1. RAN Functional Decomposition the options and interfaces…
RAN Functional Decomposition the options and interfaces… Andy Sutton Principal Network Architect Architecture & Strategy BT Technology 19th November 2018

2. Contents RAN architecture evolution RAN functional decomposition
Access network connectivity
5G network deployment
5G demo update
Summary

3. GSM - fully distributed RAN
GSM BTS is a fully distributed radio base station
All radio related protocols terminate in the BTS
Radio interface encryption terminates in the BTS
Distributed intelligence with centralised BSC
BTS
BSC
Abis interface
Core network
NOTE: IP Sec GW used between BTS and BSC with IP Abis implementation
Nokia GSM Ultrasite BTS

4. UMTS - many centralised functions
UMTS is a simple L2 radio base station (known as Node B)
All radio related protocols terminate in the RNC
Radio interface encryption terminates in the RNC
Distributed radio with centralised intelligence
NodeB
RNC
Iub interface
Core network
Nokia UMTS Ultrasite BTS

5. LTE - distribution wins again…
2600
MHz RRU
LTE eNB is a fully distributed radio base station
All radio related protocols terminate in the eNB
Radio interface encryption terminates in the eNB
X2 interface between adjacent eNBs, no centralised network controller
eNB
EPC
S1 interface
eNB
SecGW
S1 interface
Core network
Huawei 3900 eNB (+GSM BTS)

6. LTE - RAN options CPRI S1 interface CPRI S1 interface 2600 MHz RRU
LTE eNB is a fully distributed radio base station
However, this radio (eNB) is made up of two components which can be geographically separated
RRU/RRH and BBU - separated by CPRI interface
RRU
BBU
CPRI
S1 interface
RRU
BBU
CPRI
S1 interface
Huawei 3900 eNB (+GSM BTS)

7. Base station architecture - LTE
Note: a site may support one or more base station architectures for different radio channels/bands
RRU
BBU
D-RAN with cabinet RFU
S1 interface
RRU
BBU
D-RAN with external RRU
CPRI
S1 interface
RRU
BBU
CPRI
C-RAN with centralised BBU
S1 interface

8. RAN functional splits - protocol architecture
Higher layer splits
Lower layer splits S 1
RRC
PDCP
High-RLC
Low-RLC
High-MAC
Low-MAC
High-PHY
Low-PHY RF
Data
Option 1
Option 2
Option 3
Option 4
Option 5
Option 6
Option 7
Option 8
RRC
PDCP
High-RLC
Low-RLC
High-MAC
Low-MAC
High-PHY
Low-PHY RF
Data
CPRI
End to end latency
Relaxed Very low
Capacity requirement
Traffic/capacity related Very high
Reference 3GPP TR

9. RAN functional decomposition
gNB
RU* DU CU
NR (air)
interface
CPRI
eCPRI F1
interface
S1 interface (EPC+)
N2/N3 interfaces (NGC)
* RU could be integrated within AAU (mMIMO) or standalone RU (RRU/RRH)
with coaxial connections to passive antenna (typically 8T8R)

10. RAN functional decomposition - E1 interface
Additional work is on-going on:
DU-CU split for LTE (W1 interface)
E2 interface between CU and RAN Intelligent Controller (RIC)
A1/O1 interface between RIC and NMS & Orchestration layer
gNB
CU-c N2
F1-c
RU* DU
NR (air)
interface
CPRI
eCPRI E1
F1-u
CU-u N3
* RU could be integrated within AAU (mMIMO) or standalone RU (RRU/RRH)
with coaxial connections to passive antenna (typically 8T8R)

11. Base station architecture - 5G - EN-DC (Option 3x)
Note: a site may support one or more base station architectures for different radio channels/bands RU DU CU
CPRI
eCPRI
D-RAN with AAU/RRU
S1 interface RU DU CU
C-RAN with option 2 split
CPRI
eCPRI F1
S1 interface RU DU CU
CPRI
eCPRI F1
C-RAN with option 7/8 split and further CU centralisation
S1 interface
Note: In full C-RAN configuration the DU and CU may be co-located or on separate sites

12. RAN functional splits - protocol architecture
Higher layer splits
Lower layer splits S 1
RRC
SDAP/PDCP
High-RLC
Low-RLC
High-MAC
Low-MAC
High-PHY
Low-PHY RF
Data
Option 1
Option 2
Option 3
Option 4
Option 5
Option 6
Option 7
Option 8
RRC
SDAP/PDCP
High-RLC
Low-RLC
High-MAC
Low-MAC
High-PHY
Low-PHY RF
Data F1
eCPRI
CPRI
Note:
Service Data Adaptation Protocol (SDAP), has been introduced to the NR user
plane to handle flow-based Quality of Service (QoS) framework in RAN, such as
mapping between QoS flow and a data radio bearer, and QoS flow ID marking.
End to end latency
Relaxed Very low
Capacity requirement
Traffic/capacity related Very high
Reference 3GPP TR

