Next to the In-band management it is advised to also use something known as out of band management, a way to reach the management of your equipment in case of network failure.
If an IXP has a partner (or also maintains a separate network) that operates a network with different lines from the one the IXP uses one way to connect to the console of the IXP is to use out of band management over IP. A remote console that is accessible via ssh, telnet, etc. over IP is connected to a console port of the IXP switch.
IP console devices may also be reached via IPSec tunnels, although ssh may be enough security for such devices.
A common approach is to use telephone lines and connect a remote console to the IXP device console port. In this way it is possible to call the remote console via a modem on the operator's local computer over the telephone network. This is a very slow way to communicate with the device but enough to use the console and detect broken lines.