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Bug #4714

closed

SMS Message Lost Although Delivery Ack Sent

Added by matt9j over 3 years ago. Updated over 3 years ago.

Status:
Resolved
Priority:
High
Assignee:
Category:
SMS
Target version:
-
Start date:
08/16/2020
Due date:
% Done:

100%

Resolution:
Spec Reference:

Description

Hi! I've run into a strange issue in my local testing where the first SMS message of a conversation is occasionally dropped. I acknowledge this could be some issue with my local configuration, but wanted to file a ticket to keep logs and discussion in the same place. For context I'm working on migrating Rhizomatica's deployment from osmo-nitb to the split core network components. Most things are working (voice is reliable and subscriber-create-on-demand is working), but this issue is somewhat severe and blocks stable deployment.

Test setup
----------

I am using all components from the Buster latest repo, but can try and reproduce the issue with the nightly components if you all think that should make a difference.

2 UE/MS -> USRP B210 with GPSDO -> osmo-trx-uhd -> osmo-bts-trx -> osmo 2G CS core network (osmo-bsc osmo-msc osmo-stp osmo-mgw osmo-hlr osmo-sip-connector)

The MSC is configured to use an ESME with the smpp-first delivery policy. For this test the ESME just reflects the messages right back to the MSC since source and dest users are present in the local network. Logging seems to indicate this is working correctly, although the interaction of the ESME and sms delivery state machine could be part of the problem.

Problem
-------

The two test UE/MS's have sims 910540000001012 and 910540000000000. For this test I send several messages from ue0000 to ue1012. ue0000 receives message delivery notifications for all messages, shows delivery successful to the sending user, and does not retry sending. ue1012 receives the second and third message, but does not receive the first message although ue0000 displays it was sent!

Info + Speculation
------------------

I captured a fused debug journal from the msc and bsc, which is attached. I annotated it with lines starting with `# matt9j ->` to help find sections of interest in a very verbose log :) My comments are just my best understanding of what is happening, so they may be inaccurate since I'm not an expert in the 2G network. I've also attached the configs of the msc and the bsc.

It seems like there should not be a radio failure since there are only 2 UEs in a network that is very stable otherwise, but the BTS fails to setup a radio link after paging. This could be an issue with the SDR or the bts, but regardless it seems like the message should not be dropped in this case. I think the message is only lost when paging succeeds but the link then fails to be setup. I am not sure if the intended behavior should be for the message to be retried, or for there to be no delivery ack. Either would be okay, but the inconsistency caused by the message being acked but not delivered is not such a good user experience.

Please let me know if there is other debug information I can provide. I'll try to continue to look into this on my own as well and will post findings here.


Files

lost-first-message-zero-to-twelve.txt lost-first-message-zero-to-twelve.txt 310 KB fused journal log of bsc and msc when message is lost matt9j, 08/16/2020 07:06 PM
osmo-msc.cfg osmo-msc.cfg 1.28 KB matt9j, 08/16/2020 07:07 PM
osmo-bsc.cfg osmo-bsc.cfg 3.85 KB matt9j, 08/16/2020 07:07 PM
sms-test-4.pcapng sms-test-4.pcapng 735 KB matt9j, 08/17/2020 11:52 PM
sms-test-5.pcapng sms-test-5.pcapng 1.03 MB matt9j, 08/17/2020 11:52 PM
sms-test-3.pcapng sms-test-3.pcapng 1.1 MB matt9j, 08/17/2020 11:52 PM
sms-test-1-pt2.pcapng sms-test-1-pt2.pcapng 817 KB matt9j, 08/17/2020 11:52 PM
sms-test-1-pt1.pcapng sms-test-1-pt1.pcapng 293 KB matt9j, 08/17/2020 11:52 PM
sms-test-2.pcapng sms-test-2.pcapng 1.03 MB matt9j, 08/17/2020 11:52 PM

Related issues

Related to libosmocore - Bug #4731: LAPDm does not implement SAPI priorities between data link layersStalledfixeria08/26/2020

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