Weird thing about Wifi in Ubuntu

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http://askubuntu.com – There is wifi near my house which I use. It's an open wifi net but it requires login and password once I connects to it by redirecting to login page. Everything is ok because I have them because I pay for it. The funny thing is that in Ubuntu it doesn't work good unlike in Windows. It does work fast but it "disconnects" me every 30 seconds or every minute by displaying "Unable to connect to the Internet" standard page. To be able to "reconnect" I have to reload a page about 20 times. Only after that it downloads it again and works fine for about 30 seconds. But "disconnects" and "reconnect" (HowTos)