1. Open internet explorer and click on Tools>Internet Options>Connections>Settings>Advanced
2. Deselect 'Disconnect when connection may no longer be needed' and 'Disconnect if idle for options'
3. Click OK and you have done.In another case it causes by modem setting fault so follow these steps :
1. Go to Control Panel>Phone and Modems Options> Modems and select the desired modem and click on properties then >Advances>Change Default Preferences.. deselect the "Disconnect a call if idle for more than" box and its finished.
For the users who are facing case1 I will recommend them to use "Mozilla Firefox".