[srsran-users] Unable to find the ENB 4G network using u-blox SARA-R422S-01B-00 modem

[sobol6803 at gmail.com]

Hello,

My current configuration:

  * EPC and ENB runs on Intel i5-9400 (all cores in performance mode),
    Ubuntu Server 22.04.3 LTS (kernel 5.15.0-92-generic)
  * UE's: an Android tablet and a custom device with u-blox
    SARA-R422S-01B-00 modem (3GPP Release 13 LTE Cat M1)
  * Ettus USRP B210 with all 4 antennas connected, external power, no
    external clock
  * sysmocom sysmoISIM-SJA5-9FV sim cards

Everything works on the Android tablet - I can find my network and 
connect to it. The 4G works and so does the internet.

But the SARA modem cannot even find the network. It can read the 
sysmocom sim card (CCID, preferred MCCMNC), it works with other 
commercial sim cards (and their corresponding networks), but it just 
will not find my custom 4G network. I have tried to modify the IMSI and 
preferred MCCMNC of the sim card from the default 99970 to one of a 
commercial network from another country, but it did not help (worked on 
the tablet though).

Sending "AT+COPS=?" to the modem returns only commercial networks in range.
Sending "AT+COPS=1,2,"MCCMNC",7" returns "+CME ERROR: no network 
service" and both EPC and ENB logs do not show any connection attempts.

Current configuration:

# epc.conf
[mme]
mme_code = 0x1a
mme_group = 0x0001
tac = 0x0007
mcc = 999
mnc = 70
mme_bind_addr = 127.0.1.100
apn = srsapn
dns_addr = 8.8.8.8
encryption_algo = EEA0
integrity_algo = EIA1
paging_timer = 2
request_imeisv = false
lac = 0x0006

# enb.conf
[enb]
enb_id = 0x19B
mcc = 999
mnc = 70
mme_addr = 127.0.1.100
gtp_bind_addr = 127.0.1.1
s1c_bind_addr = 127.0.1.1
s1c_bind_port = 0
n_prb = 15
tm = 2
nof_ports = 2
[rf]
dl_earfcn = 1934
tx_gain = 80
rx_gain = 40
device_name = UHD
device_args = auto

# user_db.csv (anonymized)
sim1,mil,999701111111111,11111111111111111111111111111111,opc,11111111111111111111111111111111,9000,000000000464,9,dynamic

Everything else is default.

Do you know what could be the problem? Is the ENB misconfigured, or is 
the modem somehow incompatible with my network?
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