[BUG][OSMO-PCU][OSMO-SGSN] GPRS and EGPRS attach procedure is not working with Kirin Modem phones

Bipin Jaiswal Bipin.Jaiswal at celliber.com
Thu Nov 29 12:02:26 UTC 2018


We are using Honor 7X mobile phone with Huawei Kirin modem and observed that GPRS and EGPRS attach is not working with Huawei Kirin Modem phones.

There is no issue observed from OSMO-PCU. it seems either Huawei Kirin modem issue or OSMO-SGSN issue.

Please check below analysis for this issue.

1- UE send attach request with IMSI and invalid MCC and MNC to SGSN.
2- SGSN send Identity Request with IMEI to UE.
3- UE responded Identity Response with IMEI to SGSN.
4- SGSN sends ATTACH ACCEPT message to SGSN with new PMTSI but UE is not responding ATTACH COMPLETE message to SGSN and resend ATTACH REQUEST message to SGSN.
5- SO SGSN re transmit  ATTACH ACCEPT message to UE and after max number of re transmission , SGSN is release UE MM context.

It seems that UE is not accepting ATTACH ACCEPT message.

We also observed that Huawei Kirin UE is sending wrong LLC data to SGSN.
UE had set more bit in RLC LME header and send invalid LLC data with 0x2B.
So OSMO-PCU had forward this data to SGSN because more bit is set and SGSN
is complaining LLC error  for this LLC data.

Please look into this issue or let us know if we have fix for this issue.

Bipin Jaiswal

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