Sir I am from India. Currently I have two ways of Connecting to internet ie., I am using two broadband connections they are Hathaway broadband and airtel broadband through two ethernet cards one is built into motherboard and another external.

I am able to browse internet using any of the above connections. The issue is Hathaway broadband is frequently disconnecting and airtel broadband is providing services without interruption.
Hathaway is providing data download at very low cost and airtel is providing data download at very high cost.

I am using openSUSE12.3 as my operating system. When I issued the command ifconfig it is showing message as Hathaway is assigned to eth0 and airtel is assigned to eth1.

I want to achieve the following goals
1)when I download any file the system must use Hathaway ie., eth0
2)when the Hathaway broadband disconnects the system must immediately switch to airtel broadband ie., eth1
3)when again the Hathaway broadband starts working the system must be immediately switch back to Hathaway ie., eth0
4)All of the above if possible must be done without the intervention from me.

Kindly suggest how this can be done.

Regards ,
Rupesh.

I'm gonna guess this is not trivial and will require some work on your part

these may help you get started:
http://natisbad.org/dyn-net/index.html
https://www.suse.com/communities/conver ... s-sles-10/

Are there any settings available in kde network manager in order to accomplish the above job.

Instead of bonding, I would simply suggest ensuring your routing tables are setup to set a much higher cost (or metric) for eth1 in comparison to eth0.
Unfortunately NetworkManager does not seem to offer any options for setting the metric for routing - so you'll need to configure this manually i'm afraid.