Change in osmo-bts[master]: sched_lchan_tch_x: use functions to determine AMR tranmssion phase

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laforge gerrit-no-reply at
Tue Aug 31 19:35:02 UTC 2021

laforge has posted comments on this change. ( )

Change subject: sched_lchan_tch_x: use functions to determine AMR tranmssion phase

Patch Set 1:

(1 comment) 
File src/osmo-bts-trx/sched_lchan_tchf.c: 
PS1, Line 470: 				LOGL1SB(DL1P, LOGL_NOTICE, l1ts, br, "Codec (FT = %d) "
> Shouldn't we keep sending with the older type until we can change it? I'd expect the received to acc […]
I don't understand this code in general, even the current one.   We as an RTP capable BTS cannot influence at all what codec mode is transmitted in downlink.  We may receive a CMR from the MS, and we pass that on in the CMR header of the uplink RTP frames.  It is up to the sender/encoder of that RTP to then start generating the proper requested codec mode and start sending that.

The BTS is not generating/encoding the AMR, it merely relays AMR frames from Abis/RTP to Um and vice-versa.  On the Um interface we only have either CMR or CMI [depending on FN] and we can only signal a subset of up to four codec modes from the set.  On the RTP side every frame has CMI (== FT) and CMR, and we can express any of the AMR modes.

Can anyone explain to me what is happening here in this code and why?

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Gerrit-Project: osmo-bts
Gerrit-Branch: master
Gerrit-Change-Id: I94a934a6b3b397b4cd0e9da3577325de58814335
Gerrit-Change-Number: 25296
Gerrit-PatchSet: 1
Gerrit-Owner: dexter <pmaier at>
Gerrit-Reviewer: Jenkins Builder
Gerrit-Reviewer: fixeria <vyanitskiy at>
Gerrit-Reviewer: laforge <laforge at>
Gerrit-Reviewer: pespin <pespin at>
Gerrit-Comment-Date: Tue, 31 Aug 2021 19:35:02 +0000
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