Losing ACKs due TLLI changes?

Ivan Kluchnikov Ivan.Kluchnikov at fairwaves.ru
Mon Oct 28 14:17:50 UTC 2013

Hi Holger,

Can you send full pcu tbf debug log for this attach procedure?
I want to understand, in which place of TBF MS starts use new TLLI.
What do you mean by "no content resolution on the UL"?
As I know, there are content resolution on network side and on MS side.
The contention resolution at one phase access is successfully
completed on the MS side when the mobile station receives a PACKET
The contention resolution at two phase access is completed at MS when
it receives the second uplink assignment message with its TLLI

Also I can't understand why we should use IMSI in pcu?
Why it is not enough to use TLLI?

2013/10/27 Holger Hans Peter Freyther <hfreyther at sysmocom.de>:
> Hi,
> I got this log from the pcu while using my E71 (the only sub in this
> network).
> <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
> So there is an ACK for TLLI=0xe512eba3 but at the same time the tlli
> 0x88661bc6 is timing out.
> PCU->SGSN TLLI=0x88661bc6 Attach Request
> SGSN->PCU TLLI=0x88661bc6 Attach Accept (new P-TMSI)
> PCU->SGSN TLLI=0xe512eba3 Attach Complete (new TLLI) (6s later)
> Now the question is how the PCU should behave. I think the MS is
> allowed to change the TLLI (after a P-TMSI assignment) after the
> contention resolution is completed. From my reading there is no content
> resolution on the UL. My E71 appears to run into a timeout and then
> issue a RACH request to send the Attach Complete. I think I have
> seen other equipment failing to transmit the Attach Complete at
> all.
> I think for the SGSN -> PCU side we should generally look things up
> by IMSI (there is already a warning in the code), for the MS->PCU
> side. I think we should store the old and new TLLI (and then put
> new_tlli into tlli once the new one is being used).
> comments?
>         holger
> --
> - Holger Freyther <hfreyther at sysmocom.de>       http://www.sysmocom.de/
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Ivan Kluchnikov.

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