where should I start to build a strong GPRS LISTENER

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VB

ASP.NET

Hello to all

I have some GPS devices, I wanna use the messages of them in my website to show their location on the map.

The Gps sevice has tow modes to send its messages:

1)SMS:
when the gps sends the data in SMS mode, I can receive it with a message center and compile the message without any problems.

2)GPRS:
In this case, I should have a listener on my server to listen the connections and get gprs packets.

Now the question is, How to do this? I don't have any listeners, Where should I start?
additionally, it might happens if a lot of devices want to send their data in the same time, and the listener should be able to get them all and does not lose any message.

I'll be appreciate you if you can give me solution.
regards
vahid mohammadian