Change in osmo-pcu[master]: pdch.cpp: Avoid dropping existing DL TBF during rcv_resource_request

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fixeria gerrit-no-reply at lists.osmocom.org
Thu Jul 9 07:46:25 UTC 2020


fixeria has posted comments on this change. ( https://gerrit.osmocom.org/c/osmo-pcu/+/19194 )

Change subject: pdch.cpp: Avoid dropping existing DL TBF during rcv_resource_request
......................................................................


Patch Set 1:

> Patch Set 1:
> 
> I don't think this really backs up the fact that it's needed to release DL TBF upon a Packet Resource Request resceived... it's rather simply fixing the way it was being released.
> 
> Do you understand it differently?

Sorry, I don't have a strong opinion here. It looks like we should dig deeper into the history and the related specs. It's interesting that the commit message I found yesterday is basically an implicit revert of his other commit:

commit ae0a799f4472a75912b444cc2f09361aaea27963
Author: Jacob Erlbeck <jerlbeck at sysmocom.de>
Date:   Tue Sep 1 11:28:25 2015 +0200

    bts: Release DL TBF instead of killing in rcv_resource_request
    
    Currently an existing DL TBF is freed immediately, when a resource
    request is received. This makes sense since the MS might have dropped
    it when switching to the PDCH signaled via the AGCH for the SBA. But
    if the TBF still is assumed to exist on the MS side, there might be
    TFI collisions if the old TBF object is not kept to block its TFI
    for some time.
    
    This commit changes rcv_resource_request to call release() instead of
    tbf_free() on the DL TBF object (if it exists).
    
    Sponsored-by: On-Waves ehf

This piece of code has been changed so many times, see also:

e91bd3babd5c04a154f296607b401a5050dcba31
cf6ae9d12f9bf406a8f164f8109410d01328d913

and this one seems to be the origin:

commit 99a107dbeef03b2e80aff82023cdfc5c10109b5b
Author: Andreas Eversberg <jolly at eversberg.eu>
Date:   Thu Sep 27 09:21:52 2012 +0200

    Free existing UL/DL TBF, if RACH has been received from MS
    
    In this case the mobile has lost existing flows, so it make sense to free
    them. The TFI(s) can be re-used immidiately, because they are not
    associated by MS anymore.

So it looks like it was done on purpose, and then changed +100500 times.


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Gerrit-Project: osmo-pcu
Gerrit-Branch: master
Gerrit-Change-Id: Iab4afb66f0d671f7ad54909d2685a1613e12ab4d
Gerrit-Change-Number: 19194
Gerrit-PatchSet: 1
Gerrit-Owner: pespin <pespin at sysmocom.de>
Gerrit-Reviewer: Jenkins Builder
Gerrit-Reviewer: pespin <pespin at sysmocom.de>
Gerrit-CC: fixeria <vyanitskiy at sysmocom.de>
Gerrit-Comment-Date: Thu, 09 Jul 2020 07:46:25 +0000
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