reading messages from tracking device over gprs

Question

i have a tracking device Meiligao VT310 which send me messeages over gprs. I successfully read messagess with this code but it's not the same as I expected.

private void ReadCallback(IAsyncResult result)
{
   Client client = result.AsyncState as Client;
   NetworkStream networkStream = client.NetworkStream;
   int read = networkStream.EndRead(result);
   string data = this.Encoding.GetString(client.Buffer, 0, read);

   networkStream.BeginRead(client.Buffer, 0, client.Buffer.Length, ReadCallback, client);
}

I expect output in NMEA format, but output is like this:

$$\0}E!@ 5/??U154108.000,V,4619.3051,N,01549.5325,E,0.00,0,040112,,*1B|0.0|244|0000|0008,0006|0125004600323C97|0E|0000099C??\r\n

Answer 1

Meiligao VT310 uses its own protocol known as Meiligao GPRS Communication Protocol.

GPRS (TCP/UDP) packet command format are the following:

From server to tracker:

<header><L><ID><command><parameter><checksum>\r\n

From tracker to server:

<header><L><ID><command><data><checksum>\r\n

It's not NMEA at all but it may uses GPRS NMEA 0183 GPRMC protocol within its data part.

Resources of interest:

• Meiligao GPRS Communication Protocol PDF documentation.
• GpsGate relevant post in its Forum.