Internet Frequently Disconnect

I have windows 7 with broadband internet connection. For the some days frequently internet is disconnecting.

My setup is like below

Direct line is connected to one port splitter. From there one is connected to telephone and one is connected to my modem.

The modem is beetel 450 bxi adsl2 + router.

System is connected with modem using cable. In the modem Internet light is alweays blinking and turn off ferquently. After sometime it will come up and internet working.

I am confused that is the problem with modem or ISP. Telephone is working correctly