New subject: [PATCH] logging.c: log_parse_category_mask(), skip log category name... (was: Re: GPRS and PDP Context)

18 Sep 2012

Good Day,

I have been working with OpenBSC for the past few weeks and I am able to
make voice calls and send SMS messages within the private network without
issues.

I am now attempting to add GPRS to the mix, and have been having less
success.  I have been able to make it to the internet from my phones
occasionally, but in general, there appears to be an issue between
osmo-sgsn and OpenGSN.  My hope is that it is a simple configuration
issue.  However, I suspect it may be due to an issue in the code, or
perhaps something mentioned last May (I have been scouring the mail
archive) regarding foreign vs local TLLIs.

My current setup is:
One Linux workstation which runs all three pertinent executables:
osmo-nitb, osmo-sgsn and ggsn.
A nanoBTS 165BU (PCS1900)
Two Nokia 6013b phones
I am working in an RF chamber.  I have some T-Mobile SIMs so, I have the
network set to T-Mobile rather than the test network.

I had previously been able to connect to the internet perhaps 1 in 10
times, presumably because the PDP contexts were not being created (the ggsn
output would not state that it was creating a context when I tried to
connect from the phone). I modified gprs_llc.c to handle the issue that
Frank Maas mentioned in May, regarding llme_alloc not localizing the TLLI.
Now, I can usually connect with a phone more consistently (but not always)
on a fresh restart of the three executables.

However, after connecting to the internet via the phone, if I cycle the
power on the phone, I am usually not able to connect to the internet again.
Sometimes the ggsn states that it "Received create PDP context request,"
and sometimes it doesn't state it when the sgsn (apparently) makes a
request.  At times, the ggsn reports "Received packet with no
destination!!!"  During these times, when I check the PDP contexts in
osmo-sgsn, I get:

OsmoSGSN> show pdp-context all
PDP Context IMSI: 310260XXXXXXXXX, SAPI: 3, NSAPI: 5
  APN: epc.tmobile.com
  PDP Address: IPv4 192.168.100.3
 SGSN PDP Context Statistics:
  User Data  Messages ( In):        0 (0/s 0/m 0/h 0/d)
  User Data  Messages (Out):        0 (0/s 0/m 0/h 0/d)
  User Data  Bytes    ( In):        0 (0/s 0/m 0/h 0/d)
  User Data  Bytes    (Out):        0 (0/s 0/m 0/h 0/d)

The times when the ggsn does not state that it received a create PDP
context request, the "show pdp-context all" command shows nothing.

My newbie guess is that osmo-sgsn is saving the state of the phone's
connection (based on the IMSI?), and is not releasing or clearing it when
the phone is powered off.  When the phone is powered back on, it will have
different connection parameters, but it will use the original parameters
after retrieving them based on the IMSI.  I have started to look through
the code in the src/gprs directory to see if this is the case.

I am wondering if anyone might have some insight into why the connection is
not fully restored.  Or perhaps they can offer guidance where I might begin
to look in the code. I can send logs and pcap files of a typical session if
anyone is interested.

Thanks!
John