The Gateway Network refers to the grouping of interstellar "gates" that allow for instantaneous travel from one gate to another, and together encompasses two seperate networks. The Primary Gateway Network and the L-Gate Network, with the latter functioning as a means of extra-galactic travel to the L-Cluster
Science and Mechanics
Both Primary Gates and L-Gates function under a principle of quantum entanglement and gravitic lensing. The gateway uses the pull of a stars gravity well to communicate with other gates through the passage of gravitons in higher dimensions beyond normal Space Time. Once an object passes the event horizon of the gate it is broken up into its basic energy component (the strings, referenced in 20th century "string theory). The energy strands then become entangled with the energy of the destination gate and reassembled on the other side. Primary Gates can be secured by the civilization that controls them by instituting gravitic filters, blocking access to certain gates in hostile nations. If such a gate is blocked it becomes impossible for the quantum entanglement to occur and any object attempting to travel is simply rematerialized on the far side of the same gate it attempted to pass through.
L-Gates function under much the same principle, however unlike primary gates their gravitic anchor are black holes. While a primary gate is always placed on the periphery of a Stars gravitic field, an L-gate is positioned above the event horizon of a black hole. The subsequent gravitic lensing allows the L-gate to reach much farther then a primary gate, mainly, to the Terminal Egress gate in the Styx System, an extra-galactic star located several galactic radii from the Milky Way near the Magellianic Cloud. All L-Gates are locked to the Terminal Egress. The GTU has not yet been able to fully understand how they are able to harness the intense gravity of the Black Hole, but it is generally assumed the intensity is what makes it impossible for the gate to connect to other L-Gates within the Milky Way Galaxy itself. It is also impossible to install gravitic filtering on the L-Gates, meaning they can be traversed by anyone.
The intense gravity and energy around an active gateway also makes them impossible to destroy by known methods. The center of the gate itself is in essence a micro-singularity. Any weapon shot at a gate is simply bent around it harmlessly or travels through it to elsewhere. This led to much consternation in the First and Second Galactic Wars, as hostile forces routinely used captured gateways to expand their footholds into GTU and Allied territories, and retreating defenders, not for lack of trying, were unable to destroy them.
The Gates themselves are powered by a Zero Point Reactor, which while possessing an efficiency approaching the mythological perpetual reactive power generation, is still ultimately bound by the universal laws of thermodynamics. While there is no physical way to damage a gate once it is activated (or even to interact with the mechanisms powering it), eventually its onboard reactor will expend its energies. While GTU scientists have expended great effort in attempting to figure out when such an event may occur, the inherent "chaos" that governs the behavior of matter at the subatomic realm prevents them from determining any definitive time frame, with most estimates ranging from a a few thousand years, to more then a million years. What is known however is that Gates do eventually expend their power and become "derelict", as the GTU came across several deactivated gates that had clearly been placed by some ancient race. A race that was no longer around to swap out the expended reactor with a new one and restore the gate the functionality.
Use and Development
Gateways were initially un-constructable by the GTU and other galactic powers without the physics knowledge possessed by the gates creators. For centuries the galaxy relied on the gateways they had found, which were crucial to transgalactic travel and the balance of power. The First Galactic War was the earliest war were nearly all major campaign movements relied on gateways. Control of a single gateway in the former territory of the Vol Hive was the crucial strategic point of the entire war, allowing Axis forces their only means to reach the fringes of GTU territory. The Commonwealth of Kaprisi evacuated from its own gateway to former Vol Hive territory halfway through the war, as the GTU could not extend its defenses to protect the Commonwealth.
Following the war the GTU embarked on ambitious research project that unlocked the secrets of gateway travel. During the interregnum between the First Galactic War and the War in Heaven, the GTU constructed gateways in the capital star systems of each of its Commissariats. The new gateway network proved crucial to transiting Terran forces to the frontlines of the War in Heaven, and to responding to the incursion by the awakened empires into the Aurora Commissariat.