Problem with SGSN Location Update Reject during UE attach

Lam Ngoc Tuan tuanln at
Tue Oct 16 10:59:08 UTC 2018

Hello Mr. Neels Hofmeyr

Vielen Dank fuer die schnelle Antwort :-)

Actually we also have seen the "Congestion" in the log but we have not
understood why

We have modified the SGSN configuration: set auth-policy to accept-all.
We repeat the UE attach with this configuration but still MSC sends
"Location Update Reject"

I attach the new pcap file, msc log and sgsn log. I very appreciate if you
can take a look to that.

Vielen Dank
Tuan Lam

-----Original Message-----
From: Neels Hofmeyr [mailto:nhofmeyr at] 
Sent: Tuesday, October 16, 2018 5:43 PM
To: Lam Ngoc Tuan
Cc: osmocom-net-gprs at
Subject: Re: Problem with SGSN Location Update Reject during UE attach

Actually, the GMM attach doesn't complete, either.

The messages look a bit confusing, with a bunch of Location Updating Accept
followed by a final Location Updating Reject due to "Congestion". The causes
may be

- two simultaneous MM attach requests from the same subscriber,
- timeout after attaching, e.g. phone sends no TMSI Reallocation Complete

It's hard for me to see what is going on there, take a look at the MSC's

As soon as the MSC attach works out, the phone will continue to try at the

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