Phosgraph

Phosgraphs are a long-range optical communications system. They transmit colored light pulses within stabilized ‘air tunnels’ between phosgraph towers. The light pulses are recorded on photosensitive drums and read by operators.

History

Static-pair towers

Phosgraphs were invented at Tesser University in 24, as a development of pre-Enchantment signaling systems based on shuttered lights. Two towers were installed, one at the northern lighthouse and one on the roof of the House of Isles. These towers had fixed inbound and outbound lenses, forming two fixed unidirectional lanes. Only one lane could be active at a time due to light bleed between nearby air tunnels. Other early towers had the same static-pair configuration, and were mostly constructed by Stolmont and Marisa in the Mirid Archipelago to send messages between islands.

Network scheduling

In 55, engineers in Ercos developed a mechanism for the precise rotation of phosgraph lenses. Since the lenses at each end of a lane had to be aligned for a message to be sent, the Ercosian phosgraph line installed along the Whitewall relied on a centralized schedule. For example, on even hours operators would establish lanes A-B and C-D, then on odd hours lanes B-C and D-E. During an even hour, the inbound operator at B would record messages intended for C and then retransmit them during the next odd hour.

Roka developed cheap dual-purpose lenses in 57, and the Ordossa Navigation Company hired them to build single-lens towers across Marisa and on ONC ports and offices across the world, implementing the first non-linear scheduled network.

Relay balloons

In 62, Petrel Aerostatics introduced the relay balloon, a high-altitude platform for a lens-and-mirror configuration able to bounce phosgraph pulses over the horizon. These enabled cross-ocean phosgraph transmissions, and led to the construction of phosgraph networks in Kota, Qamar, and Monnais.

These networks had a mix of public and private owners. Operators working at the borders between networks often had to learn two protocols and translate messages between them.

Relay balloons require calm water and building a network with perfect lines of sight is infeasable. Manual delivery of messages between towers is a common part of transmitting messages long-distance. This translated into expensive and shifting connections between networks with different owners as local courier services changed their prices.

The Starlight Phosgraph Union

Network owners recognized that interoperability concerns could lead to popular rejection of the technology. In order to standardize protocols, operators across Monnais and Qamar founded the Starlight Phosgraph Union in 78. In 81, Starlight published its first bulletin. It contained the first attempt at an international standard of pulse-encoding messages, a complete network schedule for its members, and a cost-sharing procedure for manual forwarding.

The Ordossa Navigation Company joined in 83 as the owner of most towers in Marisa. Kota and Ercos continued to set their own schedules for some time after the founding of Starlight. They negotiated a shared schedule and standard for towers on their border, effectively forming a coherent network.

After the Locust War, many Tilian towns were built to include phosgraph towers. A Starlight branch office was opened in Fog-Line Crossing, a Tilian frontier town, to coordinate these towers as they came online. Ercos and most Kota kyros also joined Starlight in the 490s.