[Openbts-discuss] GPRS Attach issue

[Pierre B. <pie...@di...>]

Hello,

I am currently having some trouble to get a specific GPRS M2M modem 
attached to an OpenBTS GPRS network

 From what I've observed so far, It seems that either:
* the ME never receives the GPRS Attach Accept from the BTS.
* the GPRS Attach Accept never makes it out of the radio (it is sent out 
by SGSN)
* the ME never sends the GPRS Attach Acknowledgement (AttachComplete).
* the GPRS Attach Acknowledgement never arrives at SGSN (although no 
further GPRS messages such as ActivatePDPContextRequest seem to be 
received either)


(Seen with SGSN debug logs, GPRS TAP trace, and a trial of OpenBSC 
tools)

This specific GPRS modem works well with commercial networks.

You can find a piece of SGSN debug logs for both modems attached in this 
mail. Notice that for the working modem, an Identity Request is sent 
before the Attach Accept packet is sent

Here is what I got from the command 'gprs list ms -cxv' during the 
attach process

  MS#11,TLLI=800d0001 rrmode=PacketIdle Bytes:125up/57down Utilization=0%
          GMM Context: imsi=00101303099**** ptmsi=0xd0001 tlli=0xc00d0001 
state=GmmDeregistered age=2208 idle=1963 IPs=none
          MsRaCapability[GSM_850]=( RFPowerCapability=4 A5Bits=64 ESInd=1 
PS=0 VGCS=0 VBS=0 GPRSMultislotClass=10 
GPRSExtendedDynamicAllocationCapability=0)
          MsRaCapability[GSM_E]=( RFPowerCapability=4 A5Bits=64 ESInd=1 
PS=0 VGCS=0 VBS=0 GPRSMultislotClass=10 
GPRSExtendedDynamicAllocationCapability=0)
          MsRaCapability[GSM_1800]=( RFPowerCapability=1 A5Bits=64 
ESInd=1 PS=0 VGCS=0 VBS=0 GPRSMultislotClass=10 
GPRSExtendedDynamicAllocationCapability=0)
          TimingError=(1.28 min=-1.05 max=1.91 avg=0.79 N=53) RSSI=(-24 
min=-48 max=-21 avg=-35.45 N=53) CV=(27 min=27 max=31 avg=30.00 N=6) 
ILev=(0) RXQual=(0) SigVar=(0
) ChCoding=(3 min=0 max=3 avg=2.20 N=60)
          dataER:.0% (331) recent:0% (0) tbfER:.4% (12)
          rrbpER:.5% (27) recent:0% (0) ccchER:1.0% (94) recent:1.0% (30) 
low:1.0% (2)


I noticed that another GPRS M2M modem of the same brand (Cinterion), 
that _does_ work with our current setup, I get some differences in 
capabilities :

  MS#2,TLLI=c00c8001,800d0004 rrmode=PacketIdle Bytes:106up/86down 
Utilization=0%
          GMM Context: imsi=00101303099**** ptmsi=0xc8001 tlli=0xc00c8001 
state=GmmRegisteredNormal age=17 idle=2 IPs=192.168.99.1
          MsRaCapability[GSM_E]=( RFPowerCapability=4 A5Bits=64 ESInd=1 
PS=1 VGCS=0 VBS=0 GPRSMultislotClass=4 
GPRSExtendedDynamicAllocationCapability=1 SMS_VALUE=7 SM_VA
LUE=5)
          MsRaCapability[GSM_1800]=( RFPowerCapability=1 A5Bits=64 
ESInd=1 PS=1 VGCS=0 VBS=0 GPRSMultislotClass=4 
GPRSExtendedDynamicAllocationCapability=1 SMS_VALUE=7 SM
_VALUE=5)
          TimingError=(0.18 min=-0.78 max=1.59 avg=0.16 N=204) RSSI=(-63 
min=-63 max=-61 avg=-62.81 N=204) CV=(50 min=47 max=51 avg=49.43 N=7) 
ILev=(0) RXQual=(0) SigVar=
(63) ChCoding=(0)
          dataER:.7% (68) recent:.7% (55) low:.8% (38) tbfER:.14% (7)
          rrbpER:.3% (35) recent:.4% (30) low:1.0% (6) ccchER:0% (0) 
recent:0% (0)

The differences I see are:
* No GSM_850 capabilities (advertised?) in the modem that does work.
* PS=0 (pseudo-synchronisation) on the modem that does _not_ work, vs. 
PS=1
* GPRSExtendedDynamicAllocationCapability=0 on the modem that does _not_ 
work, vs. GPRSExtendedDynamicAllocationCapability=1

Do you know if this modem not being able to perform an extended dynamic 
allocation (according to the uplink packet resource request) can prevent 
it from attaching to GPRS ?
The same goes for PS (pseudo-synchronisation)
Have you ever encountered this kind of situation, or have any idea where 
to look for problems?

Best Regards,