My facetime keeps cutting out after 9 mintues, like exactally 9 minutes.. any help pleasee?

So i know my internet sometimes plays up (who's doesn't) but my facetime for the past few days cuts out after 9 minutes, like exactallly 9 minutes and im not really sure why, its not the MB cause it keeps changing from like 55MB to 66MB used.. but it keeps cutting out. any help on what could be causing this?