Sir I have one small doubt about connecting to internet. At present I have two ways of connecting to internet ie., direct cable broadband and connectimg to net using the services provided by mobile(2G).

cable broadband cable is attached to modem and mobile broadband through USB.

If suppose broadband connection failure occurred still I want to connect to internet using mobile broadband and my intention is I want to be connected to internet always. Is it possible and if possible then how can I achieve it.

What distribution are you using? Are you using a GUI or the command line?

I am using Debian wheezy AMD64bit7.0. I am new to Linux so I don't know how to use CLI so at present I am using network manager. I have basic knowledge about Unix system so if you suggest anything I can easily follow it and succeed.

No, you can't..you can only have one connection active at a time, unless for some strange reason, you WANT to be using your mobile broadband minutes constantly.

Is there some reason you can't be disconnected from the Internet for the 30 seconds or so it would take you to click on your alternate connection?

I am using a broadband cable internet which will failure frequently. As I want to download something of large volume of data so I want to keep download running at night and inorder to download successfully I want internet connection without interruption.

If your broadband connection fails frequently, have you called your ISP and told them about the problem? And a few simple solutions come to mind:

• Use a download manager, which will then allow downloads to be interrupted/resumed.
• If you're concerned about failure, manually switch to your broadband connection before starting the download.
• Write a script that will ping an Internet server on a regular basis, and activate the other connection if needed.

The script *MIGHT* be an option, but may not, depending on your connection. Wired connections are typically NOT managed by NetworkManager:
http://wiki.debian.org/NetworkManager

Bear in mind that if you have a link-connection, it will show as still active, even though your connection to the Internet is down, because there is still a valid link/IP address to your modem. Since you're using Network Manager, your USB broadband connection falls under that, and as such, can't be managed via external scripts.