Here is the full question: I have a roll-over cable with length only 5 m and I want to connect it to the console of the cisco router that is 20 m far. How can I solve this?
Twenty meters is too far for the serial link to work. I have been able to get up to about 10 meters with some, but not all, Cisco devices.
You need to set up a terminal server that plugs into the console port so you can connect to the terminal server on the network to get access to the console port of the device. There are all type of terminal server out there, but product or resource recommendations are explicitly off-topic here.