Change in osmo-msc[master]: vlr_sgs: Drop recorded LastEutranPlmnId when UE no longer associated

pespin gerrit-no-reply at
Tue Jul 6 07:51:08 UTC 2021

pespin has posted comments on this change. ( )

Change subject: vlr_sgs: Drop recorded LastEutranPlmnId when UE no longer associated

Patch Set 2:

(1 comment) 
File src/libvlr/vlr_sgs_fsm.c: 
PS2, Line 64: 	vlr_subscr_set_last_used_eutran_plmn_id(vsub, NULL);
> looking at the semantics and reading the related issue it seems that immediate removal is not necess […]
I did run the existing TTCN3 tests and actually have to change them to validate that they work as expected when applying this patch. Some of those tests validate the case where a GERAN LU is done after having done stuff over SGs, to make sure later GERAN Lu erases correctly previous state.

I think it makes sense to link the use of LastUsedEutranPLMN to the availability of the MS in the SGs interface.
If the MS came from EUTRAN (eg CSFB), the MSC passes the info to the BSC in order to accomplish fast return. However, if the MSC did GERAN LU, the MSC should avoid sending it to avoid the MS doing fast return, since it didn't come from EUTRAN in first place, so it's a good rationale to let it stay in GERAN.

The easiest and most elegant way is actually to simply drop the information when the MS stops being available on EUTRAN, as done here.
I verified in general the required paths call this to_null() function to clean up the FSm and go to NULL state (MS not handled in EUTRAN), so we are fine here.

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Gerrit-Project: osmo-msc
Gerrit-Branch: master
Gerrit-Change-Id: I0dcb1850ab4f6f7d42bfcb19665ddeae2d3b057a
Gerrit-Change-Number: 24832
Gerrit-PatchSet: 2
Gerrit-Owner: pespin <pespin at>
Gerrit-Reviewer: Jenkins Builder
Gerrit-Reviewer: dexter <pmaier at>
Gerrit-Reviewer: fixeria <vyanitskiy at>
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Gerrit-Comment-Date: Tue, 06 Jul 2021 07:51:08 +0000
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