Routing Area Update Reject (2G-GSM)

[wsoong]

Hi All,

Anyone has experience to resolve the issue describe below? Routing Area Update Reject issue.

Cell A: CI= 1234, LAC= 30301 RA = 1
Cell B: CI= 2345, LAC= 26001 RA = 1

There is a Routing Area Update Reject after a successful Location Update from Cell A to Cell B, in an dedicate mode Upload Data Session (2G GSM E******* Network).

Both Cell are in different BSC and belong to same switch.

The cause code of the Routing Area Update Reject is "Implicitly Detached".

As i am not familiar with the Core Network eg. SGSN and GGSN. Anyone can advice is there any setting need to be done? My guts feeling tell me it is due to the core side but i am not sure how to check. :(

Appreciate your expertise here!!

Regards. :)

[adewijaya]

(Implicitly Detached) – Additional Cause Code for GMM

This cause is sent to the MS either if the network has implicitly detached the MS, e.g. some while after the Mobile reachable timer has expired, or if the GMM context data related to the subscription does not exist in the SGSN e.g. because of a SGSN restart.
The MS shall change to state GMM-DEREGISTERED.NORMAL-SERVICE. The MS shall then perform a new attach procedure. The MS should also activate PDP context(s) to replace any previously active PDP contexts.

NOTE: In some cases, user interaction may be required and then the MS cannot activate the PDP context(s) automatically.

I would try to do as follows:

1)take the suspect mobile and switch it on;
2)then check out the subscriber status in SGSN (GPRS Attach/detach?) and VLR (Imsi attach/detach?).
3)If both flags are attached then wait without making any voice or data activities..It is very desirably to observe the signalling exchange concerning that subscriber on Gb- (e.g. Periodic RA Update, Detach message from SGSN etc.) and Gs-(e.g. Imsi Detach Indication etc.) interfaces.
4) If for example you will find out that after Detach timer expiry (3,5 h) in SGSN IMSI is detached also in VLR then more likely than not that your SGSN have abnormal behavior.

[zhanglw268]

Although the 2 BSCs are managed by same MSC, but they maybe managed by different SGSNs, you can check whether this is the case. If this is the case, check whether there is Gn interface between these 2 SGSNs, the Gn interface may have problem.

How about the RAU in reversed direction?

[wsoong]

Hi,

RAU in the reversed direction also failed. We are checking whether both cell belong to same SGSN.

Thanks for the advice, hopefully can find out the answer soon. :)

Regards,

[adewijaya]

OK, its CORE problem. Please Update after founding some mismatch on SGSN dBase ;)

[wsoong]

Hi,

We found out the problem already. It was because there is a co-exist of RAI in both SGSN.

RAI=LAC+RAC

This RAI is exist in both SGSN which connect to different BSC, thus giving Routing area problem.

Proposed solution is to change the RAC in one of the SGSN.

Hope this is helpful to you if you encounter this kind of problem. :p