My problem isn't just that a computer downloads/uploads at its maximum, saturating the LAN's bandwith by doing so.
The thing is it only uses 1-1.5 Mo/s when other computers on the LAN can download at 9 Mo/s (not from the Internet but between computers on the LAN).
And over this, when this computer hits its maximum of 1-1.5 Mo/sec, all computers using the same router lose access to Internet. Computers on an other router don't, though.
The network has about 20 computers, all plugged with cables, one main switch with computers and routers plugged in it.
Does anyone understand why/how this is happening?
Cable is fine, I tested it on my computer... Network card broken / too cheap maybe?