GPRS : cannot find pdp context

[abdullah689]

Hi,

I am setting up YateBTS GPRS, it shows data or G sign on mobile sometimes but othertimes it doesn't work.  Call works fine.
Log shows following error.

017-02-27_22:41:39.758056 <mbts:MILD> miniggsn.cpp:381:miniggsn_handle_read: ggsn: error: cannot find PDP context for incoming packet for IP dstaddr=192.168.99.1
2017-02-27_22:41:40.760288 <mbts:MILD> miniggsn.cpp:381:miniggsn_handle_read: ggsn: error: cannot find PDP context for incoming packet for IP dstaddr=192.168.99.1

What can be wrong?

[Ioana Stanciu]

Those messages appear when data comes from the internet to be transmitted downlink for an IP allocated to a MS and the resources allocated in the BTS for that MS have beed deleted (PdpContext has dissappeared). This can happen for various reasons (data arrives while the phone is re-attaching)

You need to post a log with debugging enabled on SGSN and GGSN which contains more information about what is happening, not just the errors.

[abdullah689]

Thanks for replying. Here are the logs.

GGSN.log

12:35:15.9:Initializing Mini GGSN Wed Mar  1 12:35:15 2017
 12:35:15.9:GGSN logging to file ggsn.log
 12:35:15.9:GGSN Configuration:
 12:35:15.9:  GGSN.MS.IP.Base=192.168.99.1
 12:35:15.9:  GGSN.MS.IP.MaxCount=254
 12:35:15.9:  GGSN.MS.IP.Route=192.168.99.0/24
 12:35:15.9:  GGSN.IP.MaxPacketSize=1520
 12:35:15.9:  GGSN.IP.ReuseTimeout=180
 12:35:15.9:  GGSN.Firewall.Enable=0
 12:35:15.9:  GGSN.IP.TossDuplicatePackets=1
 12:35:15.9:GGSN: DNS servers: 8.8.8.8 0.0.0.0
 12:35:15.9:ip link set sgsntun up
 12:35:16.2:ip route add to 192.168.99.0/24 dev sgsntun
 12:35:16.4:SGSN:service loop policy=0 priority=0
 12:35:16.4:SGSN:service loop policy=0 priority=0
 12:36:52.7:SGSN:Received GPRS SuspensionRequest for tlli=0x855ab328
 12:37:35.5:ggsn: received proto=icmp 84 byte packet from 192.168.10.13 to 192.168.99.1 at  12:37:35.5
 12:37:35.5:ggsn: error: cannot find PDP context for incoming packet for IP dstaddr=192.168.99.1
 12:37:36.5:ggsn: received proto=icmp 84 byte packet from 192.168.10.13 to 192.168.99.1 at  12:37:36.5
 12:37:36.5:ggsn: error: cannot find PDP context for incoming packet for IP dstaddr=192.168.99.1
 12:37:37.5:ggsn: received proto=icmp 84 byte packet from 192.168.10.13 to 192.168.99.1 at  12:37:37.5
 12:37:37.5:ggsn: error: cannot find PDP context for incoming packet for IP dstaddr=192.168.99.1
 12:37:38.5:ggsn: received proto=icmp 84 byte packet from 192.168.10.13 to 192.168.99.1 at  12:37:38.5
 12:37:38.5:ggsn: error: cannot find PDP context for incoming packet for IP dstaddr=192.168.99.1
 12:37:39.5:ggsn: received proto=icmp 84 byte packet from 192.168.10.13 to 192.168.99.1 at  12:37:39.5
 12:37:39.5:ggsn: error: cannot find PDP context for incoming packet for IP dstaddr=192.168.99.1

yate.log
http://pastebin.ca/3774387

[Ioana Stanciu]

The answer for what is happening is here:
  12:36:52.7:SGSN:Received GPRS SuspensionRequest for tlli=0x855ab328

This means that the phone is doing something on the CS side (voice, SMS). While doing that, data services are suspended in 2G.

[abdullah689]

Hi,

Thanks for answering again.

But my phone isn't doing any activity like that. It is idle, and i am waiting for GPRS sign to come but no use.  The logs
cannot find PDP context for incoming packet for IP keep on appending... 

Any guidance will be appreciated

[abdullah689]

My phone is not doing anything and ggsn.log are appending this frequently..
12:36:52.7:SGSN:Received GPRS SuspensionRequest for tlli=0x855ab328

[Ioana Stanciu]

Even if the phone isn't showing that is doing anything, you need to look at the logs.
Looking at it, I can see one time those error messages appearing after the phone was doing a call (you can see the call setup and release)
Another time, the phone is doing on voice a location update procedure (is registering to the BTS):
 * at 2017-03-01_12:36:52.516012 is doing location update request
 * at  2017-03-01_12:36:52.750290 the GPRS Suspension request arrives
 * at 2017-03-01_12:37:35.519890 the error messages appear

I don't know how you are testing, but until you do something on the phone to request data access, the phone won't probably try to do GPRS again. The fact that you are receiving data for downlink makes me assume that you do have at some point some data access.

Also, I don't think I see the termination of attach procedure for GPRS (an attach complete should be in the logs).
You can check the status of the GPRS registration for the phone with "mbts gprs list" in telnet window. If it says RegisteredNormal it means that the phone finished GPRS registration procedure, otherwise something fails along the way.