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12 | Whitepaper – Exploring Computing Platforms for Radio Access
Networks
techniques such as (ET, DPD), and Beamforming. The connection between the RRH and BBU
is again called the FH. The FH interface is evolving from CPRI to eCPRI, IEEE1914.3, as well
as O-RAN.
The connection to the 5G CN is called the BH. The 5G CN will contain the Access and Mobility
Function (AMF) which will perform Mobility Management, Access Authentication/Authorization,
Terminate N2 interface, and Connection Management. The Session Management Function
(SMF) will perform UE IP address allocation & Management and Traffic steering to UPF. The
User Plane Function (UPF) will perform the PDN connection, Packet routing and forwarding,
QoS handling of User Plane (UL/DL rate enforcement), and Anchor point for Intra-Inter-RAT
mobility. The United Data Management (UDM) will perform User ID handling, and Subscription
Management.
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The 5G CN was designed based on the Service Based Architecture (SBA)
principles. This direction was chosen to support cloud native based implementations and to
allow for easy integration of MEC applications.
Figure 11: 5G NR Network Architecture block diagram
An example FH functional spilt is provided in Figure 12. Note again the DU/CU interface is now
defined by 3GPP and called the F1 interface. Depending on the deployment scenario, a FH
Gateway can be inserted between the RRH and DU functions. The purpose of this FH Gateway
would be to aggregate traffic, perform any protocol conversions, distribute timing, support FH
split options, and more. A motivation of the particular DU/CU functional split shown is security.
The PDCP layer provides Integrity and Confidentiality protection to both the user and control
planes.
Figure 12: Front Haul split options for the 5G NR Network.
Figure 13 provides a more detailed diagram of the physical layer RAN FH functional splits. This
example corresponds to the Option 7.2 provided by O-RAN front haul specification. The left
side of the dashed line (denoted as FH) represents the DU/CU functionality performed by the
PHY
MAC
RLC
PDCP
SDAP
RF
MIMO
(BF)
RRH (AAS)
DFE,
ET,
DPD
DAC
/
ADC
AMF
UPF
SMF
UDM/PCF
gNB
5G CN
BBU
N6
N2
N3
N4
N11
...
FH
BH
Etc.
RRH (AAS)
BBU
5G
CN
P
H
Y
M
A
C
R
L
C
P
D
C
P
R
R
C
...
RF
ADC/DAC
DFE
P
H
Y
FH
DU
CU
N6
S
D
A
P
F1
N2/N3