Superluminal communications

Superluminal communications or FTL communications is the science and technology of transmitting information faster than conventional, EM-based means allow. Most faster-than-light communicators known today use wavespace, a colloquial term for fairly narrow slipspace layers not traversible by matter but optimal for transmitting EM signals. As such, on the basic level, wavespace communications function like normal telecommunications, albeit propagated through a medium where electromagnetic radiation can travel faster than light.

A wavespace communicator includes three principal components: a transmitter (usually a high-energy maser) a slipspace field generator that routes the maser's radiation through a small wormhole, and a receiving antenna adjoining that wormhole. Covenant systems even have gravitational lensing field-based receiving mediums built into slipspace itself, but such level of exotic engineering has remained outside the capability of the UNSC so far.

Terminology
The medium through which faster-than-light transmissions travel is known as wavespace. Covenant wavespace transceivers are commonly known as wavecasters, while the UNSC calls them wavespace relays or slipwave relays. The Phoenix Initiative's post-war commercial comm network is known as Slipnet.

Covenant wavespace transmissions, especially those of importance, are commonly known as missives.

Rules and limitations
Broadly speaking, there are two major types of wavespace communicator:
 * Broadcast: a non-focused radio signal propagated through wavespace. Most useful over short ranges (less than 50 AU for the UNSC); tends to scatter over long distances.
 * Point-to-point: effectively a high-power maser pointed at a wavespace portal, with a receiver at the other end. Most UNSC interstellar comm relay systems use this method.

Technically, there is no distinction between wavespace and slipspace; the former is merely a term for specific dimensional sets within the latter. Thus, wavespace shares many of its limitations and quirks with slipspace in general. Wavespace encompasses slipspace pathways too infinitesimal for matter to traverse, while enabling optimal and energy-efficient passage for radiation. Like normal slipspace, there are "layers" to wavespace, with "higher" layers being more efficient but more difficult to tap into. Useful wavespace bands are also very narrow, much more so than slipspace pathways, making wavespace communication like trying to thread a series of tiny needles over a distance.

This is also why focused tightbeam-like transmissions are much easier to keep coherent over a distance than omnidirectional broadcasts. Because of the chaotic, non-Euclidean nature of slipspace, the photons that carry information are increasingly prone to scattering over long ranges, and may arrive incomplete and out of order, rendering transmissions unintelligible. On ranges longer than a few AUs, one must know - at least roughly - where they're sending, and focus the data-stream to that target. Omnidirectional broadcasts are possible, but across interstellar ranges, special methods (such as Forerunner modulating crystals) are needed to maintain coherence in the signal, and even then scattering can be an issue.

Like slipspace travel, sending signals through wavespace is a complex interplay of several main factors: Energy, the "resolution" of the interface, and computing power. With enough energy, signals can be "brute-forced" through wavespace, and this is how the first UNSC communicators worked. The Covenant have an abundance of energy as well as high-resolution interfaces, enabling their wavecasters to deftly weave efficient trajectories through wavespace, like a scalpel to the UNSC's hammer. However, the limits the Covenant imposed on high-end computing also placed limits on their ability to calculate pathways, leaving them with technology that is technically very impressive but rather poorly optimized.

Universal limitations (UNSC and Covenant)

 * Wavespace has layers. The higher a layer, the further it reaches. Higher layers require more precision and more energy to tap into, and the Covenant and later the UNSC have accessed only the lowest few.
 * In order to listen to a broadcast, you have to access the layer it is being transmitted on.
 * You can transmit a narrow beam, or broadcast a signal omnidirectionally with greatly reduced range. The more focused the signal, the more reliable it is.
 * Although Wavespace is more orderly than Slipspace, it does not match up 1:1 with realspace. Locations need to be mapped to one another, and the relation between Wavespace and Realspace tends to drift.
 * A network of wavespace communicators need to broadcast often and make periodic adjustments to their aim to stay in contact. The frequency of adjustment increases as the distance between a broadcaster and a receiver increases. At the maximum range that Covenant communications can reach, it requires almost constant input or the signal will wander off target.
 * Wavespace communications cannot be used while in slipspace; it has been theorized that the stochastic interplay between the inter-nestled slipspace fields may result in a catastrophic higher-dimensional singularity.
 * The further you're transmitting, the more unpredictable the transmission. The signal may arrive late, or the information content may be out of order.

Pre- to late-war: couriers
Prior to the development of wavespace communicators, the UNSC and human civilization overall had to rely on slipspace-capable starships to deliver messages over interstellar distances. Across the Outer Colonies, communications were most often carried in the databanks of various civilian ships, such as automated freighters. However, within the Inner Colonies and other major population centers, various corporations operated entire fleets of dedicated courier ships with cargo composed entirely of hard drive space. These ships flitted in and out of systems incessantly on predetermined paths like paternoster elevators, refreshing the local system or planetary networks with new data as they moved about. On the most trafficked routes, there could be multiple courier ships carrying virtually the entire data of a system network on the way at a time.

COM launchers
Created in the later years of the Human-Covenant War, the slipspace COM launcher is a secure military system that launches a self-guided probe through slipspace at a specified destination. It has several advantages over wavespace relays. The main challenge with wavespace communications is that you're essentially trying to throw a curveball and hit a tiny target increasingly far away, whereas with slipspace travel you're actively modulating the slipspace around you as you go. This is also why the UNSC's first success with FTL comms was the COM launcher; as the probes are capable of independently navigating slipspace on the way and didn't have to do all the calculations at the source. Even after the advent of wavespace comms, the probes remain more reliable and secure for long-range comms, though they do remain prohibitively expensive.

