Problem with Benetel RAN650 – no RF activity despite PTP sync and correct OFH config

[alektoja]

Hello,

I'm trying to run srsRAN gNB with a Benetel RAN650 O-RU in a 7.2 split Open Fronthaul setup. I'm using the no-DPDK version of srsRAN (tested also with DPDK – same result), and Benetel firmware version RAN650-1v1.0.4. Although PTP synchronization is confirmed and OFH frames are being exchanged, there is no RF activity (Tx/Rx = 0) on the RU, and logs from gnb show IQ decoding errors. RU also reports No signal in CLI tools like RXMeanPower, TXMeanPower, and /var/log/kpi.

Observations
ptp4l and phc2sys indicate stable sync:

ptp4l[701699.086]: rms 4 max 7 freq -1852 +/- 6 delay 83 +/- 2
ptp4l[701699.994]: rms 2 max 3 freq -1852 +/- 3 delay 84 +/- 2
ptp4l[701700.883]: rms 3 max 7 freq -1856 +/- 5 delay 83 +/- 3
ptp4l[701701.806]: rms 2 max 4 freq -1853 +/- 4 delay 82 +/- 2

phc2sys[701495.809]: CLOCK_REALTIME phc offset 4 s3 freq -12282 delay 508
phc2sys[701495.934]: CLOCK_REALTIME phc offset 5 s3 freq -12280 delay 436
phc2sys[701496.059]: CLOCK_REALTIME phc offset 2 s3 freq -12281 delay 508
phc2sys[701496.184]: CLOCK_REALTIME phc offset 4 s3 freq -12278 delay 516

RU log shows successful initialization and OFH config:
[INFO] /etc/ru-center-frequency-mhz read
[INFO] /home/root/adrv9025/RAN650_n77u_2T2R/ directory used
[INFO] adrv9025 files OK
[INFO] Platform: RAN650_A
[INFO] Frequency: 3900.00
[INFO] SW Version: RAN650-1v1.0.4-dda1bf5
[INFO] Read EEPROM with eeprom2ram
[INFO] Read EEPROM with benetel_read_ru_eeprom.sh
[INFO] Radio bringup begin, 96.08 seconds since boot
[INFO] Initialize TDD Pattern
[INFO] Setting initialization TDD Pattern: DDDDDDDSUU
[INFO] Waiting for PTP sync
[INFO] Sync completed
[INFO] Disable transmission during radio initialisation
[INFO] Set expected DU MAC Address for C-Plane Traffic (C0319/C031A)
[INFO] Set expected DU MAC Address for U-Plane Traffic (C0315/C0316)
[INFO] Set required DU VLAN Tag Control Information for uplink U-Plane Traffic (C0318)
[INFO] Set expected DU VLAN Tag Control Information for downlink U-Plane Traffic (C0330)
[INFO] Set expected DU VLAN Tag Control Information for downlink C-Plane Traffic (C0331)
[INFO] Aligning FPGA uplink timing to arrival of uplink frame(C0303)
[INFO] The benetel_extend_eeprom check is complete and passed
[INFO] Set Downlink scaling to 6 dB (C0358)
[INFO] Enable short form PRACH (C0328)
[INFO] Compression mode: Static, Compression method: 9-bit BFP
[INFO] Aligning TDD switching relative to downlink and uplink data and with respect to PPS (C0366)
[INFO] Set expected RU PRACH Configuration Index (C0322)
[INFO] C-plane per symbol disabled and cuplane dl coupling via section ID disabled (C037B to 0x1)
[INFO] enable the LF prach compression (C0353)
[INFO] Enabling 2 SF PRACH receive paths
[INFO] Configure eAxC ID via /etc/eaxc.xml settings, as M-Plane is disabled.
[INFO] Start Radio Configuration
[INFO] Initialize RF SoC
[INFO] Center frequency set to 3900.00 MHz
[INFO] Initialize RF SoC
[INFO] Enable PA protection on transmitters
[INFO] Load GP interrupt configuration into Madura
[INFO] Call interrupt handler once to clear any sticky interrupts left over from initialization
[INFO] Configure CFR for Antenna 1 (0.47)
[INFO] Configure CFR for Antenna 3 (0.47)
[INFO] Enable FPGA-controlled TDD switching
[INFO] Enable TX on FEM
[INFO] FEM to 1_3 MIMO mode
[INFO] DPD Tx1 configuration
[INFO] DPD Tx3 configuration
[INFO] Disable transmission
[INFO] Set the gain to 25.000000 dB
[INFO] Disable transmission
[INFO] Set the bandwidth to 20000000 Hz
[INFO] Modifying the TDD pattern from default to custom
[INFO] Transmission enabled (2x2)
[INFO] Setting DL UL tuning special slot to 0xfd00000
[INFO] Radio bringup complete
20:13:54 up 4 min, load average: 0.10, 0.24, 0.13
[INFO] Launching o_ru_app

RU CLI tools (TXMeanPower, RXMeanPower) return "No signal":
root@benetelru-01:~# TXMeanPower
No signal.

root@benetelru-01:~# RXMeanPower
RX 1 RSSI: No signal dBm
RX 2 RSSI: No signal dBm
RX 3 RSSI: No signal dBm
RX 4 RSSI: No signal dBm

