Quantum Communication

Before, within a period of time known as "The Drift," while FTL Travel existed, the capability of FTL communication did not. Data loaded into drones, or passed on with transport ships, was used to transport information, with slower FTL speeds meaning information was weeks, or even months behind. The galaxy wasn't in any form of dark ages, but influence was slow, and short-distanced. Only exceptionally strong ideologies and extreme, rooted ideals stuck with any form of cohesion.
Then, came a breakthrough. Instantaneous, unlimited distance, energy-efficient information transfer. Quantum Communication.

Utility

Quantum Communication is as important to the galaxy as the internet is to those in the age of information. It leads instantaneous communication - influence stretched across thousands of light years, coordination between users in real time, a conversation with another a lifetime away.
On a simplistic scale, Quantum Communication is what caused single planetary systems to grow into a galactic scale. No longer are merely planetary systems of culture and politics the maximum size of continuous civilization - no, it is potentially possible, with the communication and FTL Travel working in unison, that civilizations could span across the entire universe, confined by nothing but resource and energy use.

Manufacturing

The creation and use of the Quantum Communication system, while not exactly complex, generally eludes most of those who use it - its terminology somewhat confusing with its various "rails" and use of the word "quantum" in almost every single phrase; yes, we get it, it's communication through quantum fields, no need to keep saying that.
Regardless, a simplistic explanation follows that non-degree holders should be able to understand:
You, the user, are the holder of a "Communications Chip" - this chip is around the size of square centimeter, and is most likely connected to your HoloGaun. This chip has a set of a few million "quantum entangled particles" all in a row, and, coupled with the Rosututin Algorithm and a process called "Post Pre-Continuity Chronolization," these particles can be manipulated into switching their state from any given set of quantum probabilities to any others. These particles, being entangled, then cause their new state to affect their entangled pairs to take a different state, whose probability field is directly consequence of the Chronolization process. These particles are located within their own Communications Chip, which is located within a building called a "Quantum Siderail."
In a practical sense, this allows the two chips to communicate with one another when provided with power and a computational unit, at any distance, instantly.
Within a Quantum Siderail, there are likely millions, if not billions of different chips, all sending information from personal commercial devices, to a different building through a single massive scaled up version of these Communications Chips, of which the device is also called a Quantum Siderail. The sent information may go through thousands of other Quantum Siderails before it eventually meets its destination - a Quantum Mainrail.
Quantum Mainrails are what the Galaxy as a whole - civilization itself - has universally agreed on to be "The Hubs" of communication. Each Mainrail building (and device, which also have the same name, again) are usually entire planets, or planet-sized complexes, which house quintillions of different connections, to millions of Quantum Siderails. Furthermore, each Quantum Mainrail communicates with every other Quantum Mainrail (few there are - though the growth of civilization requires an exponential amount of these to operate.) Quantum Mainrails, or Siderails, for that matter, do not house any information themselves, only acting as the cables between storage centers, beit your CyberRig, or a massive planetary supercomputer, they're all connected.

Backrails

Quantum Backrails are special type of Quantum Communications array, acting in an interesting manner part from other mainline communications, though are mechanically the same. Using the same techniques in standard Quantum Rails, a Backrail system uses its own Siderails and Mainrails, though typically on a much smaller scale, as these systems are completely disconnected from the usual Mainrail system. Backrail communication grids, by design, are unable to communicate with standard Cyberweb services, and need a specially keyed Communications Chip to access. Luckily, as the technology is identical, Quantum Conductors can still reconnect Backrail network chips, such as when near an FTL Com-Buoys.

Disconnection

Due to, seemingly, the nature of the Universe itself, FTL Travel breaks Quantum Communication lines, specifically by detangling Communications Chips as soon as they move faster than light. Luckily, there comes a solution in the form of a massive device, around 1 Kilometer long, named the "Quantum Conductor" (keeping with the railway theme, apparently) capable of, when in range, "re-tangling" any Communications Chips within a very large radius. This process is extremely complicated and energy intensive, typically being described by Quantum-Networking Engineers as "Like finding a knot of spaghetti strings in a pot a mile wide, reaching in with pool noodles, and untying it with your eyes closed. Oh, and you're drunk. Oh, and you're really just tying a knot that's supposed to be there, but isn't. Try that."

Access & Availability

Quantum Communication is so wide spread that it's almost impossible to find a device not on the network. The technology is everywhere, with the ability to create Quantum Backrails relatively easy enough to ensure that even the furthest rimworlds have a connection to the Cyberweb.