Sub-Wave Network

The Subwave Network is a piece of sentient software programmed to seek out anyone and everyone who could help to contact the Doctor. It worked on Subwaves, which are undetectable. It was developed by Harriet Jones and created by the Mr Copper Foundation.

When the New Dalek Empire transported the Earth to the Medusa Cascade in 2009, Harriet Jones activated the network and used it to communicate with Captain Jack Harkness, Gwen Cooper, Ianto Jones, Sarah Jane Smith and Martha Jones, while Rose Tyler was able to watch but not communicate. (DW: The Stolen Earth).