srsRAN RU emulator

[sauka]

Hey,

In the recent release we have added O-RAN radio unit (RU) emulator in srsRAN. It allows to perform end-to-end tests of the srsRAN CU/DU software solution in a 7.2 split scenario using the test mode.
The RU emulator implements some basic RU functionalities and can be run in a separate PC. Its current version performs the following tasks:

• parses configuration file, configures a NIC interface using DPDK enabling reception and transmission of Open Fronthaul (OFH) packets
• analyzes incoming OFH traffic
• responds to incoming C-Plane UL packets of standard channel filter with a dummy U-Plane UL packets

Configuration

Dummy U-Plane UL packets can be generated using static IQ data compression parameters. Allowed options include:

• 9-bit BFP compression
• 16-bit no-compression

The RU emulator accepts a configuration file in the YAML format just like the gNB application. Below you can find an example of such file:

log:
  filename: /tmp/ru_em.log
  level: warning

dpdk:
  eal_args: "--lcores (0-1)@(0-15)"

ru_emu:
  cells:
  - bandwidth: 100
    network_interface: 0000:01:00.1
    ru_mac_addr: 80:61:5f:0d:df:ab
    du_mac_addr: 64:b3:79:10:00:37
    vlan_tag: 2
    ul_port_id: [0]
    compr_method_ul: "bfp"
    compr_bitwidth_ul: 9

It is important to provide matching network configurations for both the gNB application (please refer to ru_ofh configuration parameters) and the RU emulator.

For the details on installing DPDK and binding a NIC port to it please refer to this srsRAN tutorial:
https://docs.srsran.com/projects/project/en/latest/tutorials/source/dpdk/source/index.html

Running end-to-end test

Here are the example commands for running the gNB application in test mode and the RU emulator:

• run the gNB:
  sudo apps/gnb/gnb -c cell_cfg.yml ru_emulator.yml amf --no_core true test_mode test_ue --rnti 0x1 --ri 4
  (all test_mode configuration parameters)

• run the RU emulator:
  sudo tests/integrationtests/ofh/ru_emulator -c ru_em.yml

If everything is configured correctly, you should be able to see an output from the RU emulator similar to the following one:

EAL: Detected CPU lcores: 16
EAL: Detected NUMA nodes: 1
EAL: Detected shared linkage of DPDK
EAL: Multi-process socket /var/run/dpdk/rte/mp_socket
EAL: Selected IOVA mode 'VA'
EAL: VFIO support initialized
EAL: Using IOMMU type 1 (Type 1)
EAL: Ignore mapping IO port bar(2)
EAL: Probe PCI driver: net_ixgbe (8086:10fb) device: 0000:01:00.1 (socket -1)
TELEMETRY: No legacy callbacks, legacy socket not created
Running. Waiting for incoming packets...
Cell #0: 2024-03-15 17:08:11 Received 14 UL C-Plane packets
Cell #0: 2024-03-15 17:08:12 Received 401 UL C-Plane packets
Cell #0: 2024-03-15 17:08:13 Received 795 UL C-Plane packets
Cell #0: 2024-03-15 17:08:14 Received 1195 UL C-Plane packets
Cell #0: 2024-03-15 17:08:15 Received 1595 UL C-Plane packets

At the gNB side, press t to enable the trace and observe reported DL and UL throughput.

[Zplusless]

Thanks for the detailed tutorial. Is the utilization of DPDK a prerequisite for operating an RU emulator?

[sauka]

Yes, for running the RU emulator app the DPDK is mandatory

[Zplusless]

After the release of srsRAN-24.04, I have noticed an update that introduces UNIX sockets in this commit.

Just an information update in case anyone needs it.

[mmailand]

Hello,
thanks for the great work, I tried the ru_emulator, but it seems that I cannot get the configuration right.

For the gNB I get the following log:

--== srsRAN gNB (commit 4d9f22329) ==--

Initializing the Open Fronthaul Interface for sector#0: ul_compr=[BFP,9], dl_compr=[BFP,9], prach_compr=[BFP,9], prach_cp_enabled=false, downlink_broadcast=true.
Operating a 20MHz cell over a RU with instantaneous bandwidth of 100MHz
Warning: Configured PRACH occasion collides with PUCCH RBs ([0..1) intersects [0..3)). Some interference between PUCCH and PRACH is expected.
Warning: Configured PRACH occasion collides with PUCCH RBs ([0..1) intersects [0..3)). Some interference between PUCCH and PRACH is expected.
Cell pci=1, bw=20 MHz, dl_arfcn=650000 (n78), dl_freq=3750.0 MHz, dl_ssb_arfcn=649632, ul_freq=3750.0 MHz

