI, with the help of three planes and packet-based transmission, minimizes bandwidth requirement
and decreases the high data rate demands of 5G
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It supports positioning of functional splits more flexibly, thus it can meet
different vendors and future requirements
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Macknofsky, “Understanding the Basics of CPRI Fronthaul Technology,” 2015
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Li et al
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7, pp
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1109/access
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2930214
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group, “eCPRI Specification V2
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0, p
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“Evolved Fronthaul: eCPRI Specification - VIAVI Perspectives
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Available:
https://blog
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com/2018/06/19/evolved-fronthaul-ecpri-specification/
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Kalfas et al
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Commun
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, pp
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