I have configured home network, where i have debian router that connects to ADSL via ppp and has shorewall and HTB class traffic control.

Everything is configured fine (i think) fixed and checked the configuration many times. The internet works perfect from my home computers but there is one issue. Couple of times a day, internet traffic falls to 0 (i have constant downloads and uploads) with periodic behavior. Full speed-->sudently all 0 for 5 sec-->full speed as before for 5-10 sec--> 0 for 5 sec and so on, 5-6 periods.

Internet connection doesnt disconect, but i lose my skype calls, and online games.

I thought maybe its because my router cpu runs 100% usage or memory is full, but no, its not the problem, cpu is at 4% and 400MB free memory, no special things in syslog.

I`m desperate to find solution, any tip, maybe some diagnosting tool will be very welcome.

Is this behavior can be caused by my ISP, not my router?