Tunneling is the technique that USB4 and Thunderbolt use to carry other communication protocols, such as DisplayPort video or PCI Express data, packaged inside the same underlying connection as ordinary USB traffic. Rather than switching the port entirely to a different mode, tunneling shares the connection's total bandwidth dynamically between whatever protocols are active.
This is what allows a single USB-C cable connected to a capable dock to simultaneously drive an external monitor, transfer files to a connected drive and charge a laptop, all without needing separate ports or cables for each function.
How much bandwidth is available for each tunneled protocol at any moment depends on what else is active on the connection, so a very demanding display alongside a very fast storage transfer can, in some cases, compete for the same total bandwidth. See our USB4 and Thunderbolt guide for more.
