Usually the devie will not be always powered on and connected to the network, it is not a GPS inside device or just we had not implemented the RTC in the PCB.

In these cases in every power the time will be reseted.

How to know the time,

1. Some netwrok carriers have implementations to obtain the time over USSD, other posibility is to send an SMS to the device; costly in any case.
2. Implement the NTP(Network Time protocol) using and UDP socket implementation.Recomended for high precition application. It is more hard to implement
3. Obtain the time from a internet server with protocoll RFC868. This protocoll is easy of implement and there is multiple servers in internet availables. Example of available servers:

time-a.timefreq.bldrdoc.gov
time-b.timefreq.bldrdoc.gov
time-c.timefreq.bldrdoc.gov
utcnist.colorado.edu
time-nw.nist.gov
nist1.nyc.certifiedtime.com
nist1.dc.certifiedtime.com
nist1.sjc.certifiedtime.com
nist1.datum.com
ntp2.cmc.ec.gc.ca
ntps1-0.uni-erlangen.de
ntps1-1.uni-erlangen.de
ntps1-2.uni-erlangen.de
ntps1-0.cs.tu-berlin.de
time.ien.it
ptbtime1.ptb.de
ptbtime2.ptb.de

Who works:

These servers are lisening the ports TCP/UDP 37 for inquiries. Description of the procedure for the socket TCP 37:

• Perform a connection to the time server using the port TCP 37
• After the connection the server will send to the module a 4 byte(32 bit) packet with the date/time ( In fact the information received is the seconds trancurred since 00:00:00 1/1/1900)
• The time server closes the socket

The time information will have a deviation of 0-2 seconds, depending of the connection speed and the transmition *****,

How to extract the date of the 4 Bytes:

// Calculate the seconds from 1/1/1990

secondsSince1900 = buffer[0]*16777216 + buffer[1]*65536 + buffer[2]*256 + buffer[3];

//Calculate the seconds since 1/1/1970 and convert the value to miliseconds. Reason the Java Constructor of the Date Class ***** the value in milisedonds and since 1/1/1970, that's 2208988800 seconds

miliSecondsSince1970 = secondsSince1900 - Long.parseLong("2208988800");

miliSecondsSince1970 = miliSecondsSince1970 * 1000;

// Obtain the actual time (GMT)

Date = new Date (miliSecondsSince1970);

Sytem.out.println ("Date/Time: " + datetoString());

The complete java code:

//Example to obtain the time from and RFC868 internet server

package src;

import java.util.*;

import java.io.InputStream;
import java.io.OutputStream;

import javax.microedition.io.Connector;
import javax.microedition.io.SocketConnection;

import javax.microedition.midlet.MIDlet;
import javax.microedition.midlet.MIDletStateChangeException;

public class main extends MIDlet 
{
	//Define the necessary class for the connectionn
	SocketConnection scon = null;
	InputStream is = null;
	OutputStream os = null;

	protected void startApp() throws MIDletStateChangeException 
	{
		long[] buffer = new long[4];
		int i=0;
		boolean readedTime = false;
		long secondsSince1900=0;
		long miliSecondsSince1970=0;
		Date date = null;
		
		
		//Some time RFC868 servers.
		String timeServerInternet="time-a.timefreq.bldrdoc.gov";
		/*
		String timeServerInternet="time-a.timefreq.bldrdoc.gov"
		String timeServerInternet="time-b.timefreq.bldrdoc.gov"
		String timeServerInternet="time-c.timefreq.bldrdoc.gov"
		String timeServerInternet="utcnist.colorado.edu"
		String timeServerInternet="time-nw.nist.gov"
		String timeServerInternet="nist1.nyc.certifiedtime.com"
		String timeServerInternet="nist1.dc.certifiedtime.com"
		String timeServerInternet="nist1.sjc.certifiedtime.com"
		String timeServerInternet="nist1.datum.com"
		String timeServerInternet="ntp2.cmc.ec.gc.ca"
		String timeServerInternet="ntps1-0.uni-erlangen.de"
		String timeServerInternet="ntps1-1.uni-erlangen.de"
		String timeServerInternet="ntps1-2.uni-erlangen.de"
		String timeServerInternet="ntps1-0.cs.tu-berlin.de"
		String timeServerInternet="time.ien.it"
		String timeServerInternet="ptbtime1.ptb.de"
		String timeServerInternet="ptbtime2.ptb.de"
		 */
		
		try
		{
			
			System.out.println(“App Started”);

			//Open connection. Use the data related to your carrier
			//Connect_APM
			//connection_user
			//connection_password

			scon = (SocketConnection) Connector.open("socket://" 
				+ timeServerInternet + "37;bearer_type=GPRS;
				access_point=connect_APN;username=connection_user;
				password=connection_password;dns=000.000.000.000;
				timeout=0");

			is = scon.openInputStream();
			os = scon.openOutputStream();

			
			//While until the 32 bits are received. 			
			//No exceptions implemented
			//(server no available, wrong connection data, etc)
			//—>that’s just an example ;)

			while (readedTime==false)
			{
				//Assumption that the data will be received. 
				//As mention not exception control implemented
				if (is.available() == 4) 
				{
					//Read the 4 bytes (32 bits) from the server
					for (i=0;i<4;i++) buffer[i]=is.read();
					//Once finish we can exit of the loop. 
					//Maybe a while implementation is more elegant ;)
					readedTime=true;
				}
				Thread.sleep(10);
			}

			
			//Close the sockets and the connection
			is.close();
			os.close();
			scon.close();

			
			//Calculate the seconds from 1/1/1990

			secondsSince1900=buffer[0]*16777216 + buffer[1]*65536 + 
					buffer[2]*256 + buffer[3];
			
			
			//Calculate the seconds since 1/1/1970
			//Convert the value to miliseconds.
			//Reason the Java Constructor of the 
			//Date Class ***** the value in miliseconds and since 1/1/1970
			//that's 2208988800 seconds

			miliSecondsSince1970=secondsSince1900-Long.parseLong("2208988800");
			
			miliSecondsSince1970=miliSecondsSince1970*1000;

			
			//Obtain the actual time (GMT) 

			date = new Date(miliSecondsSince1970);
			System.out.println(“Date/Time:  " + date.toString());
			
			
			//End of the program 

			destroyApp(true);
			
			
		}
		catch (Exception e)
		{
			e.printStackTrace();
		}

	}



	protected void pauseApp() {}

	protected void destroyApp(boolean arg0) throws MIDletStateChangeException 
	{
		System.out.println(“End of the application”);		
		notifyDestroyed();
	}

}

Regards

Alopez