Everytime I play Dota through Garena platform (Online), every 20 minutes it does make "Request Time out" for 15 seconds and then goes back to normal. But as I have observed, when I only surf the net, this problem does not exist.

I have 354kpbs dsl and only 1 pc im using. It does like 6 RTO lines and then goes back to normal. What's the problem of this? My modem is ZyXEL p-600 series. My OS sp3 XP. thx in advance.