The HoloNet, also spelled Holonet, was a galactic communications grid that was developed, used and maintained by the Galactic Republic and later by the Galactic Empire. The HoloNet was a near-instantaneous communications network commissioned by the Galactic Senate to provide a free flow of hologram communication and information exchange among member worlds. It vastly sped up galactic communications, which had previously depended on more circuitous subspace transmissions or relays.
A message was first broadcast from a planet, a vessel in hyperspace, or from another point of origin; from there, it was then routed from the point of origin's transmitter through potentially millions of hyperwave transceivers suspended in hyperspace to a HoloNet relay, where it was sorted, identified and logged by the relay's computer, and then routed further via appropriate transceivers to its destination. The transceivers themselves transferred information across the galaxy through s-threads. This enabled data to be sent and received at faster-than-light speeds, ensuring near-instantaneous communication from one end of the galaxy to the other, by routing information from origin, to transceiver, to HoloNet relay, to transceiver network yet again, and finally to its destination.
It should also be noted that information transmitted via the HoloNet was nearly impossible to infiltrate or corrupt, thanks to the s-thread's incredibly narrow hyperspace dimensions. The only way to do so was to attach a listening device to the sender's equipment, the relay station, or at the destination itself.
The HoloNet system was an extremely costly expenditure, both for transceiver placement/maintenance (funded by the government) and for consumer HoloNet equipment. However, it was one of the major methods of communication in the galaxy. One of HoloNet's services was the "Imperial.emp", a service that even Darth Vader used. HoloNet was also known for containing numerous forums, including one called the Naboo message exchange.
Created thanks to the Galactic Senate's efforts several thousand years BBY, the HoloNet quickly expanded throughout the galaxy, ending up with at least one emitter/receiver device located on virtually every planet of the Galactic Republic. The Holonet was operational by at least 3954 BBY.
In 22 BBY, plans to expand the HoloNet to the Outer Rim Territories were delayed due to budgetary restructuring according to the General Ministry Communications Agency. 250,000 worlds in several sectors, including Portmoak, Arkanis, Parmic, Quence, and Kathol, were not to see access for one fiscal year. Where they lacked in primary HoloNet conduits, they made up for with a network of Subspace relay stations for intersector communications, resulting in delayed galactic news reaching those sectors within days or weeks.
During the Clone Wars, the Confederacy created the CIS Shadowfeed, a network of hyperwave transceivers similar to the Republic's HoloNet News channel. During this time, both sides used the HoloNet to broadcast propaganda.
When Emperor Palpatine assumed power, large portions of the HoloNet were shut down to prevent news of the Empire's atrocities from spreading quickly. During the time of the Empire, the HoloNet was strictly controlled, used mostly for Imperial Military communications. This greatly inhibited the ability of groups like the Alliance to Restore the Republic to communicate, and arguably also had an isolating effect on the many planets over which the Empire held power. During this period, Ebenn Q3 Baobab created an alternative HoloNet since the official HoloNet disseminated only Imperial propaganda without the "complication" of unapproved free speech. After the Empire fell, HoloNet channels were reopened and security was lifted, restoring free speech.
Behind the scenes
In the non-canon mobile game Star Wars: Tiny Death Star, the HoloNet feed was portrayed similar to a real-world social media platform such as Twitter or Facebook, where NPCs known as bitizens could post statuses and other bitizens could "like" them.