It's very unusual to sniff data packages. Can't you configure where your GPS Tracker sends his data? Is it using a software coming with the GPS Tracker that receives data. You may have aso called proprietary protocol between such software and the tracker.
No matter what protocol, if it's based on TCP/IP you can use a winsock control in VFP and let it act as a server waiting for requests. As you say the tracker sends it's data, it sounds as if the software receiving the data acts as a server, the tracker as a client sending something similar to a http POST request.
Or do you really mean the tracker acts as a server listening to requests on ip xxx.xxx.xxx.xxx on port xxxx?
Anyway, the answer is using winsock in VFP to either listen to requests or send requests and listen to the answers coming back.
You should first find out, what's really true here, is the tracker acting as a server or client in regard to sending it's data? Typically devices act as a server, eg routers typically have a configuration you can open in a browser. So it would be quite unusual if the tracker would act as a http client.
Bye, Olaf.