Fwd: Losing ACKs due TLLI changes?

Vladimir Rolbin vrolbin at gmail.com
Wed Oct 30 16:26:57 UTC 2013


Hi,

I don't see any print connected to the Uplink TBF request for "Attach
accept" (by MS). At this moment the TLLI has been already updated but UL
TBF still does not exist
(what bts->tbf_by_tlli(m_tlli, GPRS_RLCMAC_UL_TBF) returns?). Corresponding
to TS 04.60, 11.2.29 Packet Uplink Assignment possibly may use DL TFI to
address the MS in place of TLLI (we still don't know if it's accepted or
not by MS). Also the uplink FN may be used to find corresponding UL TBF
context (according to Packet Uplink Assignment RRBP field) for UL Packet
Control Ack which contains relevant TLLI.  So is it really necessary to
link UL and DL TBFs in the case? ...

Regards,
Vladimir Rolbin



On Wed, Oct 30, 2013 at 1:17 PM, Holger Hans Peter Freyther <
hfreyther at sysmocom.de> wrote:

> On Sun, Oct 27, 2013 at 01:33:13PM +0100, Holger Hans Peter Freyther wrote:
>
> Hi,
>
>
> > <0007> gprs_rlcmac_meas.cpp:103 UL RSSI of TLLI=0x88661bc6: -67 dBm
> > <0002> bts.cpp:945 Got ACK, but UL TBF is gone TLLI=0xe512eba3
> > <0007> gprs_rlcmac_meas.cpp:158 DL packet loss of IMSI=274080000004765 /
> TLLI=0xe512eba3: 0%
> > <0002> tbf.cpp:668 TBF TFI=0 TLLI=0x88661bc6 T3169 timeout during
> transsmission
> > <0002> tbf.cpp:690 - Assignment was on PACCH
> > <0002> tbf.cpp:694 - No uplink data received yet
>
> this is from a routing area update (with some printf debugging):
>
>
> TBF(TFI=0 TLLI=0xb68154e6 DIR=DL) TLLLI changed......
> 0xb68154e6->0xc782d1de
> <0002> tbf.cpp:1626 TBF(TFI=0 TLLI=0xb68154e6 DIR=DL) changing tlli to
> TLLI=0xc782d1de
> <0002> bts.cpp:941 Got ACK, but UL TBF is gone TLLI=0xc782d1de
> <0007> gprs_rlcmac_meas.cpp:158 DL packet loss of IMSI=274080000004765 /
> TLLI=0xc782d1de: 0%
> <0002> tbf.cpp:664 TBF(TFI=0 TLLI=0xb68154e6 DIR=UL) T3169 timeout during
> transsmission
> <0002> tbf.cpp:686 - Assignment was on PACCH
> <0002> tbf.cpp:690 - No uplink data received yet
>
> So the DL TLLI has been changed and then we get an ACK for a UL tbf
> with the new TLLI and can't find it. And run into a timeout.
>
>
> I have applied this change:
>
> diff --git a/src/tbf.cpp b/src/tbf.cpp
> index fac5aaf..19bb83c 100644
> --- a/src/tbf.cpp
> +++ b/src/tbf.cpp
> @@ -1618,6 +1618,17 @@ void gprs_rlcmac_tbf::update_tlli(uint32_t tlli)
>         if (tlli == m_tlli)
>                 return;
>
> +       printf("%s TLLLI changed...... 0x%08x->0x%08x\n",
> +               tbf_name(this), m_tlli, tlli);
> +
> +       if (direction == GPRS_RLCMAC_DL_TBF) {
> +               gprs_rlcmac_tbf *ul_tbf;
> +               ul_tbf = bts->tbf_by_tlli(m_tlli, GPRS_RLCMAC_UL_TBF);
> +
> +               if (ul_tbf)
> +                       ul_tbf->m_tlli = tlli;
> +       }
> +
>  #warning "TODO.. find the DL/UL opposite and update the TLLI too"
>         LOGP(DRLCMAC, LOGL_NOTICE, "%s changing tlli to TLLI=0x%08x\n",
>                 tbf_name(this), tlli);
>
>
> and now the "Attach Complete" comes immediately after the Attach Accept.
> I will push something like this but we really need a better way to link
> the DL/UL TBFs together.
>
>
> holger
>
>
> --
> - Holger Freyther <hfreyther at sysmocom.de>       http://www.sysmocom.de/
> =======================================================================
> * sysmocom - systems for mobile communications GmbH
> * Schivelbeiner Str. 5
> * 10439 Berlin, Germany
> * Sitz / Registered office: Berlin, HRB 134158 B
> * Geschaeftsfuehrer / Managing Directors: Holger Freyther, Harald Welte
>
>
>
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