Dear Jacob,
Finally I managed to get everything in a working order, so I can finally start
testing the GPRS part of OpenBSC/Osmo-PCU with an USRP B200.
I am using a Cat 12 device with a 4 PDCH configuration.
In the past I wrote a little script to test the PRACH stability of OpenBTS,
which sends a single ping to the gateway address, waits until the session goes
into idle, and then tries again. The goal is to generate as many PRACH as
possible and check if there is a response.
I used this script and it turns out that around 1 out of every 20 requests the
ping is not reaching the gateway, and the UE indicates an abnormal DL TBF
release.
I attached the UE side log, so you can take a look.
During this issue there is no reasonable frequency nor timing variation
indicated on the UE side.
What I noticed is the very high number of RLC resent and RLC restarted. After a
few minutes of pinging, this is the result from the PCU:
RLC Sent : 18015 (0/s 0/m 0/h 0/d)
RLC Resent : 17596 (0/s 0/m 0/h 0/d)
RLC Restarted : 15669 (0/s 0/m 0/h 0/d)
RLC Stalled : 0 (0/s 0/m 0/h 0/d)
Please note that the ARFCN I use is completely clean, I filter the uplink with
proper duplexer and the TRX is not complaining about anything.
Also interesting that during constant pinging (the system does not need to do
PRACH), this problem is not popping up.
Will update my UHD stack from 3.8.0 to 3.9.0 just to test with the latest, but
I don't think itt will change anything about this issue. And to be hones, we've
seen similar PRACH related issues with OpenBTS GPRS too.
If you need any more logs or you have an idea what to try, I am happy to do
that. :-)
Regards,
Csaba
EVENT_GSM_L1_STATE 18:29:36.548 L1_RANDOM_ACCESS_MODE
EVENT_RANDOM_ACCESS_REQUEST 18:29:36.557 1 19311 GMAC_ONE_PHASE_ACCESS
EVENT_GSM_MESSAGE_RECEIVED 18:29:36.686 ALERTING
EVENT_GSM_MESSAGE_RECEIVED 18:29:36.732 IMMEDIATE_ASSIGNMENT
EVENT_GPRS_MAC_MSG_SENT 18:29:36.733 Message: Packet Uplink Dummy
Control Block Channel: 0
EVENT_GSM_L1_STATE 18:29:36.755 L1_TRANSFER_MODE
EVENT_GPRS_MAC_MSG_RECEIVED 18:29:40.456 Message: Packet Uplink Ack/Nack
Channel: 0
EVENT_GPRS_MAC_MSG_RECEIVED 18:29:41.236 Message: Packet Downlink
Assignment Channel: 0
EVENT_GPRS_PACKET_DOWNLINK_ASSIGNMENT18:29:41.236 Time Slot Allocation: 15,
TFI Assignment: 0
EVENT_GPRS_MAC_MSG_SENT 18:29:41.236 Message: Packet Control
Acknowledgement Channel: 0
EVENT_GPRS_MAC_MSG_RECEIVED 18:29:41.452 Message: Packet Uplink Ack/Nack
Channel: 0
EVENT_GPRS_MAC_MSG_SENT 18:29:41.452 Message: Packet Control
Acknowledgement Channel: 0
EVENT_GPRS_TBF_RELEASE 18:29:41.452 TBF Release Type: UL_TBF_NORMAL
EVENT_GPRS_MAC_MSG_SENT 18:29:41.480 Message: Packet Downlink
Ack/Nack Channel: 0
EVENT_GPRS_MAC_MSG_SENT 18:29:41.697 Message: Packet Downlink
Ack/Nack Channel: 0
EVENT_GPRS_MAC_MSG_SENT 18:29:41.918 Message: Packet Downlink
Ack/Nack Channel: 0
EVENT_GPRS_MAC_MSG_SENT 18:29:42.140 Message: Packet Downlink
Ack/Nack Channel: 0
EVENT_GPRS_MAC_MSG_SENT 18:29:42.357 Message: Packet Downlink
Ack/Nack Channel: 0
EVENT_GPRS_MAC_MSG_SENT 18:29:42.578 Message: Packet Downlink
Ack/Nack Channel: 0
EVENT_GPRS_MAC_MSG_SENT 18:29:42.800 Message: Packet Downlink
Ack/Nack Channel: 0
EVENT_GPRS_MAC_MSG_SENT 18:29:43.017 Message: Packet Downlink
Ack/Nack Channel: 0
EVENT_GPRS_MAC_MSG_SENT 18:29:43.238 Message: Packet Downlink
Ack/Nack Channel: 0
EVENT_GPRS_MAC_MSG_SENT 18:29:43.460 Message: Packet Downlink
Ack/Nack Channel: 0
