For analysing network problems Etheral proved it's worth. By now this tool is called Wireshark.
But Wireshark has got a lot more to offer than simple diagnostic functions. It is supporting most for the current network protocols and displays collected data by a graphic interface. You are even able to monitor USB and Bluetooth connections.
The link directed to the download of this free program can be found at the official homepage, or right here. On this site you will find a changelog.