Dimension seeding

Dimension seeding was an invasion method used by the Cybermen of the Cyber-Mainframe to form bridgeheads into parallel universes and begin converting their inhabitants, (AUDIO: Code Silver) as part of their campaign to upgrade the multiverse. (AUDIO: Master of Worlds)

Virtual conversion
In order to form a connection from one universe to another, the Cybermen would translocate dimension bridge technology from a universe they already inhabited to one that they had yet to gain access to. (AUDIO: Code Silver) There were at least two different methods of performing a "virtual conversion" - cyber-conversion via dimension bridge technology - that were performed by the Machine, a security system that monitored the worlds assimilated into the Cyber-Mainframe and detected if mental avatars arrived on these worlds as a result of using dimension bridge technology.

Instantaneous conversion
Once a "candidate" used dimension bridge technology, which took the form of an advanced virtual reality headset, part of their consciousness was separated from their body and transmitted to a planet conquered by the Cybermen in a parallel universe. The Machine would attempt to attack the candidate via the use of different cyber-units, so as to use the candidate's mental avatar to form a dimension bridge to the parallel universe that their body was located in. Upon being attacked, the candidate's consciousness would be returned to their body shortly before undergoing partial cyber-conversion. (AUDIO: Telepresence) A dimension gate (AUDIO: Master of Worlds) would then form as the dimension bridge created from the candidate's consciousness connected the two universes.

Conversion over a dimensional gap
However, if a candidate had used dimension bridge technology for an extended period of time, but then disconnected from the technology, they could still be cyber-converted and used as part of a link between universes, although the conversion would take significantly longer than through direct use of the dimension bridge technology, (AUDIO: Telepresence) as the upgrades had to be broadcast across a dimensional gap. (AUDIO: Code Silver)

This method involved the Machine reestablishing its connection to the candidate and commencing a data transference, slowly broadcasting into the candidate's brain information from the Cyber-Mainframe necessary to establish a link between universes; due to the sheer amount of information broadcast from the Mainframe, this process was often quite painful for the candidate. The Machine was also capable of altering the candidate's nerve impulses so as to control their response to the pain inflicted by this process, and could detect if the candidate was aware of the process being performed on them and, by extension, render them unconscious.

If rendered unconscious, the candidate would wake up in a dream-like state, alongside an individual taken from the candidate's recent memories, who would assist the Machine in further establishing the link between universes, such as advising the Machine as to whether or not the data transference should be increased, or if the candidate's cerebral functions should be limited further. Eventually, the candidate would be attacked by Mechanising Worms, shortly before final conditioning on the candidate commenced. After waking from their dream-state, the candidate would be attacked again by Mechanising Worms, this time undergoing partial cyber-conversion and having their physical strength and connection to the Cyber-Mainframe boosted. Eventually, the candidate's full virtual conversion would complete, allowing a dimension bridge to form between their universe and the universe that the Machine was making the connection from. (AUDIO: Telepresence)

Securing a foothold
After the newly-formed dimension bridge was connected between the two universes, a patrol of around ten Cybermen, led by a Cyber-Controller and a Cyber-Commander, would enter the new universe via the dimension bridge and attempt to secure a foothold in the new universe, starting with the general vicinity of the dimension gate, the endpoint of the dimension bridge. This process involved the Cybermen deleting the majority of the lifeforms in the immediate area whilst using mobile conversion units to gradually increase the Cybermen's numbers. Once the area was secured, the Cybermen would begin to spread across the planet, converting the rest of its inhabitants and securing further stronger footholds until they had eventually converted the entire planet. After this, full seeding would commence, which involved the Cybermen travelling to, and converting, further planets in the new universe, repeating their invasion methods until the entire universe was converted; due to how large a universe could be, full seeding could take thousands of years to complete. (AUDIO: Code Silver)