Try the following. These are steps for my Binatone
ADSL router....should be similar for others
1. Disconnect your airtel or other brand ADSL router from all other devices except your computer (connected via ethernet cable).
2. Load 192.168.1.1 on your computer
3. Find your router local IP settings. For me it is under Interface Setup/LAN
4. Change the router LAN IP from 192.168.1.1 to 192.168.2.1
5. Save and apply settings
6. Unplug and replug ethernet cable on your computer
7. Check network settings on your computer. You should now have an ip address of the form 192.168.2.x
8. Load this DSL router page by loading 192.168.2.1. When connected to your other ADSL router, you would be loading 192.168.1.1
9. Reconnect your hub/wireless router. If your wireless router is connected to the ADSL router, then you would I think need to do the following as well
a. Connect your computer to the Wireless router alone via ethernet cable
b. Load the wireless router config page (uusally 192.168.1.1)
c. Find interface setup as similar to the ADSL router
d. Disable DHCP. Apply/Save settings
e. Reconnect the router to your ADSL router
Edit: I'm not sure how having 2 DHCP servers active in both the ADSL routers will work. You might have to disable one. If you do that, then to use that connection, you would have to manually plug in the gateway value in your IP setting on computer.