13. Base station architecture - 5G - Next Generation Core (NGC)
Note: a site may support one or more base station architectures for different radio channels/bands RU DU CU
CPRI
eCPRI
D-RAN with AAU/RRU
N2/N3 interface RU DU CU
C-RAN with option 2 split
CPRI
eCPRI F1
N2/N3 interface RU DU CU
CPRI
eCPRI F1
C-RAN with option 7/8 split and further CU centralisation
N2/N3 interface
Note: In full C-RAN configuration the DU and CU may be co-located or on separate sites (as illustrated)

14. RAN functional splits - protocol architecture
Higher layer splits
Lower layer splits
N2-N3
RRC
SDAP/PDCP
High-RLC
Low-RLC
High-MAC
Low-MAC
High-PHY
Low-PHY RF
Data
Option 1
Option 2
Option 3
Option 4
Option 5
Option 6
Option 7
Option 8
RRC
SDAP/PDCP
High-RLC
Low-RLC
High-MAC
Low-MAC
High-PHY
Low-PHY RF
Data F1
eCPRI
CPRI
End to end latency
Relaxed Very low
Capacity requirement
Traffic/capacity related Very high

15. RAN access network connectivityRU DU CU
CPRI
eCPRI F1
S1 or N2/
N3 interface
Fronthaul
Mid-haul
Backhaul
CPRI, eCPRI or
Non-ideal fronthaul
Backhaul (in common use)
Terms; Fronthaul, mid-haul and backhaul as defined by MEF (Metro Ethernet Forum)

16. 5G within a multi-RAT network deployment - DRAN scenario
PRTC
sync source
Openreach Point to point
DWDM solution
21C IP/MPLS network
(P routers not illustrated) 3G
CSG
OSA-FC
OSA-FC
21CMSE D W M D W M
21CMSE
Mobile core networks2
4G1
n x λ
(can bypass
CSG) 5G
Future-proofed for network
sharing and RAN evolution
1 - 2G is supported on the same base station as 4G (SRAN/Multi-RAT)
2 - Includes RNC for 3G and IP Sec GW for 4G and 5G

17. 5G within a multi-RAT network deployment - DRAN scenario
PRTC
sync source
Openreach Point to point
DWDM solution
21C IP/MPLS network
(P routers not illustrated) 3G
CSG
OSA-FC
OSA-FC
21CMSE D W M D W M
21CMSE
Mobile core networks2
4G1
n x λ
(can bypass
CSG) 5G
E-Band
1 - 2G is supported on the same base station as 4G (SRAN/Multi-RAT)
2 - Includes RNC for 3G and IP Sec GW for 4G and 5G

18. 5G within a multi-RAT network deployment - DRAN scenario
PRTC
sync source
Openreach Point to point
DWDM solution
21C IP/MPLS network
(P routers not illustrated) 3G
CSG
OSA-FC
OSA-FC
21CMSE D W M D W M
21CMSE
Mobile core networks2
4G1
n x λ
(can bypass
CSG) 5G
E-Band
E-band link(s) could connect directly
to a wavelength on OSA-FC product
1 - 2G is supported on the same base station as 4G (SRAN/Multi-RAT)
2 - Includes RNC for 3G and IP Sec GW for 4G and 5G

19. 5G demo at Canary Wharf Highlights
1.3Gbps to test equipment (30 MHz LTE + 40 MHz NR)
600Mbps to Huawei 5G CPE (5 MHz LTE + 40 MHz NR)
4T4R LTE (15 MHz MHz 2600) with 64T64R NR

20. Summary
The functional decomposition of the RAN is at an advanced stage in standards, industry fora and implementation (XRAN/ORAN, 3GPP, ONAP)
Traditional 4G centric CRAN (CPRI based) is popular in Asia due to availability of dark fibre, this brings radio optimisation benefits through centralised scheduling etc.
CPRI doesn’t scale for 5G due to amount of spectrum and antennas therefore eCPRI was developed by the same industry partners who developed CPRI
Several industry groups are working towards a virtualised RAN to disaggregate the hardware from software for many functions, also enables innovative new entrants to market
Major RAN vendors offer a range of different RAN architectures to meet various deployment scenarios
BT is currently rolling out the radio, backhaul and core network infrastructure necessary to be a leader in 5G and converged networks

21. Thank You Any questions?