The advent of wavespace
While humanity has had the theoretical basis for wavespace for almost as long as slipspace theory has existed, it was only through research into Covenant slipspace technology during the war that enabled the UNSC to build the first functional FTL communicators. As with slipspace navigation, the main problem was accuracy and resolution; human technology simply could not parse the fractal dimensions of slipspace in enough detail over a distance to effectively send signals through. Slipspace travel, meanwhile, was easier because the Shaw-Fujikawa drive can constantly recalibrate the ship's flight path as it traverses slipspace.

Though prototypes of FTL communicators existed throughout the 2530s and 2540s, the first designs were large, energy-inefficient and cumbersome. The first practical wavecasters, then still limited to in-system transmissions, were installed on select remaining Inner Colony systems' early-warning listening posts in the second half of the 2540s. For that time, and for several years onward, they remained in strict FLEETCOM priority use only. These early wavecasters were very limited in the complexity of data they could reliably transmit: strings of plain text being virtually the norm until the mid-2550s. By 2552, a handful of Navy battlegroups had short-range communicators installed for in-system coordination. The first intersystem wavecasters, based on Covenant equipment captured over Reach during Operation: FORTRESS SIEGE, began to percolate throughout the Navy in late 2553.

It was only in the 2560s that the technology first panned out in commercial use, through the Phoenix Initiative-launched Slipnet project. As the UNSC's resources are limited, the construction of the colonies' slipwave communicator network was privatized to contractor companies.

The impact of superluminal communications was massive. The notion of comparatively fast communication with other star systems, or even real-time communication within a star system was if not alien, at least a speculative fancy at best to most people even in the 26th century. It would come to revolutionize how people and societies conceptualize themselves in the overall framework of the human sphere, a new information revolution akin to the telephone or the internet on Earth. And it had major ramifications on the inner workings of the UNSC and human civilization as a whole. They could now comfortably colonize worlds further away, as despite the travel time, communications took much less time. Both colonial populations were also now to talk to one another in more reasonable time spans, which in time would come to reduce alienation in many places. However, casual interaction with other star systems — such as the Internet of today — would still be some time away. Individual planets and/or systems mostly still have their own isolated networks, and interaction between those networks is more akin to old-fashioned mail than the real-time global communication provided by the Internet.

Rules

 * Interstellar slipwave signals are focused EM bursts sent through wavespace, much like tight-beam transmissions. They are not easily intercepted unless one knows exactly where and what to look for. Omnidirectional broadcasts are possible in wavespace, but they are much more prone to scattering than focused transmissions; thus they only tend to work within a star system, which is still useful as it virtually eliminates light lag. Still, if you know roughly where the recipient (e.g. a planet or ship) is, it is most useful to point your relay in their direction. As transmissions are scattered by gravity, they become warped and distorted; parts of the content are lost, or arrive in a random order, making them useless.
 * Wavespace relays (both transmitters and receivers) must be calibrated to a fairly specific distance and destination, which in practice limits them to point-to-point transmissions between individual relays; meaning a relay cannot receive messages from outside the region it is attuned to.
 * Relays constantly drift out of focus; in the early years, they must be manually recalibrated, before reliable auto-correction mechanisms are developed.
 * Similar to slipspace entry and exit points, relays should be installed in gravitationally stable locations, such as Lagrange points, to minimize interference; gravity wells can easily scatter transmissions or warp them off target.
 * Most ships do not have interstellar-capable communicators. As time goes on, more and more Navy ships have short-range communicators installed, which enable virtually real-time communication in-system; by 2565, most ships are equipped with such devices. Still, for interstellar communication, most ships must link to a local comm relay, if one is available.
 * As of the 2560s, the average speed of UNSC wavespace communications is two lightyears per hour, and though more constant than slipspace travel, this also varies based on the local slipspace topology. This puts Epsilon Eridani at around five hours from Earth, and the more distant colonies at three days away.

Applications

 * Slipbeacons are effectively wavespace broadcast transmitters. Due to the constraints of the technology, however, they have a very short range and actually require another ship to be nearby (usually within the same system) to pick up the signal; their operational lifespan is limited as well.

Covenant
Covenant slipspace communications are fast, but instantaneous only over short distances. Long-ranged missives (i.e. over hundreds or thousands of LYs) can still take days to arrive.

Ideas & specifics

 * Most Covenant wavecasters still have a limited range. However, there are devices, numbering in less than a thousand, that are capable of much greater ranges, through the use of Forerunner-sourced modulating crystals that tap into higher layers of wavespace. A special religious order formerly under the oversight of the Ministry of Edification oversaw this network, and were the only ones capable of properly maintaining it. These grand wavecasters are found in the primary domain capitals, key reliquaries, and major flagships, and were used exclusively for strategically important empire-wide communication. And unlike most long-range devices, they operated via omnidirectional broadcasts, as they were designed to raise High Charity wherever it was; yet they could not be listened in by anyone other than those with access to systems capable of reaching the same higher wavespace layers.
 * There is a sacred order borne out of the remains of the Ministry of Edification that remains capable of repairing the grand wavecasters. They are near-universally respected and allowed passage past factional borders due to the strategically crucial nature of their work.


 * The Covenant's imperial wavecaster network had a kind of "signal fire" system based around a handful of very simple encrypted and pre-programmed messages understood only by the High Council. The messages would pass through every domain's grand wavecaster without said domains' authorities being fully aware of their contents. This was a security measure to ensure delicate information did not end up in the wrong hands or was not tampered on the war, e.g. in the event a wavecaster became compromised.