here is the latest version of huawei e 173 u-1 usb 3g modem firmware update, totally free to download. you can upgrade to the latest version if you have any problems using the modem with old firmware. you can also use this update option when your modem doesn’t seem working correctly. airtel modems are usually huawei e 173
the procedure is simple. just download the firmware for huawei e 173 u-1 3g usb modem provided here. double click the exe file and you are done.