First referenced:
The Desolate Guardians (Part 2)
The Quantum Tunnel Transceiver is a device used to connect to and communicate with multiple internet and networking systems on parallel Earths in the multiverse structure. Accessed via the network node/hub on the destroyed Earth inhabited by Heath, an IT systems administrator. Used for bidirectional communication with Cristina Thompson first encountered in The Portal in the Forest, as well as Noah Fulmer and many others across the multiverse.
The network node requires a direct neural interface and virtual world environment to properly interact with all of the connected systems, which also contains a long term life support system.