==== gNodeB started ===
Type <t> to view trace
2024-03-20T08:50:25.796544 [OFH     ] [W] Missed incoming User-Plane PRACH messages for slot '250.18' and sector#0
2024-03-20T08:50:25.806558 [OFH     ] [W] Missed incoming User-Plane PRACH messages for slot '251.18' and sector#0
2024-03-20T08:50:25.816581 [OFH     ] [W] Missed incoming User-Plane PRACH messages for slot '252.18' and sector#0
2024-03-20T08:50:25.821061 [OFH     ] [W] Missed incoming User-Plane uplink messages for slot '252.7', symbol '0' and sector#0
2024-03-20T08:50:25.821063 [OFH     ] [W] Missed incoming User-Plane uplink messages for slot '252.7', symbol '1' and sector#0
2024-03-20T08:50:25.821063 [OFH     ] [W] Missed incoming User-Plane uplink messages for slot '252.7', symbol '2' and sector#0
2024-03-20T08:50:25.821064 [OFH     ] [W] Missed incoming User-Plane uplink messages for slot '252.7', symbol '3' and sector#0
2024-03-20T08:50:25.821065 [OFH     ] [W] Missed incoming User-Plane uplink messages for slot '252.7', symbol '4' and sector#0
2024-03-20T08:50:25.821065 [OFH     ] [W] Missed incoming User-Plane uplink messages for slot '252.7', symbol '5' and sector#0
2024-03-20T08:50:25.821066 [OFH     ] [W] Missed incoming User-Plane uplink messages for slot '252.7', symbol '6' and sector#0

and for the ru_emulator:

EAL: Detected CPU lcores: 16
EAL: Detected NUMA nodes: 1
EAL: Detected shared linkage of DPDK
EAL: Multi-process socket /var/run/dpdk/rte/mp_socket
EAL: Selected IOVA mode 'VA'
EAL: VFIO support initialized
EAL: Using IOMMU type 1 (Type 1)
EAL: Probe PCI driver: net_ixgbe_vf (8086:10ed) device: 0000:05:10.1 (socket -1)
TELEMETRY: No legacy callbacks, legacy socket not created
2024-03-20T08:32:32.692718 [ALL     ] [I] Task worker "ru_rx" started...
2024-03-20T08:32:32.692892 [ALL     ] [I] Task worker "ru_emu_#0" started...
Running. Waiting for incoming packets...
2024-03-20T08:32:32.786758 [RU_EMU  ] [I] Started the DPDK ethernet frame receiver
2024-03-20T08:38:45.595610 [RU_EMU  ] [D] Packet direction is downlink
2024-03-20T08:38:45.595612 [RU_EMU  ] [D] Packet direction is downlink
2024-03-20T08:38:45.595832 [RU_EMU  ] [D] Discarding U-Plane packet
2024-03-20T08:38:45.595843 [RU_EMU  ] [D] Discarding U-Plane packet
2024-03-20T08:38:45.595872 [RU_EMU  ] [D] Discarding U-Plane packet
2024-03-20T08:38:45.595872 [RU_EMU  ] [D] Discarding U-Plane packet
2024-03-20T08:38:45.595910 [RU_EMU  ] [D] Discarding U-Plane packet

Could you please provide reference configuration for the gNB and the ru_emulator.
thanks for you time.

[sauka]

Hey @mmailand ,

Thanks for your interest!

[W] Missed incoming User-Plane PRACH messages for slot '250.18' and sector#0

This warning is expected since the RU emulator doesn't send U-Plane packets with PRACH. It can be safely ignored when running the gNB in test mode. Another option is disabling PRACH C-Plane in the ru_ofh configuration by setting is_prach_cp_enabled to false.

Can you see a counter of received UL C-Plane in the RU console output? If not, then either the packets do not arrive or they are being discarded. Capturing the traffic on the NIC and checking a pcap may help here.

Here is an excerpt from the configuration files used in the example command above that was working with the example RU emulator config:

ru_ofh:
  t1a_max_cp_dl: 470
  t1a_min_cp_dl: 258
  t1a_max_cp_ul: 500
  t1a_min_cp_ul: 285
  t1a_max_up: 196
  t1a_min_up: 50
  is_prach_cp_enabled: true
  is_dl_broadcast_enabled: false
  ignore_ecpri_payload_size: 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: true
  enable_dl_static_compr_hdr: true
  iq_scaling: 1.0
  cells:
  - network_interface: 0000:51:00.1 
    ru_mac_addr: 80:61:5f:0d:df:ab
    du_mac_addr: 64:b3:79:10:00:37
    vlan_tag: 2 
    prach_port_id: [4]
    dl_port_id: [0, 1, 2, 3]
    ul_port_id: [0]

cell_cfg:
  dl_arfcn: 625000
  band: 78
  channel_bandwidth_MHz: 100
  common_scs: 30
  plmn: "00101"
  tac: 7
  pci: 1
  prach:
    prach_config_index: 159
    prach_root_sequence_index: 1
    zero_correlation_zone: 0
    prach_frequency_start: 12
  nof_antennas_dl: 4
  nof_antennas_ul: 1
  tdd_ul_dl_cfg:
    nof_dl_symbols: 7
    nof_dl_slots: 7
    nof_ul_slots: 2

hal:
  eal_args: "--lcores (0-1)@(4-11)"

[mmailand]

Hello @sauka,

I got it working, but I think there is a bug in the vlan handling of the ru_emulator.
If I use the configuration with the vlan_tag: [1-255] I get the correct vlan id in the ethernet frame.
At 256 there seems to be an overflow, for vlan_tag 256 I get frames with the vlan id of 0, for 257 an frame with 1 and so on.

Thanks for your time.

[sauka]

Thanks for reporting this @mmailand, we will provide a fix in the next release.

[Zplusless]

Hi @sauka, in our environment, the RU_emulator works with no throughput. According to the log, the packets are dropped by DPDK. More details are here.

Thanks you very much if you could provide some guidance.

[Zplusless]

problem solved, thanks