1. XRAN (eCPRI) S-Plane Sync Update
XRAN-FH.CUS.0-v01.00
April 2018

2. 5G Cloud Ran eCPRI & Next Generation Fronthaul Interface architecture
Centralized
BBUs
Cloud RAN
Core
Network
PRTC-B
vBBU
NGFI (Ethernet)
Backhaul operator
Fronthaul
RRUs
Mobile operator
Mobile operator Cs
ePRTC
APTS
CSG
Macro cell
Mobile operator
Small cells
Fronthaul
NGFI
PRTC
Mobile operator
Two challenges for NGFI: Synchronization & Latency

3. Quick Summary XRAN is perfect for TP4100
XRAN architecture focuses on engineering the Fronthaul
Macro end to end sync is still +/-1.5usec
FH timing in XRAN is +/-175nsec
The XRAN mandates a PRTC at the CU (known as Fronthaul Grandmaster or FHGM)
PRTC-B is required at the FHGM because of the stringent end to end fronthaul timing
APTS backup at the FHGM for loss of UTC at the CU
Bridging on the FHGM is strongly suggested to mitigate RU behavior on loss of GNSS
This architecture plays directly to the TP4100 strengths along with ePRTC, APTS/AAC, and Bridging

4. Summary xRAN PTP G.8275.1 and syncE
option 7 on the CPRI stack: separation of CU (CU+DU) and RU
The PRTC-GM/CU are collocated in this first version
Fronthaul GM (FHGM) to RU TE budget is +-175ns
Sync Fronthaul is defined between PRTC at CU (FHGM) to RU
Fronthaul may have a max of two (2) L2 switches
G Class B T-BC required
The CU can get sync from an upstream PRTC
UTC to FHGM output max TE is usec
The sync test and reference point for the deployment scenarios covered in first release are based on a topology where the sync PRTC/GM is located at the CU.
Optionally the PRTC/GM may be located deeper in the network.
Max 2 Switches in the fronthaul function as Class B Telecom Boundary Clocks.

5. xRAN Optional Sync Topologies

6. XRAN v01 Preferred Topologies (max 2*BC)
Only these 2 topologies are covered in version 01.00
Other topologies will be covered in a later version.

7. PTP & syncE Details/Profiles
time synchronization uses ITU-T G telecom profile,
PTP Time
PTP time on the fronthaul interface uses TAI/UTC
PTP time on the fronthaul interface must be traceable to a PRTC if a network wide sync of RU at the Air Interface (RH) is required (as in TDD 5G)
Coherent Clock
CU may use “coherent” SyncE/PTP clock on the fronthaul interfaces
i.e. SyncE & PTP clock in CU may use the same clock source
syncE
used if GNSS is not needed to achieve μsec sync
syncE implementation requires
G.8262: Clock specifications:
G.781 SSM processing
G.8264: Functional model
SSM processing parameters
Option 1 Quality Level
Accepted QL limited to PRC
Extended SSM codes are not planned in initial deployment
Note that eEEC is not specifed

8. XRAN Details: PRTC-B at Fronthaul CU Agg Point
Sync delivery as per IEEE 1914: G , syncE,
PTP on the fronthaul i/f traceable to PRTC-B (UTC) aka FHGM
Max 2 L2 switches with T-BC class B (20ns)
GNSS,
PTP
syncE
PRTC-B
(FHGM)
PTP
syncE CU RU
GNSS,
PTP
syncE
PRTC-B
(FHGM)
PTP
syncE
T-BC
(B)
T-BC
(B) CU RU

9. Timing Architecture for XRAN Fronthaul
Time Error statements for FHGM to RU
FHGM to RU nsec
+-40ns
GNSS,
PTP
syncE
PRTC-B
(FHGM)
PTP
syncE
T-BC
(B)
T-BC
(B) CU RU
+-20ns
+-20ns
+-20ns – 40ns

10. Network Timing Architecture with XRAN Fronthaul
Time Error statements from ePRTC to RU
ePRTC to FHGM usec
FHGM to RU nsec
ePRTC
T-GM
PRTC-B
(FHGM) CU
T-BC
T-BC RU

11. Time Error Limits Time Error Definitions Maximum link delay asymmetry
max|TETOTAL| maximum absolute TE at RH relative to UTC. = 1.5μs
max|rTEGM-to-RU_AIF | = 175ns
max|TEGM| = max|TETOTAL| – max|rTEGM-to- RU_AIF|
max|rTEGM-to-RU_AIF| is maximum absolute relative TE between GM and RU
the max|TEGM | = 1.325μs
It is not recommended to increase the number of L2-switches between GM & RU
this will impact dynamic noise accumulation at the RU input and may result in tighter specification for FEGM and would require a new TE accumulation and FE budget analysis.
Maximum link delay asymmetry
0.07% per km between GM and RU
Link delay asymmetry contributes to maxTETOTAL
maximum two T-BC between GM & RU.
G Class B T-BC required in L2 switches
Interfaces >10GE are FFS.
In particular 25 GbE/RS-FEC is FFS until 25GE is included in G because it will impact T-BC performance.

12. Synchronization Accuracy
Jitter
CU, L2 switch, and RU fronthaul interfaces must comply to jitter requirements defined in ITU-T G.8262 (syncE)
Time and Frequency Synchronization Requirements
Air Interface: total TE ±1.5μs, total FE +-50 ppb.
GM output absolute FE : FEGM = [±15ppb]
FEGM is defined as the maximum absolute frequency deviation of PTP, measured at the GM-output after applying a first-order low-pass measurement filter with a bandwidth of 0.1Hz to the time error samples
Measurement condition is applicable when GM is locked, excluding:
Holdover and acquiring states,
Instantaneous phase jump caused by backhaul Master Clock,
Re-sync with backhaul PTP/GNSS during holdover,

13. Loss of sync at CU / RU CU
If a CU loses sync, RF transmission on all connected RU is disabled until sync is re-established.
The CU can operate outside the sync limits, or without sync . RU
The RU only reacts to a change in SyncE SSM QL, & PTP Clock Class,
If the QL or Clock Class is unacceptable the RU goes into H/O
If an RU using GNSS loses the GNSS signal it goes into H/O.
the RU relies on the CU to take care of the changed sync state.

14. Reference Documents ITU-T G.781 sync layer functions
ITU-T G Definitions and terminology for sync networks
ITU-T G Definitions and terminology for sync in packet networks
ITU-T G Timing and sync aspects in packet networks
ITU-T G Timing characteristics of a synchronous Ethernet equipment slave clock
ITU-T G Distribution of timing information through packet networks
ITU-T G Network limits for time sync in packet networks
ITU-T G Framework of phase and time clocks
ITU-T G Precision time protocol telecom profile for phase/time

15. Thank You Eran Gilat – Systems Architect Engineer FTD eran
Thank You Eran Gilat – Systems Architect Engineer FTD