EVENT_GPRS_MAC_MSG_SENT 18:29:43.700 Message: Packet Downlink
Ack/Nack Channel: 0
EVENT_GPRS_MAC_MSG_SENT 18:29:43.917 Message: Packet Downlink
Ack/Nack Channel: 0
EVENT_GPRS_MAC_MSG_SENT 18:29:44.138 Message: Packet Downlink
Ack/Nack Channel: 0
EVENT_GPRS_MAC_MSG_SENT 18:29:44.360 Message: Packet Downlink
Ack/Nack Channel: 0
EVENT_GPRS_MAC_MSG_SENT 18:29:44.577 Message: Packet Downlink
Ack/Nack Channel: 0
EVENT_GPRS_MAC_MSG_SENT 18:29:44.798 Message: Packet Downlink
Ack/Nack Channel: 0
EVENT_GPRS_MAC_MSG_SENT 18:29:45.020 Message: Packet Downlink
Ack/Nack Channel: 0
EVENT_GPRS_MAC_MSG_SENT 18:29:45.237 Message: Packet Downlink
Ack/Nack Channel: 0
EVENT_GPRS_MAC_MSG_SENT 18:29:45.458 Message: Packet Downlink
Ack/Nack Channel: 0
EVENT_GPRS_TBF_RELEASE 18:29:46.986 TBF Release Type: DL_TBF_ABNORMAL
EVENT_GSM_L1_STATE 18:29:47.004 L1_IDLE_MODE
EVENT_GSM_L1_STATE 18:29:47.011 L1_RANDOM_ACCESS_MODE
EVENT_RANDOM_ACCESS_REQUEST 18:29:47.020 1 21578 GMAC_ONE_PHASE_ACCESS
EVENT_GSM_MESSAGE_RECEIVED 18:29:47.278 IMMEDIATE_ASSIGNMENT
EVENT_GPRS_MAC_MSG_SENT 18:29:47.279 Message: Packet Uplink Dummy
Control Block Channel: 0
EVENT_GSM_L1_STATE 18:29:47.292 L1_TRANSFER_MODE
EVENT_GPRS_MAC_MSG_RECEIVED 18:29:47.512 Message: Packet Uplink Ack/Nack
Channel: 0
EVENT_GPRS_MAC_MSG_RECEIVED 18:29:47.535 Message: Packet Downlink
Assignment Channel: 0
EVENT_GPRS_PACKET_DOWNLINK_ASSIGNMENT18:29:47.535 Time Slot Allocation: 14,
TFI Assignment: 0
EVENT_GPRS_MAC_MSG_SENT 18:29:47.536 Message: Packet Control
Acknowledgement Channel: 0
EVENT_GPRS_MAC_MSG_RECEIVED 18:29:47.752 Message: Packet Uplink Ack/Nack
Channel: 0
EVENT_GPRS_MAC_MSG_SENT 18:29:47.753 Message: Packet Control
Acknowledgement Channel: 0
EVENT_GPRS_TBF_RELEASE 18:29:47.753 TBF Release Type: UL_TBF_NORMAL
EVENT_GPRS_MAC_MSG_SENT 18:29:47.780 Message: Packet Downlink
Ack/Nack Channel: 0
EVENT_GPRS_MAC_MSG_SENT 18:29:47.997 Message: Packet Downlink
Ack/Nack Channel: 0
EVENT_GPRS_MAC_MSG_SENT 18:29:48.218 Message: Packet Downlink
Ack/Nack Channel: 0
EVENT_GPRS_MAC_MSG_SENT 18:29:48.440 Message: Packet Downlink
Ack/Nack Channel: 0
EVENT_GPRS_MAC_MSG_SENT 18:29:48.657 Message: Packet Downlink
Ack/Nack Channel: 0
EVENT_GPRS_MAC_MSG_SENT 18:29:48.878 Message: Packet Downlink
Ack/Nack Channel: 0
EVENT_GPRS_MAC_MSG_SENT 18:29:49.100 Message: Packet Downlink
Ack/Nack Channel: 0
EVENT_GPRS_MAC_MSG_SENT 18:29:49.317 Message: Packet Downlink
Ack/Nack Channel: 0
EVENT_GPRS_MAC_MSG_SENT 18:29:49.538 Message: Packet Downlink
Ack/Nack Channel: 0
EVENT_GPRS_MAC_MSG_SENT 18:29:49.760 Message: Packet Downlink
Ack/Nack Channel: 0
EVENT_GPRS_MAC_MSG_SENT 18:29:49.977 Message: Packet Downlink
Ack/Nack Channel: 0
EVENT_GPRS_MAC_MSG_SENT 18:29:50.198 Message: Packet Downlink
Ack/Nack Channel: 0
EVENT_GPRS_MAC_MSG_SENT 18:29:50.420 Message: Packet Downlink
Ack/Nack Channel: 0
EVENT_GPRS_MAC_MSG_SENT 18:29:50.637 Message: Packet Downlink
Ack/Nack Channel: 0
EVENT_GPRS_MAC_MSG_SENT 18:29:50.858 Message: Packet Downlink
Ack/Nack Channel: 0
EVENT_GPRS_MAC_MSG_SENT 18:29:51.080 Message: Packet Downlink
Ack/Nack Channel: 0
EVENT_GPRS_MAC_MSG_SENT 18:29:51.297 Message: Packet Downlink
Ack/Nack Channel: 0
EVENT_GPRS_MAC_MSG_SENT 18:29:51.518 Message: Packet Downlink
Ack/Nack Channel: 0
EVENT_GPRS_MAC_MSG_SENT 18:29:51.740 Message: Packet Downlink
Ack/Nack Channel: 0
EVENT_GPRS_MAC_MSG_SENT 18:29:51.957 Message: Packet Downlink
Ack/Nack Channel: 0
EVENT_GPRS_TBF_RELEASE 18:29:53.484 TBF Release Type: DL_TBF_NORMAL
