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

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

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

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.8273.2 Class B T-BC required The CU can get sync from an upstream PRTC UTC to FHGM output max TE is +- 1.325usec 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.

xRAN Optional Sync Topologies

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.

PTP & syncE Details/Profiles time synchronization uses ITU-T G.8275.1 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 +- 1.5μsec 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

XRAN Details: PRTC-B at Fronthaul CU Agg Point Sync delivery as per IEEE 1914: G.8275.1, 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

Timing Architecture for XRAN Fronthaul Time Error statements for FHGM to RU FHGM to RU +-175 nsec +-40ns GNSS, PTP syncE PRTC-B (FHGM) PTP syncE T-BC (B) T-BC (B) CU RU +-20ns +-20ns +-20ns – 40ns

Network Timing Architecture with XRAN Fronthaul Time Error statements from ePRTC to RU ePRTC to FHGM +-1.325 usec FHGM to RU +-175 nsec ePRTC T-GM PRTC-B (FHGM) CU T-BC T-BC RU

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.8273.2 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.8273.2 because it will impact T-BC performance.

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,

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.

Reference Documents ITU-T G.781 sync layer functions ITU-T G.810 Definitions and terminology for sync networks ITU-T G.8260 Definitions and terminology for sync in packet networks ITU-T G.8261 Timing and sync aspects in packet networks ITU-T G.8262 Timing characteristics of a synchronous Ethernet equipment slave clock ITU-T G.8264 Distribution of timing information through packet networks ITU-T G.8271.1 Network limits for time sync in packet networks ITU-T G.8273.2 Framework of phase and time clocks ITU-T G8275.1 Precision time protocol telecom profile for phase/time

Thank You Eran Gilat – Systems Architect Engineer FTD eran Thank You Eran Gilat – Systems Architect Engineer FTD eran.gilat@microsemi.com