Voice and SMS fine - Not GPRS?


Hi All,

I’ve come across an issue with a device in the field where it can communicate fine using voice or sms (i.e. can make/receive calls and send/receive txt messages) but it can’t connect using gprs.
The signal strength seems alright (between -70 & -89 dBm and my phone shows between 1 & 4 bars).

I would have taken these indicators to say that the gprs would be fine (I was able to connect if I stood in a certain area, but not reliably).

Would anybody be able to shed any more light on this issue? Any information would be most appreciated.
I’m thinking along the lines of:

  • It’s not rare that someone can text/call fine but gprs is a now show
  • I’ts not my code doing something stupid (as I could see a similar problem with my phone)
  • etc.

The area is quite rural (think farm) but i’m still stuck on the fact that calling etc. is fine.

Thanks in advance :slight_smile:


Do you have other, identical devices at other locations that can do GPRS?

The indications on a phone are largely irrelevant - it’s a totally different device, and it’s not in the same location.
You need to look at the actual indications from the device itself.

Well, if the phone’s unreliable that could mean that it can barely get GPRS - so the difference between the phone and the unit could easily be enough to go from “barely” to “not at all”.

You need to be more clear about what is and is not happening:

Does the unit get GPRS registration?

Does the unit connect to the APN?

Can the unit “see” your “server”?

Is the connection being rejected by your “server”?

etc, etc,…


Hi Awneil, thank you for taking the time to reply. sorry for the late reply :stuck_out_tongue:

I was unable to get the most complete logging of all the details while I was there (remote site, 3+ hours drive there so not the most accessible site for me to get to at this point in time :neutral_face: ).
But i’ll elaborate on what I did find out.

To clarify, the signal strength that I mentioned (-70 to -89 dBm) was coming from the device itself.
I was also able to re-position a replacement board (an exact clone of what was installed) in different places at the site, where it ‘worked’ in a couple but not in others.

As far as I can tell, with the level of debugging that I had at the time, i was able to get


all the time, but only sometimes got further than


(and then onto a good connection and communications with the server etc.)

I know that this isn’t really good information, but it’s all I have at the moment until I go down again (sometime in the future).

So I guess what I was looking for in the interim was confirmation on my assumption (as I’m by no means a cell/gprs expert :slight_smile: ) that it’s not abnormal to have ‘fine’ signal and ability to make good calls and to send/recv. sms but to have totally flaky gprs connection.
One could assume that if you’re signal is good and can make calls, that the gprs should be sweet too, no?

Any information that could lead me to better enlightenment would be most appreciated.



Not necessarily.

GPRS is an “overlay” on top of GSM - so it is possible that the “basic” GSM (calls, SMS) could be working, but GPRS service is down or faulty.

The radio part is only the first step in a long journey to complete an end-to-end IP connection: there’s also SGSN, GGSN (the “APN”); and that’s just to reach the internet - you then still have all the normal internet stuff before you actually reach the remote peer!


My point is: radio signal level is, of course, necessary - but it is by no means sufficient!

If you have good SMS and circuit-switched connectivity, then you should be looking at providing remote diagnostics over those channels…


Thank you for the excellent information. The link provided looks very interesting and informative :slight_smile:

I’m currently looking at improving the diagnostics.

Thanks again.