Cisco does not like Cisco
After months of struggling with my home network I found a solution. What I experienced was regular disturbance in the network. Listening to WinAmp radio failed after 10 minutes. Strange logs in my router. I have router Linksys RV082 (produced by Cisco). I also have IP-telephony and that device is a Cisco ATA-188. I realised yesterday that these two doesn't like each other. The problem disappeared when I placed a switch between those. I don't know why and I don't want to spend more time on that problem. I am just happy that it works now!