KPI stats show RX_TOTAL increasing, TX_TOTAL always zero:
root@benetelru-01:~# /usr/sbin/kpi.sh
SAMPLE_TIME | RX_TOTAL | RX_ON_TIME | RX_EARLY | RX_LATE | RX_ON_TIME_C | RX_EARLY_C | RX_LATE_C | TX_TOTAL
19:21:47.918703 | 45114 | -0 | 10300 | 31249 | 3394 | -0 | -0 | -0
19:21:48.921563 | 44987 | -0 | 10300 | 31261 | 3396 | -0 | -0 | -0
19:21:49.920840 | 45049 | -0 | 10300 | 31339 | 3404 | -0 | -0 | -0
19:21:50.920605 | 45055 | -0 | 10300 | 31265 | 3396 | -0 | -0 | -0
19:21:51.921739 | 45058 | -0 | 10300 | 31329 | 3402 | -0 | -0

gNB logs contain repeating messages:
2025-07-30T19:59:10.009587 [OFH ] [I] Sector#0: received Open Fronthaul message size is '334' bytes and it is smaller than the expected IQ samples size of '576'
2025-07-30T19:59:10.009588 [OFH ] [I] Sector#0: dropped received Open Fronthaul message as no section was decoded correctly for slot '129.19' and symbol '9'

2025-07-30T19:59:18.530671 [OFH ] [W] Sector#0: missed incoming User-Plane PRACH messages for slot '980.19'
2025-07-30T19:59:18.540689 [OFH ] [W] Sector#0: missed incoming User-Plane PRACH messages for slot '981.19'

2025-07-30T19:59:51.069530 [OFH ] [I] Sector#0: received Open Fronthaul message size is '334' bytes and it is smaller than the expected IQ samples size of '576'
2025-07-30T19:59:51.069530 [OFH ] [I] Sector#0: dropped received Open Fronthaul message as no section was decoded correctly for slot '138.19' and symbol '3'

Configuration details:

gNB:
cu_cp:
amf:
addr: 127.0.0.5
port: 38412
bind_addr: 127.0.0.1
supported_tracking_areas:
- tac: 7
plmn_list:
- plmn: "00101"
tai_slice_support_list:
- sst: 1

ru_ofh:
t1a_max_cp_dl: 500
t1a_min_cp_dl: 258
t1a_max_cp_ul: 465
t1a_min_cp_ul: 285
t1a_max_up: 250
t1a_min_up: 50
ta4_max: 600
ta4_min: 100
is_prach_cp_enabled: true
compr_method_ul: bfp
compr_bitwidth_ul: 9
compr_method_dl: bfp
compr_bitwidth_dl: 9
compr_method_prach: bfp
compr_bitwidth_prach: 9
enable_ul_static_compr_hdr: false
enable_dl_static_compr_hdr: false
iq_scaling: 6
cells:
- network_interface: eth2
ru_mac_addr: 70:b3:d5:e1:5c:a7
du_mac_addr: 50:7c:6f:2c:f4:1a
vlan_tag_cp: 2
vlan_tag_up: 2
prach_port_id: [4, 5]
dl_port_id: [0,1]
ul_port_id: [0,1]

cell_cfg:
dl_arfcn: 660000
band: 77
channel_bandwidth_MHz: 20
common_scs: 30
plmn: "00101"
tac: 7
pci: 1
nof_antennas_dl: 2
nof_antennas_ul: 2
ssb:
ssb_period: 20
#ssb_block_power_dbm: 0
prach:
prach_config_index: 159
prach_root_sequence_index: 1
zero_correlation_zone: 0
prach_frequency_start: 2
preamble_trans_max: 50
power_ramping_step_db: 4
pusch:
dmrs_additional_position: 2
pdsch:
dmrs_additional_position: 2
tdd_ul_dl_cfg:
dl_ul_tx_period: 10
nof_dl_slots: 7
nof_dl_symbols: 6
nof_ul_slots: 2
nof_ul_symbols: 4

expert_phy:
max_proc_delay: 10

log:
filename: /tmp/gnb2.log
all_level: info
phy_level: debug
ofh_level: info

pcap:
mac_enable: false
mac_filename: /tmp/gnb_mac.pcap
ngap_enable: false
ngap_filename: /tmp/gnb_ngap.pcap

RU:

mimo_mode=1_3

downlink_scaling=6

prach_format=short

compression=static_compressed

lf_prach_compression_enable=true

cplane_per_symbol_workaround=disabled

cuplane_dl_coupling_sectionID=disabled

flexran_prach_workaround=disabled

dl_ul_tuning_special_slot=0xfd00000

What has been verified:

1. MAC addresses and VLAN tags match between DU and RU
2. PTP is in sync and stable
3. OFH section parameters (PRACH, DL, UL) appear correct
4. TDD pattern matches on both ends

Is there anything obvious missing or misconfigured? Any hints appreciated.

[brendan-mcauliffe]

Hi @alektoja,

From the outputs you have shown, it looks like PTP is running correctly, and that the RU can sync to it.
The gNB configuration also looks fine. The warnings in the logs are of concern, though. Although I do not think it is the fault of the gNB.

I recommend that you upgrade the firmware of your RU. v1.0.4 is extremely outdated. Please contact Benetel to get the latest version. Earlier versions of the RAN650 FW are known to have bugs that can cause issues like the one you are seeing above.

[alektoja]

Thank you for your reply. Do you maybe know what is the current SW version? I will try to reach Benetel.

[brendan-mcauliffe]

Hi @alektoja, the latest version is v1.4.