Courier network

The courier network was a system of transwarp conduits in the 32nd century. They were extremely dangerous to traverse due to being filled with debris, and thus despite their name were mostly avoided, even by couriers. (DIS: "Su'Kal", "There Is A Tide...")

In 3189, Kyheem conveyed a message to Cleveland Booker through the courier network summoning him to Kwejian. (DIS: "The Sanctuary")

Later that year, Osyraa took her flagship, the Viridian, through one of the courier tunnels and surprised the USS Discovery at the Verubin Nebula. After the Viridian captured the Discovery and spore jumped away to Federation Headquarters, Booker and Michael Burnham used the network to pursue them in Booker's ship. (DIS: "Su'Kal", "There Is A Tide...")