openbts-p2.8-gprs-exp and pcu issues

[jolly]

Ivan Kluchnikov wrote:
> In attachment you can find patch for osmo-pcu.
>   

hi ivan,

i looked at you patch. it primarily removes the ability to re-assign an
existing downlink TBF on PACCH:

-       if (old_tbf) {
+       if (old_tbf&&(old_tbf->direction == GPRS_RLCMAC_UL_TBF)) {

a downlink TBF will, after polling the final ack, start T3193 and exist
until T3193 times out.  the value for that timer is set by BTS. on the
phone T3192 is running, which is a little shorter. the phone will stay
on PDCH and listens for re-assignment on PACCH until T3192 times out.
T3192 is set by system information message. what settings do you have
for these two timers?

there are three cases where assignment on PACCH is performed:

1. at gprs_rlcmac_downlink_ack() the
gprs_rlcmac_trigger_downlink_assignment() is called, if the dowlink TBF
has just finished, but more frames already arrived from SGSN. (T3193 not
started yet, but MS will have T3192 running.)
2. at gprs_bssgp_pcu_rx_dl_ud() the
gprs_rlcmac_trigger_downlink_assignment() is called, if the dowlink TBF
still exists because a frame has arrived from SGSN. (T3193 running, and
so T3192 on the MS.)
3. at gprs_bssgp_pcu_rx_dl_ud() the
gprs_rlcmac_trigger_downlink_assignment() is called, if an uplink TBF
exists because a frame has arrived from SGSN.

in your patch you changed the condition for triggering downlink
assignment on PACCH to uplink TBF only. This would break the case where
T3193 is still pending and the re-use of downlink TBF.

the case where a downlink TBF still exists would result in a PCH/AGCH
assignment, which causes problems, especially when multislot allocation
is used. this is because the selected (multiple) slots at
gprs_bssgp_pcu_rx_dl_ud() cannot be assigned on PCH/AGCH, just only one.

i cannot see what your decision for your patch was. i guess that SI 13
uses a low or no T3192 timer value.

regards,

andreas