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pespin gerrit-no-reply at lists.osmocom.orgpespin has uploaded this change for review. ( https://gerrit.osmocom.org/c/osmo-pcu/+/23511 ) Change subject: sba: Document AGCH_START_OFFSET after some experimental tests ...................................................................... sba: Document AGCH_START_OFFSET after some experimental tests Change-Id: Id1460207be25750aeb5c1d7af2fac6591cf5e424 --- M src/sba.c 1 file changed, 18 insertions(+), 2 deletions(-) git pull ssh://gerrit.osmocom.org:29418/osmo-pcu refs/changes/11/23511/1 diff --git a/src/sba.c b/src/sba.c index 2c3519d..fb9c91c 100644 --- a/src/sba.c +++ b/src/sba.c @@ -33,8 +33,24 @@ #include "pdch.h" #include "pdch_ul_controller.h" -/* starting time for assigning single slot - * This offset must be a multiple of 13. */ +/* TBF Starting Time for assigning SBA. + * See TS 44.060 12.21 "Starting Frame Number Description". + * According to spec, k=0 (offset=4) "should not be used, so as to leave time + * for the MS to analyse the message and get ready to receive or transmit". + * Hence, k=1 (offset=8-9) is hteoretically the minimum offset which could be + * used. + * + * However, it was found, empirically, that it takes around 30-40 FNs time for + * the Immaediate Assignment message creafted with this "TBF Starting Time" to + * travel from PCU->BTS and be transmitted over CCH on the Um interface. Hence, + * we must account for this delay here, otherwise the MS would be receiving eg. + * a TBF Starting Time of FN=40 while the Imm Assigned containing it is sent in + * eg. FN=50, which would be too late for the MS to answer to it. + * + * The situation described above, can even get worse on high BTS load for AGCH, + * since the Immediate Assignment will queue in the BTS waiting to be + * transmitted one after the other, hence increasing the required delay. + */ #define AGCH_START_OFFSET 52 -- To view, visit https://gerrit.osmocom.org/c/osmo-pcu/+/23511 To unsubscribe, or for help writing mail filters, visit https://gerrit.osmocom.org/settings Gerrit-Project: osmo-pcu Gerrit-Branch: master Gerrit-Change-Id: Id1460207be25750aeb5c1d7af2fac6591cf5e424 Gerrit-Change-Number: 23511 Gerrit-PatchSet: 1 Gerrit-Owner: pespin <pespin at sysmocom.de> Gerrit-MessageType: newchange -------------- next part -------------- An HTML attachment was scrubbed... URL: <http://lists.osmocom.org/pipermail/gerrit-log/attachments/20210326/94a0e7f0/attachment.htm>