Hello all,

since last weekend GPRS is working and now I am about to understand what exactly happens when I turn on my Milestone to get a position fix in googlemaps.

As I understand it, the phone (SET) queries the SUPL server (SLP) of Motorola to get assistance data. I can see in wireshark that they talk for a while but unfortunately I can only see the TCP packets. Of course I would like to see the ULP packets inside of TCP. Wireshark supports ULP but I cannot see the packets. I attached a capture. Does someone here has a ULP capture to share? Or can someone acknowledge that he/she can see the ULP packets?

I can only see the DNS query for the ip of the SUPL server and than some TCP packets going to the SUPL port (7275) and back to my mobile phone.

ULP is implemented and so maybe it is my version of wireshark which is the development version from https://launchpad.net/~dreibh/+archive/ppa

Another thing is that I get placed in googlemaps to Sao Lazaro (Macau) which is not really Berlin. It only happens when I am connected to the NanoBTS and no other position can be retrieved. It happens with a Nokia phone (N78) as well as with one from Motorola (Milestone). This is not a problem since it goes to the right position as soon as it has found enough satellites but indoors and without A-GPS working it places me to Sao Lazaro. Just curious what that could mean.

Best, Andreas

On 08/22/2010 11:35 PM, Andreas Schmidt-Dannert wrote:

Hello Dieter,

On 08/22/2010 10:17 PM, Dieter Spaar wrote:

...

Hello Andreas,

On Sun, 22 Aug 2010 21:03:46 +0200, "Andreas Schmidt-Dannert"aschmida@mail.tu-berlin.de wrote:

...

I am playing around with RRLP and since newer versions of OpenBSC also support packet data I wanted to upgrade to be able to receive A-GPS data from the internet.

I don't know whats wrong with your configuration, I can just say that here switching between different PCs running OpenBSC works without problems when the correct OML IP address has been configured for the nanoBTS ("-o" option of "ipaccess-config") and the nanoBTS was restarted.

I am interested in what you want do try with RRLP because I recently did some more experiments with it. Especially I would like to try "MS-assisted" position measurements next, however this method requires the acquisition assitance data which have to be calculated first, I don't think they can be extracted from the data of a GPS receiver. I don't know if there is some ready and tested code for this already available which would make it easier to get this up an running.

Best regards, Dieter

The idea is to find out what information can be revealed from a phone by sending different RRLP requests. Right now only ms-based positioning is possible and I played a bit around with it and was surprised how easy it was to get the position. I wonder if they even store the last known position? As far as I know it makes it easier to compute a new position if the phones knows where it roughly is. Anyway since I just have one nanoBTS I can only use GPS as positioning method and while I was playing around I realized that most MS asked for assistance data (as you also found out at HAR2009).

So bringing ms-assisted positioning to work is also a goal of me. Is it not possible to just transfer the acquired data from the GPS receiver in the MS to a A-GPS server in the network and let te server compute the acquisition assistance data? Probably I am thinking to naive here. I know it should be a server not too far away from the asking MS.

By the way there was for a while a rrlp-ephemeris tree in openbsc. What was it for and what happend with it? As i understood it one could connect an external GPS device to a laptop to get data that is needed..kind of an A-GPS server. Right?

Another tought: What about SUPL? SUPL uses IP to get assistance data from a SUPL server...so maybe it is possible to use a supl server from google or similar?

So what I do is just playing around to find out what can be done (old positions, will a phone turn GPS on when an RRLP query comes - thinking about emergency cases (E911) this would make sense) and how do different mobile phone react to different queries. I am not fuzzing

• I am sending only valid queries. I am quite new to this field but I

find it very interesting and I have fun working with OpenBSC (if it works :) maybe my problem has nothing to do with OpenBSC...I do not know).

If you have any ideas how to get ms-assisted positioning to work I would be glad to hear about it.

Best,

Andreas

Hi Harald,

On 09/07/2010 04:45 PM, Harald Welte wrote:

Hi Andreas,

On Tue, Sep 07, 2010 at 01:57:56PM +0200, Andreas Schmidt-Dannert wrote:

...

Another thing is that I get placed in googlemaps to Sao Lazaro (Macau) which is not really Berlin. It only happens when I am connected to the NanoBTS and no other position can be retrieved. It happens with a Nokia phone (N78) as well as with one from Motorola (Milestone). This is not a problem since it goes to the right position as soon as it has found enough satellites but indoors and without A-GPS working it places me to Sao Lazaro. Just curious what that could mean.

I would simply guess that it is some hard-coded default in case the MCC/MNC/LAC is not known to whichever entity on the network that decides your location based on that information.

What kind of MCC / MNC are you using? Have you tried changing them to one that exists in reality and checked where you get placed on the map now?

I used the default one in the config file but now I changed it first to 202-1 (Cosmote - Greece) and than to 268-3 (Optimus - Portugal). They both placed me in the ocean between Havanna and the Everglades. So it seems that something is hard-coded in the SUPL server but why is this value not always the same and why is that point so far away from Portugal/Greece? Maybe I should try another SUPL server and see if they place me at the same place for the same MCC/MNC combination.

Thanks,

Andreas