I created a shell script as follows and put that in Startup Applications and it works like a charm ! I am happy with this but if you can make it better I'll be very thankful.

#!/bin/bash



while true; do

    LC_ALL=C nmcli -t -f TYPE,STATE dev | grep -q "^gsm:disconnected$"

    if [ $? -eq 0 ]; then

        #jdownloader is still in the download status so stop it because

        #internet is disconnected and jdownloader won't resume download 

        #when connected again

        #jdownloader --stop-download

        #sometimes I can not get connected after disconnection when 

        #I click on <name of the network connection>. I have to disable

        #and enable Mobile Broadband

        nmcli -t nm wwan off

        sleep 1

        nmcli -t nm wwan on

        sleep 1

        nmcli -t con up id "Tata Docomo Internet"

        #wait approximately 15 sec to get connected

        #if anyone can add better command to check for it just comment it :-p 

        sleep 15

        #now connected to internet so start download

        #jdownloader --start-download

    fi

    #it does not worth keep it checking every millisecond.

    #my connection will be reestablished within 5-15 seconds

    sleep 2

    #if anyone can code it better please feel free to comment

    #TO-DO:: check for data received. if data < 15 KB after 20 seconds of connection

    #reconnect mobile broadband